Abstract:
An extrusion apparatus is provided having an extrusion worm with a threaded exterior passage and rotatably driven by a drive shaft operatively couplable with a drive motor for driving rotation of the drive shaft. A feed in device for feeding in strip form material which is to be extruded is disposed relative to the rotational axis such that the material strips fed in by the feed in device are advanced substantially parallel to the rotational axis during rotation of the drive shaft and the extrusion worm.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an extrusion apparatus and a method for extrusion. 
     Extrusion apparatus serve in the feed of material, especially plastics, whereby the extrusion apparatus is typically heated and the material that is fed in in granular or strip form is plasticized in the course of the extrusion process. In connection with the feeding in of material to be plasticized in strip form, it must be ensured that the extrusion worm is continuously supplied with sufficient material feedstock as otherwise an insufficient material feedstock leads inevitably to the inclusion of air which, depending upon the intended use of the respective extruded material, is not acceptable. In order to control the feeding in of the material feedstock, the material strip or granules are frequently fed from above to a horizontally extending worm. An example of this solution is disclosed in DE-OS 31 33 708. In this disclosed extrusion apparatus, the variations in the performance of the extrusion apparatus should be countered by a special storage zone of the extrusion worm. 
     A disadvantage of the noted solution is that a mixing occurs only on one side of a location, whereby in this respect the extrusion worm is radially loaded on one side. This condition can also result in a bending of the extrusion worm that, in turn, leads to a metal-on-metal rubbing of the side of the extrusion worm opposite to the radially loaded side, with the attendant disadvantages. 
     Research has shown that the quality of the feed is decisive for the performance of an extruder. Accordingly, efforts have been made to ensure the best possible synchronization between the feed rollers of the strip feed device and the drive of the extrusion worm. Nonetheless, there occurs in many instances involving a substantially radial feed a non-uniform degree of filling of the extrusion worm passage as a result of which it has been proposed to simultaneously fill several worm passages whenever possible. A solution of this manner is disclosed, for example, in DE-PS 40 05 400 in which it is endeavored to constantly maintain a blockage roll. 
     The just noted solution basically presents, in fact, an interesting approach. On the other hand, the material, before its actual plasticizing, is subjected to a decidedly strong shearing force that can be detrimental to the material properties. 
     SUMMARY OF THE INVENTION 
     The present invention accordingly provides a solution to the challenge of providing an extrusion apparatus that, in view of its total performance, is improved without necessitating especially burdensome measures with regard to controlling the feed of the material to be extruded. 
     In accordance with the present invention, the axial feed of material strips to the extruder permits the possibility of avoiding a one-sided radial pressure on the extrusion worm. Additionally, the extrusion worm is filled with feed material around its entire periphery, which provides the particular advantage of reducing the probability that air, which can degrade the quality of the extrudate, will be introduced in this area of the extrusion process. 
     The material strips can be fed at an angle onto the shaft between the drive motor and the extrusion worm and can be engaged by the shaft for drawing along by the shaft. In this regard, it is sufficient if the material strips are disposed at an angle in a hanging manner toward the shaft such that the engagement or take-up element of the shaft can, at the least, engage the material strips by frictional engagement. 
     In connection with this solution of the present invention, attention must be paid that a continuous feed to the extrusion worm is ensured. If the engagement or take-up element of the shaft is configured, for example, with a type of hook, the material strips can be manually hooked on at their leading ends. Thereafter, the engagement or take-up element in the form of hooks automatically draw the material strips at the proper speed and, thus, the corresponding proper feed volume for the extrusion worm and this is demonstrated in that the material fully encircles the extrusion worm in the transition area—namely, the beginning of the extrusion worm. A particular advantage is realized in this connection in that the necessity of a partial back or counter flow, which brings with it the associated problem of shear loading of the material, can be completely avoided. The uniformity that is sought by use of a blockage roll automatically results in that a uniform condition of the feed material exists around the entire periphery of the extrusion worm. 
     In an advantageous embodiment of the present invention, it is provided that the material strips, instead of being wound in a plurality of windings about the shaft, are fed to the shaft in the manner of a pipe made of a continuous winding which has been axially extended out of its wound shape. This solution is particularly advantageous if a winding socket is rotated counter to the rotation of the extrusion worm and thereby ensures the required uniformity of the fed in material. In this solution, the material strips extend in the area of the shaft over approximately three-fourths of the circumference of the shaft, whereupon the desired distribution of the material is accomplished via the rotation and the counter-rotation. 
     It is particularly advantageous if the improved chamber filling of the extrusion worm leads to an improvement of about one-fifth in the output. 
     In accordance with a particularly advantageous embodiment of the present invention, it is provided that the transition area is configured between the shaft and the extrusion worm at the front end of the extruder housing and that the extruder housing at this location is configured with a widening or enlargement such that, as viewed in the direction of flow of the material, the transition area reduces or tapers conically. In this solution, a material strip hanging down to the shaft at an angle is simultaneously automatically engaged by the shaft and worked by the extrusion worm. 
     It is to be understood that the angle at which the material is fed into the feed zone can be selected to satisfy a wide range of requirements. For example, the material strips feeder, which comprises suitable feed rollers for the material strips, can be configured such that the angle of its output axis is oriented at an angle, for example, of 30° relative to the shaft, whereby the intersection point between the output axis and the shaft is thus desirably immediately behind the beginning of the shaft—namely, adjacent the drive motor. The material strips are then directionally re-oriented upon engagement by the shaft and, in fact, re-oriented into an axis parallel direction such that the material extends parallel to the axis of the shaft upon reaching the transition area. 
