ER-9703-8

CLEANING AND CHEMICAL TREATMENT OF AIRCRAFT SURFACESTO PROVIDE OPTIMUM CLEANING PROPERTIES

Final Summary Report

(23 October 1967 to 23 October 197U)

October 1970

by

R. N. MillerF. T. HumphreyA. Bleich

Prepared Under Contract N0001 9-68-C-001 7

for

Naval Air Systetms Command BIDepcrtment of the Navy TOIS iwJ]uII."-

by

Lockheed-Georgia CompanyA Division of Lockheed Aircraft Corporation

Marietta, Georgia

c prodwuod by

NATIONAL TECHNICALINFORMATION SERVICE

R..ER -97-8

CLEANING AND CHEMICAL TREATMENT OF AIRCRAFT SURFACESTO PROVIDE OPTIMUM COATING PROPERTIES

Final Sunaitmy Report

(23 October 1967 to 23 October 1970)

October 1970

by

R. N, M llerF.Tr. mufpl-ry

A. Bleich

Prepared "JrJer Cuntract N0009-68-C-0017

for

Navo! Aii Sy.te s CommarandDeprtment. of the Navy -

by

Lockheed-Georgic CompanyA Division of Lockheed Aircraft Corporation

Marietta, Georgia

th Co or~er. NoI Ar Systems'ao. 6nd.4to.

This report was prepared by +I.a Materials Scien-ce Reseocch Laboratory, Lockheed-Georgia Company, Marietta, Georgia, for !he Na-val Air Systems Commond, Departmentof the Navy, under Contract NZJO19-68-C-4O01 7.

The work was administered by the Nava! Air Systems Command, -with Mr. A -MN. Molloyand Mr. T. A. Johnston serving as Project Engineers.

The Princioal Invcstigator was Dr. R. N. Miller. The laboratory phasKe of the p..,gOffl wasconducted in the Materials Science-. Division of the Lockheed Georgia: R,.earch L.-iborotoryunder the surveillance of Associaie Director E. E. Undervtood. F. T. uaevR. Ridley, and T. PhI'lips performed the Vrborotory evaluation of the experimenta:clean~ing procedures. J. C. %George and A. R1eich directed and conducted3 the Lockheed-Californio portion of the program.

The accomplishments of this prog-rm lnrgely resulted from the cooperation of the followingindividuals: Commander J. T. Wa'oler, l\ vy Plant Representative, Lockheed-California;Captain Ripa, Aircraft Maintenance Officer, Marine Corps Air Station, El Toro,California,- G. A. Garber, Air Force Mact Representative, Lockiieed-Georgia; P. DeKeles, Manager of Planning and Scheduling Department, Lockheeed-California;E. Moaxwell, C-141 'oint and Trim Department, Lockheed-Georgia; Major Johna Masters.Head Maintenance Officer, Futerno Air Base, Okinowa; and 0. E. Pratt, Jv., Lockhee~dField Service RE-prese-t-,tive, Futema, Okinawa.

Appreciation~ ond recogniition are extendad to Captain Waitt of El Toro Marine Corps AirStation, and to lohn Bradshaw for arranging the fina I nspection of C -130' Air--raft No.150685. The final inspection of P-3 Aircraf. No. 5T86 wo! made po.ssible by the efforts ofSquadron Leadtr 1. Bunn and Squadron Leader R. Hewitt-Cook of the Austral Iian a'-xbassyin Washingtoi-, D.C., end Squadron Leadet Jack Roe of the At.straiinn AMr Force Base atEdInborotigh, Australia.

This final repoift summaorizes the progress on the conrract for the 36-month period from23 Oc tabar ' 967 to 23 Oc;tober 1971).

[ A nCVOA eTP^OJ I Fr%% 4.

Final results are presented of a program to develop improved metheds ofc leaning aircrzft~ufoees prior to paitig

The first objective of the program was met by the development of C simple and accuratemethod for determining the degree of cleanliness of surfaces. it cons;sts, essentially, ofplacilng 5-rnicroliter drops of distilled water on the test surface, measuring the drop. -,Aumeter,and converting tt-e drop diameter to a quantitative value of surfaa.-e energy.

Nine cleani-: proceclures were evaluated by means of radioisotope, surface energy,Lrydrogen einbrttement, and coating adhesion tests. The best two procedures were appliedto iiC-130 at Lockheed-Georgia and to a P-3 aircraft at Lockheed -California before thefinal epoxy -p,,lyzmde paint systemn was applied.

The C-130 aircraft was inspected after approxi mtely 6 and 14 months of South Pacificservice. The P-3 aircraft was Inspected 6 and 21 mronths aifter it was painted. The inspec-tion results indicate that both of the experimental cleaning procedures we-.e effect-Ive inproviding a durable bond between the epoxy-polyamiae point system and the aluminumnsubstrate.

Five hand-peelable and five olkaline-removable coatings were evaluated for their abilityto protect clean surfaces from contamination. The strippable coatings wl-ich gave the bestresults in laboratory tests were applied to P-3 fvsela~je panels. Hond-strippable coatingNo. 140 provided good protection for the panels during chemical cleaning and duringdrilling, countersinking, rand riveting operations. Chemically sirippable coa-ting No. I1Iprovided good protection for the panels during the drilling, countersinking, and rivetingsteps.

*Strippable coatings are identified in Appendix A.

V

TABLE OF CONTENTS

Section Title Pg

LIST OF FIGURES ix

LIST OF TABLES xv

SUMMARY Xvi*

I INTRODUCTION 1

11 BASIC STUDY OF SURFACE CLEANLINESS 5Methods for Determining C lean lines; 5C~ritical Surface Tensien of Wettinci 6The Surfascope Surface Energy Kit 16

Surface-Energy Test for Non-horizontal Surfaces 1Surface Energy Measurements on Surfaces Inc lined More than 90a 21Identification of Contaminants an Panel Surfaces 21

Effeci of Aging on Surface Eneigy of Sulfuric A-iodized Panels 24

III LABORATORY EVALUATION O1V CLZANING PROCEDURES 33Radioisotope Evaluation Test 34

Hydrogen Emb.,ittlement Characteristics of Cleaners 39Preparation of Environmental SpeciEmens 44Surface Energy Tests 44

Environmental Exposure and Coating Adhesion Tests 46

IV LABORATORY EVALUATION OF STRIPPABLE COATINGS 157

Test Coatings 57Test Specimens 57Test Pm'edures 5

Test Results 58

FV PRODUCTION-LINE EVALUATION OF STRIPPAoBLE COATINGS 65Application of Coatings 65

l est Results 65

Vt'

TABLE OF CONTENTS (Contivued)

Sectior, Title Page

VI APPLICATION OF BEST CLEANING PROCEDURES TO AIRCRAFT 69Application of Best Procedures to C-130 Aircraft 69Cost Parameters 75

Application of Best Cleaning Methods to New P-3 Aircraft 77Cost Parameters 31

VII INSPECTION OF AIRCRAFT CLEANED BY EXPER'M :NTAL

PROCEDURES 83

P-3 Aircraft 5286 83

C-i30 A 'craft No. 150685 91

Viii DISCUSSION OF RESULTS 113

IX CONCLUSIONS 117

X RECOMMENDATIONS 1i9

REFERENCES 121

Appendix A IDENTIFICATION OF CLEANING SOLUTIONS ANDCOMPOUNDS A-]

iDENTIFICATION OF STRIPPABLE PROIECTIVE COATINGS A-i

Appendix B OPERATING PROCEDURE FOR SCRATCHMASTER PAINTADHESION TESTER B-i

viii

LIST OF FIGURES

Figure Title Page

I Milestone Chart of Key Contrack Operations 3

2 Wettobility of Various Perfluorinoted Low-Energy S.afaces by tiien-Aikane Liqu;- 7

3 Profile of Drop of Dist'lled Water on Teflon, Contact Angie 97(20XI 9

4 Profile of Drop of Distilled Victer on Glass, Contact Angle 34P(20X) 9

5 Prof~ie of Drop of Distilled Water on Alumintun, Contact Agle68P (20X) 10

6 Laboratory Measurement of Diameters of Droplets of DistilledWater on Aluminum Panels. Microsyringe at Right is Used toMeasure Drop Volume of 5 Microliters. 10

7 Relationship Between Contact Angles cnd Surface Energy of Solids 13

8 Relationship Between Drop Diameter and Critical Surface Tensionof Solid (5 Microliter Drops' 14

9 Effect of Relative Humidity on Surface Energy of 7075-T6 ClodAluminum at 77OF 15

10 Surfascope Kit and Appearance of 5-Microliter Water DropThrough Brinell Microscope i7

I I Profile of 5-Microliter Drops of Distilled Water on Horizontal andVerticcl Clad 7075-T6 Panels 20

12 Drops on Clean Pnnel are Irregular in Outline and Tend to FormContinuous Film 22

13 Drops on Contaminated Panel ore Spherical and Run Off Readi!y 22

14 Mold and Plunger Assembly for Mkr-g 1/2-inch DiameterPotassium Bromide Discs 23

At 5 Potassium Bromide Powder on Test Panei. Holder at Right isSupporting Transparent Dig. Which Was Just Removed from theMold. 23

16 Press Used for the Production of 1/2-Inch Diameter PotassiumBromide Discs 25

ix

LIST OF FIGURES (Continued)

Figure Title Pge17 Absorption Characteristics of Potossiu, Bro.ide Discs Being

Obtained with c Perkin-Ermei Model 621 Infrared Spectrophotornetef 25

18 Infrared Absorption Spectra of Conta,..inants on Aiumnzirn Panels 26

i9 Infrared Absoeptic r Spectre uf Conteomnonts on Alurninum Pcneis 28

20 Measurement of Resi"dual Radioactivity in Nuclear Meosurem-entsProportional Counter Model PC-3T 35

21 Determiring Hydrogen Embrittlemert Chrarcteristics of CleaningSoluTion with Lawrence Hydrogen Gauge 40

22 Hydrogen Detection Probea and Holder 40

23 Environmenta; Specimens Being Subjected to 5% Solt Fog 47

24 Specimens Being Subjected to Simu!cted Sun and Rain in AtlasWeotherometer 48

25 Interlor View of Weatherometer Showing Xenon Lamp 48

26 Scrotchmaster Poant Adhesion Tester 4.

27 Test Scratches on Panels with Good and Poor Point Adhesion 49

28 Lccotion of Test Panels in Fuselage of P-3 Aircraft 66

29 Test Areas at Navy C-i30 Aircraft No. 150685 70

30 C-130 Aircraft No. 150685 at Wash Rack Prior to Stripping andC leaning 71

31 Front Starbord Test Area. Only White-Capped Upper Fuselgewas Repainted. 72

32 Rear Starboard Test Area 72

33 Front Port Test Area 73

34 Rear Port Tes; Area 73

35 C-130 Aircraft Nc,. 150685 After Paintina 76

36 Profile Views of P-3 Aircraft 78

37 U. S. Navy P-3B Aircraft 7Q

x

LIST -F FIGtJRES (Continu.ed-)

FiqLvre Ttle pcge

38 Overcil Ve-A oi ?-3 Aircraft No- 5286 ;n Hangar at. RolAustrali',n A4 Foitfce ;-: E cjg-, Austrciio 8

39 Rea-r stcrb~ca r -e~g S5

AO Frontr Stcdbo -d Fuwe--ge 3

C tosr.eup View of Stxor uece8

42 rront ro,- Fteseloae ofArotNo- 52786

43 Close-up View., of Pot! FuseSagie

44Utpper Ceatr Fuseloge of P-3 Aimircift Ncp 52,26. Note CompplelleAbwerc o-' Defects 8

4 5 R -cr UJpper F use 6-:ze ol P -3 Air--r--ft N"o - 5296. Note H ighG loss

e ain rede Suf3s

46 Recr Port Fuseoir~e of ?-3 Airccoft- ?citit is in~ Near PerfectCondition. 8

47 C kseup Yi ev of Upper Sufce of Port Wing on P-3 Aimcaf --No. 58

48 C koseup View of U.=4-- Su. 'cce of 5:torrbocrd WrofP-3 A' rcroft No. 52R6 9

49 Test Areas on Navy C-130 Aircaft Ncv. 150685 92

50 C-13OlAkrraft 50T685 at ~v-%a Air Base :-n COkirawc 93

F1iront Test Area an Stx5rd S.de 9

52 Rear Test Area an Starboard 'Side 94

53 contT--,4Areaco Part Sice 93

54 RearT es.,ArecanPon Side 93

55 Top Forw-.-: Section of Fusellage, Tam! Area No- I Cffhite A.reos) 9.

56Test Arco lNo.2 9

57 Test Are.N - 3 9

58 Test Area No.4 9

UST OF FIGLJES (C-ctu-med3s

F-- Titic

3.0 Teo Are-Ne. 5

to Test AxiecN^- -6

*6i lest Axem No. 7

-62 e s! A rea o. 8 (K z ~ i N H e-- ae

-63. Tes ArccNo'

-64 ics! Area No. 10 (Do?, 5ec:cn WJcs Not Reqrinte6 d Is ,Mca C

?-ti- -A5h Testre Arez 1i

56 Tes: Arizc No>-2 i 02

4 P-1 Tes: A.-,--No. -3 !02

6 Tes: Ar-ec lso. 15 !03

MEas;e-d -,-f oD ct"esae3 Fc31te: ins m e Ara Po - 2 104A

Eak*-d View aFe Ofinc Tee i~xeI-r ;2ee 5"=irm efi- Vyixo!,ee

- 72 Ve-7'ew ci £1iusy p~cifis !Reca ir.e~ Ttst Arm -810

-73 Defect in Pcim on i-e~ c5 Futebge-. ;s Wics *NDt c Pb~to=Of te Test A=- Fc-. --- SQ92est-- the S 9c; oF ~iIiF

A4 Tes! Are iNo.* 2 - C-A30 AirSv=F i-44FO - Fk,

Oust a D:-.. 7f--m Up bypcplers-e

75 T-nst Arc No- 8 - C-30A7-u M685 -it -;Z=

E710

76 !e-tAuma -M- 5 - C-130 1-406E-3 - Fit !

Cise-Up. Vci oE 'y S~ee! Rcmastecs

77 Test Amae NZ. 9 - C-'Afti 5-Fimo isc:prir is :- C-003 r3io~

LIST OF FIGURES (Continued)

Figure Title Page

78 Test Area No. 11 - C-130 Aircraft 150685 - Final Inspection.Point Is Just Beginning to Develop a Network of Fine Cracks. 109

79 rest Area No. 14 - C-130 150685 - Final Inspection. Paint inGood Condition but Beginning to Show Fine Cracks. 109

80 Test Area No. 15 - C-30 Aircraft 150685 - Final Inspection.Probable Cause of Blistering and Bare Areas is Incomplete Rinsingof the Paste Cleaner Used on This Portion of the Aircraft. 110

81 Test Area No. 15 - C-130 Aircraft 150685 - Final Inspection.Close-Up View of Bare Spot. 110

82 Test Area No. 15 - C-130 Airc.aft 150685 - Final Inspection.C lose-Up View of Blisters and Bare Areas. 11

83 Defect in Point en Underside of Aircraft Is Unchanged inAppearance Since Last Ins 4ction. This ',Als Not a Portion of theTest Area which Was Coated with t -, Epoxy-Polyamide PaintSystem. ill

|i

LIST OF TABLES

Table Title Page

I Drop Diameter, Contact Angle, and Surface Energy Relationships 12

II Diameters of 5-Microliter Drops of Water on Inc lined Surfaces 18

III Diameters of Same 5-Microliter Drops on Horizontal and VerticalSurfaces 19

IV Band Assigrments, 7est Panel A (7075-T6 Bare) 27

V Band Assignment, Test Panel D-46 (7075-T6 Bare Anodized) 27

VI Band Assignment, Test Panel E-77 (7178-T6 Bare Anodized) 29

VII Band Assignment, Test Panel F-60 (7075-T6 Clad Chromated) 30

VIII Aging of Anodized Surfaces 31

IX Substrates and Surface Finishes 33

X Radioisotope Evaluation of Cleaning Effectiveness 36

XI Radioisotope Evaluation of Cleaning Procedures 37

XII Surface Energies of Panels Before and After Cleaning 38

XlII Hydrogen Embrittlement Properties of Cleaning Solutions 42

XIV Hydrogen Embrittlement Properties of Cleaning Solutions 43

XV Critical Surface Tension of Wettii:g of Cleaned Panels 45

XVI Scratchmaster Adhesion Test Results 51

XVII Scratchmaster Adhesion Test Results 51

XVIil Scratchmaster Adhesion Test Results 52

XIX Scratchmaster Adhesion Test Results 52

XX Scratchmaster Adhesion Test Results 53

XXI Sc ratchrmaster Adhesion Test Resu Its 53

XXII Performance Ratings of the Various Cleaning Methods on Six Substrates 55

XXIII Evaluation of Hand-Peelabie Coatings 59

XXIV Evaluation of Alkaline-Removable Coatings 60

xv

[ LIST OF TABLES (Continued)

- able Title Page

-XXV Evaluation of Alkaline-Removabi'6 Coatings 61

-XXV1 Evaluation of Hand-Peelable Coatings 62

- XX VII Surface Energy Measurements on C-130 Aircraft After FirstC leaning 74

XXVIII Surface Energy Measurements on C-130 Aircraft After SecondC leaning 75

XXIX Surface Energy Measurements on P-311 Wings After Cleaning 81

XXX Condition of Test Areas on C-1 30 Aircraft 150685 i06

[v

SUMMARY

Basic Stud, of Surface Cleanliness

A relicble and simple method of determining the degree of cleanliness of aircTcft surfaceswas developl.d. Essentially, it consists of placirg drops of distill,:kd water, 5 microliters involume, on the test surfaces and measuring the diameter of the drops with the aid of aBrinell microsccpe. Throuh the use of a special chart, which must be experimentallydetermined, the drop diameter is readily converted to the "Critical Surface Tension ofWetting" of the surface. This number is a quantitative measurement of the free energy ofthe cleaned surface.

