Sandblasting questions

[Gunner3456]

Some of you say you do it so I believe you, but I'm really surprised that a small compressor will drive a blasting cabinet.

I used to have a medium sized cabinet and it needed 8 cfm @100 psi for continuous duty. That's like two stage twin cylinder 4-5 hp in 220v. It needed continuous duty to glass bead something like a cylinder head or an exhaust manifold. I guess gun parts are smaller and don't need continuous duty? Maybe the orifices are smaller on the smaller blast cabinet guns?

I would think that the blast cabinet owner's manual would spell out how much air it needs - mine did. ?? I'd match the compressor to that.

$.02

PS I have two Speedaire 220v compressors and plugs to run both at the same time. One is 4 hp and the other is 5 hp. I chain them together to blow out my 1/2 acre sprinkler system in the late fall. I also have a high-end DeVilbiss moisture trap/pressure regulator. If anyone in the Rogue Valley wants to come over and hook up a your own cabinet to do some gun parts, send me a PM.

 

[ricsha]

No worries, I just listed the 40psi specs. My little 1 1/2 HP will still put out 3.3SCFM at 90PSI and has a maximum of 125PSI. Should work for light use. Will just have to try it and see I guess. First need the cabinet, then the media... Not enough hours in the day.
I really appreciate all the good info available on this site.
Rich

 

[Andy]

Ok, I got everything set up this evening and gave it a try. I bought a Kobalt (Lowe's) 5 Gallon air compressor (http://www.lowes.com/lowes/lkn?action=productDetail&productId=232177-45003-F215DKL&lpage=none).

It did not do the job. I spent about 5-10 seconds blasting and then the compressor kicked on. Took about a minute to get back to pressure. This got old quick. Its a nice compressor for $139, but I'm not that patient. It came with a kit of fittings, so unfortunately I will have to take apart a few things in order to return it.

So, my next step is something larger. I was thinking of a couple models at Sears. They range from 20 to 30 gallons and start around $250. Anyone have any suggestions? Is Craftsman a brand to stay away from - as far as compressors go?

Andy

 

[Gunner3456]

It's not the gallons - that's just the tank. It's the cubic feet per minute (CFM) and at what pressure will it produce that?

A big tank will give you more air to start with and will last a little longer, but then it takes even longer to pump it back up to pressure.

This is an issue of horsepower you're dealing with. Given a good compressor unit, it takes a good deal of horsepower to drive it.

Doesn't you blasting cabinet have a manual which recommends the CFM and pressure?

 

[Andy]

I know the gallons aren't the important part, it's just how the compressors are referred too in the ads.

I'll look at the cabinet recommendations and go from there.

 

[Gunner3456]

http://www.sundanceglass.com/sandblasting.htm

$195.00
Overall Dimensions
27" x 28" x 18"
Door Opening (Side Angled)
16" x 16"
Floor Work Area
25" wide x 16" deep
Inlet Fitting
1/4" NPT

Working Pressure
80 to 120 PSI

Air Consumption
5CFM at 100 PSI

Abrasive Capacity
5 LPS
Required Air Hose ID
3/8" air hose fitting
Abrasive Hose Length
34"
Internal Air Hose Length
42"
Vacuum Port
2-1/4"




From the website... Almost any size compressor will work. If a compressor is under powered, you would simply have to stop blasting once in a while to let the compressor build up the pressure before continuing blasting.

OK, that was a bit confusing at first - my bad or my eyes.

"Air Consumption
5CFM at 100 PSI"

Looked at first like SCFM but it's 5CFM (5 CFM or 5 SCFM.)

OK, in order to develop that, you're going to need at least 3 HP, twin cylinder, two stage running on 220V. No 110V or diaphragm compressors here.

Yes, you can just wait for pressure to build up, but as Andy pointed out, his 1 hp 110V diaphragm compressor would blast for about ten seconds, and then he had to wait about a minute for the tank pressure to come back up. That's a losing battle. You can't get a nice even look with spurts like that either because of fast pressure drops. You need to maintain even pressure to "paint" an even look.

My offer's still good. Any member here in S. Oregon is welcome to bring his unit here and hook to one of my Speedaire 220V 4 or 5 HP compressors and moisture trap. Either one will beat the requirements for that cabinet, continuous duty.

