JP2790029B2 - Method for producing coated fused alumina particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fused alumina particles containing titanium oxide, the surface of which is coated with aluminum titanate. It can be used as a highly refractory material.

[0002]

2. Description of the Related Art Regarding artificial abrasives JIS R6111
-Alumina abrasives produced by melting an alumina purified by the Bayer method in an electric furnace as specified in 1987 include white alumina abrasives (WA), pink alumina abrasives (PA), There is a crushed alumina abrasive (HA). Although the toughness of these abrasive grains increases in the order of HA>PA> WA, it is difficult to say that a sufficiently satisfactory grinding performance has not yet been obtained for difficult-to-cut materials such as tool steel. Attempts have been made to heat treat fused alumina particles. For example, in Japanese Patent Application Laid-Open No. 50-80305, a white fused alumina abrasive (WA) having an alumina content of 99.0% or more
It is disclosed that heat treatment is performed at 600 to 1850 ° C. for 30 minutes to 2 hours. This is because defects and fine scratches and cracks generated during grinding of ingots of fused alumina can be recovered by atom diffusion and rearrangement under high temperature, the scratches can be made shallow, and Na contained in abrasive grains can be reduced. _{It is} to improve the strength by volatilizing ₂ O, and although a certain effect is recognized, it cannot be said that the abrasive itself has essentially been improved. Further, in this publication, when abrasives containing a considerable amount of TiO ₂ , SiO _2, etc., for example, brown fused alumina abrasives (A), are burned at a temperature of about 1000 to 1300 ° C., cracks disappear to some extent and the abrasive grains are crushed. It is described that the strength is increased, and it is stated that firing at 1400 ° C. or more lowers the strength.

[0003]

The above-described heat treatment of the fused white alumina at 1600 to 1850 ° C. recovers crystal defects generated in the abrasive grains during pulverization of the ingot, and removes fine scratches and cracks. The purpose of the present invention is to improve the strength and toughness of the abrasive grains by making the tip shallower to reduce the concentration of stress. However, even when such a treatment is performed, the characteristics of the white fused alumina can be changed to the crushed alumina (H
Only the characteristics of A) are obtained, but there is no substantial improvement, and the grinding performance is not so much improved. Further, since the heat treatment is performed at a very high temperature, there are problems such as cost.

[0004]

The inventors of the present invention have made efforts to achieve the object of producing a grinding material having better grinding performance or a refractory material having excellent strength and heat resistance. I found it. That is, the fused alumina particles containing titanium oxide are heated to 1300 ° C. or more to precipitate solid solution titanium and form aluminum titanate on the surface of the particles, and then the temperature range of 1300 to 750 ° C. 300
A method for producing fused aluminum particles coated with aluminum titanate, characterized in that the particles are cooled at a rate of at least ° C / hour.

First, fused alumina containing titanium oxide will be described. This is manufactured by a method for producing general fused alumina. That is, alumina and TiO ₂ may be electromelted in an electric furnace. The TiO ₂ source of titanium oxide (rutile and / or anatase form), titanium slag (rutile ore, the ilmenite in an electric furnace, charcoal, and reduced with cokes, TiO ₂ ≧ 80 wt in that separation of the iron
%) Can be used. Other than titanium oxide obtained by adding the above TiO ₂ source to alumina, for example, alumina by the Bayer method, and melting it in an electric furnace such as an arc type, or melting and reducing bauxite together with a reducing material such as coke in an electric furnace. The fused alumina having a relatively small amount of impurities and high alumina purity is used as the fused alumina containing titanium oxide which is a raw material of the present invention. The former is a method of producing a light red alumina abrasive (PA), and the latter is similar to a method of producing a crushed alumina abrasive (HA).

[0006] The amount of titanium oxide contained in the fused alumina is, 0.1~1.5wt% in terms of TiO ₂ is preferred. When the amount of titanium oxide is less than 0.1 wt%, the amount of titanium precipitated from the solid solution state is small and the amount of aluminum titanate generated is also small, so that it is difficult to uniformly coat the entire surface of the grain, and the amount is 1.5 wt%. If the amount exceeds, the amount of precipitation increases and unreacted titanium oxide remains in addition to the generated aluminum titanate, which deteriorates the characteristics of the coating film. It is not preferable because it increases the properties of the grains. Stable can be expected to improve the particle properties, the amount of more preferred titanium oxide is 0.2～1.0Wt% in terms of TiO _2.

In the present invention, the above fused alumina is pulverized,
Use iron-removed ones, or granular ones sized to a predetermined particle size. In the present invention, the fused alumina particles containing titanium oxide are subjected to a heat treatment, which will be described. The fused alumina particles containing titanium oxide are placed in a container such as a sagger and heated in an electric furnace such as a muffle furnace or a continuous tornel-type continuous firing furnace, or the particles are directly subjected to heat treatment in a firing device such as a rotary kiln.

