Abstract:
The technical field of the invention broadly relates to molding systems, and more particularly to a flexible shoe assembly for use in a molding system. The clamp unit of a molding system includes a moving platen and a stationary platen supported by a frame. Tie bars interconnect the moving platen with the stationary platen. The tie bars are secured to the stationary platen and pass through respective openings in the moving platen. Each tie bar is supported and guided within their respective openings by a flexible shoe assembly and wear pad. The flexible shoe assembly has a force redirector for directing force away from a peripheral edge of the wear pad towards a central force area. The flexible shoe assembly also includes a load distributor to distribute the load across the wear pad surface. The flexible shoe assembly includes an upper support that is flexible about a lower support to keep the wear pad in operational contact with the tie bar.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to industrial machines such as molding systems and more particularly, the invention relates to a dynamic shoe assembly for supporting and slideably guiding a horizontal tie bar member with a platen of a molding system.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the field of industrial machines having fixed and movable members, bushings, sleeves and shoe assemblies are well known and commonly used in industry.  
           [0003]    U.S. Pat. No. 5,624,695 entitled Securing Assembly For Injection Molding Machines issued on Apr. 29, 1997 to Husky Injection Molding Systems Ltd. and discloses a platen securing assembly. A stationary platen and moving platen are interconnected through a plurality of tie bar members. The tie bar members are supported and guided by a guide shoe located between the tie bar members and moving platen. The guide shoe is a fixed solid block of material and includes an integral wearing surface.  
           [0004]    U.S. Pat. No. 5,275,550 entitled Hydromechanic Mold Clamping Mechanism issued to Industries Romi S.A., Brazil on Jan. 4, 1994 and discloses a hydromechancial clamp for injection molding machines. Two fixed platens are interconnected by a plurality of tie bar members. A moving platen is located intermediate the fixed platens and the tie bar members pass through the moving platen. A fixed solid bushing is disposed between an opening in the moving platen and the cylindrical surface of the tie bar member. The fixed solid bushing runs the entire width of the moving platen.  
           [0005]    U.S. Pat. No. 5,135,385 entitled Clamping System issued to Ube Industries Ltd., on Aug. 4, 1992 and discloses a clamping system. A fixed platen and moving platen are interconnected by a plurality of tie bar members. A fixed solid bushing is disposed between an opening in the moving platen and the cylindrical surface of the tie bar member. The fixed solid bushing runs the entire width of the moving platen.  
           [0006]    U.S. Pat. No. 5,238,394 entitled Mold Clamping Apparatus For Molding Apparatus issued to Nissei Jushi Kogyo K.K. on Aug. 24, 1993 and discloses a clamping apparatus. A fixed platen and moving platen are interconnected by a plurality of tie bar members. A fixed solid bushing is disposed between an opening in the moving platen and the cylindrical surface of the tie bar member. The fixed solid bushing runs the entire width of the moving platen.  
           [0007]    U.S. Pat. No. 4,874,309 entitled Die Clamping Apparatus issued to Mitsubishi Jukogyo Kabushiki on Oct. 17, 1989 and discloses a die clamp. A fixed platen and moving platen are interconnected by a plurality of tie bar members. The moving platen has a plurality of openings for passing each tie bar member through the moving platen without a bushing, wear pad, or shoe assembly. The tie bar member slides on a ram insert located in each opening of the moving platen.  
           [0008]    U.S. Pat. No. 4,304,540 entitled Hydraulic Press issued on Dec. 8, 1981 to Carl K. Hammon and discloses a hydraulic press including a fixed solid wedge guide mechanism. The wedge guide mechanism includes a wedge shoe adjustably mounted on a movable platen. The wedge shoe carries a removable solid wear plate that slides along an elongated solid wear plate.  
           [0009]    U.S. Pat. No. 5,137,443 entitled Apparatus For Forming Hollow Plastic Article issued on Aug. 11, 1992 to Husky Injection Molding Systems and discloses a blow molding machine. A pair of long fixed “T” shaped solid wear strips are attached on opposing sides of a pallet. The wear strips communicate with a pair of “T” shaped recesses in the channel track for reciprocal movement of the pallet with respect to the channel track.  
           [0010]    U.S. Pat. No. 5,885,458 entitled Wear Strip Assembly For Use In A Waste Water Treatment Facility issued On Mar. 23, 1999 to United States Filter Corporation and discloses a wear strip assembly for use in a waste water treatment facility. Long rigid “C” shaped wear strips are secured to a concrete floor through a number of anchor plates. Rigid “L” shaped wear shoes are secured to a flight through a rectangular upright portion. The wear shoes include a rectangular horizontal surface in contact with the wear strips. The rectangular horizontal surface slides over the wear strip during reciprocal movement of the flight in a horizontal direction.  
