JP2015062982A - Grindstone base and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grindstone base which has material characteristics suitable for high-speed rotation and enables grinding to be performed with high efficiency and high accuracy.SOLUTION: A grindstone base is formed in a disk shape and used as a grindstone by adhering abrasive grain layer to the surface. The grindstone base is composed of a metal-ceramic composite material comprising a metal material consisting of aluminum or an aluminum alloy and a ceramic material consisting of a low-thermal-expansion ceramic or a negative-thermal-expansion ceramic and has a linear expansion coefficient of 13-17 ppm/°C and a specific tensile strength of 120 MPa or higher. The configuration reduces the thermal expansion difference between the base and the abrasive grain layer and thereby prevents the occurrence of strain due to deformation of the base or the abrasive grain layer, leading to improvement of processing accuracy. The high specific tensile strength enables grinding performed with high efficiency through high-speed rotation of the grindstone.

Description

  The present invention relates to a base for a grinding wheel and a method for manufacturing the same, and particularly to a base for a grinding wheel using a metal-ceramic composite material and a method for manufacturing the same.

  A grinding wheel for grinding steel materials, ceramics and the like is basically configured by fixing a grinding stone to the periphery of a disk-type base metal by a resin bond. For the base metal, iron or an iron-based alloy having high strength is mainly used.

Japanese Patent Laid-Open No. 10-286776

  In recent years, in the grinding process, for the purpose of high efficiency and high precision, the peripheral speed of grinding with a disc type grinding wheel has been increased. However, since the iron base metal has a large specific gravity, there is a problem that the burden on the grinding machine is increased and the electric power required for rotating the grindstone is increased.

  Therefore, it is considered to use aluminum or an aluminum alloy having a small specific gravity for an iron base metal having a large specific gravity. However, the linear expansion coefficient of aluminum or aluminum alloy is as large as 21 to 23 ppm / ° C., and heat generated by grinding is transmitted to the grindstone, and when the temperature of the grindstone changes, the difference in thermal expansion between the base metal and the abrasive layer based on this temperature change. Due to the influence of the above, there is a problem that distortion due to deformation occurs in the base metal or the abrasive grain layer, and the processing accuracy is lowered.

  Patent Document 1 proposes application of a metal-ceramic composite material, which is a lightweight low thermal expansion material, to the base metal. The aluminum-alumina composite material has a specific gravity as low as 3.45 and a linear expansion coefficient as low as 12 ppm / ° C. However, since the specific strength (tensile strength / specific gravity) is lower than that of the iron base metal, it is not possible to expect a higher peripheral speed than that of the iron base metal.

  The present invention has been made in view of such circumstances, and has a base material for a grinding wheel that has material characteristics suitable for high-speed rotation, enables high-efficiency grinding processing by high-speed rotation, and high-precision processing. It aims at providing the manufacturing method.

  (1) In order to achieve the above object, a base for a grinding wheel according to the present invention is a base for a grinding wheel which is formed in a disk shape and is used as a grinding wheel by adhering an abrasive layer to the surface. And a metal-ceramic composite material having a metal material made of aluminum or an aluminum alloy and a ceramic material made of low thermal expansion ceramics or negative expansion ceramics, and having a linear expansion coefficient of 13 ppm / ° C. to 17 ppm / ° C. The strength is 120 MPa or more.

  Thereby, the difference in thermal expansion between the base metal and the abrasive grain layer is reduced, the base metal or the abrasive grain layer is prevented from being deformed and distorted, and the processing accuracy can be improved. Moreover, since the specific strength is high, the grinding wheel can be rotated at a high speed to improve the grinding efficiency. Thus, since the material characteristics of the base metal are suitable for high-speed rotation, high-precision processing is possible while improving the efficiency of grinding processing.

  (2) Further, the base for a grinding wheel of the present invention is characterized by having a specific gravity of 3.0 or less. Thus, since specific gravity is small, the burden to a grinding machine can be reduced and the electric power which grindstone rotation can be made small.

  (3) Further, the base for a grinding wheel of the present invention is characterized in that the ceramic material is made of silicon carbide, aluminum nitride or zirconium tungstate phosphate. Thereby, the addition amount of a ceramic material can be reduced, and weight reduction and low thermal expansion can be realized.

  (4) Further, in the base for the grinding wheel of the present invention, the ceramic material in which the metal-ceramic composite material is 13% by volume to 36% by volume of the metal-ceramic composite material is dispersed in the metal material. It is characterized by being formed. Thereby, specific strength can be improved, reducing content of the ceramic material with respect to a metal material, and making the linear expansion coefficient of the base metal for grinding wheels the same level as the linear expansion coefficient of an abrasive grain layer.

