Abstract:
A heavy duty rotary disc-type wood chipper containing a knife clamping system that conducts the impact and shearing loads acting upon the chipper knives along two primary axes which allows for more efficient dissipation of the impact loads and a reduction in the deleterious effects of off-axis loads resulting in the ability to use smaller holding bolts and smaller knives in the system without adversely effecting either the ability of the knives to stay fixed to the disc or the quality of chips produced.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a wood chipper and, more specifically, to a heavy duty rotary disc wood chipper, however this same concept can also be applied to clamping of knives mounted in drum chippers. 
       BACKGROUND OF THE INVENTION 
       [0002]    Heavy duty wood chippers that are capable of producing large amounts of chips in a relatively short period of time typically employ a circular disc that is mounted for rotation upon a horizontally disposed drive shaft. A plurality of rectangular knives are radially extended upon the front face of the disc. Each knife is, in turn, aligned adjacent to a chip slots that passes through the disc between its front face and back face. Logs or similar work pieces are brought into contact with the front face of the rotating disc within a stationary work station where the moving knives act in association with a stationary bed knife to remove chips from the work pieces. The chips are conducted through the chip slots and exhausted from the machine. 
         [0003]    The knives that are typically used in these heavy duty machines are subjected to high impact loads which, if not effectively resisted can adversely affect the life of the knives and quality of the product produced in the machine depending upon various loading factors. In an effort to combat these high loads, it has been customary in the industry to use knives that are relatively massive in not only size but also in weight. As a result, the apparatus for securing the knives within a chipper is generally rather complex and expensive to build and maintain. Removal of the knives from the machine for refurbishing or replacing is usually a time consuming procedure. In addition, handling the massive knives is a multi-worker task and can pose a danger to the workers and the knives if the knives are mishandled or dropped. Systems employing much smaller knives meanwhile typically compromise the strength of the knives and the holding system resulting in a weaker overall clamping and holding system. 
         [0004]    Good knife support systems must also accommodate normal variations in thickness of knives due to variability in knife manufacture tolerances and also to accommodate for contamination such as wood dust, tree sap and debris that might work itself between mated parts while still safely and adequately holding the knives in place. 
         [0005]    The apparatus used to secure a chipper knife to a disc most generally involves some type of clamping mechanism for releasably capturing the knife or knives between the clamp and a substrate on the disc. The clamping force is typically provided by bolts that pass through the clamp and are threaded into the substrate so that the axes of the bolt shanks are generally normal to the front face of the disc. When used with hardware that permits keyed or doweled contact and transmission of forces to the disc, this type of clamping arrangement is well suited to resist input loads acting parallel to or perpendicular with the axis of the bolts. The clamping arrangement, however, is not as well suited to resist loads other than those running along these two primary axes or to couples arising from loads not being applied concentrically with the disc key supports or the holding bolts. These off-axis loads and couples are generally concentrated along one edge section of the bolt heads, a condition referred to as “point loading” of the bolt head, which results in a reduction in the holding effectiveness of the clamp and clamping bolts. When point loading occurs, the bolts or knife clamps can fatigue and fail giving rise to an unsafe situation of inadequately clamped knives and knives rapidly become dull or damaged and the quality of the chips produced being greatly reduced. Gaps and clearances that are often present between clamping system components can permit parts to deflect from their stress-free manufactured states, further exacerbating the “point loading” problem referred to above and observed in practice. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore a primary object of the present invention to improve heavy duty rotary disc wood chippers. 
         [0007]    It is a further object of the present invention to improve the apparatus for supporting chipper knives in a rotary disc chipper. 
         [0008]    It is a still further object of the present invention to reduce the size and weight of the knives used in rotary disc chippers without sacrificing the strength of the holding system and efficiency of the machine or the quality of product produced. 
         [0009]    Another object of the present invention is to reduce the amount of time and effort needed to remove, refurbish and replace knives in a rotary disc chipper. 
         [0010]    Still another object of the present invention is to reduce the deleterious effects of off-axis loads and couples on the knives and knife clamping system of a heavy duty rotary chipper. 
         [0011]    A still further object of the present invention is to provide a knife clamping system that is largely uncompromised by normal variations in thickness of knives and contamination therein between clamped or coupled parts. 
