JP2003053668A - Vitrified bond grinding wheel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grinding wheel capable of obtaining stable and satisfactory cutting ability and a machined face without causing loading and dulling of the grinding wheel in super-finish machining. SOLUTION: An abrasive material layer 10 is composed of collected abrasive grains 1, a binder 2, and large air holes 3. The collected abrasive grain 1 is composed of single abrasive grains 11, a binder 12, and small air holes 13, and several hundreds of cBN abrasive grains are bound by vitrified binder to constitute the collected abrasive grain 1. Since air holes in the abrasive material layer 10 are composed of the large air holes 3 among the collected abrasive grains 1 and the small air holes 13 in the collected abrasive grains 1, the large air holes 3 increase the grinding property, the small air holes 13 increase the finish machining property, the discharge property of chips is improved, and loading does not occur easily to provide the grinding wheel provided with high grinding property.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vitrified bond grindstone used for superfinish grinding of inner and outer circumferential surfaces, end surfaces, bearing raceway surfaces, conical surfaces and the like.

[0002]

2. Description of the Related Art As a grindstone used for superfinish grinding of inner and outer circumferential surfaces, end surfaces, bearing raceway surfaces, conical surfaces, etc., an aerated type vitrified bond grindstone is used. Porous type vitrified bond grindstone is a grindstone in which pores are dispersed in an abrasive material layer in which abrasive grains are bonded with a vitrified bond, and formation of pores is usually performed during firing of a pore forming agent added to the bond. There are used a method of forming pores by eliminating them, and a method of adding a hollow body to a binder to make the hollow portions pores. These pores act as chip pockets during grinding.

In general, a vitrified bond grindstone has a low coefficient of thermal expansion and a high Young's modulus in comparison with other metal bond grindstones and resin bond grindstones, and has a higher holding power for abrasive grains than a resin bond grindstone, which makes truing and dressing easy. It has the advantage that it can be processed with high precision. However, on the other hand, the pores that should function as the chip pocket cannot always be obtained in a sufficient amount, the discharge of chips is insufficient, and there is room for improvement in improving the machinability.
Particularly in superfinishing, since the abrasive layer is used in surface contact with the workpiece, clogging and crushing are likely to occur.

With respect to such a problem, Japanese Patent Laid-Open No. 8-57
No. 768, an abrasive grain 25 having an average grain size of 40 to 160 μm.
˜45% by volume of pores in the matrix formed by binding with a vitrified binder, the volume ratio of pores / abrasive grain amount = 0.4 to 1.2
Is a vitrified bond grindstone dispersed at a ratio of, wherein the pores are small pores with an average pore diameter of 8 to 130 μm.
m pores, large pores with an average pore diameter of over 130 to 1300
A vitrified bond grindstone has been proposed which has a structure in which pores of μm are dispersed at a ratio of large pore diameter / small pore diameter = 0.2 to 0.5 in terms of volume ratio.

The small-diameter pores in this grindstone have the effect of relaxing the thermal stress applied to the abrasive grains and bond bridges during grinding and improving the cooling efficiency, and the large-diameter pores reduce the grinding resistance and further reduce the cutting chips. It is said to have a function of preventing clogging.

Further, as a measure for further increasing the abrasive grain holding force, Japanese Patent Laid-Open No. 7-108463 discloses an abrasive grain used in a vitrified bond grindstone in which a plurality of fine abrasive grains are agglomerated with a vitrified binder. A vitrified bond grindstone composed of is proposed. It is said that the average particle size of the aggregated abrasive grains is preferably 1 to 20 μm, and the ratio of fine abrasive grains to the aggregated abrasive grains is preferably 40 to 90%.

According to this grindstone, it is said that the abrasive grains are unlikely to fall off, and the action of the collective abrasive grains shows a high grinding ratio with a low grinding resistance from the initial stage of grinding, and exhibits excellent grinding performance for a long period of time. ing.

[0008]

By the way, in the vitrified bond grindstone described in JP-A-8-57768, the average particle size of the pore-forming agent is 140 to 950.
Large pores are formed by adding 5 to 15 parts by volume of NaCl having a diameter of μm, but the small pores are merely voids between particles and are not formed intentionally. In such a method of forming pores, since the large pores and the small pores are mixed in the binder, the holding force of the abrasive grains by the binder is insufficient, and the abrasive grains fall off and bond. There is a problem that sharpness reduction and abnormal wear easily occur due to surface contact.

Further, in the vitrified bond grindstone disclosed in JP-A-7-108463, the aggregated abrasive grains are a plurality of fine abrasive grains agglomerated with a vitrified bond,
Since no pores are formed inside the aggregated abrasive grains, it is difficult for a single abrasive grain in the aggregated abrasive grains to become a cutting edge in microfabrication in the surface contact state such as superfinishing, and clogging or crushing occurs during cutting. ， Image sticking is likely to occur.

