JPS58113285A - Alumina abrasive - Google Patents

Abstract

PURPOSE:To prevent the separation of sodium component from the alumina abrasive grains in a resinoid abrasive wheel, and prevent the lowering of the strength of the wheel, by attaching a specific amount of sulfate group to the grain. CONSTITUTION:Alumina abrasive grains are immersed in a dilute aqueous solution of sulfuric acid (preferably 0.01-4mol/l) e.g. at room temperature for >=10min, washed with water under the condition to leave 5-2,000ppm of the sulfate group on the grain, and dried preferably at <=300 deg.C.

Description

[Detailed Description of the Invention] The present invention relates to fused alumina abrasive grains and sintered alumina abrasive grains,
More specifically, the present invention relates to alumina abrasive grains having a specific amount of sulfuric acid radicals attached to these abrasive grains.

Alumina abrasive grains made from Bayer alumina contain soda, so contamination with soda is unavoidable.

If soda is mixed into alumina abrasive grains, the strength of the abrasive stone will be weakened when a resinoid whetstone is manufactured using the abrasive grains, and the strength after immersion in water will be weakened. Phenol resin is most often used as the resin for resinoid grinding wheels, but small amounts of other resins such as epoxy resin and unsaturated polyester resin are also used. Among these, phenolic resins are particularly affected by soda, but epoxy resins and the like are also affected. It is said that one of the reasons why the water immersion strength of a whetstone using abrasive grains containing soda decreases is that the soda and resin react to form a water-soluble compound.

Many measures have been proposed to reduce the soda content of abrasive grains, but they cannot be completely eliminated. Conventional methods generally include lowering the soda content of raw alumina, eliminating melting or sintering, and removing soda, and after melting or sintering, crushing the alumina into granules and then treating the alumina with hydrochloric acid or the like. However, even with these treatments, soda still contains about 002 weight tS even if the amount is small as Na2O.

Soda in alumina is present as free Na2O and β-alumina (Na2O・11A42C15)
This is the case when it is contained in the form of Among these, it is free Na2O that causes the above-mentioned problems in the grains.

These soda components are occluded not only on the surface of the abrasive grains but also inside them, and it is difficult to remove these occluded soda components by pickling or the like.

The trouble with the soda content of alumina abrasive grains is that this occluded soda content precipitates on the surface of the abrasive grains during the drying process after pickling or during the grindstone manufacturing process, which causes the problems mentioned above. That's true. This can be seen from the fact that when the abrasive grains are pickled, then thoroughly washed with water, dried, immersed in water, and the pH is measured, the abrasive grains exhibit alkalinity.

Therefore, by repeating washing and drying, it is possible to significantly reduce Na2O. However, repeating this operation is very disadvantageous industrially.

The present invention is an abrasive grain developed under these circumstances, and the purpose is to prevent the harmful effects of the soda content of alumina abrasive grains in resinoid grinding wheels.For this purpose, the alumina abrasive grains are acid-washed, particularly treated with an aqueous sulfuric acid solution. After that, sulfuric acid @(SO4)
It is characterized in that 5 to 2000 PPM of is attached to the abrasive grains.

Generally, hydrochloric acid is used as the acid to remove the soda content by pickling alumina abrasive grains. After processing, the product is washed with water and dried. In this product state, there is no salt attached, and if you measure the PHi of the soda content, it will show alkalinity.

Even if the abrasive grains are treated with sulfuric acid, only traces of sulfuric acid radicals will remain if the drying temperature is high or if the abrasive grains are washed thoroughly with water.

Therefore, as described above, the aqueous solution in which the abrasive grains are immersed after drying is alkaline.

In the present invention, this vC acid radical is attached to the abrasive grains in a specific manner, and for this purpose, it is necessary to select the washing conditions, drying conditions, etc. after the abrasive grains are treated with sulfur. When treated with hydrochloric acid instead of acetic acid, it was difficult to keep a specific amount of hydrogen chloride attached to the abrasive grains after drying, and the same effect as kml did not appear.

In the present invention, the amount of attached sulfate roots is 5PPM as 804.
If the amount is less, the effect will not be clearly seen as shown in the examples later, and if it exceeds 2000 P P M (because phenol resin is not affected much by weak acids, but is slightly affected by strong acids), the phenol resin becomes The disadvantages of being exposed to sulfuric acid arise.

It is unclear why the strength of the resinoid grinding wheel does not decrease due to the sulfuric acid radicals attached to the abrasive grains.
One reason is thought to be that the precipitated soda reacts with sulfate ions to generate sulfate, which prevents erosion of the resin by free soda. The second reason is that even if mat salt adheres to the surface of the abrasive grains, this corrosion prevention effect is observed, and due to the presence of sulfuric acid groups at the interface between the abrasive grains and the resin, new precipitation occurs due to some action. It is thought that this suppresses the resin corrosion caused by the soda content. In the state in which this sulfate is attached, the water immersion solution of the abrasive grains is alkaline because a soda component is further precipitated.

In the present invention, it is most desirable that the sulfuric acid radicals attached to the abrasive grains exist in the form of sulfuric acid, but the effect is recognized even in the form of salts such as sulfuric acid and soda. Also included.

To obtain the abrasive grains of the present invention, after pulverization, the abrasive grains are classified into a predetermined particle size and immersed in a dilute sulfuric acid water bath. The conditions in this case are not particularly limited, but from the viewpoint of ease of handling and treatment efficiency, the intensity of acetic acid is 0.01 to 4 mol/1%, the temperature may be room temperature, and the time is preferably 10 minutes or more.

After soaking, the abrasive grains are washed with water and dried. These conditions are selected so that the sulfuric acid radical of the abrasive grains falls within the above range. If the drying temperature is high, the sulfuric acid will volatilize or decompose, making it impossible to attach the sulfuric acid groups within the scope of the present invention, so the desirable drying temperature is 3.
The temperature is below 00℃. .

Example Fused alumina abrasive grains (particle size: JIS+60, total amount of Na2O 0.06% by weight), 100 parts by weight diluted with 114 mo/L
, /l) at 20°C for 120 minutes, then the number of water washes was changed constantly, and the drying temperature was changed from 100°C to 100°C.
The amount of iso4 ions remaining in the abrasive grains was selected within the range of 200°C and adjusted to the values shown in Table 1. A test piece was created by mixing the abrasive grains and phenol resin in the same way as a regular whetstone as follows, molding and hardening.

Abrasive grain 100 (heavy part) Liquid resin (Showa Union Synthesis ■BRL-207)
t, s powder resin (BRP-503) 65 The bulk specific gravity of the test piece after curing was 2.05.

The transverse rupture strength of this test piece (dry transverse rupture strength) and the transverse rupture strength after immersing the same test piece in 40°C hot water for 24 hours (
Wet transverse rupture strength) was measured. The results are shown in Table 2. In addition,
The amount of Na2O after pickling and drying was approximately 0.05%.

Similar to Table 2, the transverse rupture strength of sintered alumina abrasive grains was compared between cases in which no acid roots were left after pickling and cases in which 200 PPM residual adhesion was carried out. 0 No sulfate roots 160 40 Sulfate roots remaining 179 83 As described above, the pieces in which sulfuric acid radicals remain in the abrasive grains have a large transverse rupture strength, and the drop in wet transverse rupture strength is particularly small. Since grinding wheels are generally used while being sprayed with a grinding fluid such as water, wet transverse rupture strength is an important requirement. The present invention satisfies this requirement.O Applicant: Showa Denko K.K. Agent Sei Kikuchi -

Claims (1)

[Claims] Alumina abrasive grains with 5 to 2000 PPM of sulfate radicals attached.