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Bead blasting advice please

Greetings All, I have a customer who brought me some aluminum castings to repair that required welding. After welding up several deep gouges and grinding the welds flush the repaired surface doesn't resemble the original cast surface. The customer knew this would happen but would like it if I could make the repairs look like the original casting. I have tried glass bead and walnut shells but the finish is still too fine. At the same time the finish is also absorbent. So the glass beads are too sharp.The original cast surface shows clearly that the parts were sand castings and I'm wondering if steel shot or bead media might be the best to use to copy the surface. I will be blasting the complete surface of the parts to help disguise the repairs. So, can anybody point me in the right direction? Thanks, Eric

Reply to
etpm
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I was able to mimic the texture in cast iron with a needle scaler. It was a long time ago and I don't recall anything special about the repair except I used pretty low air pressure. Steve

Reply to
Up North

Try low pressure (30-40psi) and coal slag 60-120 grit, just flash the surface and it should darken a bit. Coal slag cuts aluminum FAST.

Matt

Reply to
matthew maguire

Thanks Steve. My neighbor has one of those. I'll give it a try. Eric

Reply to
etpm

That's the problem he's having now from all indications. He commented on the porous surface.

No cutting action is desired for this operation, just blending of existing surfaces. Peening is adequate

If the proper size of glass bead is coupled with the proper air pressure, there will be no cutting. Glass bead peens, but if it becomes fractured, it begins to cut. It's obvious when it does, for it changes appearance. Glass beads in good condition are a glossy off white color. As they begin to break down, they shift to a more white color, more opaque, and they begin cutting, and yielding considerable dust. Glass bead that is functioning properly yields no dusting.

Harold

Reply to
Harold and Susan Vordos

Yup, I haven't tried to blend cast/weld aluminum that I can remember, just thought the sharp pitting caused by black beauty might approximate a cast surface, and I have used it with stainless and it seemed to change things to a more uniform dull grey color, with hot work tool steel you have a tough time telling I've been there.

Don't use the beads anymore, most of my abrasive work is de-scale or de-oxidize, dry-hone or really peen. For these things I use coal slag, granite, stainless grit and steel shot.

It was just a thought... but after reading the other post, a needle scaler at a sharp angle should work well also.

Matt

Reply to
matthew maguire

Greetings Matt, What I'm trying to do is peen the surface. I don't want to cut the surface. You mentioned coal slag and I've never heard of it. I do use a black abrasive sometimes that is really sharp and cuts fast. I wonder if it is coal slag. Thanks, Eric

Reply to
etpm

Greetings Harold, The glass bead I'm using now is so fine it almost flows like water. Maybe I need to switch to a larger size. I will try lowering the pressure too. Could be it's cutting because the pressure is too high and the bead is breaking up. There has been no color change though. Thanks, Eric

Reply to
etpm

I just used GunKote on a pistol. For prep I expected to glass bead it. In the instructions for the GunKote produ ct, it recommended roughening the surface by sand blasting and a few other means. It specifically said NOT to bead blast, because it peens the surface and closes the pores. I found that a bit unusual.

BTW, I wend ahead and glass beaded it. The resultant surface certainly looked rough, and not peened.

Reply to
RB

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