Abstract:
A beater for a rotary shredder comprises an oblong base body with a pivot bearing adapted for pivotal connection of the beater to a rotor. A cutting head is formed with protruding cutting edges on opposite ends supported by the base body via the support surface. Complementary interlocking structures are provided by the support surface on the support surface and the cutting head. A releasable connection passes through the complementary structures connecting the base body with the cutting head. The complementary structures are provided by a recess formed in the support surface of the base body and a thereto complementary projection of the cutting head.

Description:
[0001]    This is a continuing application of pct application PCT/EP2006/061966 filed MAY 2,2006 which claims priority of GERMAN PATENT application DE 10 2005 023 339.2 filed MAY 17,2005. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates in general to shredding technology, and more specifically it relates to a novel design of a beater or a flail mallet adopted for use with a rotary shredder. 
       BACKGROUND OF THE INVENTION 
       [0003]    Rotary shredders contain a rotating rotor. Beater or flail mallets are pivoted to this rotating rotor. The beater or flail mallets are pivotable around axes which are in parallel with the axis of rotation of the rotor. During a rotation of the rotor the beater or flail mallets are pulled outward by the centrifugal force. Then they hit material to be comminuted or shredded like a hammer while rotating. For example, such rotary shredders are used for comminuting waste wood. If a piece of material is not comminuted by a beater or flail mallet immediately, the beater or flail mallet mounted pivotable to the rotor draws back after the hit. Many beater or flail mallets provide a cutting edge trying to chop the material to be comminuted according to the manner of an axe or a hoe. 
         [0004]    In the operation of the rotary shredder the beater or flail mallets are exposed to extensive strain and are subject to heavy wear. Generally the beater or flail mallets are wearing parts. It is known to form beater or flail mallet in two parts. A base body with considerable mass is mounted pivotable to the rotor with a pivoting bearing. A cutting head with a cutting edge striking the materials to be comminuted is attached to this base body. Nevertheless, the cutting head is subject to wear and must be replaced every so often. However, the base body does not normally need to be replaced. The cutting head, or at least the cutting edge, can be hardened. Important in doing so is to produce the attachment of the cutting head attached to the base body in such a manner able to absorb the heavy beating loads and not provide any weak points. The beating forces should be transferred from the base body (with large mass) to the cutting head and therewith to the materials to be comminuted completely. The reaction force during the impact on the materials to be comminuted should be absorbed by the base body. 
         [0005]    Different beater or flail mallets of this manner are known. 
         [0006]    U.S. Pat. No. 2,267,865 discloses a L-shaped mallet for a rotary shredder in which a first arm supports a pivot bearing on its end and a crushing body forms the second arm of the “L”. Generally this crushing body is cubical and provides pairs of cutting edges on opposite side surfaces. The cutting edges extend in parallel with the axis of rotation of the L-shaped mallet. This block-like crushing body is screwed to the first arm of the mallet with a threaded bolt. Thereby the threaded bolt extends crosswise to the cutting edges along the plan of symmetry between the side surfaces forming the cutting edges. The cutting edges are formed by almost 90° edges of the cubical crushing body. A rectangular projection is seated on the first arm to which the cubical crushing body is attached with a corresponding rectangular passage channel. The threaded bolt is passed through a bore in the projection and the passage channel. In this arrangement the forward side surface of the cubical crushing body basically is perpendicular to the moving direction. During rotation of the rotor the crushing body hammer-like strikes the materials to be comminuted with its side surface forming the cutting edges. 
         [0007]    The German patent document DE 29 43 456 A1 points out a two-part beater or flail mallet for rotary shredders. In this beater or flail mallet the cutting edges of the cutting head are aligned with the end faces of the base body. The attachment of the cutting head to the throughout plane surface of the base body is carried out with only one screw. 
         [0008]    U.S. Pat. No. 5,285,974 teaches a two-part beater or flail mallet for a rotary shredder. In this beater or flail mallet a comminuting body is screwed to a base body. The base body has a block-like main part with a pivot bearing and a flat part projecting from it with substantial less thickness. A half-moon-like comminuting body with two protruding cutting edges is screwed to this flat part. The comminuting body is vibration-isolated from the base body. The cutting edges of the comminuting body are extending over the base surface of the flat part in direction of motion of the beater or flail mallet. 
         [0009]    The published US patent application US 2004/0056129 A1 shows a two-part beater or flail mallet for a rotary shredder with a base body and a comminuting head or cutting head. The base body provides a section of larger thickness forming a pivot bearing at its end. With this pivot bearing the beater or flail mallet is pivoted to a rotor. Outwards, thus away from the pivot bearing the section of larger thickness is followed by a section of less thickness forming a basically plane and about radial to the axis of rotation extending support surface on its front side. Between the support surface and the surface of the section of larger thickness a step is provided with an inclined area. A cutting head with an approximately trapezoidal cross section is seated on the support surface. Cutting edges are provided by the acute angles of the trapezoidal cross section of the cutting head. Thereby the cutting head is seated on the support surface with its back surface corresponding to the smaller edge of the trapeze. The cutting edges are provided on the surface opposite to the support surface. The radial outer cutting edge protrudes inclined upwards and outwards beyond the end face of the base body. The other cutting edge is supported by the inclined area of the step. On the one hand the connection between the base body and the cutting head is carried out by the cutting head fitting against the support surface and the inclined area of the step as well as a threaded bolt. On the other hand a truncated pyramidal projection is provided on the support surface. The cutting head provides a truncated pyramidal recess complementary to the projection. The cutting head is attached with its recess on the projection. The threaded bolt extends through the recess and the projection. Thereby, opposite side surfaces of the pyramid are aligned with the cutting edges. 
