Superabrasive grain vitrified grindstone having large diameter pores, manufacturing method therefor, and cup-type grindstone wheel

Abstract

Provided is a superabrasive grain vitrified grindstone having large diameter pores with which grindstone preparation adjustment can be performed easily because cracks do not readily form, stable manufacturing is possible, and there is no uneven distribution of pore diameters. This segment grindstone (superabrasive grain vitrified grindstone having large diameter pores) 14 includes hollow granulated bodies 20 having outer shells 26 to which diamond abrasive grains (superabrasive grains) 18 are bonded by a vitrified bond, wherein the inner cavities of the hollow granulated bodies 20 form large diameter pores 22 in a multi-pore structure of the segment grindstone 14. As a result, the hollow granulated bodies 20 are uniformly mixed with little unevenness in a kneading material to be used for molding, and thus a segment grindstone 14 is obtained in which grindstone preparation adjustment can be performed easily because cracks do not readily form, stable manufacturing is possible, and there is no uneven distribution of pore diameters.

Description

Superabrasive vitrified grinding wheel with large pores, its manufacturing method, and cup-type grinding wheel

[0001] The present invention relates to a vitrified superabrasive grinding wheel having large pores in which superabrasive grains are bonded using a vitrified bond, a method for manufacturing the same, and a cup-type grinding wheel.

[0002] Generally, when surface grinding semiconductors such as SiC, superabrasive grains such as diamond are bonded with a vitrified bond to increase the grain retention force and favorably generate the self-sharpening action of the abrasive grains. A porous vitrified superabrasive grain grinding wheel containing large pores has been proposed to achieve this. Such a vitrified superabrasive grain grinding wheel can ensure sufficient grinding strength, allowing grinding with sufficient grinding pressure and achieving good grinding performance. Examples of such superabrasive grain vitrified grinding wheels include those described in Patent Documents 1, 2, 3, and 4.

[0003] The superabrasive vitrified grinding wheels described in Patent Documents 1 and 2 use a resin pore-forming material to form large pores, and the large pores are formed by eliminating the resin pore-forming material during the firing process. However, the resin pore-forming material has a smooth surface and a large density difference from the abrasive grains and vitrified bond, so even when kneaded, the resin pore-forming material tends to become uneven, causing large pores to be ubiquitous and cracks to occur.

[0004] The superabrasive vitrified grinding wheel described in Patent Document 3 is manufactured by mixing superabrasive grains, a vitrified bond, a gelling agent, water, and a surfactant to obtain a meringue-like foam material, then cooling the foam material in a molding die to form a molded body, baking the dried molded body, and further immersing it in a liquid resin to coat the bond bridge, which is an outer shell surrounding the pores, with a resin coating layer to increase strength. However, when manufacturing a superabrasive vitrified grinding wheel using this manufacturing method, the molded body shrinks, making it difficult to manufacture a product with a stable shape.

[0005] The superabrasive vitrified grinding wheel described in Patent Document 4 is obtained by placing a molded body with frozen particles formed inside it under vacuum, causing the frozen particles inside the molded body to sublimate, forming large pores in the areas after sublimation, and then firing the molded body. However, there are drawbacks in that it is difficult to adjust the grinding wheel's formulation and that the pore size is likely to differ between the surface and interior of the grinding wheel.

[0006] Japanese Patent No. 5414706 Japanese Patent Application Laid-Open No. 2017-1185575 Japanese Patent No. 4769488 Japanese Patent No. 6737975

[0007] The present invention has been made in light of the above circumstances, and its object is to provide a superabrasive vitrified grinding wheel that is less susceptible to cracking, can be manufactured stably, has large pores with no bias in pore diameter, and allows for easy wheel blending adjustment.

[0008] The inventors conducted extensive research in light of the above circumstances and found that densely packed hollow granules could be reliably obtained by spraying a slurry containing superabrasive grains, a vitrified bond, a binder, etc., in a spray dryer and drying it in air. They also found that press-molding and sintering the classified hollow granules resulted in a superabrasive vitrified grinding wheel with large pores that is less prone to cracking, can be manufactured stably, and has no bias in pore size, allowing for easy wheel blending. The present invention was made based on this finding.

