JPS6257873A - Super abrasive grain grindstone for specular finishing - Google Patents

Abstract

PURPOSE:To enable to provide cutting performance properly without any finished face roughness, or losing finished face characteristics such as brightness etc. by mixing cubic system boron nitride grains or diamond grains in chrome oxide at the specific rate. CONSTITUTION:Cubic system boron nitride grains or diamond grains of average grain diameter of 2mm or less are mixed in chrome oxide at the rate 2-75% of grain volume in a grindstone and bound together by vitrified binding agent to obtain a super abrasive grain grindstone for specular finishing. By mixing abrasive grains at the rate of the above, proper cutting ability can be given to the grindstone. This time, it is desirable that the binding degree of the grindstone is within the range of -20-50 in RH hardness by H Scale of Rockwell Hardness Meter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a superabrasive grindstone for mirror finishing.

[Conventional technology]

Conventionally, in super-finishing of ball bearing raceway surfaces, different types of grindstones are used to rough-finish and then mirror-finish the bearings in order to extend the life of the bearings during long-term operation. In such a case, in order to satisfy the sound quality level of the bearing at the same time, it is not necessary to achieve a mirror finish by mere rubbing, which takes a long time in the mirror finishing process, but to finish the mirror finish in a short time of 10 seconds or less. In order to satisfy the diameter machining requirement of about 3 μm, it is necessary to achieve a glossy and beautiful mirror finish.

When blending conventional white fused alumina (hereinafter referred to as ^rA) or green silicon carbide (hereinafter referred to as GC) abrasive grains with chromium oxide (Cr203), the blending If the amount is too high, there are problems such as not being able to obtain a uniformly glossy surface even if the machinability is improved, or scratch marks caused by the crushability of the abrasive grains.On the other hand, if the content is decreased, the machinability decreases. It takes a long time to obtain a uniform mirror finish, which adversely affects not only processing accuracy but also sound quality.

[Problem that the invention seeks to solve]

In this way, in the conventional technology, chromium oxide grindstones are mainly used for mirror-finishing, and they are capable of achieving a glossy finish while also achieving adequate cutting ability (for example, cutting a few micrometers in diameter in a short period of time).
[Means for Solving the Problem] In order to solve the above problem, this invention uses cubic boron nitride (hereinafter referred to as CBS) to chromium oxide. abrasive grains or diamond abrasive grains in the abrasive grain volume ratio of 2 to 15 in the whetstone.
% and bonded with a vitrified bonding agent to form a superabrasive grindstone for mirror finishing.

The details will be described below.

First, chromium oxide in this invention is a main component of the grinding wheel, and in order to achieve a mirror effect, the average particle size is 1.
0 to 1.2 μm and a small volume percentage in the whetstone (preferably around 20% in both cases. Especially when the whetstone is for polishing non-metallic materials such as ceramics, glass, and various crystals, in addition to chromium oxide) Ultrafine powders such as iron oxide, alumina, and silica, and fine powders such as titanium oxide, zinc oxide, manganese oxide, nickel oxide, zirconium oxide, and ferric oxide may be appropriately selected and used together.

Next, the CBN abrasive grains or diamond abrasive grains that are mixed with such chromium oxide are harder and stronger than conventional WA or GC abrasive grains, and are not suitable for super finishing machining using constant pressure cutting. Because the abrasive grains have excellent penetrability and are difficult to break, they are generally used for finishing (one side is rough, gold, 100% surface finishing), and mirror finishing is not recommended for scratches, etc. It has been considered that the average particle size is 2 μm JJ, for example, O-1/2.0-1.
．． If an appropriate amount of abrasive grains such as 0-2 or 1-2 are mixed, machinability can be achieved.1. You can make a grindstone for mirror finishing.

If the ratio of abrasive grains with such a particle size is less than 12% by volume of the whetstone, the cutting performance of the chopsticks will not be improved.
On the other hand, if the amount exceeds 15%, the machinability becomes too strong and it becomes difficult to achieve a mirror finish. As a binder for grinding wheels, vitriphyte oxide is most suitable as it has rigidity and can be made porous.For example, lithium fluoride (4, Vitrified bond containing 0 to 8.0 mol%) is suitable, but it can be mixed with the above-mentioned various abrasive grains 2 and molded into the desired molded body by a general-purpose molding method such as cast molding or dry powder compression molding. Bye. At this time, various conventionally widely used tissue conditioning agents or artificial pore agents may be used in combination as appropriate.

The degree of bonding of the superabrasive grinding wheel for mirror finishing according to this invention is -20 on the ■ hardness scale of the Rockwell hardness tester.
Preferably, it is within 1 ton of 50 to 50.

This is because when the hardness of the whetstone is too high, the pre-processed surface is super-finished and smooth enough, so the whetstone is difficult to get acquainted with, and furthermore, the cutting performance is reduced, and it takes a long time to achieve a uniform mirror finish. It is.

