TECHNICAL FIELD

One aspect of the present disclosure relates to a grinding wheel and a method of manufacturing a grinding wheel.

BACKGROUND ART

In the related art, as a grinding wheel, there is one described in Patent Document 1. The grinding wheel includes a core member and an abrasive portion provided around an outer periphery of the core member and including nonwoven fabric. The abrasive portion is formed with the nonwoven fabric including abrasive grains.

CITATION LIST

Patent Documents

Patent Document 1: JP 2007-290061 A

SUMMARY OF INVENTION

Technical Problem

Here, the grinding wheel described above has a problem of a large amount of the abrasive grains incorporated in the abrasive portion and a high manufacturing cost. Therefore, there has been a demand for suppressing the manufacturing cost of the grinding wheel.

SOLUTION TO PROBLEM

A grinding wheel according to an aspect of the present disclosure is a grinding wheel including an abrasive portion including nonwoven fabric, wherein the abrasive portion includes an outer peripheral portion formed with the nonwoven fabric including abrasive grains on an outer peripheral side, and an inner peripheral portion formed with the nonwoven fabric not including the abrasive grains, and a ratio of a thickness in a radial direction of the outer peripheral portion to a thickness in a radial direction of the abrasive portion is from 3% to 60%.

A grinding wheel according to an aspect of the present disclosure is a grinding wheel including an abrasive portion including nonwoven fabric, wherein the abrasive portion includes an outer peripheral portion formed on an outer peripheral side, and an inner peripheral portion softer than the outer peripheral portion, and a ratio of a thickness in a radial direction of the outer peripheral portion to a thickness in a radial direction of the abrasive portion is from 3% to 60%.

A method of manufacturing a grinding wheel according to an aspect of the present disclosure is a method of manufacturing a grinding wheel including an abrasive portion constituted by laminating a plurality of nonwoven fabric sheets, the method including the steps of: laminating a plurality of nonwoven fabric sheets in a circumferential direction, forming a gap between the nonwoven fabric sheets adjacent to each other in the circumferential direction, and incorporating abrasive grains in an outer peripheral edge portion of each of the nonwoven fabric sheets between which the gap is formed.

ADVANTAGEOUS EFFECTS OF INVENTION

According to an aspect of the present disclosure, a grinding wheel and a method of manufacturing a grinding wheel having added value while providing a suppressed manufacturing cost can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a grinding wheel according to a first embodiment of the present disclosure.

FIG. 2 is a plan view of the grinding wheel illustrated in FIG. 1.

FIGS. 3A and 3B are enlarged views of the outer peripheral portion and the inner peripheral portion.

FIGS. 4 A and 4B are enlarged views illustrating layer configurations of an abrasive portion.

FIG. 5 is a view illustrating a method of manufacturing the grinding wheel according to the first embodiment of the present disclosure.

FIG. 6 is an enlarged view illustrating a state in which abrasive grains are applied to an outer peripheral portion.

FIGS. 7A to 7C are views for explaining an action and an effect of the grinding wheel according to the first embodiment of the present disclosure.

FIGS. 8 A to 8E are views for explaining a grinding wheel according to a modification and a method of manufacturing the same.

FIG. 9 is a graph showing measurement results of grinding wheels according to examples and a comparative example.

FIG. 10 is a plan view of a grinding wheel according to a second embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Detailed descriptions of the embodiments according to the present invention will be given below with reference to the attached drawings. In the description of the drawings, identical or equivalent elements are denoted by the same reference signs, and redundant description of such elements will be omitted. First Embodiment

FIG. 1 is a perspective view of a grinding wheel 1 according to a first embodiment of the present disclosure. FIG. 2 is a plan view of the grinding wheel 1 illustrated in FIG. 1. According to the grinding wheel 1 according to the first embodiment, the following problems can be solved while a manufacturing cost is suppressed. That is, roughness of a polished surface of an object polished by using a conventional grinding wheel has been dependent on a material of the grinding wheel (nonwoven fabric, abrasive grains incorporated in nonwoven fabric, an adhesive, and the like). Accordingly, in the case of performing polishing at a plurality of stages of roughness (for example, the case of performing fine finish after performing rough finish), preparation of a plurality of grinding wheels has been required. Therefore, labor and man-hours for replacing the grinding wheels and the like have been required. With respect to such a problem, the grinding wheel 1 can stably apply a plurality of stages of abrasive force to a surface to be polished of an object.

The grinding wheel 1 is a member for polishing a surface to be polished BF (see FIG. 2) of an object W with an outer circumferential surface 2a. The grinding wheel 1 is a cylindrical member with a central axis CL as a reference. As illustrated in FIGS. 1 and 2, the grinding wheel 1 includes an abrasive portion 2 and a core member 3. Note that in the following description, a direction in which the central axis CL extends is referred to as an“axial direction.” A direction orthogonal to the central axis CL is referred to as a“radial direction.” A direction around the central axis CL is referred to as a“circumferential direction.”