           [0011]    U.S. Pat. No. 5,785,486 entitled Replaceable Wear System issued on Jul. 28, 1998 to McNeilus Truck and Manufacturing Corporation and discloses a replaceable wear system for use in refuse packing or ejecting mechanism. In one arrangement, a long rigid wear pad is substantially rectangular in cross section and includes a lengthwise triangular recess formed in the bottom of the wear pad for sliding engagement on a complimentary triangular rail located on a frame. In another arrangement, a long rigid wear pad is substantially triangular in cross section with a surface formed on the hypotenuse for sliding engagement on a complimentary wear surface located on the frame. The wear pads are retained with the packing arm through recesses for holding the wear pads and plates for securing the ends of the wear pads with the packing arm. The wear pads slide over the wear surfaces during reciprocal movement of the packing ram in a horizontal direction.  
           [0012]    U.S. Pat. No. 5,560,713 entitled Ejector Wear Shoe issued on Oct. 1, 1996 to McNeilus Truck and Manufacturing Corporation and discloses a replaceable wear shoe for use on the ejection or packing mechanisms of a refuse hauling truck. A long rigid wear shoe is “C” shaped in cross section forming an inner channel. A rigid “T” shaped (cross section) slide bar communicates with the inner channel allowing smooth operation. The wear shoe slides over the slide bar during reciprocal movement of the receptacle.  
           [0013]    The prior art devices are prone to several deficiencies and problems. For example, the fixed solid guide shoe of U.S. Pat. No. 5,624,695 has high compression loads at a peripheral edge of the wearing surface resulting in excessive wear and relatively early failure due to uneven loads.  
           [0014]    The fixed solid bushings of U.S. Pat. No. 5,275,550 and U.S. Pat. No. 5,135,385 and U.S. Pat. No. 5,238,394 require tight machining tolerances to press fit the bushing into the opening in the moving platen and to receive the cylindrical tie bar member. Alignment is critical and any misalignment of this device may cause early bushing failure. Replacement of the device requires considerable time and equipment.  
           [0015]    The prior art devices are static and cannot compensate for differing loads, non-uniform loads, bending moments, and stress profiles over the wearing surface. They are relatively expensive. Assembly of the machine and wear pads requires considerable time for lateral and longitudinal alignment of the components. The components tend to be long for maintaining alignment.  
           [0016]    Early or frequent failure of wear pads leads to maintenance problems and is undesirable for machine down time and associated costs to disassemble the machine, replace the components, and re-assemble the machine.  
           [0017]    Therefore, it is desirable to provide a shoe assembly and wearing surface which overcomes the aforedescribed problems of the prior art devices. There is a need for improving the wear characteristics of a wearing surface extending the useful life of a wear pad.  
         SUMMARY OF THE INVENTION  
         [0018]    There is a need for reducing early or frequent failure of wear pads and a need for operational dynamic alignment of a wear pad in a flexible shoe assembly.  
           [0019]    In accordance with a primary broad aspect of the present invention, there is provided a flexible shoe assembly for use in an injection molding system. The flexible shoe assembly comprises a body for supporting a load and a force redirector.  
           [0020]    The body has an upper surface for slideably engaging a complimentary surface of a supported member. The force redirector is disposed in the body in a plane below the upper surface for redirecting the force from a peripheral edge of the upper surface to a central force area in the body.  
           [0021]    The shoe assembly further comprises a load distributor disposed in a plane above the force redirector. The load distributor distributes the load across the upper surface and maintains the upper surface relatively flat under loading.  
           [0022]    In the preferred embodiment, the load distributor is formed on the upper surface.  
           [0023]    The shoe assembly further comprises a wear pad and a wear pad retainer. The wear pad retainer is formed in the upper surface of the body. The wear pad is mounted by the wear pad retainer on the upper surface. In an embodiment, the load distributor is formed on a lower surface of the wear pad.  
           [0024]    In the preferred embodiment, the load distributor is a series of stepped notches. In an embodiment, the load distributor is a contoured recess.  
           [0025]    The force redirector provides pivotal movement of the upper surface. In the preferred embodiment, the force redirector is a pair of slots in the body forming a web interconnecting the upper support member and the lower support member. In an embodiment of the invention, the force redirector is a slot forming a web interconnecting the upper support member and the lower support member.  
           [0026]    The shoe assembly further comprises a first flexation stop disposed in one slot of the pair of slots between the upper support member and the lower support member. A second flexation stop is disposed in a second slot of the pair of slots between the upper support member and the lower support member. The first and second flexation stops limit pivotal movement of the upper support.  
