Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PATTERN FOR PULPSTONE PROVIDING IMPROVED WEAR CHARACTERISTICS
Document Type and Number:
WIPO Patent Application WO/2016/108838
Kind Code:
A1
Abstract:
A cylindrical pulpstone has an outer surface that includes an abrasive. The outer surface defines a plurality of circumferentially- alternating grooves and lands extending across the outer surface of the pulpstone. The lands provide an active grinding surface area and the grooves do not provide an active grinding surface area. Each groove is defined by a pair of sidewalls separated by a flat base surface.

Inventors:
RUESTOW BRIAN A (US)
YLIKOSKI JUKKA K (FI)
Application Number:
PCT/US2014/072736
Publication Date:
July 07, 2016
Filing Date:
December 30, 2014
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
NORTON PULPSTONES INC (US)
International Classes:
D21B1/24; B24D5/02
Foreign References:
US3132815A1964-05-12
US2724222A1955-11-22
CA543998A1957-07-23
DE9017091U11991-05-08
US20030145842A12003-08-07
Attorney, Agent or Firm:
SNYDER, JR., George, L. (The Guaranty Building140 Pearl Street, Suite 10, Buffalo NY, US)
Download PDF:
Claims:
What is claimed is:

1. A pulpstone comprising: a rotational axis; and a cylindrical outer surface that comprises an abrasive, wherein the outer surface includes a plurality of circumferentially- alternating grooves and lands extending axially across the outer surface of the pulpstone, wherein the lands provide an active grinding surface area and the grooves do not provide an active grinding surface area; wherein each of the grooves is defined by a pair of sidewalls separated by a flat base surface. 2. The pulpstone of claim 1 , wherein the lands have a helical angle with respect to the rotational axis of the pulpstone, and wherein the helical angle is a value from 0° to 60°.

3. The pulpstone of claim 1 , wherein the lands are parallel to one another across the pulpstone.

4. The pulpstone of claim 1 , further comprising a core having a fixing surface and a plurality of segments connected to the fixing surface, each of the plurality of segments being formed of ceramic-bonded abrasive, wherein the plurality of segments together define the cylindrical outer surface of the pulpstone.

5. The pulpstone of claim 1 , wherein the pulpstone has a diameter greater than 1100 mm and an axial length greater than 550 mm.

6. The pulpstone of claim 1 , wherein each groove has a depth in a range from 0.5 mm through 8 mm.

7. The pulpstone of claim 1 , wherein each base surface has a width in a range from 2 mm

through 40 mm.

8. The pulpstone of claim 1 , wherein each base surface has a dimension in a circumferential direction between the pair of sidewalls of the groove equal to at least a plurality of average active grit diameters.

9. The pulpstone of claim 1 , wherein adjacent pairs of the lands are separated by a distance in a range from 20 mm through 80 mm.

10. The pulpstone of claim 1 , wherein each of the lands has a width in a range from 6 mm

through 40 mm. 11. In a pulpstone comprising a rotational axis and a cylindrical outer surface that comprises an abrasive, wherein the outer surface includes a plurality of circumferentially- alternating grooves and lands extending axially across the outer surface of the pulpstone, wherein the lands provide an active grinding surface area and the grooves do not provide an active grinding surface area, the improvement comprising: each of the plurality of lands has a circumferential width of at least 6 mm; adjacent pairs of the lands are separated by a distance of at least 20 mm; and the grooves have a flat base surface.

12. The improvement of claim 11, wherein the lands have a helical angle with respect to the rotational axis of the pulpstone, and wherein the helical angle is a value from 0° to 60°. 13. The pulpstone of claim 11, wherein the pulpstone has a diameter greater than 1100 mm and a length greater than 550 mm.

14. The pulpstone of claim 11, wherein each groove has a depth in a range from 0.5 mm through 8 mm.

15. The pulpstone of claim 11, wherein the flat base surface of the groove has a dimension equal to at least a plurality of average active grit diameters.

16. The pulpstone of claim 11, wherein each base surface has a width in a range from 2 mm through 40 mm.

Description:
PATTERN FOR PULPSTONE PROVIDING IMPROVED WEAR CHARACTERISTICS

FIELD OF THE DISCLOSURE

[0001] This disclosure relates to pulpstones 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. Each land 17 has a land width L and a separation distance S. Each groove 18 has a groove width G. Distance D describes the radial dimension from the vertex of the groove 18 deepest into the pulpstone 12 to the adjacent land 17. The distance D typically ranges from 0.5 mm to 2.03 mm, with approximately 1.1 mm being a common example. In one particular example, the separation distance S may be approximately 0.89 mm, the distance D may be approximately 1.1, and the land width L ranges from 0.91 mm to 1.2 mm. The pitch may be 0.08 to 0.55 per millimeter.

