There is constant debate about which is better: powder coating or painting. While the former can offer up a more durable and resilient coating, painting can still be the right option for a given process depending on the nature of the project. In this instance, let’s say powder coating is the ideal solution for your project. Maybe you need a thicker coat that’s consistent in both quality and time necessary to complete. Just because it can provide a better long-term solution doesn’t mean that the process of powder coating is as easy as just brushing it up and down a few times. There are a few problems and annoyances that can occur during the powder coating process. While tedious to fix, they are easily avoidable if you take the proper precautions before starting.
If there’s one thing the most common problems in powder coating have in common it’s their silly names. With a defect name like “pinhole,” you might think it’s some weirdly looking deformity. In all fairness, it most definitely is, but the defect itself is far less amusing than its name would let on.
Pinholes are generally defined as tiny circular voids found in a powder coating finish that is clearly visible to the human eye. Typically a single pinhole won’t cause that much of a problem, but when they show in bunches, then it’s a sign that you most likely need to recoat the metal. In an ideal finish, you want the metal to be smooth. Pinholes usually occur during the curing process. When the part heats up, the powder melts into a liquid which spreads into a film, causing the creation of holes or bubbles across the surface.
Pinholes don’t just happen without cause or reason. In most cases, they will appear due to a lack of proper preparation. The surface of the piece is always the game-changer. If it hasn’t been properly cleaned, then it opens up a plethora of opportunities for contamination. If the surface wasn’t properly wiped down prior to the powder coating, then dirt or other impurities such as oil, grease, or water can become trapped within the powder.
If you find pinholes on your piece, the only way to remove them is to recoat the entire surface. It’s much simpler to prepare yourself and minimize the odds of them even showing up. To avoid pinholes, clean the metal thoroughly. You can achieve this by blasting, washing appropriately, or even treating it chemically. As well, cleaning the booth and keeping the oven air clean are essential steps to avoiding these deformities. Avoid cross-contaminating the metal with other substances, like WD-40 for example. Finally, make sure that the curing temperature is set correctly before beginning the coating process.
Another common powder coating problem also shares a silly name: orange peel. Amusingly enough, the orange peel deformity got its name because, well, it looks like an orange peel. Powder coaters are notoriously humorous. Typically, a surface with an orange peel-like finish has an uneven texture on what should be a smooth finish. In that sense, it both looks and feels like the skin of an orange or any similar citrus fruit. Similar to the pinhole, fixing this imperfection will require a recoat, meaning you will have to restart from step one. The best way to avoid orange peel is by taking the necessary steps to ensure all parts of the surface are smooth.
The first step you’ll want to take to avoid the orange peel effect is to properly prepare the surface before the coating proceeds. There are several ways to do so. You can sandblast the surface or immerse it in zinc or phosphate. The former option is generally more approved due to the increase in durability that sandblasting can provide, but it also requires delicate attention from the person performing the sandblasting. If it isn’t done properly, the sandblasting can cause indentations in the surface that will also lead to orange peel. Be sure that during this preparation, you don’t cause the problem you sought to avoid. If you’re unsure, try using fine sandpaper to ensure proper protection.
Once you’re certain the surface is prepared, you can shift your attention to the powder coating itself. Powder coating revels in specifics and straying from the guidelines is begging for a deformity to appear. Adding too much or not enough powder can lead to orange peel. If the guideline suggests an amount, stick to it.
Finally, during the curing process, it’s important to maintain the proper temperatures and schedules throughout. If cured too long at too high a temperature, you can expect to see orange peel developing. The opposite is true as well. While the temperatures and curing times can vary, a happy medium can be found at around 200℃ for approximately 10 to 15 minutes. While this isn’t an explicit recommendation, most guidelines will have similar directions. Always be sure you’ve read the guidelines before attempting to cure the piece.
Continuing the silliness of the names of recurring powder coating problems is the dreaded fish eye imperfection. Not unlike its imperfection siblings, fish eyes are a result of contamination in the piece’s surface that can also cause the powder to flake or peel. The fish eye deformities are apparent to the human eye and you can spot them as a depression in the surface that almost looks like a pitching mound, where the center is elevated. They do seem somewhat similar to the other imperfections mentioned earlier in the article, but there are distinct differences between typical craters and fish eye defects.
It’s true that all these problems are caused by a form of contamination, the contamination leading to fish eye can sometimes occur before the pre-treatment which occurs before the coating itself. While the contamination can occur on the surface, other times it happens in the powder itself. This is largely dependent on the quality of powder selected. Some powders can handle contamination decently, while others, like high-flow resins, will more easily develop fish eyes. Unlike the other defects, fish eyes are nearly impossible to fix once they’ve occurred. You will need to recoat the entire piece and ensure that the surface is now cleaned and that contaminants are kept to an absolute minimum.
To prevent fish eyes from arising, it’s essential to clean the surface to perfection. Perform a white rag test afterward to ensure no contaminants, dirt, or dust make their way to the surface. As well, keep the equipment as clean as you would the surface. Any chance a contaminant gets to ruin the coating will likely occur, but mitigating this potential deformity is easy if enough attention is paid to the process.
Powder Coating: A Cleaner Dream
There’s a pattern with all these deformities and imperfections. Most of them are caused by contaminants left on the surfaces due to a lack of preparation and cleaning. Fixing these mistakes after they happen is a pain and time-consuming. Naturally, preventing these problems is a much more sustainable method than attempting to fix them. Following guidelines, cleaning thoroughly, and paying proper attention to the coating process as it happens are key elements to ensuring your coats don’t become unusable or delayed.
To avoid errors caused by tired humans, powder coaters can look to AutonomyOS™. Using 3D Perception with AI-based Task Planning and Motion Planning, manufacturing engineers and integrators can configure autonomous robotic systems to analyze and coat various pieces of metal regardless of their shape, complexities, and sizes. Contact us to learn more.