Patent Application
20090258100
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.
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.
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.
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.
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.
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.
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.
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:
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.
Referring to
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.
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.
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.
As depicted in
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.
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.
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.
