slides for coating techniques part 1 gfe schmalkalden uni
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1
Principles of Coating Technology I 1
GFE Schmalkalden e.V.
Principles of Coating Technology
Part I - Basics 1. Motivation 2. Tribology and Wear 3. Surface properties and characterization 4. Pre-and post-treatment 5. Deposition methods - Overview
Part II – Deposition methods 6. Painting 7. Electroplating and anodic oxidation
Principles of Coating Technology I 2
GFE Schmalkalden e.V.
1. Motivation
2
Principles of Coating Technology I 3
GFE Schmalkalden e.V. Motivation
4.5 % of the national product of industrialized nations
>50 Mrd € are material and energy loss by wear and corrosion on metallic parts
5 % of sales
are used for repair and maintenance (in wear intensive industry 10-15%)
10 % of production costs are maintenance costs
10 % of wear parts in industrial equipment
are involved in 70% of failures and disorders
50 % of wear loss are preventable
Some Numbers
Principles of Coating Technology I 4
GFE Schmalkalden e.V. Motivation
Loss of material and energy by wear and corrosion must be avoided
• Preventable maintanence
„to act is better than to react“
• Using functional material for machine function
wear and corrosion protection as design elements
Surface protection by functional coating and surface technology
3
Principles of Coating Technology I 5
GFE Schmalkalden e.V.
Source: Siemens AG
Costs (€) for annual production of 1 Mio units
tools
maintanance
Coating
Without coating
BALINIT®- coating
31.800 15.700
17.200
800
total 16.500 49.000
Annual coating costs (200 different models)
800 x 200 =
Savings per annual (200 different models)
32.500 x 200 =
160.000
6,5 Mio
Motivation
Example: Production of phones
Principles of Coating Technology I 6
GFE Schmalkalden e.V. Motivation
Industrial Application
Wear protection in mining
Coating of wear parts
Print roll (printing industry)
Power generation (turbine blades)
4
Principles of Coating Technology I 7
GFE Schmalkalden e.V. Motivation
Using coated „band saw“ to separate submarine „Kursk“ in 2001
Principles of Coating Technology I 8
GFE Schmalkalden e.V.
Hip implant
Synchronrings
EUROFLAMM
Engine block
Household devices
Motivation
Application samples of coated parts
5
Principles of Coating Technology I 9
GFE Schmalkalden e.V. Motivation
Application samples of coated parts
Industry Coated components
aerospace Landing gear, airbrakes
Industrial gas turbines Blades, abrasive coatings, cumbustion coatings
engines Cylinder holes, wear coatings, Synchronrings
Paper, printing, steel industry Printing and transportation rolls
Oil and gas equipment Pump engines, seals, shafts, compressor shafts
Medicine Implants, x-ray targets
Textile machines rolls
Other industries Components and parts
Consumer goods Flat irons, writing utensils, frying pan
On-site maintenance Steam generator, paper rolls, gas turbines
Principles of Coating Technology I 10
GFE Schmalkalden e.V.
2. Tribology and Wear
6
Principles of Coating Technology I 11
GFE Schmalkalden e.V. Tribology and Wear
Loss of material and energy by wear and corrosion must be avoided
enviroment
intermediary
load
Counter body
Base body
velocity
Tribological system metal mineral Liquid gaseous
liquid solid gaseous
metal mineral plasic elastomere
liqud gas dust temperarture
Protection of the surface by coating system or surface modification Consideration of the tribological system
Principles of Coating Technology I 12
GFE Schmalkalden e.V.