         [0012]    These and other objects of the invention are attained in a heavy duty rotary disc chipper by a knife hold down system that concentrates the loads acting upon the knives along two primary axes that are either parallel with or perpendicular to the front face of the disc such that the impact loads on the system are more effectively resisted and the deleterious effects of off axis loads greatly reduced. This, in turn allows for the use of smaller knives in the system without adversely effecting the efficiency of the system or the quality of the product produced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For a better understanding of these and other objects of the invention, reference shall be made to the following detailed description of the invention which should be read in conjunction with the accompanying drawings wherein: 
           [0014]      FIG. 1  is a perspective view of a heavy duty rotary disc chipper embodying the teachings of the invention; 
           [0015]      FIG. 2  is an enlarged partial sectional view taken through the disc further illustrating a portion of the disc and one of a plurality of segmented knife holder that are mounted upon the front face of the disc; 
           [0016]      FIG. 3  is a partial enlarged sectional view similar to  FIG. 2  illustrating the segmented knife holder in greater detail; 
           [0017]      FIG. 4  is a top perspective view of the body of the knife holder shown in  FIGS. 2 and 3 ; 
           [0018]      FIG. 5  is a bottom perspective view of the knife holder body shown in  FIG. 4 ; 
           [0019]      FIG. 6  is an enlarged partial sectional view taken through another part of the knife holder illustrated in  FIG. 1 ; 
           [0020]      FIG. 7  is an enlarged partial sectional view taken through yet another part of the knife holder with the clamping mechanism removed from the body of the knife holder; and 
           [0021]      FIG. 8  is a partial sectional view showing a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring initially to  FIG. 1 , there is illustrated a front perspective view of a heavy duty rotary disc wood chipper, generally referenced  10 , that embodies the teachings of the present invention. The chipper is of a well known Heavy Duty design that includes a vertically disposed disc  12  that is mounted for rotation upon a horizontal drive shaft  13 . The shaft is supported in bearing blocks that are mounted upon a stationary frame  14  along with a drive motor (not shown). 
         [0023]    The disc  12  is enclosed within a protective housing, generally referenced  17 , made up of a number of separtable sections. One of the sections  18  is shown moved back along a rail system  19  to permit clear access to the disc. A number of triangular shaped knife holders  20 , sometimes referred to as segments, are secured to the front face of the disc. As will be described in greater detail below, each knife holder supports one or more chipper knives which are drawn through a stationary chipping station  25  as the disc rotates about the drive shaft  13 . In the chipping station, the knives co-act with a stationary bedknife to remove chips from wooden work pieces, typically logs, that are brought into contact with the front face of the disc. In this particular embodiment, the work pieces are brought by a conveyor (not shown) into contact with the disc through a horizontal delivery spout  27  that is integral with the support frame  14 . Although a horizontal feed station is intended for use in the illustrated machine, a vertical gravity feed system may be similarly utilized without departing from the teachings of the present invention. 
         [0024]    Turning now more specifically to  FIGS. 2-7 , the common structural arrangement of the individual knife holders  20  will be described in greater detail. The number of knife holders that are spaced about the disc may vary depending upon the size of the disc and production required from the disc chipper. Each holder is mounted upon the disc face adjacent to a chip slot  30  that extends more or less radially along the disc and passes through the disc between its front face  22  and its back face  32  ( FIG. 2 ). As best illustrated in  FIGS. 4 and 5  each knife holder has a triangular shaped solid one piece body  20  that includes a top wall surface  34  that can be planar or flat and a nominally parallely aligned bottom wall surface  35 . The top and bottom wall surfaces are co joined by a pair of linear side wall surfaces  36  and  37  and an arcuate shaped base wall surface  38  that compliments the outer edge of the disc. In assembly the bottom wall surface of the holder body is seated upon the flat front face  22  of the disc and is secured to the disc by a plurality of studs that are passed through the disc by means of suitable clearance holes. In assembly, side wall surface  36  of the knife holder runs more or less radially along the edge  39  of the adjacent chip slot  30 . 
         [0025]    The studs securing each knife holder body to the disc include a row of smaller diameter studs  40  ( FIG. 6 ) that are mounted within clearance holes  41  that run adjacent to the chip slot. Both ends of the studs  40  contain a male thread with one end being threaded into threaded holes  42  located in the bottom of the knife holder body. A nut  43  is threaded upon the opposite end of each stud that acts against a washer  44 . Larger diameter studs  45  ( FIG. 2 ) are similarly contained within clearance holes  46  located in the disc. One end of each large diameter studs is threaded into a threaded hole  47  formed in the knife holder while the opposite end of each stud is mated with a nut  48 . Torquing down nuts  43  and  48  tightly secures the bottom wall surface of the knife holder against the front face of the disc. 
