The Sandblasting / Air Eraser / Etching thread

[u18b]

I need to order some 220. I ran out and bought the next size up at HF and warped some brass.

220 seems to be the sweet spot.  It gives a nice even finish.


I'm sure you could go to a finer grade (higher number), but I would guess the cost would go up too.

I referenced blackening wheels previously.

Well, here is a blackened wheel that was not sandblasted...


And here is a wheel that was sandblasted.  As you can see, the finish and blackening is much more even.

[u18b]

As for my set-up, I started out with pure nitrogen from a bottle.  In fact, I did all my airbrushing with it.

But then I moved and buying Nitrogen was farther away.  So about a year ago, I bough a compressor with built-in tank.
This has been great for airbrushing-- but NOT for sandblasting/air erasing.



The problem is pressure, time, and moisture.  When air brushing paint, you are probably using 18 - 30 psi depending on the thickness of the paint.
But that's not strong enough to sandblast.

Sandblasting requires 45-65 psi.  And at that pressure, my compressor has to run a lot and only turns off infrequently when I'm sandblasting.

Now compressed air, when it goes through a small opening (an expansion valve), the temperature drops and water vapor condenses out.

And sure enough, this good compressor has a water trap.


In fact, the sandblaster even has an extra water trap in the hose line.


But it wasn't enough.  After sandblasting for a while recently, I started spraying water and that ended the session.

That was enough to drive me back to nitrogen for sandblasting.
Otherwise, I would have to go to MUCH greater lengths to build a cooling/drying coil for the airbrush apparatus.  I watched a youtube video of a guy that incorporated/adapted a car internal radiator (the one under your dash) for his sandblasting.  So it can be done, but it's a lot of extra trouble.

And OH!    All of this problem is also attributable to where I live.  I live on the Gulf Coast in northwest Florida.  Today was a very dry day.... and the humidity reading was 60%!  Normally, it's a lot higher.   This area is sub-tropical and averages 60" of rain a year.
So if you live on the Oregon/Washington coast, Hawaii, or some other wet place like me, then you are going to need to work extra hard to get dry air.

Of course, if you live in the desert Southwest, then it will be less of a problem.

[u18b]

So here is my current set-up and my story.

about 30 years ago, a lady in my church lost her husband.   I was visiting her, and saw a couple of oxygen bottles.  I think I simply asked where she got them thinking I would do some more checking (at the time, I was thinking about filling something like that with plain air).
In the end, she gave them to me for free.  (I'm not even sure that would work today since the medical supply company owns these now).

I was young and naive (ok.... well, stupid!  ) and I actually airbrushed with it.  When I took the bottles to get more air, the guy behind the counter said something to the effect .... ARE YOU CRAZY!!!!  You're dealing with a bomb!  O2 and petroleum do not mix!
And knowing I was a young and naive idiot, he had compassion on me.  He said, I'll tell you what.  I'll trade those bottles for nitrogen.

The great benefit of nitrogen is that it is not volatile (no fire hazzard/explosions) and it is DRY- no moisture to worry about.

And I've been using it ever since.

Gas is just like propane for your grill.   You "sort-of" own the bottle.  But you don't keep it.  When empty, you take it somewhere and swap it out for a filled one.

Bottles are sized by the pound of the air inside.  A 20 pound bottle is easy to manage, but would run out too fast.  So I use 40 pound bottles.
They are a little heavy and unwieldy, but not too bad.



Last week I swapped out 2 bottles for full ones (about 11- 19 bucks where I live) and I bought a third bottle (not a swap).  The new bottle was about $125 and of course came filled (so it was actually a little over $100 for the bottle itself).  With three bottles, now I can go through 2 and be on the third before I have to make a run and refill.

Admittedly, almost no one is going to need three bottles like me.  But I'm doing a lot of brass, and an extra bottle saves me a lot of time.  I just shared this with you so you could have a guess what one might cost you.

So.... even though my first two bottles were free, I had to buy some equipment to make it work.


The green dial regulator on the right came with the oxygen bottle.  It is rated to 4,000 psi- which is good since the nitrogen comes at over 2,000 psi.  That one was free for me.
Then I needed a special fitting to go onto the bottle (right fitting).
Moving left, I added a second regulator.   This was is rated at 60 psi.  So it sounds weird to have two regulators, but I just leave the first one open and it tells me how much is in the bottle when I open the valve on the bottle.
The second one is the one I adjust for air brushing, sandblasting etc.  Heck, I even use this to fill the tires on my car.
In fact, that's what the left fitting is for.  I just added a quick disconnect so I could swap hoses and devices easily.  It leaks a little, but it's worth the trouble it saves.





And here is the whole set-up on my airbrushing tool cart I got for Christmas two years ago.


And by the way.... I really do use only nitrogen on my cars now.  Have you ever had to replace the tire pressure sensor inside your tire?
They go bad because of moisture from gas station hoses.  I got so sick of paying for new sensors that I ONLY put nitrogen in my tires now.

So.... a nitrogen bottle or two actually pays for itself in a couple a years (the amount of time for a tire sensor to corrode and go bad).

In fact, that may be how you convince your wife that buying a nitrogen bottle (or two?    ) is actually something that will benefit the family.
 

[Chris333]

Get a transmission cooler or an old radiator and plumb it between the compressor and the tank. This will get rid of all water.

[u18b]

Get a transmission cooler or an old radiator and plumb it between the compressor and the tank. This will get rid of all water.

Did you do that?

Show us your set-up!

[central.vermont]

Ron, thanks for showing your Nitrogen set up. It's definitely something I want to do.
Wondering just how long that 40lb bottle lasts for you. I know sandblasting uses a lot but how many
say N scale engines do you think you can paint with a bottle? Just tring to get an idea what it can cost
in the long run verses an air compressor.

