WOOD CUTTING KNIFE

Abstract

WOOD CUTTING KNIFE The present invention concerns a wood cutting knife (1) comprising a knife body (2) and about the vertical axis (a) of the wood cutting knife (1) at least one cutting edge (3), which includes an upper cutting edge portion (4) and a lower cutting edge portion (5) that intersect to form a cutting edge (6). The lower cutting edge portion (5) includes a planar wood pushing portion (7), which starts at the cutting edge (6) and is followed towards the knife body (2) by a small depression (8). The small depression is a pressure relief depression (8), which from the wood pushing portion (7) falls abruptly to a lower portion (10) of the pressure relief depression (8), and which extends from the wood pushing portion (7) to the knife body (2). The knife body (2) includes a chip guide portion (12), which from the pressure relief depression (8) rises towards the knife body (2). Selected for publication: Figure 2

Description

Description of WOOD CUTTING KNIFE Invention Engineering Field The present invention concerns a wood cutting knife comprising a knife body and with respect to a vertical axis of the wood cutting knife at least one cutting edge, which includes an upper cutting edge portion and a lower cutting edge portion intersecting at an acute angle to form a cutting edge, wherein the lower cutting edge portion includes a planar wood thrust portion, which begins at the cutting edge and is followed towards the knife body by a small depression. Background of the Invention Wood chipping blades are used in chippers to process logs into wood chips. Wood chips are produced from many different wood species, each with varying densities, moisture content, fiber length, and other specific characteristics, such as resin or frost, and are used for further processing. In order for a wood chipper blade to function properly and produce separate wood chips of a uniform size, which is essential for further processing, it must be shaped in a way that best suits the log to be cut into wood chips. However, it is typical for the industry today that the blades used have the same bottom shape regardless of the wood to be cut and processed, which can result in an increased number of chips that cannot be used for further processing due to the wrong size (too small, i.e. particulate, or oversized). The bottom shape usually includes a continuous flat surface that forms the edge of the blade. It is also known in the art to use mechanical arrangements separate from and downstream of the wood chipper blade to further break down the chips. However, such arrangements are expensive and tend to increase the number of small particles, which cannot be used for further processing and therefore must be discarded. Furthermore, a wood cutting blade can be formed as a rotatable wear insert, which has a first cutting edge and an opposing second cutting edge and which is mounted on a disc, drum or cone cutter head in a manner that is easily replaced. In the cutter head there is a wood cutting blade usually clamped in such a way that it can be rotated 180° to allow the use of the second cutting edge after the first cutting edge wears out. US Document 8 033 308 B2 discloses a wood-cutting blade according to the opening. The small concavity of the wood-cutting blade, known as the "wood-cutting blade," functions in conjunction with the beveled surface to smoothly guide the cut chips to a deflector cam, which collects chips from the worn blade-mounting insert. This results in a longer service life for the worn blade-mounting insert compared to wood-cutting blades that do not have a deflector cam arrangement. Brief Description of the Invention Although the known wood cutting blades are an improvement over some other previously known wood cutting blades, practice has shown that this type of cutting blade can have problems when one tries to cut wood with them because it does not release chips easily, that is, when the chips tend to stick together and form what is called a lump because the wood fibers are not completely separated from each other. The problem that arises then is that there is a tendency to clog the cutting machine and the quality of the chips produced is poor, which is detrimental both from a production point of view and from an environmental point of view. Against that background, it is an object of the present invention to improve a wood chipping knife in such a way that the tendency to blockage is reduced and the quality of the chips is improved. The object of the invention is achieved by means of a wood cutting knife comprising the features mentioned in the preamble and the further features that the small depression is a pressure relief small depression, which from the pushing portion the wood suddenly falls to the bottom of the pressure relief small depression, and that the knife body includes a chip guide portion, which from the pressure relief small depression