Blasting issues

[droopsnoot]

I've got a Sealey 3hp, 50ltr single phase compressor that works quite well, and over the last day or two I've been trying to use a blasting attachment I bought some time ago. I used it earlier in the year with similar issues, and wondered if anyone had any suggestions. I have a bag of media with a pipe stuck in it leading to the gun, and the item to be blasted inside a big plastic bag to keep the media from going everywhere, and so I can re-use it.

The problem is that it seems to clog quite quickly, or at least I think it's clogging. The media is something I got off ebay, "Medium glass grit" and when it's blasting, generally works quite well. The main issue is that I don't get much time blasting because I rapidly hit a point where nothing is coming out of the gun.

When I first started using it, I was using the black plastic tube to take the media to the gun. This seemed to get blocked quite quickly, so I'd have to rod it out with a bit of plastic tube to clear it, and I spent more time doing that than actually blasting. Now I have a piece of clear pipe so I can clear a blockage by tapping the outside of the pipe, but it doesn't seem to be clogging - or if it is, it's doing it in the gun itself. So now I rod it back with a bit of bent wire.

I read on the other thread where someone was asking about what equipment to buy, and noticed that the cabinets all say "don't use more than 80psi" - could that be the problem? As it's a small compressor, I figured that just having everything on maximum would be the best way to go.

Or is it just that the compressor isn't up to the job? It does cut in quite often, but I don't mind waiting for it to catch up from time to time. The times when the gun doesn't seem to be doing anything don't seem to tie up with the times when the pressure is lower - that is, if I sit back and wait for it to fill the tank, it doesn't suddenly get better.

I spent nearly a couple of hours yesterday trying to blast around the crusty bits of a petrol tank to see if it was usable, intending to do the rough edge first then go over the rest to remove surface rust, but only got to a point where I'd done some of the rough edge before it was time to pack up for the day.

 

[rtbcomp]

The biggest problem is that the end of the pickup pipe tries to bury itself in the grit, it really needs to be a cm or two from the top of the grit. I fitted to disc near the end of the pipe to stop it sinking and that helped quite a bit.

Try using a bucket instead of the bag to hold the grit.

Certainly play around with the pressure, higher pressure doesn't always mean more efficient blasting.

 

[piman]

Hello Droopsnoot,

I wonder if the bag you use to capture the grit is part of the problem. Blasting cabinets don't work unless there is an extractor system to stop it pressurising and reducing the blasting pressure.

Alec

 

[droopsnoot]

Thanks rtb. Come to think of it, I did find earlier in the year that it was digging in a bit, and periodically pull it out and stick it somewhere else in the bag. I will dig around for a suitable bucket and try that as well. Might be a use for one of those clear plastic discs that come on the top of a spindle of blank CDs that I've been saving "Just in case" for years.

Alec, I originally started out with an "exhaust" in the form of a length of rubber hose in one corner of the bag, venting any excess back to a bucket. However after using it a bit, the bag is now a long way from air tight so there's no back pressure to worry around, to the extent that I don't bother with the vent pipe now. Also yesterday I just had a couple of clips to help keep the end a bit neater, not sealed in any way. To put it in perspective, the bag was one that a mate had a new Alpine hard top delivered in, it's massive and doesn't inflate at all.

Mike

 

[Gareth J]

Quickest way I find to unjam is put my finger over the end and squirt the gun. Nothing will come out if no air can get past so push reasonably hard. Trust me. The pipe will clear instantly.

If it was working but now isn't, something's changed. Damp or dirty media? You could try sieving and drying a batch out to check. Maybe the gun's worn? The cheapy ones I've been using seem to self destruct after not too long. How long is your pick up pipe? I try to keep mine about a foot, I don't know what the lift on them is but less must be easier.

I've found about 90psi works nicely. Too much can be detrimental, especially if the gun is worn.

 

[rtbcomp]

Quickest way I find to unjam is put my finger over the end and squirt the gun. Nothing will come out if no air can get past so push reasonably hard. Trust me. The pipe will clear instantly.

...

You need to wear a thick rubber glove - if air does escape it hurts!

A better idea is to use a rubber block, I use a Metro rear bump stop.

 

[droopsnoot]

Thanks Johnser - earlier in the year I was removing the plastic pipe and using the air to clear it, never thought of just covering the nozzle. I always have welding gauntlets on, mainly to stop the grit going up my arms but also because it does hurt. I wouldn't say it's really changed since earlier in the year - it was clogging then, as well. The pipe is a little shorter than it was, I'm not sure whether the media is damp but when I stir it, it seems to move around OK, and while it's a little damper now it wasn't when I was first messing with it. The gun was from a car boot sale, the noticeable thing is that someone had removed all the spare nozzles so I'm just working with the one it came with. Maybe a smaller one will help, as per the comment in the other thread.

I am a bit relieved that no-one has said "you've got no chance with that tiny compressor", though. I'll try these out in a few days when I'm next at the shed. A future question will be "how can I repair small holes in my fuel tank" once I've got it working better.

 

[Gareth J]

You need to wear a thick rubber glove - if air does escape it hurts!

A better idea is to use a rubber block, I use a Metro rear bump stop.

I'd recommend using gloves yea. But I rarely do. Rubber block sounds very sensible indeed!

 

[Seadog]

You need to wear a thick rubber glove - if air does escape it hurts!

