JPS59187072A - Improvement of grinding particle of bn of cubic system - Google Patents

Abstract

PURPOSE:To improve grinding ability of grinding particles, by heat-treating grinding particles of BN of cubic system in a molten salt at a specific temperature so that impurities are dissolved in the bath without damaging the grinding particles. CONSTITUTION:Grinding particles of BN of cubic system are heat-treated in a molten salt (preferably water-soluble chloride of NaCl-KCl system) at 500- 1,300 deg.C, preferably 700-1,000 deg.C. The heat-treatment is preferably carried out <=5 deg.C/min low rate of heating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for modifying cubic BN abrasive grains, and more specifically, the present invention relates to a method for modifying cubic BN abrasive grains, and more specifically, the present invention relates to a method for modifying cubic BN abrasive grains.
The present invention relates to a method for improving the grinding performance of CBN abrasive grains by heat treatment in a molten salt in the temperature range of 00°C.

The present inventor previously filed a patent application for a method for modifying CBN abrasive grains (Japanese Patent Application No. 57-72585). The content relates to a modification method for improving the grinding performance of CBN abrasive grains and a method for producing grinding wheels using the modified abrasive grains. It is characterized by heat treatment performed inside or in a vacuum. According to this method, (1) release of internal stress strain generated during synthesis, (2)
Based on the two effects of removing contained impurities, the grinding performance is improved by 30 to 50% compared to before treatment. but,
This heat treatment condition belongs to a somewhat harsh category, and it is difficult to control the heating of the abrasive grains to a predetermined temperature increase rate, especially when heating in a gas atmosphere or in a vacuum. This reduces the strength, and this hinders the originally expected performance improvement.

In addition, impurities that cannot be removed by diffusion and evaporation remain when heated under the above conditions.

However, in the present invention, by performing heat treatment in a molten salt, impurities in the abrasive grains are dissolved in the bath and quickly diffused and removed. Furthermore, since molten salt has a larger heat capacity than gas, the temperature can be raised and lowered very slowly by controlling it to predetermined conditions, and therefore the movement of impurities is also slow. Since the treatment can be carried out under such mild conditions, damage to the abrasive grains is reduced, and it is thought that a decrease in grain strength due to cracking and the like is reduced.

This modified abrasive grain is resistant to thermal and mechanical shocks during whetstone production and grinding, as in the case of the above-mentioned Japanese Patent Application No. 57-72585, Because the grain strength is thicker, it has better grinding performance,
It can be widely used for vitrified whetstones, remade whetstones, electroplated whetstones, etc.

Molten salts are single-component systems or multi-component systems with two or more components, such as halides such as chlorides and fluorides, oxides such as B2O3, and carbonates, which have a melting point between 500 and 1300°C. OBN after heat treatment is used.
Considering the recovery of abrasive grains, water-soluble chloride-based materials are preferred.

In addition, the amount of molten salt used is at least a certain amount relative to the amount of CBN abrasive grains to be treated (preferably, 3
(g or more) is required; the smaller the amount, the less effective the heat treatment is preferably carried out at a temperature range of 500-1300°C at a slow heating/cooling rate of less than 5°C/min. 500°
Below C, there is almost no effect, and above 1300°C, the damage to the grains is severe. The temperature used is O
The temperature varies depending on the particle size of the BN abrasive grains, the amount of impurities contained, the type of grindstone to be produced, etc., and is generally used within the above range, but 70σ to 1000°C is preferable. A treatment time of 60 minutes or less is sufficient.

Here, a more detailed explanation will be given using a chloride system as an example.

Ru.

For chloride systems, NaCl, KCl, LiCl, M3
;C3A! 2. Single-component systems such as Ba(J2゜CaO12) or multi-component systems combining two or more of these components are used, but here the most typical one is Na0l.
-KCJ (1:1 mol) will be explained as an example. This system has a melting point of about 660°C, so if the purpose is to process at a temperature lower than that, this system cannot be used, and NaC
l-LiCd, 1((J-LiOl, NaO#
-Mgcg2. It is preferable to use a system such as Li 2 O (J BaC4).

Said Na(M-KOl powder 30.9 and particle size #80/1
After thoroughly mixing 10 carats of No. 00 CBN abrasive grains, the alumina crucible was filled and placed in an electric furnace in the atmosphere. Next, the temperature is increased at a rate of 1°C/min, maintained at a predetermined temperature for 1 hour, and then lowered at a rate of 1°C/min.

When the temperature drops below 200°C, take out the crucible, put it in water and let it boil, then NaC! 6-K (Dissolve the JJ salt. Once the salt has dissolved, boil it in hydrochloric acid for 1 hour, and dissolve the OB
Completely removes impurities adhering to the surface of N abrasive grains. After washing with water and drying, analyze the contained impurities and measure the grain strength. The analysis is carried out by ordinary chemical analysis, and the grain strength is measured as follows.

First, a certain amount of the sample sieved with the specified sieve mesh and 6
One gmm steel ball is placed in a capsule with a volume of approximately 2rnl, and pulverized for a certain period of time in a small vibrating mill.

The crushed sample is sieved through a designated sieve, and the remaining weight of the sample on the sieve is determined as a toughness value. Therefore, it can be said that the larger the toughness value, the less pulverization and the greater the grain strength.

The measurement results of the impurity content and grain strength of the OBN abrasive grain sample obtained in this way are shown in Table 1 in comparison with the results in the N2 gas flow of Japanese Patent Application No. 72585/1985.

As is clear from Table 81, the treatment in molten salt according to the present invention is superior in removing impurities and causes significantly less decrease in grain strength. In particular, it is noteworthy that impurities are sufficiently removed even at low temperatures such as 700'C, and there is almost no reduction in grain strength.

