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Homemade Blast Cabinet


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Thought I'd post up some info and pictures on my blast cabinet project. I've always wanted one as wire brushing parts is no where near as satisfying. After losing access to one via an old job I googled to see what others had done. Turns out that it is possible to build a working unit out of ply quite successfully.

After some research I ended up with the following plan:

1/. Plywood 'box' with a cone base so that used blast media collects and can re used by the gun. Steel 'target on rear wall to re-inforce. Other seemed to get away with out this, but it seemed like a good idea and I had a suitably sized bit of sheet of 1mm steel in the shed. I did think about a steel cabinet, but my welder failed after building a shelf and despite repairing (soldering in a new relay) it only lasted 10 minutes before a repeat performance - it was also rubbish when it actually worked.

2/. Suction blast gun - Mainly because of my air supply limit. I have a 3HP 200 liter air compressor. I bought one from www.blast-wash.co.uk. They were quite helpful and gave me some good tips.

3/. I wanted to run the cabinet at a vacuum/lower than atmospheric pressure so that air leaked into the cabinet rather then dust leaking out. The master plan was to have the pressure low enough that there was still a vacuum with the blast gun running. I used a Dyson DC04. Luckily it turns out that the DC04 can shift more air than my 3HP air compressor. I spent a bit of time looking at dust extraction as apparently blasting can/will produce sub micron level particle that ruin your lungs. I did think about making a cyclonic separator with a vent out of the roof of the garage. However I currently just put the dyson out side and hope for the best....

4/. Air inlet to the cabinet at the top directing air onto the glass screen. This limits the impact of blast media onto the glass.

5/. Dust/air extraction from the base so that dust is drawn down out of the viewing area

6/. Lighting so that I could see what I was doing. Others suggested painting the interior white to make it as light as possible.

I knocked up a design on CAD that would allow me to fit most items in - diff casing, brake caliper, etc. I fitted a removable side hatch so that longer items could be blasted. Intention being that a canvas extension could be fitted to the side to wrap around long items. Cabinet size was tailor to fit the space in the garage. Normal access is via lifting the front panel. This is driven by space constraints in my garage.

The space was occupied by a shelving unit. This kick started an enabling project to build a shelf above both garage doors so that the shelf unit could be removed.

One sunny day I started chopping up 2 sheets of plywood.

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I decided to make the cone hopper non symetrical with the point pushed to wards the rear so that if I sat on a stool at the blaster the cone would allow my legs to fit under the blaster. Don't do this. It makes the angles in the cone a right b***t**d to work out. I spent an evening with a piece of paper and a bottle of wine deriving the angles the edges of the cone needed to be cut at. Feeling satisfied at my superior math skills I decided to measure twice and cut once. So I made a scale cone from card and measured the angles to verify my maths. Obviously they were different from the angles I calculated. So I used the measured angles

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Looks good, I'd suggest installing some rubber on the inside (or something suitable) to adsorb the abrasive action of rebounded and non used shot.

I found with my blast enclosure that the plywood floor suffered from some splintering and the splinters where most screened out when I reused my garnet again.

The abrasion was slow, but something you may wish to consider.

Within my blast cabinet I used a3 translucent overhead projector screen sheets to protect the perspex from abrasive clouding

And within the blast cabinet, the 12v fluorescent lamp was carp.... solution I found was two diachroic 12v lamps with glass screens... good light, cheap to replace when light level dropped from frosting

Rob

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Rob,

I found that as long as I did not deliberatl blast the wood I was OK. I have gone with glossed white walls to keep it bright. I might later find the need for the rubber. I have tweaked the design slightly based on test runs, but I'll cover that in a post or two.

Adrian

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Next up was the intial leg installation - there is cross bracing to come. Finally holes for the glooves (Marigold Emperor - jubilee clipped on to 4" OD ducting) and the edging around the front opening to take the stick on foam (4mm thick double glazing foam) for the front door/hatch to seal against. The front hatch has no opening at this point as I did not have any glass - I later found the rear windows from a transit connect were a good fit and only a fiver from a scrappy.

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Next step was fitting out the interior. The horizontal copper tube has slits cut into it allong it's length and will be behind the steel back target. The idea being that it will then pull contaminated air from just above the hopper, but not get direct 'blast' from the nozzle at it. At this point I only had one outlet - 28mm copper - fits right into the Dyson hose with out the need for any fittings.

The lights are just 240V LED down lighters from screw fix. I should have fitted 3. They go into the false ceiling that the air enters into. The false ceiling directs the air onto the front window via a gap at it's front edge. The width of the gap is varied to ensure the correct vacuum is pulled in the cabinet. I did envisage a nice sliding 'thing' to adjust this. However the 1st test run used electricians tape - it does the job, so it's still there.