The temperature of the heat treatment is preferably 1300 ° C. or higher and the upper limit is preferably 1700 ° C. or lower. More preferably,
1400-1600 ° C. At around 1200 ° C., the exsolution of titanium solid-dissolved in the electrofused particles starts, and the precipitated titanium moves to the vicinity of the particle surface and reacts with alumina to produce aluminum titanate. However, when the temperature is 1300 ° C. or lower, it takes a very long time, and is not practical. More preferably 1
Above 400 ° C., at this temperature, the exsolution rate is high, so that the solid-dissolved titanium is exfoliated and precipitated without heating for a long time, moves to the surface and reacts with alumina to produce aluminum titanate. . If the temperature exceeds 1700 ° C., sintering of the particles occurs, and it is necessary to disintegrate after firing. When crushing is performed, the coating layer of aluminum titanate formed on the surface of the grains is broken, so that the strength of the grains decreases. A more preferable temperature at which the particles can be used without sintering and without crushing is 1600 ° C. or less. The holding time at the time of heating is preferably held at 1400 ° C. for 30 minutes or more,
At 1600 ° C., the heating is preferably performed for 10 minutes or more.

Another important requirement of the present invention is control of cooling after the above heat treatment. That is, 130
Rapid cooling at a rate of 300 ° C./hour or more between 0 and 750 ° C. More preferably, the temperature is 500 ° C./hour or more. The rapid cooling in this manner requires the rapid cooling of the above degree or more because the aluminum titanate formed on the grain surface is decomposed between 1300 and 750 ° C.

The fused alumina containing titanium oxide coated with aluminum titanate thus produced according to the present invention will be described. The surface of the fused alumina particles is 5-1
It is covered with a film of aluminum titanate having a thickness of 5 μm, and all the titanium elements on the surface are aluminum titanate. When the distribution of titanium present was examined by EPMA, titanium was present inside the grain as well as on the grain surface. In fused alumina containing titanium oxide, which is a raw material before heat treatment, about 60 to 70% of titanium oxide is
It is a type of Ti ₂ O ₃ and is dissolved in alumina (corundum). The remaining titanium oxide is TiO _{2 on the} grain boundaries and pore surfaces.
Or as a compound with impurities such as SiO ₂ and Na ₂ O and / or as glass. When heat treatment is performed according to the present invention, the solid oxide titanium oxide is dissolved as described above and reacts with alumina to produce aluminum titanate. SiO ₂ , N
It is considered that a compound with impurities such as a ₂ O and titanium oxide present as glass do not participate in the production of aluminum titanate.

The raw material “fused alumina containing titanium oxide” which can be used in the present invention includes, in addition to Ti, C
r, Si, Na, and Fe may be included. Since all of these elements, Cr, form a solid solution with alumina, they are used as elements for strengthening grains, and have an effect of slightly improving hardness and strength up to about 3% by weight. However, once dissolved, Cr does not change even by subsequent heating, and thus does not affect the effects and functions of the present invention. Ti, Cr
The amount of impurities other than the above is preferably 1.5 wt% or less in total as oxides. If the content exceeds 1.5% by weight, the hardness of the coated fused alumina particles obtained is low, and the properties of the abrasive are inferior.

The hardness of the fused alumina particles coated with aluminum titanate obtained according to the present invention is higher than that of the uncoated fused alumina, and is 2100 kg / mm ² or more as measured by micro Vickers hardness under a load of 500 g. After heat treatment at 1300 ° C. or higher as described above, quenched under predetermined conditions,
The mixture is cooled to room temperature, sieved again to a desired particle size by sieving or the like, and an abrasive having a desired particle size, a refractory material or the like can be obtained.

[0013]

The present invention will be described in detail below with reference to examples and comparative examples. # Solutions砕型fused alumina abrasive containing 0.30 wt% Example 1 Titanium oxide in terms of TiO ₂ (Showa Denko KK SA) 6
500 g of 0-granular particles were put into an alumina crucible, heated in a muffle furnace to 1400 ° C. in 7 hours, kept at 1400 ° C. for 2 hours, stopped heating, and allowed to cool in the furnace. At this time, the cooling time to 1300 to 750 ° C. was 1 hour, and the cooling rate in this temperature range was 550 ° C./hour. After cooling to room temperature, the particles were sized with a sieve screen of 350 to 210 μm to remove coarse particles and fine particles which adhered to each other to obtain particles corresponding to # 60 alumina abrasive. The density of the particles thus obtained is 3.96 g / cm ³ and the particle load is 500
micro Vickers hardness in grams is 2180 kg / mm ²
Met. The obtained particles were subjected to a qualitative analysis of a substance formed on the surface of the particles using an X-ray diffractometer. As a result, formation of aluminum titanate was confirmed.