The contaminants which accumulated on the surface of panels which hod been exposed to aprodu.:tion shop environment for 3 weeks were analyzed by mecns of an infrared spectra-photometer and identified as being chiefly hydrocarbon oil, solvents, and dufi.

Studies on the effect of aging on the surface energy of anodized alumi'rum ponels indicatethat aging is not u significant factor in lowering the surface energy of anodized substrates.

Laboratory Evaluation of Cleaning Procedures

Nine procedures were evaluated for their cleaning effectiveness by radioisotope andsurface energy methods. Panels of bare and claj 7075-T6 and 7178-T6 aluminum werethen cleaned by each of the procedures, coated with the Navy epoxy-polyarnide paintsystem, subjected to sot spray and simulated sun and rain expozure, and evaluated forpaint adhesion by means of a Scratchmaster Point Adhesion Test Unit. The two cleanerswhich gcrve the best overall results were Cleaners No. Ill and Vl.*

The cleaners were also investigated for their hydrogen embrittlement characteristics bymeans of the Lawrence Hydrogen Detecton Gauge. Cleaner No. IV was highlyembrittling, but the remainder were considered safe for use.

Laboratory Evaluation of Strippable C0-atings

Five hand-peelable and five alkal.ne-removable coatings were eva!uated for their abilityto protect cleaned surfaces from contamination and for their resistance to chemical pro-cesing and mechanical abrasion. The best of the hand-peelable films was Coating No.I ,* rnd the best alkaline-removabla materials was Coating No. 14.

Application of Best Cleaning Procedures to Aircraft

The two best experimental cleaning procedures, involving the use of Cleaners No. IlI andVI, were applied to the starboard and port sides, respectively, of PAR Mod C-130 aircraft

* 1150885 on September 13, 1968. After the second cleaning, the test area on top of thefuselage was repaint-d with the Navy epoxy-polyomide coating system

*See Appendix A for identification of cleaners and strippable coatings.

Xvii

A *W W% 11 IUu 1iy II= -f-mV SIFcrilu3 pruccdurtn. n estarboard wing was cleaned with Cleaner No. III, the port wing with Cleaner M'. V!,and the ftiselage was cleaned by the standard Lockheed-California procedure whis.ninvolves hand-scrubbin0 the surfaces with Scotchbr;te pads and water.

P roduction-Line Evaluation of Strippable Coatings

Strippable coatings No. 11 and 14 were applied to skin panels for a P-3 aircraft. Hand-strippable coating No. 14 was applied before the panels passed through the cleaning,deoxidizing, and Alodine tines. The chemically removable coating No. 11 was appliedafter the chemical treatments. Both coatings he!d up well during the drilling, riveting,and routine operations. Coating No. 14 provided good protection for the aluminum panelsthrough t+e chemical treatments.

Inspection of Aircraft Cleaned by Experimental Procedures

P-3 Aircraft No. 5286, which was cleaned with the two best experimental cleaningprocedures on August 5 end 7, 1968, was inspected after outdoor storage for 6 monthsunder conditions which were quite shel*ered except for exposure to sunlight. No deterio-ration of the coating system was evident. The second inspection was made on 18 May 1970,after the aircraft had been cm active service in Australia for 6 months. The coating was inexcellent condition and still had a high gloss. No defects or deterioration were evident.

C-130 Aircraft No. 150685 was inspectedatFutemaAir Base, Okinawa, on 7 Apr'l 1969after approximately 6 months of active service in the South Pacific. Except for a few minordefects, the painted surfaces were in excellent condition. Both experimental cleaningprocedures had been effective in providing good paint adhesion.

T e second inspection of the test C-130 aircraft was made on May 10, 1970. The pointwas adhering we!l and was not blistering or peeling with the exception of a small area onthe starboard side of the ducktail.

XviiI

L I - INTRODUCTION

Aircraft manufacturers hove had difficulty in obtaining consistently good adhesion ofepoxy paint fini3hes to chromnated aluminum surfcices. In an effort to solve this problem,the U. S. Naval Air 'ngineering Center() conducted an investigation of various methodsof cleaning and activating aluminum prior to pointing and recommended several procedures.One of the problems encountered by the U. S. Naval Air Engineering Center was that ofquantitatively measuring the degree of cleanliness of a freshly cleaned surgace. It was thepurpose of the program described here to

* Develop a reliable method of determining when a surface has the cleanlinessrequired for good adhesion of paint films.

* Evaluate further both the recommended and additional cleaning prccec'ures in thelaboratory.

* Apply the two best methods to both new and reconditioned aircraft surfaces toestablish cost parameters and to determine the performance of the treated surfacesunder service conditions.

The condition of the surface prior to the application of a protective coating system is oneof the critical factors in the attainment of an adherent, corrosion-resistant finish system.Points adhere to metal surfaces through a combination of two mechanisms: the keyingaction between the organic film and irregularities in the metal finish, a.-d molecularattraction between the metal and the polymeric coating. Since aircraft surfaces arealways extremely smooth, the second mechanism assumes primary importance.

Good molecular bonding is best achieved by freshly activating the surface to be coatedjust prior to the application of the protective sysiem. The activation treatment createsunsaturated bonds which have a strong affinity for the coating system. The surface must beprotected if it is not practical to activate the swrface immediately befcre the paint isapplied. A strippable film may be used to keep moisture, grease, and industrial fumesaway from metal surfaces during fabrication operations.

It is posible to achieve ideal conditions n the laboratory, where relatively small testpanels are coated and tested. However, the painting of a large aircraft presents multipleproblems. The humidity in the paint hangar i Iorgeiy regu!ated by the local weatherconditions. Another pioblem is the difficulty in educating workers to keep hands offsurfaces which have been prepared for pointing. It is rot uncommon for painters to wipedust from surfaces with their bare hands, not realizing that the grecs;, and moisture fromtheir hands is for more detrimental to the finished coating than the dust they are trying toremove.

In the selection of an optimurnm clearing and chemical treatment for aircraft surfaces, theeffectiveness under ideal conditions is important, but the ultimate test is how well thesystem holds up when recommended handling procedures are not strictly observed. For thisreason, it was decided to verify the results of the laboratory investigation by applicationof the ,elected cleaning procedures to production aircraft and to base the final recom-mendations on the results of a field-service test.

The initial phase of this program was a basic study of surface cleanliness which had theobjective of developing a simple and reliable riethod of determin;ng the degree of

cleanliness of o'rern~f csrfnrac TW ,&,,.4, ,, 4&:,, C_ -....-I A. ..- rde o sta e --e -- .......... - /...-. . - - - _ ...... 10""ddemonstrated that the water-breok free method, which is the usual criterion of cleanliness,has little value in determining whether a coating may be effectively applied to e surface.Surfaces which did not oass the water-break free test still provided good adhesion for thecoating used.

The second portion of the program was ihe laboratory evaluation of the c!eoningprocedures recommended by the Naval Air Engineering Center, plus the cleaningprocedures in current use by Lockheed-Georgia and Lockheed-California, by means ofradioisotope, surface energy, hydrogen embrittlement, and coating adhesion tests.Simultaneoutly, a laboratory evaluation of the best strippable protective coating systemswas conducted by Lockheed-Califomia.

The final phase of the program was the application of the best cleaning procedures to aC-130 o'rcraft at Lockheed-Georgia and to a P-3B aircraft at Lockheed-Calornio. Thecost parameters of the procedures were determined during application. The two test air-craft were sch,.duled for service in the severe environmental conditions of the South Pacific.

The C-130 was assigned to Futema Air Base in Okinawa and remained there until the earlypart of 1970. It was inspected after 6 and 14 months of exposure to the high heat, humidity,intense sunlight, and salt air environment of Okinawa. The P-3 circroft, originallyscheduled for delivery to the United States Navy, remained at Lockheed-California foralmost a year and was then sold to the P.oya e Austra.'ian Air Force. It was irspected inCalifornia after 6 months of exposure to California sunshine and was given a secondinspection at Edinborough Air Bose at Elizabeth, Australia, on 8 May 1970.

Figure I is c milestone chart showing the completion dates of the various phases and keysteps of this program.

2

- - -------- -~--=--MIT-

f<

Li 2' 01 < ______ _ _

4 __ ____ ____ ____ ___ ___

4l

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0 0 0

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11 BASIC STUDY OF SURFACE CLEANLINESS

Methods f~or Determining Cleanliness

The classical method of determining the surface energy of solids is the mitasurement of theheat of wetting of a known area. However, tbis cannoi b-- used for filat panels becausethe energy chaiges are too smali. This method is applicable only where it is passible touse finely divided solids having ;'arge surface areas pee gram.

A literature survey was made to find alternate metiz-4s of detenn.ining the surface energyof metals in the laboratory and in the fietd. G. J. Hof(2) disc-sses the following methods fordetermining the cleanliness of surfaces, a pfopest which is closely re!ated to surfaceenergy:

-- *Visual Examinatin. -Tis TMis effectively on!? for visible cx-ontcmincnits andpartculae mtter and is the least sensitive and most cow**~niy use m~ethod of

inspection.

0 Tissue-Paper Test - The cleaned surface is rubbed with white tissue paper andthen observed for greave or soot. Technique is limited to visible soil and is arelatively insensit ive qualitative test.

* Water Break - The surface is considered clean if the last rinse water form acontinuous film and does not Nbeod up." This condition, in the absence of ahydrophillic contaminant, indicates a zero contact angle ariJ a surfae energyof more than 72 dynes/cm.

*Atorizer Test - A water mist is applied to a cleajned dr srfac with onziomizer. Because the original surface is dry, the relting pattern- is deter-mined by the value of the advancing contact angle. This test is more zensitivethan the water-break test because no heavy water f Ilm-s are present to cover andobscu.-e small contaminated areas.

* Contact Angle of Water Drop - A drcp of distilled water is placed on the testsurface, the profile is photographed, and the contact angle is memsred. This isan =ccurate method of determining surface cleanliness but can be used only underlaboratory conditions.

4* Kerosene Viesving of Water Break - The test panel is withdrawn from water and isimmnediately subm~erged in o transparent container of kerosene which is ligh~tedFrom the bottom. Nvtor water breaks are displaced by kerosene.

0 Radioactive Tracer - A radioactive soiling compound is applied to the test ppeceand the residual radioactivity is m easured after the piece has been cleaned.This is the most sensitive of the -.uontitative methods now available.

* Fluorescent Dye - An oil-soluble fluorescent dye is mixed with an oily soilingV material and applied to the W.s panels. Afte! the panels ore cieened, the

retained soil is visible under ultraviolet light.

5 U6111181 pile Wlk

s Grovimstric - The test panels ore weighed before cM ofter cleangn. T he

sensitivity oi the wme.tod depenids on t.'e sensitivity of the bclance an'd tIe sizeof the pcnel.

o 0O1 Spot -A drop of solvent is used to deease an rea the size of 24md-.op.The drop is then picked up with a pipette arid evapormted on ground gloss. Anevaporation ring gives evidence of contomination -

* Porticulate Centcaninction - A thin filkn of polyvinyl chloride is pressed againstthe test- surfac--, Iteated to 2400F, mid cooled. h is then carefuill) str:-pped fromthe svirfcce mnd ex-a-nined under a microescope. The pafliculcte con'cmrainntswill 'oe eabedded ;n the vinyl sheet.

The rms sensitive of the above mn-thods is the radioactive trucer test in which c tir-Octivecomtrinmt is applied to a surfoce and the residual radiation is measured ofter thclea~ning ope-ration. aea--use of t+e hcotord involved, this is not suitable fcroa pro&utimnor fief-d test. However, it vrcs -,sed in this Facrm as a screei&g procecuet detern nethe most effective of the cleoanig imetihric to be evaluated.

Tiue water a ter~ sp-ay. md atn~p tests m~e %Al desicoed to dettet fhe degree ofctecinliiess at which water will cownplerely wet a surfoz-e. Point films frequertly wiIladhere tight;y to surfaces which do not meet this -tmndkwd.

After reviewing the odvantaes arod disodvcntces of the cbove- ectid-, and bearing inmind the need for a contam~ination test wh"c may be used in the pant shap as well rs. inthe la&kcrotory, it was decided to investigate a modified verscr of' ".1 contect-angletesk.

Critical S%-,fce Tension of Wettirm

W. A. Zisman of the Naval Research, L&=rayo ins devised am Poce&Pae for Q-LIr. Wrantitative value fer Ohe surfoc" -nuay of substictes. Th~s is ccamplished byreo-surrV the contaoct "nle betweca voriaas substrates and ech of a series of 1XVMo0oanUS

organic Nquids. platning the =*mie of the contact, apale versus surface tension of theN~uid in dyi-1esci* as illustrated in Figure 2, aid extrpoioting the* -*sO-ti.-V linear plot tothe point where the contact angle is equal to zero. This -:ntftcept, defined es theftCritical Surfcce Tension of Wettirna of the Solid," is chocteristic of t.he 3*iid oy andappears to give good relative charaterization of the spciric surim-mc free energy-

Dr. Zisr. used n-cikcne liquids as Mis haxologovs series for ow-eemy solids- Fi re 2sux-mmim the p"~ ich hie &btaimned fox a number of different sugforzes Cunre A is thepiot for vn-ooth, clean poiytetrofluoroetylene (Fefoa). B Ga btained for tfhe C09041merof tetrcFivoroethylene and hexlfspsop-yiene, Gnd C is f-- polyhx-uo*.== lene.D. E, and F were obtoirzeci for calem. smacth pltinu= which bcd cdsovA.ed= mc omolecular layer of a ptefluoroolkonoic mid, Ploai-'- xxily has a hgh-ErAny wofmce,but t;%e adsorbed layer caused it to act likce -matericl with a surfio ememy LoWer tha

6

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that of Teflon. These plots emphasize the importance either of painting an aircraft as soonas possible after 4 has been cleaned or of protecting the cleaned surface until the paintsystem is applied. It is also of interest that the lines which represent each type of surfacehave approximately the same slope.

In on attempt to parallel Dr. Zisman's work with a homologous series which would besu table for use on metal surfaces, a series of solutions of varying surface tensions wasprepared by adding Minnesota Mining surfactant FC 128 to distilled water. The plots ofcontact angle versus surface tension were very erratic. It was concluded that thesurfactant was being adsorbed on the solid surface. In subsequent experiments, isopropylalcohol was added as a surfactant to distilled water. Distilled water alone was used asone of the liquids in the series. Figures 3, 4, and 5 are profile views of droplets ofdistilled water on Teflon, glass, and aluminum.

It was found that the photographic method of determining the contact angle is accuratewhen the droplets are perfectly round. However, when the droplets have an irregularshape, the contact angle varies at different points, and the photographic method measuresthe angle at the profile only. The following equation, derived by Bikerman,( 4 ) gives therelationship between drop diameter, volume, and the average contact angle. This equa-tion is especially useful because it eliminates the need to actually measure the contactangle. If the drop volume is constant, only the diameter must be measured.

D 3 = 24 sin 3 aV (2 - 3 cosO + cos 3)

where D = drop Alimeter

V = drop volume

= contact angle

The equation is valid for droplets I to 8 microliters in volume. Gravity effects introduce asignificant error when larger drops are used. Contact angles are determined by measuringthe diameters of droplets of known volume and substituting in equation (11). Average valuesobtained in this manner are based on all points on the circumference of a given drop, thuseliminating the errors caused by irregular wetting. The va.idity of this relationship ledto a simple and practical method of determining the surface energy of metal surfaces afterproduction cleaning ope'ations.

The Development of the Modified Contact Angle Method

The method consists of placing droplei. of distilled water, exactly 5 mcroliters in volume,on the surfaces to be investigated, mea:.,ring the dcmeter of the droplets with thegraduated eyepiece of a microscope, and converting the droplet diameters to values whichrepresent the critial surface tension of weting of the metal surface. Figure 6 illustrate'the measurement of drop diameters.

