JP7420603B2 - Low porosity vitrified grinding wheel containing diamond abrasive grains - Google Patents

Description

The present invention relates to a vitrified grindstone containing diamond abrasive grains with high grinding efficiency.

In vitrified grinding wheels, which are made up of abrasive grains bonded together by a glassy vitrified bond, it is important that the cutting edge of the abrasive grain penetrates into the material, so the abrasive grain has a hard and sharp cutting edge. It is necessary to maintain Diamond abrasive grains are known as the ultra-hard abrasive grains with the highest hardness, but when fired at 800° C. or higher in an air atmosphere, most of the diamond abrasive grains disappear by reacting with oxygen in the air.

On the other hand, if firing is performed in a non-oxidizing atmosphere such as a reducing atmosphere, a vitrified diamond grinding wheel in which diamond abrasive grains are bonded by a vitrified bond can be obtained, but this only increases production costs due to expensive equipment. However, the wettability of the vitrified bond to the surface of the diamond abrasive grains is low, and the adhesion between the diamond abrasive grains and the vitrified bond is insufficient, making it impossible to obtain durability. For this reason, it is important to sinter a vitrified grindstone containing diamond abrasive grains in an air atmosphere.

In contrast, a method has been proposed in which a vitrified diamond grindstone is fired in an atmospheric atmosphere. For example, there is a method for manufacturing a vitrified diamond grindstone described in Patent Document 1. According to this, a vitrified diamond grindstone is fired in an air atmosphere at a temperature of 700 to 800° C. using a vitrified bond having a softening point of 650° C. or higher. This produces a vitrified diamond grindstone that is sharp and durable.

International Publication No. 2005/072912

By the way, in the method for manufacturing a vitrified diamond grinding wheel described in Patent Document 1, as explained in paragraph 0085 thereof, by using a vitrified bonding agent with a softening point higher than 650° C. at which diamond abrasive grains begin to disappear. It causes moderate disappearance of diamond abrasive grains under air atmosphere, which can improve the wettability of vitrified bonding agent to diamond abrasive grains, resulting in good grinding performance with improved abrasive grain retention. This makes it possible to manufacture vitrified diamond grindstones.

However, during firing, the diamond abrasive grains are exposed to the atmosphere at temperatures higher than 650°C, which thins the diamond abrasive grains and disrupts the cutting edge, making it difficult to achieve both workpiece surface roughness and grinding efficiency. The problem was that it was difficult to obtain.

The present invention was made against the background of the above circumstances, and its object is to provide a vitrified grindstone containing diamond abrasive grains that provides good surface roughness and high grinding efficiency.

As a result of various studies against the background of the above circumstances, the present inventors have developed main abrasive grains with a predetermined average particle diameter ratio to main abrasive grains containing alumina abrasive grains and silicon carbide abrasive grains. Diamond abrasive grains with an average grain size smaller than the diamond abrasive grains are added at a predetermined volume ratio, and the volume ratio of the vitrified bond that binds these main abrasive grains and the diamond abrasive grains is increased to the same level as the main abrasive grains, thereby increasing the porosity. It has been discovered that by producing a vitrified grinding wheel with a low viscosity, it is possible to obtain a good surface roughness of the workpiece and at the same time increase the grinding efficiency. The present invention has been made based on this knowledge. Grinding efficiency increases as the volume ratio of diamond abrasive grains added to the main abrasive grains increases, but while the surface roughness of the ground surface deteriorates, decreasing the average particle size ratio of diamond abrasive grains to the main abrasive grains Since the surface roughness is good, there is a region where the surface roughness and grinding efficiency are compatible. In addition, by increasing the volume fraction of the vitrified bond to the same level as the main abrasive grains and making the average grain size of the diamond abrasive grains relatively smaller than the main abrasive grains, it is possible to The small diamond abrasive grains are easily covered by the vitrified bond, and even when the diamond abrasive grains are diamond abrasive grains, firing in an atmospheric atmosphere becomes possible.

