Extruder screw shaft alignment apparatus and method

In a multiple screw extruder, in which multiple, mutually spaced-apart intermeshing screws rotate about longitudinal axes in response to drive motor force to apply shear forces to raw materials and thereby form a finished product, each of the intermeshing screws including a screw shaft having external splines and a free end portion, and the external splines of each screw shaft being angularly spaced apart around the longitudinal axis to interlock with, at locations proximal to the free end portion of the screw shaft, complementary internal splines in an interior of a drive coupling having a screw shaft open end portion for operatively coupling, in a timed relationship, the screw shaft to a drive motor gearbox shaft that provides the drive motor force to rotate the screw shaft, the improvement comprising:

• an alignment collar defining a central axis, the alignment collar including a first collar face that is configured to mate with a face of the drive coupling, a second collar face that is configured to receive the free end portion of the screw shaft, a circumferential exterior surface coaxially aligned with the central axis, and a circumferential interior surface coaxially aligned with the central axis and sized to receive the free end portion of the screw shaft in coaxial alignment with its longitudinal axis;
• and
• an alignment key radially protruding from the circumferential interior surface and including a wedge-shaped body having an inwardly depending portion, a front portion, and first and second axial side portions, the inwardly depending portion having an arcuate surface of complementary shape to that of a keyway section of the external splines of the free end portion of the screw shaft, the inwardly depending portion tapering toward the second collar face and toward the front portion to define a tapered front face of the alignment key, and the first and second axial side portions tapering toward the second collar face and toward each other to define respective first and second tapered side faces of the alignment key, the tapering of the tapered front face and the tapering of the first and second tapered side faces providing guide surfaces that, as the screw shaft and drive coupling are moved relative to each other to cause the external splines and internal splines to interlock, guide the alignment key to fit within the keyway section while causing self-alignment of the external splines on the screw shaft to interlock in the timed relationship with the complementary internal splines of the drive coupling.

A method of inserting, in a multiple screw extruder, screw shafts of mutually spaced-apart intermeshing screws into complementary drive couplings on output shafts of a drive motor gearbox that provides drive motor force to rotate the screw shafts about their respective longitudinal axes in a timed relationship to apply shear forces to raw materials and thereby form a finished product, and each of the drive couplings having a screw shaft open end portion and an interior with internal splines, each of the screw shafts having a free end portion and external splines, the external splines of each screw shaft being angularly spaced apart around the longitudinal axis to interlock, at locations proximal to the free end portion of the screw shaft, with internal splines of a drive coupling for operatively coupling the screw shaft to an output shaft that provides the drive motor force to rotate the screw shaft according to the timed relationship, the timed relationship being indicated by a first fiducial showing a drive coupling rotational position and a second fiducial showing a screw shaft rotational position, an axially aligned pair of free end and screw shaft open end portions including an alignment device on one of a free end and screw shaft open end portions and a keyway section in the other of the free end and screw shaft open end portions, the alignment device having an alignment key including a tapered front face and first and second tapered side faces, the method comprising:

• causing the output shafts of the drive motor gearbox to rotate the drive coupling rotational position until the first fiducial indicates the drive coupling rotational position is in a desired initial rotational position;
• setting the intermeshed screws to an initial insertion position at least partly external to the multiple screw extruder, the initial insertion position defined by the longitudinal axes of the screw shafts being in a nominal coaxial alignment with those of the drive couplings and by the second fiducial indicating the screw shafts are in a nominal rotational alignment with the desired initial rotational position;
• and
• simultaneously moving the intermeshed screws from the initial insertion position and though a barrel of the multiple screw extruder for simultaneous insertion of the free end portions of the screw shafts into the screw shaft open end portions, the moving through the barrel causing a deviation from the nominal coaxial and rotational alignments, and the simultaneous insertion causing correction of the deviation when the tapered front faces of the alignment keys incrementally adjust the nominal coaxial alignment and the tapered side faces of the alignment keys incrementally adjust the desired initial rotational position cooperatively to guide the alignment keys to fit within associated ones of the keyway sections while providing alignment of the external splines on the screw shaft to interlock in the timed relationship with the internal splines during the simultaneous insertion.