rises towards the knife body. According to the present invention, the wood thrust portion of a wood-cutting knife is planar and has a length within limits selected by the skilled person depending on the case at hand to achieve an even chip size and good chip separation, in conjunction with a second feature of the present invention. This feature is a small pressure relief depression that follows the wood thrust portion and is abruptly recessed in relation to it. In this context, the term abruptly is used to describe a small depression shape that does not smoothly or gently evolve from the jointing portion of the knife edge, as is the case in the solution of the prior art cited, but to define a small depression that with a sudden sharp transition, so to speak, pulls the rug from under the feet of the cut chip, which is still under pressure from the planar wood thrust portion and is thus exposed to sudden pressure relief.With this, the wood fibers of adjacent chips, which have not yet separated sufficiently from each other, tend to break apart and thus completely free the chips from each other. Again, superior results, namely optimal chip separation under the given circumstances, are achieved within the limits of the depth and width of the pressure relief small depressions that can be determined by a skilled person. Furthermore, thanks to the above feature it is possible according to the present invention to better control the chip dimensions, such as in particular the chip thickness, and thus achieve more consistent results. Finally, in order to avoid clogging and to extend the service life of the knife holder that holds the wood cutting knife, the knife body includes a chip guide portion that is arranged to hold the chips from the knife holder.This is best done if the small pressure relief depression rises towards the blade body relative to the vertical axis within a certain angular range. Typically, the bottom of the pressure relief basin is placed at a depth of at least 0.3 mm. However, a depth of at least 0.5 mm or at least 0.8 mm may also prove advantageous in certain circumstances. In most currently preferred solutions, the bottom of the pressure relief basin is placed in a depth interval of 0.5-2 mm, or preferably from 0.8-1.2 mm, or, currently most preferred, at a depth of about 1 mm. Depths within these limits have proven sufficient in many cases to provide a pressure relief high enough to break the lump into separate fragments. Typically, the small pressure-relieving groove between the wood and the blade body is 2.8-8 mm wide. However, a width of 3-7 mm is preferred. Currently, the most preferred width is around 6 mm. Widths within these limits have been shown to prevent clogging and reliably guide separated debris away from the debris area. According to one embodiment, the pressure relief groove of the wood cutting blade according to the present invention includes a first transition portion, which from the bottom of the pressure relief groove rises toward the wood pushing portion along a concave curve with a radius of 0.11.5 mm. However, it is preferred that the radius be 0.51.2 mm, or at 0.7-1.1 mm, or at 0.6-1.0 mm. And the most preferred radius is currently 0.8 mm. It turns out that a concave curve within these limits optimizes chip separation and provides positive transfer of the separated chips to the chip guide portion. According to some embodiments, the first transitional portion towards the wood pushing member (7) is tangentially transformed into a straight portion. By means of a small depression the pressure relief is provided with a very sharp and thus very abrupt start at the end of the wood pushing member. Preferably, the pressure relief groove of the wood cutting knife according to the present invention includes a second transition portion, which from the bottom of the pressure relief groove rises toward the knife body along a concave curve with a radius of 0.4-7 mm, or 0.5-5 mm, or 1-4 mm. However, the radius is preferably 2-3 mm. And currently the most preferred is a radius of about 2.5 mm. A transition within these limits has been shown to guide the separated chips in a well-controlled manner to the chip guide portion and thereby minimize the tendency for clogging. A further way to minimize this clogging tendency is to also have a second transition section from the small pressure relief depression that tangentially transforms into the chip guide section of the blade body. This separates the chips following a natural path to the chip guide section and is therefore less likely to fall into the disturbance and cause clogging. Typically, the chip guide portion is inclined toward the blade body at an angle to the vertical axis of 10° to 50°, or 15° to 48°, or 25 to 47 degrees. However, most preferred solutions comprise an angle of 30° to 40°. And the most preferred solutions currently comprise an angle of approximately 35°. Angles within these limits have