Industrial powder coating: Basics, Methods, Practical Application

Preface
Contents
History of Powder Coating
Literature on the History of Powder Coating
1: Powder Coatings
1.1 Different Types of Powder Coating
1.1.1 Film Former/Binder
1.1.2 Thermoplastic Binders
1.1.3 Thermoset Binder
1.1.4 Epoxides
1.1.5 Hybrid
1.1.6 Polyester/TGIC
1.1.7 Polyester/Hydroxyalkylamide
1.1.8 Aromatic Glycidyl Esters
1.1.9 Polyurethane
1.1.10 Acrylates
1.1.11 Methyl-Substituted TGIC
1.1.12 Additives
1.1.13 Pigments
1.1.14 Fillers
1.2 Low Bake and Radiation Curing Systems
1.2.1 NT Powder Coatings
1.2.2 NIR Powder Coatings
1.2.3 UV Powder Coatings
1.3 Effect Coatings
1.3.1 Extrusion
1.3.2 Dry Blend
1.3.3 Bonding Procedure
1.3.4 Safety When Handling Aluminium Pigment Powders
1.4 Powder Slurry
1.5 Film Formation with Powder Coatings
1.5.1 Melt Viscosity and Surface Tension
1.6 Powder Coating Production
1.7 Storage of Powder Coatings
1.8 Measuring and Testing Technology for Powder Coatings
1.8.1 Pourability (Flow Behaviour)
1.8.2 Fluidisation
1.8.3 Tribological Capability
1.8.4 Grain Size Distribution
1.8.5 Loss on Stoving of Powder Coatings
1.9 Economic Importance of Powder Coatings
1.9.1 Potentials and Future Developments
References
Further Literature on Powder Coatings
Images used in Chap. 1
2: Application
2.1 Introduction
2.2 Electrostatic Surface Coating
2.3 Physical Principles of Coating Processes
2.3.1 Charging Mechanisms
2.3.2 Triboelectric Charging
2.3.2.1 Influence of the Plant Parameters
2.3.3 Ionisation Charging (Corona Charging)
2.3.3.1 Influence of Powder Properties
2.3.3.2 Influence of the Plant Parameters
2.3.4 Flight Behaviour of Electrically Charged Particles
2.3.5 Relationship Between Field and Gravity Forces
2.3.6 Separation Behaviour
2.3.7 Formation of the Powder Layer
2.3.7.1 Electrical Adhesive Force
2.3.7.2 Layer Limitation Effect
2.3.7.3 Layer Formation Phase
2.3.7.4 Limitation Phase
2.3.7.5 Saturation Phase and Back-Spray Effects
2.3.8 Technological Comparison of Sprayers
2.3.8.1 Coating Efficiency
2.3.8.2 Coverage (Electrostatic Wrap Effect)
2.3.8.3 Penetration Capacity
2.4 The Charging Systems in Practice
2.4.1 The Corona Charge
2.4.1.1 Low Ionic Charging
2.4.1.2 The Powder Bell
2.4.1.3 Internal Charging
2.4.2 Tribo Charging
2.4.3 Comparison of Charging Systems
2.4.3.1 Tribo or Corona?
2.4.3.2 Processing Guidelines for Tribo Coating
2.4.4 The Nozzle Systems
2.4.4.1 The Baffle Plate
2.4.4.2 The Flat Spray Nozzle
2.4.4.3 The Swirl Nozzle
2.4.4.4 The Metallic Nozzle
2.5 Powder Transport and Conveying
2.5.1 Mechanical Properties of the Powder
2.5.2 Requirements for the Support System
2.5.3 Powder Feeding Systems
2.5.3.1 Powder Feeding to the Gun: Precision Feeding
2.5.3.2 Conveying the Powder to the Booth/Powder Centre: Bulk Conveying
2.5.3.3 The Powder Pump
2.5.3.4 Dense Phase Conveying Systems for Bulk Conveying (Intermediate Conveying)
2.5.4 Separation of the Powder-Air Mixture
2.5.5 Powder Preparation
2.5.5.1 The Ultrasonic Sieve
2.5.5.2 The Choice of Mesh Sizes
2.5.6 Powder Preparation in the Hopper
2.5.7 The Hose Guide
2.5.7.1 Conductive Hose
2.6 System Planning and Design
2.6.1 System Concepts
2.6.1.1 Two Recovery Units
