JPH07286166A - Sintered abrasive grain composed of alumina-zirconia and its production - Google Patents

Abstract

PURPOSE:To provide a sintered abrasive grain having high hardness, high toughness and excellent crack resistance, composed of an alumina-zirconia composition having specific toughness, hardness and compositional ratio and suitable for heavy abrasion work. CONSTITUTION:This sintered abrasive grain is an alumina-zirconia composition containing (A) 3-15wt.% of ZrO2, (B) 0.05-3.0wt.% of SiO2 and (C) 0.1-3.0wt.% of MgO, CoO and NiO and having a toughness of <=15 in terms of friability value and a micro-Vickers hardness of >=1,800kg/mm<2> under 500g load. The sintered abrasive grain can be produced by incorporating fine alumina powder having a purity of >=98% with 3-15wt.% of ZrO2 and 0.05-3.0wt.% of clay as the SiO2 component of the sintered abrasive grain, adding 0.1-3.0wt.% of MgO, CoO and NiO, forming the mixture and baking at 1550-1750 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina-zirconia sintered abrasive grain having high toughness characteristics suitable for heavy grinding.

[0002]

2. Description of the Related Art Conventionally, abrasive powder for heavy grinding is an abrasive grain obtained by sintering fine powder of alumina material such as bauxite (Japanese Examined Patent Publication No. 39).
-4398, JP-B 39-27612, JP-B 39
-27613, Japanese Patent Publication No. 39-27614) and fused alumina-zirconia abrasive grains (Japanese Patent Publication No. 39-16592).
And SiO _2, TiO _2, MgO, fused alumina containing CaO, etc. - zirconia abrasive grains (JP-B-50-13989) or high purity alumina fine crystal growth inhibitors such as magnesium oxide was added abrasive grains (JP No. 52-14993) or high-purity alumina fine powder, and a crystal growth inhibitor such as magnesium oxide, and an abrasive grain in which clay is added as silicon dioxide in the abrasive grain to reduce cracks in the abrasive grain (JP-A-4-205).
No. 86) is known. Also, JP-A-56-3236
Zirconia, hafnia by sol-gel method like No. 9,
Alumina sintered abrasive grains containing nickel, cobalt, zinc, magnesia, etc. are also known.

[0003]

The bauxite-based sintered abrasive grains are formed by adding alumina (A) into the bauxite (calcination) used.
l ₂ O ₃ ) about 85%, TiO ₂ , Fe ₂ O ₃ , S
The wear rate is high because it contains impurities such as iO _2, but the hardness is low. Fused alumina-zirconia abrasive grains, after melting the raw material, rapidly solidified, crushed, sized to give a product,
It is difficult to produce a particle group having a predetermined excellent property and having a required particle size range in good yield. Further, the high-purity alumina-based sintered abrasive grains used for heavy grinding have low hardness and mechanical strength, but have low toughness and a large grinding amount per hour, but because of low wear resistance, This is an obstacle to expanding the applications. In order to solve these problems, the object of the present invention is to maintain the hardness to the minimum, further improve the wear resistance by increasing the toughness of the abrasive grains, thereby improving the grinding ratio, and also the required grain size range. The object of the present invention is to prevent generation of unnecessary particle size by molding such a material by extrusion or the like.

[0004]

The inventor has found the present invention as a result of various studies to achieve the above object. That is, having a substantially alumina-zirconia composition,
(1) ₃ to 15 wt% as ZrO ₂ , (2) 0.05 to 3.0 wt% as SiO ₂ , and (3) at least one of MgO, CoO, and NiO is 0.1 to 3 as these display conversions. Alumina-zirconia sintered abrasive grains containing 0.0 wt% and having a flyability value indicating a toughness value of 15 or less and a micro Vickers hardness (Hv500) at a load of 500 g of 1800 kg / mm ² or more. The production method is as follows: 3 to 15 wt% of zirconia and 0.05 to 3.0 wt of clay as SiO ₂ in sintered abrasive grains with respect to alumina fine powder having a purity of 98 wt% or more.
%, And at least one of magnesium oxide, cobalt oxide and nickel oxide is added in an amount of 0.1 to 3 wt%, mixed, molded, and fired at 1550 to 1750 ° C. A method for producing sintered abrasive grains has been found. Further, a method for producing an alumina-zirconia sintered abrasive grain is also found, wherein the above-mentioned clay is at least one kind of bentonite, kibushi clay, gairome clay, gypsum clay and sericite clay. It was