The toughness of the grains is determined according to JIS R1268-1.
It was measured by a method defined as a C coefficient according to a test method (ball mill method) of a 975 artificial abrasive. That is, about 250 g of a sample is weighed according to JIS R6001-19.
Sieve for 10 minutes with a low tap tester using a standard sieve specified in # 87. The total amount of the sample remaining on the third-stage sieve is sieved for another 10 minutes, and 100 g of the sample remaining on the third-stage sieve is used as a test sample. This sample is JIS
Ball milling is performed according to the method specified in R6128-1975. The ground sample is sieved for 5 minutes using a standard sieve, 4
Let R (x) be the weight of the sample remaining on the sieve of the stage. The same operation was performed using # 60 black silicon carbide abrasive stipulated in JIS R6128-1975 as a standard sample, and the weight of the sample remaining at the fourth stage after ball milling was defined as R (s), The C coefficient is calculated by the following equation. C coefficient = log (100 / R (x)) / log (100
/ R (s)) The smaller this value, the higher the toughness, but the C coefficient of the coated fused alumina particles of Example 1 was 0.75.

Example 2 The heating temperature and the holding time were set at 1500 ° C. for 1 hour,
Coated particles were obtained in the same manner as in Example 1, except that the cooling rate between 0 and 750 ° C was 2200 ° C / hour. The density of the particles thus obtained is 3.98 g / cm ³ , and the micro Vickers hardness under a load of 500 g of the particles is 2170 kg.
/ Mm ² and the C coefficient was 0.73. The particles obtained were subjected to a qualitative analysis of a substance formed on the surface of the particles using an X-ray diffractometer. As a result, aluminum titanate was confirmed.

Example 3 Coated particles were obtained in the same manner as in Example 1 except that the heating temperature was 1600 ° C. and the holding time was 30 minutes. The density of the particles is 3.98 g / cm ³ , the micro Vickers hardness at a load of 500 g of the particles is 2190 kg / mm ² ,
The coefficient was 0.70. The particles obtained were subjected to a qualitative analysis of a substance formed on the surface of the particles using an X-ray diffractometer. As a result, aluminum titanate was confirmed.

Example 4 A reddish-colored fused alumina abrasive (PW manufactured by Showa Denko KK) containing 0.30% by weight of titanium oxide in terms of TiO ₂ was heated in the same manner as in Example 1 to obtain coated particles. Was. The density of the particles is 3.98 g / cm ³ , the micro Vickers hardness at a load of 500 g of the particles is 2160 kg / mm ² ,
The coefficient was 0.76. The particles obtained were subjected to a qualitative analysis of a substance formed on the surface of the particles using an X-ray diffractometer. As a result, aluminum titanate was confirmed.

Example 5 The procedure of Example 1 was repeated except that 0.7 wt% of titanium oxide was added to the Bayer method alumina, and the resulting mixture was melted in an arc furnace and pulverized and sized. Similarly, heat treatment was performed to obtain grains. The particles have a density of 3.98 g / cm ³ and a micro Vickers hardness at a load of 500 g of the particles of 2130.
kg / mm ² and the C coefficient was 0.68. The particles obtained were subjected to a qualitative analysis of a substance formed on the surface of the particles using an X-ray diffractometer. As a result, aluminum titanate was confirmed. On the other hand, the grain density before the heat treatment was 3.97 g.
/ Cm ³ , the micro Vickers hardness at a load of 500 g of the particles is 2010 kg / mm ² , and the C coefficient is 1.1.
It was 3. As a result of qualitative analysis of the particle surface portion using an X-ray diffractometer, no aluminum titanate was detected.

Comparative Examples 1 to 3 Density of # 60, micro Vickers hardness of each of white fused alumina abrasive WA, single crystal fused alumina abrasive SA and light red fused alumina abrasive PW manufactured by Showa Denko KK , And C coefficient were determined, and Comparative Examples 1 to 3 were obtained. Table 1 shows the results. Further, in the qualitative analysis of these abrasive grains by X-ray diffraction, aluminum titanate was not detected from any of the abrasive grains.

