Abstract:
Puck and collar alignment device embodiments facilitate simultaneous insertion of free end portions of screw shafts into open end portions of complementary drive couplings. The embodiments have alignment keys that correct deviations in alignment and rotation introduced while moving the screw shafts though a barrel of an extruder. Tapered front faces of the alignment keys incrementally adjust coaxial alignment, and tapered side faces of the alignment keys incrementally adjust rotational position cooperatively between the alignment devices and drive couplings. The coaxial and rotational position adjustments cooperate to simultaneously guide multiple alignment keys to fit within corresponding keyway sections while providing alignment of external splines on the screw shafts to interlock in a timed relationship with internal splines on the drive couplings during the simultaneous insertion.

Description:
COPYRIGHT NOTICE 
       [0001]    © 2014 Entek Manufacturing LLC. A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 37 CFR §1.71(d). 
       TECHNICAL FIELD 
       [0002]    This disclosure relates generally to installation of extruder screw shafts and, more particularly, to alignment devices that facilitate installation of extruder screw shafts into drive couplings attached to output shafts of a drive motor gearbox. 
       BACKGROUND INFORMATION 
       [0003]    Output shafts of an extruder drive motor gearbox rotate according to a precise timing relative to each other. The precise timing is transferred to drive couplings attached to the output shafts, and then to screw shafts attached to the couplings, by tight fitting (precise tolerance) complementary splines. The complementary splines between the screw shafts and drive couplings interlock when free end portions of the screw shafts are inserted into open end portions of drive couplings at precise orientations. The precise orientations maintain the correct timing of intermeshing screws in an extruder barrel as the 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. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    An alignment device according to a first embodiment includes an alignment puck having an apertured body that defines a central axis. The alignment puck includes a first end portion and a second end portion. The first end portion and the second end portion are configured to mate with, respectively, a drive coupling and a free end portion of a screw shaft. The first end portion includes a first circumferential exterior surface that is coaxially aligned with the central axis and is sized to fit within the screw shaft open end portion of the drive coupling. The second end portion includes a second circumferential exterior surface. The alignment puck has an alignment key that radially protrudes from the second circumferential exterior surface and includes a wedge-shaped body having a top portion, a front portion, and first and second axial side portions. The top portion has an arcuate surface of complementary shape to that of the interior of the screw shaft open end portion of the drive coupling. The top portion tapers toward the central axis of the apertured body and toward the front portion to define a tapered front face of the alignment key. The first and second axial side portions taper toward the first end portion 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 provide guide surfaces that, as the screw shaft and drive coupling are moved relative to each other to cause screw shaft external splines and drive coupling internal splines to interlock, guide the alignment key to fit within a keyway section of the screw shaft open end portion while causing self-alignment of the external splines on the screw shaft to interlock in a timed relationship with the complementary internal splines of the drive coupling. 
         [0005]    An alignment device according to a second embodiment includes an alignment collar defining a central axis. The alignment collar includes a first collar face that is configured to mate with a face of a drive coupling, a second collar face that is configured to receive a free end portion of a screw shaft, a circumferential exterior surface that is coaxially aligned with the central axis, and a circumferential interior surface that is 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. The alignment collar has an alignment key that radially protrudes from the circumferential interior surface and includes a wedge-shaped body having an inwardly depending portion, a front portion, and first and second axial side portions. The inwardly depending portion has an arcuate surface of complementary shape to that of a keyway section of external splines of the free end portion of the screw shaft. The inwardly depending portion tapers toward the second collar face and toward the front portion to define a tapered front face of the alignment key. The first and second axial side portions taper 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 provide guide surfaces that, as the screw shaft and drive coupling are moved relative to each other to cause screw shaft external splines and drive coupling 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 a timed relationship with the complementary internal splines of the drive coupling. 
         [0006]    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, entails causing the output shafts of the drive motor gearbox to rotate the drive coupling rotational position until a first fiducial indicates that 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 a 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 free end portions of the screw shafts into 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 a timed relationship with the internal splines during the simultaneous insertion. 
         [0007]    Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a top plan view of prior art extruder screw shafts having intermeshed screws and free end portions in nominal coaxial and rotational alignment with complementary drive couplings. 