The purity of the alumina raw material fine powder used in the present invention is 98 wt% or more, preferably 99 wt% or more, and the particle size is a fine powder having an average diameter d ₅₀ of preferably 10 μm or less, more preferably 2 μm or less. If the purity is less than 98 wt%, it may be difficult to adjust other components to be added and uniformity may be a problem. If the particle size exceeds 10 μm, it is difficult to obtain a dense sintered body and the sintered body is difficult to obtain. It is not preferable because the crystal size increases and the mechanical strength decreases. The zirconia used in the present invention has a purity of 98 wt% or more, d
A fine powder having a particle size of ₅₀ μm or less, preferably 10 μm or less, more preferably 1 μm or less is preferable. A suitable amount of zirconia added is 3 to 15 wt%. If it is less than 3 wt%, the effect of improving the toughness of the abrasive grains is not sufficient, and if it exceeds 15 wt%, the hardness is remarkably reduced. Further, at least one of magnesium oxide, cobalt oxide and nickel oxide is added as a crystal suppressor for abnormal grains during sintering so as to be contained in the abrasive grain structure in an amount of 0.1 to 3.0 wt%. If it is less than 0.1% by weight, the suppressing effect is small, and if it exceeds 3.0% by weight, the hardness of the abrasive grains is lowered and the mechanical strength is also unfavorable. These abnormal grain crystallization inhibitors also have a purity of 98 wt% or more, d
A fine powder having a particle size of ₅₀ μm or less, preferably 10 μm or less, more preferably 5 μm or less is preferable. In the present invention, it is preferable to add an organic binder such as PVA or methylcellulose (MC), preferably a water-soluble one thereof in an amount of about 0.2 to 3.0 wt% in order to form the abrasive grains into a columnar shape or the like. In many cases, sufficient shape retention of the molded product cannot be maintained by this alone, so in the present invention, clay is always added to improve the plasticity and flexibility of the kneaded product and reduce microcracks and the like of the molded product.

Although there are many kinds of clay, especially for the purpose of the present invention, the plasticity of the kneaded product is remarkably improved.
Bentonite, Kibushi Clay, Frog Eye Clay, ▲ Set ▼ Clay,
It is desirable to use at least one of the sericite clays. Among them, bentonant is judged based on the plasticity and the strength after drying based on the results of Examples described later.
Bentonite is the best in the order of Sericite Clay> Kibushi Clay> Frog Eye Clay> ▲ Setoku Clay. Even in the case of clay clay, it is superior in extrudability and the like as compared with the case where no clay is added, and bentonite is most preferable in the above order from the viewpoint of extrudability. The amount of clay added is the amount of Si in the sintered abrasive grains.
The amount of O ₂ contained is 0.05 to 3.0 wt%. If it is less than 0.05% by weight, the effect of improving the plasticity and flexibility of the kneaded product is not sufficient, and if it exceeds 3.0% by weight, vitreous and mullite substances are produced and the abrasion rate of the abrasive grains is increased. At the same time, the crystal grows too much due to sintering, and the strength decreases.

In the present invention, the above-mentioned raw materials, that is, fine grain alumina powder, zirconia, clay, and abnormal grain crystallization inhibitor such as magnesium oxide are blended and mixed in the above range. In this case, it is preferable to add an aqueous solution or a non-aqueous solution of an organic binder such as PVA as described above, and after sufficiently kneading, it is formed by extrusion or the like in a columnar shape. The molding is not limited to the cylindrical shape, and the forming method is not limited to the extrusion method. Then, preferably dried in the range of 100 ~ 150 ℃,
Bake. A firing temperature of 1550 to 1750 ° C is suitable. If the temperature is lower than 1550 ° C, a dense and high-density sintered body cannot be obtained, and if the temperature is higher than 1750 ° C, the crystal size is too large and the toughness and mechanical strength decrease. To do. In order to obtain abrasive grains, after firing, crushing and sizing may be performed, or after drying, crushing and sizing may be performed, and a product having a predetermined grain size may be fired.

