Patent Publication Number: US-2021169020-A1

Title: Replaceable Knife Insert

Description:
FIELD 
     This invention relates to the mounting of knife inserts in apparatuses which require occasional or frequent replacement of the knife insert due to wear or damage of the knife, as is the case in delimbing machinery used in the forestry industry. 
     BACKGROUND 
     In a variety of industrial applications, blades are used for cutting all kinds of material. Examples for such industrial applications can be found in the food and meat production industry, the building sector, and forestry industry. 
     These blades require regular or even frequent maintenance or replacement due to wear or damage induced during use. 
     In the forestry industry, an apparatus generally referred to as “tree harvester” is widely used, which allows for rapid cutting and delimbing of trees, wherein these two and potentially more functions are integrated in a so-called processing head. 
     In general, processing heads have delimb arms with knife carriers and knife inserts attached thereto, which as the name implies cut the limbs from the tree as the tree is rapidly drawn through the head with the aim of producing a clean stem. The delimb arms also serve as grappling arms to perform a variety of stem and log handling operations. 
     Due to the high processing speeds and resulting high impact forces on the cutting blades, knives of cutting heads are prone to wear, become dull and burred during use, and need regular replacement. 
     A common approach to address this need is to disassemble the whole affected delimbing arm from the chassis of the processor head and replace it with a refurbished arm, complete with a new knife insert. Another approach is to cut the knife insert from the carrier section of the arm and weld a replacement knife in place. 
     However, cutting blades for processing heads, just as any tailor-made blade in other industrial applications, are high-tech products, exhibiting special material properties such as refined steel grain structures and layer-wise construction to meet the industry&#39;s requirements in terms of toughness and wear resistance. As a consequence, the material poses high demands on the welding processes used and the personnel effecting it. 
     Another solution has been proposed in which the knife insert is bolted onto the delimb arm at densely distributed locations along the contour of the blade. However, due to the concentrated load introduction of the bolts, this solution requires the knife insert to have thick cross sections in the areas where the bolted connections are effected, resulting in a bulky and complex structure which tends to be considerably heavier than the delimb arms with welded blades. Moreover, while the bolted solution shortens the downtime of the machines used for exchanging blades when compared to the welded solution, loosening and tightening the large number of bolts typically required in this solution still takes more time than would be desirable. 
     Generally speaking, there is an ongoing need to replace knife inserts because of premature cracking as a result of the welding, along with normal wear and damage, which situation boosts maintenance costs and reduces overall production effectivity due to downtimes. 
     OBJECT OF THE INVENTION 
     It is therefore an object of the present invention to provide an assembly which overcomes or ameliorates at least one disadvantage of the prior art, or alternatively to provide the public with a useful choice. 
     Further objects of the invention will become apparent from the following description. 
     DISCLOSURE OF THE INVENTION 
     According to an aspect of the invention, there is provided a knife insert for use with a knife carrier, the knife insert comprising
         at least one blade portion;   a retention portion configured to interface with a corresponding receiving portion of the knife carrier;   a force transmission means configured to introduce a preload from the knife carrier to the knife insert, wherein the preload is configured to force the retention portion against the receiving portion along a length of the blade portion and thereby removably hold the knife insert in place in the knife carrier.       

     Preferably, the middle plane of the blade portion has an initial curvature along a length from a first end to a second end of the blade portion, wherein the initial curvature is preferably substantially arch shaped. 
     Preferably, the force transmission means is configured to introduce the preload into the blade portion such that the preload acts to alter the initial curvature of the blade portion. 
     Preferably, the retention portion is configured to allow for a predetermined alteration of the initial curvature of the blade portion at a maximum and to counteract any further alteration by resting on the receiving portion, such that the knife insert is firmly pre-stressed by the preload against the receiving portion. 
     Preferably, the blade portion substantially extends from a first end to a second end of the knife insert, wherein the force transmission means includes a first force transmission means at or near the first end and a second force transmission means at or near the second end. 
     Preferably, the force transmission means are configured to introduce the preload in a direction which is substantially parallel to the middle plane at or near the respective first and second end, respectively. 
     Preferably, the retention portion extends along and adjacent the blade portion. 
     Preferably, the retention portion is a groove in the knife insert which is configured to receive a corresponding key of the knife carrier. 
     Preferably, the retention portion is a key which protrudes from the knife insert and is configured to be received in a corresponding groove in the knife carrier. 
     Preferably, the first force transmission means is configured to introduce a compressive or a tensile force as the preload. 
     Preferably, the knife insert is made of cast steel. 
