Abstract:
A shear valve assembly for use in a high performance liquid chromatography system. The shear valve assembly includes a stator having a plurality of first fluid-conveying features; and a rotor having one or more second fluid-conveying features. The rotor is movable, relative to the stator, between a plurality of discrete positions such that, in each of the discrete positions, at least one of the one or more second fluid-conveying features overlaps with multiple ones of the first fluid conveying features to provide for fluid communication therebetween. The rotor, including the second fluid-conveying features, is formed by injection-compression molding.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to and benefit of U.S. Provisional Patent Application No. 61/661,456 entitled “Injection-Compression Molded Rotors,” filed Jun. 19, 2012, which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to injection-compression molded rotors. More particularly, the invention relates to injection-compression molded rotors for rotary shear valve assemblies for liquid chromatography applications. 
       BACKGROUND 
       [0003]    Many analytic systems incorporate valves for controlling fluid flow. An example is the use of shear valves in some chromatography systems. These valves often must retain fluid integrity, that is, such valves should not leak fluids. As a valve is cycled, however, between positions, the loads placed on the moving parts cause wear. 
         [0004]    Some valves are subjected to high pressures. For example, sample injector valves in high performance liquid chromatography (HPLC) apparatus, are exposed to pressures approximately 1,000 to 5,000 pounds per square inch (psi), as produced by common solvent pumps. Higher pressure chromatography apparatus, such as ultra high performance liquid chromatography (UHPLC) apparatus, have solvent pumps that operate at pressures up to 15,000 psi or greater. As the pressure of a system increases, wear and distortion of a valves components, such as a rotor and a stator, tends to increase, and the valve&#39;s expected lifetime may be reduced. 
       SUMMARY 
       [0005]    This invention arises, in part, from the realization that rotors for shear valve assemblies can advantageously be formed via injection-compression molding. Such configurations can provide for rotors which have a more uniform structure, are less susceptible to wear, and/or are less prone to contribute to carryover than conventional rotors. The use of injection-compression molding can also help to reduce internal stresses in the rotors, and can be a less expensive alternative to method of forming conventional rotors. 
         [0006]    In one aspect, the invention provides a shear valve assembly for use in a high performance liquid chromatography system. The shear valve assembly includes a stator having a plurality of first fluid-conveying features; and a rotor having one or more second fluid-conveying features. The rotor is movable, relative to the stator, between a plurality of discrete positions such that, in each of the discrete positions, at least one of the one or more second fluid-conveying features overlaps with multiple ones of the first fluid conveying features to provide for fluid communication therebetween. The rotor, including the second fluid-conveying features, is formed by injection-compression molding. 
         [0007]    Another aspect features a method that includes injecting molten resin into a tool cavity, and compressing the resin within the tool cavity to form a rotor for a shear valve assembly. The rotor is formed with one or more fluid-conveying features for fluid communication with a stator. 
         [0008]    A further aspect provides a rotor for a rotary shear valve assembly. The rotor has: 
         [0009]    a substantially planar surface with one or more fluid-conveying features for fluid communication with a stator. The fluid-conveying features are formed via an injection-compression molding process. 
         [0010]    Implementations may include one or more of the following features. 
         [0011]    In some implementations, the rotor is formed of a polymer filled with 20% to 50% carbon fiber (30% carbon fiber) by weight. 
         [0012]    In certain implementations, the polymer is polyether-ether-ketone. 
         [0013]    In some implementations, the one or more second fluid-conveying features include one or more arcuate grooves. 
         [0014]    In certain implementations, the one or more arcuate grooves have a width of approximately 0.005 inches to 0.020 inches (e.g., approximately 0.008 inches). 
         [0015]    In some implementations, the one or more arcuate grooves have a depth of 0.005 inches to 0.020 inches (e.g., 0.008 inches). 
         [0016]    In certain implementations, a seal formed between contacting surfaces of the rotor and the stator substantially prevents fluidic leakage up to at least 15,000 psi (e.g., between 15,000 psi and 19,000 psi). 
         [0017]    In some implementations, injecting molten resin into a tool cavity includes injecting molten resin into a tool cavity between a stationary die and a movable die. 
         [0018]    In certain implementations, compressing the resin includes displacing the movable die toward the stationary die to compress the resin within the tool cavity and thereby forming the rotor having the one or more fluid-conveying features. 
         [0019]    In some implementations, the stationary die or the movable die includes tooling features for forming the one or more fluid-conveying features in the rotor. 