 

[ricsha]

OK, I think I'm finally understanding this thing about needing a continuous large volume of air at a high pressure to make blasting work. Wish I was closer to Gunfixx, I'd take him up on his offer to use a big compressor.

Even for a small benchtop cabinet I'm going to need a 220v 3+hp compressor to get 5CFM at 100psi to run the gun on any kind of continuous basis. (I wish the sites that sell blasting guns and cabinets made this more clear in their ads; some don't even list the specs in their sales materials --you have to hunt for it...) Also, many don't list the orifice size(s) of the blast gun.

That's a way bigger compressor than I have, or want to buy, or have the circuits to operate, to do one or two pistols --I'd end up spending more than the cost of the pistol. So I see that I have maybe a couple of options:
1) I could pay someone else to blast my gun, a good option but doesn't give me as much control over the blast media, and the resulting finish (I'm looking for a two-tone effect on stainless, courser on the rounds, and smoother, more polished glass beading on the flats), or
2) I could (maybe) go to a smaller orifice blast gun that would work with my 1.5hp, 110v pancake compressor that can produce a maximum 3.3CFM at 90psi. Looking at the websites, I see that there are small blast cabinets for sale for under $200 that have a Small Pencil Blasting Gun that runs at 1.5CFM at 80-90psi, instead of the usual pistol grip blasting gun with a larger orifice that needs 5CFM.

Can someone in the know, speak to whether this small pencil blaster would work for gun refinishing? I understand that it would take longer, cover a smaller area, be limited to smaller media grits. But I'm not going to be blasting cylinder heads, or suspension parts, just small gun parts. A 1911 slide for instance is only 1" by 5". Even if the blast pattern is only 1/8 to 1/4" wide, just a few passes would cover the slide, or would it? Would I have an impossible job of "painting" or blending the passes or not? I'm not looking for a production set-up; but I don't want something that does a half-assed job either. Input needed, thanks.

 

[Gunner3456]

If you use too small an orifice, you'll have problems with streaks. You really want to hold the gun back a bit and "dust" the item.

You could try a pressure regulator at about 50 - 60 pounds and see how that works. Obviously if you run at a lower pressure, you'll use less air. To oversimplify, the regulator works as a restriction in the line. Rather than start with a regulator, you can just get a valve which would thread onto the base of your gun or the outlet from the compressor. It has a needle type valve and will cut down the air flow. I'll bet they have those cheap at Harbor Freight or elswhere.

I can't promise how well the gun will "suck" up media into the stream at lower pressures, but I suspect that the finish would be fine if it worked unless you also held the gun back from the work for smoothness and then lost velocity.

I'd be asking around guys who play with old car restorations. They can't live without a good compressor. Know anyone like that? I now paint with an HVLP with it's own air supply, but I still have my Binks #7 gun and it needs about 7-8 psi at 60 psi.

I jumped in here by saying something like "I know you guys say you do so I believe you..." but I also believed they had a lot of patience and practice.

I know of no other real good solution than a compressor which will keep up.

 

[Andy]

Yeah, that's the cabinet I have. I've seen a few medium size compressors that are at least 5 scfm at 90psi and are 110v. I'll have to look into the horsepower. There is no way I can do 220v. I don't need continuous pressure, but 50/50 time blasting and waiting would be the minimum.

I'm returning the Kobalt today after work. I'm considering a few others, but I doubt any purchases will be made until after Christmas. The worst that happens is that I buy something and take it back later.

Have a Merry Christmas everyone. I'll be back after the holidays!

Andy

 

[Gunner3456]

Yeah, that's the cabinet I have. I've seen a few medium size compressors that are at least 5 scfm at 90psi and are 110v. I'll have to look into the horsepower. There is no way I can do 220v. I don't need continuous pressure, but 50/50 time blasting and waiting would be the minimum.

I'm returning the Kobalt today after work. I'm considering a few others, but I doubt any purchases will be made until after Christmas. The worst that happens is that I buy something and take it back later.

Have a Merry Christmas everyone. I'll be back after the holidays!

Andy

Don't forget, there's peak output and there's continuous duty. You'll want MORE than (slightly more than) 5 scfm at 90 continuous duty. I can't see that happening with 110V, especially not with a diaphragm compressor.

But you're right, the closer you get to that, the less wait time you'll have.