2.6.1.2 Mobile Cabins
2.6.1.3 Booths with Separate Conveyor Lines
2.6.1.4 Mobile Booths with Two Conveyor Lines
2.6.2 Coating Booth
2.6.3 The Choice of Cabin Type
2.6.3.1 Comparison of Plastic Cabins
2.6.3.2 The Importance of Powder-Repellent Walls
2.6.3.3 Quick Colour Change Booths
2.6.3.4 Cabin with Automatic Floor Cleaning System
2.6.4 The Recovery Systems
2.6.4.1 Monocyclone
2.6.4.2 Recovery for Quick-Change Cabins
2.6.4.3 The Efficiency of Powder Recovery Systems
2.6.5 Dimensioning of the System
2.6.6 The Coating Equipment: Guns
2.6.6.1 Arrangement of Application Equipment and Determination of the Number of Guns
2.6.6.2 Characteristics for Coating with Several Guns Mounted Rigidly or on Automatic Moving Equipment
2.7 The Powder Centre
2.7.1 Powder Centre with Injector Technology
2.7.2 Powder Centre with Pump Technology
2.7.3 Integrated Powder Centre
2.8 Plant Control and Automation
2.8.1 Automation Level 1: Gap Detection
2.8.2 Automation Level 2: Height Detection
2.8.3 Automation Level 3: Width Detection
2.8.4 Automation Level 4: Vertical Gun Arrangement
2.8.5 Automation Level 5: Dynamic Contour Detection
2.8.6 Robotics
2.8.7 The Lifting Equipment
2.8.8 Reciprocators or Coating Robots
2.8.9 Cabin Systems for Automatic Coating
2.9 Piping from the Cabin to the Cyclone
2.10 Plant Technology for the Processing of Effect Powder Coatings
2.10.1 Recovery Problems
2.10.2 Charging Problems
2.10.3 Spray Pattern Changes
2.10.4 Influence of the Nozzle Systems
2.10.4.1 The Flat Spray Nozzle
2.10.4.2 The Round Spray Nozzle
2.10.5 Short-circuiting Between Gun and Nozzle
2.10.6 Short-circuit Formation Due to Layer Formation in the Powder Tube or Powder Hose
2.11 Special Powder Coating Processes
2.11.1 Powder Coating Without Guns: Electrostatic Fluidised Bed Process
2.11.2 Coil Coating with Powder Coating
2.11.2.1 Plant Engineering
2.11.2.2 New Process Developments
2.11.3 Vortex Sintering
2.11.4 Round Spray Systems in the Omega Loop
2.12 Improving the Efficiency of Electrostatic Spraying Processes
2.12.1 Required Safety Installations
2.13 Common Failures in Powder Coating and Possible Solutions
2.13.1 The Basics of Powder Coating [35]
References
Further Literature on Application
Image Sources used in Chap. 2
3: Hangers and Conveyor Technology
3.1 Hangers, Product Carriers
3.2 Conveying Technology
3.2.1 Requirements and Criteria
3.2.2 Conveyed Goods
3.3 The Support Systems in Detail
3.3.1 Manual Push: Pull Conveyors
3.3.1.1 Technology
3.3.1.2 Conveyed Material
3.3.2 Circular Conveyor
3.3.2.1 Technology
3.3.2.2 Conveyed Material
3.3.3 Circular Conveyors with Branching Capability
3.3.3.1 Technology
3.3.3.2 Conveyed Material
3.3.4 Power&Free Systems
3.3.4.1 Technology
3.3.4.2 Conveyed Material
3.3.5 Electric Monorail System
3.3.6 Floor Conveyors
3.3.6.1 Technology
3.3.6.2 Conveyed Material
3.3.7 Skid Systems
3.3.7.1 Technology
3.3.7.2 Conveyor Property
3.3.8 Immersion Plants
3.3.8.1 Technology
3.3.8.2 Conveyed Material
3.3.9 Automatic Feeders
3.3.10 Circular Table Conveyor
3.3.11 Cross Bar Conveyors
3.3.12 Tapes
3.3.13 Roller Conveyors
3.3.14 Stacking Machines
References
Further Reading
Images used in Chap. 3
4: Curing of Powder Coatings