     In another aspect of the invention, there is provided a knife carrier for use with a knife insert, preferably a delimb arm for a tree processing head, the knife carrier comprising
         a receiving portion configured to receive a corresponding retention portion of the knife insert;   force exertion means configured to exert a preload onto the knife insert, wherein the preload is configured to force the retention portion against the receiving portion along a length of the blade portion and thereby removably hold the knife insert in place in the knife carrier.       

     Preferably, the force exertion means includes a tensioner and a stop member. 
     Preferably, the tensioner is a rotary eccentric. 
     Preferably, the tensioner and the stop member are located near distal ends of the receiving portion. 
     Preferably, the receiving portion of the knife carrier has a shape that is substantially corresponding to an initial curvature of a blade portion of the knife insert, or has a slightly amplified curvature. 
     Preferably, the receiving portion is configured to allow for a predetermined alteration of the initial curvature of the blade portion at a maximum and to counteract any further alteration. 
     Preferably, the receiving portion is substantially formed as a key and is configured to receive a corresponding groove of the knife insert. 
     Preferably, the receiving portion is a groove and is configured to receive a corresponding key protruding from the knife insert. 
     In still another aspect of the invention, there is provided a system for mounting a blade to a machine or apparatus, the system including a knife insert and a knife carrier as defined in the foregoing. 
     In still another aspect of the invention, there is provided a tree processing head having at least one knife carrier as defined in the foregoing. 
     Preferably, the tree processing head includes furthermore a knife insert as defined in the foregoing. 
     In still another aspect of the invention, there is provided a method of installing a knife insert to a knife carrier, the knife insert comprising a retention portion and force transmission means, the knife carrier comprising a receiving portion and force exertion means, the method including the steps of
         engaging the retention portion of the knife insert and the receiving portion of the knife carrier;   engaging the force transmission means of the knife insert and the force exertion means of the knife carrier;   activating the force exertion means to force the retention portion against the receiving portion along a length of the blade portion and to exert a preload on the force transmission means and thus on a blade portion of the knife carrier;   locking the force exertion means to maintain the preload and to removably hold the knife insert in place in the knife carrier.       

     Preferably, the middle plane of the blade portion has an initial curvature along a length from a first end to a second end of the blade portion, wherein the initial curvature is preferably substantially arch shaped, and wherein the receiving portion of the knife carrier has a shape that is substantially corresponding to the curvature of the blade portion or has a slightly amplified curvature. 
     Preferably, the preload is introduced into the knife insert such that the preload acts to alter the initial curvature of the blade portion. 
     Preferably, the retention portion is configured to allow for a predetermined alteration of the initial curvature of the blade portion at a maximum, and to counteract any further alteration by resting on the retention portion, such that the knife insert is firmly pre-stressed by the preload against the receiving portion. 
     Preferably, the force exertion means includes a tensioner and a stop member. 
     Preferably, the tensioner is a rotary eccentric. 
    
    
     
       DRAWING DESCRIPTION 
       A number of embodiments of the invention will now be described by way of example with reference to the drawings in which 
         FIG. 1  shows a spatial view of a processing head for harvesting and delimbing trees including a knife insert and a knife carrier according to an embodiment of the invention 
         FIG. 2  shows a spatial view of the knife insert of  FIG. 1   
         FIG. 3  shows a side view of the knife insert and the knife carrier of  FIG. 1  as well as details of the end portions thereof 
         FIG. 4  shows a spatial view of an alternative knife insert 
         FIG. 5  shows a side view of the alternative knife insert of  FIG. 4  and a corresponding alternative knife carrier, as well as details of the end portions thereof 
         FIG. 6  shows a side view of yet another alternative knife insert and a corresponding alternative knife carrier, as well as details of two alternative mounting solutions 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a harvesting and processing head  1  of a tree harvester. Such processing heads  1  are commonly available as an attachment which can be installed to wheeled or tracked excavators modified for forestry applications or purpose built forestry machines. The harvesting and processing heads&#39;  1  main functions are to fell standing trees, delimb the trees to produce clean stems and then cut each stem into logs. 
     The processing head  1  has two sets of corresponding delimb arms  5 , an upper and lower set. Each set may have a different curvature arch shape so that when the four delimb arms  5  are wrapped around a tree, very good coverage of the tree&#39;s circumference is effected so that clean stems can be produced. 
     In other embodiments, the processing head  1  has only one set of delimb arms  5 , i.e. two delimb arms  5 , and there are also embodiments with three, five or more delimb arms  5 . 
