tommy humphries on fri 16 apr 99
Hello all clayarters+ACE-
I have a problem that i hope that some of you can help with. When the clay
comes out of the barrel of the pugmill it tends to separate into rings, not
unlike an onion. This is especially noticable with the large head affixed
(appx.8+ACI-) but also occurs with the smaller head ( appx. 4+ACI-).
We have tried several approaches to this including replacing the augers,
verifing proper vacume etc. , with varying results.
As this happens with both of our pugmills, and with both hard and soft clay,
I was wondering if it might have something to do with our clay body. It is a
fine grained body with no grog( max particle size around 180 mesh), that is
manufactured by a local company using an E. Texas clay (stoneware) flint and
feldspar.
As this has been an ongoing problem that we have been working around for too
long, I hope that someone has some helpful info+ACE-
THANKS+ACEAIQAhACEAIQAhACE-
Louis Katz on sat 17 apr 99
Hi,
At the Archie Bray Foundation there is a small old book on commercial brick
extrusion in their library. I really have no idea what the book is called. If
my memory serves me well I would chalk up your problem to three factors:
1. Poor deairing. Your clay, fine grained, may need more deairing despite a
good vacuum in the vacuum chamber. Better chopping of the clay within the
vacuum chamber might help. Bluebird's mills that I have seen push the clay
through a lawn with 1/4" or so holes as it enters the chamber. This is
probably not practical on a bigger mill.
2. Fine impermeable clay. Closely related to number one above. My memory was
that fine clay was listed as a problem in the book, but I read it too long ago.
It does however match my experience at the end of a 25 horsepower machine
making clay commercially. Fine grained clays were more prone to lamination when
stiff.
3. Design of the mills output end. I could be wrong about this and what is
written above. The mill we mixed with had a rippled interior that look like it
was designed to create turbulence in the stream of clay after leaving the
vacuum chamber and just before it got to the output nozzle. Somehow I have
assumed that this was to prevent lamination problems.
Louis
--
Louis Katz
lkatz@falcon.tamucc.edu
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David Hendley on sun 18 apr 99
This condition is called "Dog ears" or "Dog's teeth"
according to Hamer's Pottery Dictionary, although
I've never heard anyone use either term.
According to Hamer, it's caused by either:
1. partial blockage in the mill,
2. insufficiently polished nozzle, particularly with a
square nozzle, or
3. insufficient plasticity in the clay.
I can add a fourth possible cause, which is a change in
consistancy in the clay being fed into the pugmill, especially
if wetter clay is added after stiffer clay.
Are you using Blackjack Clay SS-2 stoneware?
If so, the clay is not the problem.
It is a very plastic claybody, and the lack of large grog particles
makes it very smooth and not at all prone to tearing.
When I mix grog, extra non-plastics, and other clays with it
I will sometimes get some "dog ears", but no-way with
straight Blackjack clay.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
At 10:12 AM 4/16/99 EDT, you wrote:
>----------------------------Original message----------------------------
>Hello all clayarters+ACE-
> I have a problem that i hope that some of you can help with. When the clay
>comes out of the barrel of the pugmill it tends to separate into rings, not
>unlike an onion. This is especially noticable with the large head affixed
>(appx.8+ACI-) but also occurs with the smaller head ( appx. 4+ACI-).
>We have tried several approaches to this including replacing the augers,
>verifing proper vacume etc. , with varying results.
>As this happens with both of our pugmills, and with both hard and soft clay,
>I was wondering if it might have something to do with our clay body. It is a
>fine grained body with no grog( max particle size around 180 mesh), that is
>manufactured by a local company using an E. Texas clay (stoneware) flint and
>feldspar.
>As this has been an ongoing problem that we have been working around for too
>long, I hope that someone has some helpful info+ACE-
>THANKS+ACEAIQAhACEAIQAhACE-
>
tommy humphries on mon 19 apr 99
Hey Dave!
Yes it is Blackjack ss-2. But i dont believe it is the condition known as
dogteeth, at least as i understand it.
The clay comes out of the barrel (round) smooth on the outside, but with
concentric rings inside. It is not completely consistent throughout, but
seems to be more noticable with stiffer clay.
The reason i was wondering wether it was the clay is that we use seperate
pugmills for the stiff clay and the softer clay and it is occuring in both.
We buy the clay by the semi trailor load, straight from the filter press,
then pug it ourselves. We are getting ready to install a muller to pre mix
the clay before pugging to eleminate some of the knots from the filter
cakes. Maybe this will help our lamination problem as well!
Thanks for your help so far!
Tommy Humphries, in Marshall Texas, where the weatherman says it will be in
the mid to upper 80`s with sunshine all week long!
David Hendley on tue 20 apr 99
At 10:43 AM 4/19/99 EDT, you wrote:
>----------------------------Original message----------------------------
>Hey Dave!
> Yes it is Blackjack ss-2. But i dont believe it is the condition known as
>dogteeth, at least as i understand it.
> The clay comes out of the barrel (round) smooth on the outside, but with
>concentric rings inside. It is not completely consistent throughout, but
>seems to be more noticable with stiffer clay.
No, that is not "dogteeth", which is what I thought you
were first describing the other day.
It sounds to me like your pugmill is simply not mixing the
clay enough. As you know, the consitancy of the filter
cakes varies quite a bit, from too stiff around the perimeter,
to 'mush' at the center.
Have you tried running the clay through the pugmill twice?
That might take care of the problem.
If it does, that would also be a good indication that putting
a muller on line would also do the trick.
I buy a pallet of filter cakes from Blackjack a couple of times a year.
I wondered where all those semis were taking all that clay!
Best wishes,
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
At 10:43 AM 4/19/99 EDT, you wrote:
>----------------------------Original message----------------------------
>Hey Dave!
> Yes it is Blackjack ss-2. But i dont believe it is the condition known as
>dogteeth, at least as i understand it.
> The clay comes out of the barrel (round) smooth on the outside, but with
>concentric rings inside. It is not completely consistent throughout, but
>seems to be more noticable with stiffer clay.
> The reason i was wondering wether it was the clay is that we use seperate
>pugmills for the stiff clay and the softer clay and it is occuring in both.
> We buy the clay by the semi trailor load, straight from the filter press,
>then pug it ourselves. We are getting ready to install a muller to pre mix
>the clay before pugging to eleminate some of the knots from the filter
>cakes. Maybe this will help our lamination problem as well!
>Thanks for your help so far!
>
>Tommy Humphries, in Marshall Texas, where the weatherman says it will be in
>the mid to upper 80`s with sunshine all week long!
>
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