Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-09-26
2002-01-29
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S051000, C451S056000, C451S061000, C451S443000, C451S210000
Reexamination Certificate
active
06341999
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a chamfering method and apparatus for processing the edges of a glass substrate for a hard disk.
2. Prior Art
A hard disk is a storage device of a computer; the surface of a thin doughnut-like circular disk is coated with a magnetic substance in which data are stored. Aluminum has been used conventionally as the material of this circular disk (hereafter referred to as “hard disk substrate”). However, recently, chemically reinforced glass or crystalline glass have been used as the substrate of a hard disk (referred to as “glass substrate”).
FIGS. 1A and 1B
schematically show a glass substrate;
FIG. 1A
is a general view, and
FIG. 1B
shows a sectional view of the outer and inner peripheries. For a glass substrate with a nominal size of 2.5 inches, for example, outer and inner diameters are 2.5 and 1 inches (about 63 mm and about 25 mm), respectively, and the thickness is about 1.6 mm. The outer and inner peripheries (also referred to as “edge portions”) are composed of end surfaces (with a width of 0.6 mm) at outer and inner peripheries, and a pair of oblique surfaces sandwiching the peripheries (with an angle of about 45°).
The aforementioned glass substrate is subjected to high-speed revolutions of several tens thousand revolution per minutes to shorten the access time of the hard disk. Consequently, the entire body thereof must be processed precisely, and a high dynamic balance must be achieved. Both surfaces of the glass substrate are finished to a mirror surface of an Rz of 1 &mgr;m or less, so that a magnetic substance can be coated at a high density to maximize memory capacity.
In addition, edges (including end surfaces and oblique surfaces) should be finished to mirror surface quality with such high accuracy and quality as required by both surfaces of the glass substrate. The reason edge portions are finished to mirror surface quality is explained below.
(1) There are microscopic cracks on a rough pear-like surface. As a result, a glass reinforcing treatment may result in unevenness, or cracks may grow due to high-speed revolutions during operation, eventually causing breakage of the substrate.
(2) Contaminants may remain in microscopic recesses of a crack, so cleaning may be incomplete, and it may be a source of contamination in a subsequent process.
Edge portions of the above-mentioned glass substrate were, in the prior art, finished to mirror surface quality first by using a formed plated grindstone,which is highly precise, and then by buffing to mirror surface quality.
However, compared to an aluminum substrate, a glass substrate provides poor machinability, so one problem was that machining efficiency, when using a plated grindstone, was low. More explicitly, although rather coarse grinding particles of #500 (grain diameter of about 30 &mgr;m) to #600 (grain diameter of about 25 &mgr;m) are used, grinding particles still peel considerably; therefore, the plated grindstone must be replaced frequently, so the continuous processing period with the machine is short and operating ratio is low because the grindstone must be replaced. In addition, since the processed surface is in a pear-like state with a rough surface, buff-polishing must be carried out for a long time (about one hour) as a subsequent process to the machining with the plated grindstone. Consequently, overall productivity is low, which is a practical problem.
SUMMARY OF THE INVENTION
The present invention aims to solve these problems. That is, an object of the present invention is to provide a chamfering method and apparatus for the glass substrate of a hard disk, with which edge portions of the substrate can be processed with high accuracy, quality, and efficiency, thereby greatly reducing the need for a subsequent process, such as buff-polishing, or even eliminating it. The present invention provides, as a method of processing end surfaces of outer and inner peripheries of a doughnut-like glass substrate (
1
) with a circular hole (
1
a
) at the center thereof and chamfering oblique surfaces sandwiching the end surfaces, a glass substrate chamfering method using a metal-bonded outer-surface grindstone (
12
) for simultaneously processing the end surface and oblique surfaces of the outer periphery, and a metal-bonded inner-surface grindstone (
14
) for simultaneously processing the end surface and oblique surfaces of the inner periphery, wherein by means of the outer-surface grindstone and the inner-surface grindstone, end surfaces and oblique surfaces of outer and inner peripheries of the glass substrate are ground at the same time, and during a grinding process, the outer-surface grindstone is dressed electrolytically to sharpen the grinding particles, and during a non-processing period to replace the glass substrate, the inner-surface grindstone is dressed electrolytically.
The present invention also provides a chamfering apparatus for processing end surfaces of inner and outer peripheries of the doughnut-like glass substrate (
1
) having a circular hole (
1
a
) at the center thereof and chamfering oblique surfaces sandwiching the end surfaces, composed of the metal-bonded outer-surface grindstone (
12
) for processing the end surface and oblique surfaces of the outer periphery, the metal-bonded inner-surface grindstone (
14
) for simultaneously processing the end surface and oblique surfaces of the inner periphery, the outer-surface electrode (
18
) for electrolytically dressing the outer-surface grindstone during the grinding process, the inner-surface electrode (
20
) for electrolytically dressing the inner-surface grindstone during the non-processing period, a grinding liquid feeder (
22
) for supplying a conductive grinding liquid between the outer-surface grindstone and the outer-surface electrode and between the inner-surface grindstone and the inner-surface electrode, and a voltage application means (
24
) for applying an electrolytically dressing voltage across the outer-surface grindstone and the outer-surface electrode and across the inner-surface grindstone and the inner-surface electrode, wherein the outer-surface grindstone is dressed electrolytically when the outer-surface grindstone is grinding the end surface and oblique surfaces of the outer periphery of the glass substrate, and during a non-processing period when the glass substrate is being replaced, the inner-surface grindstone is dressed electrolytically.
According to the method and the apparatus of the present invention, as described above, end surfaces and oblique surfaces of outer and inner peripheries of the glass substrate (
1
) can be ground simultaneously using the outer-surface grindstone (
12
) and the inner-surface grindstone (
14
). In addition, during this grinding period, the outer-surface grindstone is dressed electrolytically (also known as “in-process dressing”) using the voltage application means (
24
) while supplying a conductive grinding liquid between the grindstone and the outer-surface surface electrode (
18
), thereby even when fine grinding particles are used, the outer-surface grindstone can be sharpened, therefore, while maintaining a high efficiency, the workpiece can be processed with a high accuracy and quality. Furthermore, the conductive grinding liquid is supplied between the inner-surface grindstone and the inner-surface electrode (
20
) when the glass substrate is replaced during a non-work period, the grindstone is dressed electrolytically (also known as “interval dressing”) by the same voltage application means. Therefore, even when similar fine grinding particles are used, the inner-surface grindstone can be sharpened while maintaining high efficiency and can process a workpiece precisely with high quality.
In addition, because the outer-surface grindstone undergoes in-process dressing during grinding, and the inner-surface grindstone undergoes interval dressing during a non-processing period, the load of the voltage application means (
24
) can be averaged, and compared to an alternat
Asami Muneaki
Ohmori Hitoshi
Shigitani Sadamasa
Uzawa Akihiko
Griffin & Szipl, P.C.
Morgan Eileen P.
Riken
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