         [0026]    When the knife holder is secured in place its side wall surface  36  runs radially along one edge of the adjacent chip slot  30  and protrudes slightly into the slot. A cutout  50  is provided in the protrusion and one end of a wear plate  51  is supported in the cutout. The wear plate passes out of the cutout along the wall  39  of the slot and turns at a right angle along the rear face  32  of the disc. The angled section  49  of the wear plate is provided with a series of clearance holes that allow this section of the wear plate to be placed over the studs  40  into contact against the rear face  32 . Torquing down the stud nuts  43  secures the wear plate in place within the chip slot and helps to secure the knife holder in place with the bottom wall surface in parallel alignment with the front face of the disc. 
         [0027]    Turning now more specifically to  FIGS. 4 and 5 , each knife holder  20  contains a V-shaped knife seat generally references  53  ( FIG. 7 ) that runs along the side wall surface  36  of the holder. The seat includes an inclined wall surface  54  that passes upwardly and opens through the side wall surface  36  of the holder and a back wall  55  that is perpendicularly aligned with the inclined wall  54 . A rectangular shaped compartment  57  for housing a knife clamping mechanism is recessed in the top wall surface  34  of the knife holder body. The compartment includes a flat floor  58  that runs parallel with the bottom wall surface  34  of the holder and which opens into the knife seat through the rear wall  55  of the seat. The compartment further includes an upwardly extended back wall  59  that is substantially perpendicular to the top and bottom wall surfaces of the knife holder. A raised pedestal  60  ( FIG. 2 ) extends along the back wall of the compartment and has a flat top surface  61  and flat front surface  62  ( FIG. 7 ). The top surface of the pedestal is parallel with the top and bottom wall surfaces of the knife holder while the front surface of the pedestal is substantially perpendicular to the top and bottom surfaces of the knife holder. 
         [0028]    A knife assembly  65  is shown mounted within the knife seat  53  in  FIGS. 2 and 3 . The assembly includes an upper chipper knife  66  and a lower counter knife  67  that is mounted between the chipper knife and the inclined wall  54  of the knife seat  53 . Although a dual knife assembly is included in the description of the present invention, it should be clear from the description below that the counter knife can be eliminated from the knife assembly without departing from the teachings of the present invention. The chipper knife is of a conventional design having a rectangular body with a cutting blade  68  running laterally along a top corner edge of the knife body. The lower edge of the knife is provided with an adjusting spacer  70  which in this case is a series of babbit (cast metal) inserts that are spaced apart along the radial length of the knife body. A series of adjustable screws or wedges can be similarly employed. The spacer acts between the lower edge of the knife and the back wall  55  of the knife seat to position the tip of the blade slightly above the top wall surface  34  of the knife holder on about the axial centerline  71  of the chip slot. The back surface of the counter knife rests directly upon the rear wall of the knife seat to position the blade of the counter knife inside the chip slot in a position to act upon the chips leaving the chipper blade. As best shown in  FIG. 3 , the counter knife is secured to the knife holder body by a series of set screws  73  that are housed within countersunk bores  74  ( FIG. 3 ) within the body of the counter knife. The screws may be mated with threaded inserts  75  that are embedded within the body of holder. 
         [0029]    A keyway  80  ( FIG. 7 ) is formed in the bottom wall surface  35  of the knife holder that runs parallel with the side wall surface  36  of the holder. A key  81  having a rectangular cross section area is mounted in the keyway and secured therein by a pair of set screws  82  that are threaded into holes  83  ( FIG. 5 ) formed in the base of the keyway. In assembly, the lower portion of the key is received within an expanded recess  85  contained within the disc with the sidewall  86  of the key in contact with the sidewall  87  of the expanded recess. The key can also be made as an integral part of the knife holder body. 
         [0030]    As best illustrated in  FIG. 3 , an elongated clamp  90  is enclosed within the clamp compartment  57  of the knife holder body. The clamp extends along the radial length of the compartment and contains a first contact area  91  that rests in abutting contact with the upper surface of the chipper knife or knives mounted in the knife seat. The opposite side of the clamp contains a right angle contact area  93  that compliments the top wall  61  ( FIG. 7 ) and front wall  62  of the raised pedestal  60  which runs along the rear wall of the compartment. The bottom wall of the contact area  93  which is parallel with the bottom wall surface  35  of the knife holder abuts against the top surface  61  of the pedestal while the side wall of the cutout which is perpendicular to the bottom wall surface of the knife holder abuts the front wall  62  of the pedestal. Accordingly a tight right angle joint is established between the clamp and the knife holder body which resists input loads acting either parallel to or perpendicular with the knife holder body. 