been shown to effectively guide the separated chips away from the chip area and keep them out of the blade holding means. Typically, the planar wood thrust section from the cutting edge to the small depression is 5-10 mm wide. However, a width of 7-8 mm is currently preferred. A width of around 7.55 mm is currently the most preferred. Widths within these limits have been shown to provide suitable chip sizes for further processing. Preferably, the wood pushing portion of the wood cutting blade according to the present invention forms an angle of 83° to 89° with respect to the vertical axis. However, an angle of 85° to 87° is currently preferred. And an angle of about 86° is currently most preferred. Angles within these limits have been shown to provide optimal cutting results and optimal chip separation in conjunction with a small pressure relief depression. Furthermore, in the wood cutting blade according to the present invention, the bottom of the pressure relief groove is preferably planar and with respect to the vertical axis is preferably an angle of 70° to 93°. However, an angle of 89° to 91° is currently preferred. And an angle of about 90° is currently most preferred. A slope of the bottom within the limits of this angle can help improve the transfer of separated chips in a way that does not fall into the chip guide portion and thereby minimize the risk of further clogging. Finally, the cutting edge taper angle is typically 30° to 40°. However, an angle of 33° to 37° is currently preferred. An angle of around 35° is currently most preferred. Cutting edges with angles within these limits have proven useful for effective chipping. Short Description of Image In the drawings, a preferred embodiment of the present invention is shown schematically, wherein: Figure 1 is a cross-sectional view of a wood cutting blade according to a first embodiment of the invention mounted on a blade holder; Figure 2 is a cross-sectional view of the wood cutting blade from figure 1; Figure 3 is a cross-sectional view of a wood cutting blade according to a second embodiment of the present invention; and Figure 4 is a cross-sectional view of a wood cutting blade according to a third embodiment of the present invention. Complete Description of the Invention In the drawings and descriptions, the same reference is used for all three embodiments of the wood cutting knife (1) because the embodiments differ only in certain dimensional aspects. Furthermore, to the extent that directional indications are used in the descriptions and claims, such as the top and bottom, these refer to the drawings and therefore may differ from reality. Finally, as the machine for cutting wood is a well-known technique, only the embodiment of the wood cutting knife and the knife holder (20) for this is described and shown. The wood cutting blade (1) according to the first embodiment shown in figure 1 is mounted on a knife holder (20). The knife holder (20) like the wood cutting blade (1) itself is shown in cross-sectional view. It extends into the drawing plane along the entire length of the wood cutting blade (1), which in reality means for at least one tenth of a meter. The knife holder (20) includes a base (21) above and a clamp (22) below. Both are joined by means of a bolt (26), which makes it possible to securely clamp the woodcutter knife (1) between them. In order to fit the knife holder (20), the woodcutter knife (1) includes a central knife body (2), from which cutters (3) extend mirror-symmetrically on both sides of a vertical axis as illustrated in figures 2 and 3. Above the knife body (2) includes a central, all-flat part (13), which fits into the corresponding flat part (23) of the knife holder base (21), and into its concave groove side (14), which fits into the convex apex (24) of the knife holder base (21). Below the knife body (2) includes a central, downward-projecting apex (15), having beveled sides (16), which one by one, depending on how the woodcutter knife (1) is rotated, fit into the corresponding flat support (25) of the knife holder clamp (22). So far the wood chipper (1) described above corresponds to the previous wood chipper provided by the applicant. However, in order to deal particularly with wood which has a tendency to retain proper splinters due to the wood fiber, which is difficult to split, the wood chipper (1) according to the present invention includes a cutter (3) which is different in shape from the previous, wherein the three embodiments shown in detail in figures 2 to 4 include the same main features and differ only dimensionally. Therefore, below the three embodiments are described in general and differences are only indicated where necessary. According to the present invention, each cutter (3) (there is one on each side of the wood cutting blade (1)) includes an upper cutting edge portion (4) and a lower cutting edge portion (5). These intersect at an acute angle α of about 