Abstract:
An improved burr for sharpening the grinding surface of a pulpstone includes a novel tooth configuration for better wear of the burr and enhanced grinding properties of the pulpstone. The profile configuration of the burr teeth has a truncated tip portion in the form of a rounded tip portion, a flat tip portion, or an obtusely angled tip portion to avoid a sharply pointed tip. The tip portion connects opposite sides of the tooth, with the sides forming either a symmetrical or an asymmetrical tooth profile using linear, convex involute, and concave involute side configurations. The present invention comprises a further improvement to a pulpstone sharpening burr, wherein the lead angle of the burr teeth changes periodically over the axial length of the burr to provide the pulpstone with a wave-like groove pattern.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to pulpstones for producing wood pulp used in the paper industry, and more particularly to improved sharpening burr tooth configurations for preparing a more homogeneous grinding surface on a pulpstone.  
         BACKGROUND OF THE INVENTION  
         [0002]    The historical development and use of paper as a means to record human events is extremely rich and illustrious. However, most of the technological advances associated with papermaking have evolved slowly, or have sprouted only after long time periods have passed. For instance, until 1803, nearly two-hundred and fifty years after the development of the printing press, hand paper production methods developed by the Chinese over two-thousand years ago remained the primary means by which paper was produced. In 1803 mechanical methods to produce paper were developed. Although these newer mechanical methods were themselves viewed as a boon to the paper production industry, they actually exacerbated paper shortage problems because they increased the demand for vegetative fibers, the essential ingredient used in the production of paper.  
           [0003]    In 1843, Friedrich Gottleib Keller addressed the vegetative fiber shortage problem by devising a method and apparatus for producing and manufacturing wood pulp using a stone grinding wheel known as a “pulpstone”. Keller&#39;s invention was timely because the Industrial Revolution was just entering full swing and demand for paper fiber was high. As a result, pulp production facilities having huge pulpstones were constructed for continuously grinding massive amounts of wood into pulp. Today, Keller&#39;s pulpstone grinding methods remain relatively unchanged, except for increases in capacity and efficiency due to refinements in grinder design. In fact, pulpstones are still used to produce large amounts of the wood pulp used in paper products today. FIG. 1 shows a typical wood pulp grinder  10  comprising a rotating pulpstone  12  and a plurality of pushers  14  for pressing logs  9  against an outer grinding surface  12 A of the pulpstone. As seen in FIG. 1, pulpstone  12  rotates in a counterclockwise direction and logs  9  are arranged such that their longitudinal axes are parallel to the axis of rotation of the pulpstone. As pulpstone  12  rotates, logs  9  are fed under pressure by pushers  14  into engagement with pulpstone surface  12 A to produce wood pulp.  
           [0004]    As can be seen in FIG. 2, pulpstone  12  generally includes abrasive grains  15  held together by a bonding material  16 , and are typically manufactured from either ceramic or cement bonded abrasive. Pulpstone surface  12 A is shown in detail as including alternating land areas  17  and groove areas  18 . As pulpstone  12  rotates and the timber  9  is pushed against pulpstone surface  12 A, land areas  17  come into contact with the timber and groove areas  18  pass over the surface of the timber, thereby creating oscillation between mechanical compression and decompression that generates heat. The heat softens the lignin of the wood and the rotational forces acting on the timber loosen and remove the wood fiber. Because of the extreme pressures, high frictional forces, and heat generated during the grinding of the timber, land areas  17  of pulpstone surface  12 A eventually begin to wear and widen, and the abrasive grains  15  begin to dull. The extent of such surface wear often varies over the axial length of pulpstone  12 . Consequently, more and more energy must be expended in order to maintain a consistent quality and output of pulp. Thus, the surface quality and groove pattern of the pulpstone play a very critical role in efficient production of the desired quality pulp. It is, therefore, extremely desirable to ensure that the land/groove pattern on the pulpstone surface is maintained by regular “sharpening” or “dressing” of the pulpstone surface.  
           [0005]    The term “pulpstone sharpening” is a misnomer; pulpstone sharpening does not actually sharpen the abrasive of a pulpstone. Rather, pulpstone sharpening fractures the softer bonding material of the pulpstone to remove the dull, older abrasive grains and to uncover the sharper, newer grains and to maintain the desired grooved pattern.  
