pe canupp on sat 26 nov 11
Hello Clayart world. Need your help and expert advice.
In September 2010 I purchased a brand new pugmill with de-airing mixer. I
did a lot of research on pugmills before such a large monetary investment. =
=3D
I
learned from the clayart archives that there could be a problem with
porcelain clays in aluminum pugmills.
In fact John Tilton wrote in 2000, =3D93if you are using porcelain. The
porcelain ends up reacting with the inside of the pugmill, forming a
crystal which spalls off the mill and explodes in the firing if you are not
lucky enough to remove it in the throwing process.
I tried many solutions to this problem and eventually just bought a
different pugmill. The paint will eventually wear and if you are using
stoneware you should have no problems. On second thought, I'd sandblast it
off before pugging any clay. But I would not buy a Magnesium alloy pugmill
for porcelain.=3D94
I also wrote to my pugmill supplier about the problem before my purchase
and was told, =3D93Some porcelains recipes use soda feldspar as the fluxing
feldspar
ingredient. Soda is a salt and alumina and soda don't get along. All
manufacturers of pugmills use aluminum for their barrels and stainless stee=
=3D
l
for their augers. These two disparate metals, along with the porcelain as =
=3D
a
catalyst, set up a galvanic action which will, over time, corrode the
interior aluminum wall of the pugmill. Not all porcelains cause this
effect, and the ones that do, will take a little time to do so.
The corrosion manifests itself as a scaly build-up that may flake off
leaving small pits in the aluminum and very small aluminum oxide bits that
come off in the clay. There is no way to counteract this effect by
adjusting the PH of the clay.There are a couple of ways around this
problem. One would be to use porcelain and then clean out the pugmill
after each use, being careful not
to leave the porcelain in the machine for extended amounts of time. The
other way would be to upgrade to a stainless steel barrel.=3D94
Ok, so I use porcelain only for making stamps and molds so it was not a
problem for me. I would not be using it in my pugmill. I thoroughly
researched the porcelain problem in case I ever wanted to switch to
porcelain at a later time. In my pugmill I have used only an earthenware
clay which contains (got this information from my supplier) =3D93G200 HP po=
ta=3D
sh
feldspar. The other ingredients are par for the course-ball clay, kaolin,
silica, plus a small amount of Texas talc.=3D94
Now after one year of using my pugmill I have the problem of pitting and
bits of the flaking material in my pugged clay. I had left my clay in the
machine (as many potters do) with a wet sponge in the hopper. I have
pugged only 4 times in this one year period. I am a studio potter and no
one else has access to my equipment. So porcelain could not have been put
into the machine. When I disassembled the machine it was heavily pitted
and corroded.
Has anyone else had this problem of pitting when using an earthenware clay
or stoneware clay with aluminum pugmills? The recommendation from my
pugmill supplier when I told them of the problem was to sell the pugmill to
another potter and use that money to buy their more expensive stainless
steel model. I told them that I could not in good conscience do that
because it was pitting using only earthenware clay--no porcelain. Then
their recommendation was to clean all the affected parts with a wire brush
and switch to a different clay body.
REALLY??? And just what clay body should I switch to Mr. Pugmill Supplier?
Can anyone shed light on this earthenware clay/aluminum pugmill problem?
Thank you.
Phyllis Canupp
Virginia Beach, VA
**
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