Michael Wendt on thu 29 dec 11
Robin,
I have worked with both deairing and non-dearing pug mills.
I finally came to the conclusion that air in the clay is at
fault
for the tearing if the clay is otherwise reasonably plastic.
As evidence of this, I extrude very stiff clay through a die
to make taco holders. It is driven by a 12 ton hydraulic
jack.
The stiff clay is 50% non-plastics (see the recipe on my web
page http://www.wendtpottery.com/helmer.htm ), yet if
properly
de-aired, it extrudes without tearing even in the sharp
corners.
Part of what I do to get it even is pug out the clay I plan
to
use and then pass it through the pug mill at least twice
more
alternating with pieces form the first pugs out and the last
pugs out working back to the middle each time.
Re-pugging also make the clay drier and therefore stiffer
and easier to handle with far less warping.
regards,,
Michael Wendt
Robin wrote:
So, I have my new, lovely Peter Pugger VPM-9. Love it!
But, I am (as
usual) self taught in working with a pug mill. I have a
Scott Creek 4"
extruder that I am keeping the dies to use on the PP. My
question is that
when I try extruding through the PP into the largest hollow
square tube, the
corners of the clay peel back and rip. Too dry, not plastic
enough? Any
wetter, and the form struggles to maintain its shape. Have
added a can of
very cheap beer to the last batch I mixed (no need to waste
the good stuff),
thinking that a little yeast might help the clay liven up.
Any pointers out
there on how to get good, smooth extrusions?
Robin Wolf
Robin Wolf Pottery
Kingfisher, OK
Robin Wolf on thu 29 dec 11
So, I have my new, lovely Peter Pugger VPM-9. Love it! But, I am (as
usual) self taught in working with a pug mill. I have a Scott Creek 4"
extruder that I am keeping the dies to use on the PP. My question is that
when I try extruding through the PP into the largest hollow square tube, th=
e
corners of the clay peel back and rip. Too dry, not plastic enough? Any
wetter, and the form struggles to maintain its shape. Have added a can of
very cheap beer to the last batch I mixed (no need to waste the good stuff)=
,
thinking that a little yeast might help the clay liven up. Any pointers ou=
t
there on how to get good, smooth extrusions?
Robin Wolf
Robin Wolf Pottery
Kingfisher, OK
www.robinwolfpottery.com
David Hendley on thu 29 dec 11
Yes, too dry and/or non-plastic clay will rip at the corners when pushed
through a hollow square die. This is a classic extruder problem because
the clay at the corners moves slower than the clay closer to the center,
and because sharp corners aggravate the problem. If the form can barely
maintain its shape, wetter clay is not an option.
Here are my suggestions:
1 (most important). Use more plastic clay. I accomplish this by segregating
all my recycled clay/trimmings/slurry/throwing water, wet mixing, and
then drying in plaster bowls. I also use this clay for pulling handles.
2. Make sure the clay coming out of the barrel is consistent. If a pug
mill hasn't been used for a relatively short time, the clay around the
outside
becomes drier. With my pugmill, it can take running 30 or 40 pounds
through it before all that slightly harder clay has finally been replaced.
It
can also be helpful to run 10 or 20 pounds through the die before you
start saving any extrusions.
3. Make a die with more rounded corners. Unfortunately you can't
round the corners of your die because the material is already removed,
so you would have to start over with a new die, at least the outer part.
Use a 1/4" drill bit at each corner, then don't file the corners square but
leave them radius-cut. The extruded tube will still LOOK square, but
the corners will be rounded and it will extrude smoother.
4. I don't know if it is possible when using a PP, but it can be helpful
to slow down the rate of feed of the clay going through the die.
David Hendley
david@farmpots.com
http://www.farmpots.com
http://www.thewahooligans.com
----- Original Message -----
> So, I have my new, lovely Peter Pugger VPM-9. Love it! But, I am (as
> usual) self taught in working with a pug mill. I have a Scott Creek 4"
> extruder that I am keeping the dies to use on the PP. My question is tha=
t
> when I try extruding through the PP into the largest hollow square tube,
> the
> corners of the clay peel back and rip. Too dry, not plastic enough? Any
> wetter, and the form struggles to maintain its shape. Have added a can o=
f
> very cheap beer to the last batch I mixed (no need to waste the good
> stuff),
> thinking that a little yeast might help the clay liven up. Any pointers
> out
> there on how to get good, smooth extrusions?
Larry Kruzan on fri 30 dec 11
Hey Michael,
I have only used a deairing pugmill so my comments may be skewed by my
experience. But, I think that air in the clay is unlikely to be the issue
for Robin with a VPM9. It is a deairing pugmill and assuming proper
operation, it just will not work if there is excessive air in the clay. The
clay will just turn in the chamber unless there is a decent vacuum. Any
vacuum level that is sufficient to make the machine operate will be enough
to make a decent pug for extruding. The process of de-airing the clay also
compacts the clay body which, I think may why you see better extrusions wit=
h
de-aired clay - or it just may be both actions working together that helps.
I think that David is right on with his observations about clay that is too
dry or non-plastic. Torn corners in the extrusion are different than the ai=
r
pops we occasionally see in extrusions.
I recently saw an artist's work that featured extruded elements that were
severely torn along the edges. In this case, his work incorporated the roug=
h
edges as a element of the piece. The rips in the edges were so uniform that
they looked like they saw teeth from a distance. As we talked about the cla=
y
he used to get the effect, he disclosed that it was a non-plastic clay,
extruded very dry. Lots of big grog in the body.
Just some thoughts.
Larry Kruzan
Lost Creek Pottery
An armed man is a citizen. An unarmed man is a subject.
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Michael Wendt
Sent: Friday, December 30, 2011 1:21 AM
To: Clayart@LSV.CERAMICS.ORG
Subject: Re: Peter Pugger extrusions tearing at corners
Robin,
I have worked with both deairing and non-dearing pug mills.
I finally came to the conclusion that air in the clay is at fault for the
tearing if the clay is otherwise reasonably plastic.
As evidence of this, I extrude very stiff clay through a die to make taco
holders. It is driven by a 12 ton hydraulic jack.
The stiff clay is 50% non-plastics (see the recipe on my web page
http://www.wendtpottery.com/helmer.htm ), yet if properly de-aired, it
extrudes without tearing even in the sharp corners.
Part of what I do to get it even is pug out the clay I plan to use and the=
n
pass it through the pug mill at least twice more alternating with pieces
form the first pugs out and the last pugs out working back to the middle
each time.
Re-pugging also make the clay drier and therefore stiffer and easier to
handle with far less warping.
regards,,
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