8

I

FIGURE 3 PROFILE OF DROP OF DISTILLED WATER ON TEFLON,CONTACT ANGLE 970 (20X)

FIGURE 4 PROFILE OF DROP OF DISTILLED WATER ON GLASS,CONTACT ANGLE 340 (20X)

9

rp

FIGURE 5 PROFILE OF DROP OF DISTILLED WAT ER ON ALUMINUM:CONTACT ANGLE 680 (20X)

FIGURE 6 LABORATORY MEASUREMENT OF DIAMETERS OF DROPLETS OFDiSTILLED WATER ON ALUMINUM PANELS. MICROSYRINGEAT RIGHT IS USED TO MEASURE DROP VOLUME OF5 MICROLITERS.

10

Table I enables a rapid conversion of drop diameter to average contact angie. The first5 columns of Table I were obtained from equation (1), which was simplified by using aconstant volume of 5 microliters. The last column, heated "Critical Surface Tension CfWetting," was obtcined as follows: A drop of water having a volume of exactly 5 micro-liters was placed on a freshly cleaned aluminum panel. The contact angle was determineJby measuring the drop diameter and referring to Table !. This point was plotted as point 1on the plot of Cosine e versus Surface Ten5ion of Liquid shown in Figure 7. Data for point2 were determined by adding isopropyl alcohol to distilled water until c drop of the solutioncompletely wet the clean aluminum surface and had a zero contact angle. The surfacetension of the liquid was measured with a Fisher Model 20 Surface Tensiometer. A linewas drawn to connecT points I and 2.

A table and curve were then prepared to show the surface tension of wetting representedby a range of contact angles by making the assumption that lines on the chart whichrepresent contaminated surfaces will have the same siope as the line for freshly cleandaluminum. Dr. Zisman's data, which is summarized in Figure 2, indicate that this '.s areasonable assumption.

The last column in Table ! was then completed, and the data were plotted to oive Figure 8,the plot of Drop Diameter versus Critical Surface Tension of Wetting of SOl4. Since thedata were detennined for .randard conditions, 77OF and 50% relative he.m;dity, it wasnecessary to determine the correction factors to be applied with deviations from thestandard.

Studies were made in a humidity chamber to determine the effect of relative humidity onsurface energy. The data obtained are plotted in Figure 9. The results indicate that acorrection of 4 dynes/cm should be made for each variation of 10% from ti.e standardrelative humidity value of 50%. The correction factor should be added for readings takenat relative humidities of more than 50% and should be subt...cted for readings taken atlower relative humidities. Deviations from the standard tr nperoture of 77OF had nosignificant effect on the surface energies of the test panels.

A clean surface has a high surface energy and isreodily wet bywoter. A 5-microliter dropof distilled water applied to a clean surface has a 'ow contact angle and a lare diameter.The some size drop applied to a contaminated low-energy surface wou!d have a steepcontact angle and small diameter.

The data in Table I and Figure 8 are utilized by measuring the diameter of 5-microliterdrops of distilled water applied to the tesi surface and then reading off the correspondingsurface energy in dynes/cm. Experimental data developed in this progrom show that anysurface energy greater than 40 dynes/cm will give excellent paint adhesion.

11

TABLE I

DROP DIAMETER, CONTACT ANGLE, AND SURFACE ENERGY RELATIONSHIPS

Diameter Diameter Critical Surfoce TensionScale Units .mrr. D /v Cos 9 Angle 0 (dyne/cm)

3.7 2.627 3.63 0 90° 13.03.8 2.69 3.89 .05 8708' 16.03.9 2.76 4.20 .090 84016 ' 18.04.0 2.84 4.58 .160 80013' 22.54.1 2.91 4.93 .191 78054' 24.04.2 2.98 5.29 .250 76056' 27.54.3 3.05 5.69 .282 73037 ' 29.44.4 3.12 6.09 .331 72012' 32.04.5 3.19 6.52 .390 6703' 36.24.6 3.27 6.97 .416 65025' 37.04.7 3.34 7.43 .465 62017' 40.04.8 3.41 7.92 .531 5800' 44.04.9 3.48 8.42 .570 55015' 46.05.0 3.55 8.95 .622 51032' 49.25.1 3.62 9.49 .655 4904' 51.35.2 3.69 10.06 .700 45o34' 54.05.3 3.76 10.65 .722 43047' 55.45.4 3.83 11.27 .750 41025 ' 56.75.5 3.90 11.91 .770 39039' 58.05.6 3.97 12.57 .795 37021' 59.55.7 4.05 13.26 .805 36023' 60.05.8 4.12 13.97 .820 34055 ' 61.25.9 4.19 14.70 .839 32058' 62.06.0 4.26 15.46 .850 31047' 63.06.1 4.33 16.24 .860 30041' 63.56.2 4.40 17.06 .870 29033' 64.06.3 4.47 17.89 .880 28021' 64.76.4 4.54 18.76 .889 27015' 65.26.5 4.61 19.66 .895 26029' 65.76.6 4.69 20.58 .905 25011, 66,16.7 4.76 21.53 .912 24013 ' 66.56.8 4.83 22.51 .920 2304' 67.06.9 4.90 23.51 .929 21043' 67.57.0 4.97 24.55 .935 20046' 67.97.1 5.04 25.60 .940 19057' 68.37.2 5.11 26.68 .945 1905 ' 68.87.3 5.18 27.79 .947 18044 68.97.4 5.25 28.94 .950 18011 ' 69.07.5 5.33 30.19 .955 17015' 69.37.6 5.39 30.79 .957 160521 69.47.7 5.46 32.55 .960 160168 69.57.8 5.54 34.00 .961 1603' 69.97.9 5.61 35.31 .962 15051 ' 70.08.0 5.68 36.65 .963 15038! 70.1

12

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The Surfascope Surface Energy Kit

The relationships deterriined in this study have been integrated into a kit and a procedurefor rapidly measuring surface cleanliness in the field or shop as well as in the laboratory.This kit, known as the Surfascope, consists of a Brinell microscope which has an eyepiecegraduated in millimeters, a microsyringe to meter out drops of distilled water of knownvolume, and the experimentally determined curve for converting drop diameter readings tosurface energy units. Figure 10 shows the components of the kit. The Brinell microscopehas a built-in battery-operated light which enables accurate readings to be taken underadverse lighting conditions.

The Surfascope instrument for measuring surface cleanliness is easy to use, and a reading*can be taken in less than a minute. However, certain precautions must be observed. The

method should not be applied to grossly contominated surfaces because dust particles havethe same effect as a rough surface - they tend to increase wettability and will giveexaggerated values of surface energy. Also, the drops should not be applied to a metalsurface which has been heated from exposure to direct sunlight. The heat causes some ofthe liquid to evaporate, and as a result, the measured drop diameters are smaller than theysVou~d be. Following are the simple instructions for the use of the Surfascope.

INSTRUCTIONS FOR INSPECTION OF CLEANED SURFACES

Operating Principle

The SURFASCOPE provides a convenient . d accurate method for measuringthe degree of cleanliness of surfaces being prepared for painting, plating,bonding, anodizing, or conversion coating. Since a clean surface has a highsurface energy, it is reodily wetted by water. The curve of Figure 8 shows tterelationship between surface energy and the diameter of a 5-microliter drop ofdistilled water on a test surface. The drop diameters are measured by meansof the graduated scc!e inscribed on the eyepiece of the SURFASCOPE.

Procedure

1. Place the needle of the micosyringe into the vial of distilled water andmove the plunger up and down until air bubbles ar eliminated. Fill themicrosyringe with exactly 5 microliters of water.

2. Bring the tip of the needle within 1/2 inch of the test surface, push theplunger completely in, and gently touch the drop to the surface.

3. Place the SURFASCOPE directly over the drop. Gently press the tightswitch, being careful not to smear the drop. Read the drop diame'ter tothe nearest 0. i mm with the graduated eyepiece.

If the drop is elliptical, average the long and short axes, or apply a freshdrop. The eyep;ece may be rotated to facilitate the measurement ofelliptical drops. All readings should be mode within 2 minutes after thedrop is deposited.

16

CONTAMINATED SURFACE CLEAN SURFACEDROP DIAMETER 2.6 MM DROP DIAMETER 3.8 MMW

FIGURE 10 SURFASCOPE KIT AND APPEARANC.E OF 5-MICROLITERWATER DROP THROUGH BRINELL MICROSCOPE

17

4. Determine the surface eneigy correspondin- to the .. e-.r., dr,- dianeterthr-jtgh the jte of the plot shown in Fig-ire 8. or the doto ;n Table 1.

5. Determine the actual relative .- midity of the atm-osphere with tWe aid ofthe sling psychroeter. Correct surface energy reading oarined in (4)for deviations from 5 % re!otive ht-nidity by subtracting 4 surface energy•m.*ts for every 10% above 50% relative u.m.=ty, or by adding 4 units firevery 10% below 50% relative -umidity.

6. Comrore the corrected surface energy reodinig with minimumn occeyteblestandards for cho.-ted or anod'sed aluminum surfaces (40 dynes/cm).

Surface-Energy Test for Non-Horizontal Surface;

The mehod for ,messuri g the free energy of clened su,"fcces by measL.ring te diameter ofdrops of distilled water 5 mcroiters in volume was originmi!y devekoed fcr l ,f;zont.isurfaces. A series of experiments were conducted to determine how nuch test surfaceinclination coutd be tolerctad without introd"ucin. significant en' in the srf.acereodings. Through the use of a table which could be :ited through a renve of inclinationsfrom 0 to 90 , surface energy readings were mde on cladi 7075-- 6 oi .mnu.- panels.These -,mels were ciecned with Cleaner No. 11; ard had surface energies of 32-37, ye/o n.Table II summarizes thme date obtained by measuring dops placed on sur-aces _t ,,-iouscngies of incl..-tioit.

TABLE ii

DIAMETERS OF 5-MICROLITER DROPS OF WATER ON iNCUNED SURFACES

Angle Drc-p Dio-neter (mi) Avercaeof A Surface '=

Inclination (IJ (2) (avq) (-ne/c=)

0p 3.3 3.] 3.2 36.22 0° 3.0 3,5 3.25 37.021 3.4 2.9 3.15 32.0

3e 3.2 3.2 3.2 36.2

4 3.3 3.! 3.2 36.2

5& 3.3 3.1 3.2 36.26 0P 3}.3 3.1 3.2, -5. 2

S 70 3 .2 3.3 J .2 37.080o 3.3 3-1 3.2 36.2

900 M. 3.2 3.1 32.0

13

The d=.p dia*!een were mmcel'-Iy unifazm, desplite tho I-mm vctictiom in mc~e ofrcIinv-4i=- Looking -r!~ t.vo eidres, t;he- e are p diarefer for the bcguzontal

v 3xfaoce 3.2 trm cs cc-=xed with.-ecgedo a~ 3. __ c- !c I

svdoce. The differne ;r. znfce -ng wis edt' c.4.2 dyr.rsfc--

In obtaining the cbor-e dcto, -tjvijdji &rps vwere teed -'- eo&- -f. o in, so 2=e offfe vaizfzan haeteen the ai.'~r n Rl t d ;n4n ed ufoce r- hoee been &uetSrii di -fer-cest in the 4-O vohrmes. A sec ot of rez5s sawized ;n lcble ili.

w e by mmtwwi t&e eitretess of the ur-e &.ops an botiihoro oieA vacto

TA62-LE III

OLMIT.'l OF &WME 5-MCROIME D1ROF-S CMH.OqlOW. AL AIM V&RTiCAlr& SUFA(FS

3A 32-

3-132- 3-i42-3 . 32.0 -3. 36.I :3. 32-0 1 3-3 M.0

7 3- 1 32.o 1 32.1 328 3. 1 32.0 3-13.

93.2 3. 3.2 36.2io 1 -. 1 .. -

Ojie of 10 ses car readings- .*me~ wos eo d iffere-ce t~eihae werizcol acwe= i.-2 insacft In tim zafhwr~ cs, ! x =ci= cziate- cppers

res &tsmdk ta that the =e..%>3e et c f &eter in mk fr. -- e y cy e msa! any ongie of inclirbeian F.-= 0 to 963 withoe. Wrd;z=-2 erocs ! oc 4%=t 5 f-scin the vxfo-s-eyos-ee

ia V.kw~c Otpe!4 &--s of dmii.d 5oe iiti~ im wakque weplaced en horizont x werica pmres CE c!-' M7-46 ct%7.inia=, =6~ the pvzfies Cfi te dm*-me92 V~~S Fi- e i I is =2 ftige view oF the pwe~s -.r &the

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IO on the vacgtuc! ponl bw. -%.e d~ziemenc ir, dia~ew~ betasee vze velcc1 afizwtc do&3ohny0. 1 =

19

FIGURE 11 PROFILE OF 5-MICROLITER DROPS OF DISTILLED WATER ON

HORIZONTAL AND VERTICAL CLAD 7075-T6 PANELS

20

Surface Energy Measurements on Surfaces Inclined More Than 90°

On surfaces which are inclined more than 90 from the horizontal, such as the undersideof wing panels or lower fuselage areas, the drops are difficult to apply, and the error dueto gravity effects is increased. For these situations, it was found that qualitative deter-minations may be made with an atomizer spray. If the atomizer contains a liquid whosesurface tension is equal to the minimum acceptable "critical surface tension of wetting" ofthe turfce, the appearance and behavior of the liquid on the surface will indicatewhe.: ir or not the surface is clean enough to paint.

A DeVilbiss Model 15 atomizer was used for these experiments. It was filled with asolution of isopropyl alcohol in distilled water which had a su:rface tension of 61 dyne/cm.The appearance of the spray on a clean panel is shown in Figure 12. Tlhe drops are largeand irregular in outline and tend to merge into a continuous film, indicating that thesurface energy of the panel is equal to or greater than tht of the liquid. Figure 13 showsthe appearance of the liquid on a contaminated panel. The lvquid forms into sphericaldrops which have a large contact a.ngle. For aircraft surfa:es, the minimum surfaceenergy prior to painting should be approximately 40 dynes/cm.

identification of Contaminants on Panel Surfaces

The environmental panels were fabricated and prepared in the shop by productionpersonnel. The test panels were then stored for three weeks on too of an air conditioningunit in te shop area. This subjected them to the same atmospheric pollution, dust, andhumidity that a part for a production aircraft would receive.

The method which wps used for the identification of the contaminants was developed byW. T. M. Johnson.(5,6) The met I surface is abraded with potassium brcmide powder.The powder becomes contaminated with suriace matter and, after collection and pressinginto a potassium bromide disc, is checked for its infrared absorption properties. Theinfrared spectrum reveals the chemical composition of the contaminants.

This method can be used to analyze the surface of paint films as well as metal strfaces.In his studies, Mr. Johnson found that the chemicol composition of the top 20 angstroms ofpaint surface is often consi4erably different from the bulk ccmposition, especially wheresurface-active agents such as silicones are present. Since pigmented paints have virtually100% of the pigment content beneath the surface, the pigment hcs little effect on paintadhesion. Mr. Johnson also found that plasticizers have a tendency to concentrate in thesurface layers of paint films and, by their physical presence, to create weak boundarylayer.

The following is a detailed description of the potassium-bromide procedure used to identifythe contaminants on the aluminum panels which had been exposed to three weeks of shopenvironment.

The panel surface to be analyzed was lightly polished with 300 mg ofHcrshaw's "Spectra-Grade" potassium bromide using a flexible, stainless-steelspatula. The potassium bromide was collectea and mixed. A portion (150 mg)of the material was transferred to a 1/2-inch diameter die (shown in Figure '4)and pressed into a disc using standard techniques. Figure 15 shows potassium

21

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FIGURE 14 MOLD AND PLUNGER ASSEMBLY FOR MAKING 1]/2-INCHDIAMETER POTASSIUM BROMIDE DISCS

FIGURE 15 POTASSIUM BROMIDE POWDER ON TEST PANEL. HOLDER AT RIGHTIS SUPPORTING TRANSPARENT DISC WHICH WAS JUST REMOVEDFROM THE MOLD.

23

bromide powder on a test pariel and a molded potassium bromide disc; themolding press is shown in Figure 16.

-1Infrared spectra were obtained over the 4000 to 200 cm range wii'h aPerkin-Elmer Model 621 Infrared Spectrophotometer shown in Figure 17. Inrecording the spectra of these samples, a plain potassium bromide disc wasused in the reference beam to compensate for any absorption bands due to thematrix material.

The spectrum of Panel A, 7075-T6 Bare, is shown in Figure 18a. Tentative band nssign-

nients nre given in Table IV. The contamination appears to be a mixture, probably

containing a hydrocarbon oil and solvents.

The %rectrum of Panel D-46, anodized 7075-T6 Bare, is shown in Figure 18b, with band

assignment g:.ven in Table V. The strong indication of potassium nitrate contaminationis probably due to the meto-treating salt bath located in the shop area.

The spectrum of Panel E-77, anodized 71 78-T6 bare, is shown in Figure 19a, with band

assignment given ini Table V1. Potassium nitrate predominates, with indications of silica

(as dust) and a hydrocarbon.

The spectrum of Panel F-60, chromoted 7075-T6 clad, is shown in Figure 19b, with band

assignments given in Tb!e VII. Potoss;um nitrate predominates, with indications of silica

(as dust) and a hydrocarbon.

