The working segment of extruders
The working elements, which have different surfaces for different process tasks, can be combined with each other in almost any way to optimally take into account the respective total technical process requirements. The feed screw elements and working elements are lined up tightly to each other and are placed on the carrier shafts in a torque-proof manner and, positioned accurately both radially and axially, are driven in a co-ordinated manner by the drive.
Due to special technical process requirements, working elements are frequently reduced in length to up to one sixth of the screw diameter and are almost always shorter than the screw diameter. On the other hand, high pressure can occur between the interlocking working elements of two adjacent shafts, particularly if these elements, such as reversing screw elements, kneading blocks, blisters or toothed disks, have a diameter that corresponds to the external sectional diameter. In this way, forces occur in sheet production extruder around such working elements that lead to a considerable spread between the shafts.
These forces also lead to considerable wear in single screw extruder where the shafts are arranged around a circle with the same central angle. The task of the invention is to reduce the above-average wear around the working elements.In the invention, this is achieved by the working segments, which lead to a larger spread between two shafts than feed screw segments, being formed by a single-piece combined element comprising at least one feed screw segment and/or at least one further working segment.
By uniting a feed screw segment and a working segment, or two working segments into a longer combined element in accordance with the invention, the bending strength of the shafts is significantly improved. At the same time, the spreading forces are distributed over a larger, generally better lubricated surface and thus the surface load and therefore the wear are significantly reduced. In addition, the combination of several different technical process requirements that can be located in a segment over a relatively short length brings with it a decisive reduction in the number of parts, which results in a significant simplification of the equipment and maintenance of the shafts as well as their storage.
The working segment which is united with twin screw extruder to form a combined element made as one piece can be a reversing working segment with a diameter corresponding to the screw diameter, particularly a screw segment with a greater pitch than the feed screw segment or a pitch direction counter to the feed screw segment or a kneading block, a blister or a toothed disk. However, two working segments can also be united as an element made as one piece, e.g. two kneading blocks with opposing pitch directions or a screw segment with an opposing pitch direction and a kneading block.