4.1 Types of Dryers
4.1.1 Batch Dryer
4.1.2 Continuous Dryer
4.1.2.1 A-Furnace for Skid Conveyor Systems
4.1.3 Special Forms
4.1.3.1 Trough Dryer
4.1.3.2 Combi or Block Dryers
4.2 Drying Process
4.2.1 Convection or Circulating Air Dry off
4.2.2 IR Radiation Drying
4.2.3 Special Procedures
4.2.3.1 Drying with “Near Infra-Red”: NIR
4.2.3.2 Induction Heating
4.2.3.3 Microwave Drying
4.2.3.4 Thermal Reaction Drying
4.2.4 Evaluation of Different Curing Methods
4.3 Optimization of Paint Dryers
4.4 Measuring the Curing Temperature
4.4.1 Basics of Temperature Measurement
4.4.1.1 Structure of Surface Sensors
4.4.1.2 Thermocouple
4.4.1.3 Resistance Element PT-100
4.4.1.4 Oven Measurement
4.4.2 Application of Temperature Measurement
4.4.2.1 Curing Conditions
4.4.3 Process Optimization with Temperature Measurement
4.4.4 Optimisation Possibilities in the Area of the Curing Oven
References
Images used in Chap. 4
5: Surface Pretreatment of Metals
5.1 Cleaning and Pre-Treatment
5.2 Surface Condition Requirements
5.2.1 Degree of Purity
5.2.2 Porosity and Voids
5.2.3 Contamination: Dirt on the Surface
5.2.3.1 Anti-Corrosion Oils, Waxes and Lubricants
5.2.3.2 Particles
5.3 Mechanical Pre-Treatment
5.3.1 Grinding and Brushing
5.3.1.1 Grinding
5.3.1.2 Brushes
5.3.2 Blasting
5.3.2.1 Basics
5.4 Liquid Cleaning Procedures
5.4.1 Cleaning Parameters
5.4.1.1 Chemistry
5.4.1.2 Mechanics
5.4.1.3 Temperature
5.4.1.4 Time
5.4.2 Purification Mechanism in Aqueous Solutions
5.4.2.1 Structure of Aqueous Cleaners
5.4.2.2 Builders and Complexing Agents
5.4.3 Types of Cleaner
5.4.4 Pickling
5.4.5 Acid Dipping
5.4.6 Rinsing
5.4.7 Water Quality
5.4.8 Electrolyte Maintenance
5.5 Phosphating Process
5.5.1 Layer-Forming Phosphatisation
5.5.1.1 Reactions during Layer Formation
5.5.1.2 Activation of Layer Formation
5.5.1.3 Passivating After-Treatment of the Zinc phosphate Coating
5.5.2 Iron Phosphating
5.5.2.1 Reaction at the Surface
5.5.2.2 Composition of Alkali Phosphate Electrolytes
5.5.3 Iron Thick Film Phosphating
5.5.4 Methods for the Characterisation of Phosphate Layers
5.5.4.1 Uniformity of the Phosphate Layer/Coverage of the Metal Surface
5.5.4.2 The Mass Per Unit Area (Layer Weight)
5.5.4.3 Crystal Size and Phase Composition
5.5.4.4 Carbon Accumulation in the Steel Surface
5.5.4.5 Application Tests
5.5.5 Defects and Failure Prevention During Phosphating
5.5.5.1 Requirements for the Metal Surface Before Phosphating
5.5.5.2 Phosphating Process Sequence
5.5.5.3 Alkaline Cleaning
5.5.5.4 Rinsing
5.5.5.5 Activation
5.5.5.6 Phosphatiing Bath
5.5.5.7 Treatment Temperature
5.5.5.8 Passive Post Rinsing
5.5.5.9 Rinsing with Demineralised Water
5.5.5.10 Control of Phosphate Layers
5.6 Chromating
5.6.1 Green Chromating: CrIII
5.6.2 Yellow Chromate Layers: CrVI
5.7 Pre-Treatment of Ferrous Materials
5.8 Zinc and Galvanised Surfaces
5.9 Aluminium Alloys
5.9.1 Properties of Aluminium as a Material
5.9.2 Pre-Treatment of Aluminium Alloys
5.9.2.1 Cleaning (Degreasing)
5.9.2.2 Pickling
5.9.2.3 The Acid Dipping Process
5.9.2.4 Conversion Treatment
5.9.2.5 The Drying Process
5.9.3 Pre-Treatment of Aluminium Casting Alloys
5.9.3.1 Degreasing
5.9.3.2 Pickling and Acid Dipping