     Further advantages, details, and features are set forth in the following description of one exemplary embodiment of the present invention together with the one FIGURE of the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The one FIGURE of the drawing is a schematic side view of one embodiment of the extrusion apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The sole FIGURE of the drawing shows one embodiment of an extrusion apparatus  10  of the present invention. The extrusion apparatus  10  includes an apparatus base  12  on which a drive motor  14  is supported. The drive motor  14  is disposed on the flank of a drive device  16  from which a drive shaft  18  extends. The drive shaft  18  extends transversely over the apparatus base  12  and transitions into an extrusion worm  20 . 
     The extrusion worm  20  extends into an extruder housing  22  that is supported on the apparatus base  12  via brackets  24 ,  26 . 
     The drive shaft  18  extends over a considerable area—namely, the feed in area  28  bounded by the drive motor  16  and the extruder housing  22 . The feed in area  28  forms a portion of an axial conveying or feed advancing device  30  with which is associated a material strip supplier  34 , as is schematically shown in the sole FIGURE of the drawing. The material strip supplier  34  continuously supplies a material strip  36  comprised of polymeric material and, in particular, of an elastomer, to the feed in area  28  of the drive shaft  18 . The material strip supplier  34  comprises suitable feed rollers. The material strips  36  exit the material strip supplier  34  at its outlet  38  along an axis  40 . This axis extends at an angle to the axis  42  of the drive shaft  18  and, in fact, is arranged such that the material strips  36  are advanced in the direction of the extrusion worm upon exiting the outlet  38 . 
     It is preferred if the material strip supplier  34  is mounted adjacent the drive means or device  16  so that the material strips  36  are fed over a considerable extent above the free feed in area  28  of the drive shaft  18 . In this manner, a movement parallel to the axis  42  of the drive shaft  18  is set up. 
     The drive shaft  18  includes a concave rounded or radiused portion  43  on its drive motor adjacent area, and a plurality of engagement or take in elements  44  distributed along the entire extent of the drive shaft in the feed in area  28 , the engagement elements  44  being adapted for engaging the material strips  36 . In the illustrated embodiment, the engagement elements  44  are configured as small pegs whose pointed tips extend into the material strips  36  and prevent a slipping of the material strips being fed. Alternatively, it is also possible to provide the drive shaft  18  with an appropriately roughened top surface or with uniformly spaced hooks that can already grip a material strip in a sidewise manner if it hangs under into the area of the shaft. This solution provides a particular advantage in that the material strips can be fed to the extruder without manual intervention. 
     In the illustrated embodiment, the engagement elements  44  are configured as thorns that are arranged in a spiral manner around the outer periphery of the drive shaft  18 . In a modification of the extrusion apparatus, it is provided that a counter rotating press roller be located at the intersection location of the material strips  36  on the drive shaft  18 . The material strips that are hanging down are fed in a self-actuating manner into the space between the press roller and the drive shaft  18 . It is at that location that the material strip is engaged by the engagement elements  44  in a manner such that the material strip also remains on the drive shaft  18  upon further rotation of the drive shaft. The material strip is moved with a predetermined speed upon further rotation of the drive shaft in that the material strip remains rolled onto the drive shaft  18  until reaching the extruder housing  22 , whereupon the material is then engaged in the area of the extrusion worm  20 . 
     While with conventional extrusion apparatus special measures must be undertaken for the synchronization between the feeding in of the material and the extrusion worm, this synchronization is effectively automatically accomplished by the extrusion apparatus of the present invention by virtue of the fixed connection of the drive shaft  18  and the extrusion worm  20 . Once the first winding of fed in material on the drive shaft  18  has been effected, the drive shaft can then draw the next following material in the required amount, whereby the possibility comes into play of controlling the material strip supplier  34  via a tension sensor which measures the tension of the material strips  36 . 
     In an especially advantageous embodiment of the present invention, a winding socket  46  is provided at the material intake side of the extruder housing  22 . The winding socket  46  includes an inner threaded portion  48  and is rotatable such that the inner threaded portion  48  rotates counter to the rotation of the extrusion worm  20 . In this manner, the fixed or half-fixed material of the material strips  36  is, in the transition region  50 , subjected to a counter movement such that a uniform annular distribution of the material around the extrusion worm is enhanced; in this connection, an intake taper  52  is provided at the intake side of the extrusion worm. This solution is of particular importance if the material strips are fed via an axis parallel push movement in the area of the drive shaft  18 —in other words, fed without winding about the shaft. A material strip that has been fed in this push movement manner typically does not completely encircle the drive shaft  18 ; instead, the material strip only encircles, for example, up to three-fourths of the drive shaft. By virtue of the counter rotating inner threaded portion  48 , it is then in conjunction with the uniform application of the fed in material also ensured that no partial counter flow or a blockage roll occurs on the outer periphery of the material strips that are to be classified. 
     It is to be understood that, in accordance with the present invention, it is also further possible without the need for modification to feed in several material strips parallel to one another, if the extrusion apparatus  10  is also to operate as a mixing apparatus. For example, several material strip suppliers  34  can be arranged serially relative to one another at staggered heights or at the same axial height while nonetheless angularly offset from one another. 
     While the drive shaft  18  and the extrusion worm  20  described in connection with the illustrated embodiment of the present invention are configured as a single integrally formed component, it is also possible to configure these two elements as separable in the transition region so as to facilitate, for example, an easy removal of the extrusion worm  20  from the extruder housing  22  for cleaning purposes. 
     The specification incorporates by reference the disclosure of German priority document 199 59 174.1 of Dec. 8, 1999. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.