JP2504525B2 - Grinding wheel for grinding aluminum materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is suitable for use in polishing an aluminum alloy disc for a magnetic disk, and has flatness, small displacement,
The present invention relates to a grindstone for grinding an aluminum material, which is capable of obtaining an aluminum material excellent in plate thickness accuracy, roughness and uniformity of polishing pattern.

[Prior Art] In the manufacturing process of a ground substrate that is an aluminum alloy magnetic disk substrate, conventionally, a urethane-based grindstone is processed into a ring shape, and an aluminum alloy disc is sandwiched from both sides by this pair of grindstones. The aluminum alloy disc is polished by digging and rotating the grindstone at high speed.

Therefore, recently, the demand for small diameter discs of 3.5 inches or 5 inches has increased, but along with this, the importance of productivity has come to a great extent and further improvement of quality has been demanded. It was

Therefore, as shown in FIG. 6, a double side lapping type polishing apparatus has come to be used. In this polishing apparatus, the upper surface plate 4 and the lower surface plate 7 are fixed to the vertical shafts 5 and 8 at the centers thereof, and the upper grindstone 3 and the lower surface plate 7 are provided on the facing surfaces of the upper surface plate 4 and the lower surface plate 7, respectively. The grindstone 6 is attached.
Then, while holding several tens of aluminum alloy discs 1 for discs on one plane by the holding plate 2, these are arranged between the upper grindstone 3 and the lower grindstone 6, and the upper grindstone 3 and the lower grindstone. The disc 1 is inserted between 6 and. Then the rotary shaft 5,8
Is rotated to rotate the grindstones 3 and 6, and both surfaces of the plurality of disks 1 are simultaneously polished.

By the way, in this method, since the grindstones 3 and 6 are rotated at a low speed to grind the disk 1, it is not possible to use a urethane grindstone that is easily embrittled, and a PVA (polyvinyl alcohol) grindstone is mainly used. There is.

[Problems to be Solved by the Invention] However, even if the conditions of the polishing machine such as the shape of the grinding stone, the type and amount of the polishing liquid, and the polishing pressure are constant, the PVA-based grinding stone has a large variation in polishing quality and is stable. It is difficult to mass produce discs of the desired quality.

In other words, the characteristics of PVA-based grindstones include the type of abrasive grains (usually SiC, which has a good compatibility with the binder), the grain size of the stone, the composition of the stone (abrasive grain ratio, binder ratio, porosity), hardness , And the degree of swelling, etc., but the effect of each of these characteristics on the polishing quality of the aluminum-magnesium (Al-Mg) alloy, which is the material of the disk 1, has not yet been clarified, and it depends on the manufacturing lot of the grindstone. The problem is that the quality of the discs varies greatly. Therefore, high quality discs cannot be stably mass-produced.

The present invention has been made in view of such problems, and provides a grindstone for grinding aluminum material, which can stably obtain excellent polishing characteristics, reduce the number of dressing of the grindstone, and improve the polishing efficiency. The purpose is to do.

[Means for Solving the Problems] The grinding wheel for grinding aluminum material according to the present invention is a PVA having an abrasive grain ratio of 6 to 12% by volume, a binder rate of 12 to 18% by volume, and a porosity of 70 to 82% by volume. A plurality of system grindstones are attached to the surface plate, the grindstone has a Rockwell hardness of -180 to -250, a swelling degree of 0.8 to 2.0%, and a bulk specific gravity of 0.465 to 0.485. The difference in the Rockwell hardness between the whetstone with the maximum value and the whetstone with the minimum Rockwell hardness value is 60 or less, and the whetstone with the maximum bulk specific gravity value is the minimum value, and the bulk specific gravity value is the minimum value. The difference in bulk specific gravity from the grindstone is 0.03 or less.

[Operation] The present inventors are generally used as a final finish.
As a result of experimental research on the correspondence between the characteristic values of PVA-based grindstones of 2000 or more and the surface quality of the disk obtained by polishing, the abrasive grain ratio, the binder ratio, the porosity, the hardness, the hardness within one polished surface It has been found that the aluminum alloy, which is a constituent material of the disk, can be stably and high quality polished when the dispersion of the disc, the swelling degree, the bulk specific gravity, and the variation of the bulk specific gravity within one set are within the above numerical ranges, respectively. It was
That is, by using a PVA-based grindstone in the above numerical range, it is possible to stably manufacture an aluminum alloy plate having excellent polishing quality such as flatness, minute displacement, plate thickness accuracy, roughness and uniformity of polishing pattern. In addition, the number of times of dressing the grindstone is reduced to improve the productivity, and the yield in the disc inspection process can be increased.

[Examples] Hereinafter, the present invention will be described more specifically.

First, the relationship between each characteristic of the PVA type grindstone and the polishing quality will be described.

Whetstone composition PVA-based whetstone has abrasive grains 11 and binder 1 as shown in FIG.
2 and pores 13, the ratio of which affects the polishing rate and the polishing quality.

In this case, in the double-sided lapping method, the fallen abrasive grains and grinding debris are temporarily held in the pores 13, so that the effect of porosity on the polishing rate and the polishing quality is extremely large.
Therefore, it is necessary that the porosity is high to some extent, and it is necessary to secure the porosity of at least 70% by volume or more.