Consideration of the tribological system Determination of the wear mechnism
Wear combination loading Wear type Mechanism
Solid/solid sliding
rolling
impact
vibrations
sliding wear
rolling wear
impact wear
vibration wear
adhesion / abrasion
adhesion / fatigue
fatigue / adhesion
fatigue
Solid/liquid flowing
impact
cavitation
droplet erosion
fatigue
fatigue
Solid / gas with solid particles
flowing
impact
sliding jet wear
impact jet wear
abrasion
fatigue
Verschleißpaarungen
VE
RS
CH
LP.C
DR
Verschleißpaarung Beanspruchung Verschleißart Mechanismus
Festkörper /Festkörper
Festkörper/Flüssigkeit
Festkörper/Gas mit Fest-stoffpartikeln
Gleiten
Rollen
Prallen
Schwingen
Strömen
Prallen
Strömen
Prallen
Gleitverschleiß
Wälzverschleiß
Stoßverschleiß
Schwingverschleiß
Kavitation
Tropfenschlag
AdhäsionAbrasion
AdhäsionErmüdung
Ermüdung
AdhäsionErmüdung
Ermüdung
Ermüdung
Abrasion
Ermüdung
Gleitstrahlverschleiß
Prallstrahlverschleiß
Verschleißpaarungen
VE
RS
CH
LP.C
DR
Verschleißpaarung Beanspruchung Verschleißart Mechanismus
Festkörper /Festkörper
Festkörper/Flüssigkeit
Festkörper/Gas mit Fest-stoffpartikeln
Gleiten
Rollen
Prallen
Schwingen
Strömen
Prallen
Strömen
Prallen
Gleitverschleiß
Wälzverschleiß
Stoßverschleiß
Schwingverschleiß
Kavitation
Tropfenschlag
AdhäsionAbrasion
AdhäsionErmüdung
Ermüdung
AdhäsionErmüdung
Ermüdung
Ermüdung
Abrasion
Ermüdung
Gleitstrahlverschleiß
Prallstrahlverschleiß
Verschleißpaarungen
VE
RS
CH
LP.C
DR
Verschleißpaarung Beanspruchung Verschleißart Mechanismus
Festkörper /Festkörper
Festkörper/Flüssigkeit
Festkörper/Gas mit Fest-stoffpartikeln
Gleiten
Rollen
Prallen
Schwingen
Strömen
Prallen
Strömen
Prallen
Gleitverschleiß
Wälzverschleiß
Stoßverschleiß
Schwingverschleiß
Kavitation
Tropfenschlag
AdhäsionAbrasion
AdhäsionErmüdung
Ermüdung
AdhäsionErmüdung
Ermüdung
Ermüdung
Abrasion
Ermüdung
Gleitstrahlverschleiß
Prallstrahlverschleiß
Tribology and Wear
7
Principles of Coating Technology I 13
GFE Schmalkalden e.V. Tribology and Wear
Wear depth
Coating wear
Corrosion wear
Adhesive wear Abrasive wear
Surface fatigue wear Base material
Oxide-Reaction zone
Distubtion by forming and modified chemical composition
Adsorption layer
Outher unrelated
surface layer
Inner related surface layer
Principles of Coating Technology I 14
GFE Schmalkalden e.V. Tribology and Wear
Progress of wear
Lin
eare
r V
ers
ch
leiß
be
trag
Abrasio
n
Weg, Zeit
Adhäsion
Tribochem. Reaktion
Oberflächenzerrüttung
Source: Uni Dortmund, LWT
Lin
ear
wea
r
Distance, time
8
Principles of Coating Technology I 15
GFE Schmalkalden e.V. Tribology and Wear
Reduction of wear
Reduction of abrasion: high hardness with adequate ductility Hard phases in a ductile matrix Reduction of adhesion unrelated surface layer, lower adhesive bonding force material with heterogeneous structure Reduction of fatigue: high strength with high ductility avoiding of stress concentrations Reduction of thermal fatigue high thermal strength reduction of loading by thermal insulation layers Reduction of tribo-oxidation: avoiding of reactive layers
Principles of Coating Technology I 16
GFE Schmalkalden e.V. Tribology and Wear
Important physical processes
Adsorption: Accumulation of liquid oder gaseous materials
(adsorbens) on the surface of solid parts (adsorbat)
Saturation of bonding states on the surface leads to the
reduction of the fee energy (steady state)
Physical adsorption
• Interaction of induced or permanent
dipoles (Van-der-Waals-forces)
• Adsorption heat 4 – 40 kJ/mol
• Process is reversible
Chemical Adsorption
• Formation of a chemical bonding
• Adsorption heat 40 – 400 kJ/mol
• Process is not reversible
Absorption: infiltration of gaes or gaseous mixtures by diffusion processes in a
condensed (solid) phase
The absorbed gas will be dissolved in a steady state at defined
temperatures and concentrations, molecules will be dissociated to
atoms
9
Principles of Coating Technology I 17
GFE Schmalkalden e.V. Tribology and Wear
Important physical processes
Adhesion: adhesive forces on the contact area of two (liquid or solid) material
• Physical and chemical adhesion • Mass attraction • Mechanical clamping
Cohesion: cohesive forces within a material or body
• Primary bonding chemical bonding
• Secondary bonding partial bonding, Van-der Waals Bonding
Principles of Coating Technology I 18
GFE Schmalkalden e.V. Tribology and Wear
Important physical processes
Wetting: Formation of a contact or boundary angle at the boundary between a solid and
a liquid
In the steady state the Young Equation is valid:
𝜎𝑆 = 𝜎𝑆𝐿 + 𝜎𝐿 ∗ cos 𝜗 𝜎𝑆 , 𝜎𝐿: surface tension of the solid and the liquid 𝜎𝑆𝐿: surface tension between solid and liquid 𝜗: contact angle
Wetting: 𝜗 < 90°
No wetting: 𝜗 > 90°
Complete wetting: 𝜎𝑆 > 𝜎𝑆𝐿 + 𝜎𝐿
10
Principles of Coating Technology I 19
GFE Schmalkalden e.V.
3. Surface properties and characterization
Principles of Coating Technology I 20
GFE Schmalkalden e.V.
Deposition is the application of an adherend coating of shapeless material on a component.
