Aluminum oxide for media blasting

[sftamx1]

Any pros or cons concerning aluminum oxide blasting? I have a mostly rust free '33 Terraplane convertible coupe body that needs old paint removed.

[unimogjohn]

Fast, but it will get into everything.  An inexperienced blaster may warp panels with the heat generated.  I would at least try an aviation stripper if it was me.   Something you can do yourself, piece by piece.   http://www.kleanstrip.com/product/aircraft-paint-remover

[Barry Wolk]

Agreed, remove the bulk of the paint with stripper and then media blast. Soda won't remove rust so you'll need something aggressive and aluminum oxide, or a mix, works best. Just don't spend too much time in one area. It's like welding, you need the heat to dissipate or you'll warp sheet metal.

[Restorer32]

The warping of sheet metal from blasting has nothing to do with heat. It is caused by the peening effect of the media hitting the surface, causing it to curve. Trust me on this, we sandblasted 48 hrs/week for about 20 years. If your car were in our shop we would use chemical stripper for as much of the paint removal as possible then sand blast the edges of doors, edges of fenders,and anywhere else chemicals could not be used. We have tried many strippers and the one from the hardware store seems to work as well as any. You can blast outside in 10 degree weather and flat panels will still warp if hit head on.

[Beltfed]

I refinish metal and have used aluminum oxide for years. Good stuff for some work and not others. The above suggestions IMHO are correct. Using aluminunim oxide on panels should be left to an experienced person. I would visit local basters in your local area and ask questions. Ask for references, they will let you know what the blaster can do. Asking your friends who they use could also work.

[sftamx1]

Thanks for sharing your knowledge. This blasting would be done professionaly by a company that does mainly auto bodies.

[Barry Wolk]

The warping of sheet metal from blasting has nothing to do with heat. It is caused by the peening effect of the media hitting the surface, causing it to curve. Trust me on this, we sandblasted 48 hrs/week for about 20 years. If your car were in our shop we would use chemical stripper for as much of the paint removal as possible then sand blast the edges of doors, edges of fenders,and anywhere else chemicals could not be used. We have tried many strippers and the one from the hardware store seems to work as well as any. You can blast outside in 10 degree weather and flat panels will still warp if hit head on.

I stand corrected. There's a lot of us that are wrong, then, as that's what I've always heard.

[Restorer32]

I know it is commonly thought that heat is the culprit but it isn't. Even in a relatively low pressure glass bead cabinet, which produces no detectable heat, it is easy to warp sheet metal if you try.

[JACK M]

I have had bodies and related parts dipped, I think that's the best for cleaning.

Does away with paint, bondo and rust everywhere.

I am not surprised that those 'rust free' cars aren't.

[JustDave]

i myself dont like blasting i know in some cases its necessary,i myself would use a chemical stripper,after stripping i would sand metal prep at least twice and then use a ppg product called dp40, i know theres alot of primers out there but ppg is a sealer more than a primer,shoot it over any dents or related panels needing metal work,after the metal work is finished respray all areas with the dp 40,at that time you can use a primer surfacer and start the prep work for paint,     dave

[Restorer32]

Many shops, ours included, are reluctant to work on any body that has been dipped, especially post war cars. The dipping process removes paint and primer from areas that may be impossible to access to reapply sealer or primer. Second problem is there is always a chance that a minute amount of the dipping solution will later escape from some inaccessible seam somewhere and ruin a freshly applied paint job.

[R Walling]

 I also do a lot of sandblasting commercially and use fine Black Beauty. It is very aggressive. A friend once wanted me to blast the fenders and hood off of a 55 Chrysler 300. I explained that it would warp it. It was rusted so bad that the owner said try it carefully and if it warps, there will be no loss.

 

 I stood back about 3' and went over the entire area very quickly many, many times.

 Eventually I got it clean with out warping, I was very surprised!

[Restorer32]

When we were blasting full time we would use fresh Black Beauty to do frames, wheels and other "heavy metal". Then as it wore out we would reuse it for lighter metal and finally, when it had become little more than dust, we would use it for sheet metal. Done carefully there is little danger of warping. We even blasted most parts, including sheet metal, of a Duesenberg. I enjoyed blasting. You see immediate results, unlike many other chores involving restoring old cars. We did a number of WWII era Stearman Biplane air  frames and landing gears for a local company that would build you one from surplus if you could afford it.

[Guest Skyking]

Many shops, ours included, are reluctant to work on any body that has been dipped, especially post war cars. The dipping process removes paint and primer from areas that may be impossible to access to reapply sealer or primer. Second problem is there is always a chance that a minute amount of the dipping solution will later escape from some inaccessible seam somewhere and ruin a freshly applied paint job.

I totally agree! Way too many nooks and crannies that will never be treated!

[JACK M]

I guess I am the other way on this.

Every time I have had something blasted it would seem that the media never quits coming out of the cracks.

[Restorer32]

True, but the media doesn't melt paint.

[JACK M]

Good point. I must be waiting long enough before working on stuff that it has time to evaporate. I have only dipped two cars but never had any problems.

They pressure wash everything after the dipping and neutralizing.

Edited October 29, 2015 by JACK M (see edit history)

[Restorer32]

There are pros and cons to about every technology.

[JACK M]

Yup

[Guest rwrogers11]

The warping of sheet metal from blasting has nothing to do with heat. It is caused by the peening effect of the media hitting the surface, causing it to curve. Trust me on this, we sandblasted 48 hrs/week for about 20 years. If your car were in our shop we would use chemical stripper for as much of the paint removal as possible then sand blast the edges of doors, edges of fenders,and anywhere else chemicals could not be used. We have tried many strippers and the one from the hardware store seems to work as well as any. You can blast outside in 10 degree weather and flat panels will still warp if hit head on.

This is very true.  We use the dustless blasting system which mixes water with the media and the myth is the water keeps the metal from warping.  Like I said, the myth...  Warping comes from too large of media and too high pressure, along with a blaster that doesn't know what they are doing.  The water is great, with our mobile system, we can roll right up to your house or location and blast.  The water keeps the dust cloud down and the neighbors happy.

 

Richard

RCT Mobile Blasting

[MikeC5]

The peening effect of the blast media causes compressive residual stress on the metal surface.  Imagine you had a very small ball peen hammer and covered the surface with hits, each making little dimples.  The metal is actually deformed a bit to create the dimples which means some material get squished outward from the dimple center (and down into the thickness).  Now imagine the dimples getting so dense they crowd into each other.  The squished metal in each bumps into squished metal from its neighbors and compressive stress results.  Since the opposite side of the metal has no stress there is an imbalance of force that causes the metal to warp.  If you tried it on a strip of metal, the unpeened side would end up being on the inside of the warp (curve).  Look up Almen strips to find out more.