           [0027]    In the preferred embodiment, the wear pad retainer is a first edge lip formed at a first peripheral edge of the upper surface of the body and a second edge lip formed at a second peripheral edge of the upper surface of the body. The first edge lip and the second edge lip engage respective ends of the wear pad releasably retaining the wear pad with the shoe.  
           [0028]    In accordance with a second broad aspect of the present invention, there is provided a molding system. The molding system comprises a stationary platen for mounting a first mold half. A moving platen for mounting a second mold half. At least one tie bar member interconnecting the moving platen and the stationary platen. The moving platen having at least one opening for receiving at least one tie bar member. A flexible shoe assembly mounted in the moving platen supporting the tie bar member. The flexible shoe assembly having a body for supporting a load. The flexible shoe assembly having a force redirector. The flexible shoe assembly having an upper surface for slideably engaging a complimentary surface of the tie bar member. The force redirector disposed in the body in a plane below the upper surface for redirecting the force from a peripheral edge of the upper surface to a central force area in the body.  
           [0029]    The molding system further comprising an injection unit communicating with the first mold half for injection a molten material in the mold.  
           [0030]    The molding system further comprising a first mold half and a second mold half. The first mold half mounted on the stationary platen. The second mold half mounted on the moving platen. The first mold half and the second mold half forming a mold including a core and cavity to define a part.  
           [0031]    The present invention finds particular advantage in reducing localized wear and failure of a wear surface through force redirection and load distribution across the wear surface.  
           [0032]    The present invention also finds advantage in extending the life of wear pads by reducing the wear and early failure of the wear pad. By extending the life of wear pads, another advantage is found in reducing the maintenance cost and machine down time.  
           [0033]    The present invention also finds advantage in relatively improving the performance of a shoe assembly and wear pad by dynamically adjusting the mating surface of the wear pad to the complimentary surface of the supported member. Peak loads at the peripheral edge that lead to excessive wear, friction, and heat are reduced.  
           [0034]    The present invention also finds advantage in providing dynamic operational adjustment of a wear surface by redirecting force and distributing stress in actual operation.  
           [0035]    The present invention also finds advantage in ease of installation and initial alignment.  
           [0036]    The present invention also finds advantage in lowering the cost of maintenance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]    For a better understanding of the nature and objects of the present invention reference may be had to the accompanying diagrammatic drawings in which:  
         [0038]    [0038]FIG. 1 is a simplified plan view of a molding system;  
         [0039]    [0039]FIG. 2 is a simplified plan view of a molding system illustrating the movable platen extended to the maximum daylight position;  
         [0040]    [0040]FIG. 3 is sectional view of a tie bar member taken along line A-A of FIG. 2,  
         [0041]    [0041]FIG. 4 is a sectional view of a tie bar member taken along line A-A of FIG. 2 illustrating three shoe assemblies in relationship to a single tie bar member,  
         [0042]    [0042]FIG. 5 is a partial plan view of a tie bar member illustrating the fixed end secured to the stationary platen and a movable shoe assembly located at a distant end of the tie bar member,  
         [0043]    [0043]FIG. 6 is a partial plan view of a tie bar member illustrating the fixed end secured to the stationary platen and the movable shoe assembly located intermediate the ends of the tie bar member,  
         [0044]    [0044]FIG. 7 is a perspective view of a shoe assembly having an force redirector and integral wear surface,  
         [0045]    [0045]FIG. 8 is a perspective view of a shoe assembly having a force redirector and wear pad retainer,  
         [0046]    [0046]FIG. 9 is a perspective view of a shoe assembly having a force redirector, a load distributor, and a wear pad retainer,  
         [0047]    [0047]FIG. 10 is a perspective view of a wear pad,  
         [0048]    [0048]FIG. 11 is a perspective view of a wear pad having a load redirector,  
         [0049]    [0049]FIG. 12 is a perspective view of a shoe assembly having a force redirector, a load distributor, a wear pad retainer, a wear pad, and a stop shim,  
         [0050]    [0050]FIG. 13 is a perspective view of a shoe assembly having a force redirector, a load distributor, a wear pad retainer, a wear pad, and a stop shim inserted into one end of the force redirector,  
         [0051]    [0051]FIG. 14 is a perspective view of a clamp unit showing a fixed platen interconnected by tie bar members to a moving platen and placement of a bottom shoe assembly, and  
         [0052]    [0052]FIG. 15 is a cross sectional view taken along line B-B of FIG. 12 showing placement of a bottom shoe assembly within the platen and engagement with the tie bar member. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0053]    An embodiment of the present invention is described with initial reference to FIG. 1. The molding system includes a clamp unit  2  supported by a base  6  and an injection unit  4 . The injection unit  4  provides for injecting a molten material, for example plastic, into a mold. Alternatively, the injection unit  4  provides for injecting a molten metal, for example a metal in a thixotropic state, into the mold. The injection unit  4  may also be omitted, for example with a blow mold system wherein a preform is introduced into a mold for subsequent shaping into a bottle.  