35° to form a cutting edge (6). The lower cutting edge portion (5) includes a planar wood pushing portion (7), which starts from the cutting edge (6) and toward the blade body (2) followed by a small depression (8). The wood pushing portion (7) is preferably inclined with respect to the vertical axis a at an angle γ preferably about 86° or at least in an interval of 83° to 89°. From the cutting edge (6) to the small depression (8) of the planar wood pushing portion (7) has a width of about 7.5 mm according to the first and third embodiments and about 8.5 mm according to the second embodiment.However, widths in the 5-10 mm interval have proven to meet the existing requirements, namely to place the cut wood chips under pressure and direct them to the knife body (2). The small depression following the planar wood thrust member (7) is a pressure relief small depression (8), which from the planar wood thrust member (7) suddenly falls (or, as shown in the figure, rises) to the bottom (10) of the pressure relief small depression (8). In this context, by pressure relief is meant that the cut wood chips, which travel along the planar wood thrust member (7) and are under pressure from it, due to suddenly hollowing when the pressure relief small depression (8) is reached, experience a sudden substantial pressure release, which helps to separate the wood chips from each other and thus free them from each other. In the first and second embodiments shown the pressure relief recess (8) has a depth of about 1 mm and in the third embodiment a depth of about 0.55 mm. However, depths in an interval of 0.3-2 mm are within the scope of the present invention. The bottom (10) of the pressure relief recess (8) is planar and with respect to the vertical axis forms an angle δ of between 72° (third embodiment) and 90° (first embodiment). The width of the pressure relief recess (8) from the wooden push member (7) to the knife body (2) amounts for the first embodiment to about 5.0 mm, for the second embodiment to about 4.1 mm, and for the third embodiment to about 3 mm. However, widths in the range of 2.8-8 mm are possible within the scope of the present invention. Furthermore, in all three embodiments, the pressure relief basin (8) includes a first transition portion (9), which from the bottom portion (10) of the pressure relief basin (8) rises toward the wood pushing portion (7) along a concave curve. This curve helps to pick up and guide wood chips along the bottom portion (10) of the pressure relief basin (8), which is best accomplished with a curve radius of about 0.8 mm (first and second embodiments) or 0.5 mm (third embodiment). However, radii within an interval of 0.1-1.5 mm have been shown to be possible. At the opposite end of the pressure relief depression (8), in all three embodiments there is a second transition portion (11), which from the bottom (10) of the pressure relief depression (8) rises towards the knife body (2) along a concave curve. This curve guides wood chips from the bottom (10) of the pressure relief depression (8) to an inclined chip guide portion (12) described in more detail below. The radius of the curve of the second transition portion (11) is preferably about 0.8 mm (first and second embodiments) or 4 mm (third embodiment) but may within the scope of the present invention range from 0.5 to 5 mm. The chip guide member (12) forms part of the knife body (2). It follows a straight line, which is inclined from the pressure relief small depression (8) to the knife body (2) at an angle β to the vertical axis a which is preferably about 35° (first and second embodiments) or 47° (third embodiment). However, angles in an interval of 25° to 50° are possible, especially if they make it possible for the second transition member (11) to transform tangentially into the chip guide member (12) of the knife body (2), as this is advantageous for guiding the chips in a regular manner without a tendency to fall. The inclined chip guide portion (12) is finally followed by an inclined side (16) of the downward protruding peak (15) of the knife body (2). The slope of the inclined side (16) is, as shown, preferably less steep than the one of the chip guide portion (12). The knife holder clamp (22) preferably as shown in figure 1 also includes an inclined side (27) with a slope corresponding to one of the inclined sides (16) of the knife body (2). This makes it possible to keep the knife holder clamp (22) of the knife holder (20) out of the way of wood chips guided by the inclined side (16) of the knife body (2) and thereby to extend the service life of the knife holder (20). The skilled person realizes that the above embodiments can be modified in various ways within the scope of the applicant's claims as long as the most vital features of the invention, namely the wooden push member (7), the small pressure relief recess (8) and the chip guide member (12), are shaped and sized as indicated.

