JPH0681832B2 - Method for producing alumina-based sintered abrasive grains - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alumina-based sintered abrasive grain suitable for heavy grinding.

Conventional technology Abrasive grains for heavy grinding are abrasive grains obtained by sintering fine powder of alumina-based material such as bauxite (Japanese Examined Patent Publication No. 39-4398 and Japanese Examined Publication No. 39-27).
No. 612, Japanese Patent Publication No. 39-27613, Japanese Patent Publication No. 39-27614), fused alumina-zirconia abrasive grains (Japanese Patent Publication No. 39-16592) and high-purity alumina fine powder with a crystal grain growth inhibitor such as magnesium oxide added. Abrasive grains (Japanese Patent Laid-Open No. 52-14993) are known.

In recent years, an alumina-based sintered abrasive grain by the sol-gel method is also known, as in JP-A-56-32369.

Problems to be Solved by the Invention In order to increase the strength of the abrasive grains and improve the characteristics such as the grinding ratio, the apparent specific gravity is high, and the cracks in the abrasive grains are small in addition to the small crystal size after sintering. Need to reduce.

Abrasive grains having cracks are not all worn during grinding, are broken in the middle, fall off from the grindstone, and do not participate in grinding, resulting in a reduction in grinding ratio.

The present invention aims to improve the grinding ratio by reducing cracks in the abrasive grains, thereby reducing the number of lost abrasive grains.

Means for Solving the Problems As a result of various studies to achieve the above object, the present inventor has found that the cracks in the abrasive grains are caused by the cracks generated at the time of molding before sintering.

The shape of the abrasive grains for heavy grinding is generally cylindrical from the viewpoint of ease of production, but when molding the raw material powder into a cylindrical shape or the like, cracks occur in the molded body, and the cracks are sintered. Since it will remain in the later abrasive grains, the present inventor mixed and mixed the clay with 0.05 to 3.0 wt% as silicon dioxide in the abrasive grains with respect to high-purity alumina fine powder having a purity of 98 wt% or more. ,
A method for producing alumina-based sintered abrasive grains, which is characterized by forming and sintering, was found, and cracks existing in the abrasive grains could be significantly reduced.

The high-purity alumina raw material fine powder used in the present invention has a purity of 98 wt% or more, preferably 99 wt% or more, and a particle size of
It is a fine powder of 10 μm or less, preferably 2 μm or less. If the purity is less than 98 wt%, the strength of the sintered abrasive grains will be poor.

For this high-purity alumina fine powder, 0.1-
It is preferable to add magnesium oxide, cobalt oxide, or nickel oxide as a crystal grain growth inhibitor during sintering so that the content is 3.0 wt%. Furthermore, in order to shape the abrasive grains into a columnar shape, a water-soluble binder such as PVA is used in an amount of 0.2-3 wt
%, And the kneaded product of high-purity alumina containing water is applied to a molding machine.

Kneaded products such as these fine alumina powders lack plasticity and flexibility, and when molded, cracks easily occur inside or on the surface of the formed body.

In addition, if the water content of the kneaded product is increased to reduce the cracks, the shape retention of the molded product will be poor. Therefore, in the present invention, in addition to these raw materials such as high-purity alumina fine powder, clay is further added to improve the plasticity and flexibility of the kneaded material and reduce the cracks of the molded body.

The amount of clay added is 0.05 as silicon dioxide in the sintered abrasive grains.
~ 3.0 wt% is the amount contained. If it is less than 0.05 wt%, the effect is not sufficient, and if it exceeds 3.0 wt%, vitreous and mullite substances are generated, the wear rate of the abrasive grains is increased, and the sintered crystals grow too much and the strength is increased. descend.

There are many types of clay, but in the present invention, bentonite, which significantly improves the plasticity of the kneaded material,
It is preferable to use at least one of kibushi clay, frog clay, enamel clay, container clay and sericite clay.