The problem to be solved by the present invention is to stably obtain a good sharpness and a machined surface without causing clogging or crushing of a grindstone in superfinishing.

[0011]

According to the present invention, pores in an abrasive material layer of a vitrified bond grindstone using aggregated abrasive grains composed of a plurality of abrasive grains are formed as air holes formed between aggregated abrasive grains. And the small pores formed in the aggregated abrasive grains, and the total volume of the volume of the air holes and the volume of the small pores is 20 to 60% of the total volume of the abrasive layer. It is a whetstone.

In the grindstone of the present invention, in addition to the improvement of the grinding performance by the action of the aggregated abrasive grains, the air holes formed between the aggregated abrasive grains discharge chips generated by the aggregated abrasive grains. It acts as a pocket to improve the machinability, and the small pores formed in the aggregated abrasive grains act as a chip pocket for discharging the cutting dust generated by a single abrasive grain to enhance the finish workability. In addition, the total porosity of air holes and small pores is 20
By setting the content to -60%, the discharge property of chips is improved, clogging is prevented, and machinability is improved. When the total porosity is less than 20%, the irregularities on the surface of the abrasive grains are less likely to cause clogging or crushing, and when the total porosity is more than 60%, the strength of the abrasive grain body is insufficient and the grindstone is easily broken.

Here, it is desirable that the volume ratio of the aggregated abrasive grains to the air holes in the abrasive layer be 1: 1 to 8: 1. The volume ratio of the aggregated abrasive grains to the air holes is a factor that affects the unevenness of the grindstone surface, the contact area with the work piece, and the holding force of the aggregated abrasive particles. If it is small, the effect of improving the machinability cannot be expected, and if it exceeds the volume of the aggregated abrasive grains, the number of abrasive grains acting on the cutting is remarkably reduced, and the strength of the main body of the grindstone is lowered, which is not preferable.

It is desirable that the volume ratio of the small pores in the aggregated abrasive grains be 5 to 50%. This volume ratio is a factor that influences the size of the chip pocket on the surface of the aggregated abrasive grains that discharges chips from a single abrasive grain. If the volume ratio is less than 5%, the improvement effect of finishing workability cannot be expected,
If it exceeds 50%, the strength of the aggregated abrasive grains is lowered and the abrasive grains are likely to fall off, which is not preferable.

The size of the aggregated abrasive grains is 5 to 10 times the average grain size of the single abrasive grains, and the size of the air holes is 1/3 to 2 times the average grain size of the aggregated abrasive grains. The size of the small pores is preferably 1/3 to 2 times the average particle size of the single abrasive grain. If the size of the collective abrasive is less than 5 times the average particle size of the single abrasive, sufficient holding force for the single abrasive cannot be obtained, and if it exceeds 10 times the effect of forming the collective abrasive Will fade. If the size of the air holes is smaller than 1/3 of the average particle size of the aggregated abrasive grains, the effect of the chip pocket for discharging the chips generated by a single abrasive grain cannot be expected, and if the size exceeds 2 times, it becomes The force that holds the abrasive grains is reduced, making it easier to shed. Further, if the size of the small pores is smaller than 1/3 of the average particle size of the single abrasive grain, the effect of the chip pocket for discharging the chips generated by the single abrasive grain cannot be expected, and it exceeds 2 times. When it becomes larger, the force for holding a single abrasive grain decreases and it becomes easier to shed.

The vitrified bond grindstone according to the present invention is formed by assembling a plurality of abrasive grains such as diamond abrasive grains and cBN abrasive grains with a vitrified bond to form aggregate abrasive grains.
This aggregated abrasive grain can be manufactured by bonding with a vitrified bonding material. The size of the aggregated abrasive grains can be adjusted by adjusting the nozzle diameter, pressure, temperature, and crushing time of the fired granulated powder by the granulator, and the size and volume ratio of the small pores in the aggregated abrasive grains can be adjusted. Is the particle size of the binder,
It can be adjusted by adjusting the amount, the amount of the binder, and the type. Further, the volume ratio of the aggregated abrasive grains to the air holes in the abrasive layer can be adjusted by adjusting the addition amounts of the binder and the pore-forming agent.

[0017]

1 is a schematic view showing the structure of an abrasive layer of a vitrified bond grindstone according to an embodiment of the present invention. The abrasive layer 10 is composed of aggregated abrasive grains 1, a binder 2, and air holes 3. The collective abrasive grain 1 is composed of a single abrasive grain 11, a binder 12 and small pores 13. The single abrasive grain is a cBN abrasive grain having a grain size of # 3000 (average particle diameter of 4 to 6 μm), and hundreds of cBN abrasive grains are formed into B ₂ O ₃ —Al ₂ O ₃ —Si.
Combined with a 0 ₂ type vitrified binder to form an aggregate grain 1
I am trying. Abrasive grain concentration of the entire abrasive layer 10 is 10
It is 0.