[0004] Conventional pulpstone sharpening burrs are known to form a regular pattern of closely-spaced, narrow V-shaped grooves in outer surface 12A. 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] Wearing of the outer surface 12A affects pulp quality. 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 an improved surface pattern for a pulpstone that can improve pulpstone wear characteristics or increase the time between sharpenings.

BRIEF SUMMARY OF THE DISCLOSURE

[0009] In a first aspect, a pulpstone is disclosed. The pulpstone has a rotational axis and a cylindrical outer surface having an abrasive. The outer surface includes multiple circumferentially- alternating grooves and lands extending axially across the outer surface of the pulpstone. The lands provide an active grinding surface area and the grooves do not provide an active grinding surface area. Each of the grooves is defined by a pair of sidewalls separated by a flat base surface. [0010] The pulpstone can have a diameter greater than 1100 mm and an axial length greater than 550 mm. Each groove can have a depth in a range from 0.5 mm through 8 mm. Each base surface can have a width in a range from 2 mm through 40 mm. Adjacent pairs of the lands are separated by a distance in a range from 20 mm through 80 mm. Each of the lands can have a width in a range from 6 mm through 40 mm. Each base surface can have a dimension in a circumferential direction between the pair of sidewalls of the groove equal to at least a plurality of average active grit diameters. The lands can have a helical angle with respect to the rotational axis of the pulpstone from 0° to 60°. The lands may be parallel to one another across the pulpstone.

[0011] In one instance, the pulpstone has a core with a fixing surface and multiple segments connected to the fixing surface. Each of the segments are formed of ceramic-bonded abrasive. The segments together define the cylindrical outer surface of the pulpstone.

[0012] In a second aspect, a pulpstone is provided. The pulpstone has a rotational axis and a cylindrical outer surface that comprises an abrasive. The outer surface includes a plurality of circumferentially-alternating grooves and lands extending axially across the outer surface of the pulpstone. The lands provide an active grinding surface area and the grooves do not provide an active grinding surface area. Each of the plurality of lands has a circumferential width of at least 6 mm, adjacent pairs of the lands are separated by a distance of at least 20 mm, and the grooves have a flat base surface.

[0013] The pulpstone can have a diameter greater than 1100 mm and an axial length greater than 550 mm. Each groove can have a depth in a range from 0.5 mm through 8 mm.

Each base surface can have a width in a range from 2 mm through 40 mm. The lands can have a helical angle with respect to the rotational axis of the pulpstone from 0° to 60°. Each base surface can have a dimension in a circumferential direction between the pair of sidewalls of the groove equal to at least a plurality of average active grit diameters. DESCRIPTION OF THE DRAWINGS

[0014] 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 perspective view of a pulpstone in accordance with an embodiment of the present disclosure;

FIG. 4 is an enlarged cross-sectional view of a pulpstone surface in accordance with an embodiment of the present disclosure;

FIG. 5 is an enlarged cross-sectional view of a pulpstone surface wherein the land width is less than the groove width;

FIG. 6 is an enlarged cross-sectional view of a pulpstone surface wherein the land width is greater than the groove width; and

FIG. 7 is a flattened projection view of a pulpstone surface. DETAILED DESCRIPTION OF THE DISCLOSURE

[0015] 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. [0016] As seen in FIG. 3, a pulpstone 20 formed in accordance with an embodiment of the present disclosure has a cylindrical outer surface 21 and a rotational axis 30 Outer surface 21 includes multiple circumferentially-alternating grooves 23 and lands 22 extending axially across the outer surface 21 of the pulpstone 20. The lands 22 provide an active grinding surface area and the grooves 23 do not provide an active grinding surface area. [0017] In order to produce a particular quality of pulp, the lands 22 and grooves 23 of outer surface 21 are patterned so that a predetermined number of active grits on or in the outer surface 21 come in contact with the wood with every rotation of pulpstone 12 about rotational axis 30. These active grits are abrasive particles on lands 23 that are exposed or can contact the wood. The amount of energy transmitted to the wood through the individual active grits can determine the quality of the pulp. Grooves 23 are put into the surface of the pulpstone 20 to reduce the active grinding surface area of the pulpstone 20 and the number of active grits. The energy transmitted based on the number of active grits in the active grinding surface area will correspond to pulp freeness. Pulp freeness refers to the ability of a given pulp to drain water and is an indication of quality of the pulp being coarse or fine. Coarse pulp drains freely and is considered as having high freeness.