Surface properties and characterization
Definition of the coating deposition processes
Function of coatings are
• Decoration
• information (signals)
• corrosion protection
• wear protection
• physical effects (diffusion barrier, flame barrier, thermal isolation, electrical isolation, …)
11
Principles of Coating Technology I 21
GFE Schmalkalden e.V. Surface properties and characterization
Processes for surface modification
• mechanical (e.g. shot peening)
• thermal (partial laser hardening)
• thermo-mechanical (e.g. hot isostatic
pressing
• Thermo-chemical (e.g. nitriding)
• Pure metals (chromium, zinc, gold, …)
• Alloys for special applications (e.g.
corrosion)
• Anorganic, non-metallich (enamal,
ceramics…)
• Organic (pintings, polymers)
• Compounds
Materials for surface modification
Principles of Coating Technology I 22
GFE Schmalkalden e.V. Surface properties and characterization
Coating application fields
Coating of
new parts
optics
Repair coatings
High
Temperature
protection
Oxidation
protection Wear
protection Corrosion
protection
Elcetrical
properties
Bio-
activities
Heat
insulating
decoration
Bear-
ring
12
Principles of Coating Technology I 23
GFE Schmalkalden e.V. Surface properties and characterization
Relevant surface properties
primary
• Chemical composition
• Phase composition
• Structure and microstructure
• Residual stress
• Surface roughness
secondary
• elasticity
• hardness
• strength, fatigue strength
• friction and sliding properties
• corrosion resistance
• wear resistance
• optical properties (colour, coverage)
• electrical / thermal conductivity
Important: characterization of the properties
Principles of Coating Technology I 24
GFE Schmalkalden e.V. Tribology and Wear
key property: coating adhesion
adhesion mechanism:
• Mechanical clamping
• Adhesion
• Diffusion
• Chemical bonding
• Electrostatical forces
adhesion is influenced by
• Surface energy
• Material properties (e.g. strength,
conductivity, …)
• Surface material interaction
• Bonding mechanism
• Residual stresses (High residual
stresses lead to coating delamination
• …
Adhesion > coating strength Adhesion < coating strength
13
Principles of Coating Technology I 25
GFE Schmalkalden e.V. Surface properties and characterization
Measurement of coating properties
• coating thickness • coating adghesion strength • Hardness • Wear resitance at diferent loads • Friction coefficient • corrosion properties • Thermal properties • Mechanical properties (ductility,
elasitcity, stresses, … • Electrical properties (conductiviy,
resistance, … • Optical properties (color, brillance, …) • Surface roughness • … • …
Methods for measurements
• Metallographic investigations
• Corrosion behaviour
• Wear behaviour
• Thermal behaviour
• Mechanical behaviour
• Optical behaviour
• …
• …
Destructive and nondestructive tests are possible
Principles of Coating Technology I 26
GFE Schmalkalden e.V. Surface properties and characterization
Methods for measurements
Mechanical values of coating Bond strength test (<80 MPa) cupping test bending test measurement of residual stresses test of fatigue strength creep behaviour thermal shock test
Metallographic evaluation structure and microstructure micro- / macro- hardness phase boundaries Interface coating / substrate pores and pore distribution roughness
corrosion behaviour salt-spray test, thermal test, current density potential test
Wear behaviour Taber-Abraser-Test; pin on disc test; vibrational wear ….
Extremely high number of other tests with or without standards
14
Principles of Coating Technology I 27
GFE Schmalkalden e.V. Surface properties and characterization
Measurement examples Measurement of coating thickness d - Simple and cheap procedure - Fast measurement - Destructive method
parameters: grinding time ball diameter Preparation of a calotte grinding - friction pair coating / ball) - Measurement of the diameter
of the grinded calotte
Principles of Coating Technology I 28
GFE Schmalkalden e.V. Surface properties and characterization
Measurement examples Measurement of wear behaviour - Destructive method - Pin-On-dic method - Determination of the friction and
the wear coefficient
• Methode Ball with defined load Interaction with a coated surface Friction between ball and surface Measurement of Wear trace; Determination friction coefficient :(FR = FN * µR)
• Parameter: Normal force [N] Rotational speed [s-1 ; m-1] Speed [m/s ; m/min] Trace diameterLaufspurdurchmesser [mm] Friction length [m] rotation Friction time [min]
15
Principles of Coating Technology I 29
GFE Schmalkalden e.V. Surface properties and characterization
Measurement examples Measurement of coating hardness • Micro harndess messurement • Measurement of the indentation of an
indenter (diamond pyramide) with difined load
• Determination of hardness by relation of geometriy and load
Principles of Coating Technology I 30
GFE Schmalkalden e.V. Surface properties and characterization
Measurement examples Measurement of coating adhesion strenth • Scratch-Test • Diamond indenter will be moved with a defined
load along the coated surface • At critcal load: coating delamination or crack
formation • Determination and evaluation of the scratch
Moving direction of the probe
Acoustic emission sensor
Diamond indenter
Depth sensor
16
Principles of Coating Technology I 31
GFE Schmalkalden e.V. Surface properties and characterization
Measurement examples Measurement of roughness • Mechanical method (tactile scanning) • Measuring sensor are moved with
constant speed along the surface • Recording of the different roughness
values
R a = 0.2 - 0.45 µm R a = 0.07 - 0.15 µm
Principles of Coating Technology I 32
GFE Schmalkalden e.V.
