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Vacuum pumps for investment plaster


#1

HI, can any kind soul can recommend a suitable vacuum pump for
removing bubbles from investment plaster, the smaller and lighter the
better. Cost, as usual would be a factor. Any ideas would be welcome,

TIA,
Brendan


#2

The cheapest thing is an old automobile air conditioner compressor.
You don’t have to have one that is purged so they are really cheap.
Attach it to a motor and attach a hose to the vaccume side of the
pump and you are on your way. Frank Goss


#3

Dayton makes a Refrigeration Service Vacuum pump and it is sold
through Grangers. Their Part number is 4Z577. While it is not a
$20 pump, it is considerably less that a pump through one of the
tool suppliers. It is an exact replacement for a couple of the top
name vacuum tables. The last one I purchased was about three or
four years back, and it was a tad over $300.00. It does have the
volume and it will pull the vacuum needed for both investment and
vacuum casting.

One word of caution here for what ever pump you decide to go with.
Make sure you have a filter in the line before the pump. It is best
if it is in front of the valves. The small amount of investment that
will be ingested by the pump, will wipe it out in short order. A
good, cheep filter is a old VW Bug in line fuel filter at about
$2.50. It is very cheep insurance for your pump.

Don


#4
   The cheapest thing is an old automobile air conditioner
compressor. You don't have to have one that is purged so they are
really cheap. Attach it to a motor and attach a hose to the vaccume
side of the pump and you are on your way. 
	This will work at sea level, not at high altitudes, like Denver.

The first vacuum chamber I made was with a piece of scientific
equipment called an aspirator. Works on water running thru a tube
with a piece of sheet metal with a corkscrew twist to it, that twist
causes a vacuum. Worked at sea level, again, not at altitude. I have
one friend here in Denver that just uses a vibratory sander for wood
turned upside down to vibrate bubbles off his invested waxes.

				Richard

#5

This will work at sea level, not at high altitudes, like Denver. I have
heard of using a pressure chamber in place of a vacuum chamber for
high altitudes.

At sea level, the air pressure is around 14.x pounds per square inch.
In a vacuum chamber, the best vacuum you can possible pull is 14.x
psi less than the outside air, or zero psi. So what happens is all
the air that was trapped in your investment is at 14.x psi. The
closer to zero you can obtain in the vacuum chamber, the larger
these bubbles become and they try to rise to the surface. When you
are at maximum vacuum, the investment is boiling, producing its own
bubbles. When you release the vacuum, the 14.x psi collapses the
existing low pressure bubbles to microscopic size.

The same effect can be caused by increasing the out side pressure to
about 15 psi above the ambient pressure. This can be accomplished in
a small pressure chamber. You can make small chambers from water pipe
and fittings. Just make sure you don’t apply over about 40 Psi or you
might end up with a small bomb. This is very important. When I talk
of water pipe, I am taking about galvanized iron pipe. The plastic
pipe may not work. It would be best to do some research into the
characteristic and specifications of the pipes you are using. The key
thing here is to have a chamber you can seal off quickly after
putting the investment and flask into it, and be able to maintain the
high pressure until the investment has set.Rather than rely on the
seals to maintain the pressure, a constant supply of pressure via a
regulated air-compressor would be best. The use of a vibrator to
knock down some of the larger bubbles would also be wise here.

Don Rogers


#6

Concerning plastic pipe and pressure Schedule 80 pvc pipe was OSHA
and insurance Co. approved (recommended) for piping 150 PSI
compressed air within a sheltered workshop. Schedule 80 is usually
gray in color and has its own special fittings, pre-cleaners and
glues as well as different gluing processes. Check with a dedicated
plumbing supply house, not a hardware / box store discounter! I
believe there is also Schedule 80 pipe in iron pipe - black or
galvanized available through plumbing suppliers. Just a thought,
you might want to avoid galvanized however as the zinc could cause
contamination if its scraped or flaked off?

Just did a quick Goggle web search and found this site with links to
PVC pipe pressure specs, very reassuring, so probably Schedule 40
would be adequate, but higher is far better, we’re jewelers not
bombers after all. http://www.otool.com/new2.htm

A question for the more knowledgeable among us, since I and many
others live below 1000 feet elevation, and pressure is easier to
come by readily, will this hyperbaric(sp?) debubbling work at near
sea level pressures as well? 15 to 30+ PSI is readily obtainable
from hand/foot pumps cheaply and quietly.

Hope this helps and I 'll appreciate more illumination on this
topic.

Ed Southern Illinois is sweltering in humid heat and near draught, but
winter will soon cure that! 75 degrees, 92% humidity at am CDT


#7

I made a search and finally bought a factory reconditioned pump from
the local Heating /air-conditioning supply house. It is 6 CFM and may
be larger than required but it only cost $150. It works great an will
pull a 30" vacuum very quickly.

The same supply house will have a variety of sizes of new pumps.Look
under AC wholesale supplies.

Ben