           [0006]    Referring to FIG. 3 of the drawings, a known procedure for sharpening a pulpstone is illustrated. To sharpen a pulpstone, a sharpening burr  20  is journaled in a forked end  19  of a cross-slide (not shown), which in turn mounted on a traversing carriage of a lathe (also not shown) such that the burr&#39;s axis of rotation is parallel to that of the pulpstone. As seen in FIG. 4, burr  20  has a plurality of spaced apart teeth  22  on its outer peripheral surface that can be forced into pulpstone surface  12 A to a predetermined depth by adjustment of the cross-slide mechanism. Once burr  20  has been aligned at a side edge of pulpstone  12  and the burr depth has been set, the pulpstone is rotated, thereby imparting rotational motion to the sharpening burr. Burr  20  is then caused to traverse linearly across pulpstone surface  12 A as indicated by the bi-directional arrows in FIG. 3. The traversal of sharpening burr  20  under pressure forms a pattern in pulpstone surface  12 A by removing the old, abrasive grains and uncovering the sharp, new abrasive grains. The traversal process is repeated several times with a new sharpening burr as necessary to produce the desired pulpstone surface pattern. During the pulpstone sharpening process, the penetration depth of sharpening burr teeth  22  is critical. Proper tooth penetration depth fractures and removes abrasive grains on the surface of a pulpstone, however penetration that is too deep tends to fracture the deeper pulpstone surface bonds, creating wide grooves that promote pulpstone surface instability. Wide pulpstone grooves are undesirable because they produce long vegetative fibers and fiber bundles that are associated with lower grade pulps. In addition, pulpstone surface instability is also viewed as undesirable since it typically causes the premature wear of the pulpstone surface and failure of the groove pattern. Thus, pulpstone surface pattern and groove depth are viewed as important factors for manufacturing consistent and high quality pulps.  
           [0007]    Pulpstone sharpening also serves several additional useful purposes. First, sharpening reduces the grinding surface area of a pulpstone, lowering energy consumption. Second, sharpening controls the oscillatory frequency of compression and decompression of the wood fibers, thus controlling the requisite heat that is used to release wood fibers from the lignin. Third, pulpstone sharpening cleans the pulpstone pores and prevents grinding surface overheating, cracking, and premature wear by carrying water to the grinding zone for cooling and lubricating purposes. Finally, pulpstone sharpening and groove pattern help to carry pulp out of the grinding zone.  
           [0008]    Pulpstone sharpening burrs, for example burr  20  in FIGS. 3 and 4, have undergone very few changes over the past century, and there are currently four basic types in use today: spiral, diamond, fluted, and threaded. Spiral burrs have teeth that run parallel with one another and at an angle (known as the “lead angle”) to the rotational axis of the burr. When applied to the surface of a pulpstone, the spiral burr produces a series of diagonal impressions across the surface of the pulpstone. During grinding, the diagonal pattern formed on the pulpstone with a spiral burr removes wood fibers using a semi-shearing action. Diamond toothed burrs have teeth that form a pyramid or diamond shape. They are used primarily for truing pulpstones and for removing patterns on a pulpstone. Fluted burrs, such as burr  20  shown in FIG. 4, have teeth that run parallel to the rotational axis of the burr. When applied to a pulpstone surface, the fluted burr produces a pattern that is parallel to the rotational axis of the pulpstone. During grinding, the fluted pattern of the pulpstone removes long coarse fibers from the wood. A threaded burr produces a series of rings around the face of a pulpstone that produce a very light shearing action resulting in the production of a very high quality pulp. Pulpstone sharpening burrs are typically machined from a steel shell that is then heat treated for hardness and stress relief.  
