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sandblasting vs air pollution

5K views 15 replies 10 participants last post by  oldred 
#1 ·
As a practicing fabrication engineer, I want to know if there is any medium to replace sand for sandblasting processes. Now in India blasting by sand is banned as it causes pollution. But we are to compulsorily use a blasting processes to remove rust and scales from light, medium and heavy structures before painting. The surface finish after blasting required is SA2 !/2. I shall be grateful if i can be guided in this matter.
 
#2 ·
csrao222 said:
As a practicing fabrication engineer, I want to know if there is any medium to replace sand for sandblasting processes. Now in India blasting by sand is banned as it causes pollution. .
Hehe what do they do in a sandstorm :rolleyes: .

Vince
 
#3 ·
There are attachments for pressure washers to allow media blasting, as well as slurry blasters. The benefits are a dust-free blast, and obvious cooling of the part while you blast. One of the drawbacks is that flash rust can be a problem on ferrous parts, but I think there are other liquids that can be blasted; oils, glycerin, alcohols.
 
#4 ·
csrao222 said:
As a practicing fabrication engineer, I want to know if there is any medium to replace sand for sandblasting processes. Now in India blasting by sand is banned as it causes pollution. But we are to compulsorily use a blasting processes to remove rust and scales from light, medium and heavy structures before painting. The surface finish after blasting required is SA2 !/2. I shall be grateful if i can be guided in this matter.
I'm curious as to what the pollutant is. In any case, the new "big thing" here is soda blasting, using bicarbonate of soda. Since the soda can clump, the blaster incorporates a special valve that agitates the soda medium. One big advantage is that the soda leaves a coating on the blasted part that will prevent rust for a short period of time. You do need to wash it off prior to painting.
 
#7 ·
Here in California, unconfined sandblasting using silica based abrasives is considered pollution. Using a media with no free silica is an acceptable alternative, soda blasting is one media, but it does not leave a very pronounced profile, and makes a big mess. Coal slag, (sold under the trade names of Black Diamond, Black Beauty, ), is comparable to sand in it's cutting ability, and has less than 1% free silica. Coal slag is the product of coal fired boilers.

http://www.nstcenter.org/writeup.as...sting&page=TechResourcesAbrasiveBlasting.html


Later, mikey
 
#8 ·
I use a product called Vitro grit which is crushed glass..No free silica though glass is made with silica..go figure..cuts very well faster than sand and the PSAPCA does not complain..It is available in a number of commonly used grits so getting the finish desired can be done...Made in USA but I bet those guys would ship a container full over there..

Sam
 
#9 ·
curtis73 said:
There are attachments for pressure washers to allow media blasting, as well as slurry blasters. The benefits are a dust-free blast, and obvious cooling of the part while you blast.


As has been discussed many times in the past it is a myth that sandblasting heats the part being blasted and that warpage occurs from this heating. The warpage will still occur even if wet blasting is used on thin metal because of the peening effect of the sand which is the reason for the warpage. Wet blasting will certainly prevent free silica in the air and may have some other advantages but cooling is not one of them.
 
#10 ·
oldred said:
As has been discussed many times in the past it is a myth that sandblasting heats the part being blasted and that warpage occurs from this heating. The warpage will still occur even if wet blasting is used on thin metal because of the peening effect of the sand which is the reason for the warpage. Wet blasting will certainly prevent free silica in the air and may have some other advantages but cooling is not one of them.
Good to know. My sandblasting experience is limited to what I've figured out since I bought a cabinet last year :)
 
#11 ·
There have been a lot of parts ruined by people taking steps to prevent the metal from heating and warping (such as placing wet rags on the opposite side) when they should have taken steps to prevent distorting the metal surface which is the real culprit. If you think about it the sand is hitting the surface at high velocity like millions of tiny peening hammers and this will tend to displace metal and distort the surface causing it to expand and thus warp. Often someone will hit an area quickly and then move on to another spot returning after the previous area has "cooled" in the mistaken belief this will prevent warpage. The peening effects of the sand are cumulative however and each time an area is hit with the sand it will distort even more so the key to preventing warpage is to limit the total time spent on any one spot. Of course there is much more to it than limiting the time spent such as use the lowest pressure practical that will still do the job and try to hit the surface at an angle instead of straight on.
 
