iandol on thu 7 feb 02
Dear Vince,
I think we are substantially in agreement here. However, the Venco mills =
I have used have part flights to chop and mix clay before the final =
auger section expels it from the mill. I note that Harry Davis also uses =
the idea of part flights set at 120=B0 intervals, indexed along the =
shaft. So the mechanical action you describe may not represent the total =
picture. I think there is going to be a considerable degree of slicing =
and tumbling as the auger sections push clay into the general cavity and =
push it into the restricting cone at the exit from the barrel. =
Differences in circumferential velocity will also make the clay rotate =
or spiral between the shaft and the barrel. There is certainly enough =
force to expel air backwards, which can be heard as it pops and wheezes.
You say << But I often pug stiff clay dipped in water, and it is often =
necessary to use the plunger to get it going in the barrel. Also, I =
often pug a mix of soft and hard clay, and again the plunger is often =
needed to get this clay intermixing so that it will move through the =
mill on its own.>>
I think these tasks are best preformed in the Blunger or the Pan Mill. =
Stiff clay, even lubricated and partially softened by water, will tend =
to bend the partial flights out of alignment unless the material they =
are made from is of very substantial gauge and well attached to an =
equally substantial shaft. They tend to move away from their angular =
orientation, becoming bent almost at right angles to the axis of the =
shaft. In this position, thought they chop the clay they do not force it =
forward. Another point to consider is the force this will impose on the =
thrust bearings.
My most memorable experience with this kind of machinery was at a Chrome =
processing plant. Crushed Chromite ore was being transported by augers =
which were being stripped weekly for restoration. The flights, bearings =
and the casing were in need of constant repair. I redesigned the =
Bearings, surfaced and edged the Auger and let the Case look after =
itself, an action my client could not understand. This test section ran =
for six months without attention. Even after that time the casing was =
still in pristine condition though the flights were highly polished due =
to friction with the Chromite, though seemingly unworn. A triumph for =
the ingenuity of the person who invented the Archimedean Screw.
Having said that, I would like to know if the flights and augers in your =
Harry Davis Machine are rusty and caked with clay or clean and polished.
My best regards to you,
Ivor Lewis. Redhill, South Australia=20
vince pitelka on thu 7 feb 02
Ivor wrote:
"I think these tasks (pugging stiff clay dipped in water) are best preformed
in the Blunger or the Pan Mill. Stiff clay, even lubricated and partially
softened by water, will tend to bend the partial flights out of alignment
unless the material they are made from is of very substantial gauge and well
attached to an equally substantial shaft. They tend to move away from their
angular orientation, becoming bent almost at right angles to the axis of the
shaft. In this position, thought they chop the clay they do not force it
forward. Another point to consider is the force this will impose on the
thrust bearings."
Well now Ivor, knowing what you do about me, it might be best for you to
assume that I have been doing this for a long time and probably have it
figured out. I built my mill over twenty years ago and it has worked
perfectly ever since. No bent blades. Perfect clay every time. I can't
see the point of owning a pugmill unless it will process clay that is a
little on the stiff side. I'm not talking dry clay here, just stiff clay,
as I said. Maybe this is one of those "use of language" things. When I
refer to stiff clay, I mean plastic clay which is stiffer than you would
normally use for throwing or handbuilding.
When I built my mill I did beef it up beyond Harry's specifications, because
his design seemed entirely too light-duty. My mill is heavier and turns
faster, with a five-horse motor. It will do a beautiful job of processing
and deairing over a ton of clay an hour. And of course the Vencos are
adapted from Harry's design as well, as are the Bluebirds.
You said:
"Having said that, I would like to know if the flights and augers in your
Harry Davis Machine are rusty and caked with clay or clean and polished."
What an odd question. Of course they're polished. How could they be
otherwise?
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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