Abrasive Cabinets

[mutley]

Does anyone have any experience of the small abrasive cabinets that are available from various sources. For example ebay item 280139152186. I'm not worried about the size as I only intend to use it for small items. What does puzzle me is that I thought any form of abrasive cleaning required vast amounts of compressed air and this unit only requires 5cfm's which is relatively low.

Andy

[SteveW]

Andy,

I was a bit confused with your title but from the vast amounts of compressed air I'm guessing you're talking about grit blasting. If you're not the info below is free anyway.

A while back I needed to clean up all the bits of the club loco prior to a total respray. The many rivets and nooks and grannies meant simple abrasive techniques were out. I have a small 1.5HP compressor with a 25 litre tank. The sources (Machine Mart Cat) suggested that I'd need a 3HP compressor and of course loads of air. I bought the small spot blaster at around 18 quid as it would work on my compressor, just. I also bought a tube of 80-120 grade grit.

Expecting to make a hell of a mess I converted an old cardboard box from my 32" TV into a spray booth.. This also captures the used grit for next time (essential!). I cut two corners off an had an angled window using a bit of spare secondary double glazing. I also used strips of old carpet around the edge for a seal. I cut two arm holes about 9" dia and made a couple of sleeves out of some spare polly-sheet and taped some rubber gloves on the end. DO NOT FORGET the gloves. Another point is that you're dumping a lot of fresh air into the box and it needs to find its way out and it can take a lot of grit with it. A long bit of waste pipe helps.

I also did it in the greenhouse at the bottom of the garden and used about 40' of hose. Compressors don't like the clouds of grit you're going to generate.

The spot blaster comes with a set of rubber nozzles to capture stray grit and recycle it back into the grit pouch. This didn't really work for me and a replaced the 'L' shaped hood with a bit of waste pipe suitably drilled. This also made it a lot simpler to reload with grit.

The first pass of grit blasting went OK except for clumping in the nozzle. This was caused by moisture and cured after a trip back to Machine Mart and the purchase of their cheapest water filter. On recycling the grit I found that bits of crud and those nodules again caused clogging. A trip to the kitchen got me the family sieve. This also help to rescue any escaped bits.

The real problem is getting enough air. This meant replacing the original air tap on the compressor and replacing all the quick release connectors on the air pipe with drilled out couplings. It was then just a process of waiting for a full charge of air and letting it rip.

Forgot the most important bit. A very effective face mask and goggles are essential. As is hat, coat gloves etc (and also put the water heater on for a shower later).

The effect is like having the most effective airline you ever dreamnt of. The cutting zone is very small but is idea for all the complex bits, pipe work, steel, brass sheet nuts, bolts, etc. Paint goes on like a dream.

You do need to clean off before painting and avoid water on steel else it goes rusty as you watch.

The spray nozzle went from around a 6mm holes to over 8mm and I found a rake through the used grit with a magnet rescued a lot of iron.

The whole process is too expensive on time/air/grit so preprepare all bits by removing old paint with paint stripper. I found that a lot of the cab still had that oily sheen on it but this gets reduced to a dull matt after a good blast. Don't wast time doing a loco chassis. Protect all the threads with old screws and protect all sliding surfaces with wooden blocks and get it done professionally. If the blocks are sized correctly the chassis can sit on them during the respraying which needs to happen within the hour.

Did this help?

[chris vine]

Hi Andy,

I used grit blasting for nearly all my work on Bongo. It give a terrific surface for paint to stick on but there is one drawback: The surface, being rough, can be difficult to get clean before painting. All rags, clothes, tackrags leave bits behind on it.

I bought a cheapy blast cabinet from one of the cheap mail order companies and it was not a great success. The main problem was the pick up tube and the gun. The nozzles wear out in a few minutes use and the feed arrangements give a feast or famine effect. Look carefully at their blurb. I found out that the small print for mine said it was for glass bead media only. I think this may be a lot easier on the gun etc.

In the end I went to a firm, Anglo Scot Abrasives, who sold me a really good replacement gun with a decent feed tube. this worked brilliantly and I had no more trouble. Their number is 01942 270729. From memory they also supply a cabinet in kit form made of wood. I think its advantage, other than cost, was that it had a door in the end so you can get long items like loco frames in if you want to.

Oh yes, Air. These things do use a lot of air. One thing that seems to be recommended is to get a small compressor with a very large reservoir. This doesn't really work and you will find it very frustrating waiting for it to charge up again. It all depends on the size of the parts you are blasting. (you certainly will be "blasting" if you are working on large parts with a small compressor!)

Hope that helps
Regards
Chris.