Thanks, Jon

[Chris333]

I'll take pics later. I used a huge radiator. If you use a small cooler you may need a fan on it. Just wire the fan to come on with the compressor.

[u18b]

Well.... that's about all at this point.

As I said at the start....  I was doing this outside without proper breathing protection (look at the white powder everywhere in this shot!)



But I'm finished with doing that.

So I'm starting to build a sandblasting chamber.

I priced some, and the one at Harbor Freight was a possibility.

But I came across this article where the guy made one.
http://rrmodelcraftsman.com/building-a-sandblasting-booth/

This was a good start for inspiration.  But it is inadequate for my needs.  The key thing missing is ventilation.  So I'm planning on building something like this with a hook up for my shopvac- otherwise, it doesn't take long for the chamber to get so cloudy you can't see much.

I'll report more when I make progress.

(you can do your own research.  Just search "build a sandblasting booth").

[u18b]

Ron, thanks for showing your Nitrogen set up. It's definitely something I want to do.
Wondering just how long that 40lb bottle lasts for you. I know sandblasting uses a lot but how many
say N scale engines do you think you can paint with a bottle? Just tring to get an idea what it can cost
in the long run verses an air compressor.

Thanks, Jon

Jon,
I'm not sure.
A Milwaukee Road brass EP-2 has a lot of parts (it's really two small locomotives plus a boiler room).



 I'm guessing it takes about 1/3 to 1/2 a 40 pound bottle.   But my mind is fuzzy if that estimate is too high or low.

However, it takes a LOT of Al-Ox.
Look at this photo.



The small bottle on the right came with the air eraser.  A bottle like that came with my Paasche too.
But that is nothing.

The bottle on the left is a 2 pound bottle and I use almost a whole bottle when I do an EP-2.

Which is also a reason for me to go with a sandblasting booth.
In the past, all that Al-Ox went into the yard.

But with a sandblasting booth, I should be able to reuse it a little- assuming what I'm blasting is pretty clean.
For example, I always get all the paint I can off of brass before I blast it. 

But if I blasted the paint off, then the excess Al-Ox would be contaminated with paint particles and chips and clog the system next time around.

[Chris333]

Still no pic, but look up air compressor pre-cooler:
https://www.youtube.com/results?search_query=air+compressor+pre+cooler

I have a 60 gallon compressor in the garage and I wanted to paint a car with it. I bought 2 HF water traps and with them inline I still got water. I read about the pre-cooler. You can make them a bunch of different ways.

I ended up getting an old air dryer at work. It was a radiator about 30" square with a big electric fan blowing across it. I mounted it to the roof of my garage. The line from the pump to the tank was cut and I spiced in the radiator. Even put a short piece of pipe with a valve for a trap.

The pump makes the line to the tank red hot, so much that I can't touch it. After blowing through the radiator the line to the tank is cool to the touch and no water gets into the tank. It worked so well that I didn't even bother mounting and hooking up the fan.

[peteski]

But the moisture (water) in the air gettign compressed does not just vanish. It condenses as the pressurized air cools, and has to go somewhere.  Do you have to drain the water from anywhere in that compressed air setup?  I would think that was the water cools in that "radiator", the water would accumulate there.

[Chris333]

I dunno. This is mine, it's not pretty because it's in the garage.


Red line is from the pump to the top of the radiator. Yellow line is back to the tank. Blue line is a drain with a ball valve.


Funny it just happened to be running when I went out side to take the pic. I leave it on and the quick disconnects leak a bit. It has been "on" all summer and I just now opened the ball valve. There was very little water. And in the background is the big fan that I never even hooked up.

I though the way they described it on Youtube that it was the hot air causing the water. This cools down the air.

I still have the dual water traps before going to the hose reel, but there is never really any water in them because very little water ever gets in the tank. Whatever the end result is no more water spraying out the hose. Besides painting a car with this setup. I also sand blasted most of the car with this setup using a much bigger tank and black beauty blasting grit.

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[peteski]

Compressing gas generates heat, and reducing its pressure cools it down.  Also warm air can hold more mosture than cold air (that is why we have humid weather in the summer, and the air is very dry in the winter.

The compressor takes in the ambient air with whatever amount of moisture is in it.  Compressing that air does not generate moisture, but when that compressed air cools down, that moisture that was already in it will condense into water droplets and settle in the bottom of the holding tank.  When I use my compressor I can clearly see the difference in the amount of water that accumulates in the summer (humid days) and in the winter (cool and dry air).  On a  dry winter day my compressor's tank has almost no water to drain.

As I mentioned, the water will condense wherever the heated compressed air is cooled.  In your example, the cooling occurs in that radiator, so the water should accumulate in its drain pipe.  If it is not there then I'm can't explain as to where the water goes.  It can't just disappear. Puzzling.

[u18b]

Chris,
Thank you so much for sharing this.

However, before I read Peteski's post, I was wondering the same thing.

If moist hot compressed air rises in the red line.....

And cooler dry air (still under pressure) come down the yellow line....

Then water will condense out somewhere between the red line and the yellow line.

Where does it go?  Do you have a trap that is not shown?

Never mind.... Pete..... the water goes down the blue line.   It's a long pipe that can hold a lot of water.

[peteski]

Yes, in the "blue" pipe.  But that is not a free flowing drain (since it is all under pressure) and that pipe won't hold much water before it fills up and then the water would drain into the air tank. Chris wrote that he opened up a ball valve, and there was not much  water after running all Summer, but I'm not sure if he meant the valve in the tank, or at the end of the "blue" pipe.