Grinding stone and grinding method

Abstract

[Problem] To provide a grinding stone rod that aims to improve the surface roughness and wear resistance of the grinding surface of a workpiece. [Solution] The grinding stone rod (10) of Examples 1 and 2 is used to grind the grinding surface (S) of a workpiece (W) by pressing the front end (17) against the grinding surface (S). The grinding stone rod (10) of Examples 1 and 2 comprises inorganic long fibers (15) and resin (16) impregnated in the inorganic long fibers (15) and hardened. The inorganic long fibers (15) comprises 80-90% by weight of alumina and 20-10% by weight of silicon dioxide. The crystal structure of the inorganic long fibers (15) is that of intermediate alumina, while the silicon dioxide is in an amorphous state, and the BET specific surface area of ​​the inorganic long fibers (15) is less than 30 m² / g.

Description

Technical Field

[0001] The present invention relates to a grinding stone stick and a grinding method using the grinding stone stick. Prior Art

[0002] Patent Document 1 describes a rod-shaped grinding stone made by impregnating a bundle of inorganic long-fiber filaments with resin and curing it. The grinding stone described in the same document is used for polishing molds. The grinding stone has a rectangular or circular cross-section and is elastic enough to bend in a direction intersecting its axis. The inorganic long-fiber filaments extend in the direction of the grinding stone's axis, with the filaments exposed at the front end.

[0003] In Patent Document 1, when grinding the target surface of a workpiece, the base of the grinding stone rod is held in a tool holder. Furthermore, the tool holder is connected to the spindle of a machine tool, which rotates, pressing the tip of the grinding stone rod against the target surface of the workpiece. Here, the tool holder converts the spindle's rotation into linear reciprocating motion and rotational motion along the spindle's axis. Therefore, the tip of the grinding stone rod is intermittently pressed against the workpiece, grinding the target surface. Furthermore, the tip of the grinding stone rod rotates while in contact with the workpiece, grinding the target surface.

[0004] Patent Document 2 describes an abrasive for a grindstone. The abrasive in the same document is composed of inorganic long fibers impregnated with resin. The inorganic long fibers contain 80-90% by weight of alumina and 20-10% by weight of silica. The crystal structure of the inorganic long fibers consists of mullite crystals and intermediate alumina. The average particle size of the mullite crystals is 25 to 70 nm. The abrasive in the same document, containing at least 80% by weight of alumina, has high hardness. Furthermore, the average particle size of the mullite crystals is at least 25 nm, resulting in a high grinding force for grinding and polishing workpieces.

[0005] Patent Document 2 describes a rectangular parallelepiped grindstone made of the aforementioned abrasive. When grinding a workpiece, the entire side surface of the grindstone, extending in the longitudinal direction, is pressed against the workpiece's surface. Furthermore, the grindstone is moved back and forth along the surface. [Prior Art Literature] [Patent Document]

[0006] [Patent Document 1] Japanese Patent No. 6832555 [Patent Document 2] Japanese Patent Application Laid-Open No. 10-183427 Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] If the abrasive material for a grindstone described in Patent Document 2 is formed into a rod shape and used as a grindstone rod, the grindstone rod can provide sufficient grinding force. However, with the recent advancement in precision molds, the grindstone rod composed of the abrasive material for a grindstone described in Patent Document 2 may not be able to achieve the desired surface roughness through grinding. Furthermore, after intensive research, the inventors discovered that the wear resistance of the grindstone rod composed of the abrasive material for a grindstone described in Patent Document 2 could be improved.

[0009] In view of this, the present invention aims to provide a grinding stone rod capable of improving the surface roughness and wear resistance of the grinding target surface of a workpiece. In addition, a grinding method using such a grinding stone rod is proposed. [Methods used to solve the problem]

[0010] The present inventors, through dedicated research, have discovered that when an inorganic long fiber having an alumina component of 80-90% by weight and a silica component of 20-10% by weight, and a crystal structure of the inorganic long fiber having an intermediate composition of alumina and mullite, is used as a grinding stone, the larger the mullite crystal grains in the crystal structure, the more likely scratches (grinding scars) will form on the grinding surface of a workpiece.

[0011] The inventors, through intensive research, have discovered that when inorganic long fibers containing 80 to 90% by weight of alumina and 20 to 10% by weight of silica, with a crystal structure composed of intermediate alumina and mullite, are used as a grinding wheel, the larger the mullite grains in the structure, the greater the impact on the wear resistance of the grinding wheel. In other words, in inorganic long fibers with large grains, mullitization progresses. As mullitization progresses, the inorganic long fibers become brittle. When a rod-shaped grinding wheel using inorganic long fibers is used to grind the surface of a workpiece, the tip of the grinding wheel is pressed against the surface. Furthermore, because the rod-shaped grinding wheel has the elasticity to bend in a direction intersecting its axis, pressing the tip against the workpiece reduces the risk of the grinding wheel bouncing or vibrating on the surface, and the likelihood of the grinding wheel being damaged or broken is also reduced. Therefore, when pressing the tip of the grindstone against the surface to be polished, a relatively large pressure is applied, taking into account its elasticity, to ensure the desired grinding force. Consequently, the tip of the grindstone is susceptible to load, and as mullite formation progresses on the inorganic long fibers exposed at the tip, the inorganic long fibers become brittle and deform, leading to increased wear.

