JPH079344A - Vitrified cubic crystal boron nitride abrasive grain grinding wheel and its manufacture - Google Patents

Abstract

PURPOSE:To provide a vitrified cubic crystal boron nitride(CBN) abrasive grain grinding wheel and its manufacturing method which can suppress the generation of cristobalite from a boro-silicate glass binder as low as possible, and can improve the mechanical strength. CONSTITUTION:Aluminum borate whiskers are added to a boro-silicate glass type binder so as to combine CBN abrasive grains. A grinding wheel is obtained by mixing the binder, the whiskers, and the abrasive grains, and baking them at a relatively low temperature.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel vitrified cubic boron nitride abrasive grain grinding wheel and a method for producing the same, and particularly to a vitrified cubic boron nitride abrasive grain grinding which suppresses the formation of cristobalite as much as possible and is excellent in mechanical strength. The present invention relates to a grindstone and a manufacturing method thereof.

[0002]

2. Description of the Related Art As is well known, an abrasive grain made of cubic boron nitride (hereinafter simply referred to as CBN) has a high hardness and is called a superabrasive grain together with a diamond abrasive grain. CBN abrasive grains are widely used mainly for grinding stones for grinding steel materials.

CBN abrasive grains change in quality when fired at a temperature higher than 950 ° C., and do not change when fired at a temperature lower than that using a low-melting-point binder, and a binder showing the highest strength at 650-950 ° C. It is known to be practical (Japanese Patent Publication No. 52-3147), and CBN can be used with a binder in this range.
A borosilicate vitreous binder is used because it has a coefficient of thermal expansion that matches that of the abrasive grains and has good wettability.

Crystallized glassy materials are also used. As described above, the reason why the borosilicate glass material is used is that it is easy to match the coefficient of thermal expansion with the CBN abrasive grains and that the CBN abrasive grains are less damaged by heat by firing at a low temperature such as 650 to 950 ° C. In addition, in the case of crystallized glass, mechanical strength can be improved in addition to these reasons, but it is not sufficient.
On the other hand, when a borosilicate glass material is used as the binder, cristobalite is generated when the firing temperature is low. This phenomenon is due to borosilicate glass (Na ₂ O-B ₂ O
_3- SiO ₂ ) has two phases (Na ₂ O-) when heat treatment is inappropriate.
B ₂ O ₃ and SiO ₂ ) are known to cause phase separation,
It is thought that there is some relation to this phenomenon. SiO ₂ crystallized material called cristobalite is 100 to 20
It is known that the volume expands rapidly at 0 ° C, and a grindstone fired with this as a binder causes a large number of cracks and the grindstone becomes very weak, and vitrified using a borosilicate vitreous binder. Making CBN abrasive grain grinding wheels difficult.

Mullite (aluminosilicate mineral) is known as a material for suppressing the production of cristobalite, but in this case the mechanical strength is not sufficiently improved and the bending strength of the grindstone cannot be increased.

Therefore, an object of the present invention is to provide a vitrified CBN abrasive grain grinding wheel capable of suppressing the formation of cristobalite as much as possible and improving the mechanical strength by using a borosilicate glassy binder, and a method for producing the same. Is.

As a result of intensive studies and experiments, the present inventor has found that such an object can be achieved by adding aluminum borate whiskers to a borosilicate glassy binder.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention is a vitrified cubic boron nitride abrasive grain or a combination of the abrasive grain and another abrasive grain with a borosilicate glassy binder containing aluminum borate whiskers. A cubic boron nitride abrasive grain grinding wheel is provided.

The present invention also provides that cubic boron nitride abrasive grains or the abrasive grains and other abrasive grains are mixed with a borosilicate glassy binder containing aluminum borate whiskers, and
Provided is a method for producing a vitrified cubic boron nitride abrasive grain grinding wheel, which comprises firing in an air or inert gas atmosphere at a temperature in the range of 0 to 950 ° C.

The present invention will be described in detail below.