           [0009]    The teeth of a pulpstone sharpening burr play perhaps the most critical role in the production of wood pulp because they actually create the patterns that have such profound effects upon the amount, quality, and consistency of the final wood pulp product. Burr teeth function by fracturing pulpstone bond posts between abrasive grains, thereby forming the abrasive pattern on the surface of a pulpstone. Current and past tooth configurations have traditionally been exclusively “pointed-triangular”, as shown in FIG. 5. By “pointed-triangular” it is meant that the burr tooth  22  is formed by two converging opposite planar sides  23 A and  23 B that intersect at a substantially pointed tip  24 . The included angle of tip  24  formed by the intersection of sides  23 A and  23 B is acute, ranging from 20° to 70°. Pointed-triangular tooth configurations suffer from two main drawbacks. First, because they are extremely sharp and pointed, they tend to wear unevenly when traversed across a pulpstone surface. Thus, pointed triangular teeth ultimately place an uneven pattern on the surface of the pulpstone, a result that is particularly undesirable because an uneven pulpstone pattern produces inconsistent grades of pulp depending upon axial position along the surface of the pulpstone. Second, pointed-triangular teeth can cause “deep bond breakage” in the surface of the pulpstone. Deep bond breakage is undesirable because it causes pulpstone surface and groove pattern instability that tends to promote the premature wear of the pulpstone. Because of deep bond breakage, a pulpstone must be taken offline and re-sharpened more frequently, resulting in more frequent equipment downtimes and lowered production outputs.  
           [0010]    Thus, developing a sharpening burr that reduces the incidence of deep bond breakage and withstands wear such that a homogenous pattern can be placed across the surface of a pulpstone would be extremely beneficial to the pulpwood processing industry in terms of increased pulp quality and increased pulp production.  
         SUMMARY OF THE INVENTION  
         [0011]    It is, therefore, an object of the present invention to provide an improved pulpstone sharpening burr that slows pulpstone wear by preventing the incidence of deep bond breakage on the surface of a pulpstone during sharpening.  
           [0012]    It is another object of this invention to provide an improved pulpstone sharpening burr that is itself resistant to wear such that the burr forms a more homogeneous groove pattern across the surface of a pulpstone.  
           [0013]    In view of these objects and in accordance with the present invention, a sharpening burr having a plurality of teeth is improved by changing the profile configuration of the teeth from the traditional pointed-triangular configuration to a configuration having a truncated tip portion in the form of a rounded tip portion, a flat tip portion, or an obtusely angled tip portion. The tip portion connects opposite sides of the tooth, with the sides forming either a symmetrical or an asymmetrical tooth profile. Symmetrical side configurations include linear—linear, convex involute—convex involute, and concave involute—concave involute. Asymmetrical side configurations include linear—convex involute, linear—concave involute, and convex involute—concave involute.  
           [0014]    The present invention also encompasses a further improvement to a pulpstone sharpening burr, wherein the lead angle of the burr teeth changes periodically over the axial length of the burr to provide the pulpstone with a wave-like groove pattern. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The nature of the present invention will now be more fully described in the following detailed description of the preferred embodiments taken with the accompanying drawings and figures, in which:  
         [0016]    [0016]FIG. 1 is a schematic view showing an example of a wood pulp grinding apparatus known in the art;  
         [0017]    [0017]FIG. 2 is an enlarged cross-sectional view of a pulpstone surface showing a groove pattern formed therein;  
         [0018]    [0018]FIG. 3 is a schematic view showing a pulpstone sharpening operation using a pulpstone sharpening burr as is known in the art;  
         [0019]    [0019]FIG. 4 is a perspective view of a fluted sharpening burr of the prior art;  
         [0020]    [0020]FIG. 5 is an enlarged cross-sectional view of a pointed-triangular burr tooth of the prior art;  
         [0021]    [0021]FIG. 6A is an enlarged cross-sectional view of a burr tooth formed in accordance with a first embodiment of the present invention;  
         [0022]    [0022]FIG. 6B is an enlarged cross-sectional view of a burr tooth formed in accordance with a second embodiment of the present invention;  
         [0023]    [0023]FIG. 6C is an enlarged cross-sectional view of a burr tooth formed in accordance with a third embodiment of the present invention;  
