Abstract:
A chipping knife and assembly. The knife has a front side and a spaced apart back side, the front and back sides terminating in a cutting edge so as to define an acute knife angle, the front and back sides having respective curvilinear portions for disposition between respective knife clamping members for clamping the knife, the knife having substantially constant thickness between the respective curvilinear portions. The assembly provides upper and lower clamping members shaped to fit the knife therebetween in a stable, indexed position.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a chipping knife and assembly for use in processing logs into lumber, chips, and flakes. 
       BACKGROUND 
       [0002]    In the use of cutting apparatus for processing logs to usable lumber, the log is forced into contact with a rotating cutting head of the apparatus that typically carries a plurality of removably clamped, elongate knives. The cutting head to which the knives are clamped typically falls into one of three classes of head shape, known in the art as disc, drum, and conical. 
         [0003]    The apparatus spins at a relatively high rate compared to the rate of feed of the log, so that a single encounter between one of the knives of the apparatus and the log results in the displacement and removal of a relatively small portion of the log. With variations resulting from the variations in the rate of rotation relative to the rate of feed, the head geometry and the shape and configuration of the knives, this small portion is what is generally referred to in the art as a “chip” or a “flake” (hereinafter “chip”) of more or less controlled dimensions. The chip often has commercial value in itself and is not simply waste material, as it can be used in the production of manufactured wood products such as particle board. 
         [0004]    Typically, the cutting head rotates at thousands of revolutions per minute, so each chip is removed quickly, resulting in large forces being applied to the knives. To maintain chip quality, it is important to maintain the position of the knives against these forces. So the prior art has provided numerous knife shapes, typically defined in cross-sections perpendicular to the elongate axes of the knives, that work in cooperation with the clamping members to help secure the knives. For use in disc style cutting heads, the knives are often double-sided, providing two parallel cutting edges on either side of the knife. This allows turning the knife to expose a fresh cutting edge when the exposed cutting edge becomes worn. 
         [0005]    Schmatjen, U.S. Pat. No. 5,819,826, assigned to Key Knife, Inc. of Tualatin, Oreg., describes a double-sided knife having what have often been referred to as a pair of “deflector ridges” on the front side of the knife, i.e., the side of the knife that faces in the direction of rotation of the cutting head. The deflector ridges project from the front side of the knife and therebetween form, essentially, a keyway or channel that indexes the knife to a suitably shaped inner clamping member that receives the front side. This indexing is an example of shaping the knife in cooperation with the clamping members to stabilize the position of the knife in the apparatus, and it also provides for easy installation of the knife into proper position 
         [0006]    Hinchliff et al., U.S. Pat. No. 7,140,408, also assigned to Key Knife, Inc., describes an alternative configuration for a double-sided knife providing for indexing. This configuration typically employs a single, centrally located deflector ridge projecting from the front side of the knife. 
         [0007]    Indexing as a general concept is well known in the art, and most modern chipping knives provide for some form of indexing. The particular configurations employed vary widely, but a common thread most chipping knives is the manipulation of the thickness of the knife to form projections, recesses, or both. Some examples are shown in  FIGS. 1-3  and discussed below. 
         [0008]      FIG. 1  shows the cross-section of a knife  1  disclosed in Kokko et al., U.S. Pat. No. 5,649,579. The thickness of the knife is increased in the center portion of the knife to define the projection  2 . 
         [0009]      FIG. 2  shows the cross-section of a knife  3  disclosed in Derivaz, U.S. Pat. No. 4,610,285. The thickness of the knife is decreased in the center portion of the knife to define recesses  4  and  5 . The recess  4  also partially defines projections  6  and  7  at which the thickness of the knife is at a maximum. 
         [0010]      FIG. 3  shows the cross-section of a knife  8  disclosed in Svensson, U.S. Pat. No. 4,047,670. The knife defines a knife angle θ between, typically, planar surfaces  9  and  10 . To define this knife angle, as in all chipping knives, the thickness of the knife necessarily decreases proceeding to the right of the line referenced as “A,” and to the left of the line referenced as “B.” However, to the left of the line referenced as A, and to the right of the line referenced as B, the thickness of the knife continues to increase, so that it is discernibly greater e.g., along the lines “C” and “D” than along the lines A and B. 
         [0011]    A similar configuration is shown in  FIG. 4 , in the cross-section of the knife  11 , which is indicated in the aforementioned &#39;579 patent as being prior art to the knife  1  of  FIG. 1 . The knife  11  has a substantially constant cross-section, i.e., it is substantially constant everywhere except where the thickness is decreased to define the aforementioned knife angle. The &#39;579 patent criticizes this configuration because its sharp angles create points of undesirably high stress concentration. The preferred solution taught therein is the configuration of  FIG. 1 . Another, partial solution would be the configuration of  FIG. 3 , where because of the increase in thickness to the left of the line A and to the right of the line B, the sharpness of angles φ 1  and φ 2  is correspondingly diminished. 