           [0009]      FIG. 2  is an isometric view showing internal splines of the upper prior art drive coupling of  FIG. 1 , and a fragment of a free end portion of the upper prior art extruder screw shaft, including a tightening nut, split ring, and external splines, of  FIG. 1 . 
           [0010]      FIG. 3  is a top plan fragmentary view of the drive coupling and free end portion of the extruder screw shaft of  FIG. 2 , showing the extruder screw shaft moved along its longitudinal axis to confront an open end portion of the drive coupling during a conventional trial-and-error attempt to align the external splines with the internal splines and thereby establish a timed relationship between the extruder screw shafts. 
           [0011]      FIG. 4  is a sectional view taken along line  4 - 4  of  FIG. 3 . 
           [0012]      FIG. 5  is an enlarged detail view of an area encompassed by line  5  of  FIG. 4 , showing the precise orientation at which the external splines of the extruder screw shaft align and thereby mate with the internal splines of the drive coupling during the conventional alignment process. 
           [0013]      FIG. 6  is an isometric view of an alignment device, according to an alignment puck embodiment, having an alignment key radially protruding from a circumferential exterior surface of the alignment device. 
           [0014]      FIG. 7  is an isometric view of an open end portion of a drive coupling, showing a keyway section that is located between internal splines and is sized to receive the alignment key of  FIG. 6 . 
           [0015]      FIG. 8  is a fragmentary exploded view, showing in operational alignment, of an extruder screw shaft free end portion, the alignment device of  FIG. 6 , alignment-device fastener components, a complementary drive coupling of  FIG. 7 , and drive coupling collet retainer components. 
           [0016]      FIG. 9  is a fragmentary isometric view showing the  FIG. 8  components after assembly and showing the alignment puck fastened to the free end portion of the extruder drive shaft and positioned for insertion into the drive coupling. 
           [0017]      FIG. 10  is a fragmentary exploded view showing an alternative embodiment of a drive coupling that includes both set screw (at left, driven side) and collet split rings and nut (at right, driving side) retainer devices. 
           [0018]      FIG. 11  is a top plan view of extruder screw shafts with their screws intermeshed and their free end portions carrying the alignment puck of  FIG. 6  and positioned in nominal coaxial and rotational alignment with complementary drive couplings of  FIG. 7 . 
           [0019]      FIG. 12  is a top plan fragmentary view of the drive coupling and the free end portion of the extruder shaft of  FIG. 11 , showing the extruder screw shaft moved along its longitudinal axis to confront the open end portion of the drive coupling so that the alignment key will engage the keyway section and self-align the extruder screw shaft by moving it into the timed relationship. 
           [0020]      FIG. 13  is a detail view of an area encompassed by line  13  of  FIG. 12 , showing tapered faces of the alignment key slidably engaging the keyway section of the drive coupling to impart translational and rotational motion to the screw shafts and thereby self-align them with the drive couplings. 
           [0021]      FIG. 14  is a sectional view taken along line  14 - 14  of  FIG. 12 . 
           [0022]      FIG. 15  is an enlarged detail view of an area encompassed by line  15  of  FIG. 14 , showing the alignment key engaging the keyway section by imparting rotational motion to the screw shaft relative to the drive coupling. 
           [0023]      FIG. 16  is a top plan fragmentary view of a twin-screw, co-rotating extruder, with portions broken away to show alignment pucks of  FIG. 6  having front faces seated against those of complementary output shafts of a drive motor gearbox. 
           [0024]      FIG. 17  is an exploded view showing a free end portion, a drive coupling having double set screw retention devices, and an alignment device and its fasteners, according to an alignment collar embodiment. 
           [0025]      FIG. 18  is an isometric view of the alignment collar of  FIG. 17 . 
           [0026]      FIG. 19  is an enlarged detail view of an area encompassed by line  19  of  FIG. 18 , showing a chamfered front face of the alignment collar and an alignment key radially protruding from a circumferential interior surface. 
           [0027]      FIG. 20  is a front elevation view of the alignment collar of  FIG. 17 . 
           [0028]      FIGS. 21 and 22  are section views taken along, respectively, line  21 - 21  and line  22 - 22  of  FIG. 20 . 