That is, the gist of the low porosity vitrified whetstone containing diamond abrasive grains of the present invention is a low porosity vitrified whetstone containing diamond abrasive grains in which abrasive grains are bonded by a glassy vitrified bond. is a main abrasive grain consisting of a mixture of alumina abrasive grains and silicon carbide abrasive grains, an average particle size ratio of 0.2 to 0.8 with respect to the main abrasive grain, and 0.8 with respect to the grindstone volume. diamond abrasive grains having a volume fraction of ~4.0% by volume.

According to the low porosity vitrified grinding wheel containing diamond abrasive grains of the present invention, the abrasive grains are bonded together by a glassy vitrified bond, and the abrasive grains are made of alumina. a main abrasive grain consisting of a mixture of abrasive grains and silicon carbide abrasive grains, an average particle size ratio of 0.2 to 0.8 with respect to the main abrasive grains, and 0.8 to 4.0 with respect to the grinding wheel volume; and the diamond abrasive grains having a volume fraction of % by volume. From this, a low-porosity vitrified grindstone containing diamond abrasive grains, which provides good surface roughness and high grinding efficiency, can be obtained by firing in an atmospheric atmosphere.

Preferably, in the low porosity vitrified grindstone containing the diamond abrasive grains, the main abrasive grains are included in a proportion of 40% or more by volume based on the volume of the grindstone, and the vitrified bond is preferably contained in a proportion of 40% or more by volume based on the volume of the grindstone. It is contained in a proportion of 45% by volume or more. In this way, since the ratio of vitrified bond to the grinding wheel volume is high, the diamond abrasive grains are covered with the glassy vitrified bond during firing, so even if the diamond abrasive grains are diamond abrasive grains, they can be exposed to the atmosphere. can be fired.

Preferably, the filling rate of the abrasive grains and the vitrified bond with respect to the volume of the whetstone is 85% by volume or more, so that the diamond abrasive grains are covered with the glassy vitrified bond during firing. Even if the grains are diamond abrasive grains, firing in an atmospheric atmosphere is possible.

Preferably, since the vitrified bond has a softening point of 850° C. or higher, a low porosity vitrified bond containing diamond abrasive grains can be formed using a general vitrified bond under the firing conditions of a general vitrified grinding wheel. Can manufacture whetstones.

FIG. 2 is a perspective view schematically illustrating a tap board using a vitrified grindstone according to an example of the present embodiment. This is a graph illustrating the compositions of five types of test grindstones 1 to 5, which were otherwise produced in the same manner as the vitrified grindstone of FIG. 1, except that the content of diamond abrasive grains was different. It is a figure which shows the structure of the test grindstone 1 of FIG. 2 using EDX and SEM. It is a figure which shows the structure of the test grindstone 2 of FIG. 2 using EDX and SEM. It is a figure which shows the structure of the test grindstone 3 of FIG. 2 using EDX and SEM. 3 is a diagram showing the structure of the test grindstone 4 of FIG. 2 using EDX and SEM. FIG. FIG. 3 is a diagram showing the structure of the test grindstone 5 of FIG. 2 using EDX and SEM. 3 is a chart explaining test conditions of a grinding test using the five types of test grindstones shown in FIG. 2. FIG. 9 is a graph showing the results of a grinding test using the five types of test grindstones shown in FIG. 2 using the test conditions shown in FIG. 8, and showing the relative values of grindstone wear amount and grinding efficiency, respectively. Ten types of test grinding wheels 6 to 15 were prepared in the same manner as the vitrified grinding wheel shown in Fig. 1, and had a diamond abrasive grain content of 2.5% by volume, and differed in the particle size ratio of the diamond abrasive grains to the main abrasive grains. 9 is a graph showing the results of a grinding test using the test conditions shown in FIG. 8, showing surface roughness and grinding efficiency, respectively. Five types of test grinding wheels 16 to 20, which were manufactured in the same manner as the vitrified grinding wheel shown in Fig. 1 and differed only in the ratio of alumina abrasive grains and silicon carbide abrasive grains constituting the main abrasive grains, were used under the test conditions shown in Fig. 8. 1 is a graph showing the results of a grinding test conducted on a grinding machine, showing surface roughness and grinding efficiency, respectively.

EMBODIMENT OF THE INVENTION Below, one Example of this invention is described in detail based on drawing.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. Note that in the following embodiments, the figures are simplified or conceptualized as appropriate, and the dimensional ratios, shapes, etc. of each part are not necessarily accurately drawn.