The core member 3 is a member provided at a center position of the grinding wheel 1. The core member 3 is a cylindrical member with the central axis CL as a reference. The core member 3 is a portion through which a shaft AX (see FIG. 2) is inserted for rotating the grinding wheel 1.

The core member 3 is constituted with, for example, a material having rigidity such as a resin and a metal.

The abrasive portion 2 is provided in an outer periphery of the core member 3, and is a member including nonwoven fabric. The surface to be polished BF is polished by rotating the outer circumferential surface 2a of the abrasive portion 2 in a state where the outer circumferential surface 2a is in surface contact with the surface to be polished BF of the object W. The abrasive portion 2 includes an inner peripheral portion 2A formed on the inner peripheral side and an outer peripheral portion 2B formed on the outer peripheral side. The outer peripheral portion 2B is formed having a predetermined thickness in the radial direction from the outer circumferential surface 2a. The outer peripheral portion 2B is formed to surround the inner peripheral portion 2A across the entire region in the circumferential direction and the axial direction.

As illustrated in FIG. 3A, the outer peripheral portion 2B is formed with nonwoven fabric 11 including abrasive grains 12. The abrasive grains 12 are held in fibers of the nonwoven fabric 11 via an adhesive 13. Note that the adhesive 13 also functions to bond the fibers of the nonwoven fabric 11 together. According to such a configuration, when the outer peripheral portion 2B comes into contact with the surface to be polished BF of the object W (see FIG. 2), the surface to be polished BF can be polished with the abrasive grains 12. As illustrated in FIG. 3B, the inner peripheral portion 2A is formed with the nonwoven fabric 11 not including the abrasive grains 12. The abrasive grains 12 are not attached to the nonwoven fabric 11 of the inner peripheral portion 2A. Note that the inner peripheral portion 2A may include the adhesive 13 to bond fibers of the nonwoven fabric 11 together. Note that the inner peripheral portion 2A may include no abrasive grains 12, but when the inner peripheral portion 2A has a cushioning function as described below, the inner peripheral portion 2 A may include a slight amount of the abrasive grains 12.

As the nonwoven fabric used in the abrasive portion 2, nonwoven fabric including polyamide (for example, nylon 6 and nylon 6,6 including polycaprolactam or polyhexamethyl adipamide), a polyolefin (for example, polypropylene and polyethylene), a polyester (for example, polyethylene terephthalate), and a thermoplastic organic fiber such as polycarbonate may be used. Nonwoven fabric including nylon and polyester fibers are commonly used.

The thickness of the fiber is generally approximately from 19 to 250 pm. Intersecting, contacting points of the arranged fibers are bonded to each other by friction force, adhesive force, and the like. Bonding between the fibers may be made by using the adhesive 13 as described above, but may be made by the fibers themselves being melted.

The abrasive grains 12 include any known abrasive material, and a combination and an agglomerate of such materials. Examples of a soft abrasive material include, but are not limited to, an inorganic material such as flint, silica, pumice, and calcium carbonate, and an organic polymer material such as polyester, polyvinyl chloride, methacrylate, methyl methacrylate, polycarbonate, and polystyrene, and a combination of any of the above-described materials. Examples of a hard abrasive material include, but are not limited to, aluminum oxide such as aluminum oxide, heat- treated aluminum oxide, and white aluminum oxide, and silicon carbide, alumina zirconia, diamond, ceria, cubic boron nitride, garnet, and a combination thereof.

As the adhesive 13, a thermoset adhesive such as an aqueous suspension and an organic solvent solution of epoxy, melamine, phenol, isocyanate and isocyanurate resins, or a rubber-based polymer solution or suspension of SBR, SBS, SIS, and the like can also be used. These are applied to fibers by an immersion coating method, a roll coating method, a spray coating method, and the like, and cured to form nonwoven fabric. The adhesive 13 that bonds the fibers of the nonwoven fabric together may be different from or the same as the adhesive 13 that bonds the fibers of the nonwoven fabric 11 and the abrasive grains 12. When the same adhesive 13 is used, the bonding between the fibers of the nonwoven fabric 11 and the bonding between the fibers of the nonwoven fabric 11 and the abrasive grains 12 may be performed simultaneously.

Next, relationship between the inner peripheral portion 2A and the outer peripheral portion 2B will be described in further detail with reference to FIGS. 2, 4A and 4B. As described above, the inner peripheral portion 2A includes no abrasive grains 12 in the nonwoven fabric 11, and the outer peripheral portion 2B includes the abrasive grains 12 in the nonwoven fabric 11.

Accordingly, the abrasive portion 2 includes the outer peripheral portion 2B that is hard and formed on the outer peripheral side, and the inner peripheral portion 2A that is softer than the outer peripheral portion 2B. Thus, the abrasive portion 2 includes the inner peripheral portion 2A that functions as a cushion member at a position on the inner peripheral side than the outer peripheral portion 2B with which polishing is performed. Accordingly, as illustrated by an imaginary line in FIG. 2, when the outer circumferential surface 2a of the abrasive portion 2 is relatively subjected to force F from the outer side in the radial direction, the inner peripheral portion 2A easily deforms, and thus the outer circumferential surface 2a easily deforms toward the inner peripheral side.

