Abstract:
A two-part blade support base for mounting a chipper knife to a chipper disc wherein the parting line between the upper part and lower part is substantially parallel to a plane defined by the chipper disc. The parting line incorporates a vertical step which transmits shear forces which would cause the upper part to move outwardly of a chip receiving surface. A screw or bolt connects the upper and lower parts of the blade base. The upper part of the blade base may be constructed of a wear resistant material.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to chippers and the structures which hold the chipping knives. 
   The principal use of wood apart from its use as fuel and as a structural material is as a source of fiber. If the wood fibers are to be separated from the other constituents of wood, principally lignin, the wood must be chemically treated. The chemicals used, such as caustic soda, can damage the wood fibers if the wood fibers are exposed to the chemicals too long. For this reason, wood which is to be treated to extract the lignin is first reduced to wood chips which have a uniform thickness. These uniform wood chips minimize the time during which the wood fibers are exposed to the chemicals or cooking liquor. The wood chip allows the cooking liquor to act on all sides rapidly and uniformly, separating the wood fibers from the lignin of the wood. Of course the cutting of the wood into chips necessarily breaks some fibers and broken fibers have less or no value. Therefore a chipper which produces uniform chips and converts a high fraction of the raw logs to wood chips is desired. The production of wood fiber is a commodity business where profit margins are thin, so small improvements in quality, or in cost of production are the main sources of increased profitability. 
   Wood chippers are extremely productive machines reducing perhaps 70 to 170 cords of wood to chips in one hour. This high throughput, combined with the natural contamination of dirt and sand, results in the cutting blades and the blade supports being worn away. The blade base which is positioned directly below the cutting blades has a chip facing surface which is particularly subject to abrasion. The wood chips are actually broken into chips by colliding with this surface of the base and thus considerable wear takes place on the blade base immediately below the supported blade. One known approach is to simply replace the blade bases when they become worn, however, this adds to the cost of producing the wood chips. Another approach is to apply a surface hardening such as by flame spraying. A further approach is to weld on a piece of wear resistant material to the surface of the blade base exposed to high wear. These approaches, while extending the life of the blade bases, are undesirably labor-intensive. U.S. Pat. No. 5,765,452 describes a known technique which is to arrange a changeable blade stopper between the blade base and the blade. However U.S. Pat. No. 5,765,452 discourages using this approach. What is needed is a blade base which has a chip facing surface which can be replaced with minimal overall cost. 
   SUMMARY OF THE INVENTION 
   The chipper of this invention has a two-part blade support base wherein a parting line between the upper part and lower part is substantially parallel to a plane defined by the chipper disc and substantially perpendicular to the chip receiving surface positioned underneath a chipper blade. The parting line incorporates a vertical step which resists shear forces which would cause the upper part to move outwardly from the chip receiving surface. A screw or bolt connects the upper and lower parts of the blade base. The upper part of the blade base may be constructed of any wear resistant material. 
   It is a feature of the present invention to provide a blade support base in a wood chipper which can be maintained at lower overall cost. 
   Is a further feature of the present invention to provide a blade support base in a wood chipper which can be more readily maintained with less skilled labor. 
   Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view partly cut away of a wood chipper incorporating the blade support base of this invention. 
       FIG. 2  is a fragmentary cross-sectional view of the blade base of this invention supporting a blade on a wood chipper disc. 
       FIG. 3  is an elevational cross-sectional view of the blade support base of  FIG. 2 . 
       FIG. 4  is an elevational cross-sectional view of an alternative blade support base of this invention 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring more particularly to  FIGS. 1–4  wherein like numbers refer to similar parts, a wood chipper  20  is shown in  FIG. 1 . The wood chipper  20  has a chipper disc  22  to which knives  24  are held between upper knife holders  26  and blade support bases  28 . The each knife  24  has a cutting blade edge which engages a log  30  as the chipper disc rotates. The wood chipper disc  22  defines a plane in which the disc  22  rotates. Logs  30  are fed through a feed spout  32  against the chipper disc  22 . 