       SUMMARY 
       [0012]    A chipping knife and assembly. A knife according to the invention comprises a front side and a spaced apart back side, the front and back sides terminating in a cutting edge so as to define an acute knife angle, the front and back sides having respective curvilinear portions for disposition between respective knife clamping members for clamping the knife, the knife having substantially constant thickness between the respective curvilinear portions. 
         [0013]    A knife assembly according to the invention provides upper and lower clamping members shaped to fit the knife therebetween in a stable, indexed position. 
         [0014]    Preferably, the respective curvilinear portions define two corresponding arcs in a plane perpendicular to the cutting edge, each of the arcs having substantially continuous curvature of the same sign, wherein the arcs are circular and wherein the upper and lower clamping members are adapted to clamp the knife for use such that the lower clamping member makes substantially full contact with the knife over one of the arcs, and the upper clamping member makes no contact with the knife over substantially the entirety of the other arc. 
         [0015]    It is to be understood that this summary is provided as a means of generally determining what follows in the drawings and detailed description and is not intended to limit the scope of the invention. Objects, features and advantages of the invention will be readily understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a cross-sectional view of an elongate knife disclosed in Kokko, U.S. Pat. No. 5,649,579. 
           [0017]      FIG. 2  is a broken, pictorial view of an elongate knife disclosed in Derivaz, U.S. Pat. No. 4,610,285. 
           [0018]      FIG. 3  is a cross-sectional view of an elongate knife disclosed in Svensson, U.S. Pat. No. 4,047,670. 
           [0019]      FIG. 4  is a cross-sectional view of an elongate knife indicated in Kokko, U.S. Pat. No. 5,649,579 as being prior art to the knife of  FIG. 1 . 
           [0020]      FIG. 5  is a side elevation of a chipper disc incorporating a plurality of knife assemblies according to the present invention. 
           [0021]      FIG. 6  is the detail circle referenced in  FIG. 5 , above, as  6 - 6 . 
           [0022]      FIG. 7  is an exploded pictorial view of a preferred knife assembly for use in the chipper disc of  FIG. 5 . 
           [0023]      FIG. 8  is a side elevation of the knife assembly of  FIG. 7 , showing a lower clamping member, an elongate knife, and an upper clamping member, with the lower clamping member pivoted away from the upper clamping member, forming an open configuration of the assembly for receiving or removing the knife. 
           [0024]      FIG. 9  is a side elevation of the knife assembly of  FIG. 7 , showing the lower clamping member pivoted toward the upper clamping member so as to form a closed configuration of the assembly for clamping the knife between the two clamping members. 
           [0025]      FIG. 10  is a back-side perspective view of the knife of  FIGS. 8 and 9 . 
           [0026]      FIG. 11  is a front-side perspective view of the knife of  FIG. 10 . 
           [0027]      FIG. 12  is an end view of the knife of  FIGS. 10 and 11 . 
           [0028]      FIG. 13  is a side elevation of a knife assembly corresponding to  FIG. 8 . 
           [0029]      FIG. 14  is a side elevation of the knife assembly of  FIG. 13 , showing the lower clamping member pivoted into a position intermediate between the open position of  FIG. 8  and the closed position of  FIG. 9 . 
           [0030]      FIG. 15  is a side elevation of the knife and assembly of  FIG. 13  corresponding to  FIG. 9 . 
           [0031]      FIG. 16  is a magnified view of the knife and assembly of  FIG. 15 , showing in detail the interference between the knife and the upper and lower clamping members when the knife is clamped therebetween for use. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    Reference will now be made in detail to specific preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts or dimensions. 
         [0033]    For purposes herein, chips, flakes, and other such terms used to describe portions of logs or lumber removed by cutting apparatus as have been described above are intended to fall within the meaning of the term “chips,” where the cutting that produces these portions is referred to as “chipping,” with no loss of generality intended. Thus, it is to be understood that knives according to the invention may be used, with suitable modification, in, e.g., chipper or chipping discs, waferizers, drum chippers or flakers, ring slicers, conical chippers or canters, and any similar cutting apparatus used in the wood processing industry. Further, such knives may be used in chipping apparatus adapted for chipping materials other than wood. 
         [0034]    Chipping knives, such as those described above, are typically cut from pre-formed bars (“pre-forms”) that are formed by hot or cold-rolling to be as close to the desired cross-sectional shape as allowed by the required tolerances. The pre-forms must be over-sized to accommodate the tolerance, and the more intricate or complex the cross-section, particularly if there are sharp angles, the greater the required tolerance. Therefore, complex shapes result in more machining and waste to finish the pre-forms into their final configuration than less complex shapes. Regardless, it has been the conventional wisdom in the art that more complex shapes, especially those with sharp corners, such as those described above are either necessary or desirable to provide the desired indexing, and so the additional cost has been deemed to be worthwhile. The present invention challenges this conventional wisdom. 
