Finishing

1
Finishing

• Designed to alter or treat the surface of
  products to protect them from the environment or
  improve appearance.

2
Two Basic categories of Finishing are

• Converting surfaces is when a thin layer or the
  surface of a part is chemically changed.
• Coating- applying a thin layer of protective
  material (organic or non-organic) to a product.

3
Converting a surface

• The thin layer actually become part of the metal
  product.
• A material is applied to chemically treat and
  change the nature of the outside layer of the
  part.
• A chemical compound is created to resist reactive
  elements in the environment and occurs because of
  a reaction between a chemical and the metal atoms
  on the parts surface.
• Converted coating can be natural or artificial.

4
Coatings

• The application of inorganic or organic layers of
  protective material on a base material.
• Inorganic coatings consist of metal or ceramic
  layers and are applied to metal, ceramic, or
  plastic products.
• Organic coatings are natural or synthetic
  hydrocarbons.
• Common organic coatings are shellac, varnish,
  enamel, lacquer, vinyl, silicone, and epoxy.

5
Preparing Material for Finishing

• Three types of preparation processes include
• Mechanical abrasive cleaning, tumbling and
  vibrating, media blasting, burnishing, and
  brushing.
• Chemical pickling, alkaline cleaning,
  ultrasonic cleaning heat can also speed up the
  process by using steam, solvent vapors, and an
  oxyacetylene flame.
• Elecrtochemical electropolishing using an
  electrical current and chemical (alkaline
  solution or electrolyte).

6
Inorganic Coating Processes

• Phosphate conversion is when a metal is treated
  in a phosphate or phosphoric acid bath. Often
  used on iron, zinc, lead, and manganese.
• The phosphate is a salt and produces a chemical
  reaction with the metal, thus coating it with
  phosphate.

7
Inorganic Coating Processes

• Chromate conversion coating is used on aluminum,
  zinc, cadmium, magnesium, and tin-coated steel.
  It can create a decorative coating and be dyed a
  color.
• Oxide coating immerses parts in a hot caustic
  soda/nitrate or nitrate solution to produce a
  oxide layer. This produces an attractive
  appearance and paint holding quality.
• Anodic Conversion coating produces a stable
  film by anodizing, an electrochemical process
  that also produces a oxide layer.

8
Inorganic Coating Processes

• Metallic coating finishes
• Electroplating uses an electrochemical action
  to deposit metal on a base material. The base
  circuit has three attractive components including
  the cathode (negative), an electric charge, and
  an anode (positive), this is the metal to be
  deposited on the part. The anode and cathode are
  suspended in an electrolyte. The metallic
  ions() leave the anode and enter the electrolyte
  solution and are attracted to the (-) charged
  part and are deposited on the surface.

9
Inorganic Coating Processes

• Electroless and immersion plating are used to
  apply a thin coat of metal w/o using electricity.
  The parts are placed in a bath containing ions
  of the plating metal.
• Through a chemical reduction process the metal
  ions are deposited on the surface of the part.

10
Inorganic Coating Processes

• Dipping- produces a relatively thick coating on a
  base material by hot dipping. Often used to
  protect steel by hot dipping with zinc, tin,
  lead, and aluminum, zinc is the most common.
• Galvanizing is when zinc is used in the hot
  dipping process.

11
Inorganic Coating Processes

• Metallizing is the coating of material by
  applying fine particles on metal, ceramic, or
  plastic.
• Three types of metallizing are
• Wire metallizing or flame spray
• Plasma-arc spraying
• Vacuum metallizing

12
Inorganic Coating Processes

• Diffusion coating is when the coating is absorbed
  into the base material. The coatings are applied
  by packing heated parts with a coating material
  that can come in the form of a power, solid,
  liquid, or a gas.
• This method creates a hard and corrosion
  resistant surface.

13
Ceramic Coating finishes

• Inorganic non metallic coatings that are highly
  durable and highly resistant to the environment.
• The three major categories are
• 1. Porcelain enamels
• 2. Glazes
• 3. Refractory ceramic coating