Don Goodrich on tue 6 may 03
Jeff L asked:
>I was wondering if anyone has used a vacuum chamber to dry a plaster mold,
>and if so, thoughts on creating a vacuum chamber large enough to hold a few
>molds?
Jeff,
I tried it with greenware once, when a vacuum chamber in the factory
where I work wasn't being used. It thoroughly dried the pieces right away,
in less than an hour. Might take a bit longer for molds, since they're
thicker.
Building a vacuum chamber would be a challenge. Strength and a good seal
are the important design factors. Since atmospheric pressure is 14 PSI,
even a 12 inch cube will, when evacuated, have a ton of force on a side. If
you can design something with that kind of strength, that still opens and
shuts easily, has good seals so it doesn't leak, and is big enough to hold
a few molds, my hat's off to ya. If you DO, please post the plans on a
website for the rest of us...
Cheers,
Don Goodrich
goodrichdn@aol.com
John Rodgers on tue 6 may 03
Intriguing idea. Haven't got a clue if it would work! Never heard of it
before, but see no reason why it would not work. Go for it. You may have
really come up with something with this idea. I would think you would
want to wait until the newly cast mold has reached full heat of
hydration and has begun to cool before vacuuming however. Just to be
sure all the water that will be locked in the crystal lattice is in fact
locked in the crystal lattice.
John Rodgers
Birmingham, AL
Longtin, Jeff wrote:
>Question Gang,
>I'm in need of drying some slip-casting molds ASAP and a solution popped
>into my head. Not too long ago Craig mentioned reversing the air flow on a
>RAM press air feed tube, i.e. create a vacuum, to dry out a RAM press mold
>from the inside out.
>I was wondering if anyone has used a vacuum chamber to dry a plaster mold,
>and if so, thoughts on creating a vacuum chamber large enough to hold a few
>molds?
>Thanks
>Jeff Longtin
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
>
Longtin, Jeff on tue 6 may 03
Question Gang,
I'm in need of drying some slip-casting molds ASAP and a solution popped
into my head. Not too long ago Craig mentioned reversing the air flow on a
RAM press air feed tube, i.e. create a vacuum, to dry out a RAM press mold
from the inside out.
I was wondering if anyone has used a vacuum chamber to dry a plaster mold,
and if so, thoughts on creating a vacuum chamber large enough to hold a few
molds?
Thanks
Jeff Longtin
Des & Jan Howard on wed 7 may 03
Don
Harry Davis's vacuum filter press operated on 50-60% of a full vacuum, 60% being about 7-8 PSI.
Still, this is enough to collapse a flimsy unsupported cube.
Ivor, do you have any figures on water vapour pressures & what % of a full vacuum
at what temp would be needed to dewater damp pots?
Des
Don Goodrich wrote:
> Building a vacuum chamber would be a challenge. Strength and a good seal
> are the important design factors. Since atmospheric pressure is 14 PSI,
> even a 12 inch cube will, when evacuated, have a ton of force on a side. If
> you can design something with that kind of strength, that still opens and
> shuts easily, has good seals so it doesn't leak, and is big enough to hold
> a few molds, my hat's off to ya. If you DO, please post the plans on a
> website for the rest of us...
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Michael Wendt on wed 7 may 03
I can't say it will be true of molds, but the clay in my deairing ribbon
mixer doesn't dry our appreciably in even 1/2 hour of continuous mixing
under a 26" vacuum. I think to dry molds, you would also need to apply heat
and keep in mind that lower air pressure means you lower the boiling point
of water so if you got them hot enough at a low enough pressure, you might
experience a steam explosion. As to how to build it, that I can answer: Find
a large piece of steel (or stainless ) pipe... 20" in diameter and 24" long.
