Powder Coating is a method of using an electrostatic charge to apply a coating of resin and pigment powders to a surface. Due to the electrostatic attraction, the part holds a consistent volume of powder to its surface which in the end creates a high quality coating that is uniform and durable, as well as being free of the runs, drips, and sags that conventional wet coatings can manifest.
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How does the powder coating process work?
For the most part powder coating is a process that is used on metal surfaces, although new technologies have expanded this to include some woods and plastics. Whether it is done by manually racking and moving parts through each stage of the process, or whether they ride a conveyor system which moves them from stage to stage, achieving a quality coating on any part demands that every step in the process is included.
The process starts with the pretreatment/surface preparation of the object to be coated. This can include sandblasting in certain situations, but in most cases it is simply cleaning the metal surface and etching it in some fashion to prepare the surface to bond well with the powder during the curing process that follows.
The most widely used process includes washing the parts with an alkaline cleaner to remove grease, grit and grime, followed by a rinse bath containing an iron phosphate conversion coating. Sandblasting is used as an alternative or in addition to a washing and phosphating process, although in some cases it is simply a necessity in order to remove scale, oxide, or heavier rust which cannot be adequately managed by way of standard cleaning and phosphating stages.
After pre-treatment, the object must be brought to a state of complete dryness before powder is applied. This can be accomplished by air drying methods or in an oven setting. Once dry, the part is ready to have powder applied. The standard required temperature during powder application is that of room temperature, or around 75 degrees F. Therefore, if a dry off oven was used, the parts must be cooled before the application of powder takes place. If a part is coated at hotter temperatures it causes the coating thickness to increase, which is usually not desired. However, in some cases, that may be the objective, in which case coating the part while it is still hot from the oven may actually be called for. In any case, prior to coating, you will cool the parts as appropriate in order to meet your desired outcome as to coating thickness.
Application of the powder is accomplished by electrostatically charging the powder as it is sprayed onto the part. This takes place as the powder flows through the spray gun, which contains an electrode that accomplishes the task. This gives each particle of the powder a negative charge and results in an electrostatic attraction to the part, which is grounded or discharged for this process. The result is a uniform coating of dry powder clinging to the part.
After the coating process is complete, the part is moved to the curing oven, where the powder "melts" onto the part and cures to a hard, durable finish that is consistent in appearance and thickness. The "melting" process is more adequately described in a three-phase descriptive. The powder first gels, then flows out to create the appropriate look (color/texture-wise) which the powder in use has been designed to produce. Finally, it cures in that appearance during its remaining time in the cure oven. What actually takes place during the curing portion of this process is a chemical cross-linking between the particles of powder. This curing and cross-linking process also bonds the powder coating to the surface of the substrate and creates a very durable and long-lasting finish. As the part exits the cure oven it is totally complete, with no need to air dry or spend hours curing on a rack, so once the part is cooled off it is ready for use!
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What kinds of objects can be powder coated?
Many everyday objects we encounter are powder coated. The list on the CPC Home Page shows only a handful of the objects that can be powder coated.
All major industries use powder coating, from automotive to fixture manufacturing, and from appliances to a variety of furniture. Any surface you encounter that is made of metal and looks "painted" is quite likely a powder coated surface.
Predominantly a metal coating in years past, powder coating has in recent years advanced to include wood, ceramic and plastic in its realm of coatable surfaces. Technological advances have brought forward powder coatings that require a much lower temperature to cure, which has enabled the coating of these materials as well.
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What advantages does powder coating have versus other more traditional methods such as painting or spray painting?
There are several advantages to powder coating. First and foremost of these advantages is that powder coating is much more durable than typical liquid solution paints. Powder coated surfaces are much more resistant to chipping, scratching, and other such wear due to the bond created with the object during curing.
The coating is also much more resistant to natural fade and wear. The vibrant color of a powder coated part stays bright and fresh years after its wet painted counterpart fades away. Also, while liquid paints may vary noticeably in color from batch to batch, powder batches are virtually identical. So identical, in fact, that differences between same color batches are not detectable to the human eye.
Powder coating is also a better option than liquid paint because powder does not run, drip, or sag, giving a uniform coating that has virtually no inconsistency within a parts surface or from one part to the next.
Possibly the most important advantage to powder coating is the fact that it is VERY environmentally friendly. Liquid solution-based paints contain solvents also known as volatile organic compounds (V.O.C.) which flash dry and evaporate into the air as the paint dries onto a surface. These ingredients in the wet coating process are not only hazardous to the work environment, but they are also a huge part of the pollution and ozone concerns that come from the industrial sector of our world. Powder coatings, on the other hand, are effectively void of these concerns. They contain virtually no V.O.C., and powder waste is quite easy to control, with the disposal process being almost as simple as throwing out the trash produced at your home.
Efficiency is another benefit to choosing powder coating. A large portion of raw material is typically lost to waste in the wet coating process in the form of whatever spray misses the part during the application. When powder coating is the chosen coating, in many cases the material that does not apply to a part on the initial spraying is able to be gathered and reapplied in a later effort of application. There is much less waste produced by powder coating as compared to wet paint processes.
The bottom line is powder coating is an environmentally friendly process that requires no pollution control and is a finish that provides a uniform coating which is beautiful in appearance and superior in durability.
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Does powder coating cover up imperfections in an object?
No. Coating over an imperfection will simply give the imperfection a nice color and finish but the flaw in the surface will mirror through the finished coating. Scratches in a surface, grind marks, weld splatter, chips, dimples, rough patches, and the like are imperfections that need addressed prior to the coating of a part if you do not want to see them manifested in the finished product. Therefore, it is strongly recommended that you remove any imperfections in the surface to be coated prior to the powder coating process. Applying the coating to a smooth, clean and dry surface is key to achieving a quality finish.
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What options are available in powder as to color or appearance in the finish?
There exists a huge range of colors, textures, and special effects offered in powder coating. Color selection is virtually unlimited. If you do not find what you desire in the available stock selections of any given powder manufacturer, custom powders are no problem to accommodate. High gloss, low gloss, smooth, textured, wrinkled, metallic, multi color speckled, veined and many other looks can be produced to suit your specific desire. To best see the wide array of possibilities, simply stop by and take a look at our THOUSANDS of sample panels illustrating all of these variations of finishes.
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