[0012] On the other hand, the present inventors have discovered that when an inorganic long fiber abrasive containing 80 to 90 weight percent alumina and 20 to 10 weight percent silica is used as a grindstone, if the specific surface area of ​​the inorganic long fibers is below a predetermined value, the grinding force of the grindstone can be maintained even without mullite crystals. In other words, if the inorganic long fibers contain at least 80 weight percent alumina, the hardness of the grindstone can be maintained. Furthermore, if the specific surface area of ​​the inorganic long fibers is below a predetermined value, the inorganic long fibers can be prevented from absorbing atmospheric moisture and hindering the curing of the resin impregnated with the inorganic long fibers. Furthermore, if the specific surface area of ​​the inorganic long fibers is below a predetermined value, the inorganic long fibers have fewer pores and irregularities, which can prevent air bubbles from remaining in the resin impregnated with the inorganic long fibers. Consequently, poor resin impregnation caused by air bubbles can be suppressed. This prevents the inorganic long fibers from becoming brittle and deforming when the tip of the grindstone is pressed against the workpiece to grind the surface. Furthermore, unlike with rectangular grindstones, where the entire side surface extending in the longitudinal direction contacts the surface to grind the workpiece, the tip of the grindstone can be pressed against the surface with a pressing force that takes into account the grindstone's elasticity. Consequently, the grindstone can maintain a predetermined grinding force. The present invention is based on these insights.

[0013] To solve the above-mentioned problems, the present invention is characterized by a rod-shaped grindstone that grinds a surface of a workpiece by pressing its front end against the surface to be polished. The grindstone comprises a plurality of inorganic long fibers extending in an axial direction and a resin impregnated and cured in the inorganic long fibers. The front end of the grindstone has a cross-section where the inorganic long fibers are exposed and has elasticity to bend in a direction intersecting the axial direction. The inorganic long fibers comprise 80 to 90% by weight of an alumina component and 20 to 10% by weight of a silica component. The inorganic long fibers have a crystal structure comprising intermediate alumina, with the silica component being amorphous, and a BET specific surface area of ​​28.7 m2 / g or less.

[0014] In the grindstone of the present invention, the silica component of the inorganic long fibers is in an amorphous state. Therefore, the crystal structure of the inorganic long fibers does not contain mullite crystals. This prevents scratches (grinding marks) on the polishing surface of the workpiece caused by mullite crystals. Consequently, the surface roughness of the polishing surface can be improved. Furthermore, in the grindstone of the present invention, the silica component of the inorganic long fibers is in an amorphous state. Therefore, the inorganic long fibers do not become brittle due to mullitization. Furthermore, the BET specific surface area of ​​the inorganic long fibers is 28.7 m² / g or less. Inorganic long fibers with such a BET specific surface area have fewer pores and irregularities, which suppresses moisture absorption. This prevents or suppresses the inorganic long fibers from absorbing atmospheric moisture, which could hinder the curing of the resin impregnated in the inorganic long fibers. Furthermore, inorganic long fibers with such a high BET specific surface area have fewer pores and irregularities, which prevents or minimizes poor resin impregnation into the grinding stone due to trapped air bubbles in the resin impregnated with the inorganic long fibers. This prevents embrittlement of the inorganic long fibers and damage to the grinding stone, improving the wear resistance of the grinding stone when the tip of the grinding stone is pressed against the surface of a workpiece.

[0015] On the other hand, inorganic long fibers contain at least 80% alumina by weight, making them easier to maintain. Furthermore, inorganic long fibers with a BET specific surface area of ​​28.7 m² / g or less can prevent moisture absorption, which could hinder the curing of the resin and cause the grindstone to become brittle. Furthermore, a low BET specific surface area prevents residual air bubbles in the resin impregnated with the inorganic long fibers, which could lead to poor resin impregnation and subsequent breakage of the grindstone. Consequently, when the tip of the grindstone is pressed against the surface of a workpiece for grinding, brittle deformation of the inorganic long fibers and the grindstone is suppressed, allowing the inorganic long fibers to grip the workpiece. Furthermore, when grinding and refining a workpiece using a rod-shaped grindstone, unlike with rectangular grindstones, where the entire side surface extending in the longitudinal direction contacts the surface, grinding can be performed with the tip pressed against the surface. Furthermore, because the rod-shaped grindstone has the elasticity to bend in a direction intersecting its axis, when the tip is pressed against the surface being ground, the grindstone is less likely to bounce or vibrate on the surface, reducing the likelihood of damage or breakage. Therefore, by pressing the tip of the grindstone against the surface with a force that takes into account the grindstone's elasticity, the desired grinding force can be achieved. Consequently, the grindstone maintains its desired grinding force even without mullite crystals in its crystal structure.

[0016] In the present invention, the BET specific surface area of ​​the inorganic long fibers is preferably 12.5 m² / g or less. This improves the grinding force of the grinding wheel compared to a BET specific surface area greater than 12.5 m² / g. Furthermore, this improves wear resistance compared to a BET specific surface area greater than 12.5 m² / g.

[0017] In the present invention, the alumina content of the inorganic long fibers is preferably 85% by weight or greater. This facilitates increasing the hardness of the inorganic long fibers and, therefore, ensuring the grinding force of the grindstone.

[0018] In the present invention, it is possible that the aforementioned resin is an epoxy resin.

[0019] In the present invention, the bending strength can be increased to 500 MPa or more and the bending modulus can be increased to 50 GPa or more. In this way, it is easy to increase the pressing force of the tip of the grindstone rod on the grinding target surface, thereby obtaining the desired grinding force.

[0020] Next, the grinding method of the present invention is characterized in that the grinding stone rod is attached to a vibrating tool, and the tip of the grinding stone rod is pressed against the grinding surface of the workpiece while vibrating in the axial direction. The grinding method performed while pressing the tip of the grinding stone rod against the grinding surface of the workpiece includes a grinding method performed while pressing the tip of the grinding stone rod against the grinding surface of the workpiece.

[0021] Furthermore, the grinding method of the present invention is characterized in that the grinding stone rod is attached to a vibrating tool, and the tip of the grinding stone rod is pressed against the grinding surface of the workpiece while vibrating in the direction of the axis and in a direction intersecting the axis of the grinding stone rod. The grinding method performed while pressing the tip of the grinding stone rod against the grinding surface of the workpiece includes a grinding method performed while pressing the tip of the grinding stone rod against the grinding surface of the workpiece.