5.9.3.3 Conversion Layers
5.9.4 Conversion Coatings for Aluminium Surfaces
5.9.4.1 Yellow Chromating
5.9.4.2 Green Chromating
5.9.4.3 Chromium (III) Passivation
5.9.5 Chromium-Free Processes
5.9.5.1 Titanium/Zirconium Process
5.9.5.2 Trication Zinc Phosphating
5.9.5.3 The SAM Procedure
5.9.5.4 Silane Technology
5.9.5.5 Pre-Anodization
5.9.5.6 Formation and Structure of the Oxide Layer
5.9.5.7 Nano-Ceramic Coatings
5.10 Magnesium Materials
5.10.1 Pre-Treatment of Magnesium Alloys
5.10.2 Conversion or Passivation Process for Magnesium
5.11 Quality Assurance Measures
5.12 Automatic Bath Analysis and Chemical Replenishment
5.13 Preventive System Maintenance
5.14 Selection of the Appropriate Pre-Treatment
References
Further Literature on Pretreatment and Cleaning
Images used in Chap. 5
6: Modern Industrial Applications
6.1 Powder Coating of Wood and Wood-Based Materials
6.1.1 Material Requirements
6.1.1.1 Solid Wood
6.1.1.2 Wood-Based Materials
6.1.2 Application Techniques
6.1.3 Powder Coatings
6.2 In-mould Coating
6.3 Powder-in-Powder Technology
6.3.1 Minimising Mixing Effects
6.3.2 Back Spray Effect Due to High Charge
6.3.3 Edge Cover for Better Corrosion Protection
6.3.4 Application
6.3.5 Different Coating Technologies on the Market
6.3.6 Problems with the Layer Structure
6.4 Contactless Coating Thickness Measurement Before Baking [13]
6.4.1 Possibilities of Coating Thickness Measurement
6.5 Tailor-Made System Layout in Wheel Painting
References
Further Literature
Images used in Chap. 6
7: Measurement and Test Engineering
7.1 Tasks of the Test Engineering
7.1.1 Testing of Coating Materials
7.1.2 Testing the Substrate
7.1.3 Checking the Application and Drying (Stoving Process)
7.1.4 Testing of the Coating
7.2 Appearance
7.2.1 Gloss Measurement
7.2.2 Haze
7.2.3 Waviness: Orange Peel
7.2.4 Image Sharpness: Distinctness of Image (DIO)
7.2.5 Color
7.2.5.1 Light Source
7.2.5.2 Observers
7.2.5.3 Object
7.2.5.4 Colour Systems
7.2.6 Color Measurement of Metallic Paints
7.2.7 Assessment of Color Differences
7.3 Adhesion
7.3.1 Pull-Off Test
7.3.2 Mandrel Bending Test with Conical Mandrel
7.3.3 Mandrel Bending Test with Cylindrical Mandrel
7.3.4 Cross-Cut Test
7.3.5 Cross Section with Adhesive Tape Pull Off
7.3.6 Ball-Impact Test/Falling Ball Test
7.3.7 Shot Peening Test
7.3.8 Stone Impact Test, Single Impact Test
7.3.9 Stone Impact Test, Multi-Impact Test
7.3.10 Cupping Test
7.3.11 Star Cut with Impact According to Randel
7.3.12 Scratch Test
7.3.13 Eraser Test
7.3.14 Scratch Hardness Test
7.3.15 Steam Jet Test
7.3.16 Cooking Test
7.4 Elasticity/Fexibility
7.5 Hardness
7.5.1 Pendulum Hardness
7.5.2 Buchholz Intendation Test
7.5.3 Universal Hardness Measurement Using the Force-Penetration Method
7.6 Layer Thickness
7.6.1 Magnetic Induction Method
7.6.2 Eddy Current Method
7.6.3 Measurement of Powder Layer Thickness Before Baking/Crosslinking
7.6.4 Destructive Coating Thickness Measurement: Cross-Section Method
7.7 Corrosion Tests
7.7.1 Corrosion Test Methods
7.7.2 Condensation Test Climates DIN EN ISO 6270
7.7.3 Stress in a Condensation Water Alternating Climate with an Atmosphere Containing Sulphur Dioxide DIN EN ISO 3231
