Trying to Sandblast-Water in Air

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I made the plunge yesterday and decided not only to try and get a basic air set up in my garage(something long overdue), but also get really adventurous and try sandblasting.

I bought a 20 gallon unit from HF rated at 4.1 CFM/90psi that I know now is probably very inadequate for what I'm asking of it, but thought I'd get okay since the sandblaster I bought claimed it was okay with 2.5cfm at 50psi.

In any case, I've been going alright and getting good results at least as long as I limit it to a couple of minutes at a time. So far I haven't tripped the thermal overload on the compressor, but have been sticking to ~5 minutes or less(which has been enough for the small parts I'm doing).

When I set things up, I put one of these on the compressor outlet https://www.harborfreight.com/12-in-standard-air-filter-68279.html

I then stuck one of these on the base of the handle of the sanding gun https://www.harborfreight.com/oilwater-separator-68246.html

I have a 30ft air line between them, and have running it between 60 and 100 psi(60-70 seems to do alright for what I need to do, and is a bit gentler on cycling the compressor).

What I've found is that after say 30 minutes of intermittent use, I'll start getting water aerosols out of the blaster nozzle. Sure enough, I'll check the separator on the handle and it has a lot in it. At that point, I try pushing in the vent on the bottom of it, which will spray out a fair bit of water, but still leave a lot.

Every time that's happened, I've also gone back and hit the drain button on separator at the compressor, and it seems to not really drain anything.

Today, I was able to get back to work by taking the in-handle one apart and using an air nozzle to dry it out, although I could see/feel water at times aerosolizing out of the hose. Doing that and putting the small trap back together would get me a few more minutes of operation.

I'm a bit stumped on this. I've drained the compressor tank a few times, and it will spray out a bit of water, but nothing like the amount I seem to be getting out of the hose.

Today in particular it was relatively cool(didn't get over 60º) so the air is fairly dry. It's not like I'm trying to run this in the middle of summer with 90% RH on a 90º day.

Do I just not have enough water separator capacity, or am I missing something else?

(at least I did get some nice crusty parts cleaned up and rattlecanned so I can feel good about the car going back together).
 

JRed

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Probably need an air dryer. They make types with replaceable dessicants and most dessicants can be regenerated in the oven a few times.
 
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The issue is that the compressor not only compresses the air it compresses the moisture and at the same time it raises the temp of the air so that it can hold more water. As the now really humid air goes through the hose it cools and the water condenses all along the line and is blown into your separator at the end. The only way I know of to get a high volume of dry air from a relatively small compressor is to put a second tank in line with enough hose between them that the air can cool down and the second tank will collect the water, If you are running metal air line around your shop there are moisture traps that can be installed.
 
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Refrigerated air dryer is the only way to solve this issue if you plan on doing a lot of blasting. The small water separators won't do it. Having too small of an air compressor only makes thing worse because its running more than not so the air will be a lot warmer in the tank.

I have an 80 gallon 17 cfm compressor and its even pushed when sand blasting. My air tank gets so warm you cant touch the top for very long when sand blasting. I have a 15 cfm refrigerated air dryer that keeps the air dry but I need to make an intercooler between the compressor and the tank eventually.
 

bunnspecial

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Thanks-I should have thought of the temperature issues with it.

I had already considered a secondary tank. My garage isn't big, and I've been doing the sandblasting outside with the compressor all the way at the back.

I have a 7 gallon tank in storage, and HF has an 11 gallon one that's not too expensive. I had originally thought anyway about either using the one I have or buying the second one. In my set-up, I could-conceivably-set the compressor line to 120psi or so, have it keep the secondary tank filled, and use a regulator on the secondary tank to get to my working pressure. I'd keep the secondary tank near me when running the blaster, and with having a regulator on it could adjust the working pressure without walking to the back of the garage. I hadn't thought of the added benefit of cooling the air, and I suppose for a bit more "belt and suspenders" could also add an additional separator on the secondary tank, although it sounds like that doesn't do much by itself.

