Cleaning by blasting

[Overkill]

I've managed to pick up a large blast cabinet, large enough to get doors and fenders in - barely. I'm now looking at what media to use.

I'm staying away from soda because of the paint adhesion issues. Just don't want to get into the repeated cleaning required.

Walnuts and plastic media will remove paint, but won't remove rust from what my supplier is telling me. He says for the rust (rust pitting on bare original metal) on my 32 Ford truck parts, I should go with 80 grit garnet and turn the pressure down to 40PSI. I also realize that I need to keep the blasting at a low angle, not 90 degrees to the panel.

Anyone with experience that can help guide me as to which media, technique and pressure to use?

[Marty Comstock]

All depends on your goals, meaning, what parts and type of blasting are you going to be doing? bodypanels primarily with little rust, or are you looking at derusting certian parts?

I like an aggressive approach (aluminum oxide mixed with glass beads) but this can wear out the gun pretty fast, so I try to not put as much aluminum oxide in as I want to. Derusts ok, just slower.

For bigger stuff, panels, what have you, i use the outside blaster, so my approach may not apply well.

my .02

Marty

[Overkill]

Fenders, doors, running boards, all with fairly good rust to them. Some paint, some pits. Can clean them up with scotch brite paint removal disc, but it doesn't get the pits, and in the cracks and crevises - like on the inside edge of the wire bead area. Blasting seems to be the best, but also want to stay away from any warpage. Everything I'm asking about here is sheet metal.

I know some of the blasting places use plastic media, but the supplier told me it won't remove rust or plastic fillers. Requires fine garnet for that.

Read up on soda blasting, and with the problems that have been noted with cleaning it off afterwards, just decided to stay away from it.

Picked up a large blast cabinet 3'x3'x7' for $400. Does need some work, but I think it's a pretty good deal. Not big enough for everything, but I can't afford the 10x20 blast room the guy has for sale - nor do I have a place to put it.

[JasonJamesWrenn]

i just recently got one as well I have sand in it... sucks I need to change to somthn like marty said..

[Streetwerkz]

We blast with aluminum oxide
60-80 grit (80 grit for sheet metal)
40 psi for sheet metal
8"-12" gun to part distance
40°-60° gun angle
travel speed comes with learning to read the panel
an air dryer is a must, wet media is useless & will clog up the entire blast system

generally we will werk a 12"x12" area at a time so as to not build any heat, or distort the panel with air pressure

We prefer to remove layers as opposed to removing 3-4 coats of paint from one area.

I do not recommend the use of plastic media, or glass bead as they both leave behind microscopic streaks on the substrate which will promote coating defects & or failure.

Aluminum oxide werkz by hitting the panel & causing a microscopic "explosion" which removes the unwanted material.
Another benefit is that the aluminum oxide doesn't build or store heat in a significant amount which will help protect the panels from heat distortion.

[mutant]

I recently saw a restoration show where they used a new medium that would clean up metal nicely without damaging it. It was a form of crushed charcoal. I don't know much about it but maybe there's info out there.

[Overkill]

Does anyone have experience with copper slag? I know they've used it to replace sand due to silicosis.

[John Forbes]

Hi John,

I have a walk in booth that I use for glass and sometimes metal and my medium is silicon carbide 100 grit. I have tried garnet and aluminum oxide they work but I prefer silicon carbide because it seems to cut faster, longer and you don't need as much pressure, but it cost more. Large parts I just use the pressure pot outside with the finest grade of sand, under 40lbs pressure. Make sure you protect yourself, you don't want to be breathing that stuff.
Did you get a pressure pot and a dust collector with it ?

[Gudmundur]

since we ar talking aboud blasting i want to know have you used just drie sand has it anyproblems recedue left ore some problems . i have a huge amount of finecoars sand just on the property where i live just need to drie it

[Overkill]

I managed to PU two blast cabinets which I'm fastening together to make as single 3'x3'x7' cabinet with four glove holes. I'm using my extra large shop vac for dust removal, picking the dust up from the top, keeping the cabinet under negative pressure.

Where I came up with issues is regarding my compressor. It only makes 15 CFM, and for larger guns I needed about 50 CFM. The best rotary 10HP single phase machine I found only produces 46 CFM. So, I'm going with a smaller, pressure pot system, that uses small nozzles. I bought the large HF pressure pot unit used once for about 2/3 the price of new on craigslist.

When investigating media, I found out that plastic, walnut shell and soda will remove paint, and bondo, in some cases. However, it will not remove rust, which is one of the problems I deal with. Therefore, I decided to go with 80G glass beads. I also have 80G aluminum oxide, but it's more aggressive than the glass, so I'll stick with that.

I did try some of the black copper slag through the pressure pot. Works well, but very aggressive and leaves a rough surface on the metal.

With all of these items, I'll be running 40 to 60 PSI to keep the impact pressures down.

When discussing warping of the metal, I believe it's from several factors. The impact of the media, the amount of media and the heat thereby generated. When using large compressors with high CFM, and high pressures, just the impact of all those little rocks on a low crown panel can cause issues. Further, all that impact will cause the heat. So lowering the pressure, to reduce the force of the hit, is warranted. As is using the low blasting angles.

In my experiments, I found that with my lower CFM, and lower pressures, on flat panels, I'm not getting the heating nor the impact warping. However, I am careful with the blasting angle when I'm not in an area with a lot of shape. So I guess that there are some advantages to a small compressor and slow removal time....

Thanks for all the input.