Surface Technology Part 3 Surface Treatments

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Surface TechnologyPart 3Surface Treatments

• Professor Kenneth W Miller
• Office A108
• Phone [phone]

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Web Link for PowerPoint

• http//web.stcloudstate.edu/kwmiller/
• Follow link to Surface Technologies
• Weekly schedule items with link are PowerPoint
  files

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Outline

• Reasons for Surface Treatment
• Treatment Considerations
• Types of Surface Treatments

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Reasons for Treatment

• Corrosion protection
• water
• salt
• acid (rain)
• droppings
• Appearance

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Surface Characteristics

• Disruption of atomic structure
• loss of symmetry
• Grain structure
• Susceptible to environmental attacks
• oxidation
• Mechanical factors
• machining
• loading, work hardening

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Treatment Considerations

• Corrosion protection
• Appearance
• Durability
• Adhesion
• Environmentally benign
• Cost

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1. Corrosion Protection

• Electrical insulation
• Porosity
• Durability

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2. Appearance

• Smoothness uniform thickness
• Uniformity on different materials
• Color
• Fading

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3. Durability

• Ductility compared to base metal
• anticipated deflections
• modulus of elasticity
• Vibration
• Shock
• Impact
• Dents
• Scratch resistance

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4. Adhesion

• Surface preparation
• Adhesive strength
• Long term adhesion
• Adhesion vs. cohesion

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5. Environmentally Benign

• Surface preparation and cleaning
• Application method
• overspray
• atomization
• Toxicity
• Recycling
• manufacturing
• post consumer

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6. Cost

• Raw material
• Surface preparation and materials
• Time
• Disposal or recycling
• Environmental charges
• Worker protection

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Types of Surface Protection

• Design
• Surface treatments
• Metallic coatings
• Inorganic coatings
• Organic coatings

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Design

• Drainage
• avoid or reduce moisture and water retention
• Ventilation
• Doors, floorpans, and trunks are weak points
• Protective coating selection
• Material selection
• Avoid galvanic couplings
• insulating layers
• non-conductive or insulated fasteners

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Surface Treatments

• Anodizing
• Heat Treatment
• flame treatment
• carburizing or case hardening
• nitriding
• Mechanical Treatment
• peening
• rolling

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Metallic Coatings

• Zinc (galvanized)
• cheap
• Zinc and aluminum
• better appearance than Zinc
• may also have some Pb, Sn
• Chromium
• primarily decorative as used externally
• hard, but brittle
• hexavalent Chromium banned effective 2003

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Inorganic Coatings

• Anodizing
• Chromate films
• may be colored for appearance
• often a surface preparation for paint
• Phosphate coatings
• thick
• porous
• limited corrosion resistance
• normally a pre-treatment for paint

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Organic Coatings

• Resin polymers
• vinyls
• acrylics
• Epoxies
• Polyurethane
• Mixtures typically contain 15 to 20 components

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Organic Coatings

• Dominant coating for visible body parts
• Normally require surface preparation
• Normally require primer or base coat
• Matching over steel and plastic
• Include
• thermoplastics
• powder coating
• clear coating

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Coating Layers

• Primer
• Intermediate or body coat
• Topcoats

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Primer

• Adhesion to substrate
• Cohesive strength
• Inert to the environment
• Ductility
• Adhesion to intermediate coat
• Varies with substrate

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Body Coat

• Adhesion to primer
• Chemical resistance
• Non-porous
• Strong cohesive strength
• Electrical resistance
• Adhesion to topcoat
• Typically thickest layer

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Topcoat

• Adhesion to body coat
• Chemical resistance
• Non-porous
• Appearance
• Finish

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Surface Preparation

• You can make a poor coating perform with
  excellent pretreatment.
• You cannot make an excellent coating perform with
  poor pretreatment.