         [0054]    The clamp unit includes a stationary platen  14  and a moving platen  16 . Alternatively, the clamp unit may include more than one moving platen  16  in the case of a tandem machine. The moving platen  16  is movable quickly along the base  6  by a conventional mold stroke generator (not shown). The mold stroke generator may be hydraulic, electric, or a mechanical device to effectively open and close the mold.  
         [0055]    The stationary platen  14  and moving platen  16  are interconnected by four tie bar members  20   a,    20   b,    20   c,  and  20   d . ( 20   a  and  20   c  shown). Each tie bar member ( 20   a - 20   d ) is secured to the stationary platen by conventional means and permitted to slide axially through respective bores in the moving platen  16 . Alternatively, each tie bar member ( 20   a - 20   d ) may be secured to the moving platen by conventional means and permitted to side axially through the stationary platen.  
         [0056]    The moving platen  16  may be locked and unlocked to each tie bar member ( 20   a - 20   d ) through respective tie bar member locks  22   a ,  22   b ,  22   c , and  22   d  ( 22   a  and  22   c  shown). When the moving platen  16  is locked to each of the four tie bar members ( 20   a - 20   d ), a clamp force generator supplies a clamp force to the mold. When the moving platen  16  is unlocked from each of the four tie bar members ( 20   a - 20   d ), the clamp force generator does not supply a clamp force to the mold. The clamp force generator may be hydraulic, electric, or a mechanical device to supply the required clamp force. The clamp force generator may be a separate actuator or integral with the tie bar member locks. When the moving platen  16  is unlocked, the moving platen  16  may be axially moved by the mold stroke generator.  
         [0057]    The moving platen  16  is guided on the base. The tie bar members ( 20   a - 20   d ) are guided and aligned between the stationary platen  14  and the moving platen  16  by shoe assemblies (see FIG. 4). The tie bar members transmit the clamping force between the stationary platen  14  and the moving platen  16  during clamp up by the clamp force generator.  
         [0058]    A first mold half  8  is secured to the stationary platen  14  and a second mold half  10  is secured to the moving platen  14 . The first mold half  8  is a cavity and the second mold half  10  is a core. Alternatively, the first mold half  8  is a core and the second mold half  10  is a cavity. The first mold half  8  communicates with a channel formed in the stationary platen  14  to receive the molten material from the injection unit  4 . The first mold half  8  and the second mold half  10  form a mold for defining a part.  
         [0059]    Referring now to FIG. 2, the molding system is shown illustrating the movable platen extended to a distant end of the tie bar members ( 20   a - 20   d ). Each of the four tie bar members are identical. The tie bar member  20   a  is essentially a straight cylindrical cantilever beam having a uniform load due to gravity distributed along the length of the beam. A plurality of teeth  26   c  are formed intermediate and near a distant end of the tie bar member  20   c  for engaging complimentary teeth in the tie bar member lock  22   c . The teeth in the tie bar member lock  22   c  may be rotated into locking engagement and rotated into unlocking engagement with the teeth  26   c . In locking engagement, a clamp force generator acting with the tie bar member locks provides a clamping force. Four tie bar member slots ( 24   a - 24   d ) are formed in the distant end of the tie bar member  20   c . The teeth in the tie bar member lock  22   a  are rotated into the slot ( 24   a - 24   d ) area when unlocked permitting axial movement of the moving platen  16 . The near end of a tie bar member  20   c  is fixed in the stationary platen  14 . The distant end of the tie bar member  20   c  is supported by a shoe assembly (see FIG. 15) located in the bore  28   c  of the moving platen  16 .  
         [0060]    Referring now to FIG. 3, a cross sectional view of the tie bar member  20   c  is shown. The tie bar member  20   c  is substantially cylindrical. Multiple sets of four teeth  26   a  extend outwardly from the tie bar member  20   c . Each set of four teeth  26   a  provide locking engagement with complimentary teeth in the tie bar member lock  22   c  (not shown) to effectively lock the moving platen  16  (not shown) on the tie bar member  20   c.    
         [0061]    The tie bar member  20   c  includes a substantially square inner section formed by four tie bar slots machined into the outer surface of the tie bar member  20   c . The tie bar slots provides sliding surface to engage a wear pad. The substantially square inner section includes a top lengthwise slot  24   b , a right lengthwise slot  24   c , a bottom lengthwise slot  24   d , and a left lengthwise slot  24   a . The complimentary teeth in the tie bar member lock  22   a  (not shown) pass over the tie bar slots ( 24   a - 24   d ) unrestricted in the unlocked position permitting the moving platen to pass over the tie bar member  20   c.    