[0009] That is, the gist of the first invention is (a) a superabrasive vitrified grinding wheel having large-diameter pores within a porous structure in which superabrasive grains are bonded by a vitrified bond, and (b) the superabrasive grains include hollow granules having an outer shell bonded by the vitrified bond, and the inner cavity of the hollow granules forms the large-diameter pores.

[0010] The gist of the second invention is that in the first invention, the hollow granules have a ratio of the thickness of the outer shell to the outer diameter of the hollow granules of 0.1 to 0.4.

[0011] The gist of the third invention is that in the first invention, the porous structure contains pores with an average pore diameter of 5 to 60 μm.

[0012] The gist of a fourth invention is that, in the first or second invention, the superabrasive grains have a diameter of 10 μm or less, and the hollow granules have an outer shell with a thickness of 5 to 10 μm and an outer diameter of 10 to 100 μm.

[0013] The gist of the fifth invention is that the superabrasive vitrified grinding wheel having large pores of the first invention is a cup-shaped grinding wheel in which the superabrasive vitrified grinding wheel having large pores of the first invention is fixed to the outer periphery of a metal base metal in a row at predetermined intervals in the radial direction.

[0014] The gist of the sixth invention is a method for producing a superabrasive vitrified grinding wheel having large pores within a porous structure in which superabrasive grains are bonded by a vitrified bond, the method comprising: a slurry preparation step of preparing a slurry containing the superabrasive grains, the vitrified bond, and a binder; a spray-dry granulation step of spraying the slurry in a dryer and drying it in air to obtain hollow granules from the slurry droplets; a molding step of press-molding the hollow granules obtained in the spray-dry granulation step in a mold to obtain a green body; and a firing step of firing the green body to obtain a superabrasive vitrified grinding wheel having large pores within the porous structure in which the superabrasive grains are bonded by the vitrified bond.

[0015] In the superabrasive vitrified grinding wheel with large pores of the first invention, the superabrasive grains contain hollow granules with an outer shell bound by a vitrified bond, and the inner cavities of the hollow granules form the large pores in the porous structure of the superabrasive vitrified grinding wheel. This results in a superabrasive vitrified grinding wheel with large pores that is less likely to crack, can be manufactured stably, and has no bias in pore size, allowing for easy wheel blend adjustment.

[0016] In the superabrasive vitrified grinding wheel having large pores according to the second aspect of the present invention, the ratio of the shell thickness to the outer diameter of the hollow granules is 0.1 to 0.4. This allows the hollow structure of the hollow granules to be favorably maintained during press molding. If the ratio of the shell thickness to the outer diameter of the hollow granules is less than 0.1, the strength of the hollow granules decreases, destroying the hollow structure. If the ratio of the shell thickness to the outer diameter of the hollow granules exceeds 0.4, the hollow structure is deformed during the spray drying process, resulting in the formation of defective granules lacking a lumen, making it difficult to obtain a superabrasive vitrified grinding wheel having large pores within its porous structure.

[0017] According to the superabrasive vitrified grinding wheel having large pores of the third invention, the porous structure contains pores with an average pore diameter of 5 to 60 μm, thereby providing a superabrasive vitrified grinding wheel having large pores with high grinding performance.

[0018] In the superabrasive vitrified grinding wheel with large pores of the fourth invention, the superabrasive grains have a diameter of 10 μm or less, and the hollow granules have an outer shell with a thickness of 5 to 10 μm and an outer diameter of 10 to 100 μm. This makes it possible to obtain a superabrasive vitrified grinding wheel with large pores that is less susceptible to cracking, can be manufactured stably, and has no bias in pore diameter, allowing for easy wheel blend adjustment.

[0019] According to the cup-shaped grinding wheel of the fifth invention, the superabrasive vitrified grinding wheels having large pores of the first invention are fixed to the outer periphery of the metal base metal in a row at predetermined intervals in the radial direction, so that expensive superabrasive grains can be used effectively.