A radius (R0) of the outer circumferential surface 2a of the abrasive portion 2 is not particularly limited, but is set to approximately from 10 to 600 mm or from 20 to 300 mm, for example. A radius of an outer circumferential surface of the core member 3 is not particularly limited, but is set to be in the range approximately from 2 to 400 mm or from 3 to 200 mm, for example. The size (width) in the axial direction of the abrasive portion 2 is not particularly limited, but is set to be in the range approximately from 5 to 3000 mm or from 10 to 1500 mm, for example.

The thickness in the radial direction of the abrasive portion 2 is referred to as a“thickness Rl,” and the thickness in the radial direction of the outer peripheral portion 2B is referred to as a “thickness R2.” At this time, a ratio of the thickness R2 of the outer peripheral portion 2B to the thickness Rl of the abrasive portion 2 (= R2 ^c 100/Rl) may be set to 3% or more, and may preferably be set to 5% or more, and may be set to 10% or more. Thus, it is possible to suppress the occurrence of early wear, cracking, and the like of the outer peripheral portion 2B due to the outer peripheral portion 2B being too thin. In addition, maximum abrasive force of the abrasive portion 2 can be increased. Here, as indicated by“MG” in FIG. 7A, the maximum abrasive force refers to abrasive force by which roughness of the object W becomes substantially constant, regardless of increased pressing of the abrasive portion 2 against the object W. The maximum abrasive force is substantially equal to maximum abrasive force of an abrasive portion including the abrasive grains 12 in the entire region in the radial direction (maximum abrasive force of a graph G2 in FIG. 7A). When R2 ^c 100/Rl is within a predetermined range, a graph will have multiple stages as in a graph G1 in FIG. 7A (two stages in the case of the graph Gl). That is, in addition to a region of the maximum abrasive force, a region in which there is little change in roughness due to increased pressing (the region may be referred to as first stage abrasive force) appears. That is, a plurality of stages of roughness or amounts of abrasion can be achieved with a single wheel. In addition, the ratio may be set to 60% or less, or may be set to 50 % or less, or may be set to 40 % or less. Accordingly, it is possible to suppress difficulty in adjustment of roughness due to the outer peripheral portion 2B becoming too thick and the abrasive portion 2 becoming difficult to deform.

The maximum abrasive force varies depending on an object or application. Abrasive force is expressed by an amount of abrasion and roughness. The amount of abrasion and the roughness are correlated as long as a similar manufacturing method and a similar abrasive material are used. For example, a larger abrasive grain diameter is associated with a greater amount of abrasion and greater roughness. For example, the abrasive force is generally expressed by the roughness as in FIG. 7A in the case of finishing application, while the abrasive force is generally expressed by the amount of abrasion in the case of coarse abrasion application. Then, lower limit values and upper limit values of these are also different. In any case of application, a difference between the maximum abrasive force and the first stage abrasive force widens in the case of predetermined maximum abrasive force or more, and a multi-stage shape such as the graph G1 clearly appears. That is, a plurality of stages of abrasive force can be achieved easily with a single wheel.

Durometer hardness of the outer peripheral portion 2B of the abrasive portion 2 may be 80 or greater, may be 85 or greater, or may be 90 or greater. Note that a durometer hardness measurement method is based on JIS K 6253 (IS07619, ASTM D2240). More specifically, the grinding wheel 1 of a 50 mm width is placed lying with its radial direction horizontal to the ground, and a durometer GS-719N manufactured by Teclock Corporation was pressed against the outer peripheral portion 2B from the vertical direction (direction orthogonal to the radial direction) with respect to the ground to perform the measurement. Thus, the maximum abrasive force of the abrasive portion 2 can be increased. When the maximum abrasive force of the abrasive portion 2 is high, the width of an adjustment margin (plurality of stages) of the abrasive force becomes wider. Hardness of the outer peripheral portion 2B of the abrasive portion 2 is adjusted by, in addition to hardness of the nonwoven fabric itself, a type and an amount of an adhesive incorporated in the outer peripheral portion 2B and a type and an amount of abrasive grains incorporated in the outer peripheral portion 2B. In addition, the hardness of the outer peripheral portion 2B is also adjusted by the amount of abrasive grains incorporated in the outer peripheral portion 2B. For example, when a comparison is made between the case of using a urethane resin as an adhesive and the case of using a phenol resin as an adhesive, the outer peripheral portion 2B using a phenol resin becomes harder than the outer peripheral portion 2B using a urethane resin. That is, the maximum abrasive force is higher in the case of the outer peripheral portion 2B using a phenol resin than the case of the outer peripheral portion 2B using a urethane resin. An upper limit of the durometer hardness of the outer peripheral portion 2B of the abrasive portion 2 is not particularly limited (note that the maximum of durometer hardness is 100).

