Bead blasting help

I

Iverson Knives

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Feb 16, 2010
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237
Hi folks, I recently purchased a blast cabinet and compressor to try my hand at this type of finishing. I set the compressor at 100 psi and began with med. glass bead using an 1/8" nozzle. On a heat treated SS blade there was very little effect if any but on 6AL4V it made it cloudy but did not remove much if any of the handling marks present when I buy it. Not a very nice look.
THEN I removed the glass beads and put in silica sand everything else the same. The finish on the blade was a little courser than I wanted but thought it might be acceptable until I saw that I had warped the shit out of it. Bad deal. I did try the titanium and it also warped that however that was a scrap, the blade was not! I turned everything off and here I am begging for help. Any advice would be appreciated.
Thanks, Gene
 
Do not rely on glass bead blasting to remove "handling marks".

The glass bead bounce off the steel like little hammers to leave a nice finish.

Chances are you might not have enough media flow through your gun.

What brand of cabinet did you buy?
 
I'm not sure if there is a brand name...Chinese though. It is sturdy with a good seal on the lid, has a typical looking gun with a 3/4" hose that has a fitting with multiple holes that mechanically connects to the bottom of the hopper.
Not sure where gravity flow could be improved??
 
When the media comes out of the gun is it a good flow?

The amount of flow coming out of the nozzle makes a huge difference...little flow...little work, more flow...more work.
 
I probably have the same type cabinet you have - Harbor Freight table top. Get a piece of stainless tube with the same ID as the hose. Bend it in a U with about 8" of straight on 1 side of the U and about 2" of straight on the other side of the U. Drill a 1/4" cross hole at the low point of the U. Take the straight pipe on the end of the hose which came with the gun off and throw it away. Connect the short end of the tube to the hose. Keep the long end of the tube above the sand level. You are now pulling air in through the long end of the tube and sand in thru the cross drilled hole in the U of the tube. This will give you a much higher flow of sand. I am running it at 100 psi.

I use Grainger P/N 5WO22 on Rc60 S35VN to get a nice matt finish. If it is too coarse, use 3M ultra fine sanding pad to knock the tops off the finish.

The only problem I have is the dust inside the cabinet. I have a shop vac hooked up to the exhaust port but I still have to stop blasting every few seconds to let the dust clear out. Anyone have any thoughts on how to exhaust the dust better?

Tim
 
the "last" company i managed was a powder-coat firm, blasting is always the killer....the more CFM of air the more work you do, in our wheel cabinet (could hold a 22" rim) we were running a screw compressor that gave aprox 125 CFM @ 110 PSI, depending what was being blasted (substrate metal & finish required) media was changed, full clean down then re-loaded. pressure needs to match media.
As for dust clearance, are you in a built-up area? if not a 4" dust collector for a wood shop is great (am sure harbor freight sell them) but if you have local neighbors look at a "cyclone" filter after the blower. just my 2%
 
the "last" company i managed was a powder-coat firm, blasting is always the killer....the more CFM of air the more work you do, in our wheel cabinet (could hold a 22" rim) we were running a screw compressor that gave aprox 125 CFM @ 110 PSI, depending what was being blasted (substrate metal & finish required) media was changed, full clean down then re-loaded. pressure needs to match media.
As for dust clearance, are you in a built-up area? if not a 4" dust collector for a wood shop is great (am sure harbor freight sell them) but if you have local neighbors look at a "cyclone" filter after the blower. just my 2%
 
Wolf has the real answer.

100PSI isn't what you need most...it is high CFM. I can make 100 PSI with a bicycle pump....but you can't sandblast with it.

It takes a good size compressor delivering sufficient volume to blast finish effectively. A large air storage tank should be part of that mix. A littler HF compressor that has 4CFM@100PSI won't do much. 10CFM@100PSI is pretty much the lower limit.
 
I've done some experimenting with blast cabinet finishes and I have learned that I have a lot more to learn. I have the large freestanding cabinet from Harbor Freight. I've completely re-worked it with a quality gun, good sealing and a foot activated air switch. My compressor provides 16cfm at 90psi. I first tried #80 silicon carbide @ 90psi on 440C at 59hrc machine finished with an emory/cork belt. It was too aggressive; turned the blade very dull gray with a lot of texture. Next I lowered the pressure to 40psi. This was better in that the etch was not as deep and the color was slightly brighter but, it was still not the smooth sheen that I really wanted. I cleaned the cabinet out and added 50lbs of #80 glass bead. I started at 50psi and saw minimal effect on the hardened steel. I pushed the pressure up to 100psi and the results were still minimal. I also tried the glass bead on some polished 416 at 80psi. That gave me a beautiful satin finish!

At this point, I am thinking that #120 aluminum oxide might be the way to go for hardened blades. I'm leaning toward buying a second cabinet so I can run the glass bead for bolsters and such and blast the blades in something more aggressive.

Bob
 
Bob,
Try the Grainger media. It is a mix of Aluminum Oxide and glass beads. Try it before you spend the money to buy a second cabinet.
Tim
 
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