However, even if the number of pores 13 is too large and the abrasive grain ratio and the binder ratio are too low, the polishing rate becomes slow and the flatness also deteriorates. In order to obtain the desired polishing rate and flatness, the abrasive grain ratio is 6% by volume or more and the binder ratio is 12% by volume or more. Therefore, the porosity is 82% by volume or less. Further, since the porosity is 70% by volume or more, the total rate of the abrasive grains and the binder is 30% by volume or less. Then, the abrasive grains 11 and the binder 12
Should be compounded as follows: abrasive grain: binder = 1: 1.5 to 2.0, so the abrasive grain ratio and the binder ratio are 12% by volume or less and 18% respectively.
It will be less than the capacity%.

It should be noted that as the grain size of the grindstone becomes finer, that is, as the count becomes higher, it tends to be preferable from the viewpoint of polishing rate and polishing quality to lower the binder ratio and increase the porosity.

Hardness Hardness changes with the composition of the grindstone. If the hardness is high and hard, the aluminum alloy disc to be polished is likely to be flawed by the abrasive grains. Conversely, if the hardness is low and the hardness is soft, the polishing rate is slow and the polishing pattern is not easily aligned. For this reason, the most suitable hardness range is Rockwell hardness (superficial
15Y) is -180 to -250.

FIG. 1 is a graph showing the relationship between the hardness of the abscissa and the life of the grindstone on the ordinate.

However, the life of the grindstone is the number of times of polishing from the start of use until the grinding becomes impossible when the thickness of the grindstone is reduced by polishing and dressing. In this case, one polishing allowance is always constant. Further, dressing was performed when it took more than a predetermined time to obtain a predetermined polishing allowance due to a cause such as clogging, or when a defect in surface quality such as scratches due to abrasive grains or uneven polishing pattern occurred. .

As is apparent from FIG. 1, when the hardness is −180 or more as in the present invention, the life of the grindstone becomes 1000 times or more even if the variation is taken into consideration.

Also, in the double-sided lapping method, a large number of grindstones are attached to a surface plate having a diameter of up to about 1 m, but in this case, if the hardness of each grindstone is large, the polishing surface becomes a coddle pattern, and minute displacement occurs. appear. Therefore, the variation in hardness within one polishing surface is set to 60 or less.

FIG. 2 is a graph showing the relationship between the hardness on the horizontal axis and the life of the grindstone on the vertical axis. As is clear from this figure, when the hardness variation is 60 or less, the life of the grindstone is 1000 times or more.

Swelling degree Polyvinyl alcohol, which is a component of the PVA-based grindstone binder, has the property of swelling. Usually, this swelling property is suppressed by adding a melamine resin. When the degree of swelling is large, the flatness of the grindstone changes due to a slight change in the amount of water in the grindstone, which in turn changes the flatness of the disk. On the contrary, if the proportion of melamine is increased in order to suppress the degree of swelling, other properties are deteriorated, and therefore, appropriate swelling property is required. For this reason, the degree of swelling is 0.8 to 2.0%.

Bulk Specific Gravity The above-mentioned characteristics are not independent of each other but have a correlation function with each other, and also change depending on heat treatment conditions in the grindstone manufacturing process. Then, the inventors of the present application found that the difference in these characteristics finally appears in the change in the bulk specific gravity of the grindstone. This bulk specific gravity is 0.465 in order to achieve the object of the present invention in consideration of the results of various experimental studies and operational results.
It is necessary to set to 0.485.

FIG. 3 is a graph showing the relationship between the two by taking the bulk specific gravity on the horizontal axis and the grindstone life on the vertical axis. As is clear from FIG. 3, when the bulk specific gravity is 0.465 to 0.485, the life of the grindstone is approximately 1000 times or more.

Further, dozens of grindstones are usually attached to a lapping plate and used, but it is necessary that the variation of the bulk specific gravity in this one plate is 0.03 or less. FIG. 4 is a graph showing the relationship between the two, where the horizontal axis represents the variation of the bulk specific gravity and the vertical axis represents the life of the grindstone. As is clear from FIG. 4,
When the variation in bulk specific gravity is 0.03 or less, the grindstone life is approximately 1000 times or more.

[Effect of the Invention] According to the present invention, an aluminum material having excellent surface quality can be stably obtained by the PVA-based grindstone, and the number of dressing times of the grindstone can be reduced by improving the polishing performance. Therefore, the productivity is improved and the yield in the disc inspection can be remarkably increased.

[Brief description of drawings]

1 to 4 are graphs showing the relationship between various grinding wheel characteristics and grinding wheel life. FIG. 1 shows the relationship with hardness, FIG. 2 shows the relationship with in-plane hardness variation, and FIG. 3 shows Fig. 4 is a graph showing the relationship with bulk specific gravity, Fig. 4 is a graph showing the relationship with variation in bulk specific gravity within one set, Fig. 5 is a sectional view showing the structure of a PVA-based grindstone, and Fig. 6 is a sectional view showing a double-side polishing machine. Is. 1; disk, 3; upper grindstone, 4; upper grindstone, 6; lower grindstone, 7; lower grindstone, 11; abrasive grains, 12; binder, 13; pores

Claims (1)

(57) [Claims] 1. A plurality of PVA-based grindstones having an abrasive grain ratio of 6 to 12% by volume, a binder ratio of 12 to 18% by volume, and a porosity of 70 to 82% by volume are mounted on a surface plate, the stones having Rockwell hardness. Is -180 to -250, swelling degree is 0.8 to 2.0%, and bulk specific gravity is 0.
465 to 0.485, among the plurality of whetstones, a stone having a maximum Rockwell hardness value, and a stone having a minimum Rockwell hardness value having a Rockwell hardness difference of 60 or less, a value of bulk specific gravity The difference in bulk specific gravity between the whetstone with maximum value and the whetstone with minimum numerical value is 0.
A grindstone for grinding aluminum materials, characterized by being 03 or less.