It was anticipated that the shop contaminates would consist chiefly of hydrocarbon oil,

solvents, and dust. The appearance of the potassium nitrate band was puzzling until a

survey of the area revealed the presence of a metal-treating salt both.

Effect of Aging on Surface Energy of Sulfuric Anodized Panels

Initial determinations for freshly anodized panels showed surface energies to be very high.Wettabi!ity was excellent. Many panels were completely wetted by distilled water ofsurface tension 71.7 dynes/cm. Other investigators, however, have reported low surfaceenergies and poor wetfability for anodized surfaces. It was postulated that these surfacesundergo or, aging process which lowers surface energy. To check this, surface energieswere measured for panels immediately after anodizing and again after a period of threemonths. The panels were protected from contamination between measurements by poly-ethylene film. The results of this test are given in Table VIII.

The surface energy measurements were taken 3 months and 10 months after anodizing. Themagnitudes of the changes in surface energy after aging for 10 months range from 1 tc 8dynes/cm. This indicates that aging is not a significant factor in poor adhesion onanodized substrates.

24

FIGURE 16 PRESS UWED FOR THE PRODUCTION OF 1/2-INCH, DIAMETERPOTASSIUM BROMIDE DISCS

FIGURE 17 ABSORPTION CHARACTERISTICS OF POTASSIUM BROMIDEDISCS BEING-7 OBTAINED WITH A PERKIN-ELMER MODEL621 INFRARED SPECTROPHOTONIETER

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26

TABLE IV

BAND ASSIGNMENTS, TEST PANEL A (7073-T6 Bare)

Wavenumber Characteristic

(cm- ) Groip

3450 H20

3380 NH2

3300 NH2

2950 CH 3

2920 -CH 2-

2850 -CH 2-

1680 C = 0 (Ketone)

1600 -NH 2

1455 mor.--subsihtuted phenyl

1400 2 -

1392 CH 3

1380 gem methyl

1370

755 NH2 , rmono-substituted phenyl

685 nono-substituted phenyl

390

TABLE V

BAND ASSIGNMEN T . TEST PANEL D-46 (7075-T6 Bare Anodized)

Wavenumber Characteristic

(cm- ) Group

2420 NO

1385 NO 3

1100 SiO 2

1030 SiO 2

830 NO3

820 NO3

460 NO 3 , SiO2

27

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28

TABL.E VI

BAND ASSIGNMENT, TEST PANEL E-77 (7173 -T6 Bare Anodized)

Wavenumber Characteristic

(cm) ) Group

2920 -CH22830 C2

2445 NO 31765 NO 31385 NO3

1100 S1030 S102

830 NO3

820 NO 3520460 NO3 Ss02

29

TABLE VII

BAND ASSIGNMENT, TEST PANEL F-60 (7375-T6 Clod Chromcted)

Wa, ven bef Choracteristic(cm- ) __ _ _ _ _

3350 H202950 CH 3

2920 -CM2-

2850 --H2-

2480

2420 NO.

2400 NO 3

178

1760 NO3

1380 NO 3

1100 SiO 2

1020 SiO 2

870

833 NO 3

820 NO35=,3O

530460 NO3SIO2

30

TABLE V134

AGING C* AODJIZED SIRACES

Dec.04 196er7 (d-ns0~ 1____ S,

E 15 C, 6. 70.D 29 CI.7.06-

E__ _ _ V ___ __ __ __ 67-5__ __ _

DI0 C-W. 69- 63-5

E E107 C.W. CWj 69-5

III - LABORATORY EVALUATION OF CLEANING PROCEDURES

The corrbinaticn of aluminum substrates and surface finishes used in this program arepresented in the following table:

TABLE IX

SUBSTRATES AND SURFACE FINISHES

Panel Code Composition Finish

A 7075-T6 Bare NoneB 7075-T6 Clad NoneC 7178-T6 Bare NoneD 7075-T6 Bare AnodizedE 7178-T6 Bare AnodizedF 7075-T6 Clad Conversion Coated

The folILwing leaning methods recomriended by the Naval Air Engineering Center andthose in current use by Lockheed-Georgia and Lockheed-California were evaluated in thelaboratory by means of radioisotope, hydrogen embritt.lement, surface energy, andenvironmental exposure and adhesion tests.

Method 1 - This method consisted of brushing a coat of Cleaner IV* on thepanels, rinsing with water, neutralizing with 5% by weightaqueous NaHCO,., and again rinsing with waler. The cleanerremained on the eanels for 15 minutes before the first rinse.

Method 2 - A layer of Cleaner i11. 5 to 10 mils thick, was applied to thecontaminated panels and rinsed with water after 15 minutes.

Method 3 - The panels were wet-scrubbed with Scotrhbrite No. 447 Type Apads wetted with methyl ethyl ketone with mcderate pressure andjust o:?ng enough to abrade the surface to brigitness. The loosepowder formed by the strubbing operation was removed with papertowels wet with methyl ethyl ketone.

Method 4 - The panels were soaked for 15 minutes in a solution of Cleaner I,diluted to the manufacturer's specifications, and then rinsed withwater.

Method 5 - The substrates without surface treatments were solvent-cleaned.Cleaner V was applied for 15 minutes; the surfaces were then

*See Appendix A for identification of cleaners.

33 Preieding page blank

r4-is wirn water and dried. Spray Coating 12 was applied priorTo the 3-week shop contamination period. The anodized andchromated substrates were coated immediately after processing.

Method 6 - The panels were wiped with paper towels wet with Stoddardsolvent. They were then scrubbed to brightness with ScotchbriteNo. 447 Type A pads wet with water, given a water rinse, and afina! solvent wire.

Method 7 - The substrates without s,face treatments were solvent-cleaned.Cleaner V emulsion cleaner was applied for 15 minutes, rinsedwith water, dried, and then coated with Spray Coating 13 toprotect the surfaces from contamination. Anodized andchromated substrates were coated immediately after processing.

Method 8 - Cleaner VI, diluted according to the manufacturer's directions,was applied with a brush and permitted to remain on the panelsfor 15 minutes. It was then rinsed off with water at roomtemperature.

Method 9 - The panels were cleaned by applying a layer of Cleaner IV, 5 to10 mils thick, and rinsing with water. They were then treatedwith a solution containing 5% Na3 PO4 and given a final waterrinse.

Radioisotope Evaluation Test

The relative efficiencies of the candidate cleaning procedures were determined bycontaminating test specimens with radioactive stearic acid and measuring the 9ztivityofthe specimens before and after cleaning. Radioactive stearic acid contains C'4 whichemits beta radiation having an energy of 0.155 MEV. Stearc acid was chosen becausethis material, or a similar wax, is often used as a lubricant on interference fasteners andrepresents a typical plant contaminant.

Discs, 2 inches in diameter, were cut from each of the 6 Al substrates: 7178-T6 bare,7075-T6 bare, 7075-T6 clad, 7178-T6 bare anodized, 7075-T6 bare anodized, and7075-T6 cla chromated. Three specimens of each substrate were contaminated withstearic--C 14 acid dissolved in toluene. The stearic acid solution was spread evenly overa circle 1-1/4 inches in diameter centered on the disc. The toluene was evaporatedlecving the specimen contaminated with stearic-1-C 14 acid. The radioactivity cf thespecimens was measured with a Nuclear Measurements Corporation proportional counter,Model PC-3T (see Figure 20). Contact-angle measurements were made on the contami-nated specimens before and after cleaning to provide data for correlating the radioisotopetest results with surface-energy measurements.

Each cleaner was used in the manner prescribed by the manufacturer, with theexception of the rinsing procedure. Because of the residual radioactivity, all of therinse "ater had to be retained and transported to a disposcl point later. To reducethe amount of contaminated water and to ensure adequate rinsing, each specimen wasrinsed thoroughly with the jet fro-i a wash bottle. This method provided maximum usageof the water for rinsing without limiting the amount of water used on each specimen.

34

The isotope investigation was conducted in a laborator/ reserved for radioisotope work andconventional safety precautions were observed.

_ N

FIGURE 20 MEASUREMENT OF RESIDUAL RADIOACTIVITY IN NUCLEARMEASUREMENTS PROPOR71ONAL COUNTER MODEL PC-3T

Of the proposed 9 cleaning procedures, 6 were suitable for investigation by isotopes. Theeffectiveness of each cleaning procedure was determined by two independent methods: theresiducl radioactivity and the "criticcl surface tension of wetting" technique. The resultsof the rodiotracer tests are summarized in Table X.

Most of the cleaners did a good job of removing the radioactive stea;ic acid from the bareand the clad panels, afair job of remova! from the chromated panels, and a very poor jobon the anodized panels, This is due to the porous nature of the anodized films. Oncecontaminated, anodized surfaces are very difficult to clean.

No one cteaning method was equally effective on all substrates. In order to simplify theevaluation process, a system was used in which quality points were assigned to tlecleaning methods which ranked first, second, or third in cieaning effectiveness for eachtype of surface. Three quality points were assigned for first place, two for second, andone for third. The quality ?oints are shown in parentheses in Table X and are summarizedin Table Xl. According to this rating system, Cleaner Ill was the best of the cleaners with12 points, Cleaner IV in second place with 11 points, and Cleaner I third with 8 points.Cleaner Ill was significantly better than the other cleaners in removing contamination fromthe anodized specimens.

The surface energy data are s,mmarized in Table X.1. The use of Cleaners III, IV, and VIresulted in high surface energies on all substrates while Cleaner I resulted in a low energy

35

TABL.E X

RADIOISOTOPE EVALUATION OF CLEANING EFFECTIVENESS

Radiation Count Radiation CountSubstrate Cleaning Method Before Cleaning After Cleaning

I Counts/Min. Counts/Min.

Cleaner IV 138,000 496 (3)*7075-T6 Clad Cleaner !11 190,000 3,901Chromated Cleaner V 155,000 1,7,j1Conversion Cleaner I 120,000 1,283 (1)Coating Cleaner VII 194,000 1,350

Cleaner VI 128,000 1,067 (2)

Cleaner IV 117,000 96,0007178-T6 Cleaner Iii 109,000 36,000 (3)Bare Cleaner V 145,000 108,000Anodized Cleaner 1 99,00%0 61,000 (2)

Cleaner Vii 117,000 67,000 (1)Cleaner Vl 100,000 81,000

Cleaner IV 120,719 92,5897075-T6 Cleaner ii 108,542 36,168 (3)Bare Cleater V 145,095 108,142Anodized Cleaner I 99,000 61,000 (2)

Cleaner VII 117,000 66,000 (1)Cleaner VI 100,000 81,000

Cleaner IV 87,000 327 (3)Cleaner H1t 145,000 292 (3)

71"8-T6 Cleaner V 122,000 23,000Bare Cleaner 1 141,000 645 (2)

Cleaner VII 149,000 817 (1)Cleaner VI 141,000 3,985

Cleaner IV 93;000 583 (2)Cleaner 1i 129,000 2,4837075-46 C!eaner V 1 136,000 10,000Clod Cleaner I 1 139,000 658

Cleaner VII 162,000 613 (1)Cleaner VI 142,000 341 (3)

Cleaner IV j 102,000 282 (3)Cleaner i! 164,000 289 (3)

-075-T6 Cleaner V 11 1,000 13,000Sor Cleaner 1 123,000 3,838 (1)

Cleaner VIi I 53,000 6,065Cleaner V! 153,000 529 (2)

*Qual;t-Y Points

36

TABLE XI

RADIOISOTOPE EVALUATION RATINGS OF CLEANING PROCEDURES

Cleaners

Substrate I ScolchbriteIV I l V I+ MEK VI

7075-T6 Clod12Chromated

7176-1"6 Bare 3 2Anodized

7075-T6 Bare 3 2Anod~ized

7178-T6 Bare 3 3 2

7075-T6 Clod 2 13

7075-T6 Bare 3 3 1

Total 11 12 8 4 7

3 Quajity Points - First Place2 Quality Points - Seco nd Place1 Quality Point - Third Place

37

TABLE Xii

SURFACE ENERGiES OF PANELS BEFORE AND AFTER CLEANING

Drop Diameter I Aftee Cleanin(rm) (dynes/cm)

Substrate Cleaning Method -Before I After I Before After

Cleaning Cleaning Cleaning Cleaning

7075-T6 Cleaner IV 2.76 4.40 18.0 64.0CldT Cleaner 111 2.84 3.90 1 22.5 5-.0

Chro,nated Cleaner V 2.98 3.62 27.5 51.3Conversion C leaner ! 3.12 2.63 32.0 13.0Coating Cleaner VII 2.98 2.91 27.5 24.0

I Cleaner VI 2.98 4.33 27.5 63. 5

Cleaner IV 4.05 5.7 60.*0 70,17178-T6 Cleaner iVl 4.26 5.7 63.0 70.1

Bre Cleaner V 4.12 5.7 61.2 70.1

Anodized Cleaner i 4.33 2.6-3 63,5 !3.0i Cleaner VII 4.12 2.98 61.2 I 27.5Cleaner VI 4.12 1 5.7 61.2 70.1

Cleaner IV 4.05 5.7 60.0 70.1

7075-T6 Cleaner Ill 4.40 5.7 64.0 70.1Bare Cleaner V 3.90 5.7 58.0 70.1

Anodized Cleaner! 4.12 2.63 61.2 13.0CleanerVl 4.12 2.91 61.2 24,0Cleaner VI 4.12 5.7 61.2 70.1

Cleaner IV 3.19 4.54 36.2 65.2Cieaner Ill 3.05 I 4.97 29.4 67.9

717846 Cleaner V 2.76 3.97 18.0 59.5Bare Clecrner 1 3.12 2.63 32.0 13.0

C,eaner Vii 2.91 3.55 j 24.0 49.2Cleaner VI 3.12 4.051 32.0 60.0

Cleaner IV 3.27 4.69 37.0 66.1Cleaner Ill 3.05 4,97 29.4 67.9Cleaner V 2.91 4.05 24.0 60.0

Clod Clearer 1 3.19 2.91 36.2 24.0CleanerVI 1 3.27 4.12 37.0 61.2Cleane.VI V 3.05 5.39 29.4 69.4Clear'er IVI 1 .97CFe3ner IV 2.34 3 40.0 59.52.84 4.69 22.5 661

7075-T6 Cleaner V 2.91 3.48 29.0 46.0Bare Cleaner I 3.12 2.63 32.0 13.0

Clecne-VII 3.12 3.83 32.0 56.7Cleaner VI 2.93 3.55 27.5 49.2

38

surface on all substrates. Cleaner i appears to leave a adsorbed hydrophobic film on thesubstrate and data from the adhesion test shows that it adversely affects paint adhesion.Cleaner Vii resulted in a low energy surface on the substrates with surface treatmentsii (anodized and chromated) but provided omuch higher surface energy or. the untreated

IM panels. This indicates that this cleoning procedure is only moderately effective inremo~ving contamination from the rougher surfaces of the anodized and chromnated substrates.

I Even though the radioisotope count of the anodized panels indicate that they were notclean, the surface energies of the panels were high. This means that the residual radio-active contamination was in the pores of the anodizing and not on the surface. CleanerIV was an effective cleaner, but it also removed the chromic acid sealer from theanodized film.

Results of the radioisotope evaluation show that Cleaners Ill, IV, 1, and VI, in that order,ore the most effective in removing the radioactive contaminate. The surface energymeasurements indicate that Cleaners 11l, 11", and VI provide a high energy surface.Cleaner 1, in contrast, leoves on adsorbed hydrophobic film which creates low surfaceenergy.

Hydrogen Embritflement Choacteri~tics of Cleaners

Cleonem which cause embrittlemnen' of high-strength steel fasteners cannot be used on:aircraft surfaces. The hydrogen embrittlement properties of the candidate cleaners wereevaluated by means of the Lcw-rence Hydrogen Detection Gaouge, shown in Figure 21,which measures the hydrogen evolution characteristics of plating and cleaning ->lutions.The hydrogen gouge measures the pe.-meation of hydrogen into a steel-shelled probe(Figure 22). The pressure change caused by thte hydrogen permeation is measored alec-tronically by an ionization gauge.

Th sltions and cleaners were checked for their embritoling characteristics by immnersingthe codmium-pla.-ed steel-shelled probe in the cleaning solutions for 1 hour and for14 hours.

The successful use o~f the Lawrence Hydrogen Gauge is dependent :;pon vety close conttrolof oil operating variob'es. Detoajed instructions are given in the Instruction Manual forthe-Hydocen DetectinGue ' The following is a brief description of the testprocedures.

Probe Preparation

The mnetal-shelled probe, shown in Figure 22, -was baked out to remove residu-al hydragen.This wcs done by placing the probe in the Lcwrence Clew -Up Rock which achievre-, thenecessary high temperatures by electron boatbardmnent of the i'un collector p~late within theprobe. After coling the probe, the coated area was masked with rubber hubing sock-lythe metal window was orposed. It was then n.,aunted in the rotating fixture oiTo sand blastunit and blasted wiih 100grit a!umina %.r30 secons with aprure of ;ips-i. The pro!>ewas then wiped with pqw toweling wet witi, retwe to remove adhering altmina powder.

