I’ve learned quite a few things about soda blasting since I bought the cabinet a few weeks ago. I’m getting really good results now, so for the curious here’s how I’ve sorted things out. (Excuse the funny lines in the photo. I had to stitch together two different images, and I’m not exactly a photoshop wizard.)
Bicarbonate of soda is hydrophilic. The stuff will soak up humidity and when it does it clogs the blasting gun until it dries out again. When it’s done drying, it’ll be in hardish clump that will need to be broken up. I’m running the blasting gun at about 90 psi, which means my little 13-gallon Campbell-Hausfeld compressor was running all the time when I was blasting. Compressing air generates a lot of heat (Boyle’s Law), and hot air can absorb more moisture than cold air. When the compressor cycles every now and then the compressor tank and lines remain cold and the moisture can condense on the tank wall and make its way to the drain. But when the compressor runs all the time it eventually gets hot all over, leaving no where for the moisture to condense.
The first fix for this problem was an increase in compressor tank capacity. I found a used, 33-gallon, Craftsman compressor on Craigslist for $75. I’m now running both compressors in parallel, so I’ve essentially got a 46 gallon capacity and two compressor motors. With the two compressors’ regulators set to the exact same pressure they cycle on and off independently: sometimes neither run, sometimes one or the other, and sometimes both. This means each tank gets a chance to cool a bit between cycles, so the moisture can condense.
My second fix was to run a bunch of copper piping from the compressors to the blasting cabinet. Copper is great at conducting heat (which is why they put it on the bottoms of high-end cookware) so the copper lines allow another path for heat to escape the system, which means more moisture condensation in the lines. I ran the lines with a slight down slope (some Googling suggested a 1″ drop for each 10′ of line) so the condensation can be pulled by gravity to the low point. Now for the real trick: at the lowest point I installed a T for a drip leg. Condensed water collects there and runs into a nifty moisture filter I bought from McMaster-Carr. This little gizmo is basically a 3 oz. bowl for water to collect, and it has a float that opens a valve in the bottom whenever the bowl fills, blowing out the collected water like a delightfully wet fart.
The result of these two improvements is that my in-line moisture filter is barely collecting any water now since most moisture ends up condensing in the compressor tanks or finding its way to the the drip leg, which means the soda is drier, which means my blaster works much much better. This wasn’t just some academic exercise, by the way; when I say the blaster works better now I mean it works a LOT better. I’m cutting through 3 or 4 times the paint on the Ducati piston barrel I’m working on than I was before I added the 2nd compressor or the copper plumbing with the drip leg, and with no more effort.
UPDATE: I’ve replaced the 2 portable compressors with a big Ingersoll Rand 80 gallon, 2-stage air compressor. The blasting cabinet is in the opposite corner of the garage from the compressor, so I ran 3/4″ copper up, over, down, along, into the drip leg, and then to the blasting cabinet’s regulator. Now I’m getting moisture in the tank, very little in the drip leg, and almost none in the separator for the regulator.
UPDATE: I added several LED lights inside the cabinet. These are under cabinet lights I found at Lowes, intended for kitchens, and the best part is you can daisy chain them together. I tapped into the switch for the cabinet’s original light, which means throwing that switch now gets you the original fluorescent lights as well as the LEDs. I also realized that since I’m only using this cabinet for soda, and since soda doesn’t etch glass, there’s no need for the plastic sheet inside the cabinet window obscuring my view. Between removing that and adding the lights visibility is greatly improved.
UPDATE: When I first tried this soda blasting business I originally bought a portable unit from Harbor Freight. It works really well but made helluva mess. My inspiration for buying the cabinet was to keep the mess contained, but the results were not as good. The reason for this is the portable unit is a pressure pot, whereas the cabinet uses a siphon system. In other words, the pressure pot’s soda is forced through the system with the compressed air, whereas the cabinet’s system (which was intended for sand, walnut shell, glass bead, etc.) uses suction to draw some blasting material into the compressed air stream. The pressure pot setup simply pushes more soda through, so it works faster, but it’s also less precise. So I’ve now combined the two. I took the crappy original gun from the cabinet (so I’d have a trigger) and ran the outlet hose from the pot through a hole in the cabinet and into the base of the gun where you’d normally attach the compressed air line. The soda isn’t aggressive enough to destroy the innards of the gun. All you have to do then is cap off the gun’s original siphon line. Now I can get a much higher volume of soda into the cabinet while dropping the air pressure to just 60 psi. The drawback is this gun isn’t very precise. So, when I first toss a part into the blaster I hit it with the pressure pot gun at 60psi and take off 95% of the paint and/or gunk. Then I run the pressure back up to about 100psi and go over the part again with the cabinet’s siphon gun to really get into the nooks and crannies. Overall, I’d say I’m cleaning parts in half the time now.
One other thing to keep in mind is that soda is friable; it’s not an abrasive. Only a little material is removed by scouring when the soda impacts it. Most material is removed when the soda impacts and then bursts into smaller fragments, popping the material off the part you’re cleaning. As a result, soda loses its efficacy once it’s gone through your blasting gun once or twice because it’s can no longer break down into smaller pieces. When it reaches the consistency of sifted flour, it’s past its prime and should be discarded.
The stock clutch basket weighs 2.452 lbs. I wiped off the clutch residue before weighing it. The Barnett basket going on weighs 0.992 lbs.
