If you’re troubled with liquid paint’s durability and short lifespan, powder coating is the ideal alternative and solution for you. However, careful pretreatment and an electrostatic charge used to adhere the pigmented coating onto a surface are necessary for the application process of powder coating. Furthermore, powder coating does bring added protection from several factors. It enhances the visual and aesthetic appeal, making it an ideal option for several industries.
What Is Powder Coating?
Powder coating involves applying a dry powder onto an electrostatically charged surface. The coating within a single application is thicker than a single application of liquid paint. The electrostatic charge is applied to hold each particle of coating in place on the surface. After applying the powder coating, the coating is cured on the object. The entire process is intensive for surface preparation and coating and thus a preferable approach for bulk orders.
Ingredients of Powder Coating
There are several ingredients involved in the mix that makes powder coatings. The core element is a polymer resin, with additional elements added for other specific purposes. These include ingredients for better curing, pigmentation ingredients, and flow modifiers. These elements add color to the coating and make it a protected surface against several natural conditions after curing.
Different Types of Powder Coating
Powder coating generally exists in two types. These are thermoplastic powder coating and thermoset powder coating. Both differ in the ways they are cured and the properties they carry.
Thermoplastic Powder Coating
In thermoplastic powder coating, the coating is melted and flown when heated. During this process, it maintains its chemical composition, even after solidifying. It remains more resistant to impacts within the finished product. The thermoplastic powder coating does not need a curing cycle. Still, it needs a much more time-taking process with high temperatures required to melt enough to flow over the surface evenly. Another outcome of it not undergoing the curing process is that it can be softened to melt again at high temperatures. However, comparatively, this application process does require a much thicker millage and does not provide the best visual appearance.
Thermoset Powder Coating
This process involves a chemical change, which is irreversible by all means, resulting in a durable, hardened coating. Through a thermoset process, the coatings will melt and flow when heated. Still, unlike thermoplastic powder coatings, their chemical structure alters to form cross-links with a different chemical composition to what was originally present in the base resin. After the coating is cured, the changes become permanent and do not melt under intense temperatures. Moreover, these coatings, being more hardened, are also more scratch-resistant when compared to thermoplastics. The films developed in thermoset powder coatings are thinner, making them more visually appealing. However, the material becomes brittle and prone to cracks in thick layers.
The final decision of choosing between the two depends on what purpose you need powder coatings for specifically. Let’s look into some of the use cases surrounding powder coatings.
Different Uses of Powder Coating
There are many applications for powder coatings in several industries, including automotive, aerospace, manufacturing, and other sectors where the market desires durable finishing on their products. Thermoplastic powder coatings hold the upper hand in everyday functional applications, such as kitchenware and dishwasher racks, playground furniture, light poles, and pipes. On the other hand, thermostat powder coatings are highly preferable for use in various applications, such as products used in lawns and gardens, incorporating lawnmowers, shovels, and other garden equipment. Other applications include furniture, fencing, and building facades.
Working of Powder Coating
For adhering the powder to the product’s surface, an electrostatic process is utilized first, followed by a curing process. Meanwhile, a heat-resistant substrate is used to easily allow the parts to undergo high temperatures to set the coating. Mostly, the products are made of metal coated with this finish, which is generally heat-resistant and easily survives throughout the entire process.
Sticking to Surfaces
When electrostatic applications are used for surfaces, the metal components are grounded. The powder particles are inert. However, they gain an electrostatic charge as the particles are passed through spray guns, which spray them onto the product surface. The electrode fitting in the guns is where the electrostatic charging of the powder particles occurs. The particles are sprayed onto the grounded metal surface, sticking to the surface due to the charge. These particles are later cured, solidifying them into a densely packed coating that is melted and set to finish.
An alternative method that is not common in practice is the curing fluidized bed. The process involves heating the part then submerging the heated part into a bed of powder coating. Here, the heat melts the particles into a coating that covers the entire surface evenly. It is not a practical process for metals; however, it works for thermoplastic coatings and non-metal materials.
Protecting Surfaces from Corrosion
The thick surface produced with applying a durable powder coating over the part generally makes it resistant to impacts and scratches. Eventually, this feature makes it efficient as powder coatings generally do not need touch-ups and repairs due to chipping away or fading damages. The color provided is long-lasting and also well-suited for extreme environments.
Steps Involved In Powder Coating
There are several steps involved in powder coating. Each of which adds a way to help ensure the finish is successful, lasts long, and provides durability for your specific applications.
The process of blasting serves as a step to remove any inorganic contaminants that could hinder the process or reduce the quality of the coatings. These include elements such as welding smut, laser scale, or rust. Blasting is also done for previously finished surfaces. Abrasives are used to scrape off paint, other finish layers, rust, or other forms of corrosion. Additionally, better powder coating adhesion is ensured when the surface does not contain contamination.
Pretreatment refers to one of the most crucial steps involved in the powder coating process. It is a very critical stage, for which reason it is divided into a four-step pretreatment method.
- Alkaline Cleaning
An alkaline cleaner removes organic elements, such as organic liquids, oil, and dust contaminants. After cleaning with the alkaline cleaner, the surfaces are rinsed twice to remove any remaining debris and purify the surface from any remaining cleaning chemicals.
- Iron Phosphate Application
Subsequently, the part undergoes an iron phosphate application, which is accomplished to prepare the product surface to be more efficient in powder coating adhesion. Apart from that, it makes the product has improved corrosion resistance. After the process, dual rinses are carried out to remove the remaining iron phosphate on the product surface.
- Reverse Osmosis
A final rinse is done, which is a reverse-osmosis water rinse achieved specifically to remove any remaining solutions, debris, or contaminants from the surface. Ultimately, this step ensures that the final product is pure quality and free of contaminants.
- Zirconium Sealer Application
A chrome-free zirconium sealer is used to cover the surface. After this layer dries and seals the surface, the product becomes ready for the following stages of powder coating.
Primers being applied on the surface before powder coating are usually considered optional. However, it is advisable as it carries its advantages. For metal products such as those made of aluminum or steel, it can help the finish survive up to four times longer than non-primed surfaces. Hence, we recommend you consider priming aluminum or steel parts planned for outdoor use.
Masking is done to prevent certain product areas from getting powder coated. It ensures these areas are protected from powder coating and provides clean threads and machined areas.
The coating process can be done in one of two possible ways. An automatic system or a professional finisher is used to spray charged powder coating onto the grounded metal parts. The coating, charged with static, then sticks to the surface due to electrostatic bonds.
The process of curing involves melting the resins in powder form, which allows them to set and form a durable coating. The different factors of the curing process, such as the timing of the process and temperature to be set, are according to what coating thickness is desired, what material is being used in the substrate, the size of the product, and various other factors. In addition, these factors are used to precisely calculate the curing time needed. After the curing process, the parts are cooled down and allowed to set, after which they are packaged and ready to get shipped.
While considering everything, powder coating finishes have all the earmarks of being an ideal choice regarding metal fabrication, rapid prototyping, and other related finishing processes. Without question, it gives magnificent outcomes in a wide scope of metal parts or products, and there is no restriction to the shading or finish you can achieve. Not only that, but its cost-effectiveness additionally makes it an insightful choice for your next product design. But remember, never miss reaching out to an expert today for your professional finishing services.