         [0062]    Alternatively, the number of teeth per set and corresponding tie bar slots may be more or less than four, for example 3, 6, 9 or 12.  
         [0063]    Referring now to FIG. 4, a cross sectional view of the tie bar member  20   c  is shown in relationship to a plurality of shoe assemblies. A left shoe assembly  34  is mounted by conventional means to an inner surface of an opening in the moving platen  16  (not shown). A left wear pad  36  is mounted on the left shoe assembly  34  for sliding engagement with the left lengthwise slot  24   a.    
         [0064]    A right shoe assembly  38  is mounted by conventional means to the inner surface of an opening in the moving platen  16  (not shown). A right wear pad  40  is mounted on the right shoe assembly  38  for sliding engagement with the right lengthwise slot  24   c.    
         [0065]    The combination of the left shoe assembly  34  and left wear pad  36 , and the right shoe assembly  38  and right wear pad  40  prevent lateral movement of the tie bar member  20   a  with respect to the moving platen  16  (not shown).  
         [0066]    A bottom shoe assembly  30  is mounted by conventional means to the inner surface of an opening in the moving platen  16  (see FIG. 15). A bottom wear pad  32  is mounted on the bottom shoe assembly  30  for sliding engagement with the bottom lengthwise slot  24   d  of the tie bar member  20   c . The bottom shoe assembly  30  and wear pad  32  also support the tie bar member  20   c  from the moving platen  16  (not shown).  
         [0067]    Referring now to FIG. 5 and FIG. 6, a tie bar member  20   c  is shown with a bottom shoe assembly  30  located at the distant end of the tie bar member  20   c  in a maximum daylight position and intermediate the two ends of the tie bar member  20   c  in a minimum shut height position. These extreme positions of the shoe assembly  30  are not related to the locking teeth as the tie bar slots in the tie bar members  20   c  extend beyond the locking teeth.  
         [0068]    The tie bar member  20   c  is fixed to the stationary platen  14  and supported by the bottom shoe assembly  30  and bottom wear pad  32 . The tie bar member  20   c  tends to bend under uniform load of the tie bar member  20   c . The shoe assembly  30  is relatively short with respect to the overall length of the tie bar member  20   c  which concentrates a relatively large force over the shoe assembly.  
         [0069]    When the bottom shoe assembly  30  and bottom wear pad  32  are located at the distant end of the tie bar member  20   a  at the maximum day light position, the leading edge  42  of the bottom wear pad  32  is subjected to higher stress than the trailing edge  44  due to the bending of the tie bar member  20   c . In this configuration, the distant end of the tie bar member  20   c  tends to deflect away from the trailing edge  44  of the bottom wear pad  32  concentrating the force on a smaller area near the leading edge  44  of the bottom wear pad  32 .  
         [0070]    When the bottom shoe assembly  30  and bottom wear pad  32  are located intermediate the two ends of the tie bar member  20   c  at the minimum shut height position, the trailing edge  44  of the bottom wear pad  32  is subjected to higher stress than the leading edge  44  due to a different bending profile of the tie bar member  20   c . In this configuration, the distant end of the tie bar member  20   c  tends to deflect downward concentrating the force on a smaller area near the trailing edge  42  of the bottom wear pad  32 .  
         [0071]    The shoe assembly  30  dynamically adjusts to the tie bar member  20   c  over the entire range of the moving platen between the maximum day light position and the minimum shut height position keeping the entire surface of the wear pad in contact with the surface of the tie bar slot.  
         [0072]    Referring now to FIG. 7, a embodiment of the present invention is shown as  46 . The shoe assembly body  12  is a substantially rectangular block. The body  12  is longer about the longitudinal axis than the lateral axis. A shoe assembly body  12  has an upper surface  58  for slideably supporting a tie bar member (not shown). The upper surface  58  contains an integral wearing surface.  
         [0073]    The shoe assembly body  12  has a first slot  54  extending from an side outer edge of the body  12  inwardly towards a central web  52 . A second slot  56  extends from an opposite side edge of the body  12  inwardly towards the central web  52 . The first slot  54  and the second slot  56  are coplanar and equal in length and height. A stress relieving bore  76  is disposed at an end of the first slot  54  near the web  52  and a second stress relieving bore  78  is disposed at an end of the second slot  56  near the web  52  on the other side.  
         [0074]    The stress relieving bores ( 76  and  78 ) extend the entire width of the slots ( 54  and  56 ). The body  12  is substantially “I” shaped in cross section about the lateral axis.  