[abby]

Hi Chris I have the small Sealey blaster which I use for cleaning castings , it runs off a small 8 cfm compressor and I just run kiln dried sand through it .
I have found that it is important to sieve the sand through a flour sieve to avoid clogging. I am building a cabinet at the moment as I plan to use glass bead which I would wish to re-use over.
The finish is very good using sand and removal almost instant but it is necessary to stop at regular intervals to allow the air to catch up.

[mutley]

Morning Everyone
Steve, very ammusing and not disimilar to my own experience so far. I used a vague term in the topic heading as some people call it sand blasting, some call it grit blasting and then you get bead blasting etc.
Chris, your experince is what I was worried about, I'll investigate a diffrent gun to fit the cabinet.
Abbey , I had often wondered about just using dried sand.

All I want is a cabinet that sits on the end of the bench for doing small detail parts. One of the clubs I am a member at has a cabinet which has been great to use up till now but its a bit of trek to get there. I have a local specialist company near me who have walk in cabinets for the really large stuff and often do a handful of bits for 10-15 quid but the ecconomics suggest buying one would be a better option.
thanks
Andy

[Noddy]

Natural sand:

In most parts of the world, natural sand is going to consist predominantly of quartz (crystalline silica), This is hard enough for roughening most metals (it doesn't really touch carbides including white (chilled) cast iron), although depending on the source, the grains may have a rounded surface, and be less aggressive than sharp grains.

Crystalline silica is a bugger when it gets into your lungs!

The damaging particles are too fine to see (smaller than about 10 microns). There seem to be at least 2 ill effects:irritation caused by the sharp particles cutting your lungs and a chemical hardening of the lining of your lungs.

Like most things, the damage is proportional to dosage X length of time you're exposed.

People who worked as razor grinders, or in silica refactory works had very short but well paid careers, and died young! early compressed air rock drills were nicknamed "widow makers" for the same reason!

The underground silica sand mine where I did a lot of work used to monitor the working environment and send the workers for either annual or twice yearly chest X-rays.

Alternative abrasives such as garnet, olivine and glass don't seem to give the chemical damage to your lungs, and both garnet and olivine are denser than quartz, and so carry more energy for a given velocity.

If you get or make a cabinet, make sure that you can force vent it to the outside!

[chris vine]

Hi All and Abby!

Although I am somewhat unimpressed by endless health and safety stuff, I think it is generally not a good idea to use sand for blasting.

The proper grit, which comes in 20kg bags goes a long way, especially as it is used many times over in a cabinet.

I found a good grit size for our work is about 220.

I think that the glass bead media might be better because it would leave a smoother surface more like a satin effect. I am sure the paint will still find plenty to grip on but it will be much easier to wipe or blow clean prior to painting.

It will be interesting to hear from someone who tries this.......

Chris.

[wayne]

Hi Mutley

The cabinet you are looking at is really designed for glass bead; it uses ceramic nozzles which as pointed out above do wear out especial if operated at the wrong pressure for the media. 50psi is generally accepted as the maximum pressure for glass bead, 80psi for fine copper oxide.

You can of course make an exact copy of the nozzle in steal as on my gun, also if you use a ceramic nozzle and turn it round 120 degrease every 5 minutes, the nozzle will wear evenly and last longer. However with all the DIY blasting kits/cabinets on the current market they make a poor comparison to their larger industrial cousins, in terms of ease of use, speed of surface coverage and the vast amount of air required

Disclaimer I do work in the compressed air industry but my firm stopped selling DIY blasting cabinets due to most people been disappointed with them. (I use a 5cfm modified nozzle blast gun and a hydrovane 501 compressor)

Ps Chris if you look at any concourse vintage motorcycle the cast aluminum cases will most certainly have been beed blasted with glass bead and you get a similar finish on copper and brass.

[johnwhalley]

Hi I am the owner of the business referred to by Chris in his excellent book, many thanks for the mention Chris, I am not here to advertise but would like to put you straight on a few points mentioned above.

First Chris is correct in avoiding the use of sand, not only is it a health hazard, it has been illegal in the UK since 1948.

Do you need a vast amount of air?
Depends what you are trying to do, to clean the Forth Bridge, yes, to clean, deflux and prepare a couple of loco frames, or to derust and remove paint from an old motorcycle frame, No! the only difference between using 5cfm and 500 cfm is speed, if the machine is designed properly it will work perfectly well from 5cfm, we have many customers using smaller compressors than 5cfm by working for a short time and waiting for the compressor to catch up.

There is no such thing as a bead blasting or grit blasting or shot blasting machine, they are exactly the same thing, the media is what determines the effect on the work and any blast cleaning machine can be used with any blast media.