         [0020]    In certain implementations, the movable die includes first tooling features for forming the one or more fluid-conveying features in the in the rotor, and the stationary die includes second tooling features for forming holes in the rotor for mounting the rotor to a drive shaft. 
         [0021]    In some implementations, the one or more fluid-conveying features includes one or more arcuate grooves, and the stationary die or the movable die includes tooling features for forming the one or more arcuate grooves. 
         [0022]    In certain implementations, the one or more arcuate grooves have one or more dimensions that are 0.010 inches or less in size. 
         [0023]    In some implementations, the stationary die includes overflow ports and excess resin is forced out of the tool cavity through the overflow ports as the resin is compressed for promoting a uniform flow of the resin within the cavity. 
         [0024]    In certain implementations, the overflow ports are equally spaced apart in a radial array for promoting a symmetrical flow of the resin. 
         [0025]    In some implementations, the resin includes polyether-ether-ketone. 
         [0026]    In certain implementations the resin comprises 20% to 50% carbon fiber (e.g., 30% carbon fiber) by weight. 
         [0027]    In some implementations, the carbon fibers have a diameter of 6 microns to 8 microns (e.g., 7 microns). 
         [0028]    In certain implementations, the carbon fibers have a length of 0.002 inches to 0.020 inches. 
         [0029]    In some implementations, the one or more fluid-conveying features comprise one or more arcuate grooves. 
         [0030]    In certain implementations, the one or more fluid-conveying features have a width and a depth of less than 0.020 inches (e.g., less than 0.010 inches). 
         [0031]    In some implementations, the one or more fluid-conveying features have a width of approximately 0.005 inches to 0.020 inches (e.g., approximately 0.008 inches). 
         [0032]    In certain implementations, the one or more fluid-conveying features have a depth of 0.005 inches to 0.020 inches (e.g., 0.008 inches). 
         [0033]    In some implementations, the one or more fluid conveying features have one or more dimensions that are 0.010 inches or less in size. 
         [0034]    Implementations can provide one or more of the following advantages. 
         [0035]    In some implementations, carryover can be reduced. For example, by molding rotor grooves rather than machining, carbon fiber is fully encapsulated by resin which has a direct impact on lowering carryover. Machining shears and exposes the carbon fibers which contribute to carryover, which can adversely affect chromatographic results. 
         [0036]    In certain implementations, injection-compression molding of rotors can provide for manufacturing cost savings. In this regard, it can be less expensive to mold features rather than to machine them, particularly when the features are below 0.010 inches in size. Injection molding alone generally cannot “pack out” such small features. 
         [0037]    In some implementations, internal stresses which lead to warpage can be reduced. For example, injection molding by itself can cause internal stresses to a molded part due to non-symmetrical filling. Internal stresses can interfere with the ability to maintain a flat surface on the molded part during subsequent lapping and polishing processes. However, by adding a compression step, these internal stresses can be reduced. 
         [0038]    In certain implementations, the additional of a compression step during fabrication of a valve rotor has the ability to further flatten out carbon fibers at the surface of the rotor. Carbon fiber laying flat as opposed to being “on end,” has a tendency to wear less and more uniformly leading to a longer operating life for the shear valve assembly. This flattening effect can also help to remove flow lines which indicate that the resin mix is less uniform. 
         [0039]    Other aspects, features, and advantages are in the description, drawings, and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]      FIG. 1A  and  FIG. 1B  are side and a cross-sectional views, respectively, of an implementation of a rotary shear valve assembly comprising a stator, housing for a rotor assembly, and drive shaft clamp. 
           [0041]      FIG. 1C  is an exploded view of the rotary shear valve assembly. 
           [0042]      FIG. 1D  is an isometric view the rotary shear valve assembly from the end with the drive shaft clamp. 
           [0043]      FIG. 2A  and  FIG. 2B  are top and bottom views, respectively, of a stator of the rotary shear valve assembly of  FIG. 1A . 
           [0044]      FIG. 2C  is a perspective view of the stator of  FIG. 2A  with a fluid coupling. 
           [0045]      FIG. 3A  is side view of an implementation of a drive shaft of the rotor assembly. 
           [0046]      FIG. 3B  is a side view of the drive shaft with springs about the drive shaft stem. 
           [0047]      FIG. 3C  is a top view of the drive shaft from the end with the pins. 
           [0048]      FIG. 4A  is an isometric view of an implementation of the rotor. 
           [0049]      FIG. 4B  is a top view of the rotor. 