         [0075]    The first slot  54  and the second slot  56  define a flexible upper support  48  and a lower support  50 . The flexible upper support  48  and the lower support  50  are substantially rectangular. The upper support  48  and the lower support  50  are flexibly interconnected by the web  52 . An intermediate plane defined by the first slot  54  and the second slot  56  is parallel to a top plane defined by the upper surface  58 . A bottom plane is defined by the bottom surface  60  and is parallel to the intermediate and top planes. Alternatively, only one slot may be provided for provide one peripheral edge with the ability to flex and distribute the load. For this configuration, the body  12  is substantially “C” shaped in cross section about the vertical axis. Alternatively, the slots ( 54  and  56 ) extend outwardly from the central web  52  and upwardly towards the upper surface  58 . Alternatively, the slots ( 54  and  56 ) extend outwardly from the central web  52  and downwardly towards a bottom surface  60 . Alternatively, the web  52  is not central in the shoe assembly body  12 . Alternatively, the slots are not equal in length.  
         [0076]    A first peripheral edge  62  of the upper support  48  is dynamically vertically flexible. The second peripheral edge  64  of the upper support  48  is also dynamically vertically flexible. The vertical flexibility of these edges ( 62  and  64 ) is for uneven surface contact with a corresponding slot of a tie bar member. The edges ( 62  and  64 ) may flex independently of each other to distribute an applied load about the upper surface  58 . The height of the slot  56  and web  52  are such to permit unrestricted operational flexibility of the upper support  48 .  
         [0077]    Alternatively, the upper surface  58  may pivot about the central web  52 . The pivoting is for maintaining operational surface contact and alignment with a slot in a tie bar member during bending of the tie bar member.  
         [0078]    The web  52  is relatively thin about the vertical axis to the relatively thick upper support  48  and lower support  50 . The web  52  provides elastic deformation as the upper support  48  pivots.  
         [0079]    The vertical flexibility of the edges ( 62  and  64 ) and the pivoting of the upper support  48  are much less than the height of the slots ( 54  and  56 ).  
         [0080]    A force redirector for directing force away from a peripheral edges ( 62  and  64 ) towards a central force area is formed by the upper support  58  and the web  52 . The central force area is directly over the web  52 . The force redirector is disposed intermediate the upper support  48  and the lower support  50 . The force redirector is equidistant from the upper surface  58  and the bottom surface  60 . Alternatively, the force redirector may be formed closer to the upper surface  58 , or closer the bottom surface  60 .  
         [0081]    The first slot  54  defines a first intermediate upper support surface  82 , a first upper support edge  92 , a first intermediate lower support surface  80 , and a first lower support edge  90 .  
         [0082]    The height of the first slot  54  may be varied to limit the amount of vertical deflection. Vertical deflection of the first peripheral edge  62  is limited by the height of the first slot  54  and contact between the first upper support edge  92  and the second lower support edge  90 . The height of the first slot  54 , first upper support edge  92 , and first lower support edge  90  form a first flexation stop  96 . The first flexation stop  96  prevents plastic deformation of web  52  of the shoe assembly.  
         [0083]    The second slot  56  defines second intermediate upper support surface  86 , a second upper support edge  72 , a second intermediate lower support surface  84 , and a second lower support edge  74 .  
         [0084]    The height of the second slot  56  may be varied to limit the amount of vertical deflection. Vertical deflection of the second peripheral edge  64  is limited by the height of the second slot  56  and contact between the second upper support edge  72  and the second lower support edge  74 . The height of the second slot  56 , second upper support edge  72 , and second lower support edge  74  form a second flexation stop  70 . The second flexation stop  70  prevents plastic deformation of the web  52  of the shoe assembly. The web  52  effectively interconnects the second intermediate surfaces ( 82  and  86 ) with the first intermediate surfaces ( 80  and  84 ).  
         [0085]    The height of the first slot  54  and the height of the second slot  56  are equal for providing the same maximum amount of flexation for the first peripheral edge  62  and the second peripheral edge  64 . Alternatively, the heights of the slots ( 54  and  56 ) may be different providing different maximum amounts of flexation for the first peripheral edge  62  and the second peripheral edge  64 .  
         [0086]    The bottom surface  60  is semi cylindrical for mounting adjustment with the surface of a bore in a platen (not shown). A first fixation bore  66  and a second fixation bore  68  extend lengthwise through the lower support  50  of the shoe body assembly  12 . Fasteners extend through each bore ( 66  and  68 ) to positively retain the shoe assembly body  12  in a platen.  