Next, a layer configuration of the abrasive portion 2 will be described with reference to FIGS. 4A and 4B. As illustrated in FIG. 4A, the abrasive portion 2 is constituted by laminating a plurality of nonwoven fabric sheets 10. The plurality of nonwoven fabric sheets 10 are laminated with respect to the core member 3 in a direction substantially perpendicular to the radial direction (that is, in any of the circumferential direction and the axial direction). In the present embodiment, the nonwoven fabric sheets 10 are laminated in the circumferential direction with respect to the core member 3. The plurality of nonwoven fabric sheets 10 extend radially outward from the outer circumferential surface of the core member 3 in the radial direction. The nonwoven fabric sheets 10 adjacent in the circumferential direction are disposed in close contact with each other with no gap. In this way, the nonwoven fabric sheets 10 that are in close contact with each other in the circumferential direction are provided throughout the entire circumference in the circumferential direction.

FIG. 4B is a cross-sectional view taken from the direction of an IVb arrow in FIG. 4A. As illustrated in FIG. 4B, each one of the nonwoven fabric sheets 10 extends in the radial direction and in the axial direction. The inner peripheral portion 2A and the outer peripheral portion 2B are not divided into the nonwoven fabric sheets 10 different from each other, but a region

corresponding to the inner peripheral portion 2A and a region corresponding to the outer peripheral portions 2B are formed within one nonwoven fabric sheet 10. That is, in the radial direction, the nonwoven fabric 11 constituting the inner peripheral portion 2A and the nonwoven fabric 11 constituting the outer peripheral portion 2B are integrally constituted (diagonal lines in an entirety of FIG. 4B indicate this).

Next, with reference to FIG. 5, a method of manufacturing the grinding wheel 1 according to the present embodiment will be described. FIG. 5 is a conceptual view illustrating a method of manufacturing the grinding wheel 1 according to the present embodiment. As illustrated in the left most view in FIG. 5, first, the plurality of nonwoven fabric sheets 10 are overlapped to form a preform 17 of the abrasive portion 2. The preform 17 is disposed along the outer circumferential surface of the core member 3. An inner circumferential surface of the preform 17 is bonded to the outer circumferential surface of the core member 3. Then, both end surfaces of the preform 17 are bonded and fixed to each other, and thus the preform 17 constituted in a cylindrical shape is fixed to the outer circumferential surface of the core member 3 as illustrated in the second view from the left in FIG. 5. Such a step corresponds to a step of laminating the plurality of nonwoven fabric sheets 10 with respect to the core member 3 in the circumferential direction.

Next, as illustrated in the third view from the left in FIG. 5, a paste P including the abrasive grains 12 and an adhesive is attached only to a portion near an outer circumferential surface of the preform 17. The paste P is preferably a flowable liquid. Specifically, only the vicinity of the outer circumferential surface of the preform 17 is immersed in the paste P in a container, and the core member 3 is rotated. Thus, a configuration in which the abrasive grains 12 have penetrated the nonwoven fabric over the entire periphery in the vicinity of the outer circumferential surface of the preform 17 is made. However, rather than the configuration in which the entire periphery is immersed by rotating, a configuration in which only a portion of the periphery (for example, in stripes or in islands) is immersed may be made.

Here, as illustrated in FIG. 6, the manufacturing method includes the steps of forming a gap SP between the nonwoven fabric sheets 10 adjacent to each other in the circumferential direction, and incorporating abrasive grains in an outer peripheral edge portion of each of the nonwoven fabric sheets 10 between which the gap SP is formed.

As illustrated in FIG. 6, specifically, a protrusion 51 is formed in a bottom 50 of a container. The outer peripheral edge portion of the nonwoven fabric sheet 10 that is rotating is spaced apart from the other nonwoven fabric sheet 10 adjacent in the circumferential direction by interference with the protrusion 51. Thus, a gap is formed between the nonwoven fabric sheet 10 interfering with the protrusion 51 and the other nonwoven fabric sheet 10. As the rotation progresses further from that state, the nonwoven fabric sheet 10 having interfered with the protrusion 51 rides over the protrusion 51. Then, the nonwoven fabric sheet 10 having ridden over forms the gap SP with the nonwoven fabric sheet 10 to next interfere with the protrusion 51.

Since the protrusion 51 is formed in the bottom 50 of the container, a place where the gap SP is formed between the nonwoven fabric sheets 10 is filled with the paste P. Accordingly, the paste P together with the abrasive grains penetrates the gap SP between the nonwoven fabric sheets 10. Thus, the abrasive grains sufficiently penetrate the outer peripheral edge portion of the nonwoven fabric sheet 10.

Returning to FIG. 5, as illustrated in the fourth view from the left, an excess of the paste P is removed by rotating the abrasive portion 2 after the paste P is applied. As illustrated in the rightmost view of FIG. 5, the paste P is dried and thus the abrasive portion 2 includes the outer peripheral portion 2B including the abrasive grains and the inner peripheral portion 2A not including the abrasive grains.

Next, an operation and an effect of the grinding wheel 1 according to the present embodiment will be described.

