JP2014083621A - Vitrified grindstone of high porosity, method of producing the same and method of evaluating homogeneity of vitrified grindstone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vitrified grindstone of a high porosity which has an abrasive grain rate below 45 vol.% and prevents appropriately local clogging, glazing and falling of grindstone and scorching of a material to be ground.SOLUTION: In a vitrified grindstone of a high porosity, abrasive grains are bonded through a vitrified bond in such a state that pores are formed between abrasive grains and has an abrasive grain rate of 45 vol.% or lower. In the frequency distribution of abrasive grain area ratios representing the ratio of solid including abrasive grains per unit area at a plurality of sites in the cross section of the grindstone, the vitrified grindstone has homogeneity with a standard deviation of 10 or smaller, giving homogeneity with a high abrasive grain area ratio in the cross section of the vitrified grindstone and thereby preventing appropriately local clogging, glazing and falling and scorching of a material to be ground.

Description

  The present invention provides a high-porosity vitrified grinding wheel having a low abrasive grain ratio and a high porosity, which can obtain the shape maintaining ability and anti-burning characteristics of the grinding wheel in fields such as difficult-to-cut material grinding, screw grinding, groove grinding, and gear grinding. The present invention relates to a manufacturing method thereof and a method for evaluating the homogeneity of a vitrified grindstone.

  Generally, a high-porosity vitrified grindstone in which many pores are provided for an abrasive grain is known. For example, the porous vitrified grindstone described in Patent Document 1 is that. In such a high porosity vitrified grindstone, pores sufficiently larger than the abrasive grains are artificially formed, so that grinding heat is easily released during grinding under a grinding fluid, and the distance between the particles becomes wide. Therefore, high-efficiency grinding is possible, and even difficult-to-cut materials can be ground with high grinding efficiency.

  For this reason, in the high-porosity vitrified grindstone described in Patent Document 1, pores sufficiently larger than the abrasive grains are artificially formed and have a high porosity such that the abrasive grain ratio is less than 45% by volume. Therefore, the processing load is low, and the chip discharge is high due to the presence of the air holes. Therefore, there is an advantage that clogging and grinding burn of the high porosity vitrified grinding wheel are prevented.

JP 2003-181764 A

  However, in the conventional high-porosity vitrified grinding wheel, it is avoided that a local coarse-grain difference occurs near the boundary between a portion of pores sufficiently larger than the abrasive grains and a portion where the abrasive grains are densely packed. However, depending on the processing conditions, the abrasive wear area of the abrasive grains is locally increased in the densely-grained part of the abrasive grains. There was a case of inducing a burn.

  The present invention has been made against the background of the above circumstances, and the object of the present invention is to locally clog and crush the grindstone in a high porosity vitrified grindstone whose abrasive grain ratio is less than 45% by volume. An object of the present invention is to provide a high-porosity vitrified grindstone that does not easily fall off and burn the work material.

  Based on the above circumstances, the present inventors have made various studies on suppressing local clogging and crushing of a high porosity vitrified grinding stone with an abrasive grain ratio of less than 45% by volume and burning of the work material. As a result of reducing the size of the pores and increasing the homogeneity of the distribution of the grain area ratio in the cross section of the grinding wheel, local crushing and dropping of the grinding wheel and burning of the work material are suitably suppressed. I found the fact that. The present invention has been made based on this finding.

  That is, the gist of the vitrified grindstone of the first invention is that the abrasive grains are bonded by vitrified bonds in a state where the pores are formed between the abrasive grains, and have a high porosity having an abrasive grain ratio of 45% by volume or less. And a homogeneity having a standard deviation of 10 or less in the frequency distribution diagram of the abrasive grain area ratio, which is the ratio of the solids containing the abrasive grains per unit area at a plurality of locations in the cross section of the grindstone. Features.

  Further, the gist of the vitrified grindstone manufacturing method of the second invention is a state in which pores are formed between abrasive grains by molding a mixture of abrasive grains, vitrified bonds, and pore forming materials and then firing the mixture. In the method for producing a high porosity vitrified grinding wheel, wherein the abrasive grains are bonded by vitrified bonds and produce a high porosity vitrified grinding wheel having an abrasive grain ratio of 45% by volume or less, wherein the pore forming material comprises It has an average particle size equal to or less than the average particle size of the abrasive grains.