A better idea is to use a rubber block, I use a Metro rear bump stop.

Another good reason to wear gloves is that it can take a surprisingly small amount of air pressure to penetrate the skin, typically 6 psi I seem to remember.The last thing you want are air bubbles in your blood.

 

[mike 109444]

Thanks Johnser - earlier in the year I was removing the plastic pipe and using the air to clear it, never thought of just covering the nozzle. I always have welding gauntlets on, mainly to stop the grit going up my arms but also because it does hurt. I wouldn't say it's really changed since earlier in the year - it was clogging then, as well. The pipe is a little shorter than it was, I'm not sure whether the media is damp but when I stir it, it seems to move around OK, and while it's a little damper now it wasn't when I was first messing with it. The gun was from a car boot sale, the noticeable thing is that someone had removed all the spare nozzles so I'm just working with the one it came with. Maybe a smaller one will help, as per the comment in the other thread.

I am a bit relieved that no-one has said "you've got no chance with that tiny compressor", though. I'll try these out in a few days when I'm next at the shed. A future question will be "how can I repair small holes in my fuel tank" once I've got it working better.

Might be worth giving the tank a good "poke" with a pointed tool to make sure it's not worse than you think and save your self some time blasting !
There was an item on the "wheeler dealer" show where they got a fuel tank repaired but note the need to remove any fumes from the tank as it's a potential bomb if you go near it with a naked flame or sparks from an angle grinder. Maybe the use of the very big copper bit type soldering irons that are heated in a separate heat source.
Don't think I will be repairing my tank Did not look to bad at first then gave it a blasting with the pressure washer......

 

[mike 109444]

Also note blasting can generate sparks but not sure if that applies with "glass grit" ??

 

[rtbcomp]

Also note blasting can generate sparks but not sure if that applies with "glass grit" ??

Yes it does. I've seen "impact sparks" rather than those caused by static, but it's not worth the risk.

 

[droopsnoot]

I'm getting some pitted areas - really that's the point of blasting it, to see whether anything goes through or whether it is just pitted. Finding a replacement tank isn't easy - I've got the original one off the car, and two spares, and all three have similar issues, a build-up of rust above the seam on the offside edge. Of the three, the one that has had fuel in it most recently was emptied when I removed it from the car in about 2009 - I've heard about issues mixing sparks and fuel vapour, but I'm not sure whether six years is long enough, and that's why I hadn't thought of welding it up, I never thought of blasting causing issues. I must admit I was hoping I'd just have to clean it off, paint it, somehow remove the dent from the bottom and go from there, but it's not looking good at the moment. The section I did yesterday only revealed one pinhole though, and I did go over the rest with a spike, poking where it looked thin.

 

[brightspark]

if u sandblast the tank it will hilight any pinholes under the rust.any other metal will be sound , if theres not many of them use an acid flux and a large soldering iron heated on a gas ring and the tank will last for years no need to go poking all over it

 

[mike 109444]

As my tank is needing to be replaced (sometime in the future when build gets that far ) I did google tank replacement and found some sites that do a coating inside and out of a plastic type stuff (not the Frost slosh stuff). designed to seal up any pin holes up to a point! Think mine is beyond that though

 

[droopsnoot]

I wondered about something like that, also there used to be a putty-type product that could be used, though I don't know whether they're just snake oil or not. The large soldering iron is an option I've heard of before - I would have to get one, but as it looks like I've got three tanks to repair, it's probably worthwhile. I did have a quick go with a mains soldering iron on the first pinhole I found, and while the solder has stuck it does look very much like a weld that hasn't penetrated the metal.

 

[brightspark]

a mains soldering iron wont be much use. 2 much heat will be disipated on the tank. a large copper one heated on a gas ring or blowtorch can-retain enough heat for 5 mins of soldering. cleaned and fluxed properly u will get a nice smooth tinned surface something tis size or larger

http://www.ebay.co.uk/itm/VINTAGE-C...216308?hash=item58d2f24af4:g:guwAAOSwNphWXegE i wouldnt pay more than a tenner for it but -iff needs must

 

[droopsnoot]

Well, I had another go with this today, first on a front wishbone and then on the side of a tank, with mixed results. I've transferred the grit into a plastic bucket now, which I managed to tip over today while moving it, so it's been quite well "loosened" while I picked it all up off the floor. I've also fastened a plastic disc around 2" from the end of the pick-up pipe, and turned the pressure down a little. I got some reasonable results on the wishbone, but it got to a point where it seemed to be doing nothing at all, even though I could see it was pulling grit up the clear pick-up pipe.

I thought I'd cracked it when I saw that the nozzle was somehow quite far back into the gun, which I felt would restrict the grit path significantly. I moved it forward a bit, though, and it didn't help. Another thought was maybe the workpiece needed to be higher up than the grit, so I stuck it on an old trolley to see if it helped, but it did not. Next job is to try to find some smaller nozzles for it - it was bought from a car-boot sale, and the pack had been opened and all the spares removed, so I only have the one nozzle which is quite large.

 

[rtbcomp]

The missing nozzles may be the same size if it's a Clarke or similar. I've seen different sized air nozzles, but not blast nozzles.

 

[brightspark]

if u have a lathe make a few different size nozzles out of steel to try .but as said above there fairly -standard its only the air supply nozzle that are different sizes