The grinding wheel 1 is the grinding wheel 1 including the abrasive portion 2 including the nonwoven fabric 11, wherein the abrasive portion 2 includes the outer peripheral portion 2B formed with the nonwoven fabric 11 including the abrasive grains 12 on the outer peripheral side, and the inner peripheral portion 2A formed with the nonwoven fabric 11 not including the abrasive grains 12, and the ratio of the thickness in the radial direction of the outer peripheral portion to the thickness in the radial direction of the abrasive portion is from 3% to 60%.

The abrasive portion 2 includes the outer peripheral portion 2B formed with the nonwoven fabric 11 including the abrasive grains 12 on the outer peripheral side, and the inner peripheral portion 2A formed with the nonwoven fabric 11 not including the abrasive grains 12. Since the inner peripheral portion 2A is formed with the nonwoven fabric 11 not including the abrasive grains 12, the inner peripheral portion 2A is softer than the outer peripheral portion 2B. When the abrasive portion 2 is pressed against the object W, the inner peripheral portion 2A deforms, and thus functions as a cushion against the outer peripheral portion 2B. Therefore, rising of the abrasive force with respect to the pressing amount of the abrasive portion 2 becomes gentle. In this case, the roughness of the surface to be polished of the object W can be adjusted by adjusting the pressing amount of the abrasive portion 2. In addition, the ratio of the thickness in the radial direction of the outer peripheral portion to the thickness in the radial direction of the abrasive portion is from 3% to 60%. Since the ratio is 3% or more, it is possible to suppress the occurrence of early wear, cracking, and the like of the outer peripheral portion 2B due to the outer peripheral portion 2B being too thin. In addition, the maximum abrasive force of the abrasive portion 2 can be increased. Since the ratio is 60% or less, it is possible to suppress difficulty in adjustment of roughness due to the outer peripheral portion 2B becoming too thick and the abrading portion 2 becoming difficult to deform.

For example, FIG. 7A is a graph illustrating changes in abrasive force of the grinding wheel 1 according to the embodiment and a grinding wheel according to a comparative example. The grinding wheel according to the comparative example includes an abrasive portion including abrasive grains in the entire region. That is, the grinding wheel according to the comparative example does not include a place that functions as a cushion, such as the inner peripheral portion 2A of the abrasive portion 2 of the present embodiment. The“depth” in the horizontal axis indicates an amount of the depth of pressing (pressing amount), and is a value indicating how far the abrasive portion 2 is pressed against the object W. The depth is 0 when the outer peripheral portion 2B of the grinding wheel 1 touches the object W, and a numerical value increases as the distance from the center of the grinding wheel 1 to the object W shortens. The vertical axis indicates the roughness of the surface to be polished BF of a surface of the object W polished by the abrasive portion 2, and indicates a value indicating the abrasive force of the abrasive portion 2. The graph G1 shows results obtained when polishing is performed with the grinding wheel 1 according to the embodiment, and the graph G2 shows results obtained when polishing is performed with the grinding wheel according to the comparative example.

As shown in the graph G2, the abrasive force of the grinding wheel according to the comparative example immediately increases to the maximum abrasive force when the pressing amount is even slightly increased. In this case, it is not possible to adjust the abrasive force by adjusting the pressing amount. On the other hand, as shown in the graph Gl, the abrasive force of the grinding wheel 1 according to the embodiment gradually rises in a state where the pressing amount is low. In the graph Gl, as shown by“FG,” a place where the abrasive force does not substantially change with respect to the increase in the pressing amount is formed. When the pressing amount is increased further, the abrasive force gradually increases, and when the maximum abrasive force is reached, the abrasive force becomes substantially constant. Since the pressing amount and the abrasive force of the grinding wheel 1 have relationship such as the graph Gl, it is possible to use the grinding wheel 1 in the following manner. When the object W is polished, first, as illustrated in FIG. 7C, the polishing is performed in a state where the pressing amount of the grinding wheel 1 against the object W is increased. In this case, the polishing (for example, rough finish) can be performed with the grinding wheel 1 in a state where the abrasive force is large (see MG in the graph Gl in FIG. 7A). Next, as illustrated in FIG. 7B, the polishing is performed in a state where the pressing amount of the grinding wheel 1 against the object W is reduced, and thus the polishing (for example, fine finish) can be performed with the grinding wheel 1 in a state where small abrasive force but fine roughness are obtained (see FG in the graph Gl in FIG. 7A). According to the use in such a manner, finish polishing can be performed with the grinding wheel 1 alone, without providing a grinding wheel for rough finish and a grinding wheel for fine finish.

In addition, the grinding wheel 1 according to the present embodiment includes less abrasive grains 12 (or no abrasive grains 12) in the inner peripheral portion 2 A than in the outer peripheral portion 2B with which polishing is performed. Accordingly, since the amount of the abrasive grains 12 used in the grinding wheel 1 can be suppressed, a manufacturing cost can be suppressed.

In addition, the abrasive portion 2 of the grinding wheel 1 includes the inner peripheral portion 2A that functions as a cushion. Accordingly, the abrasive portion 2 with which polishing is performed can, to some extent, follow a shape of the surface to be polished BF of the object W.

