JPH0810848A - Method for straightening magnetic disk substrate by detonation - Google Patents

Abstract

PURPOSE:To enable straightening with high accuracy, to execute the straightening in an extremely short period of time and to shorten cycle time by applying extremely large pressurizing force on the magnetic disk substrate on a surface plate having specific flatness by detonation. CONSTITUTION:An ignition plug 5 is simultaneously operated by an ignition device 6. Detonation is induced by ignition in an ignition chamber 4 and this flame is propagated through a guide path 2 to the top end 1A of a combustion chamber 1. The flame progresses from the top end 1A to the bottom end 1B in a combustion chamber 1 but since the sectional area of this combustion chamber 1 is formed gradually smaller downward, the pressure thereof rises to an extremely high pressure at the bottom end 1B. The top end face of the pressure medium in a pressure chamber 12 faces the aperture of this bottom end IB and, therefore, the high pressure is propagated to the pressure medium and presses the magnetic disk substrate P under the equal pressure via a film member or directly on the surface plate of a metallic or ceramic system having the flatness <=27mum of a press forming device 13, by which the magnetic disk substrate is straightened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk substrate straightening method.

[0002]

2. Description of the Related Art Usually, an aluminum alloy (hereinafter simply referred to as "aluminum") is used for a magnetic disk substrate. Magnetic disks tend to have higher densities and higher capacities, so that the magnetic disks and the reading head are used closer to each other. Therefore, the magnetic disk substrate is required to have a high degree of flatness. In the manufacturing process of the magnetic disk substrate, the flatness is corrected by a straightening leveler so that the flatness falls within a predetermined value. However, the winding tendency of the material coil is often not completely corrected, a warp remains, and the flatness is 10 μm or more. It is about 50 μm. Moreover, the pattern shape of the warp shows, when measured by an interference fringe type flatness system, a middle bent type shown in FIG. 4B or an X type shown in FIG. The reading accuracy fluctuates in a wavy form during one rotation, which is not preferable, and an ideal concentric circular shape as shown in FIG. 4 (a) could not be obtained.

In order to obtain a highly accurate flatness, for example, a flatness of 2 μm and a concentric circular pattern, in JP-A-62-240112 and JP-A-5-263201, several tens of magnetic disk substrates are used as a platen. We propose a method called creep flattening, which improves the flatness of these magnetic disks by holding them for several hours by raising the temperature of the magnetic disk substrate to a temperature level at which plastic deformation is caused by the creep phenomenon and holding it for several hours. There is.

[0004]

A concrete method of implementing the above-mentioned creep flattening is a heating furnace in which several dozen magnetic disk substrates are stacked and sandwiched from above and below, and a weight for pressurization is placed thereon. Put in and heat. Therefore, since the pressure acting on the magnetic disk substrate is a load due to the weight, a large surface pressure cannot be obtained, and since it is a pressure of several atmospheres to several tens of atmospheres at the most, flatness with high accuracy cannot be obtained. As a result, the flatness level is limited to 3 μm to 20 μm. Further, since it is necessary to put it in a heating furnace and hold it for several hours or more, the cycle time is very long and the productivity is poor. Even if it is possible to correct several tens of magnetic disk substrates at one time, a considerable time is required for each magnetic disk substrate, and the work efficiency is low.

The present invention provides a method of correcting a magnetic disk substrate by detonation, which solves such a problem, enables high-accuracy correction, and can perform correction in an extremely short time to shorten the cycle time. With the goal.

[0006]

According to the present invention, the above object is to converge a detonation wave generated by igniting a combustible air-fuel mixture in a combustion chamber as it progresses, and to directly generate a high pressure obtained at the converging portion. Alternatively, it is transmitted to a pressure medium composed of a liquid or an elastic body through an exchangeable medium to convert into a hydraulic pressure or an elastic pressure, and the flatness of the magnetic disk substrate is 2 μm through the film body or directly by the hydraulic pressure or the elastic pressure. It is achieved by pressing the following metal-based or ceramic-based surface plate.

[0007]

In the present invention having such a structure, the magnetic disk substrate is straightened as follows.

The magnetic disk substrate is set on a metal-based or ceramic-based flat surface plate having a flatness of 2 μm or less.

The ignition chamber is filled with a combustible gas mixture having a theoretical mixing ratio and ignited.

When ignited, the flame advances in the combustion chamber where the cross-sectional area gradually decreases due to detonation.

At the end of the minimum cross-sectional area of the combustion chamber, the flame converges, so the pressure of the flame increases and reaches the maximum pressure.

This pressure is transmitted to the pressure medium (liquid or elastic body).

The pressure transmitted to the pressure medium becomes liquid pressure or elastic pressure through the film body or directly (1) above.
The magnetic disk substrate of (1) is pressed against the surface plate to cause plastic deformation, and a magnetic disk substrate having a flatness and a pattern shape substantially the same as that of the surface plate is obtained as a product.

In the present invention, the pressure applied to the magnetic disk substrate by the shock wave generated by the detonation is about 3000 atmospheric pressure as a result of actual measurement, which far exceeds the yield stress of 15 kgf / mm ² of this magnetic disk substrate. Therefore, the magnetic disk substrate can be sufficiently flattened to have a flat shape and the shape can be corrected. Moreover, since a pressure far exceeding the yield stress is applied, a plastic strain of 2% or more can be applied. It is said that residual stress can be removed by applying a uniform plastic strain of 2% or more. Therefore, since both shape correction and residual stress removal are realized, even when the magnetic disk substrate is polished to finish into a magnetic disk, no warpage occurs due to changes in the residual stress distribution in the magnetic disk substrate in the plate thickness direction. It has the advantage.

Conventionally, there is an impact processing method similar to the impact processing method by the detonation of the present invention, but the difference between the two is described below.

In the conventional impact processing method, the following a) to c) are used.
The method is known.

A) Explosive molding (using explosives) b) Electromagnetic molding c) High