  Further, the gist of the method for evaluating the homogeneity of the vitrified grindstone of the third invention is an evaluation method for evaluating the homogeneity of a vitrified grindstone in which abrasive grains are bonded by vitrified bonds, and a plurality of locations in the cross section of the vitrified grindstone The ratio of the solid substance containing the abrasive grains per unit area is measured and evaluated based on the spread of the frequency distribution of the ratio.

  According to the vitrified grindstone of the first invention, the vitrified grindstone is a high porosity vitrified stone having an abrasive grain ratio of 45% by volume or less, in which the abrasive grains are bonded by vitrified bonds while pores are formed between the abrasive grains. In the frequency distribution diagram of the abrasive grain area ratio, which is the ratio of the solids containing the abrasive grains per unit area at a plurality of locations in the grindstone cross section, it has a homogeneity having a standard deviation of 10 or less, so in the vitrified grindstone cross section High homogeneity of the abrasive grain area ratio is obtained, and local clogging, crushing and dropping off of the grindstone, and burning of the work material are suitably suppressed.

  Here, preferably, the standard deviation has homogeneity having a standard deviation of 9 or less in the frequency distribution diagram. Preferably, the abrasive grains have an abrasive volume ratio of 35 to 45% by volume. More preferably, the abrasive has a volume fraction of 35 to 43% by volume. As a result, a vitrified grindstone having a high porosity that has a high homogeneity with an abrasive grain area ratio and that is suitable for suppressing local clogging, crushing and dropping of the grindstone, and burning of the work material is obtained.

  According to the manufacturing method of the vitrified grindstone of the second invention, after forming a mixture of abrasive grains, vitrified bonds, and pore forming materials, the abrasive grains are formed in a state where the pores are formed between the abrasive grains by firing. In the method for producing a high-porosity vitrified whetstone for producing a high-porosity vitrified whetstone that is bonded by vitrified bonds and has an abrasive ratio of 45% by volume or less, the pore-forming material has an average particle diameter of the abrasive grains. Since it has an average particle size of equal to or less than the same size, high homogeneity of the abrasive grain area ratio in the cross section of the vitrified grinding wheel is obtained, and local clogging and crushing and falling off of the grinding stone and burning of the work material are suitable. It is suppressed.

  Here, preferably, the pore forming material is selected to have an average particle size in a range that contributes to dispersion of the abrasive grains and does not contribute to uneven distribution of the abrasive grains. For example, the pore forming material has an average particle size of 0.23 to 0.75 times the average particle size of the abrasive grains. Preferably, the pore forming material has an average particle size of 0.41 to 0.63 times the average particle size of the abrasive grains. In this way, a homogeneity with a high abrasive grain area ratio in the cross section of the vitrified grindstone can be obtained, and local clogging and clogging of the grindstone and burning of the work material are suitably suppressed. When the average particle diameter of the pore forming material is less than 0.41 times or 0.23 times the average particle diameter of the abrasive grains, the ratio of the pore forming material not contributing to the dispersion of the abrasive grains becomes high. On the contrary, when the average particle diameter of the pore forming material exceeds 0.63 times or 0.75 times the average particle diameter of the abrasive grains, the ratio of occurrence of uneven distribution of the abrasive grains is high. Become.

  Moreover, according to the homogeneity evaluation method of the vitrified grindstone of the third invention, the ratio of the solids containing the abrasive grains per unit area of a plurality of locations in the vitrified grindstone in which the abrasive grains are bonded by vitrified bonds, respectively, Since the evaluation is based on the spread of the frequency distribution of the ratio, the homogeneity of the vitrified grindstone can be evaluated easily and accurately.

  Here, preferably, a standard deviation value is calculated from the frequency distribution, and the smaller the standard deviation value is, the higher the homogeneity is evaluated. Preferably, a half width is calculated from the frequency distribution. The smaller the half width, the higher the homogeneity is evaluated.