         [0087]    Referring now to FIG. 8, another embodiment of the present invention is shown generally as  88 . A first edge lip  98  is formed at the first peripheral edge  64  of the shoe assembly body  12 . A second edge lip  100  is formed at the second peripheral edge  62  of the shoe assembly. The lips ( 98  and  100 ) are disposed opposite each other and extend outwardly from the upper surface  58  of the shoe assembly body  12 . An inner surface of the first edge lip  98  and an inner surface of the second edge lip  100  engage complimentary surfaces (see FIG. 10, first side  118  and second side  120 ) of a wear pad  94  (FIG. 10) for releasably retaining the wear pad  94  with the shoe assembly body  12 . The height of the lips ( 98  and  100 ) are such to retain the wear pad without obstructing the wear surface  110  of the wear pad  94 . The width of the lips ( 98  and  100 ) are such to retain the wear pad  106  with the shoe assembly body  12  in operation of the system. The first edge lip  98 , the second edge lip  100 , and the upper surface  58  of the shoe assembly body  12  form a wear pad retainer formed on the upper surface  58  of the shoe assembly body  12 . Alternately, the wear pad may be retained with the shoe through conventional fasteners.  
         [0088]    The wear pad may be centered on the surface  58  of the shoe assembly by a pin or key or groove through a complimentary mating surface.  
         [0089]    Referring now to FIG. 9, the another embodiment of the shoe assembly is generally shown as  102 . This embodiment includes the features previously described with respect to FIGS. 7 and 8. A load distributor  104  is formed in the upper surface  58  of the shoe assembly body  12 . A series of steps or notches are formed intermediate the first and second peripheral edge of the shoe assembly body  12 . The steps extend downwardly into the upper support  48  and are disposed lengthwise about the surface  58 . Alternatively, the load distributor may be a smoothly contoured surface.  
         [0090]    Those skilled in the art will appreciate that the steps shown in the figure are exaggerated. In an embodiment of the invention, the actual height of each step is in the range of 0.05 mm and the steps are machined into the upper surface  58  of the shoe assembly body  12 .  
         [0091]    The load distributor  104  compensates for the deflection of the upper section  48  of the shoe assembly  12  under loading conditions. The contoured surface of the load distributor creates a substantially flat surface when the upper member  48  bends under the load from a tie bar member. The number and location of each step is such to proved the substantially flat upper surface  58  during bending.  
         [0092]    Referring now to FIG. 10, a preferred embodiment of a wear pad  94  is shown generally as  102 . The wear pad  94  is substantially rectangular having a wear surface  110 , a bottom surface  114 , a first side  118  and a second side  120 . The wear pad  94  is of suitable thickness, length, and width for supporting a load. The bottom surface  114  is supported by the upper surface  58  of the shoe assembly body  12 . A first chamfer  116  is disposed on the wear surface  110  near the first side  118 . A second chamfer  112  is disposed on the wear surface  110  near the second side  120 . The chamfers ( 116  and  112 ) ease engagement for reciprocal movement in a horizontal direction with a tie bar member (not shown).  
         [0093]    Optionally, lubrication grooves  108  may be formed in the upper wearing surface  110  of the wear pad  94  including an optional through hole for supplying a lubricant.  
         [0094]    Referring now to FIG. 11, a second embodiment of the wear pad  94  is shown generally as  122 . Alternatively, a load distributor  124  as previously described with reference to FIG. 9 may be formed in the bottom surface  114  of the wear pad  94  for equally distributing the load across the length of the wear pad  94 . Those skilled in the art will appreciate that the steps shown in the load distributor  124  are exaggerated to illustrate the overall contour.  
         [0095]    Referring now to FIGS. 12 and 13, the preferred embodiment of the present invention is illustrated. The preferred embodiment includes the shoe assembly  102  of FIG. 9 in combination with the wear pad  106  of FIG. 10.  
         [0096]    A stop shim  136  prevents plastic deformation of the web  52  during installation of the shoe assembly between a moving platen and a tie bar member. The height of the slot  56  is larger than the thickness of the stop shim  136 . The stop shim  136  may be inserted into the slot  56  limiting the vertical movement of the first upper support edge  72  with respect to the first lower support edge. The limit of vertical movement is defined by thickness of the stop shim  136  . The first upper support edge  72  and first lower support edge  74  effectively close upon the stop shim  136 .  
         [0097]    The stop shim  136  may also be inserted into the slot  54  limiting the vertical movement of the second upper support edge  92  with respect to the second lower support edge  90 . Again the height of the slot  54  is larger than the thickness of the stop shim  136 . After installation of a shoe assembly, the stop shim  136  is removed from the slot.  
         [0098]    The stop shim  136  may also be used during side entry of a mold. The stop shim  136  is inserted into the slot, then a tie bar member may be de-secured from the stationary platen and pulled back through the stationary platen. As the tie bar member is pulled back, the stop shim  136  limits movement and prevents plastic deformation of the web  53 . Once the tie bar member is clear of the mold area, the mold may be mounted in the machine. Then the tie bar member is re-assembled between the stationary platen and moving platen. As the tie bar member engages the wear pad  106  of the shoe assembly, the first support edge  72  vertically deflects downwardly, resting on the stop shim  136 . The stop shim  136  is removed at the end of the operation.  
