if you have ever blasted with a 1/2" nozzle and 1200cfm ,then the 5hp is so painfully slow you just give up......another difficulty with small nozzles is water /condensation.....a single drop of water will block a tiny nozzle ,a stream of water in the grit wont affect a 3/8 nozzle.........Styoyovskis point is also important ......dont be decieved by a coarse grit ........fine abrasive dust actually cuts fastest on metal ,but the dust is very costly on removal and on equiptment wear......and more important ....it doesnt leave a "profile ",which is critically important with high build low volatiles coatings.
We use I think 220 grit aluminum oxide and the wear on the equipment is insane. We use a Clemco pressure pot we got second hand and blast inside of a couple of shipping containers with supplied breathing air from a regenerative blower (getting breathing air from the compressor is dumb IMO) and three large fans exhausting outside.
At first we were having to do repair every 10 hours of blasting. The bearings in the belt drive fans seized, the pulleys and belts wore beyond usability, the metering valve ate itself, all of the blowoff hardware failed multiple times, the inlet valve stuck, the pilot valve failed after the original unit failed, the hoses ate themselves, the couplers ate themselves, the wires got blasted, etc.
We now do maintenance every three months. These are the key things that allow us to do this:
All Clemco valves, except for the metering valves, are removed. The inlet valve is replaced with an oversized solenoid. The outlet valve is made of a custom pilot operated diaphragm valve, that the diaphragm can easily be changed out, as it does wear, but there are no moving parts to stick. Because the pilot is handled by a solenoid switching clean air into the back of the diaphragm, there is no debris from the outlet that can get into any of the small ports. The orifices in the blowoff valve that drains the tank pressure are 3/16" in diameter to prevent clogging.
Our compressor has a refrigerated air dryer. This greatly reduces clumping and plugs.
We removed all quick couplers in the blast line. Only barb fittings into the hose. The nozzle holder is upgraded to metal, and we have a process to cut the hose exactly square so it butts to the nozzle perfectly. The nozzles only last about 6 months on 30 hours/week blasting until the orifice is too large for the compressor to keep up.
We have a high flow regulator set to 50 psi. No need to have the pressure any higher than that for our stuff. It just gets louder and makes a rougher profile that is hard to cut.
We have 3d printed or metal bearing shrouds, and greatly oversized belts and pulleys to keep the fans running as long as possible. We run the motors off of a VFD at 50% of their rated power.
The control cable is routed away from the base end of the hose, which is the first part to blow through. We cut the hose back every 3 months if it has soft spots, which it usually does. I used Soow cable which has lasted 9 months so far but I will need to replace it next service interval. I'm considering using 1/4" hydraulic hose to armor it, and I want to make a new deadman switch anyway.
All of our paddle and switch endeavors failed and we just use a milspec waterproof switch from McMaster Carr that was very expensive. It's not a deadman switch, which I don't like, but its very uncomfortable to hold a paddle for several hours, as you really need to be able to switch your grip up a lot. Anyone in the blast room is well protected by PPE, and power and air can be shut off externally so it's unlikely to lead to injury. The whip is securely hooked to the ceiling so it can't flail around too far. (It can be easily unhooked for large parts).
We also have to replace the expanded steel every three months, as it gets blasted into nothing. Might switch to a formed plate table.
Breathing air is handled by a regenerative blower (same thing as a pond blower). Use pond hose, which is smooth on the inside. Corrugated hose screams in your ear. We bleed off excess pressure and the operator can control how much airflow he gets. It ranges from nothing to sticking your head out the window at 85mph. It pulls clean air from far outside and doesn't heat it up much at all. The inlet is raised and shrouded to protect it from rain, dust, exhaust, and pranks.
The floor is armored with steel plate.
We are very controlling about what we do and do not allow into the booth. Spray painted or powder coated items are okay, but never anything greasy or with sealant. At an old job they patched holes in their makeshift booth with RTV silicone to keep dust contained. It caused huge fisheye problems for weeks and had to be stripped completely. Silicone is bad for powder coat.
Cheap LED lights need replacing. About 2 of 12 go out every three months, but the kind with switches on the cord die very quickly from sand ingress.
I probably forgot a ton of stuff, but yeah, the machinery gets eaten during operation big time. We'll likely have to replace our pressure pot soon due to wear, at which point I'll probably use another regen blower to make a suction lift so sweeping and shoveling sand becomes unnecessary. I could probably also just put a door in the bottom of a suspended shop vac.