It is a front view which shows the high porosity vitrified grindstone of one Example of a present Example. It is process drawing explaining the principal part of the manufacturing method of the vitrified grindstone of FIG. It is a figure explaining the unit cell of the abrasive grain which can be regularly arranged in the closest packing state in a vitrified grindstone, (a) is composed of 4 unit lattices, and (b) is composed of 6. A unit cell is shown. It is a figure explaining the unit cell of an abrasive grain which can be arranged regularly in a uniform filling state in a vitrified grindstone, (a) is a unit cell constituted by four pieces, and (b) is a unit constituted by six pieces. A grid is shown. It is process drawing explaining the evaluation method which evaluates the homogeneity of a vitrified grindstone. It is a figure explaining the method to set the division | segmentation image (unit area) of the cross-sectional image of a vitrified grindstone in the frequency distribution map calculation process of FIG. It is a figure explaining the standard deviation value which shows the composition of Example 1 thru | or Example 6 produced according to the process of FIG. 2, and Comparative Example 1 thru | or Comparative Example 6, and its homogeneity. It is a figure explaining the structure | tissue of Example 7 thru | or Example 8 and the comparative example 7 thru | or the comparative example 8 which were created according to the process of FIG. The cross-sectional photograph after the binarization process for evaluating the homogeneity of Example 7 of FIG. 8 is shown. In order to evaluate the homogeneity of Example 7 in FIG. 8, a frequency distribution diagram obtained from the cross-sectional photograph in FIG. 9 is shown. The cross-sectional photograph after the binarization process for evaluating the homogeneity of the comparative example 7 of FIG. 8 is shown. In order to evaluate the homogeneity of Comparative Example 7 in FIG. 8, a frequency distribution diagram obtained from the cross-sectional photograph in FIG. 11 is shown. It is a figure which shows grinding performance on the two-dimensional coordinate of a power consumption axis | shaft and a grinding ratio axis | shaft from the grinding-work test result of Example 7 and 8 of FIG. 8, and Comparative Examples 7 and 8. FIG. FIGS. 8A and 8B are diagrams for explaining the wear state of the corners of the vitrified grindstones based on the grinding test results of Examples 7 and 8 and Comparative Examples 7 and 8, in which FIG. 8A shows Example 7 and FIG. Example 7 is shown respectively.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a front view showing a high-porosity vitrified grinding wheel 10 according to an embodiment of the present invention. The vitrified grindstone 10 has a thick disk shape, has a grinding surface 12 on the outer peripheral surface, and has a mounting hole 14 in the center. By attaching the attachment hole 14 to the main shaft of a grinding apparatus (not shown), the vitrified grinding wheel 10 is driven to rotate. The vitrified grindstone 10 is a disc-shaped grindstone having an outer diameter of about 205 mm, an inner diameter of about 76.2 mm, and a thickness of about 10 mm.

  The vitrified grindstone 10 has a porous vitrified grindstone structure in which general abrasive grains such as fused alumina abrasive grains (alundum) and silicon carbide abrasive grains (carborundum) are bonded by vitreous vitrified bonds. Yes. As will be described later, the vitrified grindstone 10 is a high porosity vitrified grindstone having an abrasive grain ratio of 45% by volume or less.

  The abrasive grains have, for example, a particle size of F46 to F120, that is, an average abrasive grain size of about 100 μm to 360 μm, and constitute the porous vitrified grindstone structure at a ratio of 35 to 45 volume%, for example. The vitrified bond constitutes the porous vitrified grindstone structure at a ratio of 5 to 12% by volume, for example. The remaining pores are formed in the porous vitrified grindstone structure at a ratio of 43 to 56% by volume, for example.

The vitrified bond is made of, for example, the well-known silicate glass, borosilicate glass, or crystallized glass. Preferred glass compositions for the vitrified bond include, for example, SiO ₂ : 40 to 70 parts by weight, Al ₂ O ₃ : 10 to 20 parts by weight, B ₂ O ₃ : 0 to 20 parts by weight, RO (alkaline earth metal): 20 to 10 parts by weight, R ₂ O: 2 to 10 parts by weight.

FIG. 2 is a process diagram for explaining the manufacturing process of the vitrified grindstone 10. In FIG. 2, first, in the raw material preparation stirring step P <b> 1, a grindstone material for the vitrified grindstone 10 is prepared. For example, general abrasive grains such as an Al ₂ O ₃ system known as alumina abrasive grains having a particle size of F46 to F120 (average particle diameter D is 106 to 355 μm) according to JIS R6001, and a ZrO ₂ —B ₂ O ₃ system, Vitreous vitrified bonds (inorganic binders) such as B ₂ O ₃ —Al ₂ O ₃ —SiO ₂ and R ₂ O—Al ₂ O ₃ —SiO ₂ and a certain amount of mutual cohesion during molding An organic binder for molding (a binder or an amount of glue) such as dextrin and carboxymethylcellulose for generating, and a pore-forming material having an average particle size P smaller than the average particle size D of the abrasive grains; Are weighed at a preset ratio and mixed to prepare a grindstone raw material. Table 1 shows an example of the mixing ratio of the grindstone raw material in the raw material mixing and stirring step P1.