4. Pre-and post-treatment
17
Principles of Coating Technology I 33
GFE Schmalkalden e.V.
Process steps during coating deposition
1. Pre-treatment - cleaning - Surface activation - roughening
2. Coating deposition - Determination of coating technology and parameters - Surface protection
3. Post-treatment
- Homogenization of the coating - Additional improvement of the properties
4. Measurement of coating quality g - Mechanical values - metallographic values - Wear and corrosion
Pre- and Posttreatment
Principles of Coating Technology I 34
GFE Schmalkalden e.V.
Pre- Treatment
Pre- and Posttreatment
Cleaning
- removal of dirt - removal of oils and greases - removal of paints
Blasting
- roughening - decontamination - activation
Blasting materials
- sand (improper due silkose) - corund (Al2O3) - grit - pellets - carbides
Ultrasonic assited claning - removal of blasting residues
18
Principles of Coating Technology I 35
GFE Schmalkalden e.V.
Post- Treatment
Pre- and Posttreatment
Objective: homogenization of the coating or the surface near areas to improve the
properties (e.g. corrosion resitance, wear resistance)
- reduction of porosity
- Smoothing of the surface
- Improvement coating adhesion
- Reduction of residual stresses
- Improvement of coating hardness and ductility
- Closing of cracks
Principles of Coating Technology I 36
GFE Schmalkalden e.V.
Post- Treatment
Pre- and Posttreatment
Thermal Post-Treatment: flame (z.B. acetylen/ oxygen)
arc (tungsten inertgas weld method)
Laser beam
Electron beam
induction
Thermo-mechanical hot isostatic pressing (HIP)
Mechanical final expanding hammering shot peening simultaneous spraying and peening
19
Principles of Coating Technology I 37
GFE Schmalkalden e.V.
Thermal Post-Treatment
Pre- and Posttreatment
Fuly or partial remelting of the surface with and energy source (flame, laser beam, …) for
- Smoothing of rough surfaces
- Dissolving of unwantet phases
- Creation of additional hard phases
- Hardening of thin layers
Example: Laser remelting
Bewegungsrichtung
Laserstrahl
Bauteil
Moving direction of the probe
Laser beam
Coated part
Requirements and parameters:
• Avoiding of cracks due to different thermal expansion coefficients
• Pre-heating possible
• Adjustment of process parameters
• Feed rate
• Laser power
• Laser focus point
• Shielding gas
• …
Principles of Coating Technology I 38
GFE Schmalkalden e.V.
Thermal Post-Treatment
Pre- and Posttreatment
Heat treated Ti-coating with reaction zone
Electron beam surface remelted NiCrAl coating
Laser remelted TiMo coating
20
Principles of Coating Technology I 39
GFE Schmalkalden e.V.
Thermal Post-Treatment
Pre- and Posttreatment
glue
coating
Probe
Adhesive tensile strength
According to DIN EN 582
w i e g e s p r i t z t u m g e s c h m o l -
z e n m i t
A u f m i s c h u n g
u m g e s c h m o l -
z e n m i t
R e a k t i o n s -
z o n e
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
Ad
hesiv
e t
en
sil
e s
tren
gth
[M
Pa]
w i e g e s p r i t z t u m g e s c h m o l -
z e n m i t
A u f m i s c h u n g
u m g e s c h m o l -
z e n m i t
R e a k t i o n s -
z o n e
5 7
3 8 , 5
> 6 5
As sprayed remelted fusion
remelted Reaction zone
coating
substrate
modification of the adhesive strength by different thermal post treatment processes - Remelting without reaction zone: adhesive strength is reduced - Remeling with reactive zone: increasing of adhesive strength
Principles of Coating Technology I 40
GFE Schmalkalden e.V.
Thermo-mechanical Post-Treatment
Pre- and Posttreatment
Hot isostatic pressing (HIP)
- Material will be loaded with high temperature and high pressure in one process step
- Pressure carrier is inert gas
- HIP will be used for compacting of poros structures (eg sintering of ceramics)
Processes during HIP
• diffusion
• creeping
Modification dring hip
• Structural compacting, removal of pores
• Phase formation within the coating
• Grain growth wihin coating
21
Principles of Coating Technology I 41
GFE Schmalkalden e.V.