39

FIGURE 21 DETERMINiNG HYDROGEN EMBRITTLEMENT CHARACTERISTICSor CLEANING SOLUTION WITH LAWRENCE HYDROGENGAUGE

FIGURE 22 HYDR OGEN DETECTION PROBES AND HOLDER

40

CalibroFt-n

T6e probe was immersed in a a% NoCN/5% NoONi both and cathodicolly etched for-: 180 seconds with a -.urfent density of 15 cxnps/ft2. The probe was then removed from the

both, rinsed with distill'id water., and given a finail rinse with acetone.

I he probe was in~serted in the over of the hydrogen detection gouge. The heat causes aportion of the ionic hyiroV-n in the metarl shell to be driven into the probe. The pressurechanges, measured electronically by raeans of the l-Ydrogen detection goauge, ore propor-tional to the total hydrogen originally absorbed by the steel shell. The hydrog3en valuesobtain~ed in the calibration step represents the oinooint of hydrogen which will embrittlerings of 4340 steel, heat-treated -.- 260-280,000 psi anid stressed to 95% of ultimatetensile strength.

Plotir3 of Probe

The ca'i!;.iaed probe was szrKI blo,;ted to rerimove the --xidized surface of tfe window andwasaiced ith a thin ilm of cod'nkmn oy immersing !Se Probe in a standard pla!ing both

For exzctly 6 mirmstes with a current density of 60 :5 cxnps/ft 2 . 16t was then given ati*.-ough rinve with cold water and a finol rinse with acetone.

Hydrogen Effusiona of Cleanters

The plated prob~e was pload on the cecm-jp rack and baked to remove the hydiogenabsorbad duriNg the plating operatirn. It was then inmmrsed in the cleoner beingevaluated to a depth of 1/4 inch obo~,e the plated wine.-w. T he probe was rermoved fivamthe test sotuticn and thorouqhly riraed with water ard -given a final rise with acetone.The pro~e vms then placed in the probe socket mAnd insetted inic the oxen of the hydroqzn

F delection givie to determine tiw amcunt of hydroen &=srbed by the steel :helIl.

The ratoa of tshe hydrogen evolved by the test scluton io the iqdrog-2n evolved by thecalibraffig scluti-m is defined as the 'hydrogen ef-Fsior. value' of the test solettion, rndgives an indiectioni of its embittlerne:t properties. Hydrogen effusisor values greater than1.0 cre uriacceptable~and represent soluziorts which wil em~bittle 4340 high-heat-treat-teel i-n the time ipterval used in the test. Tabies Xl1i ax' XIV = -nmrize t -b- hyroeeffiion values obtu:4-,e fcr the various cnt in 2 1 -hoir inwersion periOd --nd in aI 6-hosir immerion period.

* ~~The restus -Jf the !4xx.-r ie.resicn test inzsdc2tes that the Cleaner M~ is nnerthnwhile the Cleener WV evolved 14 tim hen taicmi allowoble iYdrCP"n. The 16-hourivmerion test results sh-owed thet the Cieaners I aid II ere v~rpleteiy oaFe. Cleaner. it'!dd yield cn ezii rxov of hydrogen afttr *.I.e polor-geci iers~on pectied.14-wever, since a ciearzing solution n==H -/ y wajdd not rzmcin on an corp' cts- for "-xreflxm 2D or 30 taiirut:, cny solution which cives a h~edrogen effusion volue of 'es n

-. he 1-h= r test period shovld be safe for use. iridr.eendent notched-ring tests --. tiheCleaner If! conducted~ teN I~ Air Oewrelopnviit Center, P1 iodelphsia, showed nhydrqSen embeitting efect within 20D fxurs expo-.are to s-..rs. Cle=Aner P/ is teonlyclean"e ir. the group which is obvi"-11y eemb-itrl!ing and which shozwld not be used forcle=a.in aircraft.

4:1

HYDROGEN EAIIl r C,

HYITROGENE-M BROTTLEMNT P, ROTiES OF CLEANING SOLUTIOI-5

16-Hnur Immersion

Ciecnng So -'io-i Code No. I Run ,.. Hydrogen Effusion Volue

0.901 2 E0.96z 3 0.44

A v er o ~ ej0 .50II I

- 2 i0.11ii 030

j Aer-3e 0.22

1 7.7fI i 2 4.8

! : ! >25

i_ A2 >25

SI2.74

2

V 3 1

. I I0. I"-I I 2I.

S 21

Av e'% az 7'

I I-2I

V., 1 2 O-S

3 -1a________________________________________ _____________.__ ____________________6 __________

Z2

!A-B- XIV

'YDROGEN EAAWTTLENCENT PROPERTIES OF CLEANING SOLUTIONS

Cle~ip So lutinCode fL,. Run N-I'bf~s~ V~

Ii23

IV a

*V~-sgea:e.m -0 i1dct *0=tesoni

13 O

Preparation of Environmental Specimens

To evaluate the effect of the efficiency of the various cleaners on the adhesion of paint,specimens were fabricated by manufacturing personnel and subjected to normal subjectedto normal shop handling and freatmen t through the chemical finsihing step. After thefinishing operation, the panels were placed on top of a shop air-conditionisN unit near thereturn-a'r intake. The specimens were exposed to normal shop pollution and dust for 3weeks. In addition, one set of panels was contaminated with hydraulic fluid (Mil-H-5606)and baked for 8 hours at 3000 F. The panels were separated into 9 groups; then eaci groupwas cleaned by one of the 9 canclidate cleoning mehod3. Surface-energy measuremenhswere taken on the panels before and after. cleaning. Table XV summarizes the surface-energy measurements. The cleaned specimens were painted in a production-line spraybooth by manufacturing personnel. The specimens were sprayed with one coat of Specifi-cation Mil-P-23377 epoxy polyamide prime- and one coal of Specification Mil-C-22750epoxy polyamide topcoat.

Surface Energy Tests

The panels were cleaned by the procedures previously described. Surface-enrgymeasurements were mode on the panel, before ad after cleaning. Tab!e XV summarizesthe surface-energy readings obtained on the panels cleaned by the methods just described.The panels with the highest critical smface tension oi wetting hove the highest surfaceenergy ;Y!d, theoretica!ly, the maxi.um degree of cleanliness. Cleaning methods 1, 2,and 9 achieved complete wetting of distilled water on the anodized .alwels and gavesurface-energy readings of more than 49 dynes/cn on the bore, clad, and chromateconversion-coated panels. This compares well with the mininmx, value for acceptablepoint adhesion. 40 dynes/cm, established in this program.

Cleaning methods 1 and 9, which use Cleaner IV, left the surfaces mottled with whiteareas. The surface energies of the white areas were greater than those of the normal areas,possibly due to surface roughness a.d powder. Cleaner IV also renioved the sealer fromthe anodized paneIs.

Method 2, using Cleaner Ill, was easy to apply. The cleaner spread evenly and rinsed offteadily with water. Surface energies of the cleaned panels ranged from 54.0 dynes/cm tovalues indicating complete wetting.

Method 8, using Cleaner VI, also gave complete wetting of the anodized paneis, butrelatively low surfoce-energy readings on the other substrates. The cleaner did not spreadreadily on the panels with the chromate conversion coating. An alternate solution ofCleaner Vi, which did not contain Stoddard solvent, gave better results.

Both methods involving the use of Scotchbrite pads, Methods 3 and 6, were laborious andtime-consuming. The fine powder of oxide and metal, which resulted fron the surfaceabrasion, was difficult to remove by rinsing, and the surface energies of the cleaned panelswere low except for the anod;zed panels. The 3ow values of the surface enemy may havebeen caused by an adsorbed fiim of solvent.

Of the entire group of cleaning procedures. Method 2, involving Cleaner IIl, gave thebest combination of ease of application, hi h-energy surfaces, and uniformly clean panels.

44

I

TABLE XV

CRITICAL SURFACE TENSION OF WETTING OF CLEANED PANELS(dynes/crn)

Paei Finish

Cleaning I j j I

Method* 7075-T6 7075-T6 7178-T6 7075-T6 7178-T6 J7075-i#,6Bare Clod Bare Bare Bare CladBae la Bre Anodized Anodized Chromated

55.4 63,5 56.7 Cw t CW 7A2 59.5 68.8 58.0 CW CW 54.0I I

29.4 27.5 13.0 46.G 61.2 24.0

4 3.0 36.2 13.0 27.5 24.0 22.5

5 12.0 36.2 36.2 13.0 13.0 16.f

6 6.0 16.0 32.0 64.0 59.5 22.5

1 7 49.2 54.0 55.4 46.0 -- 44.0

8a 27.5 32.0 40.0 CW CW 51.3

8b 64.0 70.1 68.9 CW CW 62.0

9 .2 58.0 62.0 CW CW 63.5

*See page 33 for detailed description of cieaoning method.

SCompleta Wetting

45

Environmental Exposure and Coating Adwhesion Tests

Environmental Exposure

One group of the painied specinens, representing each of the six sdbstrtes zleaned byeach of the nine methods, wo- s to a salt spray and Weatherometer cycle consistingof 14 days in the salt spray chwnbeer, 7 days in the Weatherometer, and 14 odditiona! dcrysin the salt-sprc-y chcxn.er. The ec,es of thcze panels were dipped in ceresin wax tominimize edge corrosion. A second group of pa els, duplicoiing the fi.t group, wasexposed to 100% relative humidity at I 1l0F for 48 aour3. The third group of panels wasconio.-ni rated with Specification Mil-H-_W6 hydroulic fluid, imoked at 3009F .or 8 hoursbefore cleaning. After c!eanir, those panels which hod beem cO(.tc,1l ..0t d wizhydrmulic fluid were painted with the epoxy p*lycmide system. 1he fourt% group of panelswas painted after cleaning ad was not subjected to environmantai exposure.

Figure 23 is a view of the envimnmenta, specimens in the salt r ,v c..,.r. Figu.,es 24and 25 show specimens -eing subjected to simulated sun and rain in c. Weatheoweter unit.Viswal examinations were made to determine any obvicois detrimental effects of the vaiousexposures on the coating.

it was found that the coating on the sal-spray Weatherometer specir.ns yellowed andbecome .ough and cohesive. Bistering was observed oan.= the high hidity and tempera-ture specimens clearied by certain methods.

Adhesion Tests

The adhesion tests were conducted with a 'Scmtc6 m.ster' Paint-Adiesion Tester. (T.n'sinstrument was developed by the E. I. duPont Company arnd was on loon to he LockheedReseorch Laboratory from the Aeronauticol Moterials Department, Naval Air DevelopmentCenter, Philadelphia, Penilvania.)

Since +he objective of the curre-it program -was to select fte best of a nunber of cieaningsystems, it was necessary to have as mutrh quantitative data as was obtainable.

The usual paint adhesion tests, the knife test and the tape test, ptovide only subjec:ivedata; i.e., pass or fail. The 'Scratchnaster" simulates the knife adhesion test but clsoprovides quentitative results.(8) This insrument scratches a coated test surface at o constcltrate, while the loJ on the cutting tool is varied between zero lood cAd full load. Bymesuring the length of exposed metal visible in the scratch, the 1od on. the cutting toolat 'he point where the paint is no longer being scraped from the substrate many be calculated.it should be noted that the "Scratchaster" does not measure adhesion directly but gives areading which is also affected by the other physical properties of the czating. The dataobtoned from this instrumeant might not give a valid comparisen of the adhesive propetiesof twO or more different coating systemns where lfhe paint properties such as hardness,eicmg.tion, and cohesive strength, have wide varictions. However, the "S-cratchrnaster"is ideally suited for the_ current inwestigction in which various cleaning rnethod& for asingle pcint system are being evaluated. The data obtained provide a reliable bsis forevaluating point adhesion.

Figure 26 is a photograph of the "Scratcl"rastie" paint adhesion tester. Figure 27 is ov:ew of specimens wiih good and p 0r paint adhesion. Detailed instruction; for operatinrgthe "Scraichmoster" are in Appendix 6.

46

__ T7 ---------7--- ~~-'

FIGUVE 23 ENVIRONMENTAL SPECIMENS BEING SUBhJECTEDTO 5% SALT FOG

47

FIGUP.E 24 SPECIMENSS 3BiNG SM~.W-MED TO SIMULATED SUN ANDRAIN IN ATLAS 'WIEAriER01MR

RGURE 25 ITERIOR VIEW OF WEA!iEROMVETE--RS~rI"l4G XENON LAMP

I4

EI

j:IURE 77TEST S(Y.ATCOHES %N ?PiN4i Wl 00(XC &) A-N:IIGURE 27 PAR? n ADHESION

eeo

trcis he soft c!±%zrx-j Qf eud teis reviv ce 10 the cuffiv, disc thol did A-e MeWittie epoxy coaiirs. OCem- the cer~ic disc b~d cut th~nh the 0,-,ric cofk A 6P.n-.> the clmd ~siz-sbe. b~e mrec! w~ eqxoed *I*r tentire iS= itrowel ci !4et~Th 6 mo~e as so lwed by opein w:.th no wekit exceptr-4 3=; f he- CcgCe ---A-akwxHng the ccmiege ite-g h to iicte t11* =cc cs --eirgt d=' czoved cioq t!hewricce-. Ths e-ecmziq:oe pr-;e reprad=#bWe wjit on he co ubv=tes. In cms. OiPoor maint Cdhftso'., it V,-3 $--xTd ',ix- A'- Cutting disc WO5d siAde %p -eties or crcips hEWOr the scwh W=s -~ee In va CC!, *-- Cutting dis= 5;30uld be rby liffin the bacoc.ce a=. zc~ced all p:zIir fc*s retumed to * gosuic- pm-edng thePow.t C: %romch it rze Lip C th fkies c ;- :.>~ fif"W te se'ctch..3

TCSs XV! I~ X1 Vzc~ize- twe feW~ItS Of fihe Cd-A!S;i tests. Thbe .-A-n&S in *.ne

mcalo- repfnt the Usio'== of bco o ci' ihe 'mng t=1 C4 the Pyatt ~Where the pantFi! ;s etd-te cade ca~t :,. cx ose. im betier Orer ~eeaf 6:- fl%.z Itheqmr.ef the lood cequired o ra=,vc) Sime the efficifta.cies ef tbe v s clemoinm=e.% -s depend on v~fKc-tkrC-s of Obe =eiat smf cems, a epc tc;-Se in= been cnacled for

ec of the Sim 37rctes. The fif St C01ugm of e.--h ICe qi One code g=!er oE rhe

Eriect oF CL-aIho& Met n S-ims -

I- This meyhod ihSm-c pcoid excelk& ~a cn -f ci r-sm-t. A ckody smce reczeined dte dlemig il did-toff ect oeg~fti -- si-wfce ft"g - his =etbod wim. tse~effiers in mam n Ame bvked-onb&,i f PAmd iwr ahe

c=Vo;=-t &h c~poi tixt provid ias effectmenss c!=2Cmms f-.men em!ritas.eri Cf h -s. stel -

Methed 2 - This =ethod w :st as eff ective --s I =4 9, except qhct it did r4o-effectively remce e Iokcod-cn fhy-m-ic fifid fisom the amoized

Method 3 - The sesufts of this vcthdwre poor-.1 It ws iEffective in rervviogtim hyldnvlic -.-ud f-.-,= cil o; fae szkiroe. ThecItn*bpocr adhesion. 1P~ addificci blister were c~or oexpsed to h- h b&Idrd-f, cri brisis cpeed cccsknolly -%-rperaen1s exposed to the salt sc-- t cycle.

Method .-A o-enez- sufcce resulled Ili=n the use co9 this clecL~vAppcrently, a c =po.ent in the clear v wasre !* t?.*e sub-Sim: e, =14- this ci~t=-incticn caused the low auioce energies.This ck-one dd not effective.'y re thele fhydrcii t vid. 711eotheS7cn valuem Off s-Peci;=rd e-Xposed to 100% reitie fx=:dity .1 IP ~coristentiy loYW.

SetO 5- This method, ~ihinvolves c s~mycvie, Icdss~c~ ~~tvfib=, provities excelleni peotecloa cgoinsf conton-irnafkc 1.--h

fb wcs cpplied ofter cleoning of, in the case Ow h criodsized ardcftom.=:ed substrates, ofter pmocesiang. After 4me e=posure tlo

so

sc~A~cvA~rE Ar~H~iON RESEULTS&;.re- 70.75-46 3Se Afzxm~nm= Alloyr

(Eipi -woe2e-1s ei sh= ccwmxinc idire c l

A - W

£ 2

0-96~ 02 j -C - -*I30 - ~ijei I eie069 2:

16-83 0.9251 o-2?52.796 -2c-t -7 0 l- ~-j 2-32

8.iv0.83 0-8 -83i2~1-8 0 _ 7, 0.80-22 c IMre! i!ie tf fia sesu so M% th- it wc-sce- te ci 4--

- :76 Ckcd Aficy(Exae io 3 w~*!m -c~ s;,= cl~r~o e r cti'g

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2 Z *1z0 -5 -6 32

3 0-63 1-91

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L 0.I 0 I 79 0. 0132 0.45_[-

TABU~ x1~

5 QAC-AAS E ADEO9N ES-1R91 SU155

S3 =t~mC si ~c - bervs c

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contamination, the film was stripped from the specimens, and theywere painted without any additional cleaning. The specimens weredeliberate!y contaminated with hydraulic fluid by applying the fluidover the film and allowing it to remain in contact for 24 hours.R -suits indicate that the hydraulic fluid does not permeate throughthe film.