As mentioned above, the present invention is characterized by the addition of aluminum borate whiskers to the borosilicate glassy binder. Borosilicate vitreous bond typically SiO ₂ 40 to 70% by weight of the binder,
Al ₂ O ₃ 2-20%, K ₂ O, Na ₂ O, Li ₂ O
Alkali metal oxides such as 3-17%, CaO, Mg
It has a composition of 1 to 14% of an oxide of a divalent metal containing an alkaline earth metal such as O, ZnO and BaO, and 15 to 30% of B ₂ O ₃ .

In addition to this, aluminum borate (9
Al ₂ O ₃ .2B ₂ O ₃ ) whiskers. Whiskers are so-called whiskers and usually have a cross-sectional area of 8 x 1
It is defined as a single crystal having a length of 0 ^-5 in ² or less and a length of 10 times or more of the average diameter of the cross section. Recently, attempts have been made to improve mechanical strength and chemical resistance by adding this to ceramics, plastics, and metal materials. It is said to form a perfect crystal and have a tensile strength close to the theoretical strength.

The coefficient of thermal expansion of aluminum borate whiskers is 4.7 × 10E ^-6 , and that of CBN is 3.
Since it is relatively close to 5 × 10E ^-6 , there is no risk of problems such as cracking due to heating and firing. Further, the mechanical strength can be improved, such as the bending strength being improved when the whiskers are used, as compared with the case where aluminum borate powder is used.

Whiskers include, in addition to aluminum borate, β-SiC, β-Si ₃ N ₄ , potassium titanate, magnesium oxide, zinc oxide, etc. Test result, β-S
Although iC and β-Si ₃ N ₄ had higher tensile strength than aluminum borate whiskers, they were found to be incapable of quenching cristobalite as described in Example 3. Further, it is considered that the test pellets were swollen and thus decomposed by reacting with the binder. Other whiskers are not suitable because they have lower tensile strength than aluminum borate whiskers, and divalent metals such as MgO and ZnO may dissolve in the binder to deteriorate the binder.

When this aluminum borate whisker is used, it is possible to suppress the formation of cristobalite crystals at the time of firing the borosilicate glassy binder. The whisker suppresses the formation of cristobalite crystals. Of the SiO 2 by mixing with the borosilicate vitreous binder
It is presumed that this is because the tetrahedron of AlO ₄ is formed in the network structure of ₂ . However, the present invention is not bound by such theory.

The amount of the aluminum borate whiskers added is preferably in the range of 5 to 30% with respect to the total amount (weight) of the borosilicate glassy binder and the whiskers.
If it is less than 5%, the effect of suppressing the formation of cristobalite is not sufficient, and if it exceeds 30%, the wettability between the abrasive grains and the binder decreases. In addition to the borosilicate glassy binder to which the aluminum borate whiskers have been added, a 50% aqueous dextrin solution can be added as a primary binder.

The abrasive grains to be bonded by using such a binder are mainly cubic boron nitride (CBN) abrasive grains as described above, but if necessary, in addition to such particles (primary abrasive grains), carbonization is carried out. Secondary abrasive particles such as silicon abrasive particles, alumina abrasive particles, or alumina abrasive particles composed of sintered particles composed of α-alumina crystal particles formed by a gel sintering method can be added. In that case, the primary abrasive grains are used in an abrasive grain ratio of 5 to 54% by volume, and the secondary abrasive grains are used in an abrasive grain ratio of 0 to 49% by volume.

In making a grindstone from such an abrasive grain and a binder, the above primary abrasive grain alone or both the primary abrasive grain and the secondary abrasive grain are bonded to a glass borosilicate glass containing aluminum borate whiskers. It is mixed with the agent and fired in an air or inert gas atmosphere in the range of 650 to 950 ° C. In that case, the range of 750-850 degreeC is preferable. This firing may be performed in an air atmosphere or an inert gas atmosphere such as a nitrogen atmosphere. In the case of a nitrogen atmosphere, for example, heating at 800 ° C. for 7 hours is performed in a nitrogen atmosphere, but heating from room temperature to 600 ° C. and cooling from 400 ° C. to room temperature can be performed in an air atmosphere.