[0022] Next, the grinding method of the present invention is characterized in that the grinding stone rod is mounted on a rotating tool, and the grinding stone rod is rotated while the tip end thereof is pressed against the grinding surface of the workpiece, wherein the grinding stone rod has a circular cross-section. The grinding method performed while the tip end of the grinding stone rod is pressed against the grinding surface of the workpiece includes a grinding method performed while the tip end of the grinding stone rod is pressed against the grinding surface of the workpiece. Simple diagram description

[0023] [Figure 1] is a perspective view of a grinding stone. FIG. 2 is an explanatory diagram of a method for grinding a workpiece using the grindstone of FIG. 1 . FIG. 3 is an explanatory diagram of another example of a method for grinding a workpiece using the grindstone rod of FIG. 1 . [Figure 4] is a perspective view of a cylindrical grinding stone. FIG. 5 is an explanatory diagram of a method for grinding a workpiece using the grindstone rod of FIG. 4 . FIG. 6 is an explanatory diagram of another example of a method for grinding a workpiece using the grindstone rod of FIG. 4 . FIG7 is a flow chart of a method for manufacturing a grinding stone rod. FIG8 is a diffraction pattern obtained by irradiating the inorganic long fibers of Example 1 with X-rays. FIG9 is a diffraction pattern obtained by irradiating the inorganic long fibers of Comparative Example 2 with X-rays. FIG. 10 is a roughness curve of the polishing target surface of a workpiece polished by the grindstone rod of Example 1. FIG. 11 is a roughness curve of the polishing target surface of a workpiece polished by the grindstone rod of Example 2. FIG. 12 is a roughness curve of the surface to be polished of a workpiece when the grindstone rod of Comparative Example 1 is used. FIG. 13 is a roughness curve of the polishing target surface of a workpiece polished by the grindstone rod of Comparative Example 2. FIG. 14 is a graph showing the amount of workpiece ground after the comparative test. FIG. 15 is a graph showing the wear amount of the grinding stone rod after the comparative test. FIG. 16 is a photograph of the side surface of the grinding stone rod of Example 2. FIG. 17 is a photograph of the side surface of the grinding stone rod of Comparative Example 1. Implementation Method

[0024] Hereinafter, a grinding stone rod according to an embodiment of the present invention will be described with reference to the drawings.

[0025] (Grindstone) FIG1 is a perspective view of a grindstone. FIG2 is an explanatory diagram of a method for grinding a workpiece using the grindstone of FIG1. ​​FIG3 is an explanatory diagram of another example of a method for grinding a workpiece using the grindstone of FIG1. ​​FIG4 is a perspective view of a cylindrical grindstone. FIG5 is an explanatory diagram of a method for grinding a workpiece using the grindstone of FIG4. FIG6 is an explanatory diagram of another example of a method for grinding a workpiece using the grindstone of FIG4.

[0026] As shown in Figure 1, the grindstone rod 10 is rod-shaped with a rectangular cross-section. In this embodiment, the grindstone rod 10 has a rectangular cross-section. The grindstone rod 10 comprises a plurality of inorganic long fibers 15 extending in the axial direction along its axis L, and a resin 16 impregnated and cured into the inorganic long fibers 15. The inorganic long fibers 15 are polycrystalline fibers containing 80 to 90% by weight of alumina and 20 to 10% by weight of silica. The cross-section of the inorganic long fibers 15 is exposed at the front end 17a of the grindstone rod 10.

[0027] The grindstone rod 10 has the elasticity to bend in a direction intersecting its axis L. The grinding stone rod 10 has a bending strength of 500 MPa or greater. The grinding stone rod 10 has a bending elasticity of 50 GPa or greater. More preferably, the grinding stone rod 10 has a bending strength of 800 MPa or greater and a bending elasticity of 65 GPa or greater. In FIG. 1 and other figures, the inorganic long fibers 15 are shown as chain lines for convenience. However, the inorganic long fibers 15 extend continuously from the distal end to the proximal end of the grinding stone rod 10. Furthermore, while the plurality of inorganic long fibers 15 may be inclined relative to the axis L of the grinding stone rod 10, the inclination angle in such cases is approximately 10°, and the maximum does not exceed 20°.

[0028] (Grinding method) As shown in Figure 2, a grindstone rod 10 is used with its base end attached to the head of a handheld vibration tool. The vibration tool is, for example, a pneumatic vibration tool or an ultrasonic vibration tool. The vibration tool reciprocates (vibrates) the grindstone rod 10 mounted on the head in an axial direction. The workpiece W that the grindstone rod 10 grinds is, for example, a mold for resin molding.

[0029] When grinding the workpiece W, the grindstone rod 10 presses its tip 17 obliquely against the grinding surface S of the workpiece W. Specifically, the grindstone rod 10 presses against the grinding surface S with its axis L forming an acute angle θ with the grinding surface S. In this embodiment, the grindstone rod 10 faces the grinding surface S with one of the long sides of its rectangular cross-section facing the grinding surface S. Furthermore, when grinding the workpiece W, the grindstone rod 10 is pressed against the grinding surface S of the workpiece W along the axis L with a predetermined pressing force F. Furthermore, as indicated by the arrow in FIG2 , the grindstone rod 10 vibrates in the axial direction while grinding the workpiece W. If the vibration tool 11 is a pneumatic vibration tool, the pneumatic vibration tool vibrates the grindstone rod 10 at a speed of 5000 st / min or more. If the vibration tool 11 is an ultrasonic vibration tool, the ultrasonic vibration tool vibrates the grindstone rod 10 at a speed of 15 kHz or more.