#12 ·
oldred said:
There have been a lot of parts ruined by people taking steps to prevent the metal from heating and warping (such as placing wet rags on the opposite side) when they should have taken steps to prevent distorting the metal surface which is the real culprit. If you think about it the sand is hitting the surface at high velocity like millions of tiny peening hammers and this will tend to displace metal and distort the surface causing it to expand and thus warp. Often someone will hit an area quickly and then move on to another spot returning after the previous area has "cooled" in the mistaken belief this will prevent warpage. The peening effects of the sand are cumulative however and each time an area is hit with the sand it will distort even more so the key to preventing warpage is to limit the total time spent on any one spot. Of course there is much more to it than limiting the time spent such as use the lowest pressure practical that will still do the job and try to hit the surface at an angle instead of straight on.
I had an old car magazine that did a comparison of different blasting medias, and the differing medias (even walnut shells!) have different effects on the metal being blasted. Eventually, I think all medias did the ball peen effect.
 
#13 ·
ChevelleSS_LS6 said:
I had an old car magazine that did a comparison of different blasting medias, and the differing medias (even walnut shells!) have different effects on the metal being blasted. Eventually, I think all medias did the ball peen effect.


That's a very good point! I was talking about silica sand but as you pointed out there are a lot of different types of media besides sand and some are a heck of a lot easier on the metal.
 
#14 ·
While the media itself can and will escape, a lot of the pollution probably also comes from what you are blasting off the part. Rust, paint, and so on. It is probably microscopic metal particles that are the problem.

As has already been pointed out, natural dust storms are far from unknown, and I doubt if silica sand by itself is terribly toxic. But lead from paint or solder, zinc from plating, and other common metals may be far more dangerous.

Even something like the cyclonic dust removers used in large woodworking factories (and Dyson vacuum cleaners!!) should be quite effective if fitted on the exhaust of your blasting cabinet.

If you are really keen, a wet filter or electrostatic precipetator as a second stage, will get rid of any extremely fine particles remaining.
 
#15 ·
Silver Shadow said:
While the media itself can and will escape, a lot of the pollution probably also comes from what you are blasting off the part. Rust, paint, and so on. It is probably microscopic metal particles that are the problem.

As has already been pointed out, natural dust storms are far from unknown, and I doubt if silica sand by itself is terribly toxic. But lead from paint or solder, zinc from plating, and other common metals may be far more dangerous.

Even something like the cyclonic dust removers used in large woodworking factories (and Dyson vacuum cleaners!!) should be quite effective if fitted on the exhaust of your blasting cabinet.

If you are really keen, a wet filter or electrostatic precipetator as a second stage, will get rid of any extremely fine particles remaining.
You are right about the high toxicity of the chemicals that are being blasted off, but the sand by itself is toxic.


http://en.wikipedia.org/wiki/Silicosis

Later, mikey
 
#16 ·
Silver Shadow said:
I doubt if silica sand by itself is terribly toxic.


Not toxic in the sense that it is not poisonous but it is DEADLY nonetheless! Dust in a dust storm is bad enough but it is not as bad as silica sand that is used in blasting and don't doubt the dangers of silica it can and will kill you if you don't take proper precautions! Believe it or not you can get enough silica in just one blasting session to do serious harm, it may not kill you or even make you sick at first but it is doing damage and the effects are cumulative so each exposure makes the problem worse. Silicosis is an insidious killer sometimes taking a long time for any ill effects to show up but when they do there is not much can be done so prevention is the only cure. Just think of it as breathing crushed glass dust and once in your lungs it stays there causing the tiny air sacs and the insides of your lungs to become covered with scar tissue. DON'T underestimate the dangers of silica dust, it IS that bad!
 
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