Thermo-mechanical Post-Treatment
Pre- and Posttreatment
Hot isostatic pressing (HIP) - Example
Production of metal matrix composites (MMC)
- Twisting of fibres on a base body
- Deposition of the metalic matrix
- Hot isostatic pressing
Using for brake drums, cylinder sleeves, drive shafts
Spritzpistole
Verbundwerkstoff
Faser
Stützkörper(geschliffen)
Principles of Coating Technology I 42
GFE Schmalkalden e.V.
mechanical Post-Treatment
Pre- and Posttreatment
Shot peening
Objective of mechanical post-treatment • compacting • Reduction of surface roughness
Characteristics of shot peening • Ball shaped blasting material off metal, ceramic, glass • Process similar to sand blasting • Velocity of blasting material 15-150 m/s
Simultaneous shot peening • Compacting of the whole coating • Optimization of corrosion resistance • Induction of residual compressive stresses
Thermal sprayed Ni20Cr coating before and after shot peening
22
Principles of Coating Technology I 43
GFE Schmalkalden e.V.
5. Deposition methods - Overview
Principles of Coating Technology I 44
GFE Schmalkalden e.V. Deposition methods - Overview
Classification of Deposition methods
Deposition by
welding
Deposition by
soldering
Deposition
from gaseous or voporized
state
Deposition from ionized
state by electrolytical or chemical deposition
Deposition
from solids or powders
Deposition
from liquid or pasty state
PVD / CVD Galvanic methods
Anodic methods
Powder coating with polymers or metalls
Painting Hot dipping
23
Principles of Coating Technology I 45
GFE Schmalkalden e.V. Deposition methods - Overview
Important methods
Deposition by welding
• Fusion welding (autogenously, metal inert gas, tungsten inert gas plasma welding with wire or powder, submerged , laser welding )
• Pressure welding (roll cladding or explosive plating)
Deposition by brazing
• fusion soldering (with gas, metal inert gas, plasma, oven)
Deposition from gaseous or voporized state
• Physical Vapor Deposition
• Chemical Vapor Deposition
• Combination of PVD and CVD methods
Deposition from ionized state
• Galvanic methods with and without an external current generator
• anodic methods
Principles of Coating Technology I 46
GFE Schmalkalden e.V.
method Diffused element -
Media
temperature [°C]
Aufkohlen C Gas, Paste, Pulver, Salzbad 800 - 1050
Carbonitrieren C, N Gas, Plasma, Salzbad 600 - 930
Nitrieren N (H) Gas, Plasma 350 - 550
Nitrocarburieren N, C (O, H) Gas, P lasma, Pulver, Salzbad 350 - 600
Oxidieren O Gas, Salzbad 150 - 550
Oxinitrieren N, O Gas ~ 500
Sulfidieren S Salzbad 200
Sulfonitrieren N, S Gas (Plasma) ~ 600
Sulfonitrocarburieren N, C, S Salzbad (Plasma) 570 - 580
Borieren B Gas, Paste, Plasma, Pulver 800 - 1000
Vanadieren V Pulver, Salzbad 850 - 1100
Chromieren Cr Gas, Pulver, Salzbad 900 - 1200
Chromvanadieren Cr, V Pulver 1000
Niobieren Nb Pulve r 1000 - 1100
Alitieren Al Gas, Pulver, Salzbad ~ 1200
Silizieren Si Pulver 930 - 1200
Stannieren Sn galv. Überzug 580
Manganieren Mn Pulver 1000 - 1100
Important thermochemical methods
Deposition methods - Overview
24
Principles of Coating Technology I 47
GFE Schmalkalden e.V.
Built-up-welding 6 mm
CVD / PVD 0,001 - 0,1 mm
chemical Ni 0,03 - 0,3 mm
galvanic Cr 0,01 - 0,5 mm
thermal spraying 0,05 - 3 mm
build up soldering 0,1 - 1 mm
build up welding 2 - 20 mm
roll cladding 2 - 12 mm
TiN-
coating
PVD
Thermal spraying
50 µm
APS-
Al2O3
Typical coating thickness of some methods
Deposition methods - Overview
Principles of Coating Technology I 48
GFE Schmalkalden e.V.
10 -5
10 -4
10 -3
10 -2
10 -1
1 10 100
galvanic Cr
Coating thickness [mm]
vaporation
sputtering
Ion plating
CVD / PECVD
plasmapolymerisation
galvanic Ni
Chemical Ni
Flame spraying
Plasma spraying
Arc spraying
Build-up welding
Roll cladding
Hot dipping
Typical coating thickness of some methods
Deposition methods - Overview
25
Principles of Coating Technology I 49
GFE Schmalkalden e.V.
Thermal spray
0.1 1 10 100 1000 10000
1000
800
600
400
200
0
Coating thickness (mm)
Su
bstr
ate
tem
pe
ratu
re (
°C)
PVD
II
Thermal spraying
Build-up welding
Chemical methods
(II = Ion implantation
CVD
coating thickness and substrate temperature of some methods
Deposition methods - Overview
Principles of Coating Technology I 50
GFE Schmalkalden e.V.
