Bead / grit blasting compressors

I only have domestic single phase supply here at home in the UK. I use a 3HP single phase motor to run a small compressor. This, with a 150 litre
receiver, runs a medium sized grit blast cabinet for about 30 seconds before the pressure drops off and the compressor fails woefully to keep up with demand. i ran the same cabinet fine off a 10 HP 3 phase compressor elsewhere. I need to run this cabinet efficiently, and maybe even a small commercial blast pot for de rusting things like farm machinery in a blast room (read converted shipping container... :)). Would a towable diesel pneumatic road drill type compressor run these? I assume they have no receiver, so I am unsure if they would work, or if they could use a receiver. They all seem to run at around 7 bar maximum pressure, an example of one for sale on Ebay here in the UK is at:
http://cgi.ebay.co.uk/ATLAS-COPCO-ROAD-COMPRESSOR_W0QQitemZ320179548375QQihZ011QQcategoryZ22662QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Could I use such a thing? The only other alternative I can think of is to run a compressor off my small tractor PTO (Massey Ferguson 35, about 40 BHP). Thanks for any tips!
--
Best Regards,
Chris Wilson.
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You really need to quit talking about HP and tank size and start talking about CFM (cubic feet per minute) output at the pressure you need. (or equivalent metric measurement 1 CFM is about 28 liters per minute)
The usual small blast cabinets we see in the states want 10 to 15 cfm at a steady 100psi ( 7 bar) . Somewhat higher pressure works better but air consumption is pretty much linear with pressure. A full commercial grade unit suitable for bridges would need 10 times that.
You should be able to run your cabinet on a compressor with an honest 5hp motor. You may have to go to a slightly smaller nozzle to get the flow to balance well with the compressor. The engine driven towable units are all over the map in terms of output but I'd assume 50 cfm for a very small unit, 125 cfm for a larger unit would be a good starting point.
The size of the receiver tank is not very important in blasting applications. As long as the compressor has some sort of high pressure cutout, you should be good.
Chris Wilson wrote:

http://cgi.ebay.co.uk/ATLAS-COPCO-ROAD-COMPRESSOR_W0QQitemZ320179548375QQihZ011QQcategoryZ22662QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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Chris Wilson wrote:

http://cgi.ebay.co.uk/ATLAS-COPCO-ROAD-COMPRESSOR_W0QQitemZ320179548375QQihZ011QQcategoryZ22662QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
That would be serious overkill. And yet another infernal combustion engine to keep running. You should be able to find a single-phase compressor that will put out 13.5 cfm @ 90 psi. That's pretty much the minimum standard for a small blasting cabinet, and such compressors can be had here in the US at any hardware store.
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On Fri, 09 Nov 2007 15:57:00 -0600, Rex wrote:

Thanks for the 2 replies so far, much appreciated. I don't mind overkill, as i may want to be able to grit blast (say) a full size tractor using a grit blast pot, at some stage. How would one of these towable diesel road tool compressors handle running a cabinet that needs a lot less air flow than their ultimate potential? Do they have some sort of diverter that just moves excess output flow back to the inlet or something? Thanks.
My suction cabinet blasting machine needs an absolute maximum of 100 CFM running a 1/4 inch nozzle at 80PSI, I rarely use such a big nozzle though, more like a 3/16 tip which needs 50 CFM at 80 PSI
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The only towable unit I've used was a 6 cylinder engine running with 3 cylinders for power and 3 cylinders as compressor. Whole thing fed into a suitable 50 gallon tank. A pressure valve cutout set at about 120 psi would unload the compressor stages and lower the rpm to idle. Ran a 60 pound jack hammer with NO PROBLEMS. On the other hand, I had problems living through the experience. I tended to spend much time laying on my back in the grass recuperating.
Regardless of the compressor style, any compressor package should have a cutout at high pressure, an unloader to allow starting without load, and a small to medium receiver tank.
Chris Wilson wrote:

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wrote:

The first thing I would do is call your local power utility and see if you can get a three-phase feed installed for your Home Shop. They may say yes, they may say no, they may try to charge a lot for the new service, they may do it for practically nothing - you won't know till you try.
A diesel compressor would work fine for that job - they have proportional controls so the compressor throttles down to match the load on it, and when you stop blasting the engine drops back to idle. You can always add an in-line air receiver tank before your work location to smooth out the pressure fluctuations.
If you are doing production work you might want to look at a turbine compressor running on mains power - the exact same compressor, same operating style where the compressor unloads and the motor keeps running, but it has an electric motor drive. 10-HP will do for a single blast operator.
An electric piston compressor with a conventional pressure switch is NOT the right tool for that job - you do not want the electric motor to stop and start more than four to six times an hour, or you'll burn up motors. For sand blasting where there will be almost constant air use with short stops to reposition work, you want to change any compressor over to a constant run unloader system. The "Professional" compressors can be converted to unloader operation easily, the "home" ones cannot.
The diesel engine/compressor has it's pros and cons:
PRO - you don't have to pay for the electric company to burn fuel to make electricity, and then for all the transformer and transmission losses along the way before it gets to you - where you waste more energy turning it back into rotational energy to turn the compressor. You burn the fuel to make rotation to turn the compressor - Done.
CON - You have to buy the equipment, haul fuel to it, and maintain it.
Potential PRO - you may be able to buy non-taxed (or less taxed) fuel for the engine, since it is not a highway vehicle. In the USA we have "Farm Diesel" where they add a red dye, and if you buy in bulk it's worth the trouble - but if they catch you with red fuel in a car or truck on the highway you are in serious trouble.
CON - if you have neighbors who will complain about noise and fumes.
PRO - You can keep working through a power failure (CON - It's going to get really dark in that blast cabinet with no lights.)
CON - If it won't start, you can't work.
PRO - it's very portable so you can take the tool to the work.
CON - it's very portable and there are crooks with trailer hitches.
--<< Bruce >>--
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Chris Wilson wrote:

Of course, they have 75 - 150 CFM delivery. (The one you link to on eBay may be somewhat smaller.) I assume they have no

They usually do, it just isn't so obvious in all the rest of the machine. If you can't operate a 10 Hp motor on your electric service, then you may be forced to an engine-driven one, but you don't need one that large. There are plenty of 5 and 10 Hp gas engine-driven compressors around, although getting a good deal on one may be harder than the bigger ones that no home shop wants.
One caution, especially with rotary screw compressors, which at least some Atlas/Copco units use, is they often run a LOT of oil through the compressor, and have a separator on the outlet. This ends up with a lot of oil streaming through the air. Great for the jackhammer (I guess you call that a road drill in British) but might not be good for grit/bead blasting.
Jon
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Chris, the most cost-effective solution would be to use tips with smaller holes, and possibly also reduce the size of the internal port/nozzle inside the blasting wand/gun.
Utilizing an enormous air compressor will cost many times more than operation of a smaller air compressor and a reasonably-sized tip in the blaster. Generating and releasing high volumes of compressed air can be extremely expensive, and generally creates other problems with oil and water carried in the air flow (more expenses to correct these problems). Scattered blasting grit can also be problematic. Sand blasting in a contained area will definitely require the proper equipment to supply a reliable, plentiful source of fresh air for breathing.
Paint stripping is best done by other means. Sand blasting is a very effective treatment for the cleaning of rust pits. Putting a rusted panel in a blast cabinet to begin rust removal is very wasteful of money and energy.
Preparation by other methods will be just as effective and generally much less costly. Acid treatment, followed by a quick overall pass with a wire rope cup brush on a portable/handheld grinder will eliminate a very large portion/nearly all of the loose rust. The actual neccessity for sand blasting will be greatly reduced, and operating costs (electrical power or fuel) related to the air compressor (including filters, oil, maintenance and repairs) will be minimized.
For a valuable fender, for example, that was badly rusted both on the top and under sides, it would probably be worthwhile to take it to a business that specializes in dipping large parts to completely remove the rust. Sand blasting can distort sheetmetal, and very badly at higher pressures. The chemical treatment method probably won't do any damage unless the panel is left in the tank for an excess amount of time, or left unprotected for a considerable amount of time afterward.
At some point in getting bigger equipment, operating costs may exceed the the value of the projects/jobs (which ever the case might be).
WB ......... metalworking projects www.kwagmire.com/metal_proj.html

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