Next, the alumina-zirconia sintered abrasive grain of the present invention produced by the above-mentioned manufacturing method will be described. The abrasive grain of the present invention has a composition of the above-mentioned blending raw material ratio, that is, a substantially alumina-zirconia composition, ₃ to 15 wt% as ZrO ₂ and 0.05 to 3.0 wt% as SiO ₂ .
Further, it is an abrasive grain containing at least one of MgO, CoO and NiO in an amount of 0.1 to 3.0 wt% in terms of these expressions. Abrasive grains with such a composition were also in the past,
By the above-described characteristic manufacturing method of the present invention, abrasive grains having high toughness and high hardness which have never been obtained can be produced for the first time. That is, the value of the flyability indicating the toughness value is 15 or less,
Micro Vickers hardness (Hv50
0) was 1800 kg / mm ² or more, and an alumina-zirconia sintered abrasive grain was obtained.

The method of measuring the above flyability is as follows. The measuring method is JIS R6128.
This is a method based on (Test method for toughness of artificial abrasives), but the conditions are slightly changed as follows. (1) About 300 g of an abrasive grain to be measured, which is a sample, is weighed and sieved with a low tap tester for 5 minutes using a standard mesh sieve defined by the JIS of each grain size. The total amount of the sample retained in the third stage sieve is sieved for another 5 minutes, and the sample retained in the third stage sieve is used as a test sample. (2) Accurately measure 100 g of the test sample to 0.1 g, and
Put in a 1 liter ball mill of 14mmφ and further 3/4
Place 2 kg of inch steel balls in the ball mill. (3) Grind the test sample for 15 minutes at 95 rpm mill speed. Then, the contents of the ball mill are taken out and the ground sample is collected.

(4) The ground sample is sieved for 5 minutes by a low tap tester using the same standard mesh sieve as above. (5) Accurately weigh the sample retained on each sieve. 1 to
The total amount of sample remaining on the 4th stage sieve is the test sample amount 10
Subtract from 0 g and use that value as the flyability value. That is, the lower part of the fourth stage sieve has a flyability value, and the smaller the value, the higher the toughness.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. Example 1 Calcined alumina (purity 99.5 wt%, specific surface area 5 m ² / g)
Pulverized and classified powder (d ₅₀ = 1.99 μm, d ₁₀ = 0.44 μ
m, d ₉₀ = 7.76 μm), as shown in Table 1, zirconia (Showa Denko RZ-N, # 6000F; d ₅₀ =
0.89 μm) at 3 wt%, bentonite (Kanto Bentonite Mining Co., Ltd., Tenryu) at 0.3 wt%, magnesium oxide (Kyowamag 30, Kyowa Chemical Industry, purity 99)
wt%, d ₅₀ = 4.51 μm) 0.2 wt% was added, 0.4 wt% of PVA was added as a bunder, and the mixture was put in water of 26 wt% with respect to the total weight, kneaded with a mix muller, and vacuum extruder Using JIS R6001-19
In order to obtain abrasive grains having a prescribed grain size of ^# 12 of 87, it was extruded from a die having a hole diameter of 2.2 mmφ and dried at 150 ° C. for 1 hour. This dried product was cut into a length of 2 to 6 mm and baked in a rotary kiln at 1700 ° C. for 1 hour.

The characteristics of the abrasive grains thus obtained are shown in Table 2. The intragranular cracks were obtained by observing a cross-sectional portion obtained by slicing the center of a column in the lengthwise direction with a microscope with a magnification of 10 and displaying the proportion of grains having even one crack as the content rate. The crush strength is a value obtained by [breaking load] / [projected area of abrasive grains], and the crystal size was measured by SEM.

Comparative Example 1 As shown in Table 1, no bentonite was added and the other conditions were the same as in Example 1 to obtain abrasive grains of grain size ^# 12.
The characteristic values and the like are shown in Table 2. The amount of SiO ₂ in the abrasive grains is a mixture of impurities of alumina raw material.

Comparative Example 2 As shown in Table 1, ZrO ₂ was not added and the other conditions were the same as in Example 1 to obtain abrasive grains of grain size ^# 12. The characteristic values and the like are shown in Table 2.

As can be seen from Table 2, Example 1 shows that the flyability is extremely small, the toughness is high, and the crush strength is also high. Both of these properties are believed to be largely attributable to zirconia, but the plasticity and flexibility of the kneaded product are improved several steps as an effect of adding bentonite, and as a result, the number of cracks in the abrasive grains is reduced and the abrasive grains without cracks. The ratio of is increasing.