[Table 1]
Raw material name Ratio
Alumina abrasive (average particle size 200 μm) 40 parts by volume Pore forming material (average particle size 46 to 200 μm) 10 parts by volume Vitrified bond 14 parts by volume
Amount of paste 6 parts by volume

  The pore forming material is a material that artificially or actively forms pores (spaces) in the vitrified grindstone structure after the firing treatment in the firing step P4 described later, for example, hollow or solid naphthalene, DMT, alumina balloon. (Alumina hollow body), walnut powder, polystyrene, cross-linked acrylic and the like. The pore forming material has a diameter that contributes to the dispersion of the abrasive grains and contributes to suppressing the uneven distribution or segregation of the abrasive grains. That is, unless the pore-forming material diameter is larger than the diameter of the voids formed between the closely packed (aggregated) abrasive grains, it cannot contribute to the dispersion of the abrasive grains, and the homogeneously packed abrasive grains Unless it is less than the diameter of the pores formed between them, it is not possible to contribute to suppression of uneven distribution or segregation of abrasive grains. Here, considering the assumption that the abrasive grains and pores are spherical, the packing theory is the closest packed state (the grain diameter and the center-to-center distance of the abrasive grains are D, and the abrasive grain ratio Vg = 74.0%). As shown in FIG. 3A or 3B, the unit lattice of abrasive grains that can be regularly arranged is a tetrahedron composed of four abrasive grains, or an octahedral lattice composed of six abrasive grains. The maximum particle size entering the void at the center of the tetrahedron with respect to the abrasive particle size D is 0.23D, and the maximum particle size entering the center of the octahedron is 0.41D. Therefore, the average particle diameter P of the pore forming material can contribute to the dispersion of the abrasive grains by being larger than 0.23D or 0.41D with respect to the average particle diameter D of the abrasive grains. Similarly, the unit cell of the abrasive grains that can be regularly arranged in a homogeneous filling state (abrasive grain size D, center-to-center distance 1.18 to 1.28 D, abrasive grain ratio Vg: 45 to 35%) is also the same. When a tetrahedron composed of 4 abrasive grains or an octahedral lattice composed of 6 abrasive grains is used, the maximum particle diameter entering the void in the center of the tetrahedron with respect to the abrasive grain diameter D is 0.43D to 0. 54D, the maximum particle diameter entering the center of the octahedron is 0.63D to 0.75D. When the average particle size P of the pore forming material is smaller than 0.43D to 0.54D or 0.63D to 0.75D, it can contribute to suppression of uneven distribution or segregation of abrasive grains. Therefore, the average particle diameter P of the pore-forming material is 1D or less, but a temporary effect can be obtained, but preferably 0.23 to 0.75 times the average particle diameter D of the abrasive grains, Preferably, it is 0.41 to 0.63 times. From such a viewpoint, since the average particle diameter D of the abrasive grains used in Table 1 is 200 μm, the average particle diameter P of the pore forming material in Table 1 is preferably in the range of 46 to 150 μm, The range of 80 to 126 μm is more preferable. The pore volume ratio (%) of the vitrified grindstone 10 is formed by pores artificially formed by the pore forming material and natural pores.

  Next, in the molding step P2, the mixed grinding wheel raw material is filled into a molding cavity of a predetermined molding die, and the grinding stone raw material is pressurized by a press device, thereby being the same as the vitrified grinding stone 10 shown in FIG. A shaped molded body is formed. Next, after passing through a drying step P3 for drying the molded body, in the firing step P4, the molded body is fired at a temperature of, for example, 900 to 1050 ° C. for 2 hours, whereby the vitrified grinding stone 10 shown in FIG. 1 is obtained. Then, dimension finishing is performed in the finishing process P5, and product inspection is performed in the inspection process P6.