[0018] The dimensions of the pulpstone 20 can vary. For example, the pulpstone 20 can have a diameter ranging from approximately 1 100 mm to approximately 1900 mm. The pulpstone 20 can have an axial length from approximately 550 mm to approximately 1900 mm. Of course, other dimensions are possible and these are merely examples.

[0019] The pulpstone 20 may be fabricated of or include a ceramic-bonded abrasive.

The abrasive can provide the active grits used during pulp manufacturing. Abrasive bonding used to produce the pulpstone grinding matrix may be a vitrified bond or ceramic bond.

Abrasives that are used to manufacture a pulpstone matrix can be man-made synthetic abrasives. These can be, for example, aluminum oxide, silicon carbide, boron carbide, fused alumina, zirconia, ceramics, or other materials.

[0020] In one example, the pulpstone has multiple angular segments 31-34 connected to a fixing surface 36 of a core 35. The fixing surface 36 is illustrated in FIG. 3 between the core 35 and segments 31-34. Each of the segments 31-34 is fabricated of ceramic-bonded abrasive. The respective surfaces of segments 31-34 collectively form the outer surface 21.

[0021] FIG. 4 is an enlarged cross-sectional view of a pulpstone surface 21 in accordance with an embodiment of the present disclosure. Pulpstone surface 21 has alternating lands 22 and grooves 23. Each land 22 has a land width 1 and a separation distance s. Each groove 23 has a groove width g. Land width 1 and groove width g refer to the circumferential width of the land or groove. The lands 22 may have a land width 1 in a range from approximately 6 mm through approximately 40 mm. Adjacent pairs of lands 22 may be separated by a separation distance s in a range from approximately 20 mm through approximately 80 mm. Of course, other dimensions are possible and these are merely listed as examples.

[0022] Each groove 23 is defined by a pair of sidewalls 25, 26 separated by a flat base surface 24. Thus, each groove 23 has a flat bottom. The shape of the groove 23 may be a truncated V-shaped groove wherein the sidewalls converge toward one another as they approach flat base 24, and flat base 24 eliminates the vertex of the V-shape. Alternatively, sidewalls 25, 26 may be substantially orthogonal to flat base 24. By providing a flat base 24 for each groove 23, each land 22 is defined independently between its own associated sidewalls 25, 26, thereby improving wear characteristics of the lands 22. The circumferential width of flat base 24 (or groove width g), may be in a range from approximately 2 mm through approximately 40 mm. Of course, other dimensions are possible and these are merely listed as examples. The groove width g may be less than or equal to the separation distance s. In an instance, the groove width g can have a dimension that is equivalent to multiple average active grit diameters.

[0023] Distance d describes the radial depth dimension of groove 23 from the adjacent land 22 to the flat base 24 of the groove. The distance d can be in a range from approximately 0.5 mm through approximately 8 mm, though other dimensions are possible.

[0024] In one example, the land width 1 is approximately 40 mm and the groove width g is approximately 2 mm. In another example, the land width 1 is approximately 6 mm and the groove width g is approximately 40 mm. The land widths and groove widths can be selected independently of each other and are not necessarily equal.

[0025] As also seen in comparison between FIG. 2 and FIG. 4, for a given total active grinding surface area of dimensionally similar pulpstones 12 and 20, the land width 1 of pulpstone 20 is larger than the prior art land width L of pulpstone 12, and the groove width g of pulpstone 20 is larger than the prior art groove width G of pulpstone 12. A wider land width 1 results in less breakage because more abrasive particles and bonding material are present in each land 22. Additional abrasive particles and bonding material per land 22 increases strength and durability of the land 22.

[0026] Assuming pulpstone 20 is the same size as a prior art pulpstone 12, the sum of active grinding surface areas of the lands 22 of pulpstone 20 may be approximately the same as the sum of active grinding surface areas of the lands 17 of prior art pulpstone 12. As will be understood, pulpstone 20 has fewer total lands and grooves than prior art pulpstone 12, but produces the same quality wood pulp while allowing the pulpstone to be used for longer periods of time between sharpenings due to improved wear characteristics. Of course, the total active grinding surface area is subject to choice and may depend on the wood type and desired pulp quality, among other factors. The groove depth d in FIG. 4 and prior art groove depth D in FIG. 2 may differ or be approximately the same.