         [0024]    [0024]FIG. 6D is an enlarged cross-sectional view of a burr tooth formed in accordance with a fourth embodiment of the present invention;  
         [0025]    [0025]FIG. 6E is an enlarged cross-sectional view of a burr tooth formed in accordance with a fifth embodiment of the present invention;  
         [0026]    [0026]FIG. 6F is an enlarged cross-sectional view of a burr tooth formed in accordance with a sixth embodiment of the present invention;  
         [0027]    [0027]FIG. 7A is an enlarged cross-sectional view of a burr tooth formed in accordance with a seventh embodiment of the present invention;  
         [0028]    [0028]FIG. 7B is an enlarged cross-sectional view of a burr tooth formed in accordance with an eighth embodiment of the present invention;  
         [0029]    [0029]FIG. 7C is an enlarged cross-sectional view of a burr tooth formed in accordance with a ninth embodiment of the present invention;  
         [0030]    [0030]FIG. 7D is an enlarged cross-sectional view of a burr tooth formed in accordance with a tenth embodiment of the present invention;  
         [0031]    [0031]FIG. 7E is an enlarged cross-sectional view of a burr tooth formed in accordance with an eleventh embodiment of the present invention;  
         [0032]    [0032]FIG. 7F is an enlarged cross-sectional view of a burr tooth formed in accordance with a twelfth embodiment of the present invention;  
         [0033]    [0033]FIG. 8A is an enlarged cross-sectional view of a burr tooth formed in accordance with a thirteenth embodiment of the present invention;  
         [0034]    [0034]FIG. 8B is an enlarged cross-sectional view of a burr tooth formed in accordance with a fourteenth embodiment of the present invention;  
         [0035]    [0035]FIG. 8C is an enlarged cross-sectional view of a burr tooth formed in accordance with a fifteenth embodiment of the present invention;  
         [0036]    [0036]FIG. 8D is an enlarged cross-sectional view of a burr tooth formed in accordance with a sixteenth embodiment of the present invention;  
         [0037]    [0037]FIG. 8E is an enlarged cross-sectional view of a burr tooth formed in accordance with a seventeenth embodiment of the present invention;  
         [0038]    [0038]FIG. 8F is an enlarged cross-sectional view of a burr tooth formed in accordance with an eighteenth embodiment of the present invention; and  
         [0039]    [0039]FIG. 9 is an enlarged partial perspective view of a pulpstone sharpening burr formed in accordance with a nineteenth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    Attention is directed generally to FIGS. 6A through 11C of the drawings, which depict various burr tooth configurations in accordance with the present invention. The burr teeth are shown in enlarged profile view, and it will be understood that the burr teeth are formed on an outer surface of a cylindrical body just as pointed-triangular teeth  22  are formed on an outer surface of prior art burr  20  depicted in FIG. 4.  
         [0041]    Referring more specifically to FIGS.  6 A- 6 F, innovative burr tooth configurations in accordance with first through sixth embodiments of the present invention are shown and identified respectively by reference numerals  101 ,  102 ,  103 ,  104 ,  105 , and  106 . Teeth  101 - 106  are similar to each other in that each includes a rounded tip portion  110  as a departure from the acutely angled pointed-triangular tip of the prior art. The rounded tip portion  110 , which may simply be formed as a radius, improves the tooth&#39;s ability to hold its shape and height as compared with pointed-triangular teeth of the prior art because the cordal thickness of the tip increases at a greater rate from the apex of the tooth moving toward the base of the tooth until rounded tip portion  110  merges with the sides of the tooth. The radius of tip portion  110  is chosen small enough such that the tooth still has the ability to form a major portion of the pattern land in the pulpstone. An important advantage of rounded tip portion  110  is that the tooth shape wears less and remains more consistent as the burr traverses the pulpstone, thereby forming a more consistent pattern groove depth over the entire pulpstone surface. Ultimately, this allows for better control of the composite wood fiber mix produced in the grinding operation by limiting the number of coarse and fine fiber fractions, making it easier to produce pulp fiber that is closer to the target specification. Another advantage of rounded tip portion  110  is that it reduces the incidence of deep bond breakage, thereby increasing the stability of the pulpstone surface and groove pattern. Thus, the embodiments of FIGS.  6 A- 6 F improve the wood pulp production process in two ways: first by creating a homogeneous pulpstone surface that improves overall pulp quality, and second by reducing the incidence of equipment down times that are required to perform pulpstone sharpening procedures.  
