how small a blower/vac for small bead blast cabinet -- micro cyclone?

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so, I picked up a small bead blast cabinet (made of wood, lined with
rubber) - it's about 2 feet by three feet - the hole to which one applies
vacuum is small - 1 inch in diameter - to test the unit, I just duck taped
my shop vac's hose near the hole - didn't try and seal it well or anything -
then I bead blasted some brake calipers - worked great, the air inside
stayed clear, etc - so the 1 inch hole is adequate with my shop vac sucking
on it.  After a bit of flailing around in the internet, I found equations
for the flow through a sharp orofice, which suggests that if my shop vac
pulls 5 inches of mercury (about 2.5 psi), then i would be seeing between
350 and 530 CFM of air flow - of course my shop vac has no specs (dirt devil
wet/dry) so there is no easy way to see if that is reasonable.

I'm trying to avoid running a really really loud shop vac when I'm using the
bead blaster, hence my search for info - I can't find anything on the
scalability of a cyclone type separator - anyone know if I can make a small
one with a 1 inch entry hose using a 1 or two gallon can or do these things
not scale down well?  Any ideas whether a 1/3 HP heater blower will do the
trick for evacuating the dust?  Since the unit is outside, all I need to do
is blow the dust into my garden, I think, though providing a collection bag
might improve the aesthetics -  a smaller blower, like found in shower
ventilators might work, I suppose I could just experiment, but sometimes
using collective knowlege is a good idea....

seeking thoughts - anyone?



--
bill
to email me, to to my web page, www.wbnoble.com and find my email



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Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?

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For years I've used a fractional hp squirrel cage blower on my blast cabinet
(Dayton model 2C610, 1/30 hp), and discharge the air outside, through the
wall.    You don't have to move a great deal of air, just slightly more than
the amount you're introducing from the air source.   My cabinet came with a
3" hole, so I simply connected a blower with a like sized inlet to the
cabinet with the same hose that used to connect to the noisy vacuum that
came with the cabinet.

By discharging the dirty air outside, your shop will benefit greatly.
Vacuum cleaners have a way of recycling very fine dust particles, and if
they don't, the bag is so damned restricted that they don't do a great job.
No way in hell I'll ever go back to a vacuum for my cabinet.   But then, I
live on 5 wooded acres with no close neighbors.

Harold



Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?

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A bead blast cabinet doesn't really need a vacuum unless you are using so
much air pressure that you are shattering the beads(not recommended).    I
ran mine for several years with no vacuum and had no visibility problems.  I
ran across a cheap, small shop vac at a pawn shop and hooked it up to the
cabinet on the off chance that one day I might change to a different
abrasive.  Using it with beads made no real difference and I have never
changed to a different abrasive.

Randy
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Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?

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While you ran one with what, to you, was no trouble, it's nothing less than
a stupid idea.   Glass is silicon, and silicon can make you sorry as hell
for breathing dust that comes from blasting with beads, plus what ever
you're blasting is giving up something------something you're taking into
your lungs.

Blast cabinets are pressurized by the air you introduce with the gun.   If
you don't displace at least that much air by evacuating the chamber, you can
expect to be breathing the byproducts of blasting, even if the bead isn't
breaking down to dust noticeably.    Sure as hell is hot, the bead
degenerates with use, otherwise it would have an unlimited lifespan.   It
doesn't .

Some folks can stand in a dusty wind storm and not complain.  Others don't
tolerate it well.   I try to avoid dust storms.

Harold



Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?
William Noble wrote:
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Take a look at this website:  http://oddwidget.com/Cyclone/index.htm
You'll find that this author has built just what you're looking for,
maybe a little bigger.  He uses a blower that looks just like the
blowers that are used for downdraft ranges.  I have several of these and
they move a large volume of air, although not at a very high pressure.
I have a homemade blast cabinet made from a 55 gal drum and I use one of
these blowers to evacuate it.  The blower exhausts into a filter made by
  rolling an A/C filter into a tube.  There is a can on the bottom to
collect the heavy particles.  The filter is pretty crude and works best
after it gets dirty.  I use it outside only, since the whole thing is
light enough to move outside easily.  The filter is not quite good
enough to use inside, but works just fine in open air so that I don't
get enveloped in a cloud of dust.


--
Gary Brady
Austin, TX
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Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?
thanks - that web site led me to this link
http://www.wsu.edu:8080/~gmhyde/433_web_pages/cyclones/1D2D-Cyclone-design.pdf
which has a basic design with equations - I wonder if it will scale to 100
CFM which seems to give an inlet area that is of the order of magnitude I
want - I guess I can always try it.....


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Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?
Take a look at this too. I Hope it helps...

http://billpentz.com/woodworking/cyclone/Index.cfm

Jukkis




Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?
well, that was some interesting reading.....
but, he is interested in collecting fine wood dust via a cyclone, and I want
to separate out usable glass beads (much much heavier) and will operate the
unit outside so I can blow dust out a tube pointed away from me - I'm
starting to think that almost anything will work because the beads are heavy
and the dust is light - maybe something in the 4 or 5 inch diameter with a
small motor, maybe something even smaller will work - thanks for the link.

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Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?
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want
the
heavy


I think the same theory works in both cyclones. Heavy patrticles, woodchips
/ glassbeads, fall down, dust flies up. As I have understood the idea is
just to regulate the air flow and speed exactly so separation happens. This
can be done either adjusting the fan speed  or easier, opening or closing
the air channel. This way the same cyclone can manage with several kind of
blasting media, glass beads, steel grit, plastic, aluminium oxide... Trial
and error is the way to find the suitable air speed.

Jukkis





Re: how small a blower/vac for small bead blast cabinet -- micro cyclone?
 - I can't find anything on the
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Cyclones scale down very well.  They do not scale up as well.  This is
why dyson vacuum cleaners have something like 7 cyclones in parallel.
One larger cyclone would not trap the smaller particles.

                                                            Dan


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