         [0035]    As an exemplary context for use of chipping knives according to the invention,  FIGS. 5 and 6  show a disc chipper  10 . On the side of the chipper  10  are a plurality of chipping knives  12  and associated clamps  14  for removably clamping the knives  12  to a cutting head  16  of the chipper  10 . The cutting head  16  rotates about an axis of rotation “R,” causing each knife  12  to sweep out an annular space. 
         [0036]    As best seen in  FIG. 7 , providing an exploded view of the clamps  14 , the clamps  14  typically include an upper clamping member  14   a  and a lower clamping member  14   b , the latter often referred to in the art as a “counterknife.” The upper and lower clamping members receive respective back and front sides  12   a ,  12   b  of the associated knife  12 . 
         [0037]      FIG. 7  shows a preferred embodiment for clamping the knives  12  in which each clamp  14  includes a base  14   c  which is bolted to the cutting head  16 , and the lower clamping member  14   b  is disposed between the base and the upper clamping member  14   a . Further, preferably, the lower clamping member  14   b  is adapted for pivotal adjustment about a pivot  22  of the base  14   c.    
         [0038]    The action can be seen by comparing  FIGS. 8 and 9 . An adjustment bolt  18  is threadingly received in a through-hole  19  of the upper clamping member  14   a , and an end  18   a  of the bolt is captured in a through-hole  21  of an end  24  of the lower clamping member  14   b . The lower clamping member  14   b  is supported by the bolt  18  at the end  24 , and by the base  14   c  at the pivot  22 . 
         [0039]    Turning the bolt  18  raises or lowers the bolt with respect to the upper clamping member  14   a , taking the end  24  of the lower clamping member with it. The lower clamping member  14   b  thus pivots about the pivot  22  with movement of the bolt  18 . 
         [0040]    While a knife and assembly according to the invention are described in this exemplary configuration, it should be understood that the knife and assembly may be utilized in any of the three basic classes of cutting head, i.e., disc, drum, or conical, and that a pivoting clamping methodology is not required. 
         [0041]    In  FIG. 7 , an elongate configuration of the knife  12  can be seen, the knife therefore having an elongate axis (“EA” in  FIG. 10 ).  FIGS. 8 and 9  view the knife  12  in a direction parallel to the elongate axis. 
         [0042]    In  FIG. 8  the knife  12  is clamped between the upper and lower clamping members  14   a ,  14   b . In  FIG. 9 , the lower clamping member  14   b  has been pivoted about the pivot point  22  so as to drop the knife  12  down and away from the upper clamping member. The knife is no longer clamped, and is easily accessible and held in a convenient position for removal. 
         [0043]    While providing the aforedescribed pivoting function is preferred, it is not essential for use of the knife  12 . 
         [0044]    The knife  12  is shown in perspective in  FIGS. 10 and 11  and in end view in  FIG. 12 . The knife has two parallel cutting edges  26  lying in a reference plane “A,” the edges referenced more particularly as  26   a  and  26   b . The front side  12   b  includes two substantially planar knife-edge-joining portions  27 , namely  27   a  and  27   b  that may also lie in the plane A, but which may be disposed at non-zero angles with respect to the plane A if desired. For example, even if the knife-edge joining portions are originally provided to lie in the plane A, these surfaces may be ground as known in the art to alter the knife angle  12 . 
         [0045]    The back side  12   a  of the knife has corresponding, planar knife-edge-joining portions  28 , namely  28   a  and  28   b  that, along with the knife-edge-joining portions  27 , define the respective knife angles θ (see  FIG. 12 ) for the two cutting edges  26 . The knife angles are preferably within the range of 20-45 degrees. 
         [0046]    Referring to  FIG. 11 , the knife  12  defines a plane of reflective symmetry “POS” of the knife. The plane of reflective symmetry is perpendicular to the plane A and parallel to the elongate axis EA of the knife. With this symmetry, the knife  12  can be removed from the apparatus when it is in the configuration shown in  FIG. 9 , turned end-for-end to provide a fresh cutting edge, and reinstalled. 
         [0047]    Turning to  FIG. 12 , the preferred embodiment of the knife  12  has a centrally located, curvilinear center section  12   c . This center section  12   a  of the knife  12  has upper and lower surfaces  12   c   u  and  12   c   1  that are parallel to maintain thickness. However, due to the curvature of these surfaces, they define locating features on both the front ( 12   b ) and back ( 12   a ) sides of the knife for locating or indexing the knife laterally (i.e., perpendicular to the plane POS) between the clamping members  14 . 