           [0050]      FIG. 4C  is a section view of the rotor in accordance with line A-A in  FIG. 4B . 
           [0051]      FIG. 4D  is a view of detail region A in  FIG. 4B . 
           [0052]      FIG. 4E  is a view of detail region B in  FIG. 4C . 
           [0053]      FIG. 5  illustrates an injection molding process for forming a conventional rotor puck. 
           [0054]      FIGS. 6A-6D  are side views of an injection-compression molding apparatus which illustrate an injection-molding process. 
       
    
    
       [0055]    Like reference numbers indicate like elements. 
       DETAILED DESCRIPTION 
       [0056]    Rotary shear valve assemblies described herein have a rotor formed via an injection-compression molding process. The use of the injection-compression molding process allows fluid-conveying features (e.g., grooves) of the rotor to be formed by molding rather than by machining This can be beneficial particularly in instances in which the rotor is molded from a carbon fiber filled polymer where machining of the rotor (e.g., to form the fluid-conveying features) might otherwise shear and expose the carbon fibers, which, in turn, can contribute to carryover. The use of the injection-compression molding process can also provide a rotor that has a more uniform (homogeneous) structure (e.g., with uniformly distributed carbon fibers and substantially free of resin flow lines). 
         [0057]      FIG. 1A  shows a side view of an implementation of a rotary shear valve assembly  10  including a stator  12  secured to one end of a housing  14  and a drive shaft clamp  16  at the opposite end of the housing  14 .  FIG. 1B  shows a cross-sectional view of the rotary shear valve assembly  10  taken along line A-A in  FIG. 1A ,  FIG. 1C  shows an exploded view of the rotary shear valve assembly  10 , and  FIG. 1D  shows the rotary shear valve assembly  10  from the end with the drive shaft clamp  16 . Mounting screws  18  secure the stator  12  to a flange  20  of the housing  14 . The housing  14  substantially encloses a rotor assembly  22  comprised of a disk-shaped rotor  24 , a drive shaft  26  with a head portion  28 , four springs  30  grouped in two sets of two separated and flanked by washers  32 , a spacer  34 , a thrust bearing  36  sandwiched between bearing washers  38 , and, optionally, a shim  40 . 
         [0058]    The rotor  24  is coupled to the head portion  28  of the rotor assembly  22 . Extending orthogonally from the distal face of the head portion  28  are two pins  42 - 1 ,  42 - 2  that enter corresponding openings ( FIG. 4A ) in the rotor  24 . A substantially planar surface  44  of the rotor  24  abuts an opposing surface  46  of the stator  12 . In addition, the rotor  24  sits on a raised region or dais  48  of the head portion  28 . The dais  48  concentrates the force applied to the rotor and is preferably smaller than the base surface of the rotor  24 , so that the rotor  24  may slightly teeter on the dais  48  to facilitate complete contact between the rotor and stator surfaces  44 ,  46 . 
         [0059]    The drive shaft  26  extends through an opening at the base of the housing  14 . The end of the drive shaft  26  extends into an opening  50  of the drive shaft clamp  16 , which is appropriately shaped to closely receive a notched end ( FIG. 3A ) of the drive shaft. The end of the drive shaft  26  has a notch. A threaded screw  52  passes through pincers  54 , which tightens the opening  50  about the drive shaft&#39;s end to hold the drive shaft  26  securely. When secured properly, the end of the drive shaft  26  is almost flush with the plane of the clamp  16 . Alignment grooves  56 ,  58  on the housing  14  and clamp  16 , respectively, are used to position these units appropriately for coupling the clamp  16  to the draft shaft  26 . A drive mechanism (not shown) couples to holes  60  in the clamp  16  in order to provide a rotating force about a central axis  62  ( FIG. 1B ). 
         [0060]    The compression of the springs  30  translates to an axial force to the rotor  24 , urging the rotor surface  44  against the stator surface  46  and maintaining a fluidic seal at the interface of these surfaces  44 ,  46 . In one implementation, the springs  30  are clover springs. Other types of springs can be used, for example, Belleville washers, without departing from the principles described herein. In one implementation, the compressive load achieved by the springs  30  is approximately  600  lbs. and is designed to produce a seal between the rotor and stator that can prevent leakage at fluidic pressures at least as great as 20,000 psi. For example, in UPLC instruments, the fluidic pressure typically ranges between 15,000 psi and 20,000 psi. The springs  30  maintain the applied force applied throughout the rotation of the drive shaft  26  and the rotor  24 . 