In addition, the grinding wheel 1 according to the present embodiment is the grinding wheel 1 including the abrasive portion 2 including the nonwoven fabric 11, wherein the abrasive portion 2 includes the outer peripheral portion 2B formed on the outer peripheral side, and the inner peripheral portion 2A softer than the outer peripheral portion 2B, and the ratio of the thickness in the radial direction of the outer peripheral portion to the thickness in the radial direction of the abrasive portion is from 3% to 60%.

The inner peripheral portion 2A is softer than the outer peripheral portion 2B. When the abrasive portion 2 is pressed against the object W, the inner peripheral portion 2A deforms, and thus functions as a cushion against the outer peripheral portion 2B. Thus, it is possible to obtain the same actions and effects as those described above.

The abrasive portion 2 is constituted by laminating a plurality of nonwoven fabric sheets, and the plurality of nonwoven fabric sheets are laminated in a direction substantially perpendicular to the radial direction. For example, when a long-length nonwoven fabric sheet is spirally wound on a core member, the nonwoven fabric sheet is laminated in the radial direction. In contrast, in the grinding wheel 1 according to the present embodiment, the nonwoven fabric sheets 10 are laminated in a direction substantially perpendicular to the radial direction. The nonwoven fabric sheets 10 are laminated in the circumferential direction. That is, the nonwoven fabric sheets 10 are provided to be radially formed with respect to the core member 3.

In this case, as illustrated in FIGS. 8A to 8E, unlike the case in which the nonwoven fabric sheet 10 is laminated in the axial direction, a trace can be prevented from remaining at a position corresponding to a boundary between the nonwoven fabric sheets 10 in the polished surface BF, without moving the grinding wheel 1 in the axial direction while performing polishing.

The durometer hardness of the outer peripheral portion 2B is 80 or more. In this case, it is possible to suppress reduction in the maximum abrasive force of the outer peripheral portion 2B.

The nonwoven fabric 11 of the outer peripheral portion 2B includes any of silicon carbide, diamond, and aluminum oxide as the abrasive grains 12. In this case, predetermined abrasive force is obtained.

The method of manufacturing the grinding wheel 1 according to an aspect of the present embodiment is the method of manufacturing the grinding wheel 1 including the core member 3 and the abrasive portion 2 provided around the outer periphery of the core member 3 and constituted by laminating the plurality of nonwoven fabric sheets 10, the method including the steps of, laminating the plurality of nonwoven fabric sheets 10 in the circumferential direction, forming a gap between the nonwoven fabric sheets 10 adjacent to each other in the circumferential direction, and incorporating the abrasive grains 12 in the outer peripheral edge portion of each of the nonwoven fabric sheets 10 between which the gap is formed.

The gap is formed between the nonwoven fabric sheets 10 in this way, and thus a state in which the abrasive grains 12 easily penetrate the nonwoven fabric sheets 10 can be achieved.

Then, the abrasive grains 12 are incorporated in the nonwoven fabric sheets 10 being in a state in which the gap is formed, and thus the abrasive grains 12 easily penetrate the nonwoven fabric sheets 10.

In the embodiment described above, the nonwoven fabric sheets 10 were laminated in the circumferential direction. Alternatively, the nonwoven fabric sheets 10 may be laminated in the axial direction. For example, as illustrated in FIGS. 8C and 8E, the abrasive portion 2 may be formed by overlapping in the axial direction a plurality of nonwoven fabric sheets 20 each having a disk shape.

In this case, examples of a manufacturing method include a manufacturing method illustrated in FIGS. 8A to 8C, and a manufacturing method illustrated in FIGS. 8D and 8E. In one of the manufacturing methods, as illustrated in FIG. 8A, an abrasive material (including the abrasive grains 12 and an adhesive) is applied to each nonwoven fabric sheet 20 having a disk- shape only at a position corresponding to an outer peripheral portion 20A by spraying or the like. Subsequently, as illustrated in FIG. 8B, an adhesive is applied to an entire surface of the nonwoven fabric sheet 20 having a disk shape. Next, as illustrated in FIG. 8C, the plurality of nonwoven fabric sheets 20 to which the adhesive has been applied are laminated in the axial direction. In the other manufacturing method, as illustrated in FIG. 8D, an abrasive material (including the abrasive grains 12 and an adhesive) is applied to each nonwoven fabric sheet 20 having a disk shape only at a position corresponding to the outer peripheral portion 20A by spraying or the like. Subsequently, as illustrated in FIG. 8E, the plurality of nonwoven fabric sheets 20 are laminated in the axial direction and held by a holder 25 from both sides in the axial direction.

Second Embodiment

Next, a grinding wheel 100 according to a second embodiment will be described with reference to FIG. 10. According to this grinding wheel 100, while an amount of abrasive grains is suppressed to suppress a manufacturing cost, adjustment of abrasive performance according to a need is facilitated, and at the same time abrasive performance can be stabilized even when polishing progresses and an outer peripheral portion 2B is shaved.