[0020] According to a sixth aspect of the present invention, a method for producing a vitrified superabrasive grinding wheel with large pores includes the following steps: a slurry preparation step of preparing a slurry containing superabrasive grains, a vitrified bond, and a binder; a spray-drying granulation step of spraying the slurry in a dryer and drying it in air to produce hollow granules from the slurry droplets; a molding step of press-molding the hollow granules in a mold to produce a green body; and a firing step of sintering the green body to produce a vitrified superabrasive grinding wheel with large pores within a porous structure formed by the superabrasive grains bonded by the vitrified bond. The spray-drying granulation step advantageously produces hollow granules from the slurry droplets by spraying a slurry containing superabrasive grains, a vitrified bond, and a binder in a dryer and drying it in air. The hollow granules thus produced have a relatively uniform particle size and a sharp particle size distribution, resulting in less porosity and less cracking.

[0021] 5 is a perspective view showing a cup-shaped grinding wheel equipped with a superabrasive vitrified grinding wheel having large pores according to an embodiment of the present invention. It is an optical microscope photograph showing an enlarged view of the surface of the superabrasive vitrified grinding wheel having large pores shown in FIG. 1. It is an SEM photograph showing an enlarged view of hollow granules contained in the vitrified bond in the superabrasive vitrified grinding wheel of FIG. 2. It is a diagram explaining a method for measuring the thickness and outer diameter of the outer shell of hollow granules. It is a process diagram explaining a manufacturing process for the superabrasive vitrified grinding wheel having large pores shown in FIG. 1. It is a diagram explaining the mechanism for forming hollow granules in the spray-dry granulation process of FIG. 5. It is a process diagram explaining a manufacturing method for a superabrasive vitrified grinding wheel that does not use hollow granules. It is a table showing the blend amounts and grinding test results in grinding test 1. It is a table showing the blend amounts and grinding test results in grinding test 2.

[0022] An embodiment of the present invention will be described in detail below with reference to the drawings. Note that in the following embodiment, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of the various parts are not necessarily drawn accurately.

[0023] 1 is a perspective view showing a cup-type grinding wheel 10 according to one embodiment of the present invention. The cup-type grinding wheel 10 comprises a disk-shaped base metal 12 made of metal, for example, aluminum, and a plurality of segment grinding stones 14 fixedly attached at predetermined intervals in a ring-like arrangement along the outer periphery of the underside of the base metal 12. Each segment grinding stone 14 has a grinding surface 16 that is continuous in a ring-like arrangement on the outer periphery of the underside of the base metal 12.

[0024] The metal base 12 is disk-shaped and made of metal, and is attached to the main shaft of a grinding device (not shown), thereby rotating the cup-shaped grinding wheel 10. The cup-shaped grinding wheel 10 has an outer diameter of, for example, about 250 mm, and the segment grinding wheel 14 is an arc-shaped plate with a thickness of, for example, about 3 mm. As the metal base 12 rotates, the grinding surface 16 of the segment grinding wheel 14 slides against a workpiece, such as a semiconductor wafer made of SiC, to grind or polish the workpiece into a flat surface.

[0025] The segmented grinding wheel 14 corresponds to the superabrasive vitrified grinding wheel of the present invention having large-diameter pores 22. As shown in the 200x optical microscope photograph of Figure 2, the segmented grinding wheel 14 is composed of a porous structure including superabrasive grains, such as diamond abrasive grains 18, hollow granules 20, a vitrified bond that bonds the diamond abrasive grains 18 and the hollow granules 20, and pores 24 containing the large-diameter pores 22. The inner cavities of the hollow granules 20 form the large-diameter pores 22. The composition of the segmented grinding wheel 14 is, for example, 19 to 26 vol% diamond abrasive grains 18, 9 to 12 vol% vitrified bond, and 60 to 72 vol% pores 24.

[0026] The average pore diameter of all pores 24, including the large pores 22 in the porous structure that constitutes the segment grinding wheel 14, is, for example, 5 to 60 μm, and preferably 8 to 51 μm, as the average value when the maximum diameter of the pores 24 is measured at 30 or more consecutive points using image measurement by microscope observation.