   Cutting action takes place between the moving knife blades  24  mounted to the chipper disc  22  and a fixed bed knife  34  which holds the log  30  as wood chips  36  are cut from the log  30 , as shown in  FIG. 2 . The wood chips  36  enter a chip slot  37  and slide along the underside of the knife blade  24  until they engage a chip facing surface  38  of the blade support base  28 . Hitting the chip facing surface  38  splits the chips  36  from a larger veneer  40  which the knife blade  24  removes from the log  30 . Because the wood chips  36  and a certain amount of abrasive dirt or sand move with considerable force against the chip facing surface  38 , the blade bases  28  eventually wear out and require replacement or repair. 
   The blade base  28 , as shown in  FIG. 3  is constructed of three parts, an upper part  42  which engages the knife blade  24 , a lower part  44  which engages the upper part and the chipper disc  22 , and a screw or bolt  46  which extends from the lower part  44  the upper part  42 , thus connecting the upper part  42  to the lower part  44 . The upper part  42  has an upper surface  48  which supports the knife blade  24 , a chip facing surface  38  which faces towards the wood chips as the chipper disc rotates, and a mating surface  50  which is substantially parallel to the plane defined by the chipper disc  22 . The mating surface is opposite the upper surface  48 , and faces away from the knife blade  24 . The lower part  44  also has upwardly facing surface  49  which engages and supports the knife blade  24 . The blade engaging surface  49  of the lower part  44 , and the blade engaging surface  48  of the upper part  42  are co-planer. The surfaces  49 ,  48  are brought into alignment by grinding them flat when the blade base  28  is first assemble, and whenever the upper part  42  is replaced. 
   The mating surface  50  has a projection  55  which extends away from the knife blade, and which has a rise surface  63  extending towards the lower part  44 . A recess  53  is defined adjacent the projection  55 , and together the recess and the projection define a change in height or a step  52 . The lower part  44  of the blade support base  28  has a complementary mating surface  51  which is positioned adjacent the mating surface  50  of the upper part  42 . A projection  57  extends upwardly from the lower part  44  towards the upper part  42 , and engages within the recess  53 . The lower part projection  57  has a lower rise surface  65  which extends towards the upper part  42 . The lower rise surface  65  is parallel to the upper rise surface  63  and engages against it. 
   The step  52  thus has surfaces which extend at approximately a right angle to both the chip facing surface  38  and the mating surface  50 , which prevent a force of the knife holder  26  acting in the direction of rotation of the chipper disc  22  from moving the upper part  42  in a direction towards the chip facing surface  38 . Thus the steps  52 ,  64  act to prevent the upper part  42  from shearing with respect to the lower part  44 , and thus prevents a shear load on the screw or bolt  46 . 
   The lower part  44  has a rectangular slot  54  which is received on a land  56  forming part of the chipper disc  22 , as shown in  FIG. 2 . A threaded bolt  58  bears on a bottom surface  60  of the lower part  44  of the support base  28 . The threaded bolt  58  has a hex socket head  62  which allows the bolt  58  to be rotated to raise or lower the blade base  28 . The chip facing surface  38  of the blade base  28  extends across both the upper part  42  and the lower part  44 , and extends outwardly at an angle α of about 85 degrees from the bottom surface  60 , or from the plane defined by the chipper disc  22 . It should be understood the angle α could as small as 60 degrees. The mating surfaces  50 ,  51  are substantially perpendicular to the bottom surface  60  and the plane defined by the disc  22 . 
   The combination of the mating surface  50  being substantially parallel to the bottom surface  60  which is supported by the screws  46  and the step  52  which receives the complementary step  64  on the lower part  44  allows a two-part blade base  28  of the necessary structural integrity. 
   The screw or bolt  46  extends upwardly from the lower part  44  to engage the upper portion  42 . A counterbored portion  59  of the lower part  44  positions the head  61  of the screw  46  recessed from the bottom surface  60 . 
