Slip-on elements of twin screw extruder
A sheet production extruder having at least two axially parallel support shafts with slip-on elements configured as conveying and/or working elements slipped thereon antirotationally by a shaft-to-hub connection, said elements meshing with adjacent shafts, whereby at least some of the slip-on elements have a profile portion defined by a cross-sectional profile comprising a plurality of opposite pairs of first, second and third circular arcs respectively corresponding to the maximum slip-on element diameter , the slip-on element core diameter and at most the center distance of the slip-on elements defined between respective rotation axes of said support shafts, characterized in that the slip-on element is configured so as to have an annular reinforcement segment at each opposite end which projects from said profile portion, wherein said reinforcement segments define the shaft-to-hub connection, said reinforcement segments being provided, in the thin-walled areas of the second circular arcs corresponding to the slip-on element core diameter, with contact surfaces which provide flat or partly flat contact against the support shaft so as to avoid torque transmission in the shaft-to-hub connection, and being provided with two groups of at least two splines or teeth each of which are provided for torque transmission in the shaft-to-hub connection, the distance from group to group being greater than that from tooth to tooth wherein said two groups are provided in the thick-walled areas of the slip-on element corresponding to the first circular arcs in the profile portion.
The most economical screw shaft is that with the greatest conveying volume and simultaneously the highest input torque. The total cross section of a single screw extruder system is limited by the diameter of the housing bore and the distance between adjacent housing bores. It must be distributed proportionately over four cross sections according to the technical requirements and possibilities as well as the demand. For transporting the product, the free conveying surface is first defined, which is determined by the outside diameter of the screw element and the flight depth. This also defines the core diameter of the screw element and the center distance relative to the adjacent support shaft. Secondly, the support shaft requires the calculated usable surface proportion for axially conducting the required shaft torque for the subsequent slip-on elements. Thirdly, the constructionally necessary surface requirement for transferring the proportionate torque for the slip-on element must be taken into account, and fourthly the remaining cross-sectional area of the slip-on element in relation to the support shaft torque for a dependable slip-on element is left.
Further, a variety of form-fitting shaft-to-hub connections with direct and indirect form closure with consideration of the fatigue notch factors and fatigue strength fundamental for the design of the machine. However, the hub has a constant wall thickness in these cases. In an twin screw extruder of the type wherein the screw elements or similar slip-on elements closely intermesh on the entire circumference, however, the axial profile of the slip-on element is determined by three circular arcs corresponding to the screw outside diameter, the screw core diameter and the center distance.