surface finishing processes - electroplating

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Surface Finishing ProcessesBy Hassan Habib

Table of Contents1.2.3.4.4.A4.B4.C4.D4.E4.FWhat is surface finishing?What is Electroplating?AnodizingZinc PlatingPhosphatingWhy we use electroplating?Types of electroplating?AlodiningCadmium PlatingPassivation

What is surface finishing?Surface Finishing is a set of processes that we use to achieve desired mechanical properties on different products1Purpose

What is surface finishing?Mechanical properties are desired in products as per the intended use e.g toothpaste, non-stick utensils, impeller blade

One of the most widely used process of achieving desired qualities is electroplating

Electroplating is the most widely used process, used in variations to achieve desired properties1Purpose

Why we use electroplating?Electroplating is used to deposit a foreign material on mechanical parts to protect them from corrosion, wear and tear and to increase visual aesthetics in some cases2Purpose

What is electroplating?3Process

Types of surface finishing processesFollowing types of surface finishing processes are being used world wide:

Anodizing (MIL-A-8625F, MIL-STD-171E, ASTM B-766-86)Alodining (MIL-STD-5541C, MIL-DTL-16232G)Zinc Plating (ASTM-B-117, B-633)Cadmium Plating (DEF-DTD-904)Phosphation (DOD-P-16232 F)Passivation (QQ-P-35B)4Types

4.A Anodizing

AnodizingFormation of a chemical conversion coating on metal surface by anodic oxidation is called anodizing. This process is carried out on aluminum and aluminum alloys or titanium alloys4APurpose

Anodizing4AProcess

According to MIL-STD-8625 E:

Type I Chromic acid anodizing, conventional coatings produced from chromic acid bath

Type IB Chromic acid anodizing, low voltage process, 22 2V

Type IC Non-chromic acid anodizing, for use as a non-chromate alternative for Type I and IB coatings

Type II Sulfuric acid anodizing, conventional coatings produced from sulfuric acid bath

Type IIB Thin sulfuric acid anodizing, for use as a non-chromate alternative for Type I and IB coatings

Type III Hard Anodic Coatings

Class 1 Non-dyed

Class 2 Dyed4AAnodizingTypes and Classes

Bath Concentration=10% H2SO4Current Density =10-15 A/ft2Time =Depending upon requirementTemperature =18oC-22oC 4AAnodizingProcess Specifications

4AAnodizingProcess TestsTestType ApplicableSpecimen PreparationRequirementTest methodCoating WeightI, IB, IC, II, IIB, IIISpecimen Panels:(min width 3 in, min thickness 0.032 in)3.7.1.13.7.2.1.1- ASTM B 244- Weigh- Metallographic MicroscopeCoating ThicknessIIISpecimen Panels:(min length 3 in, min width 3 in, min thickness 0.032 in)3.7.2.1- Weigh after stripping of coatingCorrosion ResistanceI, IB, IC, II, IIBSpecimen Panels:(min length 10 in, min width 3 in, min thickness 0.032 in)3.7.1.2- Salt Spray test for 336 hrsLight FastnessI, IB, IC, II, IIB for Class 2 onlySpecimen Panels:(min length 10 in, min width 3 in, min thickness 0.032 in)3.7.1.3- Ultraviolet Radiation exposure for 200 hrsAbrasion ResistanceIIISpecimen Panels:(min length 4 in, min width 3 in, min thickness 0.063 in)3.7.2.2- CS 1000 g wheels at 70 rev/min for 10,000 cycles.

4AAnodizingAdvantagesHighly DurableInexpensive to produce and maintainWont chip, flake, peel or chalkMaintains metallic appearance of aluminumEnvironmental Friendly- No heavy metals- By products aid municipal waste water treatment facilities to separate solids and neutralize pHFire Protection- Anodic oxide layers give a minor increase in the fire protection of aluminum constructions. The melting point of the oxide surface increases from approximately 650oC to approximately 2000oC

4.B Alodining

AlodiningAlodining is the chemical application of a protective chromate conversion coating on alumiunum4BPurpose

Alodining4BProcess

According to MIL-STD-5541 C:

Class 1A For minimum protection against corrosion resistance. Good quality for the surfaces to be painted or not

Class 3 For protection against corrosion where lower electrical resistance is required.4BAlodiningClasses

4BAlodiningProcess TestsTestClassApplicableSpecimen PreparationTest methodCorrosion Resistance1A, 3Specimen Panels:(min length 10 in, min width 3 in, min thickness 0.02 in)- Salt Spray test for 168 hrsAdhesion wet tape1A, 3Specimen Panels:(min length 10 in, min width 3 in, min thickness 0.02 in)- Adhesion Wet Tape TestElectrical resistance testing3Specimen Panels:(min length 4 in, min width 3 in, min thickness 0.063 in)- At 200 psi nominal electrode pressure class 3 must not have resistance greater then 5000 microhms

4BAlodiningAdvantagesAdds no measurable weightDoes not alter the dimensions of parts (does not make holes smaller)Requires essentially no cleanup after application. Encourages treatment of all small parts as they are fabricated and installedRequires no electricity or skill to apply

