A rust spot on car’s body panel that needs to be sandblasted.
As you may know, sandblasting thin metal such as body panels of a car can cause some warping issues. A recent customer contacted me asking if it is caused by heat created from the abrasive or from peening of the abrasive impacting the sheet metal.
When he realized sandblasting can warp sheet metal in the industry, he was told it was due to heat and another person said it was from peening. I have also read online that others state that sheet metal warps due to peening, not heat because the compressed air cools it.
Sheet Metal Warping Because of Heat & Peening of Sandblast Abrasive
In my honest opinion, sheet metal may warp when sandblasting due to a little bit of both reasons.
When I experimented sandblasting etched designs into Plexi-Glass (plastic acrylic glass) with aluminum oxide abrasive, I noticed it actually start to melt the plastic. It got a bit soft. Although this doesn’t have the same heat build-up as steel sheet metal, it shows that sandblasting can cause heat to build-up.
Abrasive also heats up sheet metal to being more malleable so it peens easier. So even a little bit of heat can make peening more likely.
How to Prevent Sheet Metal from Warping While Blasting
If there is a concern with thin sheet metal warping, there are a few recommendations shown below:
- Don’t Concentrate on the Same Area Too Long. The recommended technique is to move the abrasive spray back and forth across the panel instead of directing it at one area until that spot is fully clean. Otherwise it causes heat to build up too much in that particular area.
- Blast at a 45 Degree Angle. It is also recommended to aim the abrasive spray at a 45 degree angle to reduce direct peening impact and heat build-up.
- Lower Air Pressures. A lower air pressure can help reduce impact heat and peening on thin sheet metal.
- Use Fine Abrasive Grits. Most people use course abrasive such as 70 grit or larger. A finer grit of 150 or 180 may reduce peening. I am not sure if it would reduce or increase heat build-up.
- Use Softer Abrasives. Aggressive abrasives like coal slag or aluminum oxide generates more heat and peening. If there isn’t a lot of rust on the sheet metal, softer abrasives like walnut shell, soda blast, crushed glass or plastic beads are sometimes used to reduce warping of sheet metal.
Just one of two of the above suggestions can prevent your sandblaster from warping sheet metal. If you have other suggestions to reduce sheet metal from warping while blasting, please leave a comment below.
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Good Article!!!
I have found what works best for me when blasting delicate parts, and I consider sheet metal delicate. I use crushed glass, plastic media, or washed beach sand.
Dustless blasting warps as well, I own one, they are crazy when they advertise saying no warping, I’ve had to replace a few hoods and that was using crushed glass, low pressure at a 45%
Dale, thanks for the comment. That is interesting to know, especially with low pressure. The only other thing would be to not concentrate in one area too long, but we all know it takes a lot longer to remove paint that way.
If you are just removing paint, I bet using a paint stripper, then blasting at even lower pressures would do the trick. it will just fly off with ease. Those chemicals are nasty to work with but I think they have a less hazardous product on the market these days.
@Kent, these are some great suggestions. I forgot about crushed glass and have updated the article with your suggestion. Thanks!