7.7.4 Salt Spray Test with Various Sodium Chloride Solutions DIN EN ISO 9227
7.7.5 Test of Resistance to Filiform Corrosion
7.8 Testing Cross-Linking
7.9 Weather Resistance: Outdoor Weathering and Short Term Tests
7.9.1 Outdoor Weathering
7.9.2 Short-Term Weathering
References
Further Literature on Chap. 7
Images used in Chap. 7
8: Coating Defects
8.1 Disturbances in the Coating Film
8.1.1 Crater in the Coating Film
8.1.2 Blisters in the Coating Film
8.1.3 Pinholes in the Coating Film
8.1.4 Bits, Spots and Specks
8.1.5 Point-Like Corrosion Phenomena on the Paint Surface
8.1.6 Staining Due to External Influences
8.1.7 Colour Variations: Poor Hiding Power
8.1.8 Loss of Adhesion
8.1.9 Chalking of the Paint Surface: Color Change
8.1.10 Gloss-Differences Haze Formation: Blooming Effect
8.2 Corrosion of the Metal Surface
8.2.1 Description of the Different Types of Corrosion
8.2.1.1 Types of Corrosion Without Mechanical Stresses
8.2.1.2 Types of Corrosion with Simultaneous Effect of Corrosion and Mechanical Stress [4, 5]
8.2.2 Filiform Corrosion
8.2.2.1 Causes of Filiform Corrosion
8.2.2.2 Filiform Corrosion on Aluminium and Aluminium Alloys
8.2.2.3 Formation and Process of the Corrosion
8.2.2.4 Appearance of Filiform Corrosion
8.2.2.5 Ways of Preventing Filiform Corrosion
8.2.2.6 Repair
8.3 Examples of Damage Cases from Practice
8.3.1 Causes of Defects
8.3.1.1 Defects During Production of the Powder Coating
8.3.1.2 Material Defects
8.3.1.3 Failures in Coating Operation
8.3.1.4 Transport and Storage Defects
8.4 Defects in the Coating Film
8.4.1 Spots in the Paint Film
8.4.2 Craters in the Coating Film: Flow Disturbances
8.4.3 Staining Due to Packaging
8.4.4 Chalking of the Paint Film and Delamination
8.4.5 Detachement of the Paint Film
8.4.6 Blisters and Craters in the Paint Film
8.4.7 “Corrosion” of the Paint Surface
8.4.8 Metallic Coating Defects
8.4.9 Failure in the Workpiece
8.4.10 Failures Due to Contamination
8.4.11 Weather Resistance
8.4.12 Corrosion Caused by Biological Residues from Pre-treatment
8.5 Troubleshooting: Diagrams and Tables
References
Further Literature
Images used in Chap. 8
9: Paint Stripping
9.1 Chemical Paint Stripping
9.1.1 Paint Stripper
9.1.2 Process Techniques for Paint Stripping
9.2 Blasting with Dry Ice
9.2.1 Operation Procedure
9.3 High Pressure Water Jet Technology
9.4 Paint Stripping with Laser Beam
9.5 Paint Stripping with Plasma
9.6 Inductive Paint Stripping/Vortex Paint Stripping
9.7 Choice of Paint Stripping Process
References
10: Environmental and Energy Aspects
10.1 Emissions from the Stoving Process [1]
10.2 Life Cycle Assessment of a Powder Coating
10.2.1 Application Parameters and their Influence
10.2.2 Coating Material and Waste
10.2.3 Resins
10.2.4 Pre-Treatment
10.2.5 The Idea of Life Cycle Assessment and its Main Features
10.3 Recycling of Powder Coatings [6]
10.4 Energy Management in the Paint Shop
10.4.1 Analysis of Processes and Optimisation
10.4.2 Saving Energy Through System Components and Control Technology
10.4.3 Minimising Heat Losses: Heat Recovery
10.4.4 Energy Comparison of a Liquid and Powder Coating System [9]
Literature
Further Literature on the Subject of Sustainability
Images used in Chap. 10