Claims

1. A wood cutting knife (1) comprising a knife body (2) and with respect to the vertical axis (a) of the wood cutting knife (1) at least one cutting edge (3), which includes an upper cutting edge portion (4) and a lower cutting edge portion (5) that intersect at an acute angle (α) to form a cutting edge (6), wherein the lower cutting edge portion (5) includes a planar wood pushing portion (7), which starts at the cutting edge (6) and is followed toward the knife body (2) by a small depression (8), characterized in that the small depression is a pressure relief small depression (8), which from the wood pushing portion (7) suddenly falls to the lower portion (10) of the pressure relief small depression (8), and that the knife body (2) includes a chip guide portion (12), which from the pressure relief small depression (8) rises toward the knife body (2).

2. The wood cutting knife (1) according to claim 1, wherein the bottom (10) of the pressure relief small depression (8) is disposed at a depth of at least 0.3 mm, or at least 0.5 mm, or at least 0.8 mm.

3. A wood cutting knife (1) according to claim 1, wherein the bottom (10) of the pressure relief small depression (8) is disposed at a depth of 0.5-2 mm, or 0.8-1.2 mm, or about 1 mm.

4. A wood cutting knife (1) according to any one of claims 1-3, wherein the pressure relief groove (8) from the wood pushing member (7) to the knife body (2) has a width of 2.8-8 mm, or 3-7 mm, or about 6 mm.

5. A wood cutting knife (1) according to any one of claims 1-4, wherein the pressure relief small depression (8) includes a first transition portion (9), which from a lower portion (10) of the pressure relief small depression (8) rises toward the wood pushing portion (7) along a concave curve with a radius of 0.1-1.5 mm, or 0.5-1.2 mm, or 0.7-1.1 mm, or 0.6-1.0 mm, or about 0.8 mm.

6. The wood cutting knife (1) according to claim 5, wherein the first transition portion (9) towards the wood pushing portion (7) is tangentially transformed into a straight portion.

7. A wood cutting knife (1) according to any one of claims 1-6, wherein the pressure relief small depression (8) includes a second transition portion (11), which from a lower portion (10) of the pressure relief small depression (8) rises toward the knife body (2) along a concave curve with a radius of 0.4-7 mm, or 0.5-5 mm, or 1-4 mm, or 2-3 mm, or about 2.5 mm.

8. The wood cutting knife (1) according to claim 7, wherein the second transition member (11) tangentially transforms into a chip guide member (12) of the knife body (2).

9. A wood cutting knife (1) according to any one of claims 1-8, wherein said chip guide portion (12) is inclined toward the knife body (2) at an angle (β) to said vertical axis (a) of from 10° to 50°, or 15° to 48°, or from 25° to 47°, or from 30° to 40°, or about 35°.

10. A wood cutting knife (1) according to any one of claims 1-9, wherein the planar wood pushing portion (7) from the cutting edge (6) to the small depression (8) has a width of 5-10 mm, or 7-8 mm, and or about 7.55 mm.

11. A wood cutting knife (1) according to any one of claims 1-10, wherein: the wood pushing portion (7) to said vertical axis (a) forms an angle (γ) of from 83° to 89°, or from 85° to 87°, and / or about 86°.

12. A wood cutting knife (1) according to any one of claims 1-11, wherein the lower portion (10) of the pressure relief small depression (8) is planar and with respect to the vertical axis (a) forms an angle (δ) of from 70° to 93°, or from 89° to 91°, or about 90°.

13. A wood cutting knife (1) according to any one of claims 1-12, wherein the taper angle (α) of the cutting edge (6) is 30° to 40°, or 33° to 37°, or about 35°.

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