(57) An extrusion machine for making elongated articles of con crete by forcing the concrete
through a mold, the article having a relatively large core, has a rotatable spiral
conveyor (20, 22) which extends longitudinally of the mold (26) and moves the concrete
through the mold. Non-rotatable forming elements (28,30, 32) in the mold (26) form
the internal cavity, which elements are positioned immediately downstream of the conveyor
with their lower edge not more than 10% of the forming element below the lower edge
of the conveyor. The lower edge and lower side of the forming elements (28, 30, 32)
are free of any substantial ramp, and a ramp (34) on the first forming element (28)
extends upwardly from the downstream end of the conveyor (20, 22). The conveyor forces
the concrete over the forming elements to form the concrete article, and the machine
is moved forwardly by reaction as the concrete is forced against the molded concrete.
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