The particle size of the collective abrasive grain 1 is about 50 μm (about 10 times the average particle size of the cBN abrasive grain), and the size of the small pores 13 in the collective abrasive grain 1 is the average particle size of the cBN abrasive grain. The volume ratio of the small pores 13 in the aggregated abrasive grains 1 is about 10 times, and is 10%. Air holes 3 in the abrasive layer 10
Is 1/2 times the average particle size of the aggregated abrasive grains 1, and the volume ratio of the aggregated abrasive grains 1 to the air holes 3 is 2: 1.

The air holes 3 in the abrasive layer 10 are formed by burning away the pore forming agent, and the aggregate abrasive grains 1 are formed.
The small pores 13 in the inside are formed by eliminating the binder by firing. As described above, the pores in the abrasive layer 10 are composed of the air holes 3 formed between the aggregated abrasive grains 1 and the small air holes 13 formed in the aggregated abrasive grains 1, whereby the air holes 3 are formed. By improving the machinability, the small pores 13 improve the finish workability, and further, the total volume of the air holes 3 and the small pores 13 is 40% of the volume of the entire abrasive layer 10. Further, the grindstone has a good chip discharge property, is less likely to be clogged, and has high machinability.

[Test Example] The total volume ratio of the square grindstone having the abrasive layer of the above-mentioned embodiment and the air holes and the small pores is 10%.
Other than that, a square grindstone with the same specifications as the invention product (comparative product)
Then, a square grindstone (conventional product) in which an abrasive grain layer having a porosity of 30% was formed with a concentration degree of 100 without using the cBN abrasive grains of the above-described embodiment as a collective abrasive grain was manufactured and a finishing test was conducted.
The test results are shown in Table 1. Test conditions Processing machine: Cylindrical outer surface finishing machine Grinding wheel specifications: Length 10 mm, width 3 mm Ratio Workpiece: Bearing steel SUJ-2 Workpiece rotation speed: 400 min ^-1

[0021]

[Table 1] Note) Sharpness and durability are expressed as an index with the conventional product as 100.

As can be seen from Table 1, the invention product has improved sharpness by 30%, durability improved by 10%, and finished surface roughness improved as compared with the conventional product. The comparative product, in which the total volume ratio of the air holes and the small pores is outside the range of the present invention, is inferior to the invention product in terms of sharpness.

[0023]

EFFECTS OF THE INVENTION The pores in the abrasive layer of a vitrified bond grindstone using aggregated abrasive grains composed of a plurality of single abrasive grains are formed in the aggregated abrasive grains and the air holes formed between the aggregated abrasive grains. By configuring with the small pores formed, the air holes enhance the machinability, the small pores enhance the finishing workability, and further, the total porosity of the air holes and the small pores is 20 to 60%. Improves the cutting performance by improving the chip discharge performance and preventing clogging.

By setting the volume ratio of the aggregated abrasive grains to the air holes in the abrasive layer within an appropriate range, the effect of improving the machinability can be further enhanced, and the volume occupied by the small pores in the aggregated abrasive grains can be enhanced. By setting the ratio within an appropriate range, the effect of improving finish workability can be further enhanced.

By setting the sizes of the aggregated abrasive grains and the single abrasive grains, and the sizes of the air holes and the small pores within the proper ranges, the effect of forming the chip pocket and holding the abrasive grains can be further enhanced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an abrasive layer of a vitrified bond grindstone according to an embodiment of the present invention.

[Explanation of symbols]

1 aggregated grain 2 binder 3 atmosphere holes 10 Abrasive layer 11 Single abrasive grain 12 Binder 13 small pores

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tetsuya Nonoshita             210 Takeno, Odaiba, Ukiha-gun, Fukuoka             Noritake Diamond Co., Ltd. F-term (reference) 3C063 AA02 BA22 BB02 BB08 BC05                       CC01 FF20 FF23

Claims (4)

[Claims] 1. A porosity in an abrasive material layer of a vitrified bond grindstone using a collective abrasive composed of a plurality of single abrasives is formed in an atmosphere hole formed between the collective abrasives and in the collective abrasive. And the small pores formed, and the total volume of the atmosphere pores and the small pores is 20 to the total volume of the abrasive layer.
A vitrified bond grindstone with a ratio of 60%. 2. The vitrified bond grindstone according to claim 1, wherein the volume ratio of the aggregated abrasive grains to the air holes in the abrasive layer is 1: 1 to 8: 1. 3. The vitrified bond grindstone according to claim 1, wherein the volume ratio of the small pores in the aggregated abrasive grains is 5 to 50%. 4. The size of the aggregated abrasive grains is 5 to 10 times the average grain size of the single abrasive grains, and the size of the air holes is 1/3 to 2 of the average grain size of the aggregated abrasive grains. The vitrified bond grindstone according to any one of claims 1 to 3, wherein the size of the small pores is 1/3 to 2 times the average particle size of the single abrasive grain.