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Kevin in NJ · 08-29-2013, 05:59 AM

Here are some facts to understand about the blasting process.

First and foremost, warpage is NOT caused by heat.
To get heat warpage you need to get the metal up around 500 degrees. Not going to happen when you have a blast of expanding air. Keep in mind cooling done by air conditioning is caused by expansion of a liquid to a gas.

Warpage is caused by too much energy from the sand beating against the surface of the metal. Too much energy can be caused by to much velocity of small particles or too many small particles at a slower speed. So too much pressure or too much sand in the stream are what cause damage. I equate it to hammers. If one big hammer hits your head or a box of little hammers hit your head it is going to hurt real bad.

The damage is nasty. You are causing the surface of the metal to expand. That is why it creates a bulge towards the stream. There is no good repair for this problem as you can not shrink the just the surface. If you try to shrink the surface you will shrink the full thickness of the metal and now the back side is too short and the expanded surface is normal.

So in your discussions with the blasting people you need to ask questions. If they tell you it is heat that causes the problem then they just do not understand the physics of the process. Run away. If they tell you they control the pressure and control the amount of material in the stream then you are with someone that understands the process. The pressure and quantity are dependent on the media type.

My brother and I have successfully blasted 4 cars with 40 psi and just enough sand in the stream to be seen. It took a while, but NO damage to the sheet metal. We even tried to damage a piece of thinner French metal and could not do it.

Some of the cheap syphon blasters are bad because they do not regulate the amount of media in the stream. They will be more likely to cause damage even at low pressures.

Lastly, the golden rule of blasting.
The media will go everywhere and anywhere no matter how much you think you covered or sealed it. You will astonished by the amount of stuff that still comes out even though you think you got it all out.

08-29-2013, 05:59 AM	#9
Kevin in NJ Senior Member Join Date: May 2010 Location: South East NJ Posts: 3,398	Re: Body sandblasting Here are some facts to understand about the blasting process. First and foremost, warpage is NOT caused by heat. To get heat warpage you need to get the metal up around 500 degrees. Not going to happen when you have a blast of expanding air. Keep in mind cooling done by air conditioning is caused by expansion of a liquid to a gas. Warpage is caused by too much energy from the sand beating against the surface of the metal. Too much energy can be caused by to much velocity of small particles or too many small particles at a slower speed. So too much pressure or too much sand in the stream are what cause damage. I equate it to hammers. If one big hammer hits your head or a box of little hammers hit your head it is going to hurt real bad. The damage is nasty. You are causing the surface of the metal to expand. That is why it creates a bulge towards the stream. There is no good repair for this problem as you can not shrink the just the surface. If you try to shrink the surface you will shrink the full thickness of the metal and now the back side is too short and the expanded surface is normal. So in your discussions with the blasting people you need to ask questions. If they tell you it is heat that causes the problem then they just do not understand the physics of the process. Run away. If they tell you they control the pressure and control the amount of material in the stream then you are with someone that understands the process. The pressure and quantity are dependent on the media type. My brother and I have successfully blasted 4 cars with 40 psi and just enough sand in the stream to be seen. It took a while, but NO damage to the sheet metal. We even tried to damage a piece of thinner French metal and could not do it. Some of the cheap syphon blasters are bad because they do not regulate the amount of media in the stream. They will be more likely to cause damage even at low pressures. Lastly, the golden rule of blasting. The media will go everywhere and anywhere no matter how much you think you covered or sealed it. You will astonished by the amount of stuff that still comes out even though you think you got it all out.