  FIG. 5 is a process diagram illustrating a method for evaluating the homogeneity in the structure of the vitrified grindstone 10 by the evaluation computer and the frequency distribution of the abrasive grain area ratio. In FIG. 5, in the cross-sectional imaging step P <b> 11, an image captured in a state where the cross section of the vitrified grindstone 10 is enlarged through a microscope is input. Next, in the image processing step P12, the image at the predetermined depth of focus position is binarized using image processing by a computer on the micrograph obtained in the cross-sectional imaging step P11, so that the left side of FIG. A black and white cross-sectional image is generated as shown. In this cross-sectional image, the black portion indicates space, that is, pores, and the white portion indicates solid matter such as abrasive grains and vitrified bonds. In the subsequent frequency distribution diagram calculation step P13, the cross-sectional image is divided by a grid and the size of the divided region (unit image) whose one side is x (μm) is determined from the following equation (2) as the abrasive volume ratio Vg. And calculated based on the abrasive grain size D. Subsequently, for each divided region as shown on the right side of FIG. 6, the area ratio Sg (%) of the solid part of the white portion is calculated, and the horizontal axis is the size of the area ratio Sg, and the cumulative number of divided regions is calculated. A frequency distribution chart having a vertical axis is created as shown in FIG. Then, in the standard deviation calculation step P14, the standard deviation σ or the full width at half maximum (%) is calculated from the distribution shown in the created frequency distribution chart. The smaller the standard deviation σ or the half width (%), the higher the evaluation value for evaluating the homogeneity of the vitrified grinding wheel structure. The left side of (1) is the calculated value of the area of the abrasive grains contained in the square divided region with the length x of one side in the cross section of the grinding wheel with the abrasive volume ratio Vg, and the right side of (1) is the abrasive grains for 5 grains. A cross-sectional area of the abrasive grains having an average particle diameter D of (1) is a modified expression of the expression (1). In order to evaluate the homogeneity from the image cross section, it is desirable to divide the image with the number of abrasive grains of about 5 or more as a partition. If the number of abrasive grains is smaller than this, the segregation part where the abrasive grains are dense cannot be accurately reflected. On the other hand, if the number of abrasive grains is defined too much, the distribution width of the frequency distribution chart is narrowed and local segregation of abrasive grains occurs. The difference is not recognized. In order to create a highly accurate frequency distribution diagram, the cross-sectional image needs to have a division number of 100 or more, more preferably 200 or more.

^{x 2 (Vg / 100) =} 5 × (πD 2/4) ··· (1)
x = (500πD ² / 4Vg) ^0.5 (2)

  Examples 1 to 8 and Comparative Examples 1 to 8 shown in FIGS. 7 and 8 are common in that they have an abrasive grain ratio of 45% by volume or less. FIG. 7 shows six grindstone samples having different grindstone sizes in the range of F46 to F120 and different in grindstone volume ratio Vg of 45 vol% or less, that is, 35 to 45 vol%. FIG. 5 shows Examples 1 to 6 prepared in accordance with the steps and Comparative Examples 1 to 6 which were prepared in accordance with the same steps with the same grindstone particle size but differ in having a particle size exceeding the range 1D. It is a figure which shows 1 side x and standard deviation (sigma) of the division area calculated by the evaluation method. According to this, if the average particle size P of the pore forming material is within the range of 0.23D ≦ P ≦ 0.75D, the standard deviation σ is 10 or less, more precisely 9 or less in the frequency distribution diagram, Compared with Comparative Examples 1 to 6 having a standard deviation σ of 10.2 to 11.7, a homogeneous vitrified grindstone structure was obtained. In addition, when the average particle size P of the pore forming material is in the range of 0.23D ≦ P ≦ 0.75D, compared with Comparative Examples 1 to 6 in which the half-value width is 26 to 32, it is half in the frequency distribution diagram. A homogeneous vitrified grinding wheel structure having a value width of 20 or less was obtained.

