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What is powder coating?
Powder coating is a popular industrial finish that uses a resin-based dry powder to coat a variety of surfaces. You will most commonly see a powder coating finish on a metal surface, but it can be applied to all sorts of substrates. Powder coating is known for it's long-lasting and durable exterior that keeps both the coating and the substrate protected for longer than many other traditional finishes.
For a more in-depth look at what powder coating is, read our article.
Is powder coating stronger than liquid paint?
Powder coating finishes are stronger than virtually all other surface finishes. The powder coating process and application makes the coating adhere tighter to the substrate than other finishes. Conventional liquid based paint will use an evaporating solvent to get the paint to stick to the surface, which does not provide as strong of an adhesion as powder coating. The resins and powder bases give each powder coat different advantages and drawbacks. Powder coatings are often mentioned as completely resistant to rust, corrosion, impact damage, and other forms of deterioration. This is false, no powder coating is entirely resistant to harm. However even the powder coats that do not specialize in a specific area such as rust resistance, will still be less likely to rust than liquid paint and other finishing methods.
How long do powder coatings last?
The life span of a powder coated surface can vary depending on factors such as the substrate material, the kind of powder coating being used, where the powder coated item resides, and many more. The typical life span of a powder coating is around 15-20 years but can last even longer in some instances.
How is powder coating applied?
There are two major powder coating processes, but both will yield equal results. Choosing the correct method will come down to the type of powder coating being used, and the size or material of the item being powder coated.
The first and more common powder coating method involves the use of an electrostatic spray gun. The powder is pushed through the spray gun by propelling small amounts of compressed air, typically ranging from 4-7psi. The compressed air will atomize the powder and get it to flow more like a liquid. The style of spray gun used is fitted to have an electrostatic charge at its tip, and when the powder coating is forced out of the spray gun it will apply its charge to the powder. This electric charge will keep the powder particles adhered as tightly to the substrate of the part being sprayed as possible.
The other method for powder coating works by using a fluidized bed system. This process works by preheating the item to between 450-500 degrees Fahrenheit. From there the item is dipped into a tank filled with the powder coating material. The tank being used is what the 'fluidized bed' name refers to. The material inside of the fluidized bed system will have added compressed air into the tank, which causes the powder to flow in a more fluid state. These particles will melt as they contact the powder coating and will continue to flow together to form the full coating.
The Curing Process
If the electrostatic spray method was used, the part will be placed in a curing oven where it will be heated at a temperature between 325-450 degrees Fahrenheit. The total time spent in the oven will vary based on thickness of the coating, and the size and surface material of the part being coated. This can range from anywhere between 10 minutes to over an hour.
If the fluidized bed method was used, the part will be heated once again in a similar fashion to curing. This heat is only used to help the coating continue to flow across the item. The heat used should only be at or around the melting point of the powder coating used.
Choosing which of the methods above to use for your item can come down to the specific powder coating that will be used or the material of the surface being coated.
Take a closer look at the powder coating application process here.
What kinds of powder coating are there?
There are two main styles of powder coating powders, thermoset and thermoplastic. The difference between these two coatings is based on how they react chemically when exposed to high temperatures.
Thermoset powder coatings will create an irreversible cross-link of the molecules when melted, and the powder will form a cohesive coating. Once fully crossed, the chemicals will have formed a bond that makes the coating much stronger and more durable than traditional paint. This is why thermosetting powders are more suitable for the electrostatic spray application than thermoplastic powders are.
When heated, thermoplastic powder coatings do not intertwine at the molecular level. The only purpose served by melting thermoplastics is to get the powder coating back to a fluidized state. Fluidized bed systems are preferred when dealing with thermoplastic powder. The curing process for thermoplastic powder is completely reversible.
Thermoset and thermoplastic powders contain different forms of polymers called resins. These resins are the difference in the available kinds of powder coatings and are what give each specific powder it's own strengths and weaknesses. The process used to apply these types of coatings is more often decided by the general powder type (thermoplastic vs thermosetting) rather than the resin base.
Polyester. Polyester is one of the most common forms of powder coating. With a lower curing temperature than many other resin bases, polyester is a versatile coating that can be mixed with other coatings and is easier to apply to a non-metal surface. Polyesters proved added resistance to UV light and weathering, but have a lower chemical resistance. This makes them suitable for outdoor applications such as patio furniture or lawn and garden equipment.
