I found sand blasting aluminum prior to powder coating is a big no-no.

[mcaswell]

Many years ago, I was given a lecture on how sandblasting actually works. When the media hits the surface at 90 degrees, the 'shot' actually explodes on the surface. It is this explosion which blows off the rust etc. This also accounts for all the dust and the media decreasing in size gradually. If the blaster is aimed at 45 degrees, the shot will 'slide' along the surface, doing much less damage, and actually polishing the surface.
Glass beads were never intended to explode, if you wanted that to happen, use a fine al oxide. Use the glass beads for polishing, not corrosion, paint removal ?

Perhaps the problem here is that the blaster needs to be angled to prevent the explosion, which would no doubtedly explain the smaller particles embedded in the pores?

[mtumbleson]

Originally Posted by caswell

Many years ago, I was given a lecture on how sandblasting actually works. When the media hits the surface at 90 degrees, the 'shot' actually explodes on the surface. It is this explosion which blows off the rust etc. This also accounts for all the dust and the media decreasing in size gradually. If the blaster is aimed at 45 degrees, the shot will 'slide' along the surface, doing much less damage, and actually polishing the surface.
Glass beads were never intended to explode, if you wanted that to happen, use a fine al oxide. Use the glass beads for polishing, not corrosion, paint removal ?

Perhaps the problem here is that the blaster needs to be angled to prevent the explosion, which would no doubtedly explain the smaller particles embedded in the pores?

The angle of the gun does make sense. I do hold the gun mostly at 90* when blasting, which could have been the problem. But, I never new any better until now.

I am curious about using other media, it would be interesting to see if the same thing happened with other media using the same technique.

As I mentioned earlier most of what I PC comes off my mill, so really what I'm doing is de-burring and cleaning up the machining marks, so there isn't any heavy deposits to remove. I do have a process down that gives me acceptable finishes but I would like to cut down on the time spent cleaning up the parts, as it's my least favorite thing to do.

[boink]

All I have ever known on bead blasting is to hit it at a 45 degree angle. at 90 degrees, you are pushing the bead back at the gun and the window and actually slowing down the speed of the media.

[c130herc]

I have been using coal slag to blast with and I added glass bead to thin it out so it would flow through the gun better. After adding the glass I have the “sand” in the powder.
Little bumps throughout the finish. I did 3 brackets and they all came out the same. I will not be using glass bead anymore. It is too much trouble. Slag works well and is cheap I just need a little larger nozzle opening to keep the clogging down.

[lgjhn]

I really find this thread quite interesting because there are some threads in the engine building forums on the net that discuss the "no-no" of blasting aluminum pistons for the same reason: engine failures have been traced back to media coming out of the pistons after heatup...even after what was thought to be the most thorough of cleanings prior to assembly. The recommendation in that arena is either soda blasting or dry ice blasting, then a good cleaning as both of those type of media dissolve in water....
Interesting thread and one to remember.....
Thanks guys!!

[mcaswell]

Another thought.
As an alternative to blasting, take a look at our SCRUBER WHEELS. These are 6 or 8" diam buffing wheels made of a sort of pan scrub (SCOTCHBRITE type) material. I would imagine this would give you a good preparation for powder., and it will certainly remove oxides and paint. Awkward areas might be a little tricky.

[mtumbleson]

Originally Posted by caswell

As an alternative to blasting, take a look at our SCRUBER WHEELS. These are 6 or 8" diam buffing wheels made of a sort of pan scrub

Looks like something I can use, thanks for the info. I'll pick one up and give it a try...

[BerkelUSA]

Good post ! - Keep it REAL

You will also find that IF you used glass-bead to clean aluminum and tried to TIG weld it that the welds will be horrible for the same reason.. Imbedded glass heats up, melts and makes a real pourous mess like mig-welding without the gas bottle turned ON..

Friend Hank had PC'd many an aluminum intake in his day.. The way he does it is pre-heat the intake first so it expands (as thats what aluminum does) and allow it to cool a little.. then powder it and stuff the thing back in the oven for a full 20 minutes at the 400-degrees.., This way the aluminum is not expanding faster than the powder. (he just said online)

Another thought is what about the other media's like Black Beauty or Walnut shells?, When welding after blasting with walnut shells if there is any debris in the way its burnt off from the heat of the welder alone.., Maybe pre-heating the part in the oven would do the same

The pads you talk of are made by 3M are awesome, Even more-so when smaller..

The smaller 2" OD ones kick (_!_) on an angle head grinder and can remove gasket matrial from a cylinder head in minutes!, But also know that if you dont move fast that they will also slice a nice groove in an aluminum head FAST.. so the idea is to WORK FAST with them.. Not "frantic" just fast.. taking only the bad material off and moving away from the area..

But the bigger ones (3"?) I didnt get very good results with because of the OD making the outer edges move slower and they wear faster (and too big for tight areas).., So stick with the smaller ones..

PS: The pads are called 3M RoLoc's

$0.002

Rob

[jimcarry]

Hey
how’s it going sand and bead blasting usually leaves a gray dull finish if you are looking for a bright finish after blasting try soda blasting Soda blasting is a process where a surface is cleaned, rust is removed, or coatings (of any kind) are stripped from the substrate (the surface beneath the material you are trying to remove). The soda blasting machine propels a bicarbonate-of-soda-based media via water or compressed air onto the surface to be cleaned. This process gently removes the material without harming the substrate and can be done wet or dry. This link explains soda and cob blasting in great detail

What to replace sand with (blasting) ?
This process is also food safe !!!!!!

[bp]

I have to reply by saying the "dirt" you speak of may not be dirt at all and could it possibly be 'Die Pick-up' from the extrusion process? If you are using a 6063 prime alloy extrusion you should not have a problem, but if you are using a hard alloy like 6061 or a low tempered aluminum such as a T-5 you may be seeing pick-up wich is misinterpeted for dirt.
Wipe your raw part lightly with your finger tip or toilet paper. If you feel small bumps or if it catches the paper it is most likely die pickup. At this point a light sanding and tach clothing will give a perfect finish.