Filter rating for blast cabinet?

[rcx132]

I've been working on a two stage dust extractor for my blast cabinet, I'll post some photos once there's something concrete to show. It'll use a cyclone dust separator, small industrial impeller that I already had, and a canister type filter.

I bought a Chinese canister filter designed for use with blast cabinets. But after buying it I noticed it's rated for 8 microns, whereas the "proper" (not Chinese) filters are 1 micron at least. I'm wondering if I should just return the filter and pay the extra for a better 1 micron one. The aim here is to catch all the abrasive dust so that I don't have to keep covering any engines or other bits I have lying around to stop the abrasive dust damaging them.

Anyone have experience with these things and knows if 8 microns is enough?

 

[timgunn1962]

It's never quite that simple, sadly: Filtration is a whole specialist subject in itself and most normal folk don't know enough about it to even know that there is stuff they don't know.

"8 micron" can mean a number of different things, depending on how the measurement was made. There are different standards in different parts of the world and many places have multiple standards. There are "Absolute" and "nominal" micron ratings: an "absolute" 8-micron filter will stop *almost all* particles that size, where a "nominal" 8-micron filter will stop *perhaps 50%* of particles that size. Different standards will apply different values for my "almost all" and "perhaps 50%".

There are a surprisingly large number of filter applications where the dust builds a layer on the surface that itself becomes a filter, so the filtration actually improves as the filter gets dirtier.

Personally, I'd just give what you have a try and see how it goes. Of course, this assumes you are using "real" blast media and not blasting anything that has the potential to cause health problems: you are "just" dealing with a minor nuisance.

 

[rcx132]

It's never quite that simple, sadly: Filtration is a whole specialist subject in itself and most normal folk don't know enough about it to even know that there is stuff they don't know.

"8 micron" can mean a number of different things, depending on how the measurement was made. There are different standards in different parts of the world and many places have multiple standards. There are "Absolute" and "nominal" micron ratings: an "absolute" 8-micron filter will stop *almost all* particles that size, where a "nominal" 8-micron filter will stop *perhaps 50%* of particles that size. Different standards will apply different values for my "almost all" and "perhaps 50%".

There are a surprisingly large number of filter applications where the dust builds a layer on the surface that itself becomes a filter, so the filtration actually improves as the filter gets dirtier.

Personally, I'd just give what you have a try and see how it goes. Of course, this assumes you are using "real" blast media and not blasting anything that has the potential to cause health problems: you are "just" dealing with a minor nuisance.

Thanks Tim, that sounds sensible. I had read that the ratings vary but didn't think about it too much. Apparently even the EU and US HEPA ratings differ in the percentage of sub micron particles they let through.

 

[brightspark]

any dust from the cabinet hanging around is bad news there shouldnt be any thats why i vent outside using a 4 inch woodchip fan . it can suck more air out than the 28cfm blast jet can put in to the cabinet

 

[grim_d]

any dust from the cabinet hanging around is bad news there shouldnt be any thats why i vent outside using a 4 inch woodchip fan . it can suck more air out than the 28cfm blast jet can put in to the cabinet

Yep I vent outside via a separator (wood dust though not media), no worry about dust if you take the exhaust out of the equation

Probably a bit naughty but I'm not in a location where there is anyone else and barely anything makes it past the separator.

What about venting outside but with an enclosed filter so you're not causing a hazard to anyone else?

 

[rcx132]

I have the cyclone and impeller connected but haven't fitted the filter yet. I just threw some sawdust into the extractor and the cyclone caught it all. So I threw some blast media in and same result. The cyclone is catching it all !

 

[rcx132]

Yep I vent outside via a separator (wood dust though not media), no worry about dust if you take the exhaust out of the equation

Probably a bit naughty but I'm not in a location where there is anyone else and barely anything makes it past the separator.

What about venting outside but with an enclosed filter so you're not causing a hazard to anyone else?

I'm not sure what you mean by enclosed filter? I used to vent outside but the abrasive dust would spread upto 20m... wasn't fair on the neighbours.

 

[brightspark]

I'm not sure what you mean by enclosed filter? I used to vent outside but the abrasive dust would spread upto 20m... wasn't fair on the neighbours.

i posted a picture of my my fine filter in the cabinet before extraction. no loss of decent abrasive and only allows very fine dust to pass outside

 

[rcx132]

i posted a picture of my my fine filter in the cabinet before extraction. no loss of decent abrasive and only allows very fine dust to pass outside

Yes I saw your post and plan to copy you and fit such a mesh as well.

 

[brightspark]

Yes I saw your post and plan to copy you and fit such a mesh as well.

keep[ it high up the side of cabinet. it keeps the cabinet well free of dust .put a rubber mat on the mesh base inside leaving a gap of 2 inch all the way round for media to drop down it stops the blast jet blowing all the abrasive back up from the hopper causing a sandstorm

 

[grim_d]

I'm not sure what you mean by enclosed filter? I used to vent outside but the abrasive dust would spread upto 20m... wasn't fair on the neighbours.

Put the filter outside so anything that does get through isn't in your breathing space but enclose, or shelter it from the elements.

 

[dave h 2]

It's all fine till the tee piece on the bottom of the pot wears through, by the time you've said "What the f%$^ is that" there'll be plenty of grit in any half stripped engine nearby that isn't covered.

 

[brightspark]

It's all fine till the tee piece on the bottom of the pot wears through, by the time you've said "What the f%$^ is that" there'll be plenty of grit in any half stripped engine nearby that isn't covered.

ive run a 90cfm pot using expendable grit for a few years and never had the tee piece wear out yet

 

[brightspark]

another of mine that uses c couplings and 3/.4 hoses

 

[rcx132]

another of mine that uses c couplings and 3/.4 hoses

View attachment 343872

I once saw a sketch of your hopper mechanism. I just use super fine media and get away with the cheapo ball valve. But for any coarser media a better mechanism is needed.

 

[dave h 2]

another of mine that uses c couplings and 3/.4 hoses

View attachment 343872

That was like mine, probably just a void in the casting, though it was quite old.

 

[brightspark]

i made some patterns for the grit valve and cast them in aluminium. well me bruv cast them for me . a lot quicker to make and machine rather than bore out the solid steel