           [0029]      FIG. 23  is an isometric view showing bolted together the alignment collar and the drive coupling of  FIG. 17  and engaging a keyway section of the extruder screw shaft free end portion. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0030]      FIG. 1  shows a conventional co-rotating twin-screw configuration  10  for an extruder  12  ( FIG. 16 ) having intermeshing screws  14 ,  16  on multi-tooth involute-spline screw shafts  20 ,  22  coaxially aligned with complementary drive couplings  24 ,  26 . In other embodiments, twin-screw configuration  10  may be counter rotating, or it may include three or more screws. 
         [0031]      FIGS. 1-5  are useful in describing difficulties inherent in conventional attempts to align and insert free end portions  28 ,  30  of screw shafts  20 ,  22  into open end portions  32 ,  34  of complementary drive couplings  24 ,  26  so as to couple screw shafts  20 ,  22  with output shafts  36 ,  38  ( FIG. 16 ) of a drive motor gearbox  40  of extruder  12  ( FIG. 16 ). Free end portions  28 ,  30  are shown positioned prior to ( FIGS. 1 and 2 ) and during ( FIGS. 3-5 ) insertion into drive couplings  24 ,  26 , so that external splines  42 ,  44  of screw shafts  20 ,  22  interlock with internal spines  46  ( FIG. 2 ) of drive couplings  24 ,  26 . The interlocking is shown in  FIG. 5 , which depicts a precise degree of rotation (e.g., about 0.05 of a degree) at which splines are aligned before proper insertion is achieved with conventional insertion attempts. Intermeshed screws  14 ,  16  are, however, capable of about 5.2 degrees of rotation before contacting each other, so any slight rotation or coaxial offset introduced while moving (typically heavy) screw shafts  20 ,  22  through a barrel  48  ( FIG. 16 ) of extruder  12  while attempting to insert free end portions  28 ,  30  into open end portions  32 ,  34  causes misalignment between external splines  42 ,  44  and internal spines  46 . 
         [0032]    Any misalignment usually takes anywhere from 10 to 45 minutes to overcome during a conventional installation process. The conventional installation process of precisely orienting screw shafts with drive couplings is time consuming and error prone because an extrusion machine typically has limited space for an installer to observe the alignment, there are few mechanical aids for achieving the alignment, tolerances between complementary splines are very small, and the adjustment mechanisms for adjusting alignment prior to insertion are located away from free end and open end portions and out of view of the installer. 
         [0033]    Specifically,  FIG. 16  depicts several factors that contribute to the difficulty of achieving the proper positioning during installation: a small user window can be opened so that a user may look and reach a hand into a working space  50  that is dark and awkward for hands and tools; a coupling location  52  is spaced far apart from adjustment locations  54 ,  56  so that a user cannot watch as screw shafts  20 ,  22  or output shafts  36 ,  38  are adjusted; and shafts and couplings longitudinal axes  58 ,  60  are not readily coaxially aligned due to the tendency of screw shafts  20 ,  22  to rest on the interior bottom surfaces of bores (not shown) formed in barrel  48 . 
         [0034]    The conventional process for inserting free end portions  28 ,  30  is generally relegated to highly skilled maintenance technicians. This is so because typical extruder operators frequently fail to achieve proper alignment and may inadvertently damage equipment while attempting the conventional process, which includes ten steps described as follows. 
         [0035]    First, drive couplings  24 ,  26  are loosely installed on drive ends, such as distal ends  62 ,  64 , of output shafts  36 ,  38 . The loose installation allows a drive coupling to move axially along a longitudinal axis of an output shaft while still being interlocked with external driving spline teeth (not shown) around outer circumferences of distal ends  62 ,  64 . The driving spline teeth are precisely oriented and matable with internal splines  46  ( FIG. 2 ) of drive couplings  24 ,  26 , to provide a timed relationship for screws shafts  20 ,  22 . Such a timed relationship allows flights of screw  14  to freely pass through channels of a neighboring screw  16  (and vice versa) while screws  14 ,  16  rotate to apply shear forces to raw materials and thereby form a finished product. 
         [0036]    A timed relationship is a function of the relationship between the number and rotational orientation of spline teeth among output shafts, their drive couplings, and screw shafts. For example, in some embodiments, output shaft  36  has a number of splines that is different from that of output shaft  38 . Also, in some embodiments, each one of drive couplings  24 ,  26  has a different spline configuration between its screw shaft and output shaft ends, i.e., it has a different number of spline teeth at each end. According to some embodiments, the different number of spline teeth provide for various indexing positions, described as follows. 
