JPH02269567A - Manufacture of vitrified grinding wheel - Google Patents

Abstract

PURPOSE:To use vitrified bond without limitations so as to obtain a grinding wheel of high hardness by mixing non-burned grinding particles with vitrified bond and molding them, and performing burning of the grinding particles simultaneously with that of the grinding wheel. CONSTITUTION:Particles heated to temperatures from above 100 deg.C to below 1,250 deg.C within 120 seconds and held within 90 seconds for a rapid-heating treatment are used as non-burned grinding particles. These non-burned grinding particles are mixed with vitrified bond and molded, and burning of the grinding particles is carried out simultaneously with that of grinding stone. Loss of energy and growing of crystals are thereby restrained, and a vitrified grinding wheel of excellent grinding performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a vitrified grindstone containing alumina sintered abrasive grains for use in precision grinding of tool steel and the like.

[Prior Art] Abrasive grains include polycrystalline abrasive grains, which are made by crushing and classifying raw material lumps produced by electrofusion, etc., and are composed of so-called single-crystal abrasive grains and polycrystalline microcrystals.

Polycrystalline abrasive grains can be produced by forming raw material powder kneaded with a binder or the like and sintering it in a kiln, or by starting from a sol-gel method. In the case of the sol-gel method, there are cases where a dry gel is used as a state before firing, and cases where this is calcined to remove water.

Furthermore, some so-called single crystal abrasive grains are completed as abrasive grains through a baking (roasting) process.

Conventionally, in order to produce a vitrified grinding wheel that has excellent grinding performance and is made of alumina sintered abrasive grains with submicron microcrystals, it is necessary to first prepare an alumina gel 1250 particles
It was necessary to calcinate at ~1400°C to produce abrasive grains (loose grains) consisting of microcrystals of aAβ203, add a vitrified binder thereto, and calcinate at about 1220°C.

One disadvantage of this method is that it requires significant energy wastage by applying -degree energy at 1250 to 1400℃ and then thermal energy at 1220℃, and the other disadvantage is that the abrasive grains are formed during the grindstone firing process. In order to avoid the growth of microcrystals, the most commonly used high-performance vitrified bond (used at around 1300° C.) cannot be used.

[Problems to be Solved by the Invention 1] An object of the present invention is to prevent the above-mentioned energy loss and crystal growth and to economically produce a grindstone with excellent grinding performance.

[Means for Solving the Problems] As a result of intensive research to achieve the above object, the present inventors found that when manufacturing a grindstone made by firing particles that become abrasive grains when fired, the abrasive material is used. The inventors have discovered that by providing unfired abrasive grains, the firing of the abrasive grains can be performed simultaneously with the firing of the whetstone, and the present invention has been completed.

That is, the gist of the present invention resides in a method for producing a vitrified grindstone, which is characterized in that green abrasive grains are blended with vitrified bond, molded, and abrasive grain firing and grindstone firing are performed simultaneously.

The characteristics of this method include not only the use of inexpensive abrasive material before firing, but also the relaxation of restrictions on the grindstone firing temperature, which are set to prevent deterioration of the abrasive grains during grindstone firing.

To make a whetstone like this, you need 500 to 1000 gel.
Vitrified bond may be added to alumina buyer abrasive grains of a predetermined particle size calcined at °C, and the abrasive stone may be fired in the usual manner. If the temperature is lower than 500°C, the moisture in the gel cannot be removed sufficiently, which weakens the bond between the abrasive grains and the bond, which is undesirable.
If the temperature exceeds ℃, there will be little economic benefit. The lower the calcination conditions are, the better the economic efficiency is, but the size of the fired whetstone will shrink due to shrinkage, and conversely, the higher the calcination temperature is, the worse the economics will be, but the dimensional accuracy will be better.

When making a vitrified whetstone using high-alumina polycrystalline abrasive grains made starting from the conventional sol-gel method, it was necessary to fire the whetstone at a temperature considerably lower than the abrasive grain firing rate in order to suppress crystal growth. Furthermore, it was believed that the performance of the grindstone would be better if a high-temperature bond with a high grindstone firing temperature was used as long as no deterioration of the abrasive grains occurred in -1.

In the present invention, in the case of the sol-gel method, as described above, the state before firing is preferably calcined at the lowest temperature at which no water remains. That way, the grindstone firing temperature can be made higher. At this time, the grindstone firing temperature is 1200 to 1500.
°C is appropriate.

Furthermore, depending on other uses obtained by the manufacturing method of the present invention, for example, if the abrasive grains are required to have higher hardness and toughness depending on the type of material to be ground, it may be possible to sacrifice economic efficiency to some extent. If the calcined gel is rapidly heated to a temperature of 1000 to 1250°C within 120 seconds and the temperature is maintained within 90 seconds, the hardness of the rapidly heated particles will be less than 2000 (Picus, load 500g), but it will not work on a grindstone. Hardness of 2000 or more and high toughness are obtained during firing.