[0027] FIG. 5 is an enlarged cross-sectional view of a pulpstone surface 21 wherein the land width 1 is less than the groove width s. FIG. 6 is an enlarged cross-sectional view of a pulpstone surface wherein the land width 1 is greater than the groove width s. The ratio of groove width s to land width 1 can affect pulp quality. The ratio of groove width s to land width 1 can be in a range from, for example, approximately 0.025 through 2.

[0028] The selected pattern of lands 22 and grooves 23 will affect pulp freeness. The basic grinding formula is Q is proportional to Ps wherein Q is pulp quality and Ps is specific grinding pressure. This can be further simplified to read Ps is proportional to CSF wherein CSF is pulp freeness. As specific grinding pressure Ps increases, the deforming pressure on the wood fibers increases. This increases the rate of heating of the lignin, which holds the fibers in the wood. The faster softening of the lignin will cause longer fibers and more fiber bundles to be released from the wood causing an increase in pulp freeness. The formula Ps is proportional to CSF can be changed to read that the active grinding area or land width is proportional to CSF. Thus, pattern on the outer surface 21 affects specific grinding pressure Ps and, consequently, pulp quality Q. The above formulas assume constant motor load of the motor driving rotation of pulpstone 20.

[0029] Given all other grinding parameters (stone composition, rotation speed, shower water, wood quality, temperature, etc.) being equal, total effective grinding surface area is directly correlated to freeness and pulp quality produced. Effective grinding area of the pulpstone is equal to the basic surface area of the cylindrical pulpstone minus the area removed by creating the grooves in the surface pattern.

[0030] The pattern disclosed herein includes a regular series of widely-spaced lands 22 separated by flat-bottomed grooves 23. The groove width s is considerably wider than groove width S of the conventional pattern by a factor of approximately 2 to 20 times. The land width 1 is correspondingly wider than the land width L of the conventional pattern. It is the sum of the areas of these lands 22 that provides the effective grinding surface area. Equal effective grinding surface area of pulpstone 20 can be achieved in comparison to existing pulpstone designs.

Therefore, similar freeness and pulp quality can be produced using the embodiments disclosed herein, with the benefit that pulpstone 20 requires sharpening less frequently than a conventional pulpstone so that grinding "down time" is significantly reduced.

[0031] The cylindrical pulpstone surface 21 is projected as a flat surface in FIG. 7. A number of lands 22 and grooves 23 are formed axially across the pulpstone surface 21 (i.e. extending at least in a direction of rotational axis 30). Lands 22 and grooves 23 may extend axially at a helical angle Θ relative to the direction of rotational axis 30. Helical angle Θ also can affect pulp quality. The helical angle Θ can be a value in a range from 0° to approximately 60°. In this case 0° is fully parallel to rotational axis 30. The term "axially across" is intended to broadly encompass both zero and non-zero helical angles, and to encompass both partially across and fully across.

[0032] The strength of a pattern composed of V-shaped grooves made by a conventional pulpstone sharpening burr is related to the width of the base of the land. If a particular pulpstone requires a narrowly spaced groove pattern (i.e., smaller effective grinding area) to produce the desired pulp freeness and quality and this narrowly-spaced groove pattern provides five grit diameters (or less) supporting the base of the land, the pattern will be fragile and subject to breaking down easily over time. The pattern disclosed herein can provide a similar effective grinding area, but is more durable because wider lands eliminate the problem of pattern breakdown. This provides for a more stable grinding environment, longer times between sharpening, and longer pulpstone life.

[0033] Pulpstone grinding methods developed in 1843 remain relatively unchanged, except for increases in capacity and efficiency due to refinements in grinder design. It was expected that increasing land widths or groove widths would adversely affect pulp quality.

Surprisingly, use of a pulpstone surface with wider land widths and groove widths, as disclosed herein, provides the same pulp quality. For example, the total grinding surface area of the lands may be the same as a standard pulpstone with V-shaped grooves. Thus, the pulp quality produced by a pulpstone as disclosed herein can be the same as that produced with existing pulpstones, but the pulpstone as disclosed herein is more robust and is more resistant to breakage. Greater resistance to breakage of the lands means the pulpstone has higher uptime and requires fewer or less frequent sharpenings.

[0034] The dimensions of the land and grooves, helical angle, ratio of lands to grooves, or spacing of the lands or grooves can be adjusted to provide desired control parameters.

[0035] The pulpstone surface may be formed or sharpened using various methods. For example, a burr, diamond saw, laser, water jet, another abrasive system, or another tool or device can form or sharpen the pulpstone surface pattern.

[0036] 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.