         [0037]    To establish a timed relationship, there is a removed spline tooth (not shown), on each of output shafts  36 ,  38 . The removed tooth indicates the rotational position at which drive couplings  24 ,  26  are to be installed on output shafts  36 ,  38 . The removed spline tooth (or other spline gap) is sized so that upon installation of drive couplings  24 ,  26  on output shafts  36 ,  38 , its adjacent external spline teeth confront internal spline teeth adjacent a small internal spot weld located in a spline gap between the adjacent internal spline teeth of a drive coupling. Accordingly, the rotational position at which drive couplings  24 ,  26  are installed on output shafts  36 ,  38  is determined by the location of the rotational position (or so-called index position) of a spot weld. For example,  FIGS. 4 and 5  show a spot weld  66  between two adjacent internal spline teeth  68 ,  70 , (Spot weld  66  is actually located at the screw shaft end of drive coupling  24 , but it is analogous to one located at the output shaft end, and, therefore, the balance of this paragraph is relevant to both screw shaft and output shaft ends of drive couplings.) The index position of spot weld  66  between internal splines  68 ,  70  is preconfigured so that spot weld  66  is slidingly engaged by a removed spline tooth according to a predetermined index position that is selected to maintain the desired timed relationship when internal and external splines are interlocking. Spot welds at the output shaft ends also allow drive couplings  24 ,  26  to axially slide onto distal ends  62 ,  64  while maintaining the desired timed relationship for output shafts  36 ,  38  during installation of screw shafts  20 ,  22 . 
         [0038]    Second, at least partly external to extruder  12 , screws  14 ,  16  are installed on screw shafts  20 ,  22 . Screws  14  and  16  are intermeshed. 
         [0039]    Third, rotational positions of screw shafts  20 ,  22  are checked to determine whether these positions nominally match those of drive couplings  24 ,  26 . The positions are typically checked using a shaft-timing fixture, which is sometimes referred to as an eyeglass wrench. The fixture mimics drive coupling internal geometry by having teeth at locations corresponding to internal splines of drive couplings. For example, each one of free end portions  28 ,  30  has an elongated removed tooth section  72 ,  74  between adjacent external splines  42 ,  44 , Removed tooth sections  72 ,  74  are configured to precisely fit around internal spot welds (e.g., weld  66 ) on corresponding drive couplings  24 ,  26  at one rotational position when free end portions  28 ,  30  are correctly aligned and inserted into open end portions  32 ,  34 . Accordingly, in one embodiment, the fixture has one wide tooth for each removed tooth section  72 ,  74  so that the widely spaced teeth mimic spot welds and indicate desired rotational positions of removed teeth sections  72 ,  74 . Thus, screw shafts  20 ,  22  are rotated so that the widely spaced teeth fit within removed teeth sections  72 ,  74 . While outside of extruder  12 , the shaft-timing fixture is temporarily slid onto free end portions  28 ,  30  to check the positioning of screw shafts  20 ,  22  prior to their installation. 
         [0040]    Fourth, screw shafts  20 ,  22  are moved so that front faces  76 ,  78  of free end portions  28 ,  30  are flush (i.e., coplanar) with each other. An installer typically uses a straight edge (not shown) to check whether free end portions  28  and  30  are coplanar. The installer holds the straight edge parallel to the face of one shaft, and then compares it to the face of a neighboring shaft. If front faces  76 ,  78  are flush, the installer can slide the straight edge into position against front face  76 , while maintaining contact with front face  78 . If front faces  76 ,  78  are not aligned, then either the straight edge will not slide into position, or there will be a gap between front face  78  and the straight edge. 
         [0041]    Fifth, drive couplings  24 ,  26 , now on output shafts  36 ,  38 , are positioned so welds (e.g., weld  66 ) match the rotational orientation of screw shafts  20 ,  22 . This rotational positioning can be achieved by slowly rotating at location  56  an input shaft (not shown) of drive motor gearbox  40  until the desired initial rotational position of output shafts  36 ,  38  is achieved. This slow rotation is usually manually done by the installer. Location  56  may be from one foot (30.5 cm) to six feet (1.83 m) away from location  52 , which is usually not within view or reach of drive couplings  24 ,  26 . In some embodiments, there are faint welding marks on the outside of drive couplings  24 ,  26  that show timing points, but internal splines  46  are not visible by an installer or a maintenance person viewing drive couplings  24 ,  26  located in working space  50 . 