FIG. 1 is a schematic diagram showing a lapping machine 12 using a homogeneous low-porosity vitrified grinding wheel 10 (hereinafter referred to as vitrified grinding wheel 10) containing diamond abrasive grains as a lower surface plate according to an embodiment of the present invention. The vitrified grindstone 10 is provided so as to be rotationally driven around a vertical rotational center axis C by a drive device that does not have the same structure. The vitrified grindstone 10 has a disk shape, and has an outer diameter of 327 mmφ, a thickness of 25 mm, and an inner diameter of 112 mmφ, for example.

In FIG. 1, a workpiece 14, for example, an outer ring or an inner ring of a bearing, is placed on a vitrified grindstone 10, and the outer circumferential surface of the workpiece 14 is prevented from moving in the circumferential direction by a work holder (not shown). It is held so that it can rotate. A weight 16 is placed on the workpiece 14 so as to generate an appropriate grinding pressure. A grinding fluid F for wet grinding is supplied from a nozzle 18 to the upper surface of the vitrified grindstone 10. As a result, the lower surface of the workpiece 14 comes into sliding contact with the upper surface of the vitrified grindstone 10, and is lapped on one side.

As shown in FIGS. 2 to 7 described later, the vitrified grinding wheel 10 has a low porosity of about 10% by volume or less based on the volume of the grinding wheel, in which abrasive grains are bonded by a glassy vitrified bond 24. It has a vitrified grindstone structure. The above abrasive grains are mixed abrasive grains in which alumina abrasive grains (molten alumina: Al ₂ O ₃ ) and silicon carbide abrasive grains (SiC) are in a weight ratio of 2:8 to 8:2, and the particle size is For example, a main abrasive grain 20 that is F180 and an average grain size ratio of 0.2 to 0.8 to the main abrasive grain 20 (= average grain size of diamond abrasive grains 22 / average grain size of main abrasive grains 20), and diamond abrasive grains 22 having a volume ratio of 0.8 to 4.0% by volume based on the volume of the grindstone and having a grain size of, for example, #400/500. The main abrasive grains 20 are contained in a ratio of 44 to 56 volume% (50 to 62 weight%) based on the volume of the grinding wheel, and the vitrified bond 24 is contained in a proportion of 44 to 56 volume% (38 to 50 weight%) based on the volume of the grinding wheel. included in the proportion of As a result, the filling rate of the abrasive grains (main abrasive grains 20 and diamond abrasive grains 22) and the vitrified bond 24 to the grinding wheel volume is as high as 85 volume % or more, and the pore volume ratio is 15 volume % or less, preferably 10 volume %. It is said to have a low porosity of:

The vitrified bond 24 is, for example, a borosilicate glass having a softening point of 850° C. or higher, and includes, for example, 60 wt% or more of SiO ₂ , 10 wt% or more of Al ₂ O ₃ , or 1 wt% or less of B ₂ O _3. It has a chemical composition containing 20 wt% or less of CaO, MgO, K ₂ O, and Na ₂ O ₃ in total.

The above softening point is defined as the temperature at which the elongation of the glass wire becomes 1 mm when a glass wire with a diameter of 0.55 to 0.77 mmφ and a length of 235 mm is heated from room temperature at a rate of 4 to 6°C/min. be done. In the chemical composition of the vitrified bond 24, when SiO ₂ is less than 60 wt%, the coefficient of thermal expansion increases and the softening point decreases too much. If Al ₂ O ₃ is less than 10 wt%, the softening point will drop too much and phase separation of the glass will occur. If the total content of CaO, MgO, K ₂ O, and Na ₂ O ₃ exceeds 20 wt%, the softening point becomes too low.

The vitrified whetstone 10 is produced by mixing the main abrasive grains 20, diamond abrasive grains 22, and vitrified bond 24 with water, press-molding the mixture, and drying to remove the water. After that, the vitrified bond 24 is manufactured by melting the vitrified bond 24 by firing it in an air atmosphere at a firing temperature of 900° C. or higher, for example.