[0027] The particle size of the diamond abrasive grains 18 can be selected depending on the required surface roughness, but is, for example, 10 μm or less, preferably an average particle size of 0.6 μm. The vitrified bond is made of well-known borosilicate glass or borosilicate zinc glass. The glass composition is, for example, 10 to 60 wt % SiO ２ , 10 to 30 wt% B ２ O ３ , 0-65 wt% ZnO, 0-10 wt% RO, 0-10 wt% R ２ It is O.

[0028] As shown in the 1000x SEM (scanning electron microscope) photograph of Figure 3, the hollow granules 20 are composed of diamond abrasive grains 18, a vitrified bond that bonds the diamond abrasive grains 18, a spherical outer shell 26 made up of a porous structure including pores 24, and large pores 22 that are internal cavities surrounded by the outer shell 26. The hollow granules 20 preferably have an outer diameter D of 10 to 100 µm. If the outer diameter D is less than 10 µm, the number of solid granules increases, and if it exceeds 100 µm, defects such as depressions are more likely to occur.

[0029] The outer diameter D of the hollow granules 20 and the thickness T of the outer shell 26 are measured as shown in Fig. 4. First, the segment grinding wheel 14 is ground using a fixed abrasive polishing pad to expose the internal surface, and the exposed surface is observed using an optical microscope or SEM. Next, the hollow granules 20 are extracted from the observed image, and the outer diameter D and the thickness T of the outer shell 26 are measured using the image. The measurements are then performed on 30 hollow granules 20 in the image, and an average value is calculated.

[0030] The thickness T of the outer shell 26 of the hollow granules 20 is, for example, 5 to 10 μm, and preferably 8.2 to 9.6 μm. The outer diameter D of the hollow granules 20 is, for example, 10 to 100 μm, and preferably 22 to 82 μm. The ratio T / D of the thickness T of the outer shell 26 of the hollow granules 20 to the outer diameter D of the hollow granules 20 is, for example, 0.1 to 0.4, and preferably 0.1 to 0.37.

[0031] Figure 5 is a process diagram illustrating the main steps of the manufacturing process for the segment grindstone 14. In the slurry preparation step P1 in Figure 5, a slurry, which is a material for granulating the hollow granules 20, is prepared. That is, the diamond abrasive grains 18, vitrified bond, PVA, acrylic resin, and a binder such as wax are uniformly mixed in a predetermined ratio to prepare the slurry. The binder is a molding aid, and its addition ratio is determined by the pressing pressure in the molding step P3 described below, which is 100 to 400 kgf / cm. ２ The molding pressure is adjusted experimentally in advance to 100 kgf / cm ２ If the diameter is smaller than 400 kgf / cm, the adhesion between the hollow granules 20 will be weak and the molding pressure will be 400 kgf / cm ２ If the temperature exceeds this range, deformation or destruction of the hollow granules 20 occurs.

[0032] In the spray-drying granulation step P2, the slurry is sprayed in the drying furnace of the spray dryer, whereby the droplets of the slurry are dried in the air to form hollow granules 20. As shown in Figure 6, during the drying process, the diamond abrasive grains 18 and vitrified bond particles move outward, while the lumen of the droplet-like slurry expands and the outer diameter D shrinks, forming an outer shell 26, thereby forming hollow granules 20, such as those shown in Figure 3. The hollow granules 20 are classified as necessary. The method for spraying the slurry is selected from a two-fluid nozzle method, a high-pressure nozzle method, a rotating disk method, etc.

[0033] Next, in the molding step P3, the hollow granules 20 obtained in the spray-drying granulation step P2 are filled into a press die, and the pressure is, for example, 100 to 400 kgf / cm ２ It is pressed at a press molding pressure of .

[0034] In the firing step P4, the compact formed in the molding step P3 is fired at a temperature at which the vitrified bond melts, for example, 800°C, to obtain the segmented grinding wheels 14. Then, in the bonding and finishing step P5, a plurality of segmented grinding wheels 14 are bonded to the base metal 12, and a dresser is used to perform finishing processing, thereby obtaining the cup-type grinding wheel 10 shown in Figure 1.