Part II – Deposition methods 6. Painting 7. Electroplating and anodic oxidation
26
Principles of Coating Technology I 51
GFE Schmalkalden e.V. Painting
Pre-tratment
Mechanical:
• Brushing
• Blasting
Chemical:
• Etching
• lubricating
Painting systems are based on:
• pre-treatment is normally ncessary
• Using of mechanical or chemical oricesses
• Water
• Alcohole
• Organic solvents (Trichlorethylen, Toluol, …)
Principles of Coating Technology I 52
GFE Schmalkalden e.V. Painting
Mostly used industral method of painting: spray painting
Compressed air spraying - Using nozzle with defined geometry - High velocity of paint droplets - Formation of a droplet jet
Airless-nozzle Finespray-nozzle Spritzlackieren
- Spaying of the material by high pressure, high velocity or elcectrostatic fields - Ball shaped droplets are accelerated toward to the substrate
27
Principles of Coating Technology I 53
GFE Schmalkalden e.V. Painting
Compressed air nozzle
- Using compressed air
- High velocity differenz destroyed paint surface
Airless nozzle
- High pressure of the paint
- Expansion of the paint after the nozzle exit
- Priniple is used in sprays
Electrostatic nozzle
- Mechanical nebulization of the paint
- Electrostatic acceleration of the paint to the substrate
- Extremly low paint losses
nozzle geometries
Principles of Coating Technology I 54
GFE Schmalkalden e.V. Painting
Dipping
Cathodic hot dipping
- Using a dipping bath
- Dipping of the components into the bath until a fully wetting
- Hardening of the paints at the air or in a stove
- Hot dipping processes are use for mass production
28
Principles of Coating Technology I 55
GFE Schmalkalden e.V. Painting
Modifications of dipping process
Electrical hot dipping Conventional hot dipping:
• only wetting of the surface
• no additional solvents
Electrical hot dipping
• Chemical modification of the paint paint droplets
• Coagulation of paint droplets on the surface
• Hardening by heat treatment
Surface of the Component
Surface of the Component
Surface of the Component
Paint particles in aqueous solvent
Paint droplets coagulated on the
surface
Paint surface after hardening
Advantages of the dipping process Disadvantages of the dipping process
• Good automatable
• Complete painting of the components
(cavities, beadings,…)
• Low consumption of paint
• Irregular paint surface possible
• High investment costs
• High quantity of paint necessary („dipping bath“)
Principles of Coating Technology I 56
GFE Schmalkalden e.V. Painting
Hot dipping
Modifications of hot dipping process
• Zinc coating (450 – 530° C)
(galvanizing)
• Hot dip tinning (300°C)
• Aluminum coating (700°C)
• Lead coating (380 °C)
Pre treatment of the hot dipping process
• Librication in an alcalic bath
• Etching with salt acid or sulfurid acid for a
metallic surface
• Purging of the surface to remove formed salts
• Tratment with fluxes of zinc chloried or
aluminum chloride
• Precision cleaning and drying
• dipping of e metallic part in a molten metal bath
• Formation of solid or liquid reaction products at the boundaries
• After removing: solidification of the adhere pint layer
29
Principles of Coating Technology I 57
GFE Schmalkalden e.V. Painting
Hot dipping – zinc coating
Wet zinc coating
• Removal of etched parts without drying
• Flux is floated on the bath surface
• Parts are dived through flux
Hot-dip galvanizing
• Diffucion between iron and zinc
• Formation of an alloy layer of iron and zinc
(intermerallic fe-Zn phases)
• Deposition of a pure zinc layer during
removal of parts
• Corrosion improvement by formation of oxidic and carbonatic passivation layers
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GFE Schmalkalden e.V. Painting
Powder coating
• Processing of solvent-free, dry and fre-flowing powder of metals or plastic
Plastics:
• Epoxy resin (EP)
• Epoxy /polyester resin (EP/PES)
• Polyester resin (PES)
• Polyacrylic resin (PAC)
• Polyuretan PUR)
• Polyethylen (PE)
• Polyamide (PA)
• Ethylen-Vinylalkohol-Copolymerisat
• Thermosetting resing
• plastomere
Pre treatment of the powder coating process
• different pre-treatment processes
depending on application and material
• Degreasing
• Etching
• Phosphatizing (steel parts)
• Chromating (aluminum parts)
• Blasting with corund
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GFE Schmalkalden e.V. Painting
Powder coating - Powder spray coating
• Up to 100 % of material will be used
• Coating thickness 40 - 120 µm
• Specific paint sprayer with continously powder feeding and deed unit
• Processing gas: compressed air
• Electrodes generating a potential difference between sprayer and grounded part
• Powder particles (10 bis 80 µm) will be charged and accelerated by compressed air and electrostatic potential
• Condenstation of the particles on the surface
Continous oven
chain conveyor
Pre treatment unit
Podwer spray chamber
High-voltage generator with powder feeder
Poder recycling unit
give in give out
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GFE Schmalkalden e.V. Painting
Powder coating – whirl sintering
• Coating thickness 200 - 500 µm (in special cases 1000 µm)
• Component are pre-heated to sintering temperature