         [0061]    The spacer  34  serves to separate the thrust bearing  36  and bearing washers  38  from the spring stack comprised of the springs  30  and spring washers  32 . The thrust bearing  36  and bearing washers  38  facilitate rotation of the drive shaft. The shim  40  is used to achieve the desired amount of compression along the axis of the draft shaft, with additional shims being added to the drive shaft until the compressive load produced by the springs  30  reaches the desired target of, for example, approximately 600 lbs. 
         [0062]    Referring to  FIGS. 2A and 2B , the stator  12  has six ports  70  ( FIG. 2A ), each extending to an opening  71  at the contact surface  46  ( FIG. 2B ) of the stator  12 . Each port  70  couples to a fluidic tube or channel  73  ( FIG. 2C ) by which fluid flows to or from the rotary shear valve assembly  10 . The port  70  can be coupled to the fluidic tube  73  via a fitting  75 . Rotation of the rotor  24  with respect to the stator  12  changes the connectivity of the ports  70 , as described in more detail below. The stator  12  also has a guide hole  72  for receiving an alignment pin  64  ( FIG. 1C ) extending from the leading raised ring of the housing  14 . 
         [0063]    The openings  71  can be approximately 0.006 inches diameter and can be arranged in a circular array of diameter 0.1 inches. The external diameter of the stator  12  can be about 1.5 inches. The stator  12  can be manufactured from stainless steel (e.g., 316 stainless steel), or other corrosion resistant alloy. The stator contact surface  46  can be coated with a wear resistant material, for example diamond-like carbon (DLC). 
         [0064]      FIG. 3A  shows an isometric view of an implementation of the rotor assembly  22 , including the head portion  28  of the drive shaft  26 . The head portion  28  has a generally disk-like shape with the dowel pins  42 - 1 ,  42 - 2  (generally,  42 ) and the dais  48  extending from a surface thereof. The pins  42  are diametrically opposite of each other; that is, considering the pins  42  to be endpoints of an arc on the circumference of this circle having its center at the center of the dais  48 , the arc defined by the pins is semicircular (i.e., 180 degrees). These pins  42  enable torque transfer, and thus, rotation of the rotor assembly  22  as the drive shaft  26  rotates about the rotational axis  62 . In one implementation, the pins  42  are equal in length and pin  42 - 1  has a larger diameter than pin  42 - 2 . Having one pin larger than the other pin provides a keying feature that ensures only one orientation by which the head portion  28  can couple to the rotor  24 . Corresponding through-holes in the rotor  24  slideably receive the pins  42  in order to mount and align the rotor  24  relative to the drive shaft  26 . 
         [0065]    Also shown, the drive shaft  26  has a first portion  26 - 1  (adjacent the head portion  28 ) with a greater diameter than a second portion  26 - 2 . At the end of the drive shaft  26  is a notch  80 , sized to fit closely into the opening  50  ( FIG. 1C ) of the drive shaft clamp  16 .  FIG. 3B  shows the rotor assembly  22  with the various springs  30  (here, e.g., clover springs) and washers  32  slipped over the drive shaft  26  (and uncompressed). For each set of two, the concave sides of the two clover springs  30  face the same direction. In addition, the concave sides of the two clover springs  30  in each set face in the direction of the concave sides of the two clover springs  30  in the other set. Preferably, the two springs in each set are in alignment with each other during assembly, although the two sets need not be in alignment with each other. 
         [0066]      FIG. 3C  shows an end view of the leading face of the head portion  28  with the two pins  42 - 1 ,  42 - 2  and centrally located dais  48 . In one implementation, each pin  42  extends approximately 0.16 inches from a surface of the head portion  28 , pin  42 - 1  having an approximately 0.109 inch diameter, pin  42 - 2  having an approximately 0.093 inch diameter, and the centers of the pins being 0.500 inches apart, with each pin being 0.250 inches from the center of the dais  48 . In addition, in this implementation, the dais  48  is raised approximately 0.012 inches from the surface of the head portion  28 . Other pin sizes and locations can be employed without departing from the principles described herein. 
         [0067]      FIG. 4A  shows an isometric view of the disk-like shaped rotor  24  with a set of rotor grooves  90  disposed centrally on the contact surface  44  of the rotor  24 . The length and position of the grooves  90  in the rotor surface  44  align the grooves  90  for coupling to various ports  70  of the stator  12  to other ports  70  of the stator  12  when the rotor  24  and stator  12  are in particular rotational alignments. In this implementation, there are three rotor grooves (the rotor shear valve assembly being configured as an injection valve). Other implementations can have one, two, or more than three rotor grooves, for use in other types of valves, such as vent valves and column manager valves. 