As described above, the present invention provides the vitrified CB.
In the manufacture of N-abrasive grinding wheels, the addition of aluminum borate whiskers to a borosilicate glassy binder suppresses the formation of cristobalite, and the high tensile strength of the whiskers makes it possible to utilize the mechanical strength of the wheels. And also enables firing at a relatively low temperature of 650 to 950 ° C.

[0020]

【Example】

[Example 1] Chest with aluminum borate whiskers
Stovalite formation inhibitory effect: Three kinds of tests in which a borosilicate glassy binder having the composition shown in Table 1 was mixed well with different addition rates of aluminum borate whiskers as shown in Table 2 to make them homogeneous. As a result of applying a test sample obtained by molding the bond into a cylindrical pellet and firing the pellet under the conditions shown in Table 3 to an X-ray diffraction apparatus (manufactured by Rigaku Denki Co., Ltd.), as shown in FIG. It was confirmed. The peak of cristobalite found in test bond-1 in which aluminum borate whiskers were not added became smaller in test bonds-2 and 3 in which aluminum borate whiskers were added, and became smaller as the addition ratio increased. I found out that The same result was obtained in the air atmosphere and the nitrogen atmosphere. Table 1. Component composition of borosilicate glassy binder SiO ₂ 65 wt%, Al ₂ O ₃ 7 wt%, CaO 1.5 wt%, K ₂ O 0.5 wt%, Na ₂ O 5.5 wt%, Li ₂ O 0.5 wt%, B ₂ O ₃ 20 wt% Table 2. Test bond composition Table 1 Binder Aluminum borate whiskers Test bond-1 100wt% 0wt% Test bond-2 95wt% 5wt% Test bond-3 90wt% 10wt% Table 3. Test sample preparation conditions A) Pellet size: 10.5φ × 12T × OH (mm) B) Input weight: 1.5g C) Firing conditions: ● Maximum temperature 800 ° C (air atmosphere) ・ Room temperature → 550 ° C 7.5 hours・ 550 ° C → 600 ° C 3.0 hours ・ 600 ° C → 800 ° C 2.0 hours ・ Maximum temperature 800 ° C, hold for 7 hours ・ 800 ° C → 400 ° C about 7.0 hours natural cooling ・ 400 ° C → room temperature about 2. 5 hours forced cooling ● Maximum temperature 800 ℃ (nitrogen atmosphere) ・ Room temperature → 550 ℃ 7.5 hours (air atmosphere) ・ 550 ℃ → 600 ℃ 3.0 hours (air atmosphere) ・ 600 ℃ holding 1.5 hours (nitrogen) Replace with atmosphere) ・ 600 ℃ → 800 ℃ 2.0 hours (Nitrogen atmosphere) ・ Maximum temperature 800 ℃, hold for 7 hours (Nitrogen atmosphere) ・ 800 ℃ → 400 ℃ About 7.0 hours natural cooling (Nitrogen atmosphere) ・ 400 ℃ → room temperature Forced cooling for about 2.5 hours (air atmosphere) [Example 2] Confirmation of thermal expansion: A sample fired under the conditions of Table 4 using Test Bond-1 and 3 of Table 2 was made into 5 x 5 x 20 (mm). Cut out 5.5
The temperature was raised at a rate of ℃ / min, and the change in thermal expansion was measured with a thermal expansion measuring machine (TAS-100) manufactured by Rigaku Denki Co., Ltd. As a result, as shown in FIG.
While there was a rapid thermal expansion between 0 ° C, Test Bond-3 did not show a rapid thermal expansion change between 100 and 200 ° C. This is probably due to cristobalite. Table 4. Test sample preparation conditions A) Pellet size: 25.4φ × 20T × 0H (mm) B) Input weight: 15g C) Firing conditions: Maximum temperature 800 ° C (air atmosphere) ・ Room temperature → 550 ° C 7.5 hours ・ 550 ° C → 600 ° C 3.0 hours ・ 600 ° C → 800 ° C 2.0 hours ・ Maximum temperature 800 ° C, hold for 7 hours ・ 800 ° C → 400 ° C about 7.0 hours natural cooling ・ 400 ° C → room temperature about 2.5 hours forced Cooling [Example 3] Aluminum borate whiskers and other whiskers
Comparison with scars : Cristobalite formation suppression state was confirmed when whiskers other than aluminum borate whiskers were added to the borosilicate glassy binder in Table 1. As another whisker for comparison test, β- having a higher tensile strength than the aluminum borate whisker shown in Table 5 was used.
SiC those of the β-Si ₃ N ₄ test bond -4) have been added 10 wt% was added 10 wt% (using the test bond -5), three kinds of test bond with the test bond -3 cylindrical pellet As a result of applying a test sample, which was molded under the same firing conditions as shown in Table 3, to an X-ray diffractometer (manufactured by Rigaku Denki Co., Ltd.), the results shown in FIG. 3 were obtained, and β-SiC and β were obtained. It was found that the sample to which -Si ₃ N ₄ was added had a peak of cristobalite in both an air atmosphere and a nitrogen atmosphere and had no effect of suppressing the formation of cristobalite. Furthermore, the phenomenon that pellets fired in an air atmosphere of β-SiC, an air atmosphere of β-Si ₃ N ₄ and a nitrogen atmosphere swelled significantly as compared to Test Bond-3 containing aluminum borate whiskers was generated. Therefore, it is considered that the whiskers and the bonds react with each other to decompose the whiskers and promote the generation of gas, which is unsuitable for use as a material for manufacturing a grindstone. Table 5. Test bond composition (2) Test bonds -4 Table 1 binder: 90wt% β-SiC whisker: 10 wt% test bond -5 Table 1 _{binder: 90wt% β-Si 3 N} 4 whisker: 10 wt% [Example 4] Bending strength test of grindstone: Test bond-6 in which the addition rate of aluminum borate whiskers to the borosilicate glass-based binder in Table 1 was further increased to 15 wt%, and boron as another additive Test bonds-7 and 8 were prepared by adding aluminum oxide powder and mullite powder, respectively, and a CBN abrasive grain grinding wheel according to the conditions of Table 7 using these and the same test bonds-1 and 3 were used. The test sample of the grinding wheel of CBN abrasive grains was prepared under the conditions of No. 7, and 3 of each case was prepared for each.
As a result of the point bending strength test, the results shown in the right end of Table 6 were obtained.

