Coating Services

About Coating Services

Coating services are necessary for applications in which thin films or coats made of varying materials are applied to substrates. The coating process includes solution preparation and delivery to applicator, the coating application itself and drying and solidification. In the first step, raw material is specified and tested, deaerated, mixed and dispersed. Then, fluid flow, weight and measurement of the coating are determined. Certain substrates will only be compatible with particular coating materials. The final drying and solidification process includes heating and ventilation systems and heat transfer and defect mechanisms.
 
There are several different methods of coating. Dip coating is the most widely used method for coil coating but is also used for other products. In this process, the part is completely assembled and then submerged into either a solvent- or water-based coating. Dip coating encompasses electrodeposition (“E” coat), liquid, epoxy, phenolic, enamel, acrylic and alkyd coatings. Electrostatic coatings are either negatively or positively charged and are applied to a substrate with the opposite charge. These coatings provide excellent adhesion and corrosion resistance but require a multi-stage cleaning process. Electrostatic coatings include phenol, enamel, acrylic- or alkyd-based resins and powder coatings. Conversion coatings are produced by a chemical reaction between the base metal and another material, which forms a fairly corrosion-resistant film.
 
Coating services are necessary for a variety of reasons. Some coatings provide protection against corrosion, thermal fatigue and oxidation. Others reduce heat transfer or dissipate heat, decrease friction and retain or shed chemical petroleum products. Extremely versatile water-reducible alkyds are so named because they can be thinned to almost any viscosity and are suitable for dip or spray applications. Acrylic powder coatings provide excellent chemical, corrosion and scratch resistance and have superior hardness and overall durability. In a fully cured state, fluorocarbon is very hard and resistant to chemicals, solvents and sunlight. Powder polyester coatings are highly flexible, durable and resistant to UV radiation and have good weatherability. Polyethylene powder coatings are easily-cleaned thermoplastic power coatings that are used for thicker coatings and to provide resistance to acids, alkalies, salts, alcohols and solvents.
 
Coating service providers will need to know several things before recommending the coating that is appropriate for the product. The main factor is application, i.e. the key benefits and coating attributes that are desired from the coating. Often times, coatings are asked to perform multiple functions, so the coating service provider may ask for a list of desired attributes in the order of importance. What are the operating conditions of the part and what is its life expectancy? It is also important to know what alloys are in the part and what processes it has undergone (e.g. heat treatment). Are there tolerance and other rigid specifications that must be adhered to? Coating service providers might also ask what coatings or processes have been tried in the past and if price is a primary factor.

Plastic Coatings Images provided by U.S. Plastic Coatings Corporation.	Phosphate Coatings Image provided by Imagineering Finishing Tech.

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Types

• Air-dried coatings, including forced-air dried coatings, are those which are not heated above 194ºF (90ºC) for coating or drying.
  
• Air spray techniques utilize compressed air to spray liquid coating through a small opening at high pressure. The materials are not mixed with air before being sprayed through the nozzle.
  
• Baked coatings are heated to a temperature of 194ºF (90ºC) in order to cure or dry them.
  
• Chemical vapor deposition (CVD) is a thin-film coating process that produces a film by a chemical reaction. CVD processes often use unstable elements to coat cemented carbide inserts.
  
• Chromate conversion coatings have good corrosion resistance and provide a good base for paint or rubber bonding. However, chromate conversion coatings have little to no abrasion resistance.
  
• Conformal coating is a process in which dielectric coating, such as epoxy, urethane, parylene, acrylic and silicone, is sprayed onto a substrate. Conformal coatings are used to protect products from fungus, moisture, abrasion, corrosion, etc.
  
• Dry film coating is a lubrication process that helps to prevent scuffing and galling, reduces friction, provides extra protection by preventing damage from oil film failure and aids in the distribution of heat, resulting in less metal fatigue, which reduces the chance of part failure. Dry film coating does not cause any dimensional changes to the product to which it is applied, because it is impregnated directly into the metal surface.
  
• Electrocoating, also known as “electrodeposition,” “electrophoretic deposition” or “electropainting,” is a process that resembles electroplating, in that it uses an electric current to apply thin-film primers and one-coat finishes onto the metallic substrates. However, this organic finishing process does not deposit metal ions onto the substrates, but rather, waterborne paint.
  
• Electroless nickel plating is a quick, easy, economical chemical reduction application process that avoids the use of electrolytic energy. Electroless nickel plating is ideal for small parts, provides an even, uniform layer, leaves no anode shadow, does not pose disposal problems and can be applied to many metals, including all steels, irons, copper, brass, bronze, lead free solders and nickel alloys.
  
• Electrostatic spraying is a process in which the paint is given a negative or positive charge before it is sprayed and the workpiece is oppositely charged, resulting in the attraction of the paint particles, uniform dispersion and reduction of waste. Electrostatic spraying, which is well-suited to automation because it increases production rate, reduces corrosion, protects against scratching, stops contact with air, water, chemicals, etc., alters appearance of workpieces and gives good finishes.
  
• Hot melt coating is a method used to apply plastic materials to a substrate. Hot melt coating is frequently used on papers and books and does not necessitate the use of solvents.
  
• Ion-plasma coatings are very dense and are highly wear- and corrosion-resistant.
  
• Laminating is a process by which a plastic transparent film is applied to one or both sides of a product. Most frequently used for paper products, the laminate enhances both decorative and protective qualities.
  
• Liquid paint coatings are applied by spraying—atomizing the paint into a fine mist—and depositing the mist on the surface of the part, where the tiny droplets flow together to form a film. Liquid paint coatings are available in a wide variety of colors and contain binders, solvents and pigment.
  
• Manganese phosphating is a coating process that is used in the pretreatment of iron and steel surfaces prior to painting, especially military equipment that requires oil or greased paints. Manganese phosphate coatings are highly corrosion and wear resistant.
  
• Metal coating is the application of a thin or series of thin coats of any of various metals. Some types of metal coatings include electroless nickel plating, phosphate and chromium.
  
• Passivation is a process that removes excess iron molecules from the surface of stainless steel products, typically with the use of nitric acid solutions. The danger of rust then becomes negligible.
  
• Phosphate coatings chemically convert the surface of a base metal into a non-metallic, crystalline coating.
  
• Physical vapor deposition (PVD) is a thin-film process in which a material is placed inside a vacuum chamber and vaporized. The atoms are transported across the chamber onto the substrate and condense into a film on the substrate.
  
• Plastic coating is a layer of plastic material that is dried on top of a substrate. Plastic coating is ideal for odd shapes and when materials need to be coated entirely.
  
• Teflon (polytetrafluorethylene) coatings are utilized for such items as cooking utensils and other industrial applications, because of the non-sticking characteristic of Teflon.
  
• Thermal spray coatings are typically zinc or aluminum and are heated until liquefied. Liquid drops are then blown by means of a compressed air jet onto the substrate, creating a porous coat.
  
• Thin film coatings, which include physical vapor deposition (PVD) and chemical vapor deposition (CVD), are use predominantly in the manufacture of electric devices.
  
• Vacuum coating is a process in which the coating material is applied in a vacuum chamber to the substrate. Usually the material is vaporized and then transferred through a chamber to the substrate.
  
• Zinc phosphate coating is a paint pretreatment that is commonly used to develop good bonding qualities between the paint and the galvanized or galvannealed coatings on steel sheets and is applied while the steel is in a coil, to the cut sheet or to the fabricated article. Zinc phosphate coatings greatly aid paint adhesion, in that they dramatically decrease the tendency for paint disbondment during subsequent atmospheric exposure in a corrosive environment.