Snail Scott on thu 8 may 03
At 01:24 PM 5/8/03 -0400, you wrote:
>
>But how is the center of a die for a hollow form held in place by the
>extruder? All the hollow form dies that I've seen pictures of seem to have
>a "tripod" used to hold the center piece (the hollow part of the
>extrusion). But wouldn't that slice the form into 3 pieces?
It does slice it, but since the bracket that holds the
middle in place is behind the die, the pressure of
squishing the clay through the die is usually sufficient
to stick the sections back together. Separation can
sometimes occur at that point, though, and more often
with some clay bodies than with others.
-Snail
Diane Serley on thu 8 may 03
Hello all -
I have (what is probably) a pretty basic question.
I recently purchased a beautiful bud vase that was handbuilt using extruded
hollow tubes. I understand that basics of how an extruder works... when
making a solid form or slab. And I've seen pictures of extruders on the
web.
But how is the center of a die for a hollow form held in place by the
extruder? All the hollow form dies that I've seen pictures of seem to have
a "tripod" used to hold the center piece (the hollow part of the
extrusion). But wouldn't that slice the form into 3 pieces?
So can someone explain to me how it actually works?
Just wondering...
Diane
Diane Serley on thu 8 may 03
Alan -
Thanks for the explanation. I can see it in my head now.
:-)
Diane
Alan Walker on sat 10 may 03
>
> But how is the center of a die for a hollow form held in place by the
> extruder? All the hollow form dies that I've seen pictures of seem to have
> a "tripod" used to hold the center piece (the hollow part of the
> extrusion). But wouldn't that slice the form into 3 pieces?
>
When I first saw a ceramic extrusion, my first thought was "that's
impossible"!
Usually, the center piece of the die (the part that forms the hollow part in
the middle of the extrusion) is called a mandrel and the part of the die
that forms the outside surface of the extrusion is called the die bore.
The mandrel is supported by a bridge across the outer part of the die. The
bridge is at the upstream end of the die. So when the mix flows around the
bridge, yes, it splits into separate pieces. But then, the mix flows
through the gap between the mandrel and the die bore. Friction recombines
the separate flows and the mix recombines into a single extrusion.
If you get the design of the mandrel and die bore wrong (ie too short) the
flow might not combine properly, leaving a line where the extrusion is prone
to splitting or cracking.
Cheers
Alan (who has designed and used dozens of extrusion dies)
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