In the vitrified grindstone 10 configured in this way, the volume of the abrasive grains (main abrasive grains 20 and diamond abrasive grains 22) is 40 to 60 volume%, preferably 44 to 56 volume%, based on the volume of the grindstone, and the vitrified bond 24 The volume is 40 to 60% by volume relative to the volume of the grinding wheel, preferably 44 to 56% by volume, and the filling rate of the abrasive grains and vitrified bond 24 to the volume of the grinding wheel is 85% by volume or more, and the main abrasive grains 20 and the main Diamond abrasive grains 22 with a particle size ratio of 0.2 to 0.8 to the main abrasive grains 20 are included in an amount of 0.8 to 4.0% by volume of the grinding wheel so that they can be placed between the main abrasive grains 20 and the main abrasive grains 20. At the same time as the number of blades is increased, the grinding action due to the hardness of the main abrasive grains 20 and the diamond abrasive grains 22 is optimized as described below. The main abrasive grains 20 are preferably mixed abrasive grains of alumina abrasive grains and silicon carbide abrasive grains. Silicon carbide abrasive grains have excellent sharpness due to their relative hardness, but they are also easily abraded due to their high crushability. As a result, wear of the vitrified grindstone 10 is suppressed and the grinding ratio is increased.

In addition, the vitrified grindstone 10 has a low porosity of about 10% by volume or less, and as described above, the filling rate of the abrasive grains and vitrified bond 24 is 85% by volume or more, so there is a glassy layer between the main abrasive grains 20. By entering the vitrified bond 24, the oxygen supply caused by the oxide between the main abrasive grains 20 is cut off. Further, due to the high filling rate, the number of pores in the vitrified grindstone 10 is reduced, and at the same time, the number of communicating pores is reduced, so that oxygen supply from the atmosphere outside the vitrified grindstone 10 is cut off. Furthermore, the reaction layer on the surface of the vitrified grindstone 10 blocks the supply of oxygen to the inside of the vitrified grindstone 10, thereby suppressing the burnout of the diamond abrasive grains 22 due to firing.

(Experiment example 1)
_The present inventors have developed the main abrasive grains ₂₀ shown in FIG. Five types of test whetstones 1 to 5 have a volume ratio of 3.99 volume%, 2.08 volume%, 0.80 volume%, and 0.40 volume% of diamond abrasive grains 22 to the volume of the grindstone. , 0% by volume, five types of test grindstones 1 to 5 were produced using the above manufacturing process. The test wheel 1 had 40.27% by volume of main abrasive grains 20, 3.99% by volume of diamond abrasive grains 22, 44.97% by volume of vitrified bond 24, and 10.77% by volume of pores. are doing. The test wheel 2 had 41.85% by volume of main abrasive grains 20, 2.08% by volume of diamond abrasive grains 22, 48.35% by volume of vitrified bond 24, and 7.72% by volume of pores. are doing. The test whetstone 3 had 42.22% by volume of main abrasive grains 20, 0.80% by volume of diamond abrasive grains 22, 49.49% by volume of vitrified bond 24, and 7.49% by volume of pores. are doing. The test whetstone 4 had 41.45% by volume of main abrasive grains 20, 0.40% by volume of diamond abrasive grains 22, 50.74% by volume of vitrified bond 24, and 7.41% by volume of pores. are doing. The test whetstone 5 had 41.02% by volume of main abrasive grains 20, 0% by volume of diamond abrasive grains 22, 50.54% by volume of vitrified bond 24, and 8.43% by volume of pores. There is.

3 to 7 are EDX analysis photographs showing the elements and concentrations obtained using EDX (energy dispersive X-ray spectroscopy) and SEM (scanning electron microscope) for test grinding wheels 1 to 5. SEM photographs showing an enlarged view of the bonding state of the abrasive grains by the vitrified bond 24 are shown. In the actual EDX analysis photos, Al contained in alumina abrasive grains is red (indicated as red in Figures 3 to 7), and Si contained in silicon carbide abrasive grains is green (in Figures 3 to 7, shown as white). The Fe contained in the diamond abrasive grains 22 is shown in blue (the part shown as blue in FIGS. 3 to 7). The particles shown in blue become smaller and smaller as the test wheels 1 to 4 are used, and their presence cannot be confirmed in the test grindstone 5. The regions shown in green are present throughout the test grindstones 1 to 5, except for the void areas. Particles shown in red are present in test grindstones 1 to 5, although there is a slight difference in number.