In case 1 using the test bond-1, cristobalite was generated as described above, and it was considered that the bending strength was weak because the bond was cracked due to the abrupt volume change of the cristobalite. At the right end of Table 6, the bending strength in Case 1 is set to 1.00, and the numerical values in each case are indexed and shown. In Case 2 and below, a dramatic increase in bending strength is seen, which is due to the formation of cristobalite. It is considered that there was a suppressive effect.
This result also shows that the bending strength when aluminum borate whiskers are added is high.

It is considered that this is because the high tensile strength of the aluminum borate whiskers acted as a strength enhancer for the bond, which was further increased by increasing the amount of aluminum borate whiskers in Test Bond-6. It can be said from that. In addition, needle crystals were confirmed on the SEM photograph of the grinding wheel of the test bond, and it was also found that whiskers were present in the bond. It was also found that the firing atmosphere was stronger under nitrogen, which is considered to be due to the fact that whisker was less melted into the bond in the nitrogen atmosphere. Table 6. Bending strength test of grinding wheel ( manufactured by Shimadzu Corporation, using autograph) Test bond atmosphere Bending strength Case 1 Test Bond-1 (Table 1 Binder Air 1.00 100wt%) Case 2 Test Bond-3 (Table 1 Binder Air 2.11 90wt% + ABW ^* 10wt%) Case 3 Test Bond-3 (Table 1 Bond Agent Nitrogen 2.31 90wt% + ABW ^* 10wt%) Case 4 Test Bond-6 (Table 1 Binder Air 2.21 85wt% + ABW ^* 15wt%) Case 5 Test Bond-6 (Table 1 Binder Nitrogen 2.51 85wt) % + ABW ^* 15wt%) Case 6 Test bond-7 (Table 1 binder air 1.92 90wt% + ABP ^** 15wt%) Case 7 Test bond-8 (Table 1 binder air 1.90 90wt% + Mullite 15wt% ) Note * ABW: Aluminum borate whiskers Note ** ABP: Aluminum borate powder Table 7. Test sample (grinding wheel 1) preparation conditions and method a) Abrasive grains: CBN # 80/100 b) Composition: Abrasive grain volume (Vg) = 50, binder volume (Vb)
= 21, Pore volume (Vp) = 29 c) Dimension: 43L x 5T x 12W (mm) d) Firing conditions: ● Maximum temperature 800 ℃ (air atmosphere) ・ Room temperature → 550 ℃ 7.5 hours ・ 550 ℃ → 600 ℃ 3.0 hours ・ 600 ℃ → 800 ℃ 2.0 hours ・ Maximum temperature 800 ℃, hold for 7 hours ・ 800 ℃ → 400 ℃ about 7.0 hours natural cooling ・ 400 ℃ → room temperature about 2.5 hours forced cooling ● Maximum temperature 800 ° C (nitrogen atmosphere) ・ Room temperature → 550 ° C 7.5 hours (air atmosphere) ・ 550 ° C → 600 ° C 3.0 hours (air atmosphere) ・ 600 ° C holding 1.5 hours (replaced with nitrogen atmosphere) ・600 ° C → 800 ° C 2.0 hours (nitrogen atmosphere) ・ Maximum temperature 800 ° C, hold for 7 hours (nitrogen atmosphere) ・ 800 ° C → 400 ° C about 7.0 hours natural cooling (nitrogen atmosphere) ・ 400 ° C → room temperature about 2 Forced cooling for 5 hours (air atmosphere) e) Method: Determine the composition before firing. (Vg = 50