   An alternative embodiment blade base  66  is shown in  FIG. 4 . The blade base  66  has an upper part  68  and lower part  70 . The upper part  68  is joined to the lower part  70  by screws  72  which extend from the upper part  68  to engage the lower part  70 . The upper part  68  has a flat bottomed counterbored portion  74  which positions the head  76  of the screw below the blade support surface  78 . A chip facing surface  80  is set at an inward angle β of about 97.5 degrees inwardly of the chips slot  37  relative to the plane defined by the disc  22  or a bottom surface  82  of a rectangular slot  84 . It should be understood the angle β could be as much as 120 degrees. The rectangular slot  84  is received on the land  56  forming part of the chipper disc  22 . Again, threaded bolts  58  bear on a bottom surface  82  of the lower part  70  of the support base  66 . The mating surface  86  between the upper part  68  and lower part  70  on the blade base  66  again defines a step  88  on the upper part  68  which mates with a complementary step  90  formed on the lower part  70 . The stepped structure comprises a feature which is arranged to resist shear forces directed toward the chip slot  37 . A blade engaging surface  79  of the lower part  70 , and the blade engaging surface  78  of the upper part  68  are co-planer. The surfaces  49 ,  48  are brought into alignment by grinding them flat when the blade base  66  is first assemble, and whenever the upper part  68  is replaced. 
   The upper blade base parts  42  and  68  can be cost-effectively replaced when they become worn, as the cost of wear resistant materials is substantially proportional to the weight of material used, so replacing the relatively lightweight upper parts  42 , and  68  which weigh only about 20 percent–35 percent of the weight of the entire base, is substantially more cost-effective than replacing the entire blade base  28  and  66 . Replacement does not require skilled labor and requires little time beyond that necessary to gain access to the blade base itself. The design of the two-part blade bases  28  and  66  is such that the screw connecting the upper parts to the lower parts is not substantially loaded. Loads in compression are taken by the mating surfaces which are parallel to the bottom surface of the bottom parts which are supported, on chipping disc  22 , and shear loads are resisted by steps in the mating surfaces between the upper and lower parts. 
   Another advantage of replacing the upper blade base parts  42  and  46  is that the angle of the chip facing surface  38  can be changed without replacing the entire blade base. Different types of wood can benefit from the different angle α, β of the chip facing surface  38  which can generally be varied from 60 degrees to 120 degrees. In this way the operator of a wood chipper  20  can replace the upper blade base parts  42 ,  46  with an upper blade base part of a significantly different angle, to better control chip formation either because of the change of wood type, or a desire to change the chips due to a change in the way the chips are further processed. A significant change in the angle of the chip facing surface may be, for example, three to six degrees. 
   It should be understood that the step  52  in the mating surfaces  50 ,  51  between the upper part and lower part of the blade bases could be any feature which prevents shearing along the mating surfaces  50 ,  51 , such as a ridge, or a key. 
   It should be understood that the upper parts  42  and  68  can be manufactured from any wear resistant material and could be constructed of for example, mild steel, high-speed steel, tool steel, special wear resistant steel alloys, tungsten carbide with a cobalt binder, titanium carbide with a nickel-molybdenum binder or a ceramic, such as silicon carbide, any metal ceramic composite, or other type of wear resistant inserts. The upper parts  42  and  68  may themselves be constructed from two or more parts, for example a tungsten carbide piece could be bonded to the chip faces  38 ,  80  of the upper parts  42 . Thus it should be understood that the upper parts  42 , and  68  can be made of any material and construction having the necessary strength and wear resistant properties. 
   It should be understood that the angle of the chip face may advantageously be within an angle α of 60 degrees to an angle β of 120 degrees, which includes the chip face being at a 90 degree angle relative to the plane defined by the disc  22 . 
   The upper parts  42 ,  68  can be joined to the lower part  44 , 70  by a screw or bolt which is threaded into the upper or lower part. Alternatively a spring pin, or a bolt or other mechanical arrangement can be used to join the two parts. 
   It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.