[0016]

[Table 1]

[0017]

[Table 2]

Examples 2 to 5 ^# 12 abrasive grains were produced under the same conditions as in Example 1 except that the amount of zirconia added was changed as shown in Table 3. The characteristics of the obtained abrasive grains are shown in Table 3.

Comparative Examples 3 to 7 As shown in Table 3, zirconia addition amounts of less than 3 wt% and more than 15 wt% were examined. The other conditions were the same as in Example 1 to produce ^# 12 abrasive grains. The characteristics of the obtained abrasive grains are shown in Table 3.

[0020]

[Table 3]

Examples 6 to 8 and Comparative Example 8 Bentonite (Kanto Bentonite Mining Co., Ltd. (Tenryu)
[Higashi-Kabahara-gun, Niigata Prefecture], Kibushi clay (Edashita Kiln Co., Ltd., ultra-fine powdered product [Edashita, Sanage-cho, Nishikamo-gun, Aichi Prefecture]) and frog eye clay (Matsubara Ceramic Co., Ltd., elutriated product [Seto, Aichi Prefecture] City production]) 3
0.3% by weight of each clay, MgO (the same product as in Example 1) in the outer ratio to the pulverized and classified powder of the calcined alumina used as the raw material in Example 1 under the condition that the seed clay and the clay were not added. ) 0.2 wt%, PVA (same as Example 1) 0.
4 wt% and 26 wt% of water were mixed and kneaded with a mix muller. The load of the kneader was 7 to 8 A (AC) in all, including the case where no clay was added.

The penetration by the clay insulator Nestah made by Nippon Insulator showing the plasticity of the kneaded product was 13 with addition of clay and 14 with no addition. The kneaded product is Tensilon (UTM-1 manufactured by TOYO BALDWIN).
0T-PL type) was used to extrude a 3 mmφ rod at a crosshead speed of 5 mm / min. Table 4 shows the starting load and the maximum load in each case.

[0023]

[Table 4]

As can be seen from Table 4, the extrudability was excellent in the order of bentonite> kibushi clay> grape clay> no use (addition). Comparative Example 9 A pulverized and classified product of calcined bauxite as a raw material (d ₅₀ = 2μ)
m), Vander is 0.3 wt% of PVA with respect to calcined bauxite, 1400 to 1450 in rotary kiln.
Sintered abrasive grains were obtained under the same conditions as in Example 1 except that firing was carried out at 0 ° C for 1 hour. The obtained sintered abrasive grains have a flyability value of 10.3 and a Vickers hardness of 1261 kg / mm ^2.
It can be seen that the hardness is particularly lower than that of the present invention.

From Table 3, the content of zirconia is 3 to 15 wt.
In the range of%, the flyability value is 10 or less, which is smaller than that of the bauxite-type sintered abrasive grains, indicating that the toughness is high. Furthermore, Vickers hardness is 1800
Maintains at least kg / mm ² .

[0026]

EFFECTS OF THE INVENTION The abrasive grain of the present invention contains alumina in a specific amount of zirconia, clay, magnesium oxide, cobalt oxide or nickel oxide to significantly improve toughness while maintaining high hardness (flyability). Since the ability value is greatly reduced) and cracks in the abrasive grains can be further reduced, the alumina sintered abrasive grains have various excellent characteristics.

Claims (3)

[Claims] 1. A substantially alumina-zirconia-based composition, wherein (1) ZrO ₂ is 3 to 15 wt%, (2) SiO ₂ is 0.05 to 3.0 wt%, (3) MgO, CoO and At least 1 of NiO
Seed content of 0.1 to 3.0 wt% is included, the flyability value indicating the toughness value is 15 or less, and the micro Vickers hardness (Hv500) at a load of 500 g is 1800 kg / mm ² or more. Characteristic alumina-zirconia sintered abrasive grains. 2. Alumina fine powder having a purity of 98 wt% or more is added with 3 to 15 wt% of zirconia and 0.05 to 3.0 wt% of clay as SiO ₂ in sintered abrasive grains, and further magnesium oxide and oxide are added. A method for producing alumina-zirconia sintered abrasive grains, characterized in that 0.1 to 3 wt% of at least one of cobalt and nickel oxide is added, mixed, molded, and fired at 1550 to 1750 ° C. 3. The alumina according to claim 2, wherein the clay is at least one selected from bentonite, kibushi clay, frog eye clay, gypsum clay and sericite clay.
Method for manufacturing zirconia-based sintered abrasive grains.