Epoxy. Epoxy finishes provide more chemical protection as well as added corrosion resistance, and can even be used for electrical insulation. They also exhibit a smooth, uniform appearance. Epoxies are typically used for indoor applications, as one of their main drawbacks is their weakness to UV light.
Hybrids. Polyester and epoxy are two of the most popular resins used in the powder coating industry. However they have two very different sets of strengths and weaknesses. Hybrid finishes, such as epoxy-polyester, were created to maintain the advantages of both powders while helping to balance out their drawbacks.
There are a wide range of hybrid powder coatings on the market, but it is not always the right choice for your equipment. There are still times where the added corrosion durability of epoxies can outweigh the more well-rounded components of a hybrid, so be sure to consider the environment that your part will be in and know whether or not increasing the quality of UV resistance for an indoor item would be a necessity.
For more on the specific materials used in powder coats, check out our blog.
What surfaces can I apply powder coating to?
Metal surfaces are by far the most common substrate for powder coatings. Both of the methods covered here revolve around an electric charge, which surfaces like metal, stainless steel, aluminum, and other steel alloys will hold with relative ease. The powder coating process using either method will require the item be exposed to incredibly high heats, meaning that a material like rubber is not an ideal substrate. By adapting the process though it is still possible for materials like glass, wood, or plastic to be powder coated.
How do I know which powder coat is right for my job?
There are a lot of variables to take into account when choosing the right powder coating. You will want to take into account where the substrate will spend most of its time. A metal surface that is exposed to high amounts of UV and sunlight will likely need a different coating than a stainless steel appliance for your home. Other variables to consider are the level of gloss or shine you would like the finish to have, the thickness needed to coat the item, the likeliness of the coating coming into contact with a substance that may cause rust, corrosion, or physical damage, etc. There are plenty of aspects to consider so make sure to research each powder thoroughly.
How can I remove powder coating?
While the high quality, high durability finish that powder coatings provide is undoubtedly one if it's biggest advantages, it can make the removal process tricky. There are three major methods for removing powder coatings; chemical stripping, heat removal, and abrasive blasting.
Chemical Stripping. Chemical stripping is an inexpensive and readily available method for removal. It works by applying a solvent to the powder coating that will cause the coating to dissolve, soften, or swell. Once this occurs the coating will begin to fall off, but in some cases may need to be washed off.
Chemical stripping can be dangerous. The chemicals used in the process are often toxic and can be labelled as 'hazardous waste' which means you will have to follow safety guidelines for disposing of the chemical, the stripper, and the water used when rinsing the part off.
Heat Removal. Heat removal does not have the same environmental concerns that chemical stripping does and can work even faster. It works simply by burning or baking off the coating in a high-powered, industrial strength oven. The oven used to remove the coating in this case may need to reach a temperature as high as 1200 degrees Fahrenheit. When exposed to such high temperatures though, your item is at a major risk of being warped or damaged. Deformation of metal and steel can begin as early as 600 degrees Fahrenheit.
Abrasive Blasting. Abrasive Blasting is an industry favorite for removing tough coatings. Abrasive blasting includes both traditional sandblasting and Dustless Blasting®. Dustless Blasting systems use media propelled at high speed towards the surface to strip off the powder coating. Dry blasting can take place in a blast cabinet or a blast room, whereas Dustless Blasting requires minimal or no containment and can be used on large, outdoor items. Suitable to use on almost any materials, these abrasive blasting systems can clear off virtually any coating and are used across multiple industries.
Click here to read more about removal methods.
Is powder coating safe?
The powder coating process is inherently environmentally friendly. There are no solvents or dangerous chemicals used in the application process or in the powder coats themselves. Powder coats also elicit minimal volatile organic compounds (more commonly called VOCs) unlike conventional paint methods. Powder coating is already compliant with environmental protection standards, as long as the components and equipment used while powder coating are up to date. Liquid paints often contain solvents and toxins that can be potentially harmful to both nearby people and the environment.
Powder coating is also easily recyclable. With the correct retreivement systems in place, any excess powder that did not adhere to the substrate when sprayed can be picked back up and used again for the next project.
Is powder coating affordable?
Powder coating is a very cost effective process on top of being a more durable finish. The stronger finish means that as time goes on there is less maintenance required to keep the coating looking good. Material costs for powder coating are typically cheaper than that of painting because the materials used are recyclable.
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