FIG. 8 shows the grinding conditions of a lapping (grinding) test using a precision lapping machine similar to that shown in FIG. 1 for test wheels 1 to 5.

FIG. 9 is a bar graph showing the amount of grinding wheel wear (relative value with test grinding wheel 5 as 100) when using test grinding wheels 1 to 5, and a line graph showing the grinding efficiency showing the amount of reduction in workpiece wear per grinding time. . In FIG. 9, compared to the test whetstone 5 that does not contain diamond abrasive grains 22, the test whetstone 4 that contains 0.40% by volume of diamond abrasive grains 22 shows no difference in grinding efficiency; For test wheels 1 to 3 containing .8% by volume or more, a sharp improvement in grinding efficiency was observed as the proportion of diamond abrasive grains 22 increased. However, if the proportion of the diamond abrasive grains 22 is increased with the intention of further improving the grinding efficiency, the amount of bond decreases, making it impossible to obtain the necessary grindstone hardness. In addition, if the grain size of the diamond abrasive grains 22 is made coarse, the surface roughness of the workpiece 14 will become rough, making it unsuitable for finishing purposes, while if it is too fine, the grinding action of the cutting edge will become small, making it difficult to improve grinding efficiency. You won't be able to get it.

(Experiment example 2)
The present inventors used main abrasive grains 20 in which the weight ratio of alumina abrasive grains (fused alumina: Al ₂ O ₃ ) and silicon carbide abrasive grains (SiC) was 2:8, and the diamond abrasive grains 22 When containing 2.5% by volume of diamond abrasive grains 22 to main abrasive grains 20, the grain size ratio (=average grain size of diamond abrasive grains 22/average grain size of main abrasive grains 20) is from 0.1 to 1. Ten types of test grindstones 6 to 15 varying in 10 steps were produced in the same manner as in Experimental Example 1 described above. Then, a grinding test was conducted on these test wheels 6 to 15 under the same grinding test conditions as in Experimental Example 1. FIG. 10 shows the results of the grinding test. In Figure 10, ○ marks indicate values that fully satisfy the required values (Ra = 0.15 μm or less for surface roughness, 0.2 mg/min or more for grinding efficiency), and △ marks are near the boundaries of the required value range. , that is, within the range of 1.0 to 0.9 of the required value, and the x mark indicates a value that does not meet the required value at all, that is, a value that is less than 0.9 of the required value.

As shown in FIG. 10, regarding the surface roughness (surface roughness) of the workpiece 14, Ra satisfies the requirements if the grain size ratio is 0.8 or less, preferably 0.7 or less. Good results were obtained. On the other hand, regarding the grinding efficiency, good results were obtained that fully met the requirements when the particle size ratio was 0.2 or more, preferably 0.3 or more. As a result, when the particle size ratio is between 0.2 and 0.8, more preferably between 0.3 and 0.7, both the surface roughness of the workpiece 14 and the grinding efficiency are achieved. This was confirmed.

(Experiment example 3)
Furthermore, the present inventor has determined that the weight ratio of alumina abrasive grains (fused alumina: Al ₂ O ₃ ) and silicon carbide abrasive grains (SiC) constituting the main abrasive grains 20 is 1:9, 2:8, Test grindstones 16 to 20 with different ratios of 5:5, 8:2, and 9:1 were prepared in the same manner as in Experimental Example 1 described above. Then, grinding was performed under the same grinding test conditions as in Experimental Example 1 using the five types of test grindstones 16 to 20 that differed only in the weight ratio of alumina abrasive grains and silicon carbide abrasive grains of the main abrasive grains 20. , the same evaluation as in Experimental Example 2 was performed. FIG. 11 shows the results of the grinding test.