         [0031]    A number of recessed openings  95  are provided in the top surface of the clamp that are spaced apart along its radial length. Each opening contains a clearance hole  96  that allows a clamping bolt  104  to pass through the clamp. The bolt is mated with a threaded insert  98  contained within a receiving bore  99  formed within the knife holder body. Each insert contains an anti-rotation key  100  that prevents the insert from turning in the bore as the bolt is torqued down in assembly. This insert can also be made an integral component of the knife holder. 
         [0032]    The bottom surface of each bolt receiving opening is provided with a concave spherical seat  101  that is centered upon the axial centerline  102  of the clearance hole  96 . A spherical washer  103  is placed under the head of each bolt that has a convex spherical lower surface that compliments the shape of the seat  101  and which establishes a spherical joint between the bolt head  104  and the clamp when the bolts are torqued down. The spherical joint that is established between the bolt and the knife holder body serves to concentrate off-axis impact loads generating during the chipping process along the axis of the clamping bolts thereby considerably reducing the otherwise deleterious effects of unwanted off axis loads or couples. The spherical seat in the holder body can be replaced with a flat seat perpendicular to the axes of the bolt holes and separate washers with complimentary arcuate shaped mating surfaces to provide a spherical joint without departing from the teaching of the present invention. 
         [0033]    Due to the present system ability to direct all impact loads acting upon the system along two primary axes, the overall loading upon the system is more effectively resisted and the size of the knives used in the chipper can be considerably reduced. This, in turn, allows for greater ease in handling of the knives when loading, refurbishing and reloading the knives. Tasks that normally had to be carried out by more than one person can now be carried out rapidly and safely by a single worker. In addition, test have shown that multiple smaller than normal chipping knives can be safely mounted in a side by side relationship within each knife holder seat thereby further reducing handling problems typically associated with larger more massive knives. 
         [0034]      FIG. 8  illustrates a further embodiment of the present invention. Here again, the knife holder body  20  contains a bottom wall surface  35  that is parallel with the front face  22  of the rotary disc  12  of the chipping machine. As explained in detail above the holder body is generally triangular shaped and has one side wall  36  running radially along one side wall  39  of an adjacent chip slot  30 . In this embodiment, one or more chipper knives  66  are mounted within a knife seat  111  with a suitable adjustable spacer  112  for positioning the cutting edge of the knife or knives on about the central axis of the chip slot. 
         [0035]    Here again the knife holder body contains a recessed clamp compartment  113  that opens into the knife seat through the back wall of the seat. A radially extended clamp  115  is mounted inside the compartment and includes a contact area  116  that rests in abutting contact with the top surface of the knife or knives located within the knife seat. A convex spherical shaped raised key  118  extends radially along the floor of the compartment and is arranged to mate with a complimentary concave keyway that is formed in the bottom wall of the clamp to support the clamp above the floor of the compartment. A series of cylindrical headed screws  120  are passed through clearance holes formed in the clamp between the contact area  116  and the key  118  and are threaded into the body of the knife holder to support the clamp within the body of the knife holder. 
         [0036]    A rectangular shaped key  81  is mounted within a keyway that runs radially along the length of the holder body. The side walls of the key are perpendicular aligned with the bottom wall of knife holder while the top and bottom walls of the key are parallely aligned with the top and bottom walls of the holder. The key extends beyond the bottom wall of the knife holder and the extended portion of the key is received within an expanded keyway  85  formed in the front face of the disc. At least one side wall of the key is in abutting contact with one side wall of the expanded keyway  85  so as to resist loads that are generated on the system that act along the two primary load axes which, as explained above, run parallel with or perpendicular to the face of the disc. The spherical joint between the clamp and the knife holder body established by the spherical key serves to concentrate off-axis input loads generated during the chipping process along one of the primary load axes thereby reducing the otherwise deleterious effects of these otherwise harmful loads. The knife body is tightly secured against the front face of the disc by a series of studs such as stud  40 . 
         [0037]    While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof to adapt to particular situations without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope and spirit of the appended claims.