         [0010]    In this arrangement very strong forces and moments must be transferred from the cutting head to the base body, when the cutting edge lying far outwards beyond the base body strikes a part to be comminuted with a large impulse. In the beater or flail mallet according to US 2004/0056129 A1 the cutting head is weakened just at the point transferring substantially the forces and moments to the base body by the truncated pyramidal recess and the thereto aligned recess for the head of the bolt. This can lead to a breakage of the cutting head during continuous operation limiting the lifetime of the beater or flail mallet. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention relates to a beater or flail mallet for a rotary shredder which consists of an oblong base body with a pivot bearing provided for pivotal connection of the beater or flail mallet to a rotor. The arrangement is pivotable about an axis of rotation which is parallel to the rotor axis and to a support surface extending to the free end of the base body. A cutting head is formed with protruding cutting edges on opposite ends supported by the base body via the support surface. A complementary interlocking structures are provided by the support surface on the support surface and the cutting head. A releasable connection means passes through the complementary structures connecting the base body with the cutting head. 
         [0012]    It is the object of the present invention to provide a beater or flail mallet having an increased lifetime and ensuring an improved absorption of the forces affecting the cutting edge by the strong base body. 
         [0013]    One of the essential features of the invention relates to a complementary structure of the beater or flail mallet formed by a recess provided in the support surface of the base body and is complementary to a projection of the cutting head. 
         [0014]    Thus, instead of providing a recess, the cutting head contains a projection. With this a weakening of the relative thin cutting head is avoided. On the contrary the cutting head is strengthened by the projection and its additional material. The recess complementary to the projection is provided by the more massive base body. The base body is formed having mass substantially greater than the cutting head. The base body is subject to reduced wear and therefore only has to be changed sparingly, if at all. The base body should have a significant mass for increasing the effect of beating. Normally the cutting head is made of harder material. Aside from the risk of breakage the cutting head is subject to heavy wear upon the cutting edge and has to be exchanged often. Thus the cutting head should not contain an unnecessary amount of material and just ensure a proper transfer of forces to the base body. 
         [0015]    Further embodiments of the present invention with advantageous arrangements are subject matter of the subclaims. 
         [0016]    An example of an embodiment according to the present invention is described below in greater detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]      FIG. 1  shows a longitudinal section view of a beater or flail mallet for a rotary shredder; 
           [0018]      FIG. 2  shows a top view of the beater or flail mallet of  FIG. 1 ; 
           [0019]      FIG. 3  shows a bottom view of the beater or flail mallet of  FIG. 1 ; and 
           [0020]      FIG. 4  shows a top view of the base body, wherein the cutting head is removed. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    The beater or flail mallet  10  comprises a base body  12  and a cutting head  14  connected to each other. The base body  12  has an elongated configuration. At one end the base body a bore  16  is provided for a pivot bearing. The beater or flail mallet is pivoted by means of a pivotal bearing to a rotor together with other similar beaters. 
         [0022]    The base body  12  provides a support surface for the cutting head  14 . Generally the support surface is referred to with the reference number  18 . As shown in  FIG. 1 , adjacent to the thickened end part of the base body  12  containing the bore  16 , the support surface  18  provides a step with an inclined area  20 . Adjacent to that, the support surface  18  forms a shallow four-sided truncated pyramidal recess  22 . The base face of the truncated pyramid is rectangular having two longitudinal sides  24 ,  26  extending in longitudinal direction of the beater or flail mallet  10  along the side surfaces of the base body  12  and two lateral sides  28  and  30  extending across the complete width of the base body  12 . The lateral side  28  forms the border between the inclined area  20  and the recess  22 . The lateral side  30  basically forms the outer front edge of the base body  12 . The shallow recess  22  provides four trapezoidal surfaces  32 ,  34 ,  36 , and  38  adjacent to each other, from which the surfaces  32  and  34  extend longitudinal to the base body  12  and the surfaces  36  and  38  extend across the base body  12 . Adjacent and central to this shallow recess the support surface forms a steeper and deeper recess and also four-sided pyramidal recess  40 . The base face of the truncated pyramid defining the recess  40  is quadratic wherein the sides of the quadrate are aligned with the longitudinal sides of the base body  12  and lateral to them, respectively. The recess  40  has a plane bottom  42 . A bore  44  is provided in the center of the bottom  42  and through the base body  12 . The front end of the base body  12  forms a rounded end face  46 . The end face  46  returns from a front edge  50  with respect to the axis  48  of the bore  16 , this means the distance between the end face  46  and the axis  48  gets continuous smaller from the front to the back. 