When I got my first 3 hp 220V compressor years ago (a Speedaire labeled as Craftsman) I made up an extension cord for it and plugged it into my (in the garage in those days) clothes dryer plug. I'd slide the dryer out, unplug it, and plug in my compressor.

No joke. Those were the days. Most of those compressors just need 20A @ 220V.

If you have a free-standing kitchen range, that works too. Your wife will just love having the stove pulled out and a cord running across the kitchen to the garage.

Merry Christmas.

 

[ricsha]

I appreciate Gunfixx's suggestion [maybe tongue-in-cheek?] of an inexpensive air "eraser" alternative. Actually, I have a similar one, made by Badger, that runs at less than 1CFM at 35psi on a tiny air-brush compressor. Tried it the other day, and while it worked to remove the black chrome from a Kimber 1911 safety using some very fine aluminum oxide; it took 10 minutes or more (for a tiny safety) and felt like an hour. That's just TOO small, so now I'm on a quest to find some middle ground. Need a small trigger-gun or pencil gun between this micro blaster and a full-size gun that requires 5+CFM at 100psi. Will update you on my success, or lack of. The responses on this thread have been most helpful to me. Thanks to all.

 

[PinkhamR]

I've heard that you want 100 psi for sandblasting. I'm not the expert though.

Anyone, would 40 psi be ok?

For aluminum I have found that anywhere from 30-70# is a good range. Depends on the item and the type of medium that you are using. The coarser the medium, the lower the pressure (to avoid pitting). Also, if you sandblast it is very difficult to get a real high polish on it. Use the buffer for the shiny and go through the different ranges of polishing grit. JMO

 

[Andy]

UPDATE.

Ok, I bought an air compressor (used in great condition). It's 26 Gallons, 4 HP (probably peak) and claims 6.3 cfm @ 90psi, running on 110v.

I'll hook it up in the next few days and see what happens.

Andy

 

[Gunner3456]

UPDATE.

Ok, I bought an air compressor (used in great condition). It's 26 Gallons, 4 HP (probably peak) and claims 6.3 cfm @ 90psi, running on 110v.

I'll hook it up in the next few days and see what happens.

Andy

OK, be sure you have a pressure regulator for at least two reasons. First, you can adjust the force of the blast for cosmetic appearance of the product and for softer metals, and second, you can conserve air if needed. By running a lower pressure blast, your compressor can better keep up if needed.

Even a cheap line restricting valve as opposed to a true two stage pressure regulator is better than nothing, but not best.

Harbor Freight?

 

[Andy]

There's a regulator on the compressor and I have another in line with a moisture trap.

Thanks!

 

[Gunner3456]

There's a regulator on the compressor and I have another in line with a moisture trap.

Thanks!

Awesome! The moisture trap will really help. If the media picks up moisture which it would, it can clump.

 

[Andy]

The new/old air compressor worked fine. It kept blowing the 15amp circuit so I connected it to a 20amp. Works great. Had to get some courser media though. The fine media I have isn't taking out the dings.

So here's a new question. How do I dispose of the glass media? I know there a bunch of warnings on the bag about inhaling it. I want to do the right thing.

Andy

 

[Gunner3456]

Glad it's working! Yep, 20 amps...

I always re-used the media several times. The unit I had had a vacuum type bag on the back to catch dust to help keep the media cleaner, and then let the heavier particles fall to the bottom to be automatically reused. I don't know what you have.

I ALWAYS wore a dust mask when blasting because the machine leaked some dust. I also wore one when emptying the bag or the machine.

I don't know the actual correct way to dispose. I always double-bagged it in garbage bags, taped them tightly shut and put them in the garbage.

That may be a mile off from what I should have done. I suppose a guy could call the landfill people and ask them. I don't think the media is harmful except for breathing, but don't take my word for it. I think it is literally just glass but again I don't know that.

 

[Andy]

I'll reuse it, just wanted to know ahead of time what to do. I do use a mask whenever handling the media - that fine glass is nasty stuff.

 

[Andy]

Another update.

I switched to alum-oxide and then ran the glass back over it and it turned out great! Just got done putting it back together (after loosing a small ball bearing and having to order and replace it - see my post in the gunsmithing section). It almost looks brand new!

I should have taken better "before" pictures for comparison.
I'll post some of the finished product in the near future.

Andy