, Vb = 21, Vp = 29) The molding specific gravities of the abrasive grains, the binder and the primary binder (50% textrin solution in water) are determined. Abrasive grains, binder and primary binder (50% textrin solution in water) are mixed, press-molded, 40 ° C / minimum 12
Bake after drying for an hour. (Vp is 26 due to firing
Shrink to the range of ~ 28. )

[Example 5] Grinding test: From the results of the above test, it was found that the aluminum borate whiskers have a cristobalite formation inhibiting effect,
It was also found that the whisker has a high tensile strength, and therefore it also acts as a strength enhancer for the bond. Next, a grinding test was conducted to confirm the actual effect, and the results shown in Table 9 were obtained. Here, Test Bonds-3, 6 and 7 were used, and Table 8 below was used to prepare the grinding wheel. Table 8. Test sample (grinding wheel 2) preparation conditions and method a) Abrasive grain: CBN # 80/100 b) Composition: Abrasive grain volume (Vg) = 50, binder volume (Vb)
= 21, Pore volume (Vp) = 29 c) Dimensions: 350D x 20T x 152.4H x
3.5X (mm) d) Firing conditions: ● Maximum temperature 800 ° C (air atmosphere) ・ Room temperature → 550 ° C 7.5 hours ・ 550 ° C → 600 ° C 3.0 hours ・ 600 ° C → 800 ° C 2.0 hours ・Maximum temperature 800 ° C, hold for 7 hours ・ 800 ° C → 400 ° C About 7.0 hours natural cooling ・ 400 ° C → Room temperature about 2.5 hours Forced cooling ● Maximum temperature 800 ° C (nitrogen atmosphere) ・ Room temperature → 550 ° C 7.5 Time (air atmosphere) -550 ° C-600 ° C 3.0 hours (air atmosphere) -600 ° C-800 ° C 2.0 hours (nitrogen atmosphere) -Maximum temperature 800 ° C, 7 hours hold (nitrogen atmosphere) -800 ° C- 400 ° C Approx. 7.0 hours Natural cooling (Nitrogen atmosphere) -400 ° C → Room temperature Approximately 2.5 hours Forced cooling (Air atmosphere) e) Method: Determine the composition before firing. (Vg = 50
, Vb = 21, Vp = 29) The molding specific gravities of the abrasive grains, the binder and the primary binder (50% textrin solution in water) are determined. Abrasive grains, binder and primary binder (50% textrin solution in water) are mixed, press-molded, 40 ° C / minimum 12
Bake after drying for an hour. (For press molding, 28 pieces are manufactured with 42 × 4 × 22 (mm) and a curvature of 171.5R as shown in FIG. 4.) After firing, finish processing is performed, and epoxy resin is applied to a metal base metal with a diameter of 343 mm. Using it, it is applied to the portions of and shown in FIG. 4, adhered and fixed, and further subjected to finishing processing so as to have the dimension of e) above, to manufacture a grinding wheel in FIG.