         [0023]    It is assumed in this context that the (not shown) rotor rotates counter-clockwise in  FIG. 1 . Thus, considering  FIG. 1  as a snapshot, the beater or flail mallet moves from the bottom to the top of  FIG. 1 . According to this, in this context the upper surfaces in  FIG. 1  are designated as front surfaces and the bottom surfaces in  FIG. 1  are designated as back surfaces. “Inner” stands for on the side of the axis of rotation  48  and “outer” for on the side of the free end of the beater or flail mallet  10  or allocated to this end. 
         [0024]    The cutting head  14  is mounted on the support surface  18 . The cutting head  14  is formed symmetrically with respect to its longitudinal middle plane  52  as well as to a plane  54  vertical to this. Basically the back side of the cutting head  14  is complementary to the support surface  22  of the base body. This back side is shown in  FIG. 3  and generally referred to with  56 . 
         [0025]    The back side  56  of the cutting head  14  has two plane inclined surfaces  58  and  60 . These inclined surfaces form the inner and the outer end faces of the cutting head  14 , respectively. The inclined surface  58  extends from the top left to the bottom right in  FIG. 1 . The inclined surface  60  extends in symmetry to this from the top right to the bottom left in  FIG. 1 . Adjacent to the inclined surfaces  58  and  60  the back side  56  of the cutting head forms a shallow four-sided truncated pyramidal raising  62  having two trapezoidal side surfaces  64  and  66  in the longitudinal direction of the beater or flail mallet  10  and two trapezoidal side surfaces  68  and  70  lateral to them. The side surfaces  68  and  70  join to the inclined surfaces  58  and  60 , respectively. The adjacent shorter parallel sides  72 ,  74 ,  76 ,  78  of the trapezes join to one another and form a quadrate. This quadrate is the base face or a steeper and higher four-sided truncated pyramidal projection  80 . A bore  82  extends centrally through the projection  80 , which aligns with the bore  44  of the base body in a mounted state and has the same diameter like bore  44 . 
         [0026]    The front side of the cutting head  14  (in the top of  FIG. 1 ) can be seen in  FIGS. 1 and 2 . The front side of the cutting head  14  provides two rectangular near-planar or planar surfaces  84  and  86 , which are symmetric to the plane  54 . The sides of the surfaces  84  and  86  are aligned with the longitudinal and lateral direction of the beater or flail mallet. The planes of the plane surfaces  84  and  86  form an obtuse angle. Thus, the surfaces  84  and  86  arise forwards and away from the plane of symmetry and up to the end surfaces  58  and  60 , respectively. Between the surfaces  84  and  86  a plan surface  88  is provided vertical to the axis  90  of the bores  44  and  82 . Therefore the front side of the cutting head  14  forms a shallow groove limited by the surfaces  84 ,  88  and  86 . In the mid surface  88  a hexagonal recess is provided centrally to the axis  90 , which forms a shoulder  94  around the bore  82 . 
         [0027]    A threaded bolt  96  with a hexagonal head  98  extends through the bores  82  and  44 . The head  98  is hold in the recess  92  and seated on the shoulder  94 . The diameter of the shaft  100  is slightly smaller than the inner diameter of the bores  82  and  44 . Thus, an annular gap  102  is formed between the inner walls of the bores  82  an  84  and the shaft  100 . The threaded bolt  96  is tightened by a nut  104  on the back side of the beater or flail mallet  10 . The nut  104  is seated in a recess  110  on the back side of the base body  12 . 
         [0028]    Then the cutting head  14  is fixed to the support surface  22  so that the end face  58  of the cutting head  14  abuts to the inclined surface  20  of the base body and is supported by it, while the opposite end face  60  extends tangential with the end face  46  of the base body  12  and all but joins it. The cutting head  14  provides a cutting edge  106  between the surface  86  and the end face  60 . This cutting edge protrudes forwards and outwards beyond the base body. 
         [0029]    The described construction operates as follows: 
         [0030]    The comminuting of materials results primarily from the wedge effect of the protruding cutting edge. The base body is located in “the shadow” of the cutting edge and therefore is almost not subject to wear. However, the reaction forces emerging during the comminuting have to be transferred from the cutting edge to the base body. This is provided by the special shape of the base body  12  and the cutting head  14 . The cutting head is guided on the base body  12  using the complete area of support in longitudinal as well as lateral direction by the shallow four-sided truncated pyramidal recess  22  of the base body  12  and the thereto complementary raising  62  on the back side of the cutting head  14 . This is superior to the invention disclosed in U.S. Patent Publication US 2004/0056129 A1, where the cutting head is supported by a plane surface of the base body. Different to the aforementioned US 2004/0056129 A1 in the present invention, a form-closed support is achieved by a truncated pyramidal projection  80  on the cutting head  14  engaged in a recess  40  of the base body. Thus the cutting head is strengthened and not weakened. The threaded bolt  96  is passed through the bores  82  and  44  without engagement and therefore is stressed only by tensile load and not by shearing strain. 
         [0031]    If a cutting edge  106  is worn out, the cutting head can be turned around 180° by loosening the threaded bolt  96  and making further use of the cutting head with the other cutting edge  108 .