         [0042]    The embodiments of FIGS.  6 A- 6 F differ from each other with respect to the configuration of the sides of the tooth that are connected by rounded tip portion  110 . Tooth  101  of FIG. 6A includes a pair of symmetrical sides  111 A and  111 B that are linear in profile view, similar to the sides  23 A,  23 B of prior art tooth  22  shown in FIG. 5. Since tooth  101  produces the same land top width as a conventional tooth, the resulting available grinding area on the pulpstone is not compromised. Linear sides  111 A,  111 B are simpler to machine than other side configurations to be discussed at present.  
         [0043]    Tooth  102  of FIG. 6B includes a pair of symmetrical sides  112 A and  112 B that each trace a convex involute when viewed in profile. The symmetrical convex involute sides  112 A,  112 B have a normal pressure angle ranging from 20° to 70°. The form of tooth  102  is more robust in cross-section than the form of prior art tooth  22  of FIG. 5, and gives the tooth more surface area over which to spread the inherent wear that is caused while the burr is in contact with the rotating pulpstone. Since the work performed by the burr in terms of abrasive grains dislodged by breaking the bond material between grains can be correlated to the available surface area of the tooth form, tooth  102  has the potential to do more work before exhibiting excessive wear. Tooth  102  produces a wider open groove between pattern lands in the pulpstone surface, and thus is desirable in instances where it is important for the grooves to carry large volumes of shower water through the grinding zone to better transport pulp fibers and dissipate heat.  
         [0044]    [0044]FIG. 6C shows tooth  103  as including opposite sides  113 A,  113 B that are in the form of symmetrical concave involutes when viewed in profile. The primary advantage of this configuration is that it places a stronger groove pattern in the pulpstone because it produces an “involute-like” (not a pure involute) shaped land in the groove pattern.  
         [0045]    Tooth  104  shown in FIG. 6D has sides  114 A,  114 B that are asymmetrical about an imaginary radial line extending from the axis of rotation of the burr through the center of rounded tip portion  110 . A tooth form with asymmetrical sides provides a way to combine positive attributes to the leading side and trailing side of the tooth. Tooth  104  includes a convex involute leading side  114 B and a linear trailing side  114 A, giving it extra surface area and wear resistance on the side of the tooth that benefits most from these qualities.  
         [0046]    Referring now to FIG. 6E, tooth  105  includes asymmetrical sides  115 A,  115 B chosen to shape the wall of the groove in the pulpstone differently on each side. This is valuable because of the dynamic forces directed against the pulpstone groove pattern during the grinding process. As a pattern land sweeps across the face of a log during grinding, there is a reactionary tangential force against the land. If the tangential force exceeds the strength of the land, the pattern can become broken away from the pulpstone surface. Thus leading side  115 B is a concave involute in profile configuration to form a more robust involute-like wall on the trailing side of the pulpstone pattern land, while trailing side  115 A is linear to form a conventionally shaped groove wall on the leading side of the pulpstone pattern land. This extra cross-sectional thickness on the trailing side of the pulpstone land can provide added resistance to the grinding force exerted on the land to help prevent breaking away of abrasive grains from the pulpstone surface. Tooth  105  yields less difference in groove volume, total active grains, and grinding area relative to a pointed-triangular tooth of the prior art, as compared with a symmetrical concave involute tooth form such as tooth  103  shown in FIG. 6C. Consequently, the operational parameters are similar to those established for a conventional burr, with added strength at the trailing wall of the pulpstone pattern land.  
         [0047]    Asymmetrical burr tooth  106  shown in FIG. 6F combines a concave involute leading side  116 B with a convex involute trailing side  115 A. The shape of leading side  116 B adds strength to the trailing wall of the pulpstone pattern land, while the convex involute trailing side gives the leading wall of the pulpstone pattern land a concave shape that ensures sufficient groove volume.  
