We use 30/65 silica sand, is that too aggressive?
We had a customer buy us a big soda blaster to do their blasting with, it was glass bead and want to say 300-400 grit for stainless. We had a real hard time getting it to flow right even with a pressure differential between pot/hose and a vibrator on the pot.
Tex, don't get excited and go buy a soda blasting pot over this.
30/65 is way too aggressive for sign vinyl, but is just perfect for monument stencil that you'd use on redwood and HDU signage.
Soda blasters are usually set up with the ideal pressure differential system, so blasting with hard abrasive shouldn't be an issue. To reiterate: Yes, you can use hard abrasive in commercial soda blasters such as a Schmidt.
Abrasive flow is probably the number one issue everybody experiences, and making sure you have nearly 100 percent bone-dry compressed air is the first step. Aftercoolers, refrigerated dryers, coalescing filters and desiccant dryers each have their place, and there are reasons for using two or more at the same time.
Beyond that, the abrasive itself is largely responsible for its own flow through the pot. Sharp, angular (usually coarse) abrasive typically likes to "lock" together. Silica abrasive, however, is a winner in this category and usually flows very easily, since it isn't as sharp as aluminum oxide or some of the other exotic abrasives out there.
I've been at it nearly seventeen years, and I firmly believe the type of abrasive metering valve at the bottom of the pot is the key element to consistent flow. I know several manufacturers that place vibrators on their pots, and that's just downright sillyness....and it fatigues the metal as well. Of all the metering valve manufacturers, only two stand out: Empire (USA) and Saunders (England). They both utilize a pinch tube that provides a "straight shot" down and out through the bottom of the pot. All other configurations require the abrasive to go through some sort of zig zag path before making its way to the blast hose. Believe me, it really makes a difference.
I'm running a Clemco pot with an air-actuated (diaphragm) Empire Sure-Flow metering valve, shown below. It runs on a 3-way manual rotary air (valve) switch shown in the last photo. I start the blast air first, and then throw the abrasive switch once the blast air gets up to full speed. When I"m done blasting, I shut off the abrasive flow, then wait for the hose to clear and then shut off the blast air. This process eliminates the sputtering and surging associated with most blast pots starting up.
Again, the abrasive falls from the bottom of the pot in a perfectly straight line through the pinch tube valve and then into the jet stream of the blast hose. The cam-lock nipple is the "air inlet" side of the tee...it's also called the pusher hose. The blast hose connects on the opposite side of the nipple.
In the second photo, I was bench-testing the valve with an air hose to make sure it opened and closed correctly. When the valve is opened, the abrasive falls down through the large chamfered opening...which is another reason this type of valve is so crazy good. The hole leading into the pinch tube at the bottom of the large chamfer is approx. 7/8" diameter (outside diameter is a 2-inch pipe thread for reference).
Now the "bad" part...an OEM valve runs just north of $700. Mine paid for itself in just a day or two...seriously, it's that effective.
JB
