Internal Fire Museum of Power

i have stumbled upon a forum discussion from 2011 about grit blasting. its something i do a lot of in different guises so thought i would offer some advice as i have found the process invaluable for restoring old engines as almost everything is made how an engine should be...solid metal of one kind or another and no damned plastic or clever space age rubbish !!

if you restore any old iron that can be unscrewed into its individual piece parts then you can make good use of the blasting process with relatively small outlay. I have never found paying a professional blaster to be cost effective and few of them use the fine blasting media that i prefer. cleaing an RSJ is not the same as cleaning a 50+ year old piece of Dursleys finest cast iron !! if you blast it yourself then you can take much more care than someone else ever will.

the basic equipment is readily on sale in most internet hardware and plant/equipment shops. i bought a floor standing chinese made (what isn't !!) blast cabinet that gives a working area of around 150cm(H)x83cm(L)x63cm(W). it has its own built in hopper and the media recycles itself inside the unit by falling into the hopper and getting sucked up again by the gun venturi feed. it has a hole in the side for a hoover vaccum pipe and a larger hole in the back panel as the flow through vent. if you dont have a flow of exhaust air into and out of the cabinet then you will rapidly get zero vision as it fills up with dust and debris which any small vaccum cleaner (not the wifes best one !!!) will deal with. you are only dealing with a small area so a big powerful vaccum is not needed. make sure its filters are in good shape and that the work area is decently ventilated. an open workshop door or window is adequate.

i bought my blasting cabinet from man trading ltd on flea bay. under £250 and i have to say i have used it a great deal and very pleased with it. the internal lamp is crap but easily replaced with a glass dome bulkhead lamp for about £5 from any diy shop. similar cabinets are sold by other people on the internet. they are all pretty similar. no matter what you do, the internal working area is going to be a bit dim because of the build up of dusty air.

compressor wise the cabinet should ideally be powered by a 15cfm plus machine but my trusty old german 8-10cfm machine seems to cope ok.

remember, all this can be a bit botched as you will not be blasting away all day long but probably doing a few hours or so infrequently and on this basis this kit at this kind of price is, i feel, money very well spent !!

process......the first pearl of wisdom i offer is to steer well clear of sand blasting and of sand as blast material to use in a blaster. this does work but produces fine silica dust clouds which will screw up your lungs...in fact, i suggest you wear the very best full face mask you can afford regardless. eye proctection is as important as lung protection. professional blasters wear purpose made full head hoods with piped filtered air; these cost many hundreds to acquire. you can get by with a £60 full face mask and decent particle filter (the 3m 6060 series works well for me).

the magic end result of this expense and effort is that your bits of old engine will be cleaned in every nook and cranny to a degree that no other process can match. yes its filthy and dirty and time consuming to do but worth the end result.

i use 2 types of blasting media in my process. depending on the metal (aluminium or brass or machined steel or castings etc etc), i generally start by degreasing in a parts wash tank if needed then drying off and applying paint stripper to remove the worst of any old paint. i then use a pressure washer on the striped item (s) (i do this in a large old collander or garden sieve to retain any smaller parts) i then dry them all off and put them in the blasting cabinet. i first blast them using a very fine aluminium oxide powder which has a grain size about the same as fine playpit sand. you can use more coarse grades but i have found that using only fine abrasives allows you much better control and you can not really damage or ruin anything. determined rust may take 4 or more passes or attempts to get rid of but this is a gentle process (as far as blasting goes!!).

i tend to do batches of parts for blasting in a 2 stage process.

the second stage requires using ultra fine glass beads (almost the look and feel of a powder/dust more than any kind of bead shape). i only have one blast cabinet so i have to change the media over. this is easily done using the small trap door at the bottom of the hopper and using a bucket or plastic container to catch it all. I then close the trap door, hoover up any remnants of the current media from inside the cabinet and fill the hopper with the beads. (this step is necessary so you dont pollute one media with another)

the reason for using the beads is that they give an almost dull polished pewter kind of finish on most metals and present a great surface ready straight for paint (after a dust blow off and spirit degreaser wipe). I have even used glass bead only blasting on precision machined parts to no ill effect...the process only removes microns from the surface of the part being cleaned.

with practice, you will be amazed by the results. beats using a wire brush any day !!

i have yet to find any engine part (other than bearing faces etc) that does not come out very well using this very moderate blasting technique. you can mask up or shiled almost any area that you do not want media to get into or touch. i use gaffer tape or blu tak to fill up holes etc.

th fine glass beads on their own (ie no stage 1) will clean machined threads with no ill effects at all. I have done this to CAV fuel pump housings and fittings and camshafts, rocker, housings etc etc...the list is almost endless.


this gentle process does take more time but is absolutely within the remit of the engine/ tractor/tank/ space ship etc restorer !! you cant really go wrong.

one point to mention...the nozzles in the blasting gun (inside the cabinet) are made of a ceramic material that does erode away eventually. new nozzles are fairly cheap. i bought all the blasting media i needed initially for about £50. it lasts surprisingly long. the glass beads break down into a talcom powder material eventually so will need to be replenished. the aluminium oxide is very resilient. professional blaster use things like steel shot and copper slag granules which wont allow much fine control. doing it yourself you can quickly become very good at cleaning things as my neighbours constant demands for his bicycle restoration projects proove !!

anyway, hope my ramblings are of use to someone. i have found having my own blasting cabinet enables a much higher level of engine restoration and clean up. one last point. deep rust holes are not easy to overcome but if you have only light or even moderate rust. the 2 stage blasting process can even out the surface texture and make it gretaly improved by the time your new paint coat goes on top.

all the item you will need to set this kit up at home are available for delivery on the internet.

i also use a pot blaster for anything too big for the cabinet. this really is a dirty filthy prcoess and injurious to humans so i do it at the end of the garden next to the compost pile and away from all other life. i use fine ground copper slag granules as an expendable media. its cheap but works. ideal for generator base plates and large cast housings etc. i suggest you wear 3 boiler suits and a full face mask as i always seem to get grit in strange places including areas that the wife has not visited for years !!! ( no joke...how the hell it gets down there god knows but it bloody well hurts !!)
have fun and good luck...always wear protection !!!
regards,
gerry

Gerry,

Thanks for an interesting posting, do you clean your media or just use it until totally clogged, does your cabinet have a cyclone to clean the media.
your masks, are they full face or mouth and nose, in my job I have to use mouth and nose masks which have a high filtration for air in and valved exhaust so have access to them for other uses.

Martin P

We have a small wet bead blast unit here, great for brass and aluminium carb bodies etc, only takes an 8" cube though.

Currently not working as I need to rebuild the big compressor again, needs a steady 10cu ft/min.

P

Has Jon buggered another compressor

Gerry, Good overveiw of an actually very complicated industrial process for us novices. As Martin queries cleaning the media of dust and debris is of paramount importance as the fines absorb large amounts of the blast energy and cause high scouring wear on venturi and nozzle components. The commercial method which can be adapted for DIY is quite easy, by allowing the media to "dribble " over a weir which has a slot under the weir to which is connected a vacuum cleaner/ extractor this sucks the dust back whilst the heavier good media drops past to be caught and reused.
One important thing to bear in mind is that blasting cleans and modifies the surface, if cleaning heavy corrosion then there will be microscopic pits into the surface, (a bit like worm holes) these will still contain corrosion and possibly moisture and so will still be active after all treatments and so other methods of control should be considered
Happy blasting
Malcolm