         [0042]    Sixth, screw shafts  20 ,  22  are inserted into barrel  48 . As they slide the length of barrel  48  (e.g., from five to thirty feet, depending on the extruder barrel length), screw shafts  20 ,  22  deviate from the nominal coaxial and rotational alignment. This deviation happens even when screw shafts  20 ,  22  are carefully moved through the bores in barrel  48 . Consequently, it is unlikely that screw shafts  20 ,  22  remain in the timed relationship after sliding them through barrel  48 . 
         [0043]    Optionally, once screw shafts  20 ,  22  are slid into extruder  12 , if a collet-style coupling is going to be used for screw shafts  20 ,  22 , then a coupling nut  80  ( FIG. 2 ) is installed onto each one of screw shafts  20 ,  22 . Nut  80  is installed before a screw shaft is inserted in a coupling because nut  80  cannot be installed afterward. 
         [0044]    Seventh, when front faces  76 ,  78  are near open end portions  32 ,  34 , e.g., within about 0.25 of an inch (6.35 mm), the rotational orientations of screw shafts  20 ,  22  are compared those of drive couplings  24 ,  26 . If the timing is off, screw shafts  20 ,  22  are manually rotated about their longitudinal axes  58 ,  60  while they are still inside barrel  48 . This rotation is accomplished at location  54  by an installer using a wrench on screw ends of screw shafts  20 ,  22 . For example, typically screw segments are held onto screw shafts using screw tips having flat sections that allow use of a wrench for manual rotation. Such manual rotation is laborious and imprecise, and it is not within visual range of location  52 . 
         [0045]    Eighth, drive couplings  24 ,  26  are readjusted by rotating them at location  56  so that the rotational positions of drive couplings  24 ,  26  match those of free end portions  28 ,  30 . An installer typically manually performs this at location  56 . 
         [0046]    Ninth, using a combination of steps seven and eight, the capture of free end portions  28 ,  30  in drive couplings  24 ,  26  is accomplished. For example, a common method entails sliding one drive coupling towards its screw shaft and then making small adjustments to the rotation of the coupling by turning the input shaft at location  56 . After a first screw shaft is captured in its coupling, the same trial-and-error process is used to capture a second screw shaft in its coupling. 
         [0047]    Time spent on this procedure can be reduced if two installers are involved. One person can be at the couplings while the other person is at an adjustment location. The person at the couplings can test for linear resistance and communicate with the second person about the direction (clockwise or counterclockwise) and amount of desired rotational adjustment. 
         [0048]    Tenth, once screw shafts  20 ,  22  are slid into position in drive couplings  24 ,  26  and front faces  76 ,  78  contact those of output shafts  36 ,  38 , coupling retention mechanisms are fastened. For each coupling, there is a first retaining feature for an output shaft side of the coupling, and second retaining feature on a screw shaft side of the coupling. For example, upon insertion of free end portions  28 ,  30  into open end portions  32 ,  34 , drive couplings  24 ,  26  are fastened ( FIG. 2 ) by tightening nuts  80  onto coupling threads  82  and against split rings  84  or by inserting ( FIGS. 10 and 23 ) set screws  90  through bores  92  and into screw holes  94 . Some couplings use double collet retainers ( FIGS. 1-3, 7-9, 11, 12, and 16 ), others have a combination of collet and set screw retainers ( FIG. 10 ), and some others use double set screw retainers ( FIGS. 17 and 23 ). 
         [0049]      FIGS. 6-16  show an alignment device in the form of an alignment puck  100  that streamlines the foregoing conventional ten-step process. Alignment puck  100  has angled and chamfered surfaces that form a wedge to encourage self-alignment of free end portions with drive couplings, and vice versa, so that if the matable components are initially out of alignment, they can readily self-align and can be inserted without conventional manual adjustment by a person performing the installation. A simplified installation process using alignment pucks  100 ,  102  ( FIGS. 11 and 16 ) for installing screw shafts  20 ,  22  into drive couplings  104 ,  106  is as follows. 