As shown in FIG. 11, test wheels 17 to 19 in which the weight ratio of alumina abrasive grains and silicon carbide abrasive grains constituting main abrasive grains 20 ranged from 2:8 to 8:2, Good results were obtained in terms of abrasion resistance and grinding efficiency, meeting the required values. However, the test grindstone 16, in which the weight ratio of alumina abrasive grains to silicon carbide abrasive grains was 1:9, had satisfactory wear resistance but was insufficient in terms of grinding efficiency. Further, the test whetstone 20 in which the weight ratio of alumina abrasive grains to silicon carbide abrasive grains was 9:1 had satisfactory grinding efficiency, but was insufficient in wear resistance.

As described above, the vitrified whetstone 10 of the present embodiment is a low-porosity vitrified whetstone that includes diamond abrasive grains 22, in which abrasive grains are bonded by a glassy vitrified bond 24, and the abrasive grains are made of alumina. The main abrasive grains 20 are made of a mixture of abrasive grains and silicon carbide abrasive grains, and the average particle diameter ratio is 0.2 to 0.8 with respect to the main abrasive grains 20, and 0.8 to 4 with respect to the grindstone volume. diamond abrasive grains 22 having a volume fraction of .0% by volume. From this, the vitrified grindstone 10, which is a low porosity vitrified grindstone containing diamond abrasive grains 22 and which provides good surface roughness and high grinding efficiency, can be obtained by firing in an atmospheric atmosphere.

The vitrified grindstone 10 of this embodiment contains the main abrasive grains 20 in a proportion of 40% or more by volume relative to the volume of the grindstone, and the vitrified bond 24 in a proportion of 45% or more by volume relative to the volume of the grindstone. . In this way, since the ratio of the vitrified bond 24 to the grinding wheel volume is high, the diamond abrasive grains 22 are covered with the glassy vitrified bond 24 during firing, so even the diamond abrasive grains 22 can be fired in an atmospheric atmosphere. It becomes possible.

According to the vitrified grindstone 10 of this embodiment, since the filling rate of the abrasive grains and vitrified bond 24 with respect to the grindstone volume is 85% by volume or more, during firing, the diamond abrasive grains 22 are transferred to the glassy vitrified bond 24. Since the diamond abrasive grains 22 are covered with the diamond abrasive grains 22, it is possible to sinter them in an atmospheric atmosphere.

According to the vitrified whetstone 10 of the present example, since the vitrified bond 24 has a softening point of 850° C. or higher, the diamond abrasive grains 22 are heated under the firing conditions of a general vitrified bond using a general vitrified bond. The vitrified grindstone 10, which is a low porosity vitrified grindstone, can be manufactured.

Although one embodiment of the present invention has been described above based on the drawings, the present invention can also be applied to other aspects.

The above-mentioned embodiment is merely one embodiment, and although no other examples are given, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art without departing from the spirit thereof. I can do it.

10: Vitrified whetstone (low porosity vitrified whetstone containing diamond abrasive grains)
12: Lapping machine 14: Workpiece 16: Weight 18: Nozzle 20: Main abrasive grain (abrasive grain)
22: Diamond abrasive grain (abrasive grain)
24: Vitrified bond

Claims (4)

A low porosity vitrified grinding wheel containing diamond abrasive grains, the abrasive grains being bonded by a glassy vitrified bond,
The abrasive grains include main abrasive grains made of a mixture of alumina abrasive grains and silicon carbide abrasive grains, and an average particle size ratio of 0.2 to 0.8 with respect to the main abrasive grains, and with respect to the grindstone volume. A low porosity vitrified grindstone containing diamond abrasive grains, characterized in that the diamond abrasive grains have a volume ratio of 0.8 to 4.0% by volume. The low porosity vitrified grindstone containing the diamond abrasive grains contains the main abrasive grains in a proportion of 40% or more by volume relative to the volume of the grindstone, and the vitrified bond in a proportion of 45% or more by volume relative to the volume of the grindstone. A low porosity vitrified grindstone comprising diamond abrasive grains according to claim 1. The low porosity vitrified grindstone containing diamond abrasive grains according to claim 1 or 2, wherein a filling rate of the abrasive grains and the vitrified bond with respect to the grindstone volume is 85% by volume or more. The low porosity vitrified grindstone containing diamond abrasive grains according to any one of claims 1 to 3, wherein the vitrified bond has a softening point of 850°C or higher.

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