The Shop > Finishing

Grit Blasting and Moisture

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vtsteam:
oops, cross posted. I see it was only one bag.

I used to dry wood chips on the stove in a cast iron pan and measure weight before and after to get moisture content.

awemawson:
Steve,

This is not sand but Calcium Silicate manufactured grit. Blasting with sand has been made illegal in the UK for some years due to silicosis problems induced by the free silica in the sand.

Crushed glass is becoming quite popular but I've never had the opportunity to use it. To be honest the grit I'm using is not the grit of choice for blasting steel work - it's meant for stonework and brickwork. But as I have a large pile of 37 kG  sacks of the stuff I'll use it up before buying anything else. It must be old stock, as the large sacks are now also banned for handling reasons  :bugeye:

Large areas of my farmyard are becoming quite covered in the stuff  :lol:

Jonny:
Interesting I have had no end of the same trouble since changing media in a siphon based setup.
Do have a cheap pressure pot but never used it in 9 years.

True shouldn't use any form of sand but have been using kids playing sand since 1999 until last year. Rarely a problem after manually drying.

Changed gun, hose and pickup to a pro from http://www.angloscotabrasives.co.uk/
Same symptoms. Slightly better was junking above elbow and 15mm valve for a smoother stainless jobby but still have problems. Have to fire blast gun down the siphon outlet every few mins forcing it up the pipe. I also have to use bare minimum media not exerting extra pressure in the bend and pipework.
It had crossed my mind before the heat been passed in to the media then cooling off generating moisture. It was ok at first then bought two more large bags and chucked the lot in - worked.


If I leave the lid open its usually fine or better when surrounding air is not as damp ie summer.
Never checked dampness since getting the three bags 60 to 120grit aluminium oxide but pretty certain your right.
Firing up compressor generates heat that will fill up the extra old compressor tank then via 1/2"bsp regulator filter and moisture trap, yards of 15mm copper plumbing tube via another trap. Air is still warm in second tank filled from empty unless I leave a good 10 mins.

I'll let you know tomorrow I'll try drying some media.

PekkaNF:
Moist grit might be a problem, but I have had more problems with moist compressed air. Even after a moisture trap. Clogs the bottom of pot easy.

Pekka

Arbalist:
I think that's the problem I had Pekka. Mostly my fault as I don't drain the compressor as often as I should.

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