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MG Midget and Sprite Technical - Shot blasting

After a weekend and a long evening working under a huge tarpaulin and shot blasting my engine bay, I have two recurring problems:

1) The blast gun keeps blocking. Sometimes this is due to a kink in the pickup pipe, but other times I get a burst of water down the airline and that clogs it. I have a brand new air filter / regulator in the line, I've drained both it and the tank. What am I doing wrong? If I were paint spraying this would have screwed up the finish by now.

2) I wear pescription glasses, goggles over the top, and a face mask. The mask is well sealed onto my face (no dust inside it after a day of working) but my glasses and goggles keep misting up. I need dust protection rather than impact protection, so my goggles are probably not the best for the job. There must be a better way. What is it?

All suggestions appreciated. After a whole weekend and a long evening I've done about a tenth of what needs doing. That's too slow.

Ant
Ant Allen

I bought one of the blasters from here a couple of years back

http://www.acegrit.co.uk/acegrit/gritblaster/

The bloke was admanant that for best results (no clogging) both a water seperator and mist seperator be used. I did buy both and haven't had any issues. And I used them when I'm painting aswell to guarantee no moisture then.
Dean Smith ('73 RWA)

Ah ok. I'll look into mist separators then.

What protectice kit do you wear? I have to wear specs which makes things a bit harder, but what do you use, and how do you get on with it?

Ant
Ant Allen

Overalls, gloves, goggles and a small face mask. Not ideal - the stuff gets everywhere.

I'm sure i'm not H&S compliant!. Fortunately I've only had to do a few things so its bearable in small doses. At some point I'd like to do my whole engine bay....and I;d probably try and buy a proper full face mask for that.
Dean Smith ('73 RWA)

try contact lenses?
Or try rain-x or similar to prevent misting up.
Tarquin

Ant,

You could try one of the wipe-on non-fogging applications to your glasses and goggles.

When you look for the water separator, check the installation instructions. I seem to recall they need a certain configuration of hard line to mount them properly. I put one in between the compressor and the rubber line, and it didn't do much good.

Charley
C R Huff

Ant,
If you can borrow or hire an full air-fed mask this should help reduce the fogging.

Guy
Guy Weller

Ant. One of the byproducts produced when compressing humid air is water in the system. Basically, the air is highly compressible, the water is highly non-compressible. So, when you compress any air, some of the water vapor in it will wind up as moisture at the bottom of the tank and the higher the humidity on the day you are working, the more water vapor will be in the air being compressed, equaling more water in the tank.

Water should be drained from the tank on an "as needed basis", meaning that you may need to drain it only once a week when not using the compressor very much, or you might have to drain it several times a day when using it for long periods. Even here in the desert, I have to drain the tank several times a day when using the compressor extensively.

Moisture traps are an interesting thing as, depending on circumstances, they are fairly easy to fill up--at which point they become useless. I drain the water from the tank, then, drain the water from the moisture separator every day before use. There is always water there. A larger moisture trap works better than a smaller moisture trap. But, even in large, industrial operations, the items need to be drained frequently.

If you do not have rigid plumbing for you air yet, consider adding in some moisture traps if you do go to rigid tubing for the air lines. Run a couple of long "U" shaped pieces of tubing from high up to a couple of feet below the floor and put a petcock at the bottom. That helps to trap moisture before it gets to the moisture separator in line, reducing how fast the moisture separator fills up. Open the petcocks periodically to drain off the moisture which accumulates in the lower portions of the lines.

As to the fogging problem, I would think Guy's suggestion the best possible one. The second best, and one I have used, is a hood over the head, something like the old "bag over the head". Either system will give the moisture in your breath some where to collect rather than your glasses and goggles. But, considering the possible build up of crud in your lungs, the best mask system you can find is merely "good enough". Especially for you young guys who do not need to make the mistakes that we older fellows did thorough our own ignorance.

Les
Les Bengtson

Ant,

I also wear glasses and found that the goggles just did not work for me. For face protection I used a full face shield, the kind that pivots open. Over that I used the heavy cloth bag-type blasting hood, the kind with a plastic window to look out. Two problems with that, the hood kept slipping out of place and the plastic window soon turned to bathroom glass and I could no longer see clearly.

The first problem I solved by attaching Velcro tabs to both the face shield and blasting hood. This kept the hood in place, but also allowed me to reposition it if needed. To keep the window clear I cut pieces of clear acetate and slipped them into the holder in front of the window, sort of like tear-offs on your windscreen or helmet face-shield, and changed them as needed. For awhile I used plastic cut from 2-liter soda bottles for the tear-offs, they worked in a pinch, but there was too much distortion. The nice thing about the face shield is that it kept the hood from laying on my face and there was space for air circulation which helped to keep my glasses from fogging.

If you are truly using shot or chilled-grit you are probably okay with a good dust mask, but I suspect you may be using silica abrasive, or sand blasting. If that is the case you should use a supplied-air mask under the hood. There is no dusk mask certified for silica that I am aware of.

I also tried blasting inside the garage under a tent, but there was no way. The sand would escape the smallest opening and it went everywhere. (It even got into the overhead door tracks and on top of the wall cabinets?) The dust was unacceptable and I did not have a supplied-air mask. I moved the project outside and positioned myself upwind. Still not an ideal situation but I felt I had a fighting chance against the dust. Time will tell. Of course your neighbors might not be too keen on that, depending on your location. If possible, outside is good, and it does not have to be warm out, just dry.