The secondary tank seems to me that since I'm typically only going a couple of minutes at a time, I could get more run time at my desired working pressure even though it would take longer to recover when the compressor did kick back on. Still, though, it would make sense also that with longer intervals between the compressor running, I'd also have more time for the air/tank to cool.
 
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Be sure to study up on personal protective equipment for sandblasting. It's one of the prime ways to get silicosis, a nasty lung disease I certainly wouldn't want to have.

You aren't protected by using a non-quartz containing blasting agent. For a start they often have quartz in them - a small amount to be sure, but any amount is too much. And when you collect and reuse the blasting agent you will also pick up quartz.

Blasting also puts an assistant at risk as well.
 
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There are expensive air dryers that are made for use with compressed air. They consist of at least 2 dryers and cycle which one is used and dry they unused one while the one online dries the air. This way the desiccant is used over and over again.
 

Job

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Can I ask what is wrong with wet sand blasting? I thought it would be desirable. Cuts better, flushes the debris, and keeps dust down.
 

bunnspecial

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Can I ask what is wrong with wet sand blasting? I thought it would be desirable. Cuts better, flushes the debris, and keeps dust down.

Actually I did sort of wonder that.

I wet sand things a lot-whether with water or oil-and it does have a lot of advantages including control of dust.

With that said, since you're constantly pelting the surface with fresh media, rather than using the same over and over again as in sandpaper(and yes I know aluminum oxide can be reused-I've been collecting as much as I can-but still it's not like sandpaper where the same abrasive material is passing repeatedly over the surface).

My concern is two fold. One is that I know moisture can cause clumping and flow problems with some media. I don't think it's an issue with aluminum oxide, but could see it with walnut shells, for example.

The second is that flash rusting-as I've found out-is a big deal on freshly sandblasted parts, and I can't imagine spraying water on them can do them any good.
 
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Why we like sandblasting really makes a clean substrate for painting little project from last summer before after pics.
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bunnspecial

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Why we like sandblasting really makes a clean substrate for painting little project from last summer before after pics.

Nice work!

Even for what I've been able to do, it's a really satisfying process that really does get things clean.

I'm still supplementing it with wire brushing since, especially with an angle grinder, I can cover a big area quickly, or do pretty decent on smaller parts with a bench grinder or even with wire wheel on a plain ordinary drill.

Still, though, you have those areas you just can't reach with those, and sandblasting takes care of them.

This particular project is the rear suspension on the MG, which is a pretty simple leaf spring/live axle(i.e. a sports car with the rear suspension from a pickup truck) with hydraulic lever arm shocks. Back in 2015, when I first got the car, these springs were one of the first things I replaced. I took everything apart, replaced some of the hardware, and put it all back together with new rubber bushings/pads. Rubber parts for this car are terrible quality now, and some of what I put on back then is already dry rotting. Right now it's all taken apart again, and among other things I'm swapping the springs side-to-side to correct for uneven settling(on a car this light that doesn't carry a passenger that often, it's a really common thing).

In any case, one of the pieces of hardware I opted not to replace are the shackles that secure the rear eye of the spring to the frame. When I picked out all the old dry rotted rubber last time, I was left with a lot of rubber stuck on these bolts. With the poly especially, since they need to rotate, I want them as clean and smooth as I can. Last time, I just did my best to scrape off the old stuck rubber. This time, I went a bit further, but a wire wheel still didn't really get it. The sandblaster got rid of the old rubber without too much trouble. Of course I'll need to go back with some finer sandpaper to get a smoother finish, but at least I have a clean metal surface to work with.

Other places where it's been beneficial is in some of the cracks and crevices of other brackets that I really can't reach with a wheel very well.

I bought a box of walnut years ago to use to tumble cartridge brass, and I need to dig that out and use it to clean up the aluminum parts some. Of course I could also glass bead them, which I've noticed some people seem to like on softer metals.
 
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