         [0068]    In addition, the rotor  24  has two diametrically opposite openings  92 - 1 ,  92 - 2  (corresponding to the two pins of the drive shaft). The opening  92 - 1 , referred to as a mating hole, is adapted to receive the smaller pin  42 - 2  of the rotor assembly  22  closely with tight tolerance. In one implementation, the mating hole  92 - 1  has a diameter of approximately 0.095 inches for closely receiving the 0.093 diameter implementation of the smaller pin  42 - 2 . The opening  92 - 2  is an elliptically shaped slot adapted to receive the larger pin  42 - 1  of the two pins, with a greater measure of tolerance along the direction of the major axis of the slot than along the minor axis. In one implementation, the minor axis of the slot  92 - 2  is approximately 0.110 inches wide for receiving the 0.109 diameter implementation of the larger pin  42 - 1 . The rotor  24  can slide onto the pins  42  of the head portion  28  without pressing. The ends of the pins  42  within the holes  92  of the rotor are approximately flush with the contact surface  44  of the rotor. 
         [0069]      FIG. 4B  shows a top view of the rotor  24  with a cross-sectional line A-A bisecting the openings  92 - 1 ,  92 - 2  and center point  94  of the rotor and passing though the ends of two of the rotor grooves. The center point  94  is the center of rotation of the rotor  24 . The center point  94  can have a diameter of 0.005 inches to 0.015 inches. In one implementation, the center point  94  has an approximately 0.010 inch diameter. Detail region  96  encircles the rotor grooves  90  and center point  94 . 
         [0070]      FIG. 4C  shows a cross-section of the rotor  24  taken along the line A-A of  FIG. 4B . In the cross-section, each opening  92 - 1 ,  92 - 2  extends entirely through the rotor  24 . In addition, to provide a sense of scale, the center point  94  and rotor grooves  90  appear as dark dots immediately below the surface  44  of the rotor  24 . Detail region  98  surrounds the center point  94  and the one of the rotor grooves  90 . 
         [0071]      FIG. 4D  show a view of the detail region  96  of  FIG. 4B , including the three rotor grooves  90 - 1 ,  90 - 2 , and  90 - 3  (generally,  90 ). The rotor grooves  90  are arcuate in shape, and reside equidistant from the central point  94 . In one implementation, the rotor groove  90 - 1  forms an approximately 74 degree arc and rotor grooves  90 - 1  and  90 - 2  form 60 degree arcs, each groove being approximately 0.005 inches to 0.020 inches in width, e.g., 0.008 inches in width.  FIG. 4E  shows a view of detail region  98  of  FIG. 4C , the rotor groove  90 - 3  (representative of all grooves  90 ) being a shallow channel and the center point being a shallow hemisphere formed in the surface  44  of the rotor  24 . In one implementation, the depths of the grooves  90  and center point  94  are approximately 0.005 inches to 0.020 inches, e.g., 0.008 inches. The external diameter of the rotor  24  can be about 0.5 inches to 1.0 inches, e.g., 0.7 inches. The rotor  24  has a thickness of 0.120 inches to 0.150 inches, e.g., 0.141 inches. 
         [0072]    The rotor  24  can be manufactured from polyether-ether-ketone, such as PEEK™ polymer (available from Victrex PLC, Lancashire, United Kingdom), filled with 20% to 50% carbon fiber by weight, e.g., 30% carbon fiber by weight. The carbon fibers have a diameter of 6 microns to 8 microns, e.g., 7 microns, and a length of 0.002 inches to 0.020 inches. Notably, the rotor  24  is formed in an injection-compression molding process. 
         [0073]    Conventional rotors are often manufactured by first injection molding a rotor puck (a pre-part), and then performing machining processes and polishing steps performed to complete the part.  FIG. 5  illustrates an injection molding process for forming a conventional rotor puck. As shown in  FIG. 5 , a resin flow  100  is injected into a tool cavity  102  through a side gate  104 . As illustrated in  FIG. 5 , the injection molding process can produce resin flow lines  106  which represent non-uniformities in the structure of the rotor puck being formed. Between flow lines  106  there are darker regions  108  which are resin rich and/or include carbon fiber on end (i.e., with a longitudinal axis of the carbon fibers extending substantially perpendicular to the plane of the rotor contact surface). Such an orientation of the carbon fibers contributes to wear, since the carbon fibers tend to wear more quickly at exposed ends. In addition, other regions include carbon fibers  112  having an orientation which follows the flow lines  106 , and, consequently, the carbon fibers  112  are not uniformly distributed throughout the part, but, instead, exhibit a tendency to form grains, which can contribute to uneven wear. Injection molding by itself can cause internal stresses to the part due to non-symmetrical filling. These internal stresses can interfere with maintaining a flat part during subsequent lapping and polishing processes. 