This will be explained below using examples.

Example 1 Various particle sizes (#L60/80. #8Q/100. #
120/140. #140/170. #170/2
00. #270/325) OBN abrasive grains with NaC1
-K(J (1: 1 mol) in a molten salt at 700 °C1
Heat treatment was performed for 1 hour. Both heating and cooling rates were 1°C/min. After heat treatment, the molten salt was dissolved as described above, washed with acid water, and dried to obtain a sample.

Table 1 First, the impurities contained and grain strength of these samples were measured. As a result, the amount of impurities contained in all grain sizes was reduced to about half of the initial amount (untreated)12, and the grain strength hardly decreased. Next, #80/1 from these samples
00 was selected, and a vitrified grindstone was manufactured in the following manner.

Formulation The above compound was press-molded into an arc shape (thickness: 3 mm, width: 7 mm, arc length: 32 mm, outer radius of curvature of 75 mm, inner radius of curvature of 72 mm), and dried at 120"C for 1 hour. A segment was obtained by firing at 900°C for 1 hour.This segment contained about 3 volumes of CBN abrasive grains.
A flat whetstone was made by pasting it with adhesive on the outer periphery of a metal disk of y5 mra and thickness of 7 mm.

Example 2 OBN abrasive grains of various particle sizes similar to Example 1 were mixed with N, +cl(
60% /L=%) -I-i0#) Tear 00 in molten salt
The heat treatment was carried out for 11 hours.The temperature rise and fall rates were both 1'Cl min.After the heat treatment, samples were obtained in the same manner as in Example 1. ), and the grain strength was approximately 92% of its original value.
%, or about 8%.

#80/100 was selected from these samples and used in Example 1.
A vitrified grinding wheel with the same dimensions was manufactured under the same conditions.

Example 3 Using the #140/17o abrasive grains obtained in Example 1, a resinoid grindstone was manufactured in the following manner.

First, in order to improve the abrasive grain retention with the resin bond, approximately 60% by weight Ni coating was performed using Muden Super as an electroless Ni plating solution that is commonly used.

Blend 10 B N abrasive grain #1.40/170 (Ni coated grain)
64' TfE ta % A metal disk with an outer diameter of 144 $ mm, an inner diameter of 50896 mm, and a thickness of 7 mm was placed concentrically inside a mold with an inner diameter of 150 mm, and the above composition was applied to the inner wall of the mold and the outer periphery of the disk. The abrasive grain layer was filled with abrasives, hot-pressed (approximately 180 mm and held for 11 hours), and fired at 190°C for 12 hours to make a flat grindstone.
Contains about 25 volumes of N abrasive grains.

Example 4 Using the 4NO 8V1oo abrasive grains obtained in Example 1,
Abrasive grains were fixed in a single layer by electroplating on the outer periphery of a metal disk having an outer diameter of 15093 mm, an inner diameter of 508 inches, and a thickness of 7 mm to obtain an electrodeposited grindstone. The thickness of the electrodeposited layer is approximately 110 μm in % of the abrasive grain diameter.

Comparative Example 1 For comparison, untreated OBN with particle size #80/1oo
A vitrified grindstone with the same dimensions as in Example 1 was manufactured using abrasive grains under the same conditions as in Example 1.

The results of the grinding test are shown in Table 2.

Comparative Example 2 For comparison, untreated CB with particle size ##8o/100
The N abrasive grains were heat-treated at 700°C for 1 hour in a N2 stream. The temperature increase/decrease rate was 1°C/min. Using this abrasive grain,
A vitrified grindstone with the same dimensions as in Example 1 was manufactured under the same conditions.

The results of the grinding test are shown in Table 2.

The grinding test conditions in Table 2 are: grinding wheel peripheral speed 1500 m/min;
The table feed speed was 15 m/min, and the saddle feed was 2 mm. The work material was JIS SKH, -57 (Rockwell hardness O scale 63, length 200 mm, width 100 mm), and the total grinding depth was 3.0 mm.

Table 2 * Grinding ratio - amount of grinding (ffl) ÷ amount of grinding wheel wear (d) The vitrified grinding wheels of Examples 1 and 2 are comparative examples] The grinding ratio is improved compared to both of Examples 1 and 2, and the grinding ratio is improved compared to both of Examples 1 and 2. This shows that the grain modification effect is significant.

Comparative Example 3 For comparison, the particle size of untreated grains was 41-140/] 7
A resinoid grindstone having the same dimensions as in Example 3 was manufactured using OBN abrasive grains having the same dimensions as in Example 3.

The results of the grinding test are shown in Table 3. The grinding test conditions were as described in Comparative Example 2.

The grinding ratio of the resinoid grindstone of Example 3 was improved compared to that of Comparative Example 3, indicating that the abrasive grains were modified by the molten salt treatment.

Comparative Example 4 For comparison, an electrodeposited grindstone with the same dimensions as in Example 4 was manufactured using untreated grain size #80/100 under the same conditions as in Example 4.

The grinding test results are shown in Table 41. The grinding test conditions were as described in Comparative Example 2. However, the comparison was made based on the amount of grinding.

The amount of grinding of the electrodeposited grindstone of Example 4 was increased compared to that of Comparative Example 4, indicating that the abrasive grains were modified by the molten salt treatment.

Applicant: Showa Denko Co., Ltd. Agent: Patent Attorney Sei Kikuchi

Claims (1)

[Claims] A method for modifying cubic BN abrasive grains, which comprises heat-treating cubic BN abrasive grains in a molten salt at a temperature range of 500 to 1300°C.