[0020]

[Table 1]

Comparative Example 4 For the purpose of a supplementary test in Japanese Patent Application Laid-Open No. 50-80305, 500 g of the same # 60 WA abrasive as in Comparative Example 1 was placed in an alumina crucible.
The temperature was raised to 1700 ° C. for 7 hours in a muffle furnace, kept for 30 minutes, stopped heating, and allowed to cool naturally in the furnace. After cooling to room temperature, grains equivalent to abrasives of # 60 sieved were obtained in the same manner as in Example 1. The particle has a density of 3.98 g / cm ³ and a micro Vickers hardness at a load of 500 g of the particles of 206.
It was 0 kg / mm ² and the C coefficient was 0.97. Further, analysis by an X-ray diffractometer revealed that the diffraction peak intensity of the β-alumina phase decreased after the heat treatment, but no other change was observed.

Comparative Example 5 The same SA abrasive material as in Example 1 was heated at a heating temperature and for 125
# 6 in the same manner as in Example 1 except that the temperature was changed to 0 ° C. for 5 hours.
0 grains were obtained. The density of these grains is 3.95 g / cm ³ ,
The micro Vickers hardness at a load of 500 g of the particles is 20.
It was 70 kg / mm ² and the C coefficient was 0.88.
Further, as a result of qualitative analysis of a substance formed on the particle surface of the obtained particle using an X-ray diffractometer, aluminum titanate was not confirmed.

COMPARATIVE EXAMPLE 6 In Example 1, the cooling rate between 1300 and 750.degree.
Grains were obtained in the same manner as in Example 1 except that the temperature was changed to ° C./hour.
The density of the particles is 3.98 g / cm ³ and the particle load is 50
Micro Vickers hardness at 0 g is 2190 kg / mm
² , and the C coefficient was 0.73. The obtained particles were subjected to a qualitative analysis of a substance formed on the surface of the particles using an X-ray diffractometer. As a result, rutile-type titanium oxide and a very small amount of aluminum titanate were confirmed.

Examples 6 to 10 and Comparative Examples 7 to 12 For 100 parts by weight of grains equivalent to # 60 abrasive in Examples 1 to 5 and Comparative Examples 1 to 6, dry phenol was used as a bond for a resinoid grindstone. (Showa Polymer BRP-
5428), 3.6 parts by weight of liquid phenol (BRL-204 manufactured by Showa Polymer), and 9.8 parts by weight of cryolite (44 μmF) as a filler were mixed by a mixer. After mixing, press molding was performed to produce a molded body having an abrasive grain ratio of 46%. After drying this at 120 ° C. for 5 hours, 18
Firing at 0 ° C. for 15 hours. Thus, JIS R6
A resinoid grindstone having a 212 degree bond K was prepared. The dimensions of the whetstone are all 200mmφ x 19mm x
The inner diameter is 50.8 mmφ.

Examples 11 to 15 and Comparative Examples 13 to 18 The resinoid grindstones of Examples 6 to 10 and Comparative Examples 7 to 12 were ground under the following test conditions to evaluate the grinding performance.

[0026] Test Conditions Grinding machines: manufactured) Okamoto Machine Tool Works surface grinding machine PSG-52DX (3.7kw) Grinding method: plunge grinding down cut _{Workpiece: SUJ-2 (H RC 60} ), 100mm
Length × 50mm height × 10mm thickness Grinding wheel peripheral speed: 1800m / min Table speed: 20m / min Cutting depth: 15μm / pass Total cutting dimension: 5mm Grinding width: 10mm Grinding oil: Noritake Cool K-82B (water-soluble grinding oil) 80 Double solution Dressing condition: single stone diamond dresser Depth of cut: 20 μm / pass As a result, the values shown in Table 2 were obtained for the grinding ratio, maximum power consumption value (value excluding no-load power), and surface roughness.

[0027]

[Table 2]

As can be seen from Table 2, when the alumina particles according to the method of the present invention are used as the abrasive, the grinding ratio is about 2.5 times that of the commercially available white fused alumina abrasive, and the commercially available single-crystalline A value showing about 1.8 times higher performance than the fused alumina abrasive was obtained. In addition, despite the high grinding ratio, the maximum power consumption value was lower than that of the comparative example, and the surface roughness of the ground surface of the workpiece tended to be smaller than that of the comparative example.

[0029]

According to the method of the present invention for producing fused alumina particles containing titanium oxide coated with aluminum titanate, a grinding material having excellent hardness, toughness and grinding performance as compared with conventional grinding materials can be obtained. be able to.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C01F 7/02 B24D 3/00 320 C09K 3/14 550

Claims (1)

(57) [Claims] 1. An electrofused alumina particle containing titanium oxide is heated to 1300 ° C. or more to precipitate solid solution titanium and form aluminum titanate on the surface of the particle.
A method for producing aluminum titanate-coated fused alumina particles, characterized in that a temperature range of 1300 to 750 ° C is cooled at a rate of 300 ° C / hour or more.