FIELD OF THE DISCLOSURE

[0001] This disclosure relates to tools for sharping pulpstones that are used in the paper industry for the production of ground wood pulp.

BACKGROUND OF THE DISCLOSURE

[0002] A pulpstone is used for papermaking to grind or shred wood. These pulpstones usually take the form of a large, abrasive wheel that is rotated. FIG. 1 shows a typical wood pulp grinder 10 with a rotating pulpstone 12 and multiple pushers 14 for pressing logs 9 against an outer surface 12A of the pulpstone 12. As seen in FIG. 1, the 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 12. As the pulpstone 12 rotates, logs 9 are fed under pressure by the pushers 14 into engagement with the outer surface 12A to produce wood pulp.

[0003] As can be seen in FIG. 2, the pulpstone 12 has an outer surface 12A that includes abrasive grains 15 held together by a bonding material 16. The outer surface 12A is typically manufactured from either ceramic or cement-bonded abrasive. The outer surface 12A is shown in detail with alternating lands 17 and grooves 18. Conventional pulpstone sharpening burrs are known to form a regular pattern of closely-spaced, narrow V-shaped grooves in outer surface 12 A. The grooves are formed when the V-shaped teeth of the burr (generally having a 42° included angle) crush form the ceramic-bonded abrasive material of the pulpstone 12. This conventional pattern has a large number of closely spaced lands 17 separated by a large number of closely spaced V-shaped grooves 18.

[0004] As the pulpstone 12 rotates and the logs 9 are pushed against the outer surface

12A, lands 17 come into contact with the logs 9 and groove areas 18 pass over the surface of the logs 9, 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 logs 9 loosen and remove the wood fiber.

[0005] Because of the extreme pressures, high frictional forces, and heat generated during the grinding of the logs 9, the lands 17 of the outer surface 12A eventually begin to wear and change in dimension, the abrasive grains 15 begin to dull, and the pulpstone 12 becomes less abrasive. The extent of such surface wear often varies over the axial length of the pulpstone 12. Consequently, 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 12 can play an important role in efficient production of the desired quality pulp. It is, therefore, desirable to ensure that the land/groove pattern on the outer surface 12A is maintained by regular

"sharpening" or "dressing" of the outer surface 12A.

[0006] 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, to uncover the sharper, newer grains, and to maintain the desired grooved pattern. Generally, the current methods of "sharpening" the outer surface of a pulpstone are intended to remove defined amounts of abrasive material. Pulpstone sharpening may be accomplished in various ways. The most common sharpening methods in use today are treatment of the outer surface with a steel shell sharpening burr, treatment of the outer surface with an ultra-high pressure water jet, or a combination of both of these techniques.

[0007] Referring to FIG. 3 of the drawings, a known procedure for sharpening a pulpstone 12 is illustrated. To sharpen a pulpstone 12, a sharpening burr 20 is journaled in a forked end 19 of a cross-slide mechanism, which is mounted on a traversing carriage of a lathe (not shown) such that the axis of rotation of the burr 20 is parallel to that of the pulpstone 12. The burr 20 has a plurality of spaced apart teeth 22 on its outer peripheral surface that can be forced into the pulpstone surface 12A to a predetermined depth by adjustment of the cross-slide mechanism. Once the burr 20 has been aligned at a side edge of pulpstone 12 and the burr depth has been set, the pulpstone 12 is rotated, thereby imparting rotational motion to the burr 20. The burr 20 is then moved linearly across the pulpstone surface 12 A as indicated by the bi-directional arrows in FIG. 3. This traversal of sharpening burr 20 across pulpstone surface 12A under pressure forms a pattern in pulpstone surface 12A by removing the old, abrasive grains and uncovering the sharp, new abrasive grains. The traversal process is performed one or more times using one or more burrs to produce the desired surface pattern in the pulpstone 12.

[0008] Sharpening the pulpstone can reduce or eliminate the effect of wear to the outer surface 12 A, but this is a time-consuming process. The stone groundwood industry is under pressure to provide increased efficiency, so any manufacturing downtime is undesirable.

Therefore, what is needed is a tool for sharpening a pulpstone to have an improved surface pattern with better wear characteristics.

BRIEF SUMMARY OF THE DISCLOSURE [0009] In a first aspect, a tool for sharpening a pulpstone is provided. The tool has a body with a cylindrical engaging surface and an axis of rotation. The engaging surface has multiple circumferentially-alternating lands and spacer grooves extending in an axial direction of the body. Each land is configured to crush form a pulpstone groove in a bonded abrasive pulpstone. The pulpstone groove is defined by two sidewalls separated by a flat base surface. The body of the tool can be fabricated of, for example, carbon steel, a carbide, an abrasive, or a ceramic.