         [0050]    First, alignment pucks  100 ,  102  are fastened onto free end portions  28 ,  30  of screw shafts  20 ,  22 . Fastening components are shown in  FIG. 8  and described below, but initially,  FIGS. 6 and 7  show and the following describes details of alignment puck  100  and drive coupling  104 . 
         [0051]    Alignment puck  100  has an apertured body  112  defining a central axis  114  and including a first end portion  116  and a second end portion  118  that are configured to mate with, respectively, drive coupling  104  and free end portion  28  of screw shaft  20 . First end portion  116  includes a first circumferential exterior surface  124  coaxially aligned with central axis  114  and sized to fit within open end portion  32  of drive coupling  104 , and second end portion  118  includes a second circumferential exterior surface  130 . An alignment key  134  radially protrudes from second circumferential exterior surface  130  and includes a wedge-shaped body  136  having a top portion  140 , a front portion  142 , and first and second axial side portions  144 ,  146 . Top portion  140  has an arcuate surface  152  of complementary shape to that of the interior of open end portion  32  of drive coupling  104  (see e.g.,  FIGS. 14 and 15 ). For example, drive coupling  104  has a removed tooth providing a keyway section  158  for alignment key  134 . Top portion  140  tapers toward central axis  114  and toward front portion  142  to define a tapered front face  164  of alignment key  134 . First and second axial side portions  144 ,  146  taper toward first end portion  116  and toward each other to define respective first and second tapered side faces  170 ,  172  of alignment key  134 . Alternative embodiments may include rounded guide surfaces, beveled surfaces, or chamfered surfaces. 
         [0052]    As shown in  FIG. 8 , a spring pin (or dowel)  174  is inserted into bores (not shown) on front face  76  and second end portion  118  so that alignment puck  100  is maintained at a desired rotational position when attaching it to front face  76 . A retaining bolt  178  is then placed through apertured body  112  to fasten alignment puck  100  to front face  76 . 
         [0053]    Second, drive couplings  104 ,  106  are loosely installed onto output shafts  36 ,  38 . As described previously for the foregoing conventional process, the intent of this step is for a drive coupling to interlock with the external driving splines on an output shaft, but still being able to move axially along the axis of the output shaft. 
         [0054]    Third, extruder screws  14 ,  16  are intermeshed at least partly external to extruder  12 . This step is similar to the second step of the foregoing conventional process. 
         [0055]    Fourth, drive couplings  104 ,  106  are positioned by a person positioned at location  56  so that fiducials (e.g., reference mark  182 ,  FIG. 9 ), are located at desired rotational positions, such as a two o&#39;clock position (as viewed from location  50  looking at output shafts  36 ,  38 ). Reference mark  182  in drive coupling is a notch that can be painted. The notch, therefore, inhibits normal wear from removing the paint. 
         [0056]    Fifth, the timing between screw shafts  20 ,  22  is checked. A shaft-timing fixture need not be used for checking the timing because the nominal timing does not need to be so precise as it does in the conventional process. Accordingly, fiducials (e.g., reference mark  184 ,  FIG. 9 ) on alignment pucks  100 ,  102  provide a visual indication of whether the nominal rotational positions correspond to those of fiducials on drive couplings. For example,  FIG. 11  shows fiducials  182 ,  184  are in the proper alignment. 
         [0057]    Sixth, a straight edge is used to check whether front faces  186 ,  188  ( FIG. 11 ) of alignment pucks  100 ,  102  are flush with each other. 
         [0058]    Seventh, screw shafts  20 ,  22  are inserted into barrel  48 , while care is taken to maintain the orientation of screws  14 ,  16  as they slide into barrel  48 . As noted previously, a coupling nut is optionally installed on screw shafts  20 ,  22  once they are slid into extruder  12 . When front faces  186 ,  188  reach open end portions  32 ,  34 , as shown in  FIGS. 12-15 , axial force is applied to screw shafts  20 ,  22  so that alignment keys engage keyway sections of drive couplings. For example, tapering of tapered front face  164  and tapering of first and second tapered side faces  170 ,  172  provide guide surfaces  190  (shown in hatching,  FIG. 13 ) that—as screw shaft  20  and drive coupling  104  are moved relative to each other to cause external splines  42  and internal splines  46  to interlock—guide alignment key  134  to fit within keyway section  158  (shown in hatching of  FIG. 13 ) while causing self-alignment of external splines  42  to interlock in the timed relationship with complementary internal splines  46 . 