     To effect the delimbing, the processing head  1  includes a pair of rotary conveying means  7  configured to engage a trunk and pull it through and enable the delimb arms  5 , the position of which will be adjusted to meet the diameter of the trunk, to cut off the limbs from the tree. 
     The delimb arms  5  each comprise a knife carrier  100  and a knife insert  200  mounted thereto. 
     The knife insert  200  of the depicted embodiment includes two opposing blade portions  210 , which enable bi-directional processing of logs by the processing head  1 , depending only on the direction from which the conveying means  7  pull the logs along the delimb arms  5 . In other embodiments however, the knife insert  200  may only have one blade portion  210 . 
     Turning to  FIG. 2 , the blade portions  210  extend from a first end  202  of the knife insert  200  to a second end  204  thereof, wherein a middle plane of the blade portions  200  has an initial unloaded curvature along a length of the blade portions  200  from the first end  202  to the second end. In the depicted embodiment, the initial curvature is substantially arch shaped, as indicated by double arrow e in  FIG. 2 , which arrow represents a depth in the curvature of the blade portion  210 . Another characterisation of the initial curvature shown in  FIGS. 2 and 3  is that the curvature is concave in view of the side facing away from the knife carrier  100 . As will be appreciated by the representation of  FIG. 3 , the initial curvature of the blade portions  210  has a curvilinearity which exhibits, in a side view, an inflection point  212 . 
     However, other shapes of the initial curvature are also envisaged, for example a sector of a circle, as is the case in the embodiment shown in  FIGS. 4 and 5 , or a substantially straight shape. In the embodiment depicted in  FIGS. 4 and 5 , like reference numerals were used for like features, and the explanations given in the foregoing apply to this embodiment as well. In an embodiment of a processing head  1  according to the invention, a first pair of delimb arms  5  is shaped according to the representation of  FIGS. 2 and 3 , while a second pair of delimb arms of the processing head  1  is formed as shown in  FIGS. 4 and 5 . This configuration has turned out to be particularly versatile in use. 
     The knife insert  200  furthermore includes a retention portion  220  configured to interface with a correspondingly shaped receiving portion  120  of the knife carrier  100 . In the shown embodiment, the retention portion  220  extends substantially continuously along and adjacent the blade portions  210 , wherein the retention portion  220  has the form of a groove in the knife insert  200  and extends between the two blade portions  210 . As will be appreciated by the representation of  FIGS. 3 and 4 , the receiving portion  120  of the knife carrier  100  in these embodiments is configured as a key which continuously extends along the contour of the knife carrier  120 . In other embodiments, the retention portion  220  of the knife insert  200  has the form of a key protruding from the knife insert  200  while the receiving portion  120  of the knife carrier  100  is substantially formed as a groove. 
     In some embodiments, the receiving portion  120  and/or the retention portion  220  may comprise complementary shoulders configured to support each other in the assembled state of the knife insert  200  and the knife carrier  100 . 
     As shown in  FIGS. 2 and 4 , the knife insert  200  comprises a first force transmission means  232  at the first end  202  and a second force transmission means  234  at the second end  204 , which together form a force transmission means  230  configured to introduce a preload from the knife carrier  100  to the knife insert  200 . To effect the preload, the knife carrier  100  includes corresponding force exertion means  130  which can be locked once the force is applied, and which will be described in more detail further below. 
     In the depicted embodiments, the first  232  and second  234  force transmission means are formed as lugs or cams that exhibit a wedge-like shape and each have an undercut  402 ,  404  to accommodate the corresponding force exertion means  130  of the knife carrier  100 . Comparing the embodiment shown in  FIG. 3B  with the one shown in  FIG. 5D , it will be appreciated that the undercut  404  is more pronounced in  FIG. 3B  than in  FIG. 5D . This is due to the particular shape of the initial curvature of the blade portion  210  near the second end  204  in  FIG. 3 , where a component of a holding force is required that pulls the knife insert  200  flat against the knife carrier  100 . 
     The first  232  and second  234  force transmission means can be welded, bonded, bolted or swaged to the retention portion  200  or to the blade portion  210 , or attached thereto by means of form fit, e.g. by an arrangement of suitable keys and slots. 
     It should be mentioned that in some embodiments, the knife insert  200  is made of cast steel. Advantageously in these embodiments, the first  232  and second  234  force transmission means may be integrally cast with the first  202  and second end  204  of the knife insert  200 . On top of that, the use of cast steel to manufacture the knife insert  200  has turned out to be beneficial in terms of reliability and wear resistance. 