In other words, the advantage in this case is that the shrinkage at the abrasive grain stage is large (
The specific gravity increases from 35 to 398), so the dimensional accuracy of the grindstone increases, and when the abrasive grains are rapidly heated, a large number of α-Aρ203 nuclei are generated and become fine crystals, increasing the toughness of the abrasive grains.

In the present invention, vitrified bond refers to SiO3, A(
2203, NazOl A composition containing K2O, CaO1 and other small amounts was made into a powder of about 10μ, and
Melt by heating at ℃ for about 15 minutes, cool down, and crush again to give about 1
This refers to powder that has a particle size of 0μ. However, melting and re-grinding are not necessarily necessary. For example, melting and re-grinding are necessary to suppress excessive reaction between the abrasive grains and the bond (bonding strength is lost without some reaction), but this is not necessary in most of the methods of the present invention. . This is because the calcined gel is microcrystalline α-Af2
This is thought to be because forming 2o3 is more advantageous than reacting with the bond.

Further, by applying chromium oxide in advance to particles that become abrasive grains when fired, the abrasive grain portions become ruby-colored and a ruby abrasive stone is obtained.

[Example 1] Three mixtures were made with the following formulations:

Mixture 1: 3 g of 840-1410 LL amine gel calcined at 500°C for 12 hours, 1 g of vitrified bond Mixture 2
Mixture 3: 3 g of 840-1410 μm amine gel calcined at 50°C for 4 hours and 1 g of vitrified bond. 5iOJ6%, i□0312%
, Ca09%, Na2O2%, K2O3%, and other substances containing small amounts of oxides were once dissolved at 1400'C,
The powder was ground to about 10 LL.

An aqueous solution of gum arabic was added to the mixture of these three types, formed into pellets of about 20 mmφ x 10 mm, placed in a Matsufuru furnace, heated to 1350°C for 11 hours, held at 1350”C for 2 hours, and then brought to room temperature in 9 hours. Cut each of the returned pellet-shaped grindstones in half, then mirror-polish them to a micro-picchus hardness of the abrasive grains under a load of 500 g.
When measured, all three types were 2100 kg/mm''.Then, when these cut lumps were crushed and subjected to X-ray diffraction, only αA!2203 was detected, which is thought to be generated when the bond and abrasive grains react. Mullite etc. were not identified.

[Example 2] A pellet-shaped grindstone was fired in the same manner as in Example 1 except that the alumina gel calcined in Example 1 was coated with 0.3 u of CrzOa at 1% to the gel in advance. The abrasive grains became ruby colored and a ruby abrasive stone was obtained.

[Example 31 The same lot of alumina gel used in Mixture 2 in Example 1 was heat treated in a small rotary kiln. The heat treatment conditions are as follows: the raw material is transferred from the feed end (room temperature) to the soaking end (119
0° C.) in 60 seconds, passed through a thermal zone (1190° C.) in 60 seconds, and was discharged outside the kiln for cooling.

Next, 3g of heat-treated particles were bonded with vitrified bond (
310265%, Aj2 203 25%,
Na204.5%, K2[)35%, Ca
00.5%, other small amounts of ingredients) Add Ig and a small amount of gum arabic aqueous solution, mix well, and mix about 20 mm x 1
．． It was molded into a 0mm pellet.

After drying the pellet, put it in the Matsufuru furnace and it will become 1150 in 10 hours.
The temperature was raised to .degree. C., maintained at this temperature for 10 hours, and then returned to room temperature in 9 hours. When the abrasive grains of the pellet were examined in the same manner as in Example 1, the micropicchus hardness was 2300 (load 50
0g), and the crystal size was 18!1 (average value determined from SEM photographs). Also, a part of the beret is about 10LL
The particles were crushed to obtain an X-ray diffraction sample, but compounds such as mullite, which are thought to be produced by the reaction between particles and pounds, were not identified.

[Effects of the Invention] According to the method for producing a vitrified grindstone according to the present invention, a grindstone with high hardness can be produced using vitrified bond without any restrictions.

Claims (3)

[Claims] (1) A method for producing a vitrified whetstone, which comprises blending green abrasive grains with vitrified bond, molding the mixture, and simultaneously firing the abrasive grains and firing the whetstone. (2) The method for producing a vitrified grindstone according to claim 1, wherein the unfired abrasive grains are particles that have been subjected to a rapid heat treatment in which the unfired abrasive grains are heated in advance to a temperature of 1000° C. to 1250° C. within 120 seconds and maintained within 90 seconds. (3) The method for producing a vitrified grindstone according to claim 1, wherein the unfired abrasive grains are coated with chromium oxide in advance.