         [0099]    Referring now to FIG. 14, a pair of bottom shoe assemblies are shown mounted within a moving platen. The stationary platen  14  is interconnected to the moving platen  16  through four tie bar members ( 20   a ,  20   b ,  20   c , and  20   d ). Each tie bar member is fixed to the stationary platen  14  by conventional securing ( 128   a ,  128   b ,  128   c , and  128   d ). The moving platen  16  may be reciprocated between a maximum daylight position and a minimum shut height position about the stationary platen  14 . Each of the four tie bar members ( 20   a ,  20   b ,  20   c , and  20   d ) pass through respective bores in the moving platen  16 . A first bottom shoe assembly  126   a  is disposed in a bore of the moving platen and slideably engages a surface of the tie bar member  20   a . A second bottom shoe assembly  126   c  is disposed in a bore of the moving platen and slideably engages a surface of the tie bar member  20   c . A third and forth shoe assembly (not shown) are disposed in respective bores and slideably engage respective surfaces of tie bar member  20   b  and tie bar member  20   c.    
         [0100]    Referring now to FIG. 15, a cross sectional view of a bottom shoe assembly  126   c  is shown mounted in a bore  28   c  of the moving platen  16  engaging a bottom lengthwise slot  24   c  of a tie bar member  20   c . The bore  28   c  of the moving platen  16  includes a inner cylindrical surface  134  and an annular ridge wall  130 . A bottom surface  60  (see FIG. 7) of the bottom shoe assembly  126   c  engages and rests upon a portion of the complimentary cylindrical surface  134 . A side of the bottom shoe assembly  126   c  engages a portion of the annular ridge wall  130 . The annular ridge wall  130  includes a pair of threaded bores (not shown) to secure each shoe assembly in the bore of the moving platen. A pair of threaded fasteners  132  (one shown) pass through the respective fixations bores ( 66  and  68 ) of the shoe assembly for tightly securing each shoe assembly in the bore of the moving platen.  
         [0101]    The tie bar member may not have perfect orientation during installation with the respective bore  28   c  causing the tie bar slots ( 24   d  shown) to be slightly offset by a few degrees of rotation either to the left or the right of center. The bore surface  134  is cylindrical and the bottom surface  60  (see FIG. 7) of the shoe assembly is a complimentary semi-cylindrical surface that provides positioning and adjustment of the shoe assembly, left or right of center, in the bore  28   c  during installation.  
         [0102]    In an embodiment of the shoe assembly for a Husky E900 clamp unit, the wear pad size is 100 mm long by 51 mm wide by 8 mm thick and the shoe assembly was 110 mm long by 55 mm wide by 50 mm thick. In another embodiment of the show assembly for a Husky E8000 clamp unit, the wear pad size is 290 mm long by 142 mm wide by 8 mm thick and the shoe assembly was 300 mm long by 150 mm wide by 75 mm high. Those skilled in the art understand the dimensions of the wear pad and shoe assembly depend on the unit load capacity, strength and flexibility requirements. The web dimensions are selected to support the load and allow elastic flexation of each peripheral edge.  
         [0103]    In an embodiment, the shoe assembly is a integral steel block. Alternatively, the shoe assembly may be cast or a weldment of separate components.  
         [0104]    The wear pad material must posses certain physical and chemical properties which permit it to operate properly (fatigue resistance, conformability, thermal conductivity, corrosion resistance, and load capacity). The wear pad surface is substantially flat and the surface of the tie bar slots are substantially flat. Alternatively, the wear pad surface and surface of the tie bar slots may be other complimentary shapes, for example concave or convex.  
         [0105]    In an embodiment, the shoe assembly is retained by fixtures passing through the fixation bores. Alternatively, a housing or fixation plate may secure the shoe assembly.  
         [0106]    In operation, the movable platen may be rapidly cycled between open and closed positions for stroking the mold. The movable platen may also move relatively slowly to clamp up. The upper support of the shoe assembly is flexible and pivots about the web keeping the surface of the wear pad in operational contact with the tie bar as the tie bar bends during movement of the platen between the maximum day light position and the minimum shut height position. The force redirector directs forces away from the peripheral edges of the wear pad to a central force area over the web during operation. The load distributor compensates for deflection of the upper support under load and maintains a relatively flat upper surface distributing the load over the entire surface.  
         [0107]    It is to be understood by those skilled in the art that the present invention is not limited to the illustrations described and shown herein, which are deemed to be illustrative of an embodiment of the invention and may be modified without departing from the scope and spirit of the invention. The invention is intended to encompass all modifications, which are within its scope and spirit as defined by the attached claims.