Powder coating requires an object to be heated. When it is, impurities or gases can rise to the surface and create a cosmetic defect in the part. These rising gases cause pinholes in the coating that can also result in damage to the coating as moisture can get in them and allow for corrosion. These gases can come from a number of different sources so a number of different techniques are utilized to eliminate them from the process and craft a flawless powder coat.
In this post, we’ll break down the cause of outgassing while powder coating and go over some of the ways that we combat this phenomenon so we can ensure that your parts come out not only appealing to the eye, but free from damage.
What Causes Outgassing?
Before we can talk about how to go about preventing the negative effects of outgassing, we must discuss the circumstances that allow it to occur. The four most common causes of outgassing are listed below. We’ll start with how human error can cause outgassing and then discuss the ways that the properties of the object itself can cause the problem.
- Surface Contamination – Oil, dirt, grease and other forms of contamination on the surface of the object can vaporize while the piece is being heated and cause gas to bubble to the surface. Surface contamination can cause other problems with the powder coating process as well and is such an easily avoided human error that it is not generally thought of as a cause of outgassing. It is mentioned here for the sake of completeness.
- Coating Thickness – If too thick of a film coating is used during the process then it can cause gases to be given off during the curing process which make their way to the top of the surface and cause imperfections. Some powder coating materials are more likely than others to cause this problem, so knowledge of the materials used is an important factor when powder coating.
- Castings – We are done discussing the ways that human error can cause outgassing and are now going to move on to the aspects of the object itself that can cause the problem. Cast metal is a common material used as a base for powder coating. The problem with cast metal is that gases can become trapped in the metal during the casting process. When heated, these gases will be released and cause outgassing.
- Galvanization – Steel is highly susceptible to corrosion. One of the best ways to combat corrosion on steel is to coat it with a layer of metallic zinc using a process known as galvanization. This is great for the steel but can cause problems during powder coating. This is because gases can become trapped during the galvanization process in the same way that they do during metal casting. For that reason, powder coating galvanized steel can be just as tricky as powder coating cast metal items.
How is Outgassing Prevented?
Now you know how gases, or substances that can become vaporized into gases at high temperatures, can get trapped and cause outgassing. Next, we can discuss ways to prevent problems from arising so you are always happy with the final results.
- Clean Contamination – Before powder coating can begin, objects should be thoroughly cleaned and degreased so that any contaminants which may vaporize during the process are removed from the equation. This not only eliminates a cause of gas-related problems but ensures the best adhesion of the powder to the material.
- Control Thickness – Some jobs require a heavy film, but this does not mean that it must be applied in one coat. By understanding the materials used in coating and making sure to use multiple coats of necessary, outgassing caused by applying too heavy of a film coat can be avoided.
- Add a Primer – Applying a sealant as a primer coat before powder coating can ensure that any gases that may be released during the heating process are contained and unable to bubble up into the coating. It is important to note that this is not a replacement for thorough cleaning in the pre-treatment phase.
- Powder Additives – The real problem with outgassing is that the gases are escaping as the powder is hardening. This is what causes the pinholes on the surface. For certain powder materials, additives can be used that will cause the powder to remain in liquid form for longer. This will give the gas extra time to escape before the powder hardens around the bubbles.
- Preheat the Part – Since outgassing is caused by gas bubbles being released when the object is heated during the powder coating process, it can be avoided by heating the object before the coating process begins. This will cause all of the gas bubbles to expel themselves from the material before the powder coating even begins.
Knowing all of the ways that problems like outgassing can pop up is key to a successful powder coat. Someone who doesn’t know what they are doing could very easily end up with a botched job. At AR Powder Coating, we have years of experience that allows us to foresee problems not only with outgassing, but the many other issues that can crop up during a powder coating job.
Our pre-treatment process for powder coating involves a DI rinse, degreaser, iron phosphate, and a sealer and our experience working with a variety of powder coating materials means we’ll always get the right thickness the first time. Our high degree of professionalism, therefore, eliminates the potential for human error caused outgassing. You can also trust us to know what to do if you bring in a cast metal or galvanized steel object so that you get that object back with the exceptional quality that you expect from a team of professionals.
If you are looking to have a powder coating job complete, please feel free to contact us today with any question you have. We’ll be glad to help and look forward to doing business with you.