Paul on mon 6 oct 03
Is there any potential problems in using a vaccum pump that is way more
powerful than needed for a pugmill? The first one i bought from a used
machinery dealer was pretty strong, but they lost it before i had time to
pick it up. Since i still had the receipt, they said i could pick out
another one, so i naturally decided on the best one i could find, which i
later found out is a two-stage 40cfm pump that lists for over $3000. The
only thing i can think is it may have a tendency to clog the line with clay
because of the force involved, but i don't know that this would really
happen. Any thoughts on this from the engineers out there? thanks,
Paul B
Falmouth, Ky
David Hendley on mon 6 oct 03
I don't know anything about this, so I should probably quit typing, but it
seems to me that it would be possible to install a regulator on a vacuum
pump, just as they are installed on compressors.
Something as simple as a bypass valve to divert part of the vacuum away
from the pugmill could do the trick.
David Hendley
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> Is there any potential problems in using a vaccum pump that is way more
> powerful than needed for a pugmill? The first one i bought from a used
Lee Love on tue 7 oct 03
----- Original Message -----
From: "David Hendley"
> I don't know anything about this, so I should probably quit typing, but it
> seems to me that it would be possible to install a regulator on a vacuum
> pump, just as they are installed on compressors.
> Something as simple as a bypass valve to divert part of the vacuum away
> from the pugmill could do the trick.
The deairing pugmill at my teacher's workshop had such a valve. The
practice was to open the valve when you were finished pugging, to release
the pressure from the pugmill.
Lee In Mashiko
Louis Katz on tue 7 oct 03
Its not the amount of air removed that is directly a problem it is an
inches pressure problem. Oddly enough too much de-airing creates a
bigger de-lamination problem. That is the clay comes apart where two
pieces have been pressed together in the mill. My source is an old book
on making brick in the Bray library in Helena.
A simple bleed valve will probably solve your problem de-lamination if
one develops but you will also need a vacuum gauge. I don't think the
added vacuum will cause any more of a line plugging problem as the
difference in pressure between a hard vacuum and the partial vacuum you
want is very small.
It is necessary to put a particle and moisture trap between the vacuum
pump and the mill.
Someone from one of the bigger clay companies may have more specific
information for you.
Louis
On Tuesday, October 7, 2003, at 01:22 AM, Lee Love wrote:
> ----- Original Message -----
> From: "David Hendley"
>
>> I don't know anything about this, so I should probably quit typing,
>> but it
>> seems to me that it would be possible to install a regulator on a
>> vacuum
>> pump, just as they are installed on compressors.
>> Something as simple as a bypass valve to divert part of the vacuum
>> away
>> from the pugmill could do the trick.
>
> The deairing pugmill at my teacher's workshop had such a valve. The
> practice was to open the valve when you were finished pugging, to
> release
> the pressure from the pugmill.
>
> Lee In Mashiko
>
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Michael Wendt on tue 7 oct 03
Paul,
You are in luck! A vacuum is a vacuum. A 100 horsepower induced vacuum is no
different from a 1/4 horsepower induced vacuum. The most you would get even
with a perfect vaccum is zero atmospheric pressure. Around here, that's
about 30 inches of mercury so don't worry. The big difference is delivery
rate.
Your big pump can reach the near perfect vacuum faster than my small pump
and that is the advantage. Also, it can overcome small system leaks mine
can't.
Do add a large filter on the suction side between the mixer and the pump to
prevent the unit from pulling fine dust in.
Also, it is a good idea to install a ball valve on a "TEE" so that you can
bleed the vacuum from the suction line when you turn the vaccum pump off.
This will prevent "back motoring" as air gets sucked back through the vacuum
pump into the vaccum of the pug chamber and lines.
Dirt is the main enemy so be careful with your lines and the assembly.
If you are worried, I will trade you my little 1/4 hp Gast rotary vane pump
straight accross... ;-)
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
wendtpot@lewiston.com
wendtpottery.com
WHC228@AOL.COM on tue 7 oct 03
It is not the high vacuum that is the problem, it probably is the heat.
Water boils at 212F at sealevel. At higher altitudes there is less pressure
and water boils at a lower temperature. In a vacuum it is like being in outer
space. The vapor that comes off the clay creates a skin and no amount of
pressure will cause the clay to go back without that delamination spot.
When a pugmill begins to wear out, clay will often begin to spin in the
barrel, and cause heat. There are a number of fixes for this problem. Welding
enough additional material on the flights inside the barrel will sometimes work,
and sometimes folks weld flutes laterally on the inside of the barrel to stop
the clay from spinning. This is not an easy fix. It is a lot of trial and error.
I have found that after many years of pugging clay that having the most
vacuum is the best.
Often the problem lies with the operator not keeping the hopper that feeds
the mill full enough and air is allowed into the vacuum chamber.
Sometimes there are small holes that have been worn into the sides if the
barrel and air is being sucked back into the vacuum chamber,
A meter on the vacuum chamber on the mill is a must. If you don't have that
you have no idea what is going on in your mill.
I make porcelain clay every day and have for twenty-five years. It is crucial
to me that the clay does not delaminate. I have owned a number of different
mills over that length of time. I have spent a great deal of time learning what
makes a pugmill work.