Method 6 - This method is similar to Method 3, except that water is substitutedfor MEK as the liquid in the scouring processing. There was nosignificant blistering with this method and its efficiency inremoving hydraulic fluid is better than that of Method 3. However,the low adhesion results on untreated substrates contaminated withhydraulic fluid and generally lower adhesion values from the highhumidity conditioning cause this method to be rated lower thanMethod 2. Adhesion values from different panels exposed to thesame conditioning were often erratic.

Method 7 - This method involves a sprayable protective film removedchemically. Its performance is comparable with Method 5. Thechoice between the two methods would depend only on theeconomics or preference of the type of removal procedure:chemical or hand-strippable.

Method 8 - Cleaner VI, diluted with a mixture of water and Stoddard solvent,was used in the laboratory evaluation of this procedure and gavegood reults on all tests. Several months after the laboratoryevaluation was under way, Lockheed-Georgia began to useCleaner VI, diluted with water only, for cleaning productionaircraft. Since this formulation was giving ex-cellent results,chromated 7075-T6 clad alum;num panels, cleaned with an aqueousdiluticn of Cleaner VI, were subjected to the battery of environ-mental and adhesion tests. The results are lisied in Table XXI.The elimination of the Stoddard solvent improved the adhesionvalues on the paneis subjected to high humidity at 110 0F and onpanels contaminated with hydraulic fluid. Based on these results,Method 8, with no Stoddard solvent, was selected as one of thetwo best cleaning procedures.

Method 9 - This method is the same as the previous Method 1, except that afinal phosphate rinse was added to improve adhesion. The phos-phate rinse did not improve adhesion. All other commentsconcerning Method 1 apply to this method.

The cleaning methods were compared by adding the adhesion values obtained for each ofthe four test conditions (Tables XVI through XXI), and ranking the totals for each substrate,the highest adhesion total being assigned 5 points and the lowest total assigned 1 point.The cleaners which were disqualified because of hydrogen embrittlement charcacteristicsand the methods which included the use of strippable protective films were not consideredin the final rankings. The strippable protective films were extensively evaluated, alongwith other tempore'ry protective films, at the Lockheed-California Laboratory. Table XXIIsummarizes the ranking of the qualified cleaning methods and gives the grand total foreach method on all substrates. The highest point total represents the method providing thebest overall paint adhesion.

54

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55

U~tCUIL-tr -'- .l* .u . ... *... ill t,-4 6k m ,, 1 rnt;nnr nf tht rdeonina procedureseligible for cc-.sideration. Methods 6 and 8 ranked second and third in total adhesionscores. Method 6 involves the use of Scotchbri'e pods and Method 8 uses Cleaner VI.Method 8 gave t'ie best performance of ony of the cleaners on the chromated substratewhich is of primary significance in this evaluation. Method 6 required considerably morehand labor and was prone to blistering when exposed to 100% relative humidity at ?200F.

On the basis of this analysis, Methods 2 and 8, which use Cleaners IIl and VI respectively,were selected as the cleoning procedures for use in the field tests on Navy C-130 andP-3B aircraft.

56

IV - LABORATORY EVALUATION OF STRIPPABLE COATINGS

6 clai ,clu-ninu.' alloy were fabricated, clec-ned, cnd chromted %,,ithiing Lockheed-Caoifomnia procedures thro-ughout. They were immediately, hand-Feelable and five cl'emical!y removable protective coatirtas. One

:as sent to Point Lama, California, or outdoor exposure tests. The,onels was subjected to a battery of evoluction tesis.

Test Coatings

hond-peeloble coatings were coded as Nos. 10, 12: 14, 16, n-d 18. The chemically.Jovable coatings were Nos. 11, 13, 15, 17, and 19. Tihe monufactaurer -nd .cndor

.asignations correspo- jing to each number cre listed in Appendix A.)

Test Specimens

The 7075-T6 clod aluminum specimens, three per test, were 3 x 6 x 0.04 inches in size,except for the table abrader panels, which were 4 x 4 x 0.04 inches. The chemicaliyremovable coatings were 2 mils thick, and the hctd-peeable coafings were 3 mils.

Test Procedu.es

The han6-peelable coatings were applied to Alodifne 1200 treated panels. These werethen subjected to the Lockheed-California cleanirg and chromating process, consist;ng ofon nlkoline ceaning, deoxidizir.ng, alkaline etch, deox'dizing, chromic acid, deoxi-dizing, Alodine 1200, hot rinse, =d hot-air-dry sequence. The chemically removablecoatings were subjected to the same test sequence, except for the oikaline cleaning, whichwould have removed the coatings. The --octed pan.els were then subjected to the fo!iowingtests:

1. Scratch and mar resistance (ASTM D2197-63T)

2. Heat resistance (Fed-Std-141, Method 6051)

3. Bending over conical mandrel (ASTM D522-60)

4. Taber Abraser, 1000 g.a load CS-17 wheel (Feb-Std-141a, Method 6192)

5. Drill and countersink

6. Ease of removal

7. Wet-patch tape test after par.els were coated with P-3 paint system (Fed-Std-141,Method 6301.

57

. . ..- r , J ; -. ' - -- - - - -

- - rnr..' -

F8. Outdoor expcsure of two coated panels on racks at Pt. Loma, California.

Test Resu!ts

The results of the laboratory evaluation tests of the strippab!e coatings cre summarized inTables XXII; through XXVI. Three of the five hcnd-pee!able coatings withstood the testsequence. Of these three, Coating No. 14 was best able to withstand drilling andcountersinking, ieaving good edge definition with the least amount of fraying.

All of the chemically removed test co-otings could be readily drilled and countersunk.Coating No. 15 was the hardest to remove after heat-aging for one hour at 3000F.Coatings No. 13, 17, and 19 crack.ed upon flexing. However, Coating No. 11 wasconsistently good. It had good sprovabi!ity, it flexed without cradking on a conicalmandrel, and it could be removed easily before and after heat-aging at 300°F for onehour. The Teber abrasion and Taber scratch tests, before and after baking, producedresults indicating that Coating No. 11 is acceptable.

On the basis of the evaluation tests, the best of the hanc--strippabie coatings is CoatingNo. I', and the best of the chemically removable coatings is Coating No. 14. Bothcoatings are compatible with Rule 66 for the prevention of atmospheric contamination(County of Los Argeles-Air Pollution Control District - July 28, 1966). The two coatingswill be applied to fuseloge panels for a production P-3B aircraft (No. 5510). The aircraftwill be inspected six months after it has been painted and put into service. Because of thelong delay between the fabrication of fuselage panels and the cleaning and painting of thefinished aircrcft, the panels with the strippable coatings could not be placed on the sameaircraft which serve as a test bed for the cleaning procedures.

58

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L -PR&)'CTION-LIME EIVALUiATIONq OF STRIPAB-E CA-rig

On tt,.e basis of lc-bca-tx-y evla-cno :e: rcepncd ;n cdei! :-i eee I, tlh e . o.;the -trpf~e ~ I , cm est 04 :.* cnemsccty

comtmgss Was cow-mlg Na. -

70 ev~jit~te ~,e c; y w~ the ccctirs lo =o et d pti n s an

=sec~ly o c-os, stipaeble cotn No Ii c;ied -Ao P -3Si An omeks (P WN 90)3-M-65. =id -33-67, bd slrippcv--e coctinr INo. 14 W=S -:iiadto twoa ediocen pamtsie sikin cn=es (P-N 907238-3 *iftd M-1728-5. T;.-e gomtizo- Omskin P--s on heP-3 fusek e is shorm in Na-jrz 23..

Bothi cocticas were sorcyed onIy ande xer sides af iIe pnels. Cecting S1410- I: th~en-vd-s~eiabe coating, bsolei rre ti-e xcreis wena tr=-tg h tia cte=Zii-,

decxidiz;Pna, cn-d Aladine liner . Coc;n Mlo- 11, ".1 cbvemkCHIY romwoi~e n--, IC

cpplied after -he cle.L, 6oxidiz~-V. mad Ataodne tmt~s. 1he a~trtsdso ll.mne -e were protected b7 zimcc cc=,!e --vu-er c-,plied ovw sr. es wrce .ith

Prior 6.0 the cpp!;Ct-icn Of Coatin~g N0. 14, iife ipc--s ~edm-a d -;y iLVeew; h~ rethlI etiw! Re-tace. -TIhey vtes -- he u-shid With c =r cidc oe

re thorotighigy rkuzed crd dried - Dje to t ore size ofth skia mx~res, = 6iit-vwms envcotntered in cc-on-eel y remo-tLV Ithe pbQzr*xxk- c;,& AlSO, "Iesec of4si~oows No. 14 ccoting cxtericl reqaire-d ccnide Ie skill on the p~rt ci the F~trThe c~cticn Of coting INo. i I F~oeedei t oycd meSep-ted nc diffixulties.

After being coated, !ile S'Sip. p~els i-*r ocen o the fuszeloge cseecbty *eo of the P;a,vhere they weme drilled, ccoi-mk, cr d rivefred. Ina additlice, wibda-*s W'er cut *Lt bynaeons of aorojter.. The oarels mese Lrstalied in P-3 Aimzr-at %.*-5 The

co ~re med on !est peels xati "fl, cirrof.t was =ve i tibe pciat shp.A!.bat time, the- cootfngs were -- zpvred, 21e . cair ir-rft W= ~je e to om-.-C clecr.;aperati*-s. ad the primex cr4 =p cc&.s were cppi;ed.

Test gesuIts

7me hod-stipble cocoag No. 14 =nided gao o eio Che ok= - pzaelthz.- gh !;)e GlcL.e~ c lener, dcoxicfizer_ =-A Alodiae vcomnt.Oi -~ oz*in9, ---

:aveI m ..:aan were uxcessuAy pefr med on the coad Q &km Cc~ No. 14 isVISCOUS c=ed is d-iffiku! E to apply unifa6-mly. w~t tne spro=n difuliscdhe-iethrouGh th use of ciriess-s=-ov eqj;entI.

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The chemically, removonle canting No. I ; which wOn aonlhed after the Viaineil had beenprocessed through the chemical cleaning line, also held up well during the drilling,riveting, and routine operations. Because it is a hard coating, it is extremely scratch-resistant.

The four panels which were covered with the strippable coatings were protected fromabrasion and scuffing, and the surfaces were kept clean. Because additional time wasrequired for special set-up of the panels for application of the strippable coatings, it wasdifficult to establish reliable cost parameters. However, the cost of applying strippablecoatings on a routine basis would be comparable to that required for the application of aone-component paint.

67

VI - APPLICATION OF BEST CLEANING PROCEDURES TO AIRCRAFT

Application of Best Procedures to C-130 Airctaft

The two best experimental cleaning procedures were applied to PAR Mod C-130 aircraft#150685. The usual sequence in overhauling a Navy C-130 is to remove the engines,scrub the wheel wells and engine mounts, strip the white cap and walkway coatings fromareas which ore to be repainted, give the aircraft a thorough first cleaning, makenecessary repairs and modifications, give the aircraft a second cleaning, and apply thepaint system.

The principal test area is the top of the fuselage (see Figure 29), which is coated with thewhite epoxy paint. As this area is cleaned twice, once after the old coating is strippedand once immediately before the final coating is appiied, it was decided to use the experi-mental cleaning procedures for both cleaning operaticns. Cleaner VI was applied to theport side of the aircraft and Cleaner II to the starboard side.

* Figure 30 is a view of C-130 aircraft 1150685. Figures 31, 32, 33, and 34 are cloeupviews of the four major test areas. The white-capped upper portion of the fuselage wasstripped, cleaned by the experimental Procedures, cleaned again after the 4-week over-haul and repair period, and then repainted.

The two best cleaners were applied cccording to the fallowing procedures. Steps I through6 were common o both the first and second cleaning. Step 7a was applicable to the firstcleaning only, and steps 7b, 8, and 9 were used in the second cleaning.

1. Dilute cleaners - Cleaner VI (First cleaning: 1 part cleaner to 5 parts water)

(Second c'eaning: 1 part cleaner to 7 parts water)- Cleaner III (1 part cleaner to i part water)

2. Spray or brush apply cleaner to aircraft surfaces.

3. Allow cleaner to soak a minimum cf ten minutes. Reapply as necessary toprevent cleaner from drying on surface.

4. Scrub with brush.

5. Flush thoroughly with water.

6. Reapply cleaner, as necessari, io obtain a clean surface and rinse again. Use agenerous amount of water to %mpletely remove chemicals. Start at the bottom andrinse up to the top, followed by another rinse from the top downward to the bottom.

7a. (First Cleaning Only) Spray surfaces with 0.2 to 0.3 percent chromic acid solu-tion to obtain neutral or slightly acid (litmus paper red) surfaces. Aliow acidsolution to dwell on surface 2 to 5 minutes followed by a water rinse.1; AUIQN: Do not allow the chromic acid to dry on the surface.

7b. (Second Cleaning) Apply Mit-C-5541 chemical surface treatment rinse withwater, and air dry 2 to 12 hours.

1" 69 Preceding page blank

PORT SIDETEST AREA

STARBOARD SIDETEST AREA

FIGURE 29 TEST AREAS ON NAVY C-130 AIRCRAFT NO. 150685

70

-1

0-

166

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(l)

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71

IAI

FIGURE 31 FRONT STARBOARD TEST AREA. ONLY WHITE-CAPPED UPPERFU'SELAGE WAS REPAINTED.

FIGURE 32 REAR STARBOARD TEST AREA

72

FIGLJRE33 FRONT PORT TEST AREA

FIGURE 34 REAR PORT TEST AREA

73

8. (Second Cleaning) Tloroughly wipe surfaces with clean rags moistened with cleankornvi or bitvl nlknl f r, ymn, rpt:hinl mnuttarn ndr 4nnwRr frnm ehkmF_-"surface treatment.

9. (Second Cleaning) Apply point system as soon as possible.

Special precautions were taken to prevent liquid from one test area from running over theadjacent test area. This was done by masking one half of the top of the fuselage when theother half was being cleaned.

The C-130 did not require a control area because Cleaner VI, which gave the second-bestresults on the laboratory tests, is the standard cleaner u.ed at Lockheed-Georgia forcleaning prior to painting.

At the end of the first cleaning sequence, a chromic-acid rinse wos used to protect the barealumnum from corrosion while the repairs and modifications were being made. At the end of thesecord cleaning, the surface wasgiven a conversion treatment and was then thoroughly wipedwith rags moistened with isopropyl or butyl alcohol to remove residual powder and moisture.

After the C-i 30 aircraft had been subjected to the first cleaning, surfcce-energy readings weretaken on both sides of the aircraft. Table XXV!I summarizes the data obtained.

TABLE XXVI

SURFACE ENERGY MEASUREMENTS ON KC-130 AIRCRAFTAFTER FIRST CLEANING

(dyne/cm)

Port Side Starboard Side

Front Fuselage - Top 55, 60, 54 58, 55, 55

Wing Panel - Front 54, 54, 60 40, 40, 36

- Rear 48, 38, 46 34, 32, 28

Empennage 5i, 61, 54 58, 54, 61

Wheel Well -Top 36, 54, 38 61, 60, 60

- Front 58, 58, 61- Midd!e 16, 12

- Rear 54, 46

The above data dramatically emphasize the wide variation in the cleanliness obtained bymerely applying a cleaner to an aircrcft, brushing the surfaces, and rinsing the surfaceswith water. Huwever, this was a preliminary cleaning operation. The second cleaningprocedure include5 steps which assure a more uniform surface. condition prior to painting.The port side of the aircraft was cleaned with Cleaner VI and the starboard side with

Cleaner Ill. Where tee surfaces were thoroughl scrubbed, such as the top of the wheelwell, Cleaner Ill gave higher surface energies than did Cleaner VI. This was consistent

74

with the results of the laboratory tests. The surface eneray reodnns nn the starbccr A Zideo, 16 fuselage and wing surfaces were somewhat lower thn the port side readings. It wasobserve,( thiat, in an effort to prevent overspray to the adja:ent test arec, Cleaner Ill wasnot as generously applied to the top of the fuselage as to thesides and the wheel wells.

Aircraft 150685 was given the second cleaning and was painted on September 13th.Figure 35 is a photograph of the aircraft after the painting operation. Table XXVIIIsummarizes the surface energy measurements which were made after the second cleaning.

TABLE XXVIII

SURFACE ENERGY MEASUREMENTS ON C-130 AIRCRAFTAFTER SECOND CLEANING

(dynes/cm)

Port Side Starboard Side

FrontFuse!age- Top C.W.?* C.W. 66, 68, 68

Wing Panel - Front 46, 59.5, 54 64.5, 66, 65.5- Rear 63, 63, 59.5 65.5, 65, 64

Empennage C.W., C.W. C.W., 71, C.W.