         [0059]      FIGS. 14 and 15  show that alignment key  134  and keyway section  158  provide about 2.00 degrees of rotational adjustment. Skilled persons will recognize, however, that the amount of rotational adjustment depends on widths of second tapered side faces  170 ,  172  and keyway section  158 . For example, assuming that keyway section  158  has a width equal to one spline gap of a 24-spline drive coupling, then the maximum clockwise (or counterclockwise) rotational adjustment is 7.5 degrees (360 degrees, divided by 24 spline teeth, divided by two), which is one-half the included angle between splines  196 ,  198 . 
         [0060]    Another visual feature (i.e., a fiducial) may be included on screw shafts  20 ,  22  to indicate that they are inserted into drive couplings  24 ,  26  to a desired depth. This desired depth is the point at which faces  186 ,  188  of alignment pucks  100 ,  102  contact those of output shafts  36 ,  38 , as shown in  FIG. 16 . Faces  186 ,  188  extend equal with or past a head surface (not shown) of bolt  178  so that they can transfer axial force to a thrust bearing (not shown) during operation of extruder  12 . The material of a component containing the alignment feature can be optimized for wear, machinability, or other optimizations. 
         [0061]    Eighth, coupling retaining mechanism are fastened once screw shafts  20 ,  22  are slid into position in drive couplings  104 ,  106  and faces  186 ,  188  are contacting those of output shafts  36 ,  38 . 
         [0062]    Skilled persons will recognize that one or more of the aforementioned steps may be performed in a different sequence from the one set forth. Likewise, one or more steps may be skipped in certain embodiments. For example, an alignment feature may be a machined feature of a screw shaft or of a drive coupling. 
         [0063]      FIGS. 17-23  show a second embodiment of alignment device in the form of an alignment collar  200  that is fastened to a drive coupling  202 .  FIG. 17  shows alignment collar  200  defines a central axis  204 , and includes a first collar face  206  that is configured to mate with (e.g., pin  208  and bolt  210  to) a face  212  of drive coupling  202 . A second collar face  214  is configured to receive a free end portion  220  of a screw shaft  222 . A circumferential exterior surface  226  is coaxially aligned with central axis  204 . A circumferential interior surface  230  is coaxially aligned with central axis  204  and sized to receive free end portion  220  in coaxial alignment with its longitudinal axis  240 . 
         [0064]      FIGS. 18 and 19  show that alignment collar  200  has an alignment key  244  radially protruding from interior surface  230 . Alignment key  244  includes a wedge-shaped body  250  having an inwardly depending portion  252 , a front portion  254 , and first and second axial side portions  260 ,  262 . Inwardly depending portion  252  has an arcuate surface  266  of complementary shape to that of a keyway section  270  ( FIG. 17 ) of external splines  272  ( FIG. 17 ). Inwardly depending portion  252  tapers toward second collar face  214  and toward front portion  254  to define a tapered front face  280  of alignment key  244 . First and second axial side portions  260 ,  262  taper toward second collar face  214  and toward each other to define respective first and second tapered side faces  284 ,  286  of alignment key  244 . 
         [0065]    The tapering of tapered front face  280  and the tapering of first and second tapered side faces  284 ,  286  provide guide surfaces that, as screw shaft  220  and drive coupling  202  are moved relative to each other to cause external splines  272  and internal splines  290  ( FIG. 17 ) to interlock, guide alignment key  244  to fit within keyway section  270  while causing self-alignment of external splines  272  to interlock in the timed relationship with complementary internal splines. For example, chamfering of tapered front face  280  facilitates axial alignment of screw shaft  222  being inserted through collar  200 , whereas chamfering of tapered side faces  284 ,  286  adjusts rotational alignment. 
         [0066]    Notably, collar  200  functions in a similar manner as described previously with respect to alignment pucks  100 ,  102 , but collar  200  is attached to a coupling instead of a free end portion. Thus, keyway section  270  is a removed spline, which also serves as a fiducial  294  for checking the timing alignment based on a rotational position of a fiducial  296  of alignment key  244 . 
         [0067]    It will be understood by skilled persons that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.