         [0048]    Preferably, the surfaces  12   c   u  and  12   c   1  are circular arcs in cross-section as shown. The arcs preferably span an angle α of at least 30 degrees, preferably at least 60 degrees, and most preferably greater than 90 degrees (96 degrees is shown). If the curvilinear surfaces  12   c   u  and  12   c   1  define other than circular arcs, the dimensions of the corresponding central section is nevertheless preferably similar. 
         [0049]    In their circular configuration, the surfaces  12   c   u  and  12   c   1  differ in their radii of curvature “r 1 ” and “r 2 ” measured from the same center. The difference r 1 -r 2  is the thickness of the knife, which is substantially constant for the knife everywhere except to the right of the line “A” and to the left of the line “B” where the knife thickness decreases for the purpose of defining the knife angles θ. 
         [0050]    The location of the center of curvature relative to the surfaces  12   c   u  and  12   c   1  defines whether the sign of the curvature, i.e., whether the curvature is positive or negative. For a center of curvature C +   1  as shown in  FIG. 12 , the curvature is arbitrarily defined for purposes herein as being positive because it is above the surfaces (relative to the orientation of  FIG. 12 , which is also arbitrary), so that a center of curvature below the surfaces would define negative curvature. A circular arc has a single radius of curvature. It should also be understood that any curvilinear line or arc can be defined by a series or sequence of circular arcs with centers of curvature spaced arbitrarily close together. Therefore, a non-circular arc may be defined by an unbroken or continuous sequence of circular arcs. Further, if all of these circular arcs have centers of curvature of the same sign, then the arc can be considered to have a curvature of a single sign. The surfaces  12   c   u  and  12   c   1  as shown in  FIG. 12  could be replaced with a non-circular arc having a curvature of a single sign without departing from the principles of the invention. 
         [0051]    An outstanding advantage of the configuration of the knife  12  is that the curvilinear surfaces  12   c   u  and  12   c   1  essentially eliminate stress concentration while continuing to provide the desired indexing. Moreover, the substantially constant thickness of the knife makes it relatively easy to manufacture, utilizing a minimum amount of material and a minimum number of forming operations. 
         [0052]    Preferably, the knife cross-section is further defined by curvilinear portions on either side of the center section  12   c . In the case of a symmetrical knife, these are defined by a center of curvature C +   2  and a set of radii “r 3 ” and “r 4 ” extending therefrom where, again, the difference between the radii is the thickness of the knife. A line drawn between the centers of curvature C + , and C +   2  defines a corresponding side of the spanning angle α discussed above. In the preferred embodiment shown, dimensions “D 1 ” and “D 2 ” are 0.840″ and 0.447″ respectively, r 1 =r 3 =0.200″, and r 2 =r 4 =0.400″ where  FIG. 12  is drawn to scale. 
         [0053]      FIGS. 13-15  illustrate stages of the process of clamping the knife  12  between the clamping members  14 . More particularly,  FIG. 13  shows the lower clamping member  14   b  pivoted away from the upper clamping member  14   a  (pivot center-point “P”), forming an open configuration of the assembly for receiving or removing the knife  12  (also shown in  FIG. 8 );  FIG. 15  shows the lower clamping member pivoted toward the upper clamping member so as to form a closed configuration of the assembly, for clamping the knife between the two clamping members (also shown in  FIG. 9 ); and intermediate  FIG. 14  shows the lower clamping member pivoted so as to form a configuration that is intermediate to the open and closed configurations. 
         [0054]      FIG. 16  shows in more detail the manner in which the knife  12  mates with the upper and lower clamping members in the closed configuration of  FIG. 15 . Particularly, moving in the direction of the arrow “S,” there is a transition at approximately the point referenced as “A” (at about the end of the surface  12   c   u ) from full contact between the knife  12  and the upper clamping member  14   a  to a very slight gap of between about 0.001-0.005″ between these parts. 
         [0055]    In this, closed configuration, bolts  30  (see also  FIG. 7 ) hold the upper clamping member  14   a  in place so as to resist forces “F” applied to the cutting edge  26  of the knife  12 . The forces F produce a moment “M” about points “P 1 ” where the bolts connect to the base  14   c  (see also  FIG. 7 ). The aforementioned gap ensures that the resistive force “R” is applied by the lower clamping member at locations thereon at which maximum mechanical advantage is obtained, while still providing for indexing and consequent lateral stability of the knife to within an acceptably small tolerance. 
         [0056]    As indicated in  FIG. 16 , the lower clamping member  14   b  preferably mates to the knife  12  such that over at least the surface  12   c   1  there is substantially full contact. 
         [0057]    It is to be understood that, while a specific knife and assembly has been shown and described as preferred, other configurations and methods could be utilized, in addition to those already mentioned, without departing from the principles of the invention. 
         [0058]    The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions to exclude equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.