• Dipping the component into the whirl sintering bath
• Wetting of the component by floating powder particles
• After short dipping melting of the particles to a solid coating
• Cooling on air or in water (on air lead to a smoother surface)
• Useful for small components and large number of pieces
• Good automation
air
Powder cloud
Porous Intermediate
layer
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GFE Schmalkalden e.V. Painting
Powder coating – rotation sintering
• Shake or rotation sintering
• Internal coatings in pipes
• Pre-heating to sinter temperature
• Filling with powder
• Processing time 7- 10 s
• Homogenous layer by heating and shaking
give out
pipes
Heating
cooling
Powderdeposition
Smoothing
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GFE Schmalkalden e.V. Painting
Powder coating – powders and powder properties
properties unit Powder type
PE PVC PA EP EVAL
Pre treatment: blasting yes yes yes yes yes
Etching / phosphatizing (without passivation)
no no no yes yes
Adhesion layer yes yes yes yes yes
Processing temperature °C 320-360 270-360 270-360 200 180-360
Post treatmend yes yes yes yes no
Minimal sheet thickness mm 1 1 1 - 0,5
Shore hardnees 70 80 95 95 85
Melting tange °C 105-110 70-150 186 - 105-108
Thermal expansion K-1 2,5 x 10-5 8 x 10-5 12 x 10-5 4 x 10-5 13 x 10-5
Heat conductivity W/Km 0,35 0,15 0,29 0,15 0,28
Spez. heat kJ/kgK 2,3 0,98 2,4 1,7 1,9
Water absorption (24 Std. RT) % 0 0,2 0,8-1,5 0,3-1,5 0,2
Chemical stability good moderate moderate moderate good
Weather resistance bad moderate moderate bad good
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7. Electroplating and anodic oxidation
Principles of Coating Technology I 64
GFE Schmalkalden e.V. Electroplating and anodic oxidation
electroplating
Electroplating (wtih external energy source)
• Using an electrolytic bath
• Part will be used as cathode (metallic layer)
• Metallic ions of electrolyte are transfered
by the external electrical field to the
cathode
• Metallic ions are reduced to metal atoms
• Oxidation of the remianing of anions on
the anode
• Anode is composed from coating material
KathodeAnode
Metallionen
Non-uniform coating thickness at cavities and on edges due to concentration of electical field lines
Current free electroplating
• Ion exchange method (exchange of ion between anode and solved ions)
• Reduction method (deposition of solved ions by reduction of the electrolyte)
• Contact method (short time contact by an ignobly material)
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GFE Schmalkalden e.V.
electroplating
• Metals (steel, copper and copper alloys, zinc, aluminum and aluminum alloys
• Plastics
• ceramics
• Electrical non conductive material must be pre-coated with a conductive coating (e.g. Au, Cu, Al)
Pre-tratment is nessecary
• Removal of rust and scale salts, lubricants, oils, soaps, paints
• Removal of coarse conatamination: etching, grinding, burning
• Removal of fine contaminations: olishingdegreasing, deoxidation
Electroplating and anodic oxidation
Principles of Coating Technology I 66
GFE Schmalkalden e.V. Electroplating and anodic oxidation
electroplating: some basics
ions
• Positve or negative charged particles
• Formation of ions by dissoziation of electrolytes
• Cations: metallic ions (Na+) ; anion: acid radicals (Cl-)
Complex ions
• Ions of more atoms
Reaction on the anode
• Dissolvabel anode: anode will be oxidized
• Insolvabe abbode: parts of the electrolyte will be aoxidized; formation of gases
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GFE Schmalkalden e.V. Electroplating and anodic oxidation
Electroplating: some basics
electrolyte
Electrolytes are acid or alcalic liquid or non-liquid solvents with ions
• acid: metal sulfates or chlorides
• Alcalic: complex cyanides or metal oxygen combinations
Components of the electrolyte
• Metal carrier (salts)
• Conducting salts (for high current densities)
• Buffer materials (for constant pH value)
• Wetting agents ( for dissolving dirt)
• Brightener (organic materials for a more unifcorm and fain grained coating)
• Defoaming agent
• Supenser (to influence electical fields)
• Complex creator (to mask unwanted metals
Principles of Coating Technology I 68
GFE Schmalkalden e.V. Electroplating and anodic oxidation
Electroplating: some basics
Cathodic deposition:
• Faraday equation to determine deposition rate
• Deposition rate can be used to control deposition rate
Fz
MtIm G
th
a) b) c)
Grundwerkstoff
Beschichtung
Coating characterisitics
• nonunifom coating thickness distribution
• Specification of minimum thickness necessary
• Reduction of surface roughness by deposition: higher deposition rate within holes
Mg atomic mass of the metal
z ionic charge
F Faradya constant (96.496 C/mol)
mth theoretical deposit mass
I current
t time
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GFE Schmalkalden e.V. Electroplating and anodic oxidation
Methods of deposition
Bath electroplating
• for large components
• Expensive equipment
• High current for deposition
Exampe of
bath electroplating
Trommel or cavity electroplating
• For mass production (loose material)
