"Sand" Blasting


Blast Media

Let me start off by saying sand blasting is sort of a misnomer these days. Why, because I don't really use sand. These days there are a variety of blast media in use such as:

Compressor

First, you need a compressor. Most blast guns need at least 10-12 cfm @90 psi worth of air pressure to enable them to pick up the blast media through their suction tube and spray it against an object with sufficent force to remove rust and scale. Before buying a compressor, make sure it can deliver the necessary quantity of air. Most of the small "hot dog" or "pancake" compressors just can't handle it. Many of the 20 gallon tank compressors these days won't do the job either. My wife and I bought a 20 gallon Coleman compressor 25 years ago to handle her pottery work. When I hooked it up to my first blast cabinet it worked just fine. Eventually it gave out and I had to buy a new compressor. Because I didn't RTFM I assumed (yes it made an ass out of me) it would work. No, not even close. So I bought a 20 gallon tank model at Harbor Freight figuring (wrong again) that all 20 gallon compressors could put out enough air. Next up Tractor Supply for a 60 gallon Porter-Cable. I finally got smart and checked the air output capacity and it fit the bill.

Next lesson. Smaller compressors come complete with tank pressure guage, regulator to adjust the outgoing pressure, and a outgoing pressure guage. Apparently not the big boys. Apparently they're meant to be sold to professionals who know what they're doing. After getting mine home and unwrapped I went to attach the air hose. Whoa Betsy; there's this big hole in the side of the tank and no place to screw in the ¼ " coupler for the hose. Now I came to the part no one likes: Read The Fine Manual! Next stop, my local Hose Power store. They fixed me up with a regulator, guage, and assorted nipples and adapters. A little teflon tape and they were soon assembled.

Next lesson. All those nice smaller, hobbiest friendly compressors come with an electrical cord with a plug conveniently attached to the end. Not this one! First it needed 220 volts. Not a big deal, my TIG runs on 220. However, the amperage is different. And as any electrician knows with 220, different amperage, sometimes different plug (you ought to see the 110 amp plug). So another trip to Home Depot for some outdoor electrical cord and I wired the compressor directly into the service box with it's own circuit breaker.

Checked the oil level. Drum roll please .... it works! The tank filled and it dutifully shut off.

Blast Cabinet

Unless you want to spray blast media all over hell's half acre you'll need a blast cabinet. It's basically a box to contain and catch the media and keep the dust down to a dull roar. A light inside the cabinet is necessary addition (if the cabinet didn't come with one) and a vacuum system is a really nice to have. During operation the media and dust makes viewing through the view port problematic at best. Cabinets come with two rubber gloved ports so you can put your hands inside the cabinet during operation to handle the item being cleaned and the blast gun. A word, the blast gun won't blast through the gloves and strip you skin down to the bone. Often I hold the object in my hand (inside the cabinet) and blast clean while I rotate it in my hand.

Cleaning with cold? (source: Dry Ice Blast Cleaning.com)

Yes, that's right! Cleaning with below freezing dry ice. This new development is quickly expanding around the world. One system uses small hard pellets of dry ice the size of rice shooting them out of a jet nozzle with compressed air. Yet the dry ice is softer than sand or glass beads, so it doesn't spoil the substrata. It works somewhat like sandblasting or high-pressure water or steam blasting, but with different results - often better. The frigid temperature of the dry ice -109.3°F or -78.5°C "exploding" against the material to be removed, causes it to shrink and loose adhesion from its sub surface. Additionally when some of of dry ice penetrates through the material to be removed, it comes in contact with the underlying surface. The warmer sub surface causes the dry ice to convert back into carbon dioxide gas. This gas has 800 times greater volume and spreads out underneath the material which speeds up its removal. Paint, oil, grease, asphalt, tar, decals, soot, dirt, ink, resins, jet exhaust tars, and adhesives, are some of the materials removed by this procedure. Only the removed material must be disposed of, as the dry ice sublimes into the atmosphere. Another system shaves dry ice off a block of dry ice and then sprays it in a wider pattern cleaning faster than sand blasting ever could.




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