         [0048]    Teeth  201 ,  202 ,  203 ,  204 ,  205 , and  206  illustrated in FIGS.  7 A- 7 F correspond respectively to teeth  101 ,  102 ,  103 ,  104 ,  105 , and  106  with regard to the profile configuration of their opposite sides, and thus experience the same benefits discussed above. Tooth  201  has symmetrical linear sides  211 A,  211 B; tooth  202  has symmetrical convex involute sides  212 A,  212 B; tooth  203  has symmetrical concave involute sides  213 A,  213 B; tooth  204  has a convex involute leading side  214 B and a linear trailing side  214 A; tooth  205  has a concave involute leading side  215 B and a linear trailing side  215 A; and tooth  216  has a concave involute leading side  216 B and a convex involute trailing side  216 A. Teeth  201 - 206  differ from teeth  101 - 106  in that they each include a flat tip portion  210  connecting the sides of the tooth and running parallel to the base of the tooth. The relative size of flat tip portion  210  depicted in FIGS.  7 A- 7 F is exaggerated, and the actual size of flat tip portion  210  is much smaller in relation to the remainder of the tooth. This type of configuration exhibits tremendously greater wear resistance compared to the pointed-triangular tooth form of the prior art, thereby producing a more consistent groove pattern across the surface of the pulpstone. Moreover, deep bond breakage in the pulpstone composite abrasive is significantly reduced by the elimination of a sharp point in the tooth.  
         [0049]    Teeth  301 ,  302 ,  303 ,  304 ,  305 , and  306  illustrated in FIGS.  8 A- 8 F also correspond respectively to teeth  101 ,  102 ,  103 ,  104 ,  105 , and  106  with regard to the profile configuration of their opposite sides, and thus experience the same benefits discussed above. Tooth  301  has symmetrical linear sides  311 A,  311 B; tooth  302  has symmetrical convex involute sides  312 A,  312 B; tooth  303  has symmetrical concave involute sides  313 A,  313 B; tooth  304  has a convex involute leading side  314 B and a linear trailing side  314 A; tooth  305  has a concave involute leading side  315 B and a linear trailing side  315 A; and tooth  316  has a concave involute leading side  216 B and a convex involute trailing side  316 A. In contrast to the rounded tip portion  110  and flat tip portion  210  of the previous embodiments, a pointed tip portion  310  is common to teeth  301 - 306 , and includes a pair of surfaces  310 A and  310 B that intersect to form an obtuse angle when viewed in profile. The angled tip portion  310 , due to its obtuse design, has the ability to hold shape and height better and cause less deep bond breakage than the traditional acutely angled pointed triangular tooth of the prior art. The angled tip portion  310  transitions to the sides at a location that allows the tooth sides to perform their intended pattern-forming function with respect to the pulpstone. Accordingly, a more homogenous pattern is created across the pulpstone surface resulting in the production of more homogenous wood pulp fibers.  
         [0050]    Reference is now made to FIG. 9, wherein a portion of a burr  400  is shown to illustrate another improvement to pulpstone burr technology according to the present invention. As mentioned above with regard to background art, the teeth of a spiral burr extend parallel each other and at a lead angle relative to the rotational axis of the burr. Heretofore, burrs have been made such that the lead angle of a burr remains constant from one end of the burr to the other, without deviation along the length of the burr. As will be apparent from FIG. 9, which shows a pair of adjacent teeth  402  of burr  400 , the lead angle of teeth  402  varies in an undulating fashion over the axial length of the burr. The lead angle of each tooth preferably changes in a regular periodic manner, most preferably in a sinusoidal manner, many times over the axial length of burr  400 . This innovation can be practiced in combination with the traditional pointed-triangular tooth form as shown in FIG. 9, or with any other novel tooth forms, including but not limited to tooth forms disclosed herein. Burr  400  having undulating teeth  402  provides a corresponding wave-shaped groove pattern on the pulpstone surface, instead of the traditional straight-line pattern now employed. Those skilled in the art of wood pulp production realize that a “combing” mechanism takes place by the pulpstone pattern as the lignin softens and allows the wood fibers to be released in the grinding zone. More specifically, when a small lead angle is used, the wood fibers tend to be combed out in long strands, whereas when a large lead angle is used, the wood fibers tend to be combed out in shorter strands. Burr  400  having undulating teeth  402  is designed to provide the pulpstone surface with a groove pattern that yields a combination of both combing effects. During pulpstone patterning, the burr  400  must be permitted to shift phase back and forth axially along its journal axis in forked end  19  of the lathe cross-slide (see FIG. 3) to allow the burr to shift a sufficient amount to allow the tooth form on the burr to mesh properly with the undulating lead pattern that may already exist on the pulpstone surface; otherwise, the existing pattern on the pulpstone might be destroyed.