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Shotblaster and compressor question

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Andy.I

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Hi Chaps,

I have assembled a wet bead blaster which works extremely well on aluminium ally castings, except where the component is clogged with burnt-on oil or corroded, pitted and discoloured. With a bit of experimentation I discovered that giving the corroded components a pre-blast of fine crushed glass gives the perfect surface which can then be wet bead blasted to a finely peened finish.

Having looked at dry blasters I have become aware that they require much higher airflow from the compressor due to the fact that the media is delivered to the bun by being sucked up by the venturi effect of the gun, as opposed to a wet bead blaster where a slurry pump pumps the water and bead mix to the gun and compressed air is used to propel the jet.

I have looked through the well-known sources (Ebay, Amazon, Machine Mart etc) and a 220L dry blast cabinet seems to be the order of the day, but they they all seem to require 15-25CFM and my compressor is 14CFM:

Does anybody have any practical experience of using one of these blast cabinets and can they advise me whether my Clarke Boxer will be sufficient:

If it's on the weak side I think there are a couple of different mods to improve things:

1.) to expand the compressor's capacity by adding a 47kg (ca 100l) propane tank
2.) by modifying the hopper feed to the media pipe by introducing an air jet to drive the media up the pipe to the gun

Has anybody got experience of performing either of these types of modification, or indeed any others which might improve performance, please?
 

Spectric

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Hi there

With blasting it is down to sheer airflow, 25 CFM is not a lot in the world of shot blasting and although you have 14 you could try an extra tank, take longer to reach pressure but if you do it in shorter steps it could help.
 

clogs

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look on the MIG welding forum.....
there's a guy who's tuned one up for better efficiency.....or lower air consumption......

I did a few old tractors and car chassis......after burning out 2 big garage type comps
bought a road compressor with a 100 meters of hose (to keep it away from me).....
never a problem after that....
have a monster compressor now and a good session with the blast cabinet will keep it running constantly.....
 

Inspector

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1.) to expand the compressor's capacity by adding a 47kg (ca 100l) propane tank
I advise against using an old propane tank. The propane can be in the grain of the metal and leach out in time. You don't want have an air gas mix scooting along in your hoses. In all likelihood you'll get away with it but there is a chance you won't.

Pete
 

Deadeye

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I advise against using an old propane tank. The propane can be in the grain of the metal and leach out in time. You don't want have an air gas mix scooting along in your hoses. In all likelihood you'll get away with it but there is a chance you won't.

Pete
Really? Has there been a case of ignition? Propane will have miniscule solubility in metal, nowhere near enough to give the concentration in compressed air required for any sort of explosion. The lower flammability limit of propane in air is 2.1%; you're not going to get 2.1litres of propane "leaching out of metal" in a 100l tank. Actually I suspect you'd need a sensitive mass spectrometer to find *any*.
Happy to be wrong, but will be astonished if there's data supporting this concern.
 

Andy.I

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look on the MIG welding forum.....
there's a guy who's tuned one up for better efficiency.....or lower air consumption......
[Snip]
Thank you Frank, that's very interesting and it looks as if this might be the answer to my question; it looks as if the design of the blaster's media metering system is crude and inefficient and that with a simple modification the necessary working pressure can be reduced down as low as 25PSI. (y)
 
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