  (5) A method for producing a base for a grinding wheel according to the present invention is the above-described method for producing a base for a grinding wheel, wherein a low thermal expansion ceramic or negative expansion is applied to a metal material obtained by melting aluminum or an aluminum alloy. A step of producing a mixed material by dispersing ceramic powder made of ceramic, a step of casting into a mold using the mixed material, and a member formed by the casting at a hot rate at an upsetting rate of 10% to 40% And forging and heat treatment.

  Thereby, the base metal for a grinding wheel with a small machining expansion difference of a base metal and an abrasive grain layer and high processing precision can be produced. In addition, a base for a grinding wheel with high specific strength and high efficiency in grinding can be produced.

  According to the present invention, the material characteristics of the grinding wheel base metal are suitable for high-speed rotation, and it is possible to increase the efficiency and accuracy of grinding by high-speed rotation.

It is a table | surface which shows the preparation conditions and evaluation result of an Example and a comparative example.

  Next, an embodiment of the present invention will be described.

  As a result of diligent research to solve the above problems, the inventors of the present invention have formed a metal base made of aluminum or an aluminum alloy and a ceramic material made of low thermal expansion ceramics or negative expansion ceramics on a grinding wheel base metal. The use of the metal-ceramic composite material has led to the completion of the present invention by obtaining knowledge that a base for a grinding wheel corresponding to high-speed rotation can be obtained.

(Configuration of grinding wheel base metal)
The base for a grinding wheel of the present invention is formed in a disk shape, and is used as a grinding wheel by adhering an abrasive layer to the surface. The base for a grinding wheel is formed of a metal-ceramic composite material having a metal material made of aluminum or an aluminum alloy and a ceramic material made of low thermal expansion ceramics or negative expansion ceramics.

  The low thermal expansion ceramic is a ceramic having a linear expansion coefficient of 0 ppm / ° C. to 4 ppm / ° C., and the negative expansion ceramic is a ceramic having a linear expansion coefficient of less than 0 ppm / ° C.

  During grinding, heat generated by the rotation of the spindle to which the grinding wheel is attached or heat generated by processing is transmitted to the grinding wheel, and the temperature of the grinding wheel changes. Due to the difference in thermal expansion between the base metal and the abrasive grain layer based on this temperature change, distortion due to deformation occurs in the base metal or the abrasive grain layer, and the processing accuracy can be lowered.

  When grinding was performed at a room temperature of 20 ° C. and a peripheral speed of 120 m / sec using a grindstone having a base metal outer diameter of 450 mm, the temperature of the abrasive layer on the outer peripheral portion was about 70 ° C., and the temperature of the base metal Is about 40 ° C. The linear expansion coefficient of the abrasive layer composed of diamond abrasive grains or cubic boron nitride abrasive grains and a resin binder is 5 to 7 ppm / ° C. Accordingly, the inner diameter change amount of the abrasive layer is 0.11 to 0.16 mm, and in order to match the change amount of the outer diameter of the base metal, the linear expansion coefficient of the base metal is 13 to 17 ppm / ° C. Is preferred.

  The specific strength of the base for the grinding wheel is 120 MPa or more. Since the specific strength is high, the grinding wheel can be rotated at high speed to improve the grinding efficiency. Thus, since the material characteristics of the base metal are suitable for high-speed rotation, high-precision processing is possible while improving the efficiency of grinding processing.

  Further, in order to obtain a specific strength of 120 MPa or higher, which is larger than that of the iron base metal, it is preferable to use a base metal having a specific gravity of 3.0 or less and a tensile strength of 360 MPa or more. Note that the specific gravity of the base metal is preferably as small as possible because the load on the drive system such as a motor can be reduced. Furthermore, the stress generated in the grindstone during high-speed rotation can be reduced by increasing the specific strength.

  The specific gravity of the base for the grinding wheel is preferably 3.0 or less. Since the specific gravity is small, the burden on the grinding machine can be reduced and the electric power required for rotating the grindstone can be reduced. At this time, it is preferable that the tensile strength of the base for the grinding wheel is 360 MPa or more.

  By using a metal-ceramic composite material for the base for the grinding wheel, the weight can be reduced and the thermal expansion can be reduced. In particular, by using low thermal expansion ceramics such as silicon carbide and aluminum nitride or negative expansion ceramics such as zirconium phosphate tungstate as ceramic materials, it is possible to reduce the amount of ceramic materials added and reduce weight and thermal expansion. Become. Such a material is a lightweight low thermal expansion material and has little reaction with molten aluminum.