[0030] As shown in Figure 3 , the grindstone rod 10 has its front end face 17a pressed perpendicularly against the grinding surface S of the workpiece W, thereby grinding the workpiece W. In this case, the grindstone rod 10 is pressed against the grinding surface S with a pressing force F along the axis L. Furthermore, as indicated by the solid arrow in Figure 3 , the grindstone rod 10 is vibrated axially by the vibration tool 11. If the vibration tool 11 is a pneumatic vibration tool, the pneumatic vibration tool vibrates the grindstone rod 10 at a speed of 5000 st / min or higher. If the vibration tool 11 is an ultrasonic vibration tool, the ultrasonic vibration tool vibrates the grindstone rod 10 at a speed of 15 kHz or higher.

[0031] Here, as indicated by the solid and chain arrows in FIG3 , when a pneumatic vibration tool is used, the grinding stone 10 may be vibrated in the axial direction and in a direction perpendicular to the axis L. In this case, the pneumatic vibration tool oscillates the grinding stone 10 along an elliptical path between strokes that vibrate the grinding stone 10 in the axial direction, thereby vibrating the grinding stone 10 in the axial direction and in a direction perpendicular to the axis L. In this case, the pneumatic vibration tool vibrates the grinding stone 10 at a speed of 5000 st / min or more.

[0032] 2, when the front end portion 17 of the grindstone rod 10 is pressed against the grinding target surface S from an oblique direction to grind the workpiece W, there is also a case where the grindstone rod 10 is vibrated in the axial direction and in a direction perpendicular to the axis L.

[0033] Furthermore, as shown in FIG5 , the grindstone 10 is used with its base end attached to the head of a handheld rotary tool 11′. In this case, the grindstone 10′ attached to the rotary tool 11′ is preferably a grindstone 10′ having a circular cross-section, as shown in FIG4 . In other words, the rotary tool 11′ is preferably a cylindrical grindstone 10′. The rotary tool 11′ is, for example, an electric rotary tool or a pneumatic rotary tool. As indicated by the solid arrow in FIG5 , the rotary tool 11′ rotates the grindstone 10′ about its axis.

[0034] As shown in Figure 5, when grinding a workpiece W, the grindstone rod 10' has its tip 17 pressed obliquely against the grinding surface S of the workpiece W. Specifically, the grindstone rod 10' is pressed against the grinding surface S with its axis L and the grinding surface S forming an acute angle θ. Furthermore, when grinding the workpiece W, the grindstone rod 10' is pressed against the grinding surface S of the workpiece W with a predetermined pressing force F along the axis L. Furthermore, the grindstone rod 10' rotates about its axis while the tip 17 is pressed against the grinding surface S. The rotary tool 11' rotates the grindstone rod 10 at a speed of at least 100 revolutions per minute.

[0035] Here, when grinding with the grindstone rod 10' mounted on a rotating tool 11', as shown in FIG6 , the front end surface 17a of the grindstone rod 10' is pressed perpendicularly against the grinding surface S of the workpiece W while being rotated. In this case, the grindstone rod 10' is pressed against the grinding surface S with a pressing force F along the axis L. Furthermore, the rotating tool 11' rotates the grindstone rod 10 at a speed of 100 revolutions per minute or more.

[0036] Here, in any of the above-mentioned grinding methods, when the grinding surface S of the workpiece is ground by the grindstone rod 10, the grindstone rod 10 may bend in a direction intersecting its axis L due to the pressing force F pressing the grindstone rod 10 against the grinding surface S or the reaction force from the side of the grinding surface S.

[0037] In addition, the grinding rods 10 and 10' can also be used without being attached to a vibration tool, etc. In this case, the operator presses the front end 17 of the grinding rods 10 and 10' against the grinding target surface S of the workpiece W to perform manual grinding.

[0038] (Manufacturing method of grinding stone rod) Figure 7 is a flow chart of the method for manufacturing the grinding stone rod 10. As shown in Figure 7, the method for manufacturing the grinding stone rod 10 sequentially comprises a spinning process ST1, a pre-firing process ST2, a sintering process ST3, and a resin impregnation molding process ST4. In the spinning process ST1, an aqueous spinning solution composed of hydrous aluminum chloride, colloidal silica, and polyvinyl alcohol is dry-spun to produce a precursor fiber. In the pre-firing process ST2, the precursor fiber is sintered at a temperature between 900°C and 1300°C to ceramicize it, producing an inorganic long fiber. In the sintering process ST3, the inorganic long fiber is heated at a high temperature of 1300°C or higher for approximately 20 seconds. The heating temperature in the sintering process ST3 is higher than that in the pre-firing process ST2.

[0039] In the resin impregnation molding process ST4, the inorganic long fibers are appropriately drawn and aligned to form a filament aggregate. Furthermore, in the resin impregnation molding process ST4, the filament aggregate is impregnated with a thermosetting resin such as epoxy resin or phenolic resin. Furthermore, in the resin impregnation molding process ST4, the resin-impregnated filament aggregate is drawn and aligned to form a filament bundle. Furthermore, in the resin impregnation molding process ST4, the resin-impregnated filament bundle is drawn through a mold having an opening of a predetermined shape and then cured in a heating furnace. The cured resin bundle is then cut into a predetermined length. This results in a grinding stone rod 10 having a predetermined length and a predetermined cross-sectional shape.

[0040] A specific example of the manufacturing method is described below. First, in the spinning process ST1, 2.5 kg of partially saponified polyvinyl alcohol with an average degree of polymerization of 1700 is dissolved in 34 kg of a saline aluminum chloride aqueous solution containing 13.2% by weight of aluminum ions and 11.45% by weight of chloride ions, and 7.5 kg of colloidal silica containing 20% ​​by weight of silica, to prepare a spinning solution with a viscosity of approximately 1000 poise / 20°C. The spinning solution is then extruded through a 1000-hole spinning nozzle for dry spinning. In the pre-firing process ST2, the spun inorganic filaments are sintered at 900°C to 1300°C to ceramicize them, producing a pre-fibered yarn. In the sintering process ST3, this pre-fibered yarn is passed through a tube furnace at 1300°C to 1400°C and continuously wound onto a first bobbin under applied tension. At this time, the speed of the collection yarn is adjusted so that the heating time is 20 seconds. Here, the collection yarn is wound on a plurality of first bobbins.