Specifically, in addition to an inner peripheral portion 2A and the outer peripheral portion 2B, an abrasive portion 2 of the grinding wheel 100 includes an intermediate portion 2C between the outer peripheral portion 2B and the inner peripheral portion 2A, as a layer different from the outer peripheral portion 2B and the inner peripheral portion 2A.

The thickness in the radial direction of the abrasive portion 2 is referred to as a“thickness Rl,” and the thickness in the radial direction of the intermediate portion 2C is referred to as a “thickness R3.” At this time, a ratio of a sum of the thickness R3 of the intermediate portion 2C and the thickness R2 of the outer peripheral portion 2B to the thickness Rl of the abrasive portion 2 (= (R3 + R2) x 100/Rl) may be set to 3% or more, may preferably be set to 5% or more, and may be set to 10 % or more.

The intermediate portion 2C includes at least a resin material. A similar material to the materials exemplified for the above-described adhesive 13 can be used as the resin material. The outer peripheral portion 2B and the intermediate portion 2C may include the same resin material. Alternatively, the outer peripheral portion 2B and the intermediate portion 2C may include different resin materials.

Hardness of the intermediate portion 2C will be described. The hardness of the intermediate portion 2C may be set appropriately according to abrasive performance required of the grinding wheel 100, and the like. The intermediate portion 2C may be harder than the inner peripheral portion 2A. Durometer hardness of the intermediate portion 2C may be, for example, +1 or more, may be +3 or more, or may be +5 or more as compared to the inner peripheral portion 2A. In this case, the intermediate portion 2C can support the outer peripheral portion 2B more firmly than the inner peripheral portion 2A. For example, a state such as hardness of the outer peripheral portion 2B changes between the start of polishing and after polishing for a long period of time. The intermediate portion 2C supports the outer peripheral portion 2B more firmly than the inner peripheral portion 2A, and thus can reduce the influence of the change in the outer peripheral portion 2B. Thus, the abrasive performance of the grinding wheel 100 can be stabilized.

The intermediate portion 2C may be harder than, softer than, or as hard as the outer peripheral portion 2B. However, when the intermediate portion 2C is harder than the outer peripheral portion 2B, the intermediate portion 2C that is hard can support the outer peripheral portion 2B from underneath to suppress deformation of the outer peripheral portion 2B that is soft and that attempts to deform toward the inner peripheral side more than necessary at the time of polishing. Note that in a case where the intermediate portion 2C is made harder than the outer peripheral portion 2B, the durometer hardness of the intermediate portion 2C may be, for example, +1 or more, may be +3 or greater, or may be +5 or greater, as compared to the outer peripheral portion 2B.

When the outer peripheral portion 2B includes a lubricant, the effect of the intermediate portion 2C supporting the outer peripheral portion 2B from underneath becomes more significant. The lubricant may be of powder or may be of liquid. The lubricant functions as a material for suppressing a“smear” (smearing inhibitor) during polishing. Generally undesirable smearing may occur when a workpiece that is in contact with the resin material of the outer peripheral portion 2B becomes sufficiently hot, and some of the resin material of the outer peripheral portion 2B softens and moves to the workpiece. When the lubricant is incorporated in the outer peripheral portion 2B in this manner, although smearing can be suppressed, the outer peripheral portion 2B becomes soft. In this case, the intermediate portion 2C that is hard can suppress deformation of the outer peripheral portion 2B that becomes soft due to the influence of the lubricant and that attempts to deform toward the inner peripheral side more than necessary during polishing.

Examples of the lubricant include a metal salt of a fatty acid (for example, lithium stearate, zinc stearate), a solid lubricant (for example, (poly) tetrafluoroethylene (PTFE), graphite and molybdenum disulfide), mineral oil and wax, carboxylic acid ester (for example, butyl stearate), poly (dimethylsiloxane) gum, and a combination thereof. Such lubricants and sources of such commercially available lubricants are known in the art.

A method of manufacturing the grinding wheel 100 according to the second embodiment will be described. First, as illustrated in FIG. 5, a case where a paste P is attached in the vicinity of an outer circumferential surface of a preform 17 will be described. In this case, first, the paste P associated with the resin material for forming the intermediate portion 2C is attached to the preform 17. Subsequently, the paste P associated with the resin material for forming the outer peripheral portion 2B is attached to the preform 17. In the second attachment step, the paste P is prevented from being attached to a portion corresponding to the intermediate portion 2C, and the paste P is attached only to a portion corresponding to the outer peripheral portion 2B.

The method illustrated in FIGS. 8 A to 8E may also be used for manufacturing the grinding wheel 100 according to the second embodiment. In this case, the resin material for the outer peripheral portion 2B is applied to the portion corresponding to the outer peripheral portion 2B, and the resin material for the intermediate portion 2C is applied to the portion corresponding to the intermediate portion 2C.

As described above, in the grinding wheel 100 according to the second embodiment, the abrasive portion 2 includes the outer peripheral portion 2B formed on the outer peripheral side, the inner peripheral portion 2A softer than the outer peripheral portion 2B, and the intermediate portion 2C disposed between the outer peripheral portion 2B and the inner peripheral portion 2A, the intermediate portion 2C being a layer different from the outer peripheral portion 2B and the inner peripheral portion 2A, and including at least the resin material.

