What is Powder Coating?
Many people are unfamiliar with powder coating, but it is a crucial step in the manufacturing process. You might not know it, but a great deal of products we purchase and use every day have been powder coated before being packaged and prepared for retail. Basketball rims, refrigerators, and lawn furniture are all great examples of powder coating in our everyday lives.
Invented in 1945, powder coating utilizes a technique called electrostatic spray deposition or a fluidized bed application to apply coatings to surfaces which are then cured with heat or ultra violet light.
Why is it important? In this article we will explore the technique of powder coating, and how it has shaped manufacturing procedures. We will also look into the benefits of powder coating versus traditional paint, and how it can be safer to use than solvent based materials.
Polymer Resin
The materials used to create the coating are based around Polymer resins. This resin is created from refined petrochemicals such as ethane or propane. Using a heating process called catalytic cracking, the materials are further broken down into ethylene and propylene or other types of hydrocarbons. Once the substance has been cracked, a catalyst is added to create a powder known as a polymer.
This polymer is then combined with pigments and other substances that add certain characteristics to the coating such as gloss, or matte finishes. There are thousands of different polymer-based powder resins available to both professionals and consumers, and it is important to understand which resin is right for your product. We use exterior grade powder as a minimum on everything. If choosing the right coating seems like a daunting task, The Powder Coaters can assist you in making the right selection.
Pretreatment
Once the appropriate coating has been determined, the next step in the procedure is the pretreatment of the item to prepare it for the coat. There are many different types of cleaners, but acid and solvents are the most commonly used depending on the product. To clear away any impurities the cleaning agent is either sprayed directly to the surface of the item, or it is dipped into a pool containing the cleaning material. The Powder coaters are one of the only coating companies on Vancouver Island that use heated dunk tanks to ensure that every product is properly cleaned before the coating is applied.
ESD or FBA
Now that the item has been properly pretreated, it is time to apply the powder coat. As we mentioned earlier, there are two ways to apply powder coatings: Electrostatic spray deposition (ESD) or fluidized bed applications. Although both processes have their advantages and disadvantages, the most common way to apply powder coating is through Electrostatic spray deposition. This is because ESD is a more flexible and versatile method. The Powder Coaters are experts in the art of ESD and we have used this method to coat thousands of items throughout the years.
Grounding or Pre-Heating
When applying a powder coat to metal, the item in question must be grounded. It is common for powder coating guns to come with a “stock” ground wire, but in order to properly apply powder coats, a dedicated grounding rod is required. Our shop is fully outfitted with high-quality grounding rods to ensure that we can safely and effectively apply powder coats to almost any metallic object.
If you wish to apply a powder coat to an object that is not metal, the item must be pre-heated before applying the powder. Therefore, it has to be able to withstand a certain amount of heat (400 degrees F) before the coat is sprayed on.
Once the piece is properly grounded or pre-heated, it is time to spray on the coat.
Electrostatic Spray Deposition (ESD)
The actual application of the powder coat is done using a specialized spray gun powered by compressed air which fluidizes the powder and applies an electrostatic charge to the particles.
After pressing the trigger on the gun, the compressed air forces the particles into the barrel of the mechanism where they are electrostatically charged through a magnetic coil. With the gun pointed at the item to be sprayed, the powder exits the nozzle and is drawn to the grounded piece by electromagnetic attraction.
When coating a non-metallic piece, the heat emanating from the object melts the powder upon contact and causes it to stick. It is important not to apply too thick of a coat if employing this method because this could cause the coat to run much like normal paint. Too much coating can also cause flaws in the finish or durability issues.
Curing
The final step in the powder coating process is curing. This step involves heating the item and its new coat to a temperature range varying between 350-400 degrees Fahrenheit (160-210 degrees Celsius). Heating the object to this temperature bonds the synthetic polymer chains to each other in a process called cross linking. Cross linking is what makes powder coating so durable when compared to traditional coating methods.
In order to achieve the best cure possible, a curing schedule is required. The schedule is based around the part metal temperature or (PMT). This means that the part must reach a target curing temperature before the timer can begin. The only way to determine this temperature is by utilizing a laser or infrared temperature gun.
If the timer on the oven is started before the object reaches the correct temperature under-curing can occur. An under-cured coat may be brittle, and unable to resist chemicals and UV light. The coat may also craze (crack in many directions) and delaminate.
The opposite of under-curing is over-curing. This condition is caused by baking the object for longer than necessary or at too high of a temperature. If over-cured, the coat will become brittle, and in extreme cases, it may burn.
There are a number or different methods available to cure powder coated objects. In many instances it is possible to cure a coat using a heat gun, but to get a professional finish, an oven dedicated to curing is used. It is possible to use a conventional oven to cure coats, but one should never use an oven that has been used to cook food.
There are a number or different methods available to cure powder coated objects. In many instances it is possible to cure a coat using a heat gun, but to get a professional finish, an oven dedicated to curing is used. It is possible to use a conventional oven to cure coats, but one should never use an oven that has been used to cook food.
At The Powder Coaters, we use a batch system with dedicated racks that we roll into our 24-foot convectional gas oven in order to make sure each item we coat is cured properly.