The best thing to know is that without the most vacuum that you can get you
don't get the best clay.
If you are not getting good clay feel the barrel of your mill. If it is hot
you probably need to fix the problem there.
Check your seals where the barrel joins the rest of the mill and see if you
have a bad gasket. I had a small hole eight inches downsteram of the vacuum
chamber in my mill and it sucked the air through the clay. It took me three weeks
to find the problem.
When I cut the new pugs off the mill, I cut a slice about 1/2" thick. I bend
that piece to determine if there is any delamination. The spiral cracks that
appear when the clay is stretched is the problem.
Sometime you can get away with using a worn out mill if you are making softer
clay. Hard clay creates more heat.
I had the people that owned Bluebird tell me to relieve the vacuum in the
vacuum chamber twenty years ago. It didn't work. They also had me do the welding
on the inside of the barrel. That did work.
If you are making porcelain you need a good pugmill, you can however get away
with a lot more if you are using stoneware.
Good luck.
Most of what is known about pugmills is a lot of mumbo jumbo. I have talked
with folks like Cliff Fiedler from Western Machinery, and a number of other
manufacturers and most of them have different opinions about pugmill design.
Cliff, after fifty years of making them still really didn't know what really makes
them work.
Vince Pitelka on tue 7 oct 03
> Is there any potential problems in using a vaccum pump that is way more
> powerful than needed for a pugmill? The first one i bought from a used
> machinery dealer was pretty strong, but they lost it before i had time to
> pick it up. Since i still had the receipt, they said i could pick out
> another one, so i naturally decided on the best one i could find, which i
> later found out is a two-stage 40cfm pump that lists for over $3000.
Paul -
This would have been way overkill. I side with Louis on this, in that there
are problems if you draw too high a vacuum. When I built my pugmill I was
lucky to find a used rotary vane-type vacuum pump from a dairy - I bought it
for $35 from a big farm supply place in Ferndale, CA. If their are dairies
in your area, you might find a used pump at a farm supply place.
The unit I bought already had a vacuum relief valve installed on a tee on
the inlet. If you are familiar with larger-size pressure-relief valves such
as are installed on steam boilers and compressed air systems, this is just
the opposite. A pressure relief valve or pop-off valve relieves excess
accumulated pressure if it rises above the preset level. The vacuum relief
valve lets IN air from the outside if the vacuum rises above the preset
level. The unit is adjustable, so once I had the system working I just
played with the adjustment so that it allowed in enough bleed air to
maintain the correct vacuum in the system. The nice thing about that,
versus a bleed valve that is always left partway open, is that the relief
valve only works when the vacuum exceeds the set level. So, when you turn
on the vacuum pump, it pulls the vacuum very quickly, and then the relief
valve kicks in to prevent excess vacuum. I purchased an small air filter
unit for a gasoline engine and installed it on the vacuum relief valve, so
that the air drawn into the vacuum pump would be filtered.
And Louis is right that you need to have a moisture/debris trap in the line
between the pugmill and the vacuum pump. Vacuum pumps are very expensive,
so you want to take very good care of yours. Any moisture/debris trap made
for an air compressor will work fine, but make sure it is hooked up in
reverse as compared to the installation for a compressor.
Whatever kind of vacuum pump you get, make sure to use the correct oil in
the sump, check the level frequently, and change it once every few years.
Piston vacuum pumps usually just use ordinary motor oil in the sump, but
rotary vacuum pumps, as are used on milking machines, use special vacuum
pump oil.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
Michael Wendt on tue 7 oct 03
I mix all my clay in a dearing ribbon mixer similar to the dough mixers or
Blue Bird mixers. It is all stainless and lets me mix in a hard vacuum any
length of time I choose. The clay is "punched" down at 5 minute intervals to
assure true random mixing since it gradually builds up against the drive
wall and no longer gets deaired if left longer. The results of 20 minutes of
true dearing are astounding. Clay goes in short and grouchy and comes out
plastic and mellow. Handles pull like magic and if you think this is a small
feat, my clay body is only 38% Helmer Kaolin with the rest non plastics.
I suspect that the delamination that occurs in standard pug mills occurs
because the cores of the rods extruded into the vacuum chamber are not
deaired and the cavern structure of air trapped in those rods results in the
rupture, not the zones where the deaired clay is rejoined by the pug
extruder auger. More vacuum will make the problem worse because the rods
expand when they enter the vacuum chamber and the caverns get larger more
easily if there is 14 psi less pressure around the outsides than inside the
bubbles.
Once the caverns expand, it is much harder to recollapse them during the
extrusion process so they appear as discreet discontinuities in the clay
extrusion which people sometimes call auger memory. I think it is just a
record of the physical process of auger extrusion which is naturally a
spiral structure.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
wendtpot@lewiston.com
wendtpottery.com
Louis wrote:
>Its not the amount of air removed that is directly a problem it is an
inches pressure problem. Oddly enough too much de-airing creates a
bigger de-lamination problem. That is the clay comes apart where two
pieces have been pressed together in the mill. My source is an old book
>on making brick in the Bray library in Helena.
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