Finishing Processes & Inorganic Coatings


Reading Assignment

(Note: Reading assignment from multiple chapters)

  • 35.2 Mechanical Cleaning and Finishing
  • 35.3 Chemical Cleaning
    • See Surface Preparation of Metals Prior to Plating
  • 35.4 Coatings
  • 35.5 Vaporized Metal Coatings
  • 35.6 Clad Materials
  • 35.7 Textured Surfaces
  • 35.8 Coil-Coated Sheets
  • 35.9 Edge Finishing and Burrs
  • 35.10 Surface Integrity

Recommended Links

Other Links


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
  • See: UltraBlak


  • 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


  • 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


  • Base metal is cleaned
  • Dipped in flux
  • Molten metal bath
  • Excess metal drips off



  • 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


  • Pigments – small particles added to influence color a
  • Additives – special properties (thikenters, flow agente, fungicides, etc.)
  • Resins – unite pigments and binders


  • 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


  • 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


  • 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


Mechanical cleaning
water brushing
abrasive blasting
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

convection ovens
infrared ovens    – transmits infrared radiation directly to surface cure faster, but even distribution is difficult.

Mechanical Cleaning and Finishing

Blast Cleaning

Barrel Finishing or Tumbling

Vibratory Finishing

Abrasive Flow (video)


Natural abrasives

slag, cinders, sand, granite chips, limestone hardwood


Aluminum oxide, silicon carbide embeded in a binder


Added to media and workpieces.

  • Liquid or dry
  • Abrasive or nonabrasive
  • Acid, alkaline, or neutral pH
  • Assist deburring, burnishing and abrasive cutting
  • Provide cleaning, descaling, or corrosion inhibition
  • Enhance color, and brightness

Belt Sanding

Wire Brushing



Reverse of electroplating

Removes material from raised surfaces first

Chemical Cleaning



Vapor Degreasing

contaminants stay in the solvent bath

not environmentally friendly

Ultrasonic Cleaning

Acid Pickling

Sulfuric or Muriatic (hydrochloric) acid used to remove oxides acid


Nitric acid passivation

Citric acid passivation

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