In addition, the negative (minus) value of RH hardness is 178L for pressure).
When a J steel ball is used, the test load is 60 kg, and the numerical value indicated on the dial 13 (in red) is used, the long hand passes the set point of 30, passes the 0 point, and stops.

〔Example〕

Chromium oxide (commercially available) with an average particle size of 1.0 to 1.2 μm,
CBN abrasive grains (201 manufactured by General Electric Co., USA) with an average particle size of O ~ 211 m, +800 with an average particle size of 1 μm
0WA abrasive grains (Fujimi Abrasive Industry Co., Ltd. 4FJ) and vitrified bond composition (manufactured in-house: mol% of each component: S10272.8%, Al2031.4.5%, Mg
O2, 8%, Ca0O, 9%, Na2O2, 2%, K2
O2, 3%, Fe2030.2%, Fe00.1%, L
iF4.2%) as fFFF, chromium oxide and CBN
Or, the vitrified bond composition should be applied in 15 parts based on the total weight of each WA abrasive grain of 100 parts, and the volume ratio of chromium oxide and CBN or WA abrasive grains after firing should be 27% and 10%, respectively. %. After mixing each raw material, it is molded into a lump by the pouring method, and after drying, it is heated in an electric furnace in a nitrogen atmosphere for a maximum of 12 min.
The temperature was maintained at 00° C. for 1 hour, and firing was performed for a required time of 38 hours. A test whetstone was cut from the resulting fired product. In addition, during casting, organic particles were added in a ratio of 1 to the structure conditioner so that the λH hardness of the molded product after firing was around 110 and the degree of bonding to the grindstone was around 30.

The performance test of the obtained test grindstone was performed using the following method. In other words, the material is bearing steel (SUJ2, hardness II RC58).
A cylindrical workpiece (outer diameter 41 mm, width 13 mm) rotates at 157 per minute at a speed of 157 times per minute.
mm) to give the grindstone 1800 vibrations per minute and a vibration of 2 mm on both sides, while pneumatic pressure is applied to the grindstone surface at a constant pressure of 15 kg/cm to perform a plunge cut. 5 parts sulfurized fatty oil and 9 parts mineral oil
A mixed oil of 5 parts was used. In addition, the pre-processing roughness is
A workpiece that has been superfinished using a #3000 vitrified grinding wheel and has a center line average roughness of approximately 0.05 μm La (tested with stiffness). The cutting direction angle (maximum inclination angle) of the sine wave is 30.In order to make the surface of the test grinding wheel uniform in contact with the workpiece, diamond abrasive grains ( Dressing molding was carried out using a jig in which 2 micron grade 4O-60 (manufactured by General Electric Co., USA) was applied.

The blending ratio of the test whetstones is summarized in Table 1, and the test results are summarized in Table 2.

Table 1 Table 1 ↓ Among the four types of whetstones (Examples) to 4 shown below,
Examples 1 and 2 in which the abrasive grain volume ratio was approximately 10% and the λH hardness was around -10, and the R H hardness was 30 ff.
Among the grindstones of Examples 3 and 4 which were prepared after 1iT, Examples 1 and 3 contained WA abrasive grains, and Examples 2 and 4 contained CBN abrasive grains. And when pressing the whetstone, the pressure is 1
When the machining time is extended while keeping it constant at 5 kg/ccn, in Examples 1 and 3 containing WA abrasive grains, there is almost no increase in the cutting amount even if the machining time exceeds 10 seconds. In Examples 2 and 4 in which CBS abrasive grains were blended, the machinability was not lost even after long machining (Table 2 shows that the deformation increased). Regarding the amount of cutting, the grindstones containing WA abrasive grains (Examples 1 and 3) have a low cutting ability of less than 2 μm, while the grindstones containing CBN abrasive grains (Examples 2 and 4) have a low cutting ability of 2 μm (examples 1 and 3). The diameter of the grindstone is 3 μm, which is preferable as a grindstone for mirror finishing.The amount of wear of each grindstone was so small that it could not be measured.

Regarding the finished surface roughness, Example 1 has a machining time of 1
In 5 seconds or more, the residual grains from the previous processing were removed and a uniform mirror finish was obtained, but in Example 3, residual grains were observed throughout the machining time, and an uneven finish was observed, with scratch marks partially observed.

On the other hand, in Examples 2 and 4, no residual roughness was observed after the machining time of 5 seconds, and the surface roughness was 0.025.
It was in a mirror state with an Ra of μmRa or less, which was satisfactory.

〔effect〕

As is clear from the above, the superabrasive grinding wheel of the present invention is a chromium oxide grinding wheel intended for mirror finishing, but it can achieve finishes such as roughness and gloss without impairing surface retention. Since it can exhibit appropriate cutting performance, it can be said that the significance of this invention is extremely large.

Claims (1)

[Claims] A super-abrasive grinding wheel for mirror finishing, characterized in that cubic boron nitride abrasive grains or diamond abrasive grains are blended with chromium oxide in an amount of 2 to 15% by volume of the abrasive grains in the whetstone, and the mixture is bonded with a vitrified bonding agent.