     The first  232  and second  234  force transmission means are shaped such that the preload is introduced into the knife insert  200  in a plane distant from the blade portion  210  on the side of the knife carrier  100 , as indicated in  FIGS. 3 and 5  by eccentricities  302 ,  304 . As a technical effect, this arrangement keeps the blade portion  210  clear of any parts that might in use turn out to be obstacles in the cutting process. 
     According to the invention, the preload is configured to removably hold the knife insert  200  in place in the knife carrier  100 , thereby overcoming the need to weld the knife insert  200  onto the knife carrier  100 . This setup eliminates or diminishes several drawbacks of prior art solutions, for example downtimes of the processing head  1  as well as undesired embrittlement, recrystallization, or warping of the blade portions  210  due to welding. 
     Contrary to state-of-the-art knife inserts with bolted connections along the contour of the blade as mentioned above, the preload interacts with the continuous retention portion  220  and receiving portion  120  to allow for a slender, consistent cross section of the blade insert  200  along the contour of the blade with improved handling in mounting and demounting. In addition, due to the continuous attachment of the knife insert  200  to the knife carrier  100  in the present invention, stress concentrations at local force introduction points are avoided, which turns out to be beneficial in terms of risks of material fatigue and brittle failure. 
     In an embodiment, the force transmission means  230  is configured to introduce the preload into the knife insert  200  such that the preload acts to alter the initial curvature of the blade portion  210 . This way, the blade portions  210  are pre-stressed and become more rigid to withstand forces aiming at a deformation of the blade portions  210  or the knife insert  200  in general, as will occur during operation of the processing head  1 . As shown in the figures and to this end, the force transmission means  230  is configured to introduce the preload in a direction which is substantially parallel to the middle plane of the blade portions  210  at or near the respective first  202  and second end  204 . 
     This feature is indicated in  FIGS. 3 and 5  by force arrows F 1  and F 2 , indicating directions of forces exerted by a tensioner  134  and a stop member  132 , which are located near distal ends of the receiving portion  120  and which together form the force exertion means  130  of the knife carrier  100 . In one embodiment of the invention, the tensioner  134  is a rotary eccentric which is manually or automatically activated by simply rotating a screw or the like, as shown in the detailed views B and D of  FIGS. 3 and 5 , respectively. The skilled person will appreciate that components of the forces F 1  and F 2  interact with the initial depth e of the blade portion  210  to further open or stretch the curvature of the blade portions  210 . 
     In this context, it is pointed out that the preload introduced into the blade portions  210  along force arrows F 1  and F 2  involves local bending moments caused by the first  232  and second  234  force transmission means and their corresponding eccentricities  302 ,  304  discussed above. By adjusting the eccentricities  302 ,  304  adequately in view of the curvature of the blade portion  210 , a particularly tight fit between the knife insert  200  and the knife carrier  100  can be achieved. 
     The retention portion  220  of the knife insert  200  is configured to allow for a predetermined alteration of the initial curvature of the knife insert  200  at a maximum and to counteract any further alteration by resting on the receiving portion  120 , such that the knife insert  200  is firmly pre-stressed by the preload against the receiving portion  120  of the knife carrier  100 . This can be achieved, for example, by an adequate selection of the stiffness ratio between the knife insert  200  and the knife carrier  100 . In an embodiment, the receiving portion  120  of the knife carrier  100  has a shape that has a slightly amplified curvature when compared to the curvature of the blade portion  210 , which feature serves to allow for a small amount of deformation of the knife insert  200  during the introduction of the preload. The receiving portion  120  may be configured to allow for a predetermined alteration of the initial curvature of the blade portion  210  at a maximum and to counteract any further increase. This way, a snug fit between the knife insert  200  and the knife carrier  100  is achieved. 
     The skilled person will understand that the predetermined alteration of the initial curvature of the knife insert  200  may vary in terms of magnitude, inter alia depending on the stiffness of the parts involved. In cases where the knife insert  200  is relatively rigid, the predetermined alteration of the initial curvature may be relatively small, and may even lie within the range of the production tolerances of the knife insert  200 , which means that during pre-stressing of the knife insert  200  against the receiving portion  120  of the knife carrier  100 , these production tolerances are compensated for by deformation so that the knife insert  200  and the knife carrier  100  have a snug fit and the distribution of preload along the knife insert  200  is homogeneous. 
     In other cases, it might be desirable to allow for a bigger amount of alteration of the initial curvature in order to achieve a higher level of pre-stress in the knife insert  200  and the blade portion  210 . In these cases, it might be possible to identify an initial gap between the knife insert  200  and the knife carrier  100  with the naked eye before the preload is applied. In this way, compressive pre-stressing may be achieved in parts of the knife insert  200  that are subject to cyclic loading. As the skilled person will appreciate, compressive pre-stressing reduces the level of tensile stresses in use and can turn out to be beneficial for the fatigue resistance of the assembly. 
