Plastic Coating or Powder Coating -- Is There A Difference?
Manufacturers that want to coat a part or finished product often want to know the difference between plastic and powder coatings. They soon find out that there really is no difference, since powder coating material is actually finely ground plastic.
Powder coating--the application of fused plastic particles to a metal surface--is being used with increasing frequency as an alternative to conventional painting and electroplating. Many manufacturers have discovered the advantages of powder coating, which make it ideal for providing both decorative and functional finishes for many types of industrial and consumer products.
There are many reasons why manufacturers choose to powder coat their products. These include making the products resistant to chipping and abrasion; providing resistance to chemicals and corrosion; providing a decorative, impact-resistant finish; adding electrical or thermal insulation; providing resistance to ultraviolet light; and adding sound-deadening properties.
Although durability is perhaps its greatest advantage, another important benefit of powder coating is the minimization of the need for secondary operations, such as polishing, grinding, and deburring. It also solves the problem of sharp or rough surfaces.
The process can be used to provide parts with many different functional properties, such as a high or low coefficient of friction. Decorative coatings, in a choice of textured or smooth, high or low gloss finishes, cover surface imperfections and provide a uniform product finish.
Powder coatings are polymers that, upon application of heat, melt and flow out to a continuous and even film. Nylon, epoxies, vinyl, polyolefins, polyester, and polyethylene are the materials most frequently used for custom powder coating. All are available in a full selection of colors.
Five basic methods are used to apply plastic coatings. The best method for a particular application depends on several factors, including the size of the part to be coated, the thickness of the coating required, and the production rate.
The fluidized bed method was developed to provide economical encapsulation of parts in a wide range of sizes, in either small or large quantities. The fluidized bed consists of a tank of dry powdered plastic that is aerated from below. Aeration causes the plastic particles to become suspended, making a fluid-like 'bath' of turbulent particles.
When a preheated metal part is immersed in the tank, the plastic particles melt and adhere to its hot surface. When the part is removed, all the particles on the surface fuse into a continuous coating. If necessary, the part can then be placed in an oven for additional curing.
Parts may be masked to prevent the coating from adhering to areas where it is not wanted, such as where electrical contact must be made. With standard thicknesses from 0.007 to 0.015 inch (and 0.040 inch achievable), the fluidized bed method is especially effective providing edge coverage on sharp metal stampings, coating corners or recesses, and bridging separation in spot-weldcd metal. It provides a thorough, very uniform coating for applications requiring corrosion and wear resistance or insulation.
The electrostatic spray method can be used to coat items in an almost unlimited size range. With this method, the cold part is sprayed with electrostatically charged plastic powder. The particles cling to selected surfaces of the piece, while unadhered powder is reclaimed to be used again. The piece is then heated in an oven for curing.
This process results in very thin coatings to meet close tolerance requirements. Standard thicknesses are from 0.001 to 0.004 inch, although thicknesses of up to 0.015 inch can be achieved. Electrostatic spraying's thin coatings, and the ability to recover and reuse virtually all over-spray, save money and protect the environment.
Flame spray coating is a relatively new method, used for its functionality and durability, rather than for decorative purposes. It can handle very large parts and can be applied on-site or at the custom coater's facility, under all temperature conditions.
A hand-held applicator is used, with the plastic powder being fed into a propane/compressed air-fueled flame, where it is melted and then blown against the surface to be coated at a high velocity. The plastic material immediately bonds with the substrate, resulting in an extremely tough, tightly adhering coating that is free of pinholes.
The semi-automated dip-to-line process allows coating to a specified height, where a line of demarcation is not aesthetically required. Standard thicknesses range from 0.007 to 0.015 inch, although a coating of up to 0.025 inch can be applied when necessary. It is more economical than processes that require masking. It can be used to impart sound deadening properties, as well as lubricity, electrical and thermal insulation, impact resistance, and abrasion resistance.
For high volume applications, the flo-clad (mini-coat) method is often used. The large amount of automation associated with the flo-clad method keeps costs down. This tumbling process ensures complete encapsulation of small parts, with no holding scar. Thicknesses of 0.002 to 0.007 inch are standard, with a 0.020 inch thickness achievable.
Custom powder coating can be an excellent means to improve the performance of a part or to solve a specific problem. The best way to determine if a particular coating material and/or process is right for a certain application is to find a coating service that will provide test coating of the part. This procedure will ensure the effectiveness of the coating before final production begins.
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