[0010] The lands can extend parallel to one another across the tool. The lands can have a lead angle with respect to an axial direction of the tool from 0° to 60° _. The spacer grooves of the tool can have a groove width in a range from 6 mm through 40 mm and a land width in a range from 2 mm through 40 mm. The land support width may be greater than the land width and this land support width can be in a range from 20 mm through 80 mm.

[0011] The lands can have a smooth surface or a non-smooth surface treatment. The surface treatment can be a fluted pattern or a diamond pattern.

[0012] In a second aspect, a method of sharpening a pulpstone is provided. A tool engages an outer surface of the pulpstone. The tool has multiple circumferentially-alternating lands and spacer grooves on a cylindrical engaging surface. The pulpstone rotates while the engaging surface of the tool is engaged with the outer surface of the pulpstone. The tool is traversed axially across the outer surface of the pulpstone as the pulpstone rotates to crush form a plurality of pulpstone grooves in the outer surface of the pulpstone with the lands of the tool. Each of the pulpstone grooves is defined by two sidewalls separated by a flat base surface.

DESCRIPTION OF THE DRAWINGS

[0013] For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the

accompanying drawings, in which: FIG. 1 is a schematic view showing an example of a wood pulp grinding apparatus known in the art;

FIG. 2 is an enlarged cross-sectional view of an outer surface of a pulpstone showing a V-shaped groove pattern formed therein according to the prior art;

FIG. 3 is a schematic view showing a pulpstone sharpening operation using a pulpstone sharpening burr as is known in the art;

FIG. 4 is a perspective view of a tool used for pulpstone sharpening in accordance with an embodiment of the present disclosure;

FIG. 5 is a perspective view of a tool used for pulpstone sharpening in accordance with an embodiment of the present disclosure, wherein the lands and grooves of the tool have a non-zero lead angle;

FIG. 6 is an enlarged cross-sectional view showing a portion of a tool formed in accordance with another embodiment of the present disclosure;

FIG. 7 is an enlarged perspective view showing one possible surface treatment of the lands of the tool in accordance with an embodiment of the present disclosure;

FIG. 8 is an enlarged perspective view showing another possible surface treatment of the lands of the tool in accordance with an embodiment of the present disclosure; and

FIG. 9 is an enlarged cross-sectional view of a pulpstone surface formed in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE DISCLOSURE

[0014] Although claimed subject matter will be described in terms of certain

embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure. Accordingly, the scope of the disclosure is defined only by reference to the appended claims.

[0015] FIG. 4 is a perspective view of a tool 30 used for pulpstone sharpening in accordance with an embodiment of the present disclosure. The tool 30 can be used to crush form a pattern into the outer surface of a pulpstone, such as the pulpstone 12 of FIG. 3. This tool 30 can be fabricated of carbon steel, a carbide, an abrasive, a ceramic, or other materials known to those skilled in the art. [0016] The tool 30 has a cylindrical body with an outer surface 31 for engaging the pulpstone surface. The tool 30 may be hollow, as seen in FIG. 4, or may be a solid cylinder. The outer surface 31 includes multiple circumferentially- alternating lands 32 and spacer grooves 33 extending axially across the outer surface 31. Each of the lands 32 can crush form a groove in a ceramic abrasive pulpstone. The lands 32 are radially raised relative to the bottom surface of the spacer grooves 33. For example, the lands 32 may be radially raised relative to the bottom surface of the spacer grooves 33 in a range from approximately 0.5 mm through approximately 5.0 mm. The lands 32 extend axially across outer surface 31 of tool 30 at a lead angle Θ with respect to a rotational axis 34 of tool 30. This lead angle Θ may be in a range from

approximately 0° (i.e., parallel to the rotational axis) through approximately 60°. The term "axially across" is intended to broadly encompass both zero and non-zero lead angles, and to encompass both partially across and fully across.

[0017] The tool 30 can have an outer diameter in a range from approximately 100 mm through approximately 150 mm, an inner diameter in a range from approximately 90 mm through approximately 120 mm, and a width along the axial direction in a range from

approximately 40 mm through approximately 100 mm. The lands 32 can have a land width L in a range from approximately 2 mm through approximately 40 mm. The spacer grooves 33 can have a groove width G measured at the base of the groove in a range from approximately 6 mm through approximately 40 mm. As may be seen in FIG. 6, each spacer groove 33 may be in the form of a truncated V-shape wherein sidewalls 33A and 33B of the spacer groove diverge from one another as they approach respective adjacent lands 32 of the tool, such that a land support region 35 below each land 32 has a land support width S that is greater than the land width L. As may be understood, this land support width defines a separation distance between adjacent lands formed on the pulpstone surface. By way of example, the land support width S may be in a range from 20 mm through 80 mm. Of course, other dimensions are possible and these are merely listed as examples.