I C.W., C.W. 69.5

Wheel Well C.W., C.W. C.W., C.W., 64, 63, 63

*Complete Wetting

After the second cleaning, the surface energies of the aircraft were considerably higherthan after the first cleaning. The applied droplets completely wet the surface in manyinstances. On the wing panels, the surface energies were slightly higher on the starboardside, where Cleaner II was used. With that exception, there was little difference in theability of the cleaners to yield a cleanr, high-energy surface.

Cleaner Il clung to the surface tenaciously after the apptication and scrubbing operationand was more difficult to iinse off completely. Also, brush marks were visible wheretraces of the cleaner remained on paint -d surfaces. Approximately 10 manhours of extrahand scrubbing were required to remove these streaks from the starboard s-de of theaircraft.

Cost Parameters

With the exception of the hand labor required to remove brush marks from pointed surfaceswhen Cleaner Ill was used, there was no significant difference in the time required toapply and rinse the two cleaners. Following is a breakdown of the manhours and maferialscost for the clecning operations on C-130 Aircraft No. 150685. (Total surface area -9000 sq. ft.)

75

z

LL.

Lr

76

Material 'costs (ter each cleaning. ot entire aircraft)

40 gallons Cleanr VI @ $ 2.00/gal $ 80.0040 gallons Cleaner lil @ SIO.00/gal $400.00

Assuming a labor co-t of $5.OOAr, the cost per sq. ft. of surface for Cleaner III is:

100 manhiours x $5.00/manhour + 40 gal cleaner x SIO.00/al O-0/f29000 sq. ft.

T he cost per sq. ft. using Cleaner VI is:

90.-nanhours x $5.22/mrihour + 40 al cleaner x S 2 .N9Jga 29000 sq. ft. - a .0.o05?/ft 2

AP-plication of Best Cleaning Methods to Mew P-3 kircraft

To evaluate thit effectiveness of the cleaners anid to establish cost parometers forproduction-11ine cleaning procedures for new aircraft, the two best clenn:g aracedureswere applied to aircraft No. 5286, a P-3B aircraft manufactured for the Navy by theLockheed-California Company. (See Figures 36 end 37.) The proedvres were modifiedby the inclusion of a solvent wipe to remove oily contaminants accumuldated during manu-facture. The fuselage was cleaned by the standard Lockheed-Ccliforia m~ethod usingSc-otcibrite pads. The wings, which ore assembledt arid cleaned before being joined to thefuselage, were used as the test areas for the experimental cleaning procedures.

The current Lockheed-California procedure for c.'tonirQg the P-3 aircraft is as fellows:

1. Clean surfaces with methyl ethyl ketone.

2. Wipe using petroletum-bose solvent, LAC 32-367.

3. Scrub surfaces with Scotelbrite pods aend water.

4. Wash with piiosphoric acid cleaner,, LAC 32-260.

5. Rinse with water.

6. Apply MIL-C-5541 chemical conversion treotmeni. Rinse#- with water. Air-dry2 to 12 hours.

7. Wipe with mild acid cleaner, LAC 32-266.

8. Wipe using petroleum base solvent, LAC 32-367.

77

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FIGURE 36 PZOFILE VIEWS OF P-~3 MkC~AFT

78

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The procedure for application of the two test cleaners, modified to adapt 'a productonconditions for new aircraft, is described below. The port wing .f the tirc:'a. cleanedwith Cleaner VI (1 part cl~cner to 5 parts water) and the starboard wing with Cleaner Ill(I part cleaner to 1 part water).

1. Clean surfaces with methyl ethyl ketone.

2. Wipe using petroleum base solvent.

3. Spray or brush-apply cleaner to wing surfaces. Allow cleaner to soak atleast 10 minutes. Reapply, as necessary, to prevent cleaner from drying onurfnces.

4. Scrub surfaces with brush.

5. Fush thoroughly with water.

6. Test dry surface with Surfascope to determine the relative cleanliness. Reapplycleaner, as necessary, to obtain acceptably clean surfaces (surface energygreater than 40 dynes/cm), and rinse again. Use a generous amount of water toremove chemicals completely.

Spray surfaces with 0.2 to 0.3 percent chromic acid solution to obtain a neutralor slightly acid (litmus paper red) surface. Allow acid solution to dwell onsurface 2 to 5 minutes; then rinse with water. (CAUTION: Do not allow thechromic acid to dry on the surface.

8. Apply MIL-C-5541 chemical conversion treatment. (CAUTION: Do not allowthe solution to remain on the surface longer than 5 minutes.) Rinse with water.Air-dry 2 to 12 hours.

9. Thoroughly wipe surfaces with clean rags moistened with clean isopropyl or butylalcohol to remove residual powd-erand moisture.

The port wing of P-3B aircraft No. 5286 was cleaned on August 5th and the starboard wingon August 7th, using the experimental cleaning procedures. The wing was masked incertain areas and placed in a vertical positior surrounded by scaffolding. The workmenfound that Cleaner VI was easier to apply and r;nse than was Cleaner HI. The only prob-lem encountered was that a high-pressure water strbz:.i loosened the masking paper on thestarboard wing and allowed some of the Cleaner III to enter the nacelle areas. Table XXIXlists the surface energy readings after each wing was cleaned.

The readings indiccte that a high degree of surface cleanliness was achieved. On thestarboard wing, where Cleaner Ill was used, every test resulted in complete wetting whichindicates a surface energy of more than 72.4 dynes/cm. On October 1, 1968, numerouswet-patch tnpe tests were performed on the two wings of aircraft No. 5286. All resultswere satisfactory.

80

TABLE XXIX

SURFACE ENERGY MEASUREMENTS ON P-3B WINGS AFTER CLEANING(dynes/cm)

Port Wing Starboard Wing

60 C.W.

70 C.W.

60 C.W.

C-W.* C. W.

72 C.W.

*Complete Wetting

Cost Parameters

The normal time required to clean a P-3B wing by the standard Lockheed-Californ;aprocedures is approximately 35 manhours. The time required to clean a wing with theCleaner Il procedure was 40 n',onhouri, and the time required using the Cleaner V! pro-cedure was 35 manhours. However, approximately 5 hours of this time was due to theunfamiliarity of the cleaning crew with the procedures and to the mixing and checking ofthe cleaning and rinse solutions. Each wing has approximately 1200 square feet of area onthe upper and lower surfaces combined. Ten gallons of cleaner were used for each wing.

Assuming a labor cost of $5.00/hr, and making allowance for the unfamiliarity of thecleaning crew with the experimental procedures, the estimated cost per square foot byeach cleaning procedure is as follows:

Cleaner ill:

35 manhours x,35.00/manhour + 10 gal Cleaner Illi $10.00!agal = $0.229/ft21200 sq. ft.

Cleaner V;:

30 manhours x $5.00/manhour + 10 gal Cleaner VI @ $ 2.00/gal = $0.14111t 2

1200 sq. ft.

Current Method:

35 manhours x $5.00/manhour + $25.00 for Scotchbrite pads = $0.166/ft21200 sq. ft.

The above figures are approximations for comparison purposes only and do not include thecosts of the additional solverts and chemical solutions. They cannot be compared withthe cost figures for cleaning C-130 aircraft because extra steps involved in the P-3Bprocedures. Also the C-130 surfaces are considerably larger and the cleaning cost per squarefoot decreases as the surface sizes increase.

81

liII Ik I C ri1 lSk I IA* P. * ,--

v,, - ,,O., ,.,-, , ,r Ai C1-AiF- CLEANED BY EXPERIMtNTAL PRKOCEDUR.S

P-3 Aircruft 5286

Results of 6-Month Inspection

Aircraft 5286 was originally rcheduled for service in the South Pacific. A few weeks afterit had been painted, a change of Navy orders rereived by Lockheed-California called foran extensive modification of this aircraft before it was assigned to active service. Pendingmodification, the aircraft was stored outdoors under conditions which were quite shelteredexcept for exposure to sunlight. A 6-month inspection revealed the accumulation of adu!t coating but no deterioration of the protective coating system.

Results of Final Inspection

The P-3 aircraft which was cleaned by the experinental procedures before painting, andwhich is now the property of the Royal Australian Air Force, was inspected at EdinboroughAir Base at Elizabeth, Australiz, on 18 May 1970. Squadron Leader Jack Roe arrangedthe details of the visit and inspection. The P-3 air'j-oft was originally cleaned and paintedon 7August 1968. It was stored outdoors at Lockheed-California for almost a year and wassold to the Australian Air Force in August of 1969. Since then it had been operating as apatrol aircraft out of Edinborough Air Base in Australia.

Figure 38 is an overall view -" the P-3 aircraft in its hengar at Edinborugh Air Base inAustralia. Figures 38 to 41 are views of the starboard side of the aircraft, while Figures42 and 43 show the port side. The appearance of the aircraft was that of one wh;ch hasjust been pointed.

As shown by the close-up views in Figures 44 through 48, all painted surfaces of theaircraft were in excellent condition. There was good gloss and no indication of blisteringor peeling. The painted surfaces were smooth to the touch, but the beginning of surfaceoxidation was evidenced by the white powder which came off when a hand was rubbed onthe surface. There was no detectable difference between the point on the fuselage, theport wing (Figure 47), and the starboard wing (Figure 48). Each of these surfaces had beensubjected to a different cleaning procedure prior to the application of the paint system.The fuselage had been hand-scrubbed with Scotch Brite, and the port and starboard wingshad been treated by the experimental procedures developed under the Navy contract. Theabsence of blistering or peeling indicates that ali the cleaning procedures provide adequateadhesion between the point and the metal.

The excellent condition of the pointed surfaces is partly due to the excellent maintenanceand washing procedures used by the Australian Air Force. Every time the aircraft comesback from a patrol mission, it is washed with 2,000 gallons of demineralized water. Onceevery 2 weeks it. is washed with a Turco detergent and 0'ised with demineralized water.

1g83 Preceding page blank

- - - -.---- ~------- -- ~ m -

0*-r

hV~ C

t mrl-l- Z

r~Ill

z

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I--

uz

o

84

FIGURE 39 1REAR STARBOARD FUSELAGE

LFIGURE 40

2 FRONT STARBOARD FUSELAGE

85

FIGURE 41

CLOSEUP VIEW OFSTARBOARD FUSELAGE

FIGURE 42

FRONT PORT FUSELAGE OFAIRCRAFT NO. 5286

86

FIGURE 43 CLOSEUP VIEW OF PORT FUSELAGE

87

- s x,~

Fg 7- am-

FIUR 4 PERCETR UELGEO P3AICRF N.526NOECMLTIBEC FDFCS

XS:~z

FIGURE 4 UPER CENTER FUSELAGE OF P-3 AIRCRAFT NO. 5286.NOTE OMHPLEOASENC OF DEFECTDSUFCS

N _

IIg

FICGURE 46 REAR PORT FUSELAGE OF P-3 AIRCRAFT.PAINT IS IN NEAR PERFECT CONDITION.

FIGURE 47 CLOSEUP VIEW C+ UPPER SURFACE OF PORT WINGON F-3 AIRCP.AFT NO. 5,286

89

FIGRE 8 CO3'JVIOF0 U??ER StRFACE OF STARB0A-M WNOF P-3 AIRC&AFT NO. - .5

90

After Atibe reO6,kt; csv~~ er4 me c led, C-1130~A.if No.150695 w=smi to Fus A;- 8=-- :-- Ok=-c . .-s oimsoft w,- op'ec7:i=:vs c tm=xe ;nth e~ t- c After cpF I CitL =xg ci serk -ircf m:; isseed -- 2

FL-e= A i -a co 7 A--;I I Mf

The por-e fimekge c.b a=;! Safce wt~e cciely ewm CrA cdt &mi~dW---- .6. -.,r~ test c.-xs. nwhe-- ftc ach tc~~~~~te es:cr-2s of Fe 49-. (F-b~ss 3DI~~i 72 z.-ine cir-t o~it -.-S!

Thue i- w a-rde-e ci biisen =r peeling ezept x c snmi! c oen cn-.hSI--itowad Zse a f!- eaemre V-3zzc 65 ond 7-11. .Itse the pcat S=6 fgz ff. a-P-.i

KIidoxam Smu, e~h cbot twma sq=-e '9 Ees is V,- %tpr- 1 d&yae tox.a F CIteA No. 3, w4 is e-r~elew= endo' od-F-,I to~ The

uliie epwq-po~2de ocantw E,.Xz ma chwmi c Sme -.b sze CE --- sitw,- &Ikxr on e-cc sle =-E tL-e ciammmt WERe =oil rt 'd IIC==Ys. C- !E Sczt

port. ww a of 6e Emeoe, Hhe poit PC!a -'

tile hatsteer 5 ixe 6an- 70). Ihi sco-ze tb -.,i ;mfefiT. ine epxy-pohvid! pim syemTdv=hr -f

=01I~s TW-3 seest of SO- =iiei..s4, coee -0o e-h hod ±ei&:cewsa-e2 ha.i fmiimr 62, 63, c= d 74~ - Ie ;m±~~~e t!!e reea *i ile

m& Ixd cppaty been d&mced i=g 2!e im liItim zF tie S& 3

in -Vdba good pint, C-rsn A=w'7~ci -: S,9 f the pinted swew e ;-.e lemo canitkn cfuer 6 imsx.tms cE exo-e im Ivieto -=d~

Oes~s cf R~c Ir~ti

C- Jico No- 1556 w=s gie c fI9o! k at e ?? Cc Air toat El Tor, oCcif-=, cm Aloy 1I4 , 197B, 19 o:K- cfer it !Lrfii~d ~ie FAMcde ji-co-- - Mhee amtio.-cft., umh3cb porae -, See-r 1 3. 1963.ha ~-Lem

0==e t ak~tcS x *zce:y 14o ==H= omd W= toi El %'Av. e CcTu-Air Stoi= d~rin O~e first fim~ cf 1970.

17he ointed test.,,~e .~ efily cx~ima, o d wero sz te==usbeing ezvy L5- m ;e in irsa Rc! Paz%& C-3 -- ,.e s ecd

w;S pm;z! om i s CEC&LviJa. k.. ='M- Crams , e to

Tobie XXX ==ci= the Cp#l-wa -m mqo a:e :esi - sl', iNmzt 7.4 !o : 5 e ph =cgq~Ons ci st te st

Thee d carzdlIS ---: Che ap?-o!C e jCiat SYS= c C-130 We± ~ uski ogzj Gn cs4 a cas flne po-=it w=s zi-;~iy =-S cnd chaky

to t-%.- tc=h A pva j$omve oC~oF w~ c te *= r. Aed Ii ly - tle oe%rover, cct h. *A-- sOn'b Siae of *je &tX i f be -a= t4f %le ci -.: cldo

bofe =c:. un L~e ixo-;Td Pon~ 3;-: of t !miSeoe, tL-e joira -a cd*m n we~i =mj knot buste;n or peejing.

PORT SIDETEST AREA

922

8 __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

- - --- -~ - >Z22~- - - -- - - -- -

-i

I Ai

II

I - _ ~ ~- ~

- ___ _

FIGURE 50 C-13OAIRCRAFT 150685 AT FUTEMA AIR BASE IN OKINAWA

-I4

I

93

IF

FIGURE 51 FAONT TEST AREA ON STARBOARD SIDE

FIGURE 52 REAR TEST AREA ON STARBOARD SIDE

94

- 'GR 53 FRON TEST- ARAOOTSD

FGURE 5 FRNT TEST AREA ON PORT SIDE

95

0-A

FIGURE 55 TOP FORWARD SECTION OF FUSELAGE,

TEST AREA NO. I (WHITE AREAS)

96

AM-

FIGURE 56 TEST AREA NO. 2

FIGURE 57 iEST AREA NO. 3

97

FIGURE 58 TEST AREA NO. 4

X. I.

FIGURE 59 TEST AREA NO. 5

98

N-

~f.

,~ -

FIGURE 60 TEST AREA NO. 6IIT

II

tI

11FIGURE 61 TEST AREA NO. 7

-I 99~1

IA

FIGURE 62 TEST AREA NO. 8 (NOTE RUSTYPHILLIPS HEAD FASTENERS)

FIGURE 63 TEST AREA NO. 9

loo

F!GURE 64 TEST AREA NO. 10 (DARK SECTION WAS NOT0EPAlMTED% Aklr IC 1,11-T A PrT! O N OF THETEST AREA)

I77

FIGURE 65 TEST AREA NO. I1I

i01

FIGURE 66 TEST AREA NO. 12

FIGURE 67 TEST AREA NO. 13

102

Mm

F;GlkE69 TESTAREA tNO.. 15

103

-4f

FIGURE 70 ENLARGED VIEW OF DARKENED FASTENER HEADS IN TEST AREA NO. 2

-1k, 3--Z

~~104

iSi

105

TABLE XXX

CONDITION OF TEST AREAS ON C-130 AIRCRAFT 1530685

(NAL INSPECTION)

Test Area No. Observations

I Paint ia good condition.

