When you’ve designed, engineered and fabricated a large motor base, machine frame or piece of agricultural equipment you want it to last. You might also want it to impress. (You may not asses the quality of your reading material by the design of the dust jacket, but plenty of folks do.) A high-quality final coating takes care of both those goals.
For many customers their default coating is paint. That’s not necessarily bad, but how about powder coating instead?
That question is often met with raised eyebrows and a list of questions, but we think, especially for large weldments, powder has some advantages. To save time in the future it seemed like a good idea to document those questions and our answers in an FAQ.
10 FAQ’s about Powder Coating Large Weldments
1. Isn’t powder coating for small parts?
It’s often used on small parts but the process has no size limitation. Any fabricator who installs the equipment can powder coat large parts as well as small. We regularly powder coat weldments of 1,000 pounds or more.
2. Why powder coat rather than paint?
There are several reasons and it helps to understand the fundamental difference. Paint incorporates solvents that help it flow. These evaporate during the drying process and the larger the weldment the bigger the problem. In contrast, powder has no solvents. That avoids all the environmental problems of volatile organic compound (VOC) emissions and all the mess that paint can create.
Another difference is drying. Paint can be left to air dry, which takes hours or even days. A powder coat needs heating to fuse the particles but is handling-ready minutes afterwards. That can help in getting your weldment delivered faster.
As far as the actual coating goes, a powder coating is thicker than paint and can provide more appearance options. This goes beyond matte or gloss to textures and even sparkles. We’re not often asked for sparkly coatings on large weldments but if you need it, (maybe for parts of a fairground ride,) it’s possible.
3. Will powder coat hide imperfections?
It can, but don’t look at it as a substitute for thorough preparation. It shouldn’t be used to cover up rust for example. However, powder can be applied to give a textured surface that will hide rough or uneven spots, so to that extent, yes it can hide imperfections.
4. Is powder coating more durable than paint?
Somewhat debatable, but we’d say yes. In truth, durability depends more on preparation and application than the material itself. However, with paint the solvents evaporate, and which leaves microscopic imperfections. Those can allow moisture in, and we all know what happens when water meets steel!
A second point to mention is color-fastness or UV resistance. Modern powder formulations are extremely good in this regard, which makes powder a good choice for fabrications that will live outdoors.
5. Which is better, powder coating or anodizing?
This is like asking which is our favorite child! They’re just different, and each has special strengths. Anodizing produces beautiful metallic finishes in a wide range of colors. It’s hard, scratch-resistant and holds up to corrosion. Powder has more color and appearance options but isn’t as hard-wearing.
Two things to remember are, first, powder is a coating. It’s put on and it can be taken off. And second, anodizing is actually a change to the surface of the metal. It’s used mostly on aluminum but can also be performed for stainless steel and titanium. Unless your weldment is fabricated from one of these, anodizing isn’t an option.
6. What causes powder coat to flake off?
Poor surface preparation. Next question.
Okay, to add more detail, powder coating is like painting: it’s all about adhesion to the substrate. With paint a primer is usually applied to the metal, and then the top coat goes on top. Powder coating is a single layer process, but it needs a surface that’s free of dust and oil to bond. So to ensure the powder stays bonded to the metal, prep the metal thoroughly.
7. Can you powder coat over paint?
Just because you can do something, it doesn’t mean you should. You can drive 80mph on the highway but we wouldn’t recommend it, and the same goes for applying powder over paint. The powder will bond to the paint but you’re trusting that the paint is well bonded to the steel. It’s always better to strip the weldment back to bare metal and clean it thoroughly before powder coating.
8. Is powder coating rust-proof?
Short answer: yes, but really, it’s a bit more complicated than that. If you mean, will a powder coating hold up to rain and snow, yes, it will. If you’re referring to performance in ASTM-style corrosion tests, (salt spray, things like that,) well it depends on preparation and application process details. A powder coating certainly can be rust-proof, but if it’s a big concern let’s discuss your requirements in detail.
9. What is the environmental impact of powder coating?
Paint’s big problem is the solvents. Those evaporating VOCs cause all kinds of health and safety hazards and so need expensive protection and mitigation gear. The water systems used for catching overspray can be an issue too as the resulting sludge needs proper disposal.
Powder coating is virtually VOC-free, which is a big advantage. Plus, overspray is just dry powder which can be swept or vacuumed up, (and reused, if you’re diligent about not mixing colors.) Heating the powder is a bit of a negative, but overall powder coating is significantly better for the environment than liquid paint.
10. Is surface preparation important for powder coating?
Is Indiana a great State? (If you’re unsure, the answer to both is “Yes”.)
Whether you’re painting or powder coating surface prep is very important. To repeat what we said above, durability depends on adhesion, and neither paint or powder can adhere well to a dirty, rusted or oily surface.
Castings with surface rust go through grit or bead blasting to ensure they’re completely corrosion-free. Surface dust is blown off and then the casting might be washed to ensure it’s completely clean. In some cases a preheat is used to burn off any contamination that’s found it’s way into the surface.
A brand-new, rust-free weldment needs good prep too. There’s usually some surface oil that must be removed, and welds will be ground to keep them smooth and clean. Then there’s blow-off and maybe washing and preheating as necessary.
Getting the Job Done, Faster
Powder coating is an excellent alternative to painting for large weldments and fabrications. It’s hard-wearing, durable and available in a wide variety of colors and finishes. As there’s no need for extended drying times it’s faster than painting too. That lets us get your job out of our shop and into yours in less time, which is something everyone can appreciate. If you’d like to learn more, just call or email.