Sandblasting Cabinet filter design Question.

[Franz©]

Bear in mind every stage added to a system adds a dramatic drop in CFM moved.

I have an aversion to filters primarily due to cost. This can be overcome to a degree by employing washable filters such as restaurant hood grease filters lightly sprayed with peanut oil as long as you can buld filter cleaning into the job cost.

Perhaps the best down & dirty trick to drawing fines from a blower discharge is a barrel with a few inches of water in the bottom. Discharge the blower into the water pool about 6" above the water or higher to eliminate splashing and the water will grab and hold the fines. Then you need a plan to clean the water, but that's fairly easy.

[Mr Fixit]

Hi Franz,

Great suggestion on the water trap for fines. I've seen this done before and it does work well,, except that the water gets pond scum pretty fast as I recall. Maybe for DIY/HSM use I'll fill it each time I use it and dump it after the session is done, that way it can't grow anything. Could also toss in a bit of bleach to sterilize the water.

Appreciate the feedback.

TX
Mr fixit for the family
Chris

[rzbill]

Cyclone separators work because air flow creates a directional velocity to start the air spinning.
You need to blow the air through. Sucking the air through just pulls the air around a corner and
down to the bottom where it exits. No spinning is induced. Yes it will drop the dust from the downward
direction change, but nothing is spinning in there. Blow through a cyclone.

We had a huge sandblast system when I worked at Michelin, and they got rid of it for whatever reason.
The centrifugal blower sucked right out of the cabinet, exposed to the abrasive sand. When they
dismantled it, I looked over the blower real good, and the impeller was made of 1/8" steel plate.
While white and clean, it looked pretty good as far as wear goes. It had a 3hp motor as I recall.
I would not worry about sucking abrasive with a blower. Conventional wisdom might be to think that
isolating the blower from abrasive by installing it as a suck through system, after the filter might
be the best thing... but then the cyclone really does not work at all. It becomes minimally effective
and the filter life is really bad as a result.


-Doozer

Air movement is actuated by a difference in pressure from source to sink. How that pressure difference is accomplished is immaterial. It is not possible for an observer inside a cyclone to know which system is being used.

we have a number of vacuum driven cyclones that work very well. In my industry, the standard is blow through but it is antequated because reclaim goes through the fan which is detrimental to the quality of the reclaim. Vacuum systems avoid fan contact with the reclaimed material. Big quality improvement.

[Tundra Twin Track]

That thing just dwarfs the bead blast cabinet. My shop ceilings aren't high enough for anything like that. I'm sure it works well but I find it hard to believe that we have to go to that length to get a good dust collector.

JL..................

The Cabinet is 3' sqaure,prevous owner added Tophats to each door so can fit 5' long peices cross ways under 10" in dia.The whole setup was a $1000 cdn. Had been looking for Blast Cabinet for a few years,did not know these Preasure Style ones existed and how pricey they are new ones like this are around $13000.00
With dust collector stacked on reclaimer it's 16' high.

[Doozer]

Air movement is actuated by a difference in pressure from source to sink. How that pressure difference is accomplished is immaterial. It is not possible for an observer inside a cyclone to know which system is being used.

we have a number of vacuum driven cyclones that work very well. In my industry, the standard is blow through but it is antequated because reclaim goes through the fan which is detrimental to the quality of the reclaim. Vacuum systems avoid fan contact with the reclaimed material. Big quality improvement.

A suck through system only has the blower add energy to the air.
A blow through system has the blower adding energy to the air and the dust particles.
The energy in the air AND the dust is carried to the cyclone and goes to making it all spin.
Less chance of dust dropping out of suspension on it's way to the cyclone when you
have the blower adding energy to the dust as well as the air.
That is the difference.

-D

[J Tiers]

One benefit of a pull-through system is that leaks do not poof-out dust. And there will be leaks, if not yet, then later.

The advantage of a blow-through system is that it can go above the pressure difference of a pull-thru system, which is limited to some fraction of 14.7 psi depending on blower capability.

I do not really see why a cyclone would not work either way.... it is just pressure difference, more at input and less at output. Blower just can get a larger difference, resulting in higher possible velocity, and potentially better separation.

[metalmagpie]

I built a dust trap from a 30 gallon drum once. My idea was to put it inline with my shop vac's suction hose. There was a shop vac port in the center of the top, to which the hose from the shop vac connected. By an edge of the top was another shop vac port, which was glued to an ABS 90 degree fitting inside the tank. The shop vac pulls from the center, and the dust-laden air swirled around to drop most of its dust. That was the idea, anyway. It was a rather spectacular fail. What happened was that the hose between the shop vac and the tank collapsed flat from the suction. Crushed, I sold it cheap and never looked back. This was probably 25 years ago, back in the days when you could buy shop vac hose fittings at Home Depot and the like.

Today I would probably try to find a sturdier suction hose. But be aware there is an upper limit to how much suction shop vac hoses can transmit.

metalmagpie

[rzbill]

A suck through system only has the blower add energy to the air.
A blow through system has the blower adding energy to the air and the dust particles.
The energy in the air AND the dust is carried to the cyclone and goes to making it all spin.
Less chance of dust dropping out of suspension on it's way to the cyclone when you
have the blower adding energy to the dust as well as the air.
That is the difference.

-D

So you are saying that on the blow though systems you use, the particulate is NOT suspended in the air going into the blower but is being dumped into the blower inlet in some sort of unsuspended manner, is accelerated directly in dense form by the blower blades and exits the blower suspended in a dilute mixture for high speed air transport. I have never seen anything of this sort so that is why I am asking. All blow throughs i have seen use two methods. One is the air velocity entering the blower picks up the particulate so it is a already a dilute mixture entering the blower. Energy added to air, air adds energy to particulate to pick it up. If the incoming air did not transfer energy to the particulate, no particulate would flow from its resting point upstream of the blower. The other way was for a rotary metering valve to drop particulate into the moving airstream. Again, particles get their energy from the airstream.

it has been a while since I designed material transport systems. My memory says air flow rates were the calculation. The particulates did not enter the calc other than via a table that gave guidelines for air velocities to use.

[djgooie]

Search up Thein baffle or Thein separator and save a lot of aggravation. Use one for your primary after the cabinet and you'll increase filter life considerably.

Sucking through a filter is preferred over blowing into a filter. Sucking maximizes filter surface in use, blowing minimizes and quickly causes holes.

Far as reclaiming is concerned, generally not worth the cost since the sharp edges are gone. Best case you get 2 passes, one cutting and delivering the cost of the compressed air and a second where cost of air kills profit.