When the abrasive portion 2 includes only the inner peripheral portion 2A and the outer peripheral portion 2B, parameters that can be adjusted according to required abrasive performance are only sizes and materials of the two layers, but when the abrasive portion 2 includes the intermediate portion 2C, a size and a material of the intermediate portion 2C can also be adjusted. Accordingly, adjustment of the grinding wheel 100 according to required abrasive performance is facilitated. Note that since the grinding wheel 100 can correspond to various needs, for example, when polishing at two stages such as rough finish and fine finish as in the case of the first embodiment is not required, there may be a case where the abrasive performance as illustrated by the graph G2 in FIG. 7A is required. The grinding wheel 100 according to the second embodiment can correspond to the abrasive performance required in such polishing at one stage.

In addition, the grinding wheel 100 according to the second embodiment also includes less abrasive grains 12 (or no abrasive grains 12) in the inner peripheral portion 2 A than in the outer peripheral portion 2B with which polishing is performed. Accordingly, since an amount of the abrasive grains 12 used in the grinding wheel 100 can be suppressed, a manufacturing cost can be suppressed.

The intermediate portion 2C may be harder than the inner peripheral portion 2A. In this case, even when the hardness of the outer peripheral portion 2B changes between the start of polishing and after the progress of the polishing, abrasive performance can be stabilized by the intermediate portion 2C supporting the outer peripheral portion 2B.

The intermediate portion 2C may be harder than the outer peripheral portion 2B. In this case, even when the outer peripheral portion 2B is soft, the outer peripheral portion 2B can be supported from underneath and it is possible to suppress the outer peripheral portion 2B deforming too far toward the inner peripheral side.

The outer peripheral portion 2B may include the lubricant. The lubricant functions, for example, as a smearing inhibitor. In addition, although the outer peripheral portion 2B easily becomes soft when the lubricant is included, the intermediate portion 2C supports the outer peripheral portion 2B from underneath, and thus high abrasive performance can be exhibited while smearing is suppressed. The outer peripheral portion 2B and the intermediate portion 2C may include the same resin material. In this case, manufacturing is made easy. In addition, since there is no mixing of different resins when the outer peripheral portion 2B and the intermediate portion 2C are formed, product stability is improved.

EXAMPLES

Next, examples will be described, but the grinding wheel according to the present disclosure is not limited to the following grinding wheels.

Grinding wheels according to Examples 1 to 4 and a grinding wheel according to a comparative example were prepared. In the grinding wheel of each of Example 1 to 4 and the comparative example, an overall radius was 152.5 mm, the thickness in the radial direction of the entire abrasive portion was 84 mm, and a dimension in the axial direction (width of the grinding wheel) was 50 mm. Then, an outer peripheral portion of the grinding wheel of Example 1 had a thickness in the radial direction of 5 mm (ratio is 5.9%). An outer peripheral portion of the grinding wheel of Example 2 had a thickness in the radial direction of 10 mm (ratio is 11.9%) . An outer peripheral portion of the grinding wheel of Example 3 had a thickness in the radial direction of 20 mm (ratio is 23.8%). An outer peripheral portion of the grinding wheel of Example 4 had a thickness in the radial direction of 30 mm (ratio is 35.7%). The grinding wheel of the comparative example had no outer peripheral portion and no inner peripheral portion, and an abrasive portion entirely included abrasive grains (ratio is 100%).

Other conditions for the grinding wheels of Examples 1 to 4 and the comparative example were as follows. That is, an adhesive for holding abrasive grains was an adhesive based on a phenol resin. A material of the abrasive grains was silicon carbide. Nonwoven fabric sheets were laminated in the circumferential direction. The outer peripheral portion included the abrasive grains by an amount of 162 gram. The inner peripheral portion included no abrasive grains in nonwoven fabric. As regards durometer hardness of the outer peripheral portions of such grinding wheels, the durometer hardness was 93.2 for the comparative example, 90.4 for Example 1, 92.1 for Example 2, 92.6 for Example 3, and 93 for Example 4. In addition, an object made of a material such as JIS G 3141 compliant SPCC-SB (cold-rolled steel plate, standard hardness, and bright finish) was polished while the depth was changed. Conditions of a planar abrader were as follows:“wheel rotation speed: 2000 rpm, test work feed speed: 1 MPM, lubricant: water.” Roughness of a polished surface of the object was measured. Measurement results are shown in FIG. 9.

In an experiment of FIG. 9, to confirm the effect specific to the grinding wheel according to the first embodiment, observation was made in a viewpoint of whether a plurality of stages of abrasive force can be applied stably to the surface to be polished of the object. Here, although the grinding wheel according to the second embodiment includes a grinding wheel that exhibits a curve close to that of“Comparative Example” in FIG. 9 in the experiment of FIG. 9, the effect of the second embodiment is not denied, and the second embodiment is not excluded from the scope of the present invention.