From the viewpoint of ease of production, it is preferable to add clay in an amount of 0.05 to 3.0 wt% as silicon dioxide in the sintered abrasive grains, sufficiently knead with a kneader such as a mix muller or a kneader. It is molded by an extrusion molding machine for molding into a cylindrical shape, and is appropriately cut so that the length / diameter of the cylindrical shape becomes 1 to 3 positions. This compact is fired at 1650 to 1750 ° C. for 30 minutes to 2 hours while rolling in a rotary kiln to produce sintered abrasive grains having a crystal size of 10 μm or less.

If the crystal size is too large, the mechanical strength is poor, so 10
It is necessary to make the thickness below μm.

Examples The present invention will be described in detail with reference to Examples.

Examples 1 and 2 Sintered alumina (Al ₂ O ₃ 99.5
0.4% by weight of bentonite is added to PVA and magnesia as shown in Table 1. About 30% by weight of the total weight of water is added and kneaded with a mix muller, then vacuum type JIS R6001-1973 particle size # 10 and # using extruder
To obtain 16 abrasive grains, the particles were extruded from a die having a hole diameter of 2.4 mmφ and 1.5 mmφ, respectively, and dried at 150 ° C. for about 1 hour.
This dried product has a length of 2 to 7 mm for # 10 and 1-4 for # 16.
It was cut to a length of mm and baked in a rotary kiln at 1700 ° C. for 1 hour. The characteristics of the thus obtained abrasive grains such as crack content and crushing strength are shown in Table 1 below.

The intragranular cracks were observed by observing a cross-sectional portion obtained by slicing the center of a columnar abrasive grain in the lengthwise direction with a 10 × microscope.

The crush strength is a value obtained by (crushing load) / (projected area of abrasive grains), and the crystal size was measured by SEM.

Comparative Examples 1 and 2 Abrasive grains having particle sizes # 10 and # 16 were obtained under the same conditions as in Examples 1 and 2 except that bentonite was not added. The characteristic values are shown in Table 1.

Incidentally, SiO ₂ content in the abrasive grain of Comparative Example 1 and 2 is the amount that is mixed as impurities in the alumina feed. As can be seen from Table 1, the addition of bentonite to both # 10 and # 16 abrasive grains has a low content rate of crack grains, and the effect of adding bentonite to reduce cracks is remarkable, and the crush strength is also high.

Examples 3 to 6 For # 10 abrasive grains, the bentonite content was changed as shown in Table 2 and the SiO ₂ content in the abrasive grains was 0.05, 0.25, 1.0 and 3.0 wt% under the same conditions as in Examples 1 and 2. I made abrasive grains.

The crack grain content and crystal size values of those abrasive grains are shown in the table.
2 shows.

Comparative Examples 3 and 4 Samples containing bentonite at 7.0 and 9.0 wt% and SiO ₂ contents in the abrasive grains of 4.0 and 5.5 wt% were prepared under the same conditions as in Examples 3 to 6. Table 2 shows the content of crack grains and the crystal size value of these abrasive grains.

Table 2 shows that the SiO ₂ content in the abrasive grains in the range of 0.05 to 3.0 wt% has a small crack grain content and maintains the crystal size of 10 μm or less.

If the crystal size exceeds 10 μm, the grain strength is adversely affected, which is not preferable.

It was found that, in addition to bentonite, knotobushi clay, frog eye clay, enamel clay, container clay, and sericite clay also significantly improve the plasticity of the kneaded material and reduce the crack grain content similarly to bentonite.

Effects of the Invention According to the production method of the present invention, by adding low-priced clay, it is possible to reduce the addition amount of the organic molding aid as compared with the conventional method, so that the raw material cost can be reduced,
It is possible to reduce the number of cracks in the abrasive grains and to manufacture alumina-based sintered abrasive grains having high strength and excellent characteristics.

Claims (2)

[Claims] 1. A high-purity alumina fine powder having a purity of 98 wt% or more, and clay of 0.05 to 3.0 wt% as silicon dioxide in the abrasive grains.
%, Added and mixed so as to contain, and molded and sintered. A method for producing an alumina-based sintered abrasive grain. 2. The alumina-based sintered abrasive grain according to claim 1, wherein the clay is at least one selected from bentonite, kibushi clay, gairome clay, enamel clay, container clay and sericite clay. Manufacturing method.