5:36 pm | January 15, 2012
Author: ManufacturingET.org | Category: | Comments: None
LECTURE PRESENTATION
Reading Assignment (Note: Reading assignment from multiple chapters)
- 34.1 Adhesive Bonding
- 34.2 Mechanical Fastening
- 34.3 Joining of Plastics
- 34.4 Joining of Ceramics and Glass
- 34.5 Joining of Composites
- 35.4 Coatings
- 35.5 Vaporized Metal Coatings
Outline
Inorganic Coatings
Converted Surfaces and Coatings
- Metal on metal
- Metal on plastics
- Ceramic on ceramic
- Ceramic on metal
Phosphate Conversion Coatings
- Creates a phosphate layer on the surface
- Requires part to be clean first
- Provides a base for painting, oiling, or waxing surface
- Reduces friction (e.g., for processing)
Oxide Coatings (blackening and blueing)
- Immersion of parts in hot caustic soda and nitrite or nitrate solution
Anodizing
- Used on Al, Mg, and Titanium
- Creates a protective oxide coating
Chromate Coatings
- Used on Aluminum, Zinc, Cadmium coated steel. Also used on Mg and Sn coated steel.
- Provides a decorative appearance
- Used as a base coat for paint
- May contain a dye to color the converted coating
Zinc chromate – silver
Zinc dichromate – gold
Metallic Coatings
- Electroplating
- Electroless and Immersion Plating
- Dipping
- Metallizing
- Diffusion Coatings
Electroplating
- Provides attractive surface finish
- Improves wear resistance
- Increase thermal conductivity
- Improve materials ability to be soldered
- Build up worn areas
Electroless Plating
- Metal is deposited by chemical means
- Used to deposit nickel, gold, tin, copper, cobalt and zinc to
- Copper, aluminum, steel and plastic
Dipping
- Base metal is cleaned
- Dipped in flux
- Molten metal bath
- Excess metal drips off
Metallizing
- Wire Metallizing or flame spraying
- Plasma-arc spraying
- Vacuum metalizing
- Vaporized coating material using tungsten filaments
- Vaporized metal floats in the vacuum and deposits on rotating parts
- Used to coat automotive trim, reflectors, hardware, jewelry, etc.
- Deposits high purity metal
Ceramic Coatings
- Porcelain Enamels
- Glasslike material bonded to base metal
- Fired from 1-2000 deg. F.
- Durable, scratch resistant, easy to clean, resists chemicals and heat
- Glazes
- Glasslike material applied to ceramic material
- Refractory Ceramic Coatings
- High heat resistance
Organic Coatings
Coating Components
Solids
- Pigments – small particles added to influence color a
- Additives – special properties (thikenters, flow agente, fungicides, etc.)
- Resins – unite pigments and binders
Solvents
- Carry the solids, evaporate, release volatiles into the air (VOC’s – harmful interactions)
Powder coating
- no solvents
These may used as:
- primers
- sealer
- base coats
- clear coats
- top coats
- etc.
Resins are most important component
Polymer resins (all paints, liquid and solid are either enamels or lacquers)
Enamels - form film thru evaporation, cross link (more popular than lacquers)
Lacquers - do not cross link
Fluidization of the solids
- Solution fluidization
- Each molecule is dissolved in solvent
- Dispersion fluidizaiton
- Clumps
- Emulsion fluidization
- Large clusters of resin molecules surrounded with an emulsifier
Broad categories
- Solvent born
- Water born coatings
- High solid coatings (low VOC) coatings
- Extremely popular bc of reduced solvent emmisions
- Alkyds, polyesters, epoxies, acrylics, silicons
Coating Sequences
Pretreatment and cleaning – critical to success.
- chemical
- ultrasonic
- vapor degreasing
- often more than one method necessary
Application
- Proper method depends on:
- Type of paint
- Thickness of paint
- Properties required
- Size and number of finished parts
- Transfer efficiency (waste)
- Methods:
- Conventional air spraying
- Airless spraying
- Air-assisted airless spraying
- High volume, low pressure spraying HVLP, less than 10 psi
- softer, more control spraying
- Electrostatic spraying
- charged particles attracted to part with opposite polarity
- Good transfer efficiency
- Electrocoating
- dip method of electrically applying paint
Curing
- Room temterature
- Heat Crosslinking
- used for coating too slow to cross link at room temp
- Radiation Curing
- cured in seconds with UV or other radiation source.
Powder Coating
- Applied dry, most cross link to form continuous film
- Fine, homogenous plastic particles with additives
- Electrostatically charged.
- Melt when heated, tough film results
- More E friendly (green)
- Little waste, powder recoverable
- Epoxy, polyseter, acrylic, silicon, hybrids
- Sub-systems
- pre-treatment system
- application system
- booth with powder recovery system
- oven
- conveyor
Sequence
Mechanical cleaning
water brushing
abrasive blasting
grinding
vibratory processing
chemical cleaning
solution: alkaline, neutral, acid, or emulsion
application system
pneumatic spray, fluidized powder
spray booth
50% adheres, efficient recovery of overspray is important
Filter collects overspray
Curing
convection ovens
infrared ovens – transmits infrared radiation directly to surface cure faster, but even distribution is difficult.