Weld a plate on for the bottom. Caulk the seam with silicone rubber on the
outside when cool. Weld a 1" flange on the top edge to act as a gasket
mating face. Caulk the outside of that seam too. Drill a hole for the vacuum
hose barb and one for the vacuum gauge. Weld on two handles to allow the lid
to be lifted easily.Install a double row of EPDM rubber self adhesive door
gasket on the underside of a lid made of 1/4" aluminum. Offset the joints
180 degrees for best seal. Attach a vacuum pump via hose and suck to your
hearts content. The reason this will stand the outside pressure is it is
round. Square boxes need to be much heavier to stand the atmospheric
pressure once the air is removed.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Avenue
Lewiston, Idaho 83501
1-208-746-3724
wendtpottery.com
Kay Howard & Phil Chaban on wed 7 may 03
I do not remember where I saw it but put a single mold wrapped in screening
(to allow circulation) in a strong rubber or plastic bag (not garbage or
zip !!!) and suck it down on the screen. I used to be in vacuum form
prototype shops, maybe I saw them there. Another place you could look is in
tool and die shop supply houses. They sometimes use STRONG rubber sheet to
stretch steel as a one sided die. You also could go to a plumbing shop and
get a sheet of what they use to make tile shower floors waterproof. I have a
sheet and it looks darn tough. How about place your mold on a board, build a
wood wall around to protect mold and clamp/glue or whatever the sheet to a
flat board. A wet dry vac will not pull nearly one atmosphere. Probably no
more than a third of an atmosphere. The vacuum will help hold the sheet to
the board. Try it first without the mold !!--- Phil in Grass Lake, MI
-----Original Message-----
From: John Rodgers
To: CLAYART@LSV.CERAMICS.ORG
Date: Wednesday, May 07, 2003 2:24 AM
Subject: Re: Vacuum Drying Plaster Molds
>Intriguing idea. Haven't got a clue if it would work! Never heard of it
>before, but see no reason why it would not work. Go for it. You may have
>really come up with something with this idea. I would think you would
>want to wait until the newly cast mold has reached full heat of
>hydration and has begun to cool before vacuuming however. Just to be
>sure all the water that will be locked in the crystal lattice is in fact
>locked in the crystal lattice.
>
>John Rodgers
>Birmingham, AL
>
>Longtin, Jeff wrote:
>
>>Question Gang,
>>I'm in need of drying some slip-casting molds ASAP and a solution popped
>>into my head. Not too long ago Craig mentioned reversing the air flow on a
>>RAM press air feed tube, i.e. create a vacuum, to dry out a RAM press
mold
>>from the inside out.
>>I was wondering if anyone has used a vacuum chamber to dry a plaster mold,
>>and if so, thoughts on creating a vacuum chamber large enough to hold a
few
>>molds?
>>Thanks
>>Jeff Longtin
>>
>>__________________________________________________________________________
____
>>Send postings to clayart@lsv.ceramics.org
>>
>>You may look at the archives for the list or change your subscription
>>settings from http://www.ceramics.org/clayart/
>>
>>Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>>
>>
>>
>
>___________________________________________________________________________
___
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Bryan on wed 7 may 03
> Jeff L asked:
> >I was wondering if anyone has used a vacuum chamber to dry a plaster
mold,
> >and if so, thoughts on creating a vacuum chamber large enough to hold
a few
> >molds?
>
There is a combination clothes washer-dryer that uses this approach to
drying clothes as a way to be energy efficient. If there is a cycle
that stops the drum from turning you could combine the two and keep all
your dirty pottery clothes in the pottery. The clothes come out feeling
a tiny bit damp.
Bryan
Roger Korn on wed 7 may 03
You don't need a rigid chamber. Make a bag of 6 mil Visqueen and duct
tape, insert the plaster mold wrapped in a towel or other porous cloth,
tape it shut except for a hose to the vacuum pump, and pump away. Should
work just fine.
Roger
Don Goodrich wrote:
>Jeff L asked:
>
>
>>I was wondering if anyone has used a vacuum chamber to dry a plaster mold,
>>and if so, thoughts on creating a vacuum chamber large enough to hold a few
>>molds?
>>
>>
>
>
>Jeff,
> I tried it with greenware once, when a vacuum chamber in the factory
>where I work wasn't being used. It thoroughly dried the pieces right away,
>in less than an hour. Might take a bit longer for molds, since they're
>thicker.
