We hate pinholes. And if you’re reading this blog post, we’re guessing you do too. Pinholes have many causes, so it could be that after years of coating a part with the exact same process, suddenly you have a pinhole problem.
Want to get to the bottom of your pinhole problem fast? Systematically go through our checklist of causes, in the order listed.
If the seasons have changed and suddenly you’ve got a pinhole problem, surface humidity may be to blame. Some coatings such as Xylan and other PTFE products are sensitive to humidity and may show pinholes when the temperature of the part is below dew point.
Solution: Easy answer here - preheat the part to above dew point.
This is the most well-known cause of pinholes. For every 100 degrees that you raise the temperature of a part, gasses trapped inside the substrate will double in volume. That’s why, during the curing process, it’s common for gasses trapped inside the substrate to push out and escape through the surface of the part, creating pinholes.
Solution: Preheating is the most common solution to this problem, although with some parts it may be impossible to preheat them enough to get all the gasses out. In this case. it’s time to look at the quality of the substrate.
Contamination is the number one cause of pinholes, and most of the time, it’s the air quality that you’ll want to pay attention to. The big three sources of pinhole-causing contamination are moisture, particulates, and oil.
Solution: There are a number of places to start looking for a contamination problem, but we’d suggest looking at the air filtration system. Make sure that the air is dry, filtered, and that there’s a good working oil separator in the filter. After that, check out the conditions of the spray environment and the oven. A environmentally controlled application room may be required.
If the application technique isn’t great, or simply if the coating is too thin, you’re going to get pinholes.
Solution: Increase the thickness of the coating, if possible. Also, make sure you’re using an experienced coater who is well-trained on your part. Application technique makes a difference!
It’s Not the Coating
Remember this: it’s extremely uncommon for a coating itself to cause pinholes. So if you have a coating that you’re otherwise satisfied with, change everything else first before you change the coating itself. If you can’t eliminate the problem using the coating you have, it’s unlikely that changing the coating will help (because the conditions causing the pinholes will still be present.)
Because pinholes are such an important issue, we check pinhole-critical parts before they leave the shop. To do this, we use a Holiday Detector, which was created for the purpose of detecting pinholes and porosity, and is the best tool for the job. The Holiday Detector uses water and runs from 12 - 90 volts across the surface of the part to find pinholes. If you part has a pinhole, the Holiday Detector is the most efficient and effective way to find it.
Get Rid of your Pinhole Problem in 4 Simple Steps
AIC Staff Writers, November 2013
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