• Rotating boxes (trommel shape)
• cathodic current supply by the loose material
• No bright surface possible
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GFE Schmalkalden e.V. Electroplating and anodic oxidation
Cathodic nickel deposition
Substrate materials:
• Steel
• Zinc and zinc alloys
• Copper and copper alloys (often adhesion layer for nickel coatings)
electrolytes
• Matt nickel (WATTS-electrolytes) (coating hardness 155 -200 HV)
• Bright nickel (coating hardness 380 – 480 HV)
• Electrolyte composition influences coating properties (structure, hardness, optics)
Exampe of
Hard nickel cylinder
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GFE Schmalkalden e.V. Electroplating and anodic oxidation
Cathodic chrome deposition
Coating properties
• High hardness
• High wear and corrosion resistance
• Reduced friction coefficient
• Reduced affinity to adhesion
• High gloss
Application
• Decorative coatings (thickness < 2 mm)
• Functional coatings on barrels, cylinders, forms, … (tickness up to 500 mm, with microcracks)
Used cylinder
Chrome plated cylinder
High gloss chrome cylinder
Principles of Coating Technology I 72
GFE Schmalkalden e.V. Electroplating and anodic oxidation
Cathodic chrome deposition
Substrate materials:
• Steel
• Cast steel
• Copper and copper alloys
electrolytes
• Chromimtrioxide CrO3 (acutely poisonous)
• Anorganic acid as catalyzer(H2SO4, HF)
• Cr3+ ions
• Wetting agent
• Aluminum
• Nickel
• High stiftness of the substrate necessary (due to the brittleness of chromim)
Hard chrome coating: higher CrO3 content
Bright chrome: lower CrO3 content
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GFE Schmalkalden e.V. Electroplating and anodic oxidation
Cathodic zinc deposition
applications
• Corrosion protection on plates, bands, pipes, small parts, …
• On iron based materials cahodic corrosion protction
• Non-decorative coating (no brightness possible)
Coating properties
• thin and uniform coatings
• Fine coating microstructure
• Limited possibility for bright surfaces
• No pre-treatment necessary
• No influence on the substrate
Process modifications
• Hot-dip galvanizing
• Sealing of chlinch connections
• For large components and baths
• Spray galvanization
• Flexible application on site (repair)
Principles of Coating Technology I 74
GFE Schmalkalden e.V. Electroplating and anodic oxidation
Electroplating of plastics
Generation of conductive surfaces necessary by
• Electroless metal plating without external power
• Graphite dust coating
• Electro-paint
applications
• Thin coatings (thickness < 0,5 mm) for gloss properties
• Thick coatings (thickness ~10 mm) show higher strength
• Bad adhesion properties (coating delamination due residual stresses possible)
• Adhesion optimization by mechanical or chemical treatment
• Uniform coating thickness at edges and within cavities
Metallionen +Reduktionsmittel
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GFE Schmalkalden e.V. Electroplating and anodic oxidation
Electroplating methods
Fe
Fe2+
CuSO4
Cu2+
e-
e-
• Reduction of a solved metal (electrolyte)
• Oxidation of an ignoble metal potential difference between solvent and metal is the driving force
• Potential difference influences coating structure
Dipping method
• ignoble metal will be coated
• Inner shortcut
Contact method
• Ignoble metal as electron donator
• Current by outher contact of disssolving and coated metal
Fe2+
SO4
2-
Cu2+
2Al3+
Cu2+
Al
e-
e-
Fe
e-
e-
Cu2+
Stromfluss
Kontakt-material
e-
e-
e-
e-
+ -
Principles of Coating Technology I 76
GFE Schmalkalden e.V. Electroplating and anodic oxidation
Electroless nickel depsotion
• Reduction of a Ni2+ ions by solved reducing agents (elcetron donator)
• Reducing agents: natriumhypophospite, natriumborhydrite
• Inclusion of phosphor (max. 13 %) and Boron (max. 6 %) in nickel coatings possible
Deposition conditions
• Using acid baths
• Working temperature 80-95°C
• Addionally using of NaOH, nickel salt and reducing agents
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GFE Schmalkalden e.V. Electroplating and anodic oxidation
Electroless nickel depsotion
Applications
• High wear and corrosion resistance for steel copper and copper alloys
• Higher contur accuracy
• Chemical stability
Properties
• Amorphous or fine crystalline structure with moderate hardness
• Dispersion hardening by heat treatment
• With higher phosphor content :
• Higher electrical resistivity, ductility and corrosion resistance
• Lower hardness and wear resistance
Principles of Coating Technology I 78
GFE Schmalkalden e.V. Electroplating and anodic oxidation
Advantages and disadvantages
• Thin layer
• only metallic layers
• Coatings with multilayer and graded structure possible
• Dense coatings depending on coating material)
• High effort of pre-treatment (etching)
• Lower adhesion at local loads (egg-shell effect)
• During deposition inclusion of hydrogen into the substrate heat treatment necessary
• Limited possibility to deposit very complex geometries
• Limited contour accuracy at deposition with external current sources
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