[0041] In the resin impregnation molding process ST4, the collective yarns are drawn out from the plurality of first bobbins and passed through a resin tank containing uncured resin. Furthermore, the resin-impregnated collective yarns passing through the resin tank are aligned into a bundle and passed through a heating furnace.

[0042] The resin in which the assembled yarns and the assembled yarn bundles are impregnated may have the following composition. Epoxy resin (jER828, manufactured by Mitsubishi Chemical Corporation) 100 parts by weight 85 parts by weight of tetrahydromethylphthalic anhydride (HN 2200, manufactured by Hitachi Chemical Co., Ltd.) Imidazole (2E4MZ-CN, manufactured by Shikoku Chemicals Co., Ltd.) 2 parts by weight

[0043] In the resin infusion molding process ST4, the bundle of resin-impregnated filaments passes through a mold with a predetermined opening before reaching the heating furnace. This ensures that the cross-sectional shape of the bundle of resin-impregnated filaments corresponds to the shape of the mold opening. Furthermore, during the resin infusion molding process ST4, the impregnated resin hardens by passing through the heating furnace. The cured bundle of filaments is then cut into predetermined sizes. This allows for a grinding rod with a rectangular cross section and a predetermined length if the mold opening is rectangular. Furthermore, a grinding rod with a circular cross section and a predetermined length if the mold opening is circular can be obtained.

[0044] (Example 1) The grindstone rod 10 of Example 1 is rod-shaped, with a rectangular cross-section perpendicular to the axis. The grindstone rod 10 has a thickness (the dimension along the short side of the cross-section) of 1 mm, a width (the dimension along the long side of the cross-section) of 4 mm, and a length of 100 mm. The grindstone rod 10 has a flexural strength of 1200 MPa and a flexural elasticity of 110 GPa.

[0045] The grindstone rod 10 of Example 1 comprises inorganic long fibers 15 and a resin 16 impregnated within the inorganic long fibers 15. The inorganic long fibers 15 comprise 85% by weight of alumina and 15% by weight of silica. The crystal structure of the inorganic long fibers 15 is intermediate alumina. The silica component is amorphous. In other words, the crystal structure of the inorganic long fibers 15 lacks mullite crystals. The BET specific surface area of ​​the inorganic long fibers 15 is less than 15 m² / g. In this embodiment, the BET specific surface area of ​​the inorganic long fibers 15 is 12.5 m² / g. A cross-section of the inorganic long fibers 15 is exposed at the front end 17a of the grindstone rod 10.

[0046] In manufacturing the grinding stone rod 10 of Example 1, the heating temperature of the pre-firing process ST2 is 1000° C. The heating temperature of the sintering process ST3 is 1350° C. The heating time in the sintering process ST3 is 20 seconds.

[0047] The BET specific surface area is determined by the gas adsorption method (BET method). The BET specific surface area is measured after the sintering process ST3 is completed and before the resin impregnation process ST4.

[0048] Here, the fact that the inorganic long fibers 15 do not contain mullite crystals in their crystal structure is evaluated using X-ray diffraction. Specifically, in Example 1, after the sintering process ST3 and before the resin impregnation molding process ST4, the inorganic long fibers 15 were irradiated with X-rays to obtain a diffraction pattern. Furthermore, in the diffraction pattern, it was confirmed that no peak (peak) of the diffraction line of the mullite (210) plane appeared near 26° at 2θ. Figure 8 is a diffraction pattern obtained by irradiating the inorganic long fibers 15 of Example 1 with X-rays. In the diffraction pattern of Figure 8, no peak (peak) appeared near 26° at 2θ.

[0049] (Example 2) The grindstone rod 10 of Example 2 is rod-shaped, with a rectangular cross-section perpendicular to the axis. The grindstone rod 10 has a thickness (the dimension along the short side of the cross-section) of 1 mm, a width (the dimension along the long side of the cross-section) of 4 mm, and a length of 100 mm. The grindstone rod 10 has a flexural strength of 1200 MPa and a flexural elasticity of 108 GPa.

[0050] The grindstone rod 10 of Example 2 comprises inorganic long fibers 15 and a resin 16 impregnated within the inorganic long fibers 15. The inorganic long fibers 15 comprise 85% by weight of alumina and 15% by weight of silica. The crystal structure of the inorganic long fibers 15 is composed of intermediate alumina. The silica component is amorphous. In other words, the crystal structure of the inorganic long fibers 15 lacks mullite crystals. The BET specific surface area of ​​the inorganic long fibers 15 is greater than 15 m² / g and less than 30 m² / g. In this example, the BET specific surface area of ​​the inorganic long fibers 15 is 28.7 m² / g. A cross-section of the inorganic long fibers 15 is exposed at the front end 17a of the grindstone rod 10.

[0051] In manufacturing the grinding stone rod 10 of Example 2, the heating temperature of the pre-firing process ST2 is 1000° C. The heating temperature of the sintering process ST3 is 1330° C. The heating time in the sintering process ST3 is 20 seconds.

[0052] Although not shown in the figure, in the diffraction pattern obtained by irradiating the inorganic long fibers 15 of Example 2 with X-rays, there is no peak near 26° at 2θ.

[0053] Here, the heating temperature of the sintering step ST3 in Example 1 is higher than the heating temperature of the sintering step ST3 in Example 2. Consequently, the BET specific surface area of ​​the inorganic long fibers 15 in the grinding stone rod 10 of Example 1 is less than half the BET specific surface area of ​​the inorganic long fibers 15 in the grinding stone rod 10 of Example 2. In other words, by controlling the heating temperature and heating time of the sintering step ST3 during the manufacture of the grinding stone rod 10, the BET specific surface area of ​​the inorganic long fibers 15 can be controlled.