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Then I put in the rear steel target. I put a nice fold into this at the local college when I was supposed to be welding. The 'floor' is just 20 x 20 x3 angles. This works, but later I put a mesh sheet across the top which is much better/more stable.

I also built the grit pick up. Based on info from the web and some tips from the guy at blast-wash this has a 45 degree cut to maximise the opening. The copper pipe (brake pipe) is an air line. You can't suck the grit up the suction hose with out some air to entrain/blow it along. The copper pipe provides the air supply to the 45 degree inlet. This sticks into the drain at the bottom - I just hole sawed a hole and glued in some drain/waste pipe and fitted a screw on cap at the bottom. The other pipe is for a return line from the exhaust for any grit that drops out.

I also fitted the window (Ford Transit connect rear door glass). This is sealed to the door with more 4mm double glazing sticky foam strip. I quickly found that the glass gets etched. I now have a sheet of florists cellophane trapped on the inside to provide a sacrificial layer.

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The 1st test - would the hoover pull a vaccum in the cabinet?

http://vid46.photobucket.com/albums/f101/Breg90/blaster%20cabinet/IMG_2587.mp4

My son and the neighbours kids seemed to think this was interesting...

The link gets the response, for me at least (a person without a photobucket account), of

Sorry, the requested page does not exist.

Please check the URL for correct spelling and capitalization.

Regards.

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Finally will it blast something. I grabbed the nearest bit of steel I had and set too:

http://vid46.photobucket.com/albums/f101/Breg90/blaster%20cabinet/IMG_2701.mp4

After that success and a cider to celebrate I dug out an old Disco 2 caliper I had previously retrieved from a skip for a portal axle braking project:

http://vid46.photobucket.com/albums/f101/Breg90/blaster%20cabinet/IMG_2702.mp4

Seems to do the job!

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What media are using?

I use garnet for paint removal, and surface corrosion

Glass beads for aluminium and a light polish.

And aluminium oxide for heavy rust... must admit I don't use the aluminium oxide as its a bit too abrasive for me.... plus landrovers and rust plus aluminium oxide and a pressure post blaster normally equals holes in axle tubes..... garnet more forgiving.... and a little slower

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Rob,

In the video I was using some machine mart Aluminium Oxide. It's dusty. I have since bought a 25 KG bag of Aluminium Oxide and while I was paying postage added some glass beads for good measure. Not used them though yet.

Adrian

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I bought mine from Na Robinson Poulton le Fylde (nr Blackpool), but it's local to me, they do everything blasting, including an in-house barn size double blast cabinet

Wouldn't waste the glass beads on steel, they are best for the more delicate stuff, plus they go powdery quick

I use my dyson to vacuum up the media too... as they have a cyclonic filter, it is good for separating the more dense material for reusefrom the dust.... stops you blasting powder about.

Suggest using a good water trap or two in parallel... or using a coil of copper tube in a bucket of cold water (add ice if you require... but tap water can be quite cold here too) before the water trap as a home made dryer too

Rob

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I find the sponge after filter on the dyson blocks and I loose suction. Do you have this issue?

I'll pick up on that point in a minute.

I managed to infer from your first post that the build posts were to be a record of history, so decided it was pointless posting until the cabinet was in use.

Perhaps 10 years ago a friend and I co-operated to build a very similar cabinet, modifying a set of plans to suit my requirements.

Once installed I modified the cabinet in the light of experience gained over several years. Those experiences inform my comments here.

I was advised to use air filters, but soon found they blocked very quickly.

My advice now is to use no dry filters anywhere. Dry being sponge, foam, cloth, paper, anything the dust laden air has to pass through.

I don't know the Dyson you are using, it's possible the filter is to ensure the air passing over the motor is clean. If so, change the vacuum cleaner to one that doesn't use the same motor cooling technique, or throw away the filter and let the motor take it's chance.

I use a different (older) style of vacuum cleaner, where any motor cooling air flow is totally separate from the dirty 'vacuumed' air flow.

My circumstances permit me to vent the air to the outside without filtration. The vent in the garage wall is about 12" above the ground, into an overgrown area of the garden. The plants disrupt the flow of dust. I would never use a roof vent as it allows too great an opportunity for dust and noise to spead over a larger area.

If I was to install a filter it would be a wet one, where the dust laden air passes over a liquid, probably with a couple of baffles in the air stream to direct the air down towards the liquid, where the heavier dust will continue down into the liquid, while the lighter air flows up past the baffle, along to the next baffle and then the exit pipe.

There are other aspects deserving of comment, but that will do for now.

Regards.