  In addition, the metal-ceramic composite material is preferably formed by dispersing in a metal material a ceramic material that is 13 volume% or more and 36 volume% or less of the metal-ceramic composite material. Thereby, specific strength can be improved, reducing content of the ceramic material with respect to a metal material, and making the linear expansion coefficient of the base metal for grinding wheels the same level as the linear expansion coefficient of an abrasive grain layer.

(Manufacturing method of base metal for grinding wheel)
A method for manufacturing a base for a grinding wheel will be described below. After the molten aluminum or aluminum alloy in which the ceramic powder is dispersed is cast into a mold such as a sand mold, it is hot forged at an upsetting rate of 10 to 40% and further subjected to heat treatment.

As the ceramic material, a ceramic powder having an average particle diameter of 2 to 80 μm and a tap density of 1.7 g / cm ³ or more is prepared. An appropriate amount of Mg powder is added to this and mixed. The obtained mixed powder is filled into a container, an aluminum or aluminum alloy ingot is placed thereon, and aluminum or aluminum alloy is impregnated under pressure at a temperature of 700 to 1000 ° C. in a nitrogen atmosphere.

  A ceramic powder made of low thermal expansion ceramics or negative expansion ceramics is dispersed in a metal material in which aluminum or an aluminum alloy is melted to produce a mixed material. The mixed material is preferably prepared by dispersing ceramic powder that is 13 volume% or more and 36 volume% or less of the metal-ceramic composite material with respect to the metal material.

  As described above, a composite material that is an intermediate material obtained by cooling a mixed material in which a metal material is impregnated with no pressure is produced. The composite material is re-melted in a crucible at a predetermined temperature, and a predetermined amount of separately melted aluminum or aluminum alloy is added thereto, and the mixture is sufficiently stirred and diluted. Then, the diluted composite material is cooled to produce a metal / ceramic composite material for casting. If the metal-ceramic composite material diluted in this way is remelted, a molten metal having excellent fluidity can be obtained. This can be cast into a mold such as a sand mold, a plaster mold, or a mold to produce a disk-shaped cast product.

  The produced disk-shaped cast product is hot forged at an upsetting rate of 10 to 40% while maintaining the temperature at 100 to 450 ° C., and the relative density is set to 98% or more. In this way, a metal-ceramic composite material having a high tensile strength can be obtained.

  The hot forging of the metal-ceramic composite material is heated in a temperature range of 100 to 450 ° C., preferably 200 to 400 ° C. Thereby, an upsetting rate can be performed in 10 to 40% of range. If the heating temperature is less than 100 ° C., the deformability of the material is poor, and the upsetting rate cannot be increased.

  In addition, when the heating temperature is 200 ° C. or higher, the disk-shaped cast product is softened, the deformability is increased, and the forging pressure can be lowered when performing hot forging at a desired upsetting rate. On the other hand, when the heating temperature exceeds 450 ° C., the adhesion between the mold and the disc-shaped casting product is remarkably generated. Therefore, the upper limit needs to be stopped at 450 ° C., preferably 400 ° C. However, if the upsetting rate exceeds 40% even in the above temperature range, forging cracks are likely to occur.

  A heat treatment process is a process which consists of a solution treatment and an aging precipitation process. In the solution treatment, the precipitated phase in the aluminum alloy is heated to 460 to 490 ° C. and uniformly dissolved, and then rapidly cooled by water quenching to obtain a supersaturated solid solution. In the aging precipitation treatment, the precipitate phase (intermetallic compound) is precipitated and dispersed from the supersaturated solid solution by holding at 110 to 200 ° C. for 3 to 28 hours. If the solution treatment temperature is less than 460 ° C., all the precipitated components are not uniformly dissolved in the aluminum matrix. On the other hand, the effect does not change even when the temperature exceeds 490 ° C. Will occur.

  In addition, in the aging precipitation treatment, when the temperature is less than 110 ° C. or when the time is less than 3 hours, a sufficient precipitation compound cannot be obtained, and when the temperature exceeds 200 ° C. or the time is 28 hours. In the case of exceeding, the precipitated compound grows and coarsens, resulting in a decrease in strength. The temperature and time are appropriately combined with the required characteristics within the above range.

  By producing the metal-ceramic composite material by the above method, a base for a grinding wheel corresponding to high-speed rotation can be obtained.