4.C Zinc Plating

Zinc PlatingZinc Plating is an electroplating process performed by using Zinc Sulphate solution. It is a low cost process making it feasible for smaller parts

4CPurpose

Zinc Plating4CProcess

Zinc Plating4CTypes and ClassesAccording to ASTM B-633:

Classification NumberService ConditionThicknessFe/Zn 25 SC 4 (Very Severe) 25Fe/Zn 12 SC 3 (Severe) 12Fe/Zn 8 SC 2 (Moderate) 8Fe/Zn 5 SC 1 (Mild) 5

Type I Zinc, as platedType II Zinc, w/colored chromate CoatingType III Zinc, w/colorless chromate CoatingType IV Zinc, w/phosphate conversion Coating

Zinc Plating4CProcess TestsTestSpecimen PreparationTest methodCoating ThicknessSpecimen Panels:(min length 100 mm, min width 25 mm, min thickness 1 mm)- B487, B499AdhesionSpecimen Panels:(min length 150 mm, min width 100 mm, min thickness 1 mm)- B571Corrosion ResistanceSpecimen Panels:(min length 254 mm, min width 76.2, min thickness 0.02 in)- Salt Spray TestHydrogen Embrittlement relief testDefined By Purchaser- Sustained Load of 75% of UTS

Zinc Plating4CAdvantagesChromate protected zinc offers higher corrosion resistanceThe process is cheapElectrolytic zinc coatings are used to protect and improve the appearance of ferrous metals, (i.e iron and steel) as a corrosion barrier, and then as a sacrificial coating

4.D Cadmium Plating

Cadmium PlatingCadmium Plating is an electroplating process performed by using Cadmium cyanide solution

4DPurpose

Cadmium Plating4DProcess

Cadmium Plating4DTypes and ClassesAccording to QQ-P-416 F:

TypesI As platedII Supplementary Chromate CoatingIII Supplementary Phosphate Coating

Classes1 0.005 in minimum thickness2 0.003 in minimum thickness3 0.002 in minimum thickness

Cadmium Plating4DProcess TestsClassesMinimum ThicknessFor external surface that can be touched by a ball 0.79 in in diameterFor external surface that can not be touched by a ball 0.79 in in diameterInch MicrometerInch Micrometer10.0050180.00030820.003080.00020530.002050.000154

Cadmium Plating4DAdvantagesCadmium Plating is the preferred method of protecting close-tolerance steel parts against corrosionIt is particularly useful for reducing or avoiding bi-metallic corrosion and is suitable for solderingCadmium plating is liable to rapid attack by vapors emanating from certain woods, varnishes, plastics and other organic materials, particularly in poorly ventilated or humid conditionsThis plating is mostly used on carbon steel and low alloy steel parts for protection against corrosion

4.E Passivation

PassivationPassivation is a post plating process and is normally applied to cadmium and zinc plated parts and to zinc based alloy die-casted parts. Passivation process on plated surfaces reduces corrosion.4EPurpose

Passivation4EProcess

Passivation4ETypes and ClassesAccording to QQ-P-35 C:

TypesI Nitric Acid + Sodium Dichromate solution 70-90oFII Nitric Acid + Sodium Dichromate solution 120-130oFIII Nitric Acid + Sodium Dichromate solution 145-155oFIV For steels containing large amounts of sulfur or selenium (0.15%)V Part Anodic at 3-5 V for high carbon martensitic (440) steelsVI Concentrated Nitric Acid solution 70-90oFVII Concentrated Nitric Acid solution 120-140oFVIII Concentrated Nitric Acid solution 120-130oF

Passivation4EProcess TestsTestTest SpecimenTest methodWater Immersion TestThe specimen shall consists of samples of parts that are submitted orselected for acceptance inspection.MIL-STD-753BParts shall be cleaned with acetoneParts then must be immersed in distilled water for 1 hour and allowed to dry for 24 hrsNo stains or rust must be visibleHigh Humidity TestThe specimen shall consists of samples of parts that are submitted orselected for acceptance inspection.- MIL-STD-753BParts shall be cleaned with acetoneParts shall be subjected to 100% humidity at 100oF for 24 hoursNo stains or rust must be visibleSalt Spray TestThe specimen shall consists of samples of parts that are submitted orselected for acceptance inspection.Salt Spray Test for 2 hrsASTM B117Copper Sulfate TestThe specimen shall consists of samples of parts that are submitted orselected for acceptance inspection.MIL-STD-753BParts shall be cleaned with acetoneParts then must be swabbed with copper sulfate solution for 6 minutesParts must not show copper deposits

Passivation4EAdvantagesPassivation process on plated surfaces reduces corrosion white rusting of cadmium and zinc under humid conditionsIt helps to reduce the attack on both metals by certain vapors and organic substancesIt improves the performances of subsequently applied partsIt can remove sulfides exposed on the surface of free-machining stainless alloysIt can remove surface contamination, such as particles of iron-contai

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