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Suggest using a good water trap or two in parallel... or using a coil of copper tube in a bucket of cold water (add ice if you require... but tap water can be quite cold here too) before the water trap as a home made dryer too

Rob

I'm just making one up for mine now - half way there.

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I ditched all the filters in the dyson, first I used the original upright dyson, dc01... got for £10 at a car boot.... lasted about 5 years of garage use.... the plastic bits broke before the mechanical... back to the local car boot, and picked up a dc07 which I've had for about 2 years... again about £20... think of them as consumable.... but cheap to replace via local tip or car boot.

I have a secondary fans in the garage to provide good air change too (when plasma cutting for example)

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I'll give a water filter/trap a go and see what difference it makes. I'm reluctant to ditch the air filter in the Dyson as the fine powder is not to good for me or the side ways on my mill/lathe.

My more pressing need is more air. My compressor can keep up, but only if it runs 100% of the time. Suspect that longer term that this will not be too good for it. I've also had issues with damp air once the compressor/air tank get hot. I now have a section of the air line jacketed with the garage water supply. Turn on the tap and it cools the air and causes much more water to drop out in the coalescer.

Adrian

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"... the fine powder is not to good for me or the side ways on my mill/lathe.".

For just those reasons you should be ducting the air outside; I use the sort of automatically closing louvred flap sold for clothes dryer outlets.

"My compressor can keep up, but only if it runs 100% of the time.".

I'm afraid that is a given.

It doesn't matter if you run a suction gun system or a pressure pot system, the compressor will run full time.

As a matter of interest, what line pressure are you trying to run?

I find it better to run a pressure low enough to be consitantly maintained, rather than try for a high pressure which lasts for 1 minute, and then falls.

Plan your air line to have minimum restrictions, thus no right angle bends and no quick release couplings. This ties in with your planned DIY full flow condensor.

Use the largest bore pipe you can get. I use the uncontrolled outlet from the compressor tank, my pressure regulator (and gauge) is on the front of the cabinet, where I can check what pressure is being maintained.

As the nozzle of the gun wears so the pressure will fall, and the cleaning performance decrease.

All the above comments have assumed that mainly you are cleaning corrosion off Land Rover parts. If you are mainly keying an almost clean surface, like your bit of rusty plate in the video, so that the paint will have a good key, then you can operate successfully at a lower pressure. But even so, you should expect compressor run time to only vary between 100 and 95%.

Regards.

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Running out of air is why I use two 3hp compressors in parallel... again... sorry I think of them as a bit consumable.... most made in China and the days of getting spares seem over or pointless... budget on £150 for a 3hp/50 litre.

Air pressure is something which needs to be adjusted so your media does not turn to dust too fast and your part disappears.

A secondary ducted fan with the duct placed close to your dyson outlet will help.

You can try adding a bucket with a lid to act as an initial air trap... the problem will filters is surface area.... for dusty environments you want large surface area so that as it begins to clog you still have sufficient surface area so that it lasts long enough to perform the task... the small dyson is not built for that task... but you could always buy a few dyson ones wash and change them regularly as needed... whatever works for you.

Problem with water is media clumping... and as you are using a vacuum blast gun, even more so... the water cooling is fine, but you may want to run filters and separators of connection size 1/2" and run them in parallel which will half their resistance ( but their effectiveness remains the same)... all depends how much you want to do... how long for... and how much you need that perfect setup...

I've said it before that quick connect fittings can take a load of pressure out of the available pressure... suggest you put a male and female together and blow through them using your breath... then try something like the pcl XF (extra flow)... the difference is great... although pcl xf are expensive, if you search for the airline fitting number, you will see that many manufacturers make a compatible airline male and female... maybe at lower cost... hence why I use very small bore quick connects of suitable pressure rating for my mig and tig, to share gasses if u need to (post regulator). Machine Mart long quick connects are particularly bad... all mine have been removed from tools.

(Just one person's view / experience)

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I've not built one ... but there are links to silicon desiccant air dryers using silicon beads and a length of oversize steel tube, where they change the desiccant regularly... and recharge (dry it out) in a domestic oven .... swmbo out shopping.... spa day away... whatever works for you...

I have been thinking of making a regenerative one with a heater or purge supply in reverse ... or both... as it is very useful for consumables life with plasma... but time short, projects many... pipe dream projects / distractions easy...

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2 x air compressors - I've been looking at costs for a second compressor!

Dyson filters -I'm not blasting every day, so I may yet just get a few spare filters as you suggest.

The water jacketed air cooler works. I get far more water in the coelescer on the regulator. However I am sure there is a more efficient coelescer than the one I have.

I think my next step is to look at more air capacity - I do not run out of air, but running,my compressor flat out will kill it eventually.

Adrian

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