Metal working – Method of mechanical manufacture – Shaping one-piece blank by removing material
Reexamination Certificate
1998-05-06
2001-07-10
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Shaping one-piece blank by removing material
C451S054000
Reexamination Certificate
active
06256860
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a process of fabricating a magnetic hard disk substrate having an excellent surface flatness.
b) Description of the Prior Art
There has been a general trend toward a higher density and larger capacity of a magnetic hard disk device as a storage device of a computer and the like and it has, therefore, been an important technical aspect to finish a magnetic hard disk substrate used for the device to a desired surface roughness and flatness. Particularly, there has been achieved a conspicuous development in the reduction of levitation based on an improvement in the head side part for the realization of a high density recording and thereby, the gap between a head and a medium has been narrowed and in company with this, further improvement in not only the surface flatness of a magnetic hard disk substrate but also the surface roughness thereof has strongly been demanded in order to prevent a head crash.
It is common that a magnetic hard disk substrate is fabricated by a process comprising the steps of: obtaining a blank by blanking a rolled coil of aluminum or aluminum alloy (hereinafter referred to as simply aluminum); grinding a surface of the blank so as to have surface damage, waviness and the like removed to attain a substrate; effecting Ni-P plating on the surface; performing finish polishing on the plated surface; thereafter performing magnetic sputtering on the polished surface to form a magnetic coating layer; and applying an overcoat on the layer to obtain a sputtering medium. In order to control the surface roughness and flatness within a predetermined range in the process, in the grinding step applied prior to the Ni-P plating step, the magnetic hard disk substrate (as a blank) is subjected to rough grinding by a grinding stone with a grain size of the order of #800 in a double-surface grinding machine, which is followed by finish grinding by a grinding stone with a grain size of the order of #3000 in the grinding machine. This kind of grinding is called a G—G (Grinding-Grinding) process, for this grinding step comprises two sub-steps of grinding.
In a conventional G—G process, however, since a first step of rough grinding has been applied on plural Aluminum blanks in one operation by a grinding stone or the like, the removal of stock by grinding is limited and a stock removal large enough to effect grinding off a bow, waviness or the like has been hard to achieve. Therefore, in a second step of grinding, which is performed following the rough grinding in a similar way thereto, the removal of stock is obliged to be larger, even with which it is still difficult to reduce the substrate-to-substrate thickness variation. Instead of the G—G process, there is also a well-known process, which is a so-called T-G process, in which in a first step, turning is performed and in a second step, grinding is performed. According to the T-G process, as a first step, turning by use of a precision lathe is performed and as a second step following the first step, grinding is performed, so that while a bow, waviness and the like of a magnetic hard disk substrate are eliminated, the magnitude of a grinding stress is dispersed by an uneven stock removal, which is, in turn, caused by a substrate-to-substrate thickness variation, and a deteriorated surface flatness of the substrate results, which have been causes for making severe requirements for a magnetic hard disk substrate difficult to satisfy.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic hard disk substrate having an excellent surface flatness and a process of fabricating the same.
The present invention has been made based on the finding that an aluminum magnetic hard disk substrate is prevented from deteriorating in surface flatness and can satisfy severe requirements therefor by application of the process steps of removing the stock of a blank by a depth in the range of 20 to 150 &mgr;m by precision turning with an NC automatic lathe to adjust the thickness of a substrate; and further removing the stock off the blank by a depth of 10 &mgr;m or less by grinding. That is, according to the present invention, there is provided an aluminum magnetic hard disk substrate and a process of fabricating the aluminum magnetic hard disk substrate in which an aluminum alloy blank, before an Ni-P plating treatment, is subjected to precision turning with stock removal on each surface in the range of 20 to 150 &mgr;m in depth, which is followed by grinding with stock removal on each surface of 10 &mgr;m or less in depth.
The precision turning is preferably performed in a way in which both surfaces of a blank are machined in a uniform manner, the rotational speed of a main spindle of an NC automatic lathe is set at a value in the range of 500 to 10000 rpm, or preferably in the range of 3000 to 6000 rpm and the feed rate of a diamond tool is set at a value in the range of 0.010 to 0.500 mm/rev., or preferably in the range of 0.05 to 0.20 mm/rev. The grinding is preferably performed on two or more blanks simultaneously and the spread of the thickness distribution of the blanks to be ground in one batch is prepared at a value of 10 &mgr;m or less, or preferably 5 &mgr;m or less.
Other objects and features of the present invention will become obvious from the following description or the recitation in the appended claims.
REFERENCES:
patent: 1949515 (1934-03-01), Norton
patent: 3218763 (1965-11-01), Kikuchi et al.
patent: 3528665 (1970-09-01), Redlich
patent: 3763602 (1973-10-01), Boettcher
patent: 3801293 (1974-04-01), Kiser
patent: 3888050 (1975-06-01), Elm
patent: 4445300 (1984-05-01), Sekiya et al.
patent: 4517772 (1985-05-01), Elliott
patent: 4586296 (1986-05-01), Saunders
patent: 4640651 (1987-02-01), Runyon
patent: 4724599 (1988-02-01), Corkin
patent: 5136819 (1992-08-01), Takagi et al.
patent: 5202810 (1993-04-01), Nakamura et al.
patent: 5342067 (1994-08-01), Adler et al.
patent: 5413850 (1995-05-01), Nehring
patent: 5482497 (1996-01-01), Gonnella et al.
patent: 5749769 (1998-05-01), Church et al.
patent: 3-141023 (1991-06-01), None
patent: 07262554 (1995-10-01), None
Kanouchi Shoichiro
Matsubara Hiromichi
Flynn ,Thiel, Boutell & Tanis, P.C.
Hughes S. Thomas
Showa Denko K. K.
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