[0035] (Description of Grinding Test) Next, the details of Grinding Tests 1 and 2 conducted by the present inventors using the grinding (polishing) conditions shown below and the results of Grinding Tests 1 and 2 will be described below.

[0036] In grinding test 1, Comparative Example 1 and Example Examples 1-4 shown in the table in FIG. 8 were used. Example Examples 1-4 are superabrasive vitrified grinding wheels manufactured with the composition shown in FIG. 8, containing hollow granules 20 and having large-diameter pores 22. As shown in FIG. 8, the compositions are different. Comparative Example 1 is a superabrasive vitrified grinding wheel manufactured using the composition shown in FIG. 8 and the manufacturing process shown in FIG. 7, but without hollow granules 20. In the manufacturing process shown in FIG. 7, in the slurry preparation process P11, diamond abrasive grains 18, a vitrified bond, and a binder such as PVA, acrylic resin, or wax are uniformly mixed in a predetermined ratio to prepare a slurry. Next, in the drying and stirring process P12, the slurry is dried and stirred using an electric mortar and pestle, and then granulated by sieving. In the molding step P13, the firing step P14, and the bonding and finishing step P15, molding, firing, bonding and finishing are performed in the same manner as in the molding step P3, the firing step P4, and the bonding and finishing step P5 in FIG.

[0037] Grinding test 2 used Comparative Example 2 and Examples 5 and 6 shown in the table in Fig. 9. Examples 5 and 6 are superabrasive vitrified grinding wheels having large pores 22 due to the inclusion of hollow granules 20, which were manufactured using the composition shown in Fig. 9 and the process shown in Fig. 5, and have different compositions as shown in Fig. 9. Comparative Example 2 is a superabrasive vitrified grinding wheel that does not contain hollow granules 20, which was manufactured using the composition shown in Fig. 9 and the manufacturing process shown in Fig. 7.

[0038] (Grinding conditions for grinding test 1) Grinding machine: vertical surface grinding machine Workpiece: C surface of 4-inch SiC wafer Grinding wheel rotation speed: 2400 rpm Table rotation speed: 150 rpm Grinding wheel axis feed speed: 0.4 μm / sec Wafer removal allowance: 8 μm Grinding fluid: Water

[0039] (Grinding conditions for grinding test 2) Grinding machine: vertical surface grinding machine Workpiece: C surface of 6-inch SiC wafer Grinding wheel rotation speed: 2500 rpm Table rotation speed: 311 rpm Grinding wheel axis feed speed: 0.6 μm / sec Wafer removal allowance: 20 μm Grinding fluid: water

[0040] In Grinding Test 1, as shown in Figure 8, Examples 1 to 4 did not show a significant difference in current value (A) compared to Comparative Example 1, but the amount of wear (μm) was clearly less, resulting in high grinding wheel performance, i.e., grinding efficiency. This is presumably because the presence of large-diameter pores 22 formed by hollow granules 20 increases abrasive grain retention and suppresses clogging, thereby favorably achieving the self-sharpening action of the abrasive grains. Examples 1 to 4 have different shapes of hollow granules 20 contained in the superabrasive vitrified grinding wheel.

[0041] 8, the compositions containing hollow granules 20 in Examples 1 to 4 have smaller abrasive grain volume fractions and vitrified bond volume fractions, but larger average pore diameters, than Comparative Example 1. Examples 1 to 4 have abrasive grain volume fractions of 19.3 to 24.4 vol%, vitrified bond volume fractions of 9.6 to 12.0 vol%, average pore diameters of 8 to 45 μm, and hollow granule 20 outer diameters D of 22 to 82 μm. Furthermore, the ratio T / D of the thickness T of the outer shell 26 of the hollow granules 20 contained in Examples 1 to 4 to the outer diameter D is 0.1 to 0.37.

[0042] Among Examples 1 to 4, Example 1 had a ratio T / D of the thickness T of the outer shell 26 of the hollow granules 20 to the outer diameter D of the hollow granules 20 of 0.37, which means that the amount of wear was 2.3 times or more greater than that of Examples 2 to 4. Example 1 had a smaller average pore diameter and a larger T / D ratio than Examples 2 to 4, which is thought to be because it had fewer sufficiently large pore structures.

