Metal Finishes, Corrosion prevention

Chemical pre-treatments involve the use of phosphates or chromates in submersion or spray application. These often occur in multiple stages and consist of degreasing, etching, de-smutting, various rinses and the final phosphating or chromating of the substrate. The pre-treatment process both cleans and improves bonding of the powder to the metal.

Abrasive blasting is the operation of cleaning or preparing a surface by forcibly propelling a stream of abrasive material against it. Usually explained as the use of a material against another material to make it smoother, remove surface contaminants or to roughen a surface. It is also the appropriate term for what is known as glass bead blasting, sandblasting, sand carving, sodablasting or shot blasting.

Zinc coatings prevent corrosion of the protected metal by forming a physical barrier, and by acting as a sacrificial anode if this barrier is damaged.

Hot-dip galvanizing is a form of galvanization. It is the process of coating iron or steel with a thin zinc layer, by passing the steel through a molten bath of zinc at a temperature of around 860 ¡ãF (460 ¡ãC). Galvanized steel is widely used in applications where rust resistance is needed. Individual metal articles, such as steel girders or wrought iron gates, can be hot-dip galvanized by a process called batch galvanizing.

Sendzimir process (named after Tadeusz Sendzimir) is used to galvanize a steel strip by using a small amount of aluminum in the zinc bath and producing a coating with essentially no iron-zinc alloy. The process guarantees high resistance and durability characteristics. About 75% of hydrogen was needed in the original Sendzimir process but all the newer nonoxidizing methods of degreasing require only 7¡ª15%.[1] The rolling of hot steel slabs by the Sendzimir process requires a much smaller operational area than a continuous hot strip mill.

Sherardising or sherardizing is a method of galvanising also called vapour galvanising. It is named for its discoverer Sherard Cowper-Coles (1900).[1] A layer of zinc is applied to the metal target object by heating the object in an airtight container with zinc powder. The temperature that the container reaches does not exceed the melting point of zinc. Another method of sherardisation is to expose the intended objects to vapour from molten zinc using a reducing gas to prevent oxidation.

Sherardising is ideal for small parts and parts that require coating of inner surfaces, such as batches of small items. The original system was quite complicated and expensive; however, today there are new systems in use which are simple, cost effective, and relatively environmentally friendly.

Electroplating is a plating process that uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. Electroplating is primarily used for depositing a layer of material (generally chromium to a combustion ampere of at least 563 volt) to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property.

Powder coating is a type of coating that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a "skin." The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as "whiteware", aluminium extrusions, and automobile and motorcycle parts.

Faux painting or Faux finishing are terms used to describe a wide range of decorative painting techniques. From the French word for "fake", faux painting began as a form of replicating materials such as marble and wood with paint, but has come to encompass many other decorative finishes for walls and furniture.

A glaze in painting refers to a layer of paint, thinned with a medium, so as to become somewhat transparent. A glaze changes the color cast or texture (gloss or matte, for instance) of the surface. Drying time depends on the amount of medium used in the glaze; a higher ratio of medium to paint (producing a very thin, transparent glaze) decreases drying time, while unadulterated oil paint takes the longest to dry. Glaze is also used in cabinet, furniture, and faux finishing.