  Next, the four kinds of vitrified grinding wheel samples shown in FIG. 8, ie, Example 7, Example 8, Comparative Example 7, and Comparative Example 8, are for performing a grinding test under the test conditions shown in Table 2 below. It is. Example 7 and Example 8, and Comparative Example 7 and Comparative Example 8 have the same abrasive grain type, abrasive grain size, and abrasive volume fraction Vg, and the volume fraction of vitrified bond is that of Example 7 and Comparative Example. Comparative Example 7 is different from Example 7 and Example 8 and Comparative Example 8 in that Example 7 and Example 8 are homogenous grindstones because the pore forming material (120 μm) is included in the grindstone raw material. This is different from Comparative Example 8. As a result, according to the evaluation method of the frequency distribution of the abrasive grain area ratio shown in FIG. 5, the standard deviation σ of Example 7 is 8.56 and the standard deviation σ of Example 8 is 8.44. The standard deviation σ is 11.4, and the standard deviation σ of Comparative Example 8 is 11.2. 9 shows a cross-sectional image of Example 7, and FIG. 10 shows a frequency distribution diagram and a standard deviation obtained from the cross-sectional image of Example 7. FIG. 11 shows a cross-sectional image of Comparative Example 7, and FIG. 12 shows a frequency distribution diagram and standard deviation obtained from the cross-sectional image of Comparative Example 7.

[Table 2]
Grinding test conditions
Grinding machine Surface grinder Grinding method Wet plunge grinding Workpiece Heat resistant steel Table feed rate 20m / min
Cutting depth 10μm / pass
Total depth of cut 3mm
Wheel size 205 × 19 × 76.2
Grinding oil Water-soluble grinding fluid
Grinding wheel speed 3000rpm

  FIG. 13 shows the results of a grinding test conducted by the inventors. FIG. 13 is a two-dimensional coordinate of an axis indicating the power consumption per unit width of the grindstone and an axis indicating the grinding ratio. The rhombus marks indicate the performance of Example 7 and Example 8, and the triangle marks indicate Comparative Example 7. And the performance of Comparative Example 8 is shown. The vitrified grindstones of Example 7 and Example 8 have the performance that the power consumption is low and the grinding ratio is high, that is, the sharpness is high and difficult to reduce, as compared with Comparative Example 7 and Comparative Example 8.

  FIG. 14 also shows the result of the grinding test conducted by the present inventors. FIG. 14 is a diagram showing the end of the grinding surface of the vitrified grindstone, that is, the angle of the radial section of the vitrified grindstone, in the two-dimensional coordinates of the axis representing the grindstone width direction dimension and the axis representing the grindstone radial dimension. The white part shows the square shape consumed by grinding. 14A shows the square shape after the grinding test of Example 7, and FIG. 14B shows the square shape after the grinding test of Comparative Example 7. FIG. The consumption amount of Example 7 is 70% or less as compared with Comparative Example 7. Also from this, it is clear that Example 7 has the performance that the sharpness is high and is not easily reduced.

  As described above, according to the present example, the high-porosity vitrified grinding wheel having the abrasive grain ratio of 45 volume% or less, in which the abrasive grains are bonded by vitrified bonds while the pores are formed between the abrasive grains. In addition, since it has a homogeneity having a standard deviation of 9 or less in the frequency distribution of the abrasive grain area ratio, which is the ratio of the solids containing the abrasive grains per unit area at a plurality of locations in the grinding wheel cross section, the vitrified grinding wheel cross section High uniformity of the abrasive grain area ratio is obtained, and local clogging, crushing and falling off of the grindstone, and burning of the work material are suitably suppressed.

  Further, according to the present embodiment, after forming a mixture of abrasive grains, vitrified bond, and pore forming material, firing is performed, and the abrasive grains are bonded by vitrified bond in a state where the pores are formed between the abrasive grains. A high porosity vitrified grinding wheel for producing a high porosity vitrified grinding wheel having an abrasive grain ratio of 45% by volume or less, wherein the pore forming material is equal to the average grain size of the abrasive grains. Since it has the following average particle size, high homogeneity of the abrasive grain area ratio in the cross section of the vitrified wheel is obtained, and local clogging, crushing and falling off of the wheel, and burning of the work material are suitably suppressed. The

  Further, according to the present example, the pore diameter forming material is selected to have an average particle diameter in a range that contributes to the dispersion of the abrasive grains and does not contribute to the uneven distribution of the abrasive grains, and the average particle diameter of the abrasive grains is 0.23. The average particle size is not less than twice and not more than 0.75 times, or 0.41 times and not more than 0.63 times the average particle size of the abrasive grains. For this reason, homogeneity with a high abrasive grain area ratio in the cross section of the vitrified grindstone is obtained, and local clogging, crushing and falling off of the grindstone, and burning of the work material are suitably suppressed. When the average particle diameter of the pore forming material is less than 0.41 times or 0.23 times the average particle diameter of the abrasive grains, the ratio of the pore forming material not contributing to the dispersion of the abrasive grains becomes high. On the contrary, when the average particle diameter of the pore forming material exceeds 0.63 times or 0.75 times the average particle diameter of the abrasive grains, the ratio of occurrence of uneven distribution of the abrasive grains is high. Become.