[0018] Each of the lands 32 can be smooth or may have a surface treatment to help in forming a corresponding groove in the pulpstone surface. FIGs. 7 and 8 illustrate two different surface treatments. FIG. 7 illustrates a diamond pattern 41. FIG. 8 illustrates a fluted pattern 42. Other surface treatments to help form a groove in a pulpstone are possible. [0019] Use of tool 30 in forming a pattern in an outer surface of a pulpstone will now be described, and may be substantially similar to a known procedure for sharpening a pulpstone using a conventional sharpening burr. As a set up step, tool 30 is mounted in a cross-slide mechanism of a lathe fitted with a cylindrical plug for receiving the tool. The plug may have an outer diameter that is slightly greater than the inner diameter of tool 30, such that the plug receives tool 30 by press fitting the tool onto the plug. A hydraulic press mechanism may be used to perform the press-fit. Other arrangements and methods for mounting tool 30 onto the cross-slide mechanism of a lathe may be employed, including, for example, a cylindrical screw- type expansion holder received within the inner diameter of the tool that mechanically expands to achieve a tight fit with the tool, and a rubber cushion holder having a resilient outer layer for snugly fitting within the inner diameter of the tool.

[0020] To crush form a pattern in an outer surface of a pulpstone, the tool is engaged with the outer surface of the pulpstone with the rotational axis 34 of tool 30 parallel to a rotational axis of the pulpstone. The radial position of tool 30 relative to the pulpstone is adjusted such that the lands 32 of tool 30 protrude into the bonded abrasive of the pulpstone to a desired depth. The pulpstone is then rotated while the tool 30 is engaged with the outer surface of the pulpstone, and the cross-slide mechanism of the lathe is operated to traverse the tool 30 axially across the pulpstone. Multiple traverses of the pulpstone at incremental depth settings may be needed. In this way, grooves and lands are crush formed in the pulpstone surface. Crush forming involves shaping the outer surface of the pulpstone by forcing the rotating tool 30 into the bonded abrasive of the pulpstone surface. This process may be used to bring a newly installed pulpstone into cylindrical truth by eliminating rotational "run-out," impart a grinding pattern, remove burned or broken abrasive areas, and/or smooth the pulpstone surface by removing an existing surface pattern of the pulpstone. [0021] FIG. 9 is an enlarged cross-sectional view of a pulpstone surface formed in accordance with an embodiment of the present disclosure. The outer surface 51 of the cylindrical pulpstone 50 can be formed using the tool 30 of FIG. 4. There are multiple circumferentially- alternating grooves 53 and lands 52 extending axially across the outer surface 51 of the pulpstone 50. The lands 52 provide an active grinding surface area and the grooves 53 do not provide an active grinding surface area. Each groove 53 is defined by two sidewalls 55, 56 separated by a flat base surface 54. The width of each flat base 54 may be in a range from approximately 2 mm through approximately 40 mm and the width of each land 52 may be in a range from approximately 6 mm through approximately 40 mm, though these are merely examples and other dimensions are possible. The flat base 54 may be perpendicular to the sidewalls 55, 56 or may be at some non-perpendicular angle to the sidewalls 55, 56.

[0022] Use of a pulpstone surface comprising wider lands 52 and grooves 53 characterized by a flat base surface 54 provides the same pulp quality. However, the pulpstone 50 with the flat base surface 54 between lands 52 is more robust and is more resistant to breakage. Greater resistance to breakage of the lands 52 means the pulpstone 50 has higher uptime and requires fewer or less frequent sharpenings.

[0023] The tool 30 of the present invention represents a major departure from pulpstone sharpening burrs of the prior art which have been in use for more than a century. Tool 30 is configured to create a pulpstone surface pattern that avoids closely spaced lands separated by V- shaped grooves in favor of fewer and wider lands separated at a greater distance from one another by flat-bottomed grooves. Tool 30 provides a pulpstone surface that matches prior art pulpstone surfaces in terms of wood pulp quality, but surpasses prior art pulpstone surfaces in terms of longevity so that the mill may experience greater productivity from increased up time.

[0024] Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure. Hence, the present disclosure is deemed limited only by the appended claims and the reasonable interpretation thereof.