[0054] The crystal structure of the inorganic long fibers 15 in the grindstone rod 10 of Example 1 is in a state before mullite crystals appear in the crystal structure due to sintering.

[0055] (Comparative Example 1) The grindstone rod of Comparative Example 1 is rod-shaped, with a rectangular cross-section perpendicular to the axis L. The grindstone rod of Comparative Example 1 has a thickness (the dimension along the short side of the cross-section) of 1 mm, a width (the dimension along the long side of the cross-section) of 4 mm, and a length of 100 mm. The grindstone rod of Comparative Example 1 has a flexural strength of 1100 MPa and a flexural elasticity of 105 GPa.

[0056] The grinding wheel of Comparative Example 1 comprises a plurality of inorganic long fibers extending in the axial direction and a resin impregnated within the inorganic long fibers. The inorganic long fibers comprise 85% by weight of alumina and 15% by weight of silica. The crystal structure of the inorganic long fibers is composed of intermediate alumina. The silica component is amorphous. In other words, the crystal structure of the inorganic long fibers lacks mullite crystals. The BET specific surface area of ​​the inorganic long fibers is greater than 30 m² / g. In this embodiment, the BET specific surface area of ​​the inorganic long fibers is 51.0 m² / g. A cross-section of the inorganic long fibers is exposed at the front end of the grinding wheel of Comparative Example 1.

[0057] In manufacturing the grinding stone rod of Comparative Example 1, the heating temperature of the pre-firing process ST2 was 1000° C. The heating temperature of the sintering process ST3 was 1310° C. The heating time in the sintering process ST3 was 20 seconds.

[0058] The heating temperature in sintering step ST3 of Comparative Example 1 is lower than that in sintering step ST3 of Examples 1 and 2. As a result, the BET specific surface area of ​​the inorganic long fibers of Comparative Example 1 is larger than that of the inorganic long fibers of Examples 1 and 2. Furthermore, the BET specific surface area of ​​the inorganic long fibers can be controlled by adjusting the heating temperature and heating time in sintering step ST3.

[0059] Although not shown in the figure, in the diffraction pattern obtained by irradiating the inorganic long fibers of Comparative Example 1 with X-rays, no peak appears near 26° at 2θ.

[0060] (Comparative Example 2) The grindstone rod of Comparative Example 2 is rod-shaped, with a rectangular cross-section perpendicular to the axis L. The grindstone rod of Comparative Example 2 has a thickness (the dimension along the short side of the cross-section) of 1 mm, a width (the dimension along the long side of the cross-section) of 4 mm, and a length of 100 mm. The grindstone rod of Comparative Example 2 has a flexural strength of 1200 MPa and a flexural elasticity of 120 GPa.

[0061] The grinding wheel of Comparative Example 2 comprises a plurality of inorganic long fibers extending in the axial direction and a resin impregnated within the inorganic long fibers. The inorganic long fibers comprise 85% by weight of alumina and 15% by weight of silica. The crystal structure of the inorganic long fibers comprises mullite crystals and intermediate alumina. The average particle size of the mullite crystals is greater than 30 nm. The BET specific surface area of ​​the inorganic long fibers is 0.5 m² / g. A cross-section of the inorganic long fibers is exposed at the front end of the grinding wheel of Comparative Example 2.

[0062] In manufacturing the grinding stone rod of Comparative Example 2, the heating temperature in the pre-firing process ST2 was 1000° C. The heating temperature in the sintering process ST3 was 1390° C. The heating time in the sintering process ST3 was 30 seconds.

[0063] The heating temperature in sintering step ST3 of Comparative Example 2 is higher than that in sintering step ST3 of Examples 1 and 2. Furthermore, the heating time in sintering step ST3 of Comparative Example 2 is longer than that in sintering step ST3 of Examples 1 and 2. Therefore, the grinding stone rod of Comparative Example 2 contains mullite crystals in its crystal structure. In other words, by controlling the heating temperature and heating time in sintering step ST3 during the manufacture of the grinding stone rod of Comparative Example 2, the presence or absence of mullite crystals in the crystal structure of the inorganic long fibers can be controlled.

[0064] Here, the fact that the inorganic long fibers have mullite crystals in their crystal structure was evaluated using X-ray diffraction. Specifically, in Comparative Example 2, after the sintering process ST3 and before the resin impregnation molding process ST4, the inorganic long fibers were irradiated with X-rays to obtain a diffraction pattern. Furthermore, in the diffraction pattern, a peak of diffraction lines corresponding to the (210) plane of mullite was observed near 26° at 2θ. Figure 9 shows a diffraction pattern obtained by irradiating the inorganic long fibers of Comparative Example 2 with X-rays. In the diffraction pattern shown in Figure 9, a peak appears near 26° at 2θ.

[0065] The average particle size of the mullite crystals in the crystal structure of the inorganic long fibers was calculated from the following general formula based on the above diffraction pattern.

[0066] D hkl: average particle size of (210) plane λ: wavelength of X-rays θ: X-ray oblique angle β 1 / 2: Half width of the diffraction line of the (210) plane of mullite appearing at around 26° in the crystal structure 2θ of X-ray diffraction

[0067] (Comparative Test) Comparative tests were conducted on the grinding of workpieces W using the grindstone rods 10 of Examples 1 and 2 and the grindstone rods of Comparative Examples 1 and 2. Figure 10 is a graph showing the roughness of the workpiece surface being ground using the grindstone rod 10 of Example 1. Figure 11 is a graph showing the roughness of the workpiece surface being ground using the grindstone rod 10 of Example 2. Figure 12 is a graph showing the roughness of the workpiece surface being ground using the grindstone rod of Comparative Example 1. Figure 13 is a graph showing the roughness of the workpiece surface being ground using the grindstone rod of Comparative Example 2. Figure 14 is a graph showing the amount of workpiece W removed after the comparative test using the grindstone rods 10 of Examples 1 and 2 and the grindstone rods of Comparative Examples 1 and 2. Figure 15 is a graph showing the amount of wear of each grindstone rod after the comparative test using the grindstone rods 10 of Examples 1 and 2 and the grindstone rods of Comparative Examples 1 and 2.