  Further, according to this example, the evaluation method for evaluating the homogeneity of the vitrified grindstone in which the abrasive grains are bonded by vitrified bonds, the solid containing the abrasive grains per unit area at a plurality of locations in the cross section of the vitrified grindstone. Since the ratio of each object is measured and evaluated based on the spread of the frequency distribution of the ratio, the homogeneity of the vitrified grindstone is easily and accurately evaluated.

  Further, according to the present embodiment, the standard deviation value or the half value width is calculated from the frequency distribution, and the smaller the standard deviation value or the half value width, the higher the homogeneity is evaluated. Therefore, the homogeneity of the vitrified grindstone is increased. Easily and accurately evaluated.

  As mentioned above, although one Example of this invention was described in detail with reference to drawings, this invention is not limited to this Example, It can implement in another aspect.

  For example, in the above-described embodiment, the vitrified grindstone of the present invention is not provided with an underlayer or a core, and is entirely composed of a vitrified grindstone structure, but the grindstone layer fixed on the underlayer or the core. May be applied. Moreover, you may apply with respect to the whole or surface layer of other types of grindstones, such as a cup-shaped grindstone and a block-shaped grindstone.

  It should be noted that the above description is merely an embodiment, and other examples are not illustrated. However, the present invention is implemented in variously modified and improved modes based on the knowledge of those skilled in the art without departing from the gist of the present invention. Can do.

10: Vitrified grinding wheel with high porosity

Claims (8)

A high-porosity vitrified grindstone having an abrasive grain ratio of 45% by volume or less, wherein the abrasive grains are bonded by vitrified bonds in a state where pores are formed between the abrasive grains,
A high-porosity characterized by having a homogeneity having a standard deviation of 10 or less in a frequency distribution diagram of an abrasive grain area ratio, which is a ratio of solids including the abrasive grains per unit area at a plurality of locations in a cross section of a grindstone Vitrified grinding wheel.   The high-porosity vitrified grindstone according to claim 1, wherein the abrasive grains have an abrasive volume ratio of 35 to 45 vol%.   The high-porosity vitrified grinding wheel according to claim 1, wherein the abrasive grains have an abrasive volume ratio of 35 to 45% by volume and have a standard deviation of 9 or less in the frequency distribution diagram. A mixture of abrasive grains, vitrified bond, and pore forming material is molded and then baked to bond the abrasive grains with vitrified bond in a state in which pores are formed between the abrasive grains, and 45% by volume or less of abrasive grains A method for producing a high porosity vitrified grinding wheel for producing a high porosity vitrified grinding wheel having a rate,
The method for producing a high porosity vitrified grindstone, wherein the pore forming material has an average particle size equal to or less than the average particle size of the abrasive grains.   5. The high-porosity vitrified grinding wheel according to claim 4, wherein the pore-forming material has an average particle size of 0.23 times or more and 0.75 times or less the average particle size of the abrasive grains. Production method.   5. The high porosity vitrified grindstone according to claim 4, wherein the pore forming material has an average particle size of 0.41 to 0.63 times the average particle size of the abrasive grains. Production method. An evaluation method for evaluating the homogeneity of a vitrified grindstone in which abrasive grains are bonded by vitrified bonds,
A method for evaluating the homogeneity of a vitrified grindstone, characterized by measuring a ratio of solids containing the abrasive grains per unit area at a plurality of locations in the cross section of the vitrified grindstone, and evaluating based on a spread of a frequency distribution of the ratio .   8. The method of evaluating homogeneity of a vitrified grindstone according to claim 7, wherein a standard deviation value or a half width is calculated from the frequency distribution, and the homogeneity is evaluated higher as the standard deviation value or the half width is smaller.

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