[0043] 9, in Grinding Test 2, there was no significant difference in current value (A) between Examples 5 and 6 and Comparative Example 2, as in Grinding Test 1, but the amount of wear (μm) was significantly less, resulting in high grinding wheel performance, i.e., high grinding efficiency. This is also presumably due to the presence of large-diameter pores 22 formed in hollow granules 20, which increase abrasive grain retention and suppress clogging, thereby favorably achieving the self-sharpening action of the abrasive grains.

[0044] As shown in Figure 9, the compositions containing hollow granules 20 in Examples 5 and 6 have similar abrasive grain volume ratios and vitrified bond volume ratios compared to Comparative Example 2, but have larger average pore diameters. The abrasive grain volume ratios of Examples 5 and 6 are larger than those of Examples 1 to 4, but the vitrified bond volume ratios and average pore diameters are similar. The ratio T / D, which is the ratio of the thickness T of the outer shell 26 of the hollow granules 20 to the outer diameter D, is within the range of Examples 1 to 4.

[0045] In Examples 1 to 6, the abrasive grain volume fraction was 19.3 to 25.9 vol %, the vitrified bond volume fraction was 9.3 to 12.0 vol %, the average pore diameter was 8 to 51 μm, and the outer diameter D of the hollow granules 20 was 22 to 82 μm.

[0046] As described above, the segmented grinding wheel (superabrasive vitrified grinding wheel with large pores) 14 of this embodiment includes hollow granules 20 having an outer shell 26 in which diamond abrasive grains (superabrasive grains) 18 are bonded with a vitrified bond, and the inner cavity of the hollow granules 20 forms large pores 22 within the porous structure of the segmented grinding wheel 14. As a result, the hollow granules 20 are uniformly mixed in the mixed material with little uneven distribution, resulting in a segmented grinding wheel 14 that is less likely to crack, can be manufactured stably, and has no bias in pore size, allowing for easy grinding wheel blend adjustment.

[0047] Furthermore, in the segment grinding wheel 14 of this embodiment, the hollow granules 20 have a ratio (T / D) of the thickness T of the outer shell 26 to the outer diameter D of the hollow granules 20 of 0.1 to 0.4, preferably 0.1 to 0.37. This ensures that the hollow structure of the hollow granules 20 is maintained during press molding. If the ratio (T / D) of the thickness T of the outer shell 26 to the outer diameter D of the hollow granules 20 is less than 0.1, the strength of the hollow granules 20 decreases, resulting in destruction of the hollow structure. If the ratio (T / D) of the thickness T of the outer shell 26 to the outer diameter D of the hollow granules 20 exceeds 0.37, the hollow structure is deformed during the spray-drying process, resulting in the formation of defective granules with no internal cavity, making it difficult to obtain the segment grinding wheel 14 within the porous structure.

[0048] Furthermore, according to the segmented grinding wheel 14 of this embodiment, the porous structure contains pores 24 with an average pore diameter of 5 to 60 μm, preferably 8 to 51 μm, thereby providing a segmented grinding wheel 14 with high grinding performance.

[0049] Furthermore, in the segmented grinding wheel 14 of this embodiment, the diamond abrasive grains 18 are 10 μmφ or less, and the hollow granules 20 have an outer shell 26 with a thickness T of 5 to 10 μm, preferably 8.2 to 9.6 μm, and an outer diameter D of 10 to 100 μm, preferably 22 to 82 μm. This makes it possible to obtain a segmented grinding wheel (super abrasive vitrified grinding wheel) 14 that is less susceptible to cracking, can be manufactured stably, and has large pores with no bias in pore diameter, allowing for easy grinding wheel blend adjustment.

[0050] In this embodiment, the segment grinding stones 14 are fixed to the outer periphery of the metal base metal 12 in a row at predetermined intervals in the radial direction to form the cup-shaped grinding wheel 10. This allows the expensive diamond abrasive grains 18 to be used effectively.