[0068] In a comparative test, the base ends of the grindstone rods 10 of Examples 1 and 2 and the grindstone rods of Comparative Examples 1 and 2 were attached to the head of a handheld vibrating tool 11 to grind the target surface S of a workpiece W. The vibrating tool was a pneumatic vibrating tool. The workpiece W to be ground was a mold. The material of the workpiece W was S50C (carbon steel for machine structures).

[0069] More specifically, as shown in Figure 2, during the grinding of a workpiece W, the grinding rods 10 of Examples 1 and 2 and the grinding rods of Comparative Examples 1 and 2 were positioned so that the angle θ between their axis L and the grinding surface S was 30°. Furthermore, the tip 17 of the grinding rods 10 of Examples 1 and 2 and the tip 17 of the grinding rods of Comparative Examples 1 and 2 were pressed against the grinding surface S with a pressing force F of 6 N. Furthermore, the grinding rods 10 of Examples 1 and 2 and the grinding rods of Comparative Examples 1 and 2 were vibrated axially at a rate of 21,000 st / min using a vibrating tool 11. The workpiece W was then dry-ground for three minutes continuously over a grinding area of ​​30 mm x 30 mm.

[0070] As can be seen from the graph of workpiece removal after the comparative test shown in FIG14 , the grindstones 10 of Examples 1 and 2 exhibit comparable grinding forces to the grindstone of Comparative Example 2. In other words, even if the crystal structure of the inorganic long fibers does not include mullite crystals, a grindstone 10 having a BET specific surface area of ​​30 m² / g or less of the inorganic long fibers 15, which includes mullite crystals and intermediate alumina in its crystal structure, can achieve comparable grinding forces to a grindstone having mullite crystals with an average particle size of 30 nm or greater.

[0071] Next, as shown in the graph of workpiece removal after the comparative test in Figure 14, the grinding force of the grinding stone of Comparative Example 1 is inferior to that of the grinding stone of Comparative Example 2. Specifically, the grinding stone of Comparative Example 1, in which the crystal structure of the inorganic long fibers does not contain mullite crystals and the BET specific surface area of ​​the inorganic long fibers 15 is greater than 30 m² / g, exhibits inferior grinding force compared to the grinding stone of Comparative Example 2, in which the crystal structure of the inorganic long fibers contains mullite crystals and intermediate alumina and mullite crystals with an average particle size of 30 nm or greater.

[0072] Furthermore, the occurrence of scratches in the roughness curve of the polishing surface S of the workpiece W when polished using the grindstone rods 10 of Examples 1 and 2 shown in Figures 10 and 11 was less than the occurrence of scratches in the roughness curve of the polishing surface S of the workpiece W when polished using the grindstone rod of Comparative Example 2 shown in Figure 13. In other words, when polishing using the grindstone rods 10 of Examples 1 and 2, whose inorganic long fibers do not have mullite crystals in their crystal structure, the occurrence of scratches was suppressed compared to when polishing using the grindstone rod of Comparative Example 2, whose inorganic long fibers have mullite crystals in their crystal structure.

[0073] Furthermore, the surface roughness of the polishing surface S of the workpiece W polished with the grindstone rod 10 of Example 1 was Rz2.0 μm. The surface roughness of the polishing surface S of the workpiece W polished with the grindstone rod 10 of Example 2 was Rz1.9 μm. The surface roughness of the polishing surface S of the workpiece W polished with the grindstone rod of Comparative Example 2 was Rz4.1 μm. Therefore, when polishing with the grindstone rods 10 of Examples 1 and 2, whose inorganic long fibers do not contain mullite crystals, the surface roughness of the polishing surface S of the workpiece W can be improved compared to when polishing with the grindstone rod of Comparative Example 2, whose inorganic long fibers contain mullite crystals.

[0074] Furthermore, the graph of the wear of the grinding stones after the comparative test shown in FIG15 shows that the wear of the grinding stones 10 of Examples 1 and 2 is less than that of the grinding stones of Comparative Examples 1 and 2. Therefore, the grinding stone 10, whose inorganic long fibers have a crystal structure without mullite crystals and whose inorganic long fibers 15 have a BET specific surface area of ​​30 m² / g or less, has improved wear resistance compared to the grinding stone of Comparative Example 1, whose inorganic long fibers have a crystal structure without mullite crystals and whose inorganic long fibers 15 have a BET specific surface area of ​​more than 30 m² / g. Furthermore, the grinding stone 10, whose inorganic long fibers have a crystal structure without mullite crystals and whose inorganic long fibers 15 have a BET specific surface area of ​​30 m² / g or less, has improved wear resistance compared to the grinding stone of Comparative Example 2, whose inorganic long fibers have a crystal structure without mullite crystals.

[0075] Here, according to the graph of the grinding amount of the workpiece W after the comparative test shown in FIG14 , the grinding force of the grindstone rod 10 of Example 1, in which the BET specific surface area of ​​the inorganic long fibers 15 was less than 15 m 2 / g, was significantly improved compared to the grindstone rod 10 of Example 2, in which the BET specific surface area exceeded 15 m 2 / g. Furthermore, according to the graph of the wear amount of the grindstone rod after the comparative test shown in FIG15 , the wear resistance of the grindstone rod 10 of Example 1, in which the BET specific surface area of ​​the inorganic long fibers 15 was less than 15 m 2 / g, was significantly improved compared to the grindstone rod 10 of Example 2, in which the BET specific surface area exceeded 15 m 2 / g.

[0076] (Function and Effect) In the grinding stones 10 of Examples 1 and 2, the silica component of the inorganic long fibers 15 is in an amorphous state. Therefore, the crystal structure of the inorganic long fibers 15 lacks mullite crystals. This prevents scratches (grinding marks) on the polishing surface of the workpiece caused by mullite crystals. Consequently, the surface roughness of the polishing surface can be improved.

