(57) This publication describes a slipforming extruder for production of hollow-core concrete
elements (23), movable in respect to a casting bed (4) and comprising a frame (18)
which is movable, e.g. supported by wheels (19), and provided with at least two adjacent
auger flights (2, 25) with flights (5) and core-forming mandrels (3), mounted to the
final end of each auger flight (2). Furthermore, the machine comprises a primary drive
and power train system (7, 15, 16, 17) for rotating the auger flights (2) and a feed
apparatus attached to the frame (18), e.g. a hopper (1), for feeding the auger flights
(2) with the concrete mix to be cast. According to the invention, a secondary drive
and power train system (8...14) is adapted to move the core-forming mandrel extensions
(3) of the adjacent auger flights (e.g. 2 and 25) in a synchronized and counterphased
reciprocating manner in the axial direction with respect to each other so as to make
an annular slot (29) remaining between the final end of auger flights (2, 25) and
corresponding core-forming mandrels (3, 30) alternately widen and narrow due to the
relative movement between the auger flight (2, 25) and the corresponding counterphased
moving core-forming mandrel (3, 30), thus mixing the concrete.
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