Regarding the moisture problem, my water separator was on the blast canister rather than upstream at the compressor. Moisture will condense inside the hose even after it has gone through the separator. Even so, it did clog up once or twice, but not often. And the process is oh so slow. My compressor was marginal so I frequently had to wait for it to rebuild pressure. I finally resorted to borrowing another and running two compressors to speed things up. It was a lot of effort, but a completely clean and rust-free engine bay is worth it.

Paul
Paul Noeth

Is it cold where your blasting....most likely your pulling cold air into the tank, which is warm, thus the air is changing temp in rapid rate...thus mositure....compared to say in summer time.

Gas under pressure is always colder...Id imagine the same is true for oxygen.

prop
Prop***The End in 2012

Ant,

As far as eye protection without steaming up your Gregory Pecks is concerned, try your local farm supply shop for a full-face shield as worn by operators of knapsack sprayers or motorized strimmers.

Works for me (when strimming anyway)

Dave
Penwithian

Unfortunately Prop the reverse is true. When you pressurise air/gas, it gives of heat On the other hand, you are thinking of a gas cylinder that when in use freezes. This is because when you release the pressure from the cylinder "liquid Gas" changes from a liquid to a gas and this process requires heat that is taken from the cylinder which freezes as a result.

The reason why goggles mist up is because warm air can "hold" more moisture than cold. Thus the warm air expelled from our mouths (please no jokes at my expense) hits the cold surface of the goggles and thus water condenses (mist) on the goggles.

Ant I find at work the wearing a dust mask with goggles is not good. Exhalled Breath always seems to vent out above the nose joint and into the goggles with the same result as you are having. The oly way I find of stopping it is to try and have a gap between the bottom of the goggles and my face mask. Not easy and I must admit I find the face visor (as Dave suggests) a better option as it has a bit of ventilation around it.
Robert (Bob) Midget Turbo

Why not buy a proper sandblasting hood. £15 -£20 from someone like Northern tools and equipment. Cheers, Dave
DM Gibson

I wonder if you can just use a little ol fashioned LOU-GY SPIT, like for when your swimming with goggles....of coarse they make that dog snot in a jar for the same purpose, for those that are grossed out by using there own spit on goggles when swimming.


What about rain-X, the stuff you put in windshild washer fluid to keep from fogging up the windshild

just a thought

prop
Prop***The End in 2012

Thats intresting BOB, I had always asumed that gas gets colder when compressed because it always comes out of a compressed bottle colder with mositure when realiesd

But thinking of it like a radiator water pressure, or a SU fuel pump on a super hot day does make more scence.


prop
Prop***The End in 2012

Prop. When the gas is compressed, it gives off heat which must be disposed of. When it is decompressed, it absorbs heat. We call this air conditioning, for either the vehicle or the home. Take a look at how those systems operate and you will understand better how these things work. I agree with Bob. I have never been able to wear a mouth/nose mask and not have my glasses fog up due to the exhaled moisture. That is why a tight fitting mask, with breathing ports to the sides, or a positive flow mask is the best thing to use for this type of work if you wear glasses or safety goggles. But, unless you are blasting in an enclosed cabinet, you need both goggles and a face shield (even if wearing prescription glasses) as the media can easily get around both the face shield and the glasses. I use a pair of chemical goggles given to me by a friend who is a chemistry professor.

Les
Les Bengtson

Back in my army days (when Lord Kitchener were just a lad), before putting on a Gas Respirator you coated the eyepieces (and your specs)with something from a tin labeled 'Anti-Dim'

By the time you had done this, the nerve gas had got you!!!

Now, isn't that helpfull.

Dave
Penwithian

Safety equipment is reeeeeeealy important.


rob multi-sheds thomas

Guys - Thanks for all the tips.

I've now discovered a dead easy way to unclog the gun so water in the airline is less of an issue. When the gun cloggs I put my finger over the end of the blast gun, flick the trigger a couple of times, and the gun pumps air down the pickup pipe and therefore empties itself. Once I see the sand in the bucket jump then it's clog free and we're ready to go again. Takes seconds.

For the mask / goggles I like the sound of the proper blasting hoods. I didn't know such things exist (doh!). Only thing is, surely if I'm breathing inside a huge hood then it's bound to fog up. I don't mind spending the £20 to buy one (seems like a bargain to me) but if it still fogs up then there's no point. I'm wondering if there's one which the filter of the mask sticks though so my breath is put outside the mask when I breath out. I seem to recall seeing something like that but can't find one now. Any pointers?

Ant
Ant Allen

Ant Health and safety-- make sure you are wearing a glove if you do the finger trick -- compressed air is dangerous
Mick - The engine is in!

Mick - certainly am. One huge pair of heavy duty gauntlets is worn at all times.
Ant Allen

Im glad I dont wear glasses, what about a piece of PVC pipe 4 inches long X 3/4" dia. with a cloth/dust mask rubberbanded over one end, and the other end in your mouth and a cloths pin on your nose, and just breath thur the pipe... No dust mask, needed, and no fogged up glasses....But gez what a sight LOL, If you do this, We want photos

prop
Prop***The End in 2012

From motorcycle visor experience, washing up liquid is good for anti-fogging. Wipe it neat on the inside of the goggles, then polish until clear.
Paulgertie

This thread was discussed between 15/01/2009 and 16/01/2009

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