[0077] Furthermore, in the grinding stones 10 of Examples 1 and 2, the silica component of the inorganic long fibers 15 is in an amorphous state. In other words, the crystal structure of the inorganic long fibers 15 does not contain mullite crystals. Therefore, the inorganic long fibers 15 are not embrittled by mullitization.

[0078] Next, in the grinding stones 10 of Examples 1 and 2, the BET specific surface area of ​​the inorganic long fibers 15 is 30 m² / g or less. Inorganic long fibers 15 with such a BET specific surface area have fewer pores and irregularities, which suppresses moisture absorption. This prevents or suppresses the inorganic long fibers 15 from absorbing atmospheric moisture, which could hinder the curing of the resin 16 impregnated within the inorganic long fibers 15.

[0079] Furthermore, the inorganic long fibers 15 having such a BET specific surface area have fewer pores and irregularities, which can prevent poor impregnation of the resin 16 impregnated with the inorganic long fibers 15 due to residual bubbles in the resin 16. Therefore, the grinding stone 10 can be prevented from becoming brittle.

[0080] Figure 16 is a photograph of the side surface of the grindstone 10 of Example 2. Figure 17 is a photograph of the side surface of the grindstone 10 of Comparative Example 1. As shown in Figure 17, the grindstone 10 of Comparative Example 1, which has inorganic long fibers 15 with a large BET specific surface area, exhibits poor impregnation of the resin 16 due to bubbles remaining in the resin 16, resulting in a rough surface (the rough areas appear white in the photograph). In contrast, the grindstone 10 of Example 2, whose inorganic long fibers 15 have a BET specific surface area of ​​30 m² / g or less, exhibits no surface roughness. In other words, poor impregnation of the resin 16 is not observed in the grindstone 10 of Example 2, whose inorganic long fibers 15 have a BET specific surface area of ​​30 m² / g or less. Furthermore, when the side surface of the grindstone 10 of Example 1 is photographed, a photograph similar to that in Figure 16 is obtained. Therefore, poor impregnation of the resin 16 is not observed in the grindstone 10 of Example 1 either.

[0081] In the grindstone rods 10 of Examples 1 and 2, the inorganic long fibers 15 contain an alumina content of 80% by weight or more. Therefore, the hardness of the inorganic long fibers 15 can be maintained. Furthermore, in the inorganic long fibers 15 having a BET specific surface area of ​​30 m² / g or less, the hardening of the moisture-inhibiting resin 16 is suppressed, which would otherwise cause the grindstone rods 10 of Examples 1 and 2 to become brittle. Furthermore, in the grindstone rods 10 of Examples 1 and 2 having the inorganic long fibers 15 having a BET specific surface area of ​​30 m² / g or less, the occurrence of poor resin impregnation is suppressed, thereby preventing the grindstone rods 10 of Examples 1 and 2 from becoming brittle. Furthermore, unlike rectangular parallelepiped grindstones, which grind with their entire side surfaces in contact with the surface to be polished of the workpiece W, the grindstone rod 10 performs grinding by pressing its tip 17 against the surface to be polished of the workpiece W. Furthermore, because the grindstone rod 10 has the elasticity to bend in a direction intersecting its axis L, the tip 17 of the grindstone rod 10 can be pressed against the surface to be polished with a pressing force F that takes into account the elasticity of the grindstone rod 10. Therefore, the grindstone rods 10 of Examples 1 and 2 can maintain a sufficient grinding force even though their crystal structure does not contain mullite crystals.

[0082] 10: Grindstone 11: Vibration grinding tool 15: Inorganic long fiber 16: Resin 17: front end 17a: front face ST1: Spinning process ST2: Pre-burning process ST3: Sintering process ST4: Resin impregnation molding process

Claims

1. A grinding stone rod, a rod-shaped grinding stone rod for grinding a workpiece by pressing its front end against the surface to be ground, the grinding stone rod comprising: a plurality of inorganic long fibers extending in the axial direction and a resin impregnated and hardened in the inorganic long fibers; wherein, The front end has a cross section exposing the aforementioned inorganic long fibers; it has the elasticity to bend in a direction intersecting the aforementioned axis; the aforementioned inorganic long fibers contain 80 to 90% by weight of alumina and 20 to 10% by weight of silicon dioxide; the crystal structure of the aforementioned inorganic long fibers contains intermediate alumina; the aforementioned silicon dioxide is in an amorphous state; the BET specific surface area of ​​the aforementioned inorganic long fibers is less than 28.7 m² / g.

2. The whetstone as described in claim 1, wherein, The BET specific surface area of ​​the aforementioned inorganic long fibers is less than 12.5 m² / g.

3. The whetstone as described in claim 1, wherein, The aforementioned inorganic long fibers contain more than 85% alumina by weight.

4. The whetstone as described in claim 1, wherein, The aforementioned resin is epoxy resin.

5. The whetstone as described in claim 1, wherein, The bending strength is above 500 MPa, while the bending elasticity is above 50 GPa.

6. A grinding method comprising: mounting a grinding stone as described in claim 1 to a vibrating tool; and pressing the front end of the aforementioned grinding stone onto the grinding surface of a workpiece while vibrating it in the aforementioned axial direction.

7. A grinding method comprising: mounting a grinding stone as described in claim 1 to a vibrating tool; and pressing the front end of the aforementioned grinding stone onto the grinding surface of a workpiece while vibrating it in the aforementioned axial direction and in a direction intersecting the axis of the aforementioned grinding stone.

8. A grinding method comprising: mounting a grinding stone as described in claim 1 to a rotary tool; and rotating the front end of the grinding stone while it is pressed against the grinding surface of a workpiece, wherein the cross-section of the grinding stone is circular.

Images