iandol on mon 19 jun 00
Although it seems reasonable to believe that circular section extrusions =
can be thrown, the problem may not be due to consolidation of the clay =
(I find it is not compressible, always squirts back past my thumb when I =
try to contain it).
In the brick and pipe industries they use cores to create holes. The =
disc in a potters extruder die set which is supported by the U bolts is =
the same sort of core. As the clay move past the bolts it is divided. A =
cavity can be created due to the lowering of pressure behind the bend in =
the bolt. This fills with water vapour. In the case of a brick or pipe =
die the space between the bridge, effectively behaving like the U bolt, =
and the die/core aperture is much longer so there is time for the clay =
to seal on to itself preventing laminations. The bridge to die/core =
distance in a potters extruder is very short so there may not be enough =
time for the clay to seal back onto itself. I suggest reducing the speed =
of extrusion and trying again. The alternative is to increase the length =
and taper of the core and the thickness of the die plate.
Ivor Lewis. Redhill, S.Oz
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