sand blasting sheet metal is hell

[Tim Rostar]

Hey i just got back from a trip to hell or sand blasting my air shout on a newway ch 5hp engine.well i have a pressurised 40 lb sand blaster and i set the pressure low like 70 lb and i went to work about 4 inchs away and the metal is pretty solid and i did about quarter of it and took my blasting hat off and something looked bent but i said that cant be and the more i looked the worse i could see that i have alot of work straightening out this mess.I cant remember having sheet metal worp like this CAN I GET SOME ADVISE ON HOW TO CLEAN UP MY SHROUD .

[KeithW]

If you use much preasure at all sheet metal will warp like crazy, expecially flat pieces. Try a chemical rust stripper or electrolysis. Finish it up with the lowest pressure that will remove any rust that is left or just sand it.

You should see what a brass Wico mag cover does when you glass bead blast it.

keithw

[Harry]

I am certainly not an expert, but I've done some blasting. Increase your distance and be sure to blast at a 45 degree angle - not straight on. You evidently were making heat to warp it. Glass beads in a cabinet would be better.

Can't help you with the damage done.

[Joe Musser]

yep totally ruined a wico cover in my glass bead cabinet that way, but on the bright side I wanted a new set from Marks anyway

[Andrew Mackey]

for severe local warping, you need an oxy acetylene outfit. Heat the high spot in the center, about 1/4" in diameter, dull red. take away the torch as soon as hot, and quench with water. metal shrinkage should take out warp. practice on waste piece before trying on the good stuff, and do not try on galvanized! (Drive shaft shops use this technique to true shafts, and I have seen good body shops use the same techinque!
Andrew

[KeithW]

With the Wico cover I new it would be a problem so I lowered the pressure and increased the distance. I alternated doing the inside and the outside. I'd do one side till it started to warp then the other side till it straightened out. It does not warp it by heat, the metal is peened and streached on the side the media hits. Another method for heat shrinking is to heat a dime size spot red hot at witch point the metal will expand and dimple up. Thake a small hammer and tap the red hot dimple flat. As the metal cools it will draw in. It takes lots of time and dimples to shrink a large area.

keithw