  Hereinafter, examples of the present invention will be described together with comparative examples (Examples 1 to 8, Comparative Examples 1 to 3). FIG. 1 is a table showing production conditions and evaluation results of Examples and Comparative Examples.

(1) A commercially available silicon carbide powder as produced ceramic material cast composite material (mean particle size 17 .mu.m, a tap density of 1.8 g / cm ^3), aluminum nitride powder (average particle size 20 [mu] m, a tap density of 1.7 g / cm ³ ) And zirconium tungstate phosphate powder (average particle size 15 μm, tap density 2.2 g / cm ³ ), 1 wt% of Mg powder was added and mixed for 15 minutes with a V-type mixer. Each of the obtained mixed powders is filled into a 200 x 200 x 200 mm deep graphoyl container, and then an ingot of an aluminum alloy (AC3A, AC5C) 1.2 times the mixed powder is placed on the container and placed in an electric furnace. I set it. This was held in a N ² gas stream at a temperature of 800 ° C. for 12 hours to infiltrate the aluminum alloy under no pressure and then cooled to prepare a composite material for casting.

(2) Manufacture of disc type cast product A predetermined amount of the prepared composite material and the ingot of the aluminum alloy was put in a crucible so that the ceramic material in the composite material for casting had the filling rate shown in FIG. Then, they were melted at a temperature of 610 ° C. and stirred for 2 hours to prepare a molten metal. The molten metal was raised to 720 ° C. without cooling and further stirred, and poured into a sand mold at around 700 ° C. to produce a disk-shaped cast product of φ450 × 50 mm.

(3) Forging and heat treatment The produced disk mold casting was hot forged at the temperature and upsetting rate shown in FIG. Next, the solution was heated to 470 ° C. and rapidly cooled by water quenching, and then kept at 180 ° C. for 20 hours for aging precipitation treatment.

  In Comparative Example 1, since forging cracks occurred during hot forging, it was decided not to perform hot forging. Moreover, in Comparative Example 3, since the ceramic addition rate was high, the fluidity of the molten metal was not obtained, and a disk-type cast product could not be produced.

(4) Evaluation The bulk density, linear expansion coefficient, and tensile strength of the forged product thus obtained were measured. The result is shown in FIG. The bulk density was measured by the Archimedes method. The linear expansion coefficient in the temperature range of 20 to 200 ° C. was measured using a thermomechanical analyzer (Rigaku Thermo plus 2) under the condition where the temperature rising rate was 2 (° C./min) in the atmosphere. In addition, the tensile strength was measured according to JIS Z 2241 by cutting into a small dumbbell.

  Then, the forging is processed to an outer diameter of 450 mm and a thickness of 30 mm to produce a base metal, and an abrasive layer is bonded to the outer peripheral portion to form a grinding wheel, which is ground at a high speed of 120 m / sec. It was.

The result is shown in FIG. In Examples 1 to 8, no damage to the base metal and the abrasive layer was observed even when grinding was performed at high speed. On the other hand, in Comparative Example 1 where the specific strength is low, the base metal is damaged, and in Comparative Example 2 where the linear expansion coefficient of the base metal is high, the base metal expands from the abrasive layer due to temperature changes during grinding. Cracks occurred.

Claims (5)

A base for a grinding wheel that is formed in a disk shape and is used as a grinding wheel by adhering an abrasive layer to the surface,
Formed of a metal-ceramic composite material having a metal material made of aluminum or aluminum alloy and a ceramic material made of low thermal expansion ceramics or negative expansion ceramics,
A base metal for a grinding wheel having a linear expansion coefficient of 13 ppm / ° C. or more and 17 ppm / ° C. or less and a specific strength of 120 MPa or more.   2. The base for a grinding wheel according to claim 1, wherein the specific gravity is 3.0 or less.   The base for a grinding wheel according to claim 1 or 2, wherein the ceramic material is made of silicon carbide, aluminum nitride, or zirconium tungstate phosphate.   4. The metal-ceramic composite material is formed by dispersing the ceramic material in the metal material in an amount of 13% by volume to 36% by volume of the metal-ceramic composite material. Base metal for grinding wheels. A method for producing a base for a grinding wheel according to any one of claims 1 to 4,
A step of producing a mixed material by dispersing ceramic powder made of low thermal expansion ceramics or negative expansion ceramics in a metal material obtained by melting aluminum or an aluminum alloy;
Casting into a mold using the mixed material;
And a step of hot forging the member formed by the casting at an upsetting rate of 10% to 40% and performing a heat treatment.

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