I am not putting a link to our website as I dont think this is the place to do so, but a search will find us easily enough, and there is a page on there called FAQs which will answer most of your questions, if you are anywhere near us in Wigan we are always pleased to demonstrate what you can do with 5cfm telephone me first.

John

[chris vine]

Hi John,

Thanks for the comments. I am very sorry that for some reason you were missed out at the back of the book in the list of addresses of suppliers. It was an oversight.

Why not put your details and website url etc on this site on the Trade Sales and wants page?

Thanks for your help when I needed it!!

Chris.

[ron]

Hi Andy
I used a small Screwfix cabinet to blast various parts of a TR6 when I was restoring it, after a bit of trial and error it was highly successful. Here is what I found;
You need a reasonably large compressor, ie 13cfm with a water separator
An extraction system on the outlet of the cabinet, I used an old industrial vac, if you don't have extraction you end up unable to see what you're doing, particularly when the blast medium gets dirty.
Ceramic nozzles of various sizes.
I ended up using an external halogen spot light as the internal one wasn't very effective.
It's a dirty filthy job that no matter how good the cabinet seal is I still had to wear a good quality dust mask.
I think if you were only blasting small parts you could probably get away with a smaller compressor until the nozzles start to wear which even ceramic and tungsten carbide ones do quite quickly with a carbide medium.
Glass beads were of limited effect and only really good for giving a nice finish on soft metals.
They are a very handy tool that will clean rust etc off metal far more effectively than anything else I've tried.
Ron
PS By the time the resto was finished the cabinet was only fit for a trip to the local dump

[circlip]

One point seems to have been missed in this thread, which I found by reading/talking to external trade sources and finally using an industrial machine myself is that for contaminated parts, first get rid of any grease and oil by whatever chemical cleaning methods required,(solvent or other liquid means) then attack the bits using an abrasive media. This gets rid of the surface paint/rust or other surface staining media, but it OPENS the material surface which is ideal for a paint primer. If you want a smooth/polished surface, especially on alloys you should then go over it with a glass bead type media to CLOSE the surface down again. It gives a peening type operation. DON'T bead blast onto contaminated surfaces cos you're sealing the muck in, it will eventually be cleaned but you will have removed more base material than necessary. The final point is, EVEN as a FRUGAL Yorkshireman, DO NOT re-use filtered media on dissimilar materials, ever seen alloys and bright stainless rust? You're impinging the previous crud into the material. I'm NOT speaking as a trader or EXPERT but as someone who has been involved in the dinnertime government manufacturing industry wearing the teeshirt and erasing the video.

[mutley]

Hi All
Thanks for the comments, slighty less confused than before now. I thought this would be a simple question ,oh well. I will let you know when I've found a small cabinet.

[SteveW]

Guys,

A word of caution on bead/grit blasting on soft metals.

A long while back someone told me a story of how a company won the contract (as the lowest bidder) to remove the paint from a small commercial satellite dish prior to a new paint job. The recommended but more expensive method being that nasty paint stripper stuff, a lot of hard work and loads of messy and expensive hand work.

Anyway the job was done and the dish was returned to service. Trouble was it didn't work as a dish any more. They used a bead blast which was very effective at removing the old paint but equally effective at planishing the surface causing it to stretch and no longer follow the necessary accurate parabola.

Of course no one believed what had happened so a two segments of a dish were made to model the problem. Sure enough the bead blasted one was totally sh..

[wayne]

I thought i would reply to some of the comment made since my last post.

Using a compressor smaller than the cfm of the equipment will cause the compressor to run longer and harder, this will cause on a piston machine, overheating, oil carry over passed the rings, carboning the valves up. On a vane or rotary screw compressor you will get oil carry over which will contaminate the work and blast media and do the compressor no good if run for long enough. As some one mentioned 5 or 500cfm machines you are correct the aforementioned applies regardless of the size of compressor if it’s too small for the job

Second my experience of the small 5 cfm cabinet was that with glass bead was the results were good and aluminium oxide results were ok but with copperoixde or anything heavier/ coarser for rust or paint removal the cabinets performance was poor due to the suction pick struggling and venture ejector struggling/clogging with heavier grits. I have tested several makes and found the same results. Note the correct pressure for the media was used.

Also the comment that a 5 cfm cabinet will use any media, i did say they are really designed and work best with glass bead and stand by this comment, in other words very light blast medias . I also will not put the firm I work for’s web site up, mainly as there would be no point as we stop selling and for a reason, the cheap 5 cfm cabinet was c***p and second I am not on this forum to benefit the firm I work for,