         [0074]      FIGS. 6A-6D  illustrate an injection-compression molding process and apparatus for forming a rotor  24  in accordance with the invention. Referring to  FIG. 6A , an injection-compression molding apparatus  200  includes a stationary die  210  and a movable die  212 . The injection-compression molding apparatus  200  includes features  220   a  that form the grooves  90  and center point  94  ( FIG. 4A ) and features  220   b  that form the openings  92 - 1 ,  92 - 2  ( FIG. 4A ) in the rotor  24  during the injection-compression molding process. These features  220   a,    220   b  may be inserts disposed within the stationary die  210  and/or the movable die  212 . For example, in one implementation, the stationary die  210  includes replaceable inserts for forming the openings  92 - 1 ,  92 - 2  and the movable die  212  includes an insert for forming the grooves  90  and center point  94 . Alternatively or additionally, the features  220   a,    220   b  can be machined into the stationary die  210  and/or the movable die  212 . The stationary die  210  and the movable die  212  can be formed from P20 tool steel. 
         [0075]    In the injection-compression molding process, the movable die  212  is moved into a first position relative to the stationary die  210 . As shown in  FIG. 6A , in the first position, a compression gap  222  is maintained between the movable die  212  and the stationary die  210 . With the movable die  212  in the first position, molten resin  224  (e.g., molten PEEK polymer containing 20% to 50% carbon fiber by weight (e.g., 30% carbon fiber by weight)) is injected, into a cavity  226  that is formed by a recess  227  in the stationary die  210  and the movable die  212 , as illustrated in  FIG. 6B . In this regard, the molten resin  224  is injected, at a temperature of 644° F. and 700° F. and a pressure of 1,000 psi to 10,000 psi through a side gate  228  in the stationary die  210  from a nozzle attached to an injection apparatus (not shown). 
         [0076]    Then, the side gate  228  is closed and the volume of the cavity  226  is reduced, to compress the melted resin in the cavity, by moving the movable die  212  toward a second position relative to the stationary die  210 , as illustrated in  FIG. 6C . In this regard, the movable die  212  is moved 0.020 inches to 0.060 inches toward the stationary die  210 , thereby closing the compression gap  222  and compressing the injected resin to form the rotor. As the resin is compressed (e.g., at pressures of 10,000 psi to 25,000 psi), excess material exits the cavity  226  through symmetrical overflow ports  230  in the stationary die  210 . In one implementation, the stationary die  210  includes four overflow ports  230  spaced equally in a radial array. The use of symmetrical overflow ports  230  helps to further reduce the presence of resin flow lines and help to contribute to a more uniform flow, and, thus, a final molded product with a more homogeneous structure, as compared to a conventional injection molded part. As result, flow lines may be avoided, carbon fiber lay may be more random, and more carbon fiber may lay flat rather than on end. 
         [0077]    This compression step causes flow lines, from the injection of the resin, to disperse and causes the carbon fibers to lay more flat (i.e., with the longitudinal axes of the fibers extending substantially parallel to the plane of the rotor contact surface  44 ) for better wear. The compression step also helps to resin to “pack out” better, i.e., as compared to conventional injection molding, to help fill intricate details such as the rotor grooves. This allows the rotor grooves  90  to be molded, and, molding the rotor grooves, rather than machining, helps to ensure that the carbon fiber remains fully encapsulated by the polymer which helps to reduce carryover. Machining, on the other hand, shears and exposes the carbon fibers which can contribute to carryover. Such machining is typically required as a subsequent processing step in the formation of conventional injection molded rotors. The compressed polymer is allowed to cool, and, then, the mold is opened by moving the movable die  212  away from the stationary die  210 , and the molded part (the rotor  24 , including grooves  90 , center point  94 , and openings  92 - 1 ,  92 - 2 ) is ejected, as illustrated in  FIG. 6D . Following ejection, the rotor contact surface  44  is lapped down 0.006 inches to 0.010 inches and polished. 
         [0078]    While the invention has been shown and described with reference to specific implementations, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as recited in the accompanying claims.