Table 9. Grinding conditions a) Grinding machine: Toyota Koki Co., Ltd./GPN-5P
-32 × 100 type CNC general-purpose cylindrical grinder b) Grinding method: Wet brunge grinding c) Wheel speed (V): 4,500 m / min d) Work speed (V): 7.5 m / min e) Work: S55C ( HRC = 58) f) Work size: 60D × 3.5T × 24H (mm) g) Peripheral speed ratio: V / v = 4,500 / 7.5 = 6
00 (Up cut) h) Grinding efficiency (Z '): Z' = 30mm3 / mm ・ SEC
(2.5φ removal) Z ′ = 3.0 mm3 / mm · SEC (0.5φ removal) Spark-out 6 seconds Klecut NET-500B (50 times dilution) The grinding ratio of 120 cuts of the workpieces was compared. This test result shows that the bond in which the aluminum borate whiskers are added at a high rate has a high grinding ratio, and even in the case of the same addition rate, this is higher in the nitrogen atmosphere.

This is nothing but the effect of suppressing the formation of cristobalite and the effect of tensile strength.

[0026]

By adding aluminum borate whiskers to the borosilicate vitreous binder, a high-performance grinding wheel can be supplied, which makes a great contribution to the grinding industry.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of pellet samples prepared by using Test Bonds 1 to 3 in Example 1 of the present invention, showing A, B, and C.
Is a diagram obtained by firing the test bonds 1, 2, and 3 in an air atmosphere, and D, E, and F are samples obtained by firing the test bonds 1, 2, and 3 in a nitrogen atmosphere. Figure by.

FIG. 2 is a graph showing the results of measuring the thermal expansion of pellet samples made using test bonds 1 and 3 in Example 2 of the present invention, A is a graph of the sample obtained using test bond 3, and B is a graph. The graph of the sample obtained using the test bond 1.

FIG. 3 is an X-ray diffraction diagram of a pellet sample obtained by using test bonds 4 and 5 in Example 3 of the present invention, and A and B are prepared by firing test bonds 4 and 5 in an air atmosphere. Figure with pellet sample, C and D are test bonds 4, 5
The figure by the pellet sample produced by baking in a nitrogen atmosphere using.

FIG. 4 is a perspective view of a segment grindstone sample according to a fourth embodiment of the present invention.

5 is a perspective view of a grinding wheel made from the segment sample of FIG.

[Explanation of symbols]

 1 Segment sample 2 of Figure 4

Claims (2)

[Claims] 1. A vitrified cubic boron nitride abrasive grain grinding wheel in which cubic boron nitride abrasive grains or the abrasive grains and other abrasive grains are bonded with a borosilicate glassy binder containing aluminum borate whiskers. 2. Cubic boron nitride abrasive grains or said grains and other abrasive grains are mixed with a borosilicate glassy binder containing aluminum borate whiskers, and the mixture is mixed with air at a temperature in the range of 650 to 950.degree. A method for producing a vitrified cubic boron nitride abrasive grain grinding wheel, which comprises firing in an active gas atmosphere.