[0051] The manufacturing method of the segmented grinding wheel 14 of this embodiment includes a slurry preparation process P1 in which a slurry containing diamond abrasive grains 18, a vitrified bond, and a binder is prepared, a spray-dry granulation process P2 in which the slurry is sprayed in a dryer and dried in air to obtain hollow granules 20 from the slurry droplets, a molding process P3 in which the hollow granules 20 are press-molded in a mold to obtain a green body, and a firing process P4 in which the green body is fired to obtain the segmented grinding wheel 14 in a porous structure in which the diamond abrasive grains 18 are bonded by the vitrified bond. In the spray-dry granulation process P2, a slurry containing diamond abrasive grains 18, a vitrified bond, and a binder is sprayed in a dryer and dried in air, thereby suitably obtaining hollow granules 20 from the slurry droplets. The hollow granules 20 granulated in this manner have a relatively uniform particle size and a sharp particle size distribution, so that the pores 24 in the segment grinding wheel 14 have less variation and bias, and cracks are less likely to occur.

[0052] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the present invention is not limited to this embodiment and can be implemented in other modes.

[0053] For example, in the above-described embodiment, diamond abrasive grains 18 are used, but other superabrasive grains, such as CBN abrasive grains, may also be used.

[0054] In the above-described embodiment, a cup-shaped grinding wheel 10 was used in which a plurality of segment grinding stones 14 formed into a thick arc-shaped plate were fixed to the outer periphery of the base metal 12, but the segment grinding stones 14 may be grinding stones of other shapes. For example, they may be cup-shaped or disk-shaped vitrified grinding wheels having a predetermined thickness.

[0055] Alternatively, the segment grinding wheel 14 may have a two-layer structure in which the surface layer is made of a super-abrasive vitrified grinding wheel containing diamond abrasive grains 18, and the lower layer is made of aggregate (general abrasive grains or inorganic powder) bonded with a vitrified bond.

[0056] The above is merely one embodiment, and although other examples will not be given, the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art within the scope of the present invention.

[0057] 10: Cup-shaped grinding wheel 12: Base metal 14: Segment grinding wheel (superabrasive vitrified grinding wheel with large-diameter pores) 18: Diamond abrasive grains (superabrasive grains) 20: Hollow granules 22: Large-diameter pores 24: Pores 26: Outer shell T: Thickness (thickness of outer shell) D: Outer diameter (outer diameter of hollow granules)

Claims

1. A superabrasive vitrified grinding wheel having large pores within a porous structure in which superabrasive grains are bonded by a vitrified bond, wherein the superabrasive grains comprise hollow granules having an outer shell bonded by the vitrified bond, and the large pores are formed by the inner cavities of the hollow granules.

2. The superabrasive vitrified grinding wheel with large pores according to claim 1, characterized in that the ratio of the thickness of the outer shell to the outer diameter of the hollow granules is 0.1 to 0.

4.

3. The superabrasive vitrified grinding wheel with large pores according to claim 1, characterized in that the porous structure contains pores with an average pore diameter of 5 to 60 μm.

4. The vitrified superabrasive grinding wheel with large pores according to claim 1 or 2, characterized in that the superabrasive grains are 10 μm diameter or less, and the hollow granules have an outer shell with a thickness of 5 to 10 μm and an outer diameter of 10 to 100 μm.

5. A cup-shaped grinding wheel in which the superabrasive vitrified grinding stone having large pores according to claim 1 is fixed to the outer periphery of a metal base metal in a row at predetermined intervals in the radial direction.

6. A method for producing a superabrasive vitrified grinding wheel having large pores in a porous structure formed by bonding superabrasive grains with a vitrified bond, the method comprising: a slurry preparation step of preparing a slurry containing the superabrasive grains, the vitrified bond, and a binder; a spray-dry granulation step of spraying the slurry in a dryer and drying it in air to obtain hollow granules from the slurry droplets; a molding step of press-molding the hollow granules obtained in the spray-dry granulation step in a mold to obtain a green body; and a firing step of firing the green body to obtain a superabrasive vitrified grinding wheel having large pores in a porous structure formed by bonding superabrasive grains with the vitrified bond.

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