Presumably it's the chamber in the extrusion machine or something.

Not sure that "paste" is the word though.

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Note added at 1 hr (2007-10-22 17:45:38 GMT)
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Maybe "extrusion chamber" would amount to the same thing:

The screw is turned, pushing the dough through the extrusion chamber. As it is moved through, ... At the end of the extrusion chamber are the forming dies. ...
www.madehow.com/Volume-5/Dog-Biscuit.html

Plastically moldable ceramic batch material, which may be flowably extruded under ... When utilizing a piston and cylinder type of extrusion chamber, ...
www.freepatentsonline.com/3981657.html

Ceramic powders and organics are added to a special mixing device and ... The resultant mix is removed from the mixer and added to the extrusion chamber ...
www.morgantechnicalceramics.com/process_animations/ac_extru...



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Note added at 1 hr (2007-10-22 17:47:49 GMT)
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"Ceramic paste" appears to be OK:

2 illustrates the flow velocity profile of a ceramic paste extruded through a conventional flat-sheet die in the outlet of the die for various viscosities ...
www.freepatentsonline.com/7108817.html


data of organic forming aids A and B at varied extruding pressures. Fig.5 is an example of a stroke-time curves of ceramic paste mixed with inorganic ...
www.shimadzu.com.br/analitica/aplicacoes/caract_materiais/r...

The roller extrusion of a stiff model ceramic paste has been studied experimentally using a fully instrumented roller apparatus that allows simultaneous ...
pubs.acs.org/cgi-bin/abstract.cgi/iecred/2005/44/i11/abs/ie040270g.html