     In another embodiment, one or both of the force transmission means  230  are configured as force exertion means, e.g. as rotary eccentrics, while the force exertion means  130  are configured to provide reaction forces only. In this case, when inserting the knife insert  200  into the knife carrier  100 , an operator would activate and subsequently lock the rotary eccentric at the knife insert  200  to apply the preload to the blade portion  200 . 
     While the figures show an embodiment in which the preload induces a compressive force and a bending moment into the blade portions  210 , embodiments are envisaged in which the preload is a tensile force or a tensile force combined with a bending moment. Such embodiments encompass knife inserts  200  the blade portion  210  of which exhibit a curvature which is convex in view of the side facing away from the knife carrier  100 . In these cases, a tensile preload induced at the first  202  and second  204  end pulls the blade portion  210  onto the correspondingly shaped receiving portion  120  of the knife carrier  100  and thus effects the blade portion&#39;s  210  desired resistance to deformation and removable attachment to the knife carrier  100 . 
     In the embodiments shown in  FIGS. 2-5 , the force exertion means  130  includes basically two spatially separate parts, namely the stop member  132  and the tensioner  134 . Similarly, the force transmission means  230  has been described as including two separate parts, namely the first  232  and second  234  force transmission means. In other embodiments however, as shown in  FIG. 6 , the force exertion means  130  and force transmission means  230  each comprise one compact subassembly that interact to exert a preload on the knife insert  100  at a central portion thereof and to thus fix it onto the knife carrier  200 . 
     In the embodiment depicted in  FIG. 6 , like reference numerals were used for like features, and the explanations given in the foregoing apply to this embodiment as well. As mentioned, contrary to the embodiments described in the foregoing, the force exertion means  130  and the force transmission means each include one compact subassembly, which feature is generally represented by arrow F, indicating a direction of force along which the preload can be introduced into the knife insert  200 . 
     As can be seen in the Figure, the knife insert  200  and the knife carrier  100  each exhibit an initial curvature, with an initial gap  500  between the knife insert  200  and the knife carrier  100  resulting from a difference in initial curvature between these parts. It will be appreciated by the skilled person that the amplitude of the initial gap  500  is not to scale in the Figure but is exaggerated, and reference is made to the explanations made in the foregoing. 
     Detail A-A in  FIG. 6  shows a cross-sectional view of the knife insert  200  and the knife carrier  100  before the initial gap  500  is closed. In this embodiment, the retention portion  220  of the knife insert  200  is a notch and the receiving portion  120  of the knife carrier  100  is formed by a mating surface thereof. When the knife insert  200  is fixed to the knife carrier  100  by exertion of a clamping force along arrow F, the initial gap  500  will close and the knife insert  200  will be snugly attached to the knife carrier  100  by interaction of the retention portion  220  and the receiving portion  120  as described above. 
     Details regarding the exertion of this clamping force will be now be described. 
     As shown in detail A of  FIG. 6 , the force exertion means  130  is a threaded bolt  140  inserted in a corresponding hole in the knife carrier  100 . The threaded bolt  140  interacts with a nut  142  attached to or integrally formed in the knife insert  200 . Hence, in this embodiment, the nut  142  corresponds to the force transmission means  230 . In order to introduce the preload into the knife insert  200 , the threaded bolt  140  engages the nut  142  and is tightened to pull the knife insert  200  towards the knife carrier  100  until the initial gap  500  closes under the effect of the preload and the retention portion  220  and receiving portion  120  mate. 
     In detail B of  FIG. 6 , the force transmission means  230  is designed as a lug  152  having a bore in it, which lug  152  can be received by a corresponding clearance  154  in the knife carrier  100 . An eccentric  150  inserted in a bore in the knife carrier  100  which also extends through the bore of the lug  152  in a mounted state forms the force exertion means  130 . When the eccentric  150  engages the bore of the lug  152  and is tightened by a bolt head or the like as indicated in the figure, the initial gap  500  closes under the effect of the preload and the retention portion  220  and receiving portion  120  mate. 
     As is apparent from the foregoing, the knife carrier  100  and the knife insert  200  together form a system for mounting a blade to a machine or apparatus. While this system has been described in context with a processing head  1  of a tree harvester, it can be applied in other technical fields as well, for example in the food and meat industry or in apparatuses for carving wood.