Extruder having an entry region
In an extruder for kneading and extruding rubber and synthetic material mixtures; said twin screw extruder having an entry region; a cylindrical housing, which includes a housing wall and a housing interior; a screw, which is rotatably mounted in said housing and is provided with recesses; the improvement in combination therewith which comprises: pin bodies inserted in said wall of said housing and said pin bodies having at least a first end portion which projects freely into said interior of said housing between said recesses of said screws; an electrical monitoring circuit arranged externally of said housing;
A respective insert provided at least for those pin bodies associated with the entry region of single screw extruder, said inserts being incorporated into said monitoring circuit, being insulated relative to said pin bodies, and said inserts comprising a conductor material of which the electrical resistance varies as a consequence of deformations thereof. The pin bodies, which serve to split up and rearrange or fold over the mass flow as a result of considerable turbulences in the otherwise predominantly laminar flow directly within the worm-lands or threads of the screw, and hence serve for intensive mixing of the extrusion material, are generally disposed in a plurality of radial planes which are respectively distributed in a star-shaped orientation over the length of the extruder housing. Extruders which are provided with such screw housings, generally known as "pin cylinders" or also "cross-current mixing cylinders", have proven themselves in operation, and have completely fulfilled expectations associated with the generation of profiled strands having improved homogeneity. However, failure or breakage of individual pins surprisingly occurred over and over again during operation; these failures generally also resulted in further secondary or consequential damages.
Since at the beginning of the kneading or mixing process, the extrusion mass is still relatively viscous and does not flow readily, primarily those pin bodies which are located in the entry region of sheet production extruder are struck, so that under the effect of the pressure of the plastic mass flow, which is particularly great in this region, particularly those pins located here are subject to failure or breakage. During further transport to the nozzle or orifice of the extruder, the loose metallic pieces of the broken pins are carried along and cause even worse damage to the subsequently arranged pin bodies as well as to the screw, the housing walls, and the nozzle of the extruder. These damaging effects can even be observed outside the extruder on other subsequently arranged equipment, such as calender rolls. Since the pin bodies project with only slight lateral free space into the recesses expressly provided therefor in the lands or threads of the screw, even slight deformations which are short of a break are already enough to bring them into direct contact with the threads of the screw, resulting in either their complete breaking off or at least to deformation or a breaking off of the threads of the screw. In all cases, lengthy and expensive repair work is unavoidable. All attempts to prevent the danger of breakage by means of a special shape of the pin bodies, have proven up to now to be unsuccessful.