2 Bare spot cpproxirately 12 inche. -vide and 18 incheslong several feet in pront of propeller line.

3 Corresponding area on the starboard side of fuselage wasmuch rougher than other painted surfaces.

4 Chalky powder rubbed off on hands.

5 Chalky powder rubbed off on hands.

6 In good condition.

7 In good condition. (Walkway coating in center offuselage, which was not a port of the test area, isbeginning 'o come off at demar-ation line between thetwo areas. This may be due to paint stripper gettingunder the mcsking tape at the time the test area wasstripped ond painted.!

8 In good condition. (Four cadmium-coated steel fastenersin this area were badly corroded.)

9 in good condition.

10 Point is just beginning to develop a iietwork of fine cracks.

11 Paint is just beginning to develop a network of fine cracks.

12 In good condition.

13 This area has several rusty steel fasteners with most of theoriginal cadmium plating gone.

14 Paint is in good condition, but is just beginning to crack.

15 This was the worst area on the aircraft. Blistering inmany smoll spots. Bare areas the size of a half dollar.Paint very thin on forward portion.

106

'I -il

FIGURE 74 TEST AREA NO. 2 - C-130 AIRCRAFT 150685 -FINAL INSPECTION.BARE SPOT APPROXIMATELY 12" x 18" MAY HAVE BEEN CAUSEDBY DUST & DIRT THROWN UP BY PROPELLER REVERSAL DURINGLANDINGS.

FIGURE 75 TEST AREA NO. 8 - C-130) AIRCRAFT 150685 - FINAL INSPECTION.PAINT IS IN GOOD CONDITION EXCEPT FOR FOUR RUSTEDSTEEL FASTENERS.

107

FIGURE 76 TE ST AREA NO. 8 - C-130 AIRCRAFT 150685 - FINAL INSPECTION.CILOSEIP VI"EW OF RUSTY STEEL FASTENERS.

FIGURE 77 TES( AREA NO. 9- C-130 AIRCRAFT 1I0685 -FINAL INSPECTION.PAINT I- IN GOO'D CON1DITION.

VIM- 0

FIGURE -8 TEST AREA NO. I1 I C-130 AIRCRAFT 150685 - FINAL INSPECTION.PAINT -1c AUST BEG,'NNING TO DEVELOP A NETWORK OF FINECRACKS.

FIGURE 79 TEST AREA NO. 14 C-1 30 AIRCRAFT 1506C5 - FNAL INSPECTION.PAINT IN GOOD CONDITON BUT BEGINNING TO SHOW FINECRACKS.

109

i25

70

FIGURE 80 TEST AREA NO. 15 - C-130 AIRCRAFT 150685 -FINAL INSPECTION.PROBABLE CAUSE OF BLISTERING AND BARE AREAS IS INCOMPLETERINSING OF THE PASTE CLEANER USED ON THIS PORTION O HAIRCRAFT.-

- -

in

2_

FIGURE~ 81TS RAN.Ir10 PCAF F65-FNLISETON

CLOS-UPVIE OF ARESPO.~

-IUR 82TS RAN.q.-C10ARCAT108 INA NPCINCLOSEUP ~ ~ VI' OFBITRSADBREAES

411. -

FIUR 83DFC0N-PITOINESM FARRF I NHNE

APPERANC SICE LST NSPETION ME FIGRE 6.) i -v

WAS_ NO A0.TO FTETS AE HC SCAE

WITHIE EFXY-PWAMIE PA~llSC-,M

The blistered area on the ducktail had blcri noted in the first inspection and was attributedto incomplete rinsing of the paste cleaner used on that side of the circraft priot tc theapplication of the point. Ccptain lVoitt, the Marine Corps officer who coordinated thefinal inspection of the oircrat, suggested that the bare area on the port fuselage (Figure74) may have been caused as sand and dust were thrown up by the propellers when theywere reversed to slow the aircraft during landing operot,ons.

The overall results of the finai inapection indicated that the cieaning proceduces used onthe aircraft prior to painting were satisfactory and hod provided adequate adhesionbetween the paint system and the subsirate.

ximI -ir vzKzin t-%rl~K ci n~~ *2Tc

All objectives of th~s program, (1) developmen' _4 a relinbie method for measu.ring surfaceclecaliness, (2) evaluation of candidate cleanirz'g procedures in the laboratory, P3) evollu-ation of strippable coatings, (4) application of the tv.o best cleaning methods tooa C-130and a P-3 aircraft ^o establish co;1 prame~ers and determine performance under serviceconditions, huve been -uccessfully accomplished.

Meihod for Determining Surface Cleanliness

The Surfoscope surface energy kit, which measures surface cleanliness on the basi!. of drapdiameters, proved to be an accurate, rapid, and reliable irnstrumnent foi determiningwhether a surface I%:, the clecrnliness requjired for good point odhesion. It is of specialinterest that, in the course of applying the two best c leaning procedures to the NavyC-3j) airctaft, suifece-energy readings were taken on vertical panels of the fuselage withlittle difficulty.

T'he results of the adhesion tests on panels which were deliberately contomined with stearicacid before they were pointed showed that good adhesion wais not obtained when th e surfaceenergy wos less tl.kn 30 dymes/ cm. The minimum acceptable surface energy for each sub-strate imust be determined expt metally. This value should be at least 10 dynes/c.shiher than the critical surface energy below which point will not adhere. A goodstcndord for chromaoted clad oluminum aircraft surfaces is 40 dvnes/cm.

The development of c rapid m~ethod for measuring surface energy end the experimental%-erification -that amny suwfoce energy create.- than 40 dynes/ .cr wiill give excel!ent pointadhes;on ore highly significant. These facts show that the prese-nt water-bcreak-freemethod of checking for cleanline.s, which represents a surface eneW~ of 72 dye/cm, issevere, in the post, aircraft surfa-ces which shorvred water breaks during the finol rinsewere considered uniacceptable for pointing cnd were recleaned. The use of the Surfoscopeand the dorinizer sprmv test w;Il reveal the degree of cleanliness and can help rediceCleonino costs. Loclhieed Air Services of Ontario, California, is prodmaing cni distribu-ting the surface cleanliness inspection kits- The latest U~. S. N~avy Corros;o ControlMimnuol recanvends the use of the S-infascope to check aircroft surfaces before they arepointed.

Laoraatory Eva luation of Ctecninq Proceauies

Thebateryof evoluation tests demostrated thai Clearters III end V/1 were the -- s

effective of the group which suiccessfully pa--sed the h g-mrnerntscreenira iest.on the basis of surfoce-ene.N measuremients, C lecrier No. III didoa slghilv better job ofcdeonina tbmo Cleaner Nlo. V, but clemning efficifencies of both -We very high. 1heapplication of the - cimees to the C-13I n-d P-3 circroft evecled other differen-tces.%-leaner No. "A rnixed readily, was easy to apply, and- -. s -- ;i rinsed off after th-escrubbing opeation. Cleonef No. !!! vwus rcre diffikkult tm mix because it wa's in psteEorm. It was saroyed~ on c.-. cdherent, yellow froth vrhict. provred to be qu i e diff-cult torinse off after tize scrubbing step. Si.ush a ere visbiMe on p sined surfaces re therinsing wms not qoite cdeqxte, =4# ezr--r=2 oucs weie -used in r tlecrm Chs reof..Cleziner III w;Il s!teir R~h-ace painted sunrfaes, =nd trie initial cos' ae gametn is fi'vetimes that of Cleanri VC Cleaer VI sim-1-d be used on all sur.faces of tinz aircraft exc-

113

t1~nep -kf nrexC.C4 - " M - I.-A-, l -C leaner I Il m;gb! be iistif;ed in these ereas because of it-, clecnir-9 abifitieis and adherent

Evaluation of St. irpable Coatin~gs

The !obovatory tests derronstroe, the etfectiveness oi the strippczble coatings ;n protectingfreshly C eaned surfaces fmom cocitz'i-qnotio during fabrication opeiations. Ccating No.I I wus the bes! olkoline-removable maoterial, and Coating No. 14 was the best of thehand-peelcble zotng.Bt co2ting~ k r further evaluated in the prodtntion of P-3fuselage panels. H-and-strippoble Ccwo;$'g No. M4 prvvded Sood protectior. for the o-ne.'sduring ciiemicot iecnimg ond during dril!n, --c- 'eriknand riveting operation-s.Cheically strippable Coating Na. I i pro-vrded good proatection for the panels during the

-dring, counter.sinkOng, and riye!-r- seps.

C-ost Parameters

The cost parameter study of the use of the tVst-&.o h ~ mevo clecaing procedures o--the C- i 3Doirc rnft shoiwed a cost of 5 OIS9A fo'Clecet No. III as compared wiethSo .059/ft 2 for C leaier No. V1.

The costs of - lecnhng the P-3 aircraft were greeter because of th;-e smaller svrfaces ci: thextr ~?ps n th P- ~eninpro.eires. Phe cost of surface peparation wns 5.2/t

with Cleaner No. Ml a~id SO- 141Jft I.. Cleaner No. V', ;*hile fhe current mnethod,',A,;cb requires the u-,e of Scotc*'iepds a O 6/t 2 .

Results of Field inspec-tions

After the init~al inspection, of C-130 Aircmft !-SD@5 was completed, c canfec..-ce VMSheld With Mojor JAo Masters, the Heai ontrne Off-ker, cn with Mr. Ed Prc-tt, t0*Lockheed FieW-d Service Rere5entati-ve or. Okrnawa . Major Masters %ims concerned withthe corrolion ond ;p;ting an the urmpao Xnted creas of- oarrft staticned at Okciriv mid

op~tflgi Vietnarrt. P., 5ad Shot frequently the wind wL-ild blow a! c velocit of 25 to30 ifes --n hw ;ar1 dwis at a t!=te, hminqk SQ'It sprcy =1d ari! cn lhe oiroft

high vekoc ities. Even Ole Oltxminuim-cL6d stwivfes pit =-d corrode an-C-e the ccriins.-ootb surficc ;v- er bmi-en -He emrp-si'e' tme reed for 100% pointing of tHem air-craft insfecd of paintina tk,;Af seL~scd cveacs. He otso ir--tioned the con-asiam. w.*hoc--uzred becusm, =flt wva- 4,6eedte crevices between vdjocen& skin ptaels. and he.,,sed if if a~ be posible --a %eel flhse cre-ekaes. Phe ieeal mterial 56.- +.is would be

*t;,e --f3vei PA14i'., whkin :,- used by L-c~teed nn Prc=!o air-cufi.studbe rmm Nb-e *t '-i -- !hL bead of '.ris --.zeric I --t e= h c.re-vke --Z to vbame aff thee~S* oio the tecled joi-nt is fkrh vzt'h .11e 9surface ur- t)he- f~selice --. wing pane..

ite vrclresut af the 6--vi i-s4ection ofe C-I3 A -rft z185 !rdce !ha-t i-i~ac~eantn Proerkses s-ei-e effictive cmd flmf good Pain, Qdhesion -C-S

,*L-;*;e ~ ~ ~ o ,... '316 fim vfih3 -f-frMek"% O 1M reveoted"fl th +-

pa~nt sy$!e-n d t r ut, it the ae-o ofwe SOCOl area-. f±hwa ohz~gwell -=d 'wO, =' blislefrg or pe~a

Tlh.e fin. -'-sec!ion 01' lie P-2- *orcrft re4eczed ls.=fa1 dsRafoces were in e=-celle-niConc-!;Zn. Ner- oeee a;ffrc ;n tthe aca!a #fr Pcint or- the Ahm-

maior test arem. eoach of wich 6--e be-e c Ied by. q ciffe.rnt psst-,Ot'.1 Tim. -. ;,

the P~eld inspecti.zs indkote that all the exxerimental clemiimc pcedurf used CO~ theC-UMJ an P-3 a rn peryiA smru~i rh- e!;e hetsubstrte-

IX - CONCLUSIONS

I. The drop-diameter method is c reliable and accurate procedure for determining thedegree of cleanliness of aircraft surfaces.

2. The Navy epoxy-polyamide paint system adheres welt to chromated aluminum surfaceswhich have a surface energy greater than 40 dynes/cm.

3. The water-break test, which represents a surface energy of 72.4 dynes/cm, is severeand frequently results in overcleaning of aircraft surfaces prior to painting.

4. On the basis of the laboratory evaluation tests, Cleaners itI and VI gave the bestcombination of ease of oppli:ation, high surface energy, and cicceptable paintadhesion.

5. Hand--strippabl e coating No. 14 will provide good protection for aluminum panelsduring chemical cleaning and during drilling, countersinking, and riveting operations.

6. Chemically strippable coaling No. 11 will provide good protection for aluminumpanels during drilling, countersinking, and riveting operations.

7. The results of the field inspections of C-130 Aircraft 150685 and P-3 Aircraft 5286indicate that both of the experimental cleaning procedures which were used prior tothe application of the Navy epoxy-palyamide paint system (utilizing CIeaners Ill andVI) were effective in providing good adhesion for the coating.

B. Aircraft which are scheduled for South Pacicf c service shculd be given 100% paintcoverage.

9. Ctevices between adjacent wing and fuselage panels should be sealed to preventfoying-surface corrosion.

117 Preceding page blank

X - RECOWMF-rAT1ONSr

The results of this program have demonstrated, through both laboratory and field 'servicetests, that the cleaning procedures using Cleaner No. V1 ore simple, economical, andprovide the high surface energy necessary for good paint adhesion. it is recommended thctthese procedures be used in the surface treatmeni of cli Navy aircraft prior to painting.

The water-break-free test currentl used as a standard of surface cleanliness is severe andfrequently results in unnecessary c eaning operations. It is recommended that the suriace-cleanliness measurement technique- developed in this prog-arn be used as standardinspection procedures at all aircraft painting facilities.

Despite the good adherence provided by the surface treatments prior to poinring, theepoxy-polyamide paint system on C-130 150685 is beginning to deteriorate after appruxi-rrotely 18 months of South Pacific service. The ci.alking ancd cracking are caused byultraviolet degradation and embrittling of the paint film. It is recommended that a

t) program be initiated to develop a paint system which will resist photo-deg"adation for att least 3 years.

IF

9_. I

.2

7' . • ,. •• n m m

REFERENCES

1. P. J. Sabotini, "Reactivation of Chromated Conversmrn Co--tings for Maximum Pa.ntAdhesion," U. S. Naval Air Engineering Center Report AML -2503, September 1966.

2. G. J. Hlof, "Present Practices in the Verification of Cleanliness," Sandia Corpora-tion Technical Merrmrandum 147-63 (25), September 1963.

3. W. A. Zisman, "Constitutional Effects on Adhesion and Abhesion," Adhesion andCohesinr., Eksev'er Publishing Co., 1962.

4. J. J. Bikemon, "A Method of Measuring Contact Angles," Industrial and EngineerineChemistry 13 (6), 443-444, 1941.

5. W. T. M. Johnson, "Surface Analysis ard Adhesion," Official Digest, Federation ofSocieties for Point Technology, November 1961.

6, W. T. M. Johnson, "The Chemical Nature of Pair.t Film Surfaces," Official Dic .st.Federction of Societies for Paint Technology, August 1960.

7. Instruction Manual for Lawrence Hydr0gen Detection Gauge Model HDG 401,Larence Electronics Company, Seattle, Washington.

8. M. S. Lion, 'Evaluation of the 'Scratchmaster' Paint Adhesion Tester," Nav-A AirEngineering Center Report No. NAEC 2018, 17 August 1964.

121

-- Iz v- F M -Z

APPENDIX 8

- OPERATING FRCCEDURE FOR SCRATCHMASTER PAINT ADHESION TESTER

1.Lack th~s balance arm ;n'.o the levelt position. The readingj of the Ames gage or theright side of th~e "achine is faken as the zero point with the platform set a! theI-certsmeter mr.ak

2. Plocat a panel io tze ri.-4 de : ;rko platform with one edge squcrely against the riser.Moderatey tighten the IXMo- clamp adjustment knob. Avoid excessive pressure,which wilf buckis the panel.I3. Lower the balance arm. so that the blade rests on the surface of the panel., 11hrougbthe use of the clamp adjustment on the bWade holder, level the bajance arm o thereading of the Ames gage agrees with the zero point previously determin-ed. Lock theblade holder with the setscrew on the left side. It is necesr/ to zero the balanceaim only once for each panel. Subsequent scratches can be made with good repro-ducibilit.y by approximating a standard tension on the panel with the --amp adjustment.T This saves much time, since the platform need not be run bock to the I -centime-.er

mark for adjustment before reaking each new scratch.

4. The readinig for ea-vh parial is the overage of three scratches which -ib not differ inlength by more thcus 1 .0 centims-ter. The scratch length ussed to calculate the end-point lood in kilogeams is the diference between the measured length af the cut onthe panel ond the total blade travel of 14 centimeters.

5. The load on the cutting l'nife at the end point is culculated by using the followingformula:

L1= K WDjL = load a.,end point

K =calibratim' constant (0P.067 for this instrument)

D =difference between measured scratch length and 14 centimeters

WI total weight of carriaige.