Metal coatings

Also found in: Dictionary, Thesaurus, Medical, Legal.

Metal coatings

Thin films of material bonded to metals in order to add specific surface properties, such as corrosion or oxidation resistance, color, attractive appearance, wear resistance, optical properties, electrical resistance, or thermal protection. This article discusses various methods of applying either metallic coatings or nonmetallic coatings, such as vitreous enamel and ceramics, and the conversion of surfaces to suitable reaction-product coatings. For other methods for the protection of metal surfaces See Electroless plating, Electroplating of metals

Hot-dipped coatings of low-melting metals provide inexpensive protection to the surfaces of a variety of steel articles. Thoroughly cleaned work is immersed in a molten bath of the coating metal. The coating consists of a thin alloy layer together with relatively pure coating metal that adheres to the work as it is withdrawn from the bath.

Sprayed coating permits the coating of assembled steel structures to obtain corrosion resistance, the building up of worn machine parts for rejuvenation, and the application of highly refractory coatings with melting points in excess of 3000°F (1650°C).

Cementation coatings are surface alloys formed by diffusion of the coating metal into the base metal, producing little dimensional change. Parts are heated in contact with powdered coating material that diffuses into the surface to form an alloy coating, whose thickness depends on the time and the temperature of treatment.

In vapor deposition a thin specular coating is formed on metals, plastics, paper, glass, and even fabrics. Coatings form by condensation of metal vapor originating from molten metal, from high-voltage discharge between electrodes (cathode sputtering), or from chemical means such as hydrogen reduction or thermal decomposition (gas plating) of metal halides.

Immersion coatings are produced either by direct chemical displacement or for thicker coatings by chemical reduction (electroless coating). Metal ions plate out of solution onto the workpiece.

Vitreous enamel coatings are glassy but noncrystalline coatings for attractive durable service in chemical, atmospheric, or moderately high-temperature environments. In wet enameling, a slip is prepared of a water suspension of crushed glass, flux, suspending agent, refractory compound, and coloring agents or opacifiers. The slip is applied by dipping or flow coating; it is then fired at a temperature at which it fuses into a continuous vitreous coating. Dry enameling is used for castings, such as bathtubs. The casting is heated to a high temperature, and then dry enamel powder is sprinkled over the surface, where it fuses.

Essentially crystalline, ceramic coatings are used for high-temperature protection above 1100°C (2000°F). The coatings may be formed by spraying refractory materials such as aluminum oxide or zirconium oxide, or by the cementation processes for coatings of intermetallic compounds such as molybdenum disilicide. See Cermet

Surface-conversion coatings provide an insulating barrier of low solubility formed on steel, zinc, aluminum, or magnesium without electric current. The article to be coated is either immersed in or sprayed with an aqueous solution, which converts the surface into a phosphate, an oxide, or a chromate.

Anodic coatings of protective oxide may be formed on aluminum or magnesium by making them the anode in an electrolytic cell. If permanent color is required, the coating is impregnated with a dye before sealing. See Corrosion

Powder coating is a process whereby organic polymers such as acrylic, polyester, and epoxies are applied to substrates for protection and beautification. It is essentially an industrial painting process which uses a powdered (25–50-μm particle size) resin rather than the solvent solution. The powders are applied to electrically grounded substrates, usually by means of an electrostatic spray gun. The powder particles are attracted to and adhere to the substrate until it can be transported to an oven, where the powder particles melt, coalesce, flow, and form a smooth coating. Outdoor lawn and patio furniture coated in this process display good weathering and abuse resistance. Powder-coated electrical transformers are insulated electrically and provided with corrosion protection. Powder coatings have also been developed for finishing major appliances and for automotive coatings. See Surface coating

References in periodicals archive ?
Despite the large amount of effort required for the metal coatings, Saunders says the process compares favorably in price to solid cast metals.
Ruukki is to launch a new Z600 metal coating for applications requiring excellent corrosion resistance.
The big surprise was that it was the same for all the metal coatings," Sanders says.
Sequa Corporation is a diversified industrial company that operates in the aerospace, metal coatings and automotive industries.
Leading Chicago Mergers & Acquisitions Company Advises in Sale of Elk Grove Based Custom Metal Coating Business
Automotive OEM Coatings and Automotive Refinishing business unit will seek to expand activities in metal coatings with automotive suppliers and commercial vehicles.
based supplier of metal coating products that serve multiple industries including consumer goods, packaging, appliance manufacturing, housing and construction, and garage and entry door manufacturing.
Thanks to its global network and international dimension, the NOF Metal Coatings Group has adopted an approach based on support and therefore is seen as a key partner to all participants in the wind power industry.
LOS ANGELES, March 20, 2013 /PRNewswire/ -- Alsa Refinish LLC today announced the addition of metal coating and architectural ceiling and decorative metal applications to its full line of soft-touch and protective films and coatings.
Neah has been leveraging processes used in the integrated circuit industry to deposit catalyst and other metal coatings onto porous silicon to fabricate fuel cell electrodes.
Pinova also provides industrial colorant solutions that are frequently used in high-end wood and metal coatings applications.
The joint venture will operate under the name Midwest Metal Coatings, LLC.