>
> Building a vacuum chamber would be a challenge. Strength and a good seal
>are the important design factors. Since atmospheric pressure is 14 PSI,
>even a 12 inch cube will, when evacuated, have a ton of force on a side. If
>you can design something with that kind of strength, that still opens and
>shuts easily, has good seals so it doesn't leak, and is big enough to hold
>a few molds, my hat's off to ya. If you DO, please post the plans on a
>website for the rest of us...
>
> Cheers,
> Don Goodrich
>goodrichdn@aol.com
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
>
--
Roger Korn
McKay Creek Ceramics
In AZ: PO Box 463
4215 Culpepper Ranch Rd
Rimrock, AZ 86335
928-567-5699 <-
In OR: PO Box 436
31330 NW Pacific Ave.
North Plains, OR 97133
503-647-5464
Donald Burroughs on wed 7 may 03
Jeff check out article link on my site.
Go to http://www.autobahn.mb.ca/~donaldo/pages/Links_page.htm
Then click the link at that page.
It is near the top of the page.
Donald
Alan Walker on thu 8 may 03
> Question Gang,
> I'm in need of drying some slip-casting molds ASAP and a solution popped
> into my head. Not too long ago Craig mentioned reversing the air flow on a
> RAM press air feed tube, i.e. create a vacuum, to dry out a RAM press
mold
> from the inside out.
> I was wondering if anyone has used a vacuum chamber to dry a plaster mold,
> and if so, thoughts on creating a vacuum chamber large enough to hold a
few
> molds?
Depends. If you have a sealed chamber, pull a vacuum and leave the molds in
there they won't dry much faster. Air flow speeds things up a little, but
the best way to speed up mold drying is warmth. Don't get them too warm, as
this can degrade the plaster. A box with a little fan heater works well.
Temeprature around 80 F - 100 F works well.
Cheers
AW
Don Goodrich on thu 8 may 03
Hey there, vacuum fans!
I couldn't resist the allure of Jeff's question. It was a good excuse to
play with one of the big toys. So, last night I weighed a couple of molds
that are nearly the same size, soaked them, weighed them again and wrapped
'em in plastic bags.
This morning I unwrapped them, set the first one in a conveniently
unemployed vacuum chamber and left the other on my desk. The first ten
minutes were the most interesting. With a 29 inch vacuum, water boiled from
the lower portion of the first mold, and formed a puddle around it. By the
end of ten minutes, the puddle had evaporated too, so I weighed both molds
again.
Back to the vacuum, this time for an hour, and another weigh-in.
Finally, vacuum for 4 more hours, and a final weighing. Here are the
results:
Mold 1 Mold 2
Dry weight 3.25 2.50
Wet weight 3.87 3.12
Water weight 0.62 0.62
___________________________
Weight after vacuum air
10 minutes 3.80 3.12
70 minutes 3.66 3.10
5 hours 3.42 3.04
____________________________
Water removed 0.45 0.08
Water remaining 0.17 0.54
Weights are in pounds. Sorry, I couldn't get a gram scale that would read
that high. The molds are 1 inch thick plaster slabs used to make Currie
test tiles. The vacuum victim felt cold when I removed it from the chamber,
which implies that the water molecules remaining in the plaster were the
slow-moving ones.
An obvious improvement to the setup would be to add a couple of heat
lamps to the vacuum chamber. Sadly, my job does require me to actually work
from time to time, so I was unable to devote any efforts in this direction.
A link to a picture of the setup is at the end of this post.
The short answer to Jeff's question is yes, vacuum helps dry out molds a
lot. Vacuum and heat would be better. Someone else can determine whether
the same amount of time in an oven (at a temperature safe for plaster)
would do better. I think Roger's suggestion to bag 'em and suck has
promise, because the clear plastic would allow the application of heat
lamps. Hope somebody tries it.
Cheers,
Don Goodrich in cool, green, Zion, Illinois
goodrichdn@aol.com
http://members.aol.com/goodrichdn/vacuum.jpg
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