Abstract:
An improved extrusion assembly is disclosed which better adapts to thermal changes resultant from the transport of high-temperature extrudate. An extrusion screw present in the assembly includes a hollow portion. A biasing member is disposed in the hollow portion. When the assembly is transporting high-temperature extrudate, the biasing member&#39;s included Belleville washer component compensates for the thermal expansion and contraction of the extrusion screw.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to co-pending patent application Ser. No. ______ filed ______ and entitled “Multi-Head Extruder Assembly,” which is incorporated by reference for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to an extruder assembly, and, more particularly, to an assembly including an apparatus which compensates for thermal expansion and contraction of an extruder screw during use. 
       BACKGROUND 
       [0003]    Extrusion is a common step in the manufacturing process for a variety of goods. For example, in the manufacture of pet food, the food base is extruded through a die to form end product of a desired size. This extrusion is commonly accomplished by use of extruder assemblies. Such extruder assemblies typically are comprised of a motor, a housing, an extrusion screw, and a supportive structure. The motor causes the extrusion screw to rotate, forcing product along a path to a fixed destination. Some examples of conventional extruders are those of U.S. Pat. Nos. 2,946,089, 3,696,913 and 6,015,226. 
       SUMMARY 
       [0004]    The present invention or assembly, accordingly, provides an improved apparatus which better compensates for thermal expansion or contraction of an extruder screw in an extrusion assembly. The improved apparatus includes a housing and an extrusion screw disposed in the housing. At least a portion of the extrusion screw is hollow, the hollow portion communicating with an aperture formed in one end of the extrusion screw. 
         [0005]    The apparatus also includes a race disposed in the housing. The race is adapted to support the extrusion screw in the housing. This race helps maintain the extrusion screw in a substantially fixed alignment. The apparatus uses a motor to rotate the extrusion screw in the housing. 
         [0006]    The apparatus also includes a biasing member that extends through the aperture of the extrusion screw into the hollow portion of the extrusion screw. The biasing member is in mechanical communication with a bearing. The biasing member compensates for thermal growth of the extrusion screw while the extrusion assembly is in use. The biasing member includes a threaded rod, at least one resilient washer, at least one generally cylindrical resilient seal, and an end cap. 
         [0007]    The threaded rod of the biasing member has a biasing end and an opposite threaded end. The threaded end extends through the aperture of the extrusion screw into the hollow portion of the extrusion screw. The biasing end is in mechanical communication with a bearing, the bearing being in mechanical communication with the race. The at least one resilient washer is generally conical in shape, such as a Belleville washer, and generally has an outer diameter less than the diameter of the hollow portion and aperture of the extrusion screw. The end cap and at least one resilient seal are both about the same diameter as the diameter of the hollow portion and aperture of the extrusion screw. The end cap, resilient washer, and resilient seal all surround the threaded rod, with at least one resilient seal being located between the end cap and the resilient washer. 
         [0008]    Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a cross-sectional side view of an extrusion assembly in accordance with a preferred embodiment of the invention; 
           [0011]      FIG. 2  is a cross-sectional side view of an extrusion screw in accordance with a preferred embodiment of the invention; 
           [0012]      FIG. 3  is a cross-sectional side view of a portion of a biasing member in accordance with a preferred embodiment of the invention; and 
           [0013]      FIG. 4  is an isometric view of a portion of a biasing member in accordance with a preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In the discussion of the FIGURES, the same reference numerals will be used throughout to refer to the same or similar components. Various components known to the art, such as extrusion devices and extruder die plates, have not been shown or discussed for the purpose of conciseness. 
         [0015]    Referring to  FIG. 1  and  FIG. 2  of the drawings, the reference numeral  100  generally designates an extruder screw assembly in accordance with a preferred embodiment of the present invention. The assembly  100  includes a housing  101 , an extrusion screw  103  disposed for rotation within housing  101 , and a biasing member  109 . 
         [0016]    The exterior of the extrusion screw  103  includes a number of threads or flights  135  which, when the extrusion screw  103  is rotated, apply mechanical work to the extrudate, generating a flow in the direction of the terminal end  131  of the assembly  100 . The extrusion screw  103  includes an aperture  129  formed in one end of the extrusion screw  103 , which communicates with a hollow portion  105  of the extrusion screw  103 , and is located proximate to the terminal end  131  of the assembly  100 . The aperture  129  and the hollow portion  105  together form a bore or receptacle that allows for supporting components to be secured to the extrusion screw  103  with reduced interference with its generation of a flow of extrudate. Although not shown, a mandrel fits within the hollow portion  105  of the extrusion screw  103  and the biasing member  109  is secured to the mandrel by threaded rod  111 . For most purposes, the mandrel can be considered part of extrusion screw  103 . 
         [0017]    A biasing member or spring  109  is dimensioned to fit inside the hollow portion  105  of the extrusion screw  103  to generally provide a seal for and support for the extrusion screw  103 . The biasing member  109  includes a pair of resilient seals  119  and eight Belleville washers  117 , which abut one another and are captured between an end cap  123  and an internal shoulder within the hollow portion  105  of the extrusion screw  103 . 
         [0018]    At the center of the biasing member  109  is the threaded rod  111 , which includes a biasing end  113  and an opposite threaded end  115 . The threaded end  115  is disposed inside and secured to the mandrel in the hollow portion  105  of the extrusion screw  103 . The biasing end  113  is located outside of the extrusion screw  103  but still inside the housing  101 , and includes a bearing surface  133  which is preferably formed of tungsten carbide. Bearing surface  133  generally operates to provide support for one end of the extrusion screw  103  by cooperating with three bearing points  139 . These bearing points  139  are preferably comprised of tungsten carbide and are secured to the housing  101  by adjustable rods  137 . Together, the bearing surface  133  and bearing points  139  are referred to as a bearing. This engagement between the bearing points  139  and bearing surface  133  provides support for maintaining the assembly in a desired alignment while permitting the rotation of the extrusion screw  103 . 
         [0019]      FIG. 3  and  FIG. 4  of the drawings further illustrate a portion of the biasing member  109 . Two resilient seals or discs  119  and  121  are depicted and are generally cylindrical in shape, having 3.255 inch outer diameter×1.065 inch inner diameter and, preferably, are comprised of TEFLON®. Extending through the aperture  129  is a generally frusto-conical end cap  123 , where a portion of the end cap  123  is generally cylindrical in shape. The generally cylindrical portion of the end cap  123  is dimensioned for a sliding fit within the aperture  129  of the extrusion screw  103 . The Belleville washers  117  are generally disposed between the resilient seals  119  and  121 . A plurality of spacer washers  125  are provided and are generally disposed on both sides of each of the two resilient seals  119  and  121 , which allows for a generally uniform force across the surface areas of each of the resilient seals  119  and  121 . The Belleville washers  117  are arranged in a manner such that they oppositely face each other in order to provide longitudinal force, operating as a spring. The entire Belleville washers  117 , resilient disc or seals  119  and  121 , and spacer washers  125  assembly is axially confined or captured between end cap  123  and an internal shoulder in hollow portion  105  of the extrusion screw  103 . Components  117 ,  119 ,  121 ,  123 , and  125  of the biasing member  109  are generally resilient and can expand and contract in response to thermal expansion while maintaining a generally uniform longitudinal force. In other words, as extrusion screw  103  expands longitudinally as it heats, the expansion is accommodated by the biasing member  109 , and resilient seals  119  and  121  are further compressed and radially expand to enhance their sealing capability. 
         [0020]    As depicted in  FIG. 1 , and as stated above, the biasing member  109  provides a generally uniform axial or thrust force on the extrusion screw  103 , regardless of thermal expansion or contraction effects. To accomplish this, Belleville washers  117  are compressed against the extrusion screw  103  within the hollow portion  105  of the extrusion screw  103 . Resting next to the Belleville washers  117  are resilient seals  119  and  121 . As compressive force is applied to each Belleville washer  117  (during assembly or in operation as a result of axial thermal expansion of the extrusion screw  103 ), the resilient seals  119  and  121  are compressed or “squeezed,” forcing the resilient seals  119  and  121  to expand radially in response to this pre-load. This provides a generally uniform fluid seal between at least a portion of the hollow portion  105  of the extrusion screw  103  and the exterior of the extrusion screw  103 . 
         [0021]    Providing the force to “squeeze” the resilient seals  119  and  121  are the Belleville washers  117  (which act as a spring) and another set of “squeezed” spacer washers  125 . Biased against a spacer washer  125  is the end cap  123 , which is secured to the extrusion screw  103  by the threaded rod  111  (which extends through other components comprising the biasing member  109 ). Thus, the threaded rod  111  can be secured to the extrusion screw  103 , “squeezing” both resilient seals  119  and  121  to provide a generally uniform fluid seal between the hollow portion  105  of the extrusion screw  103  and the exterior of the extrusion screw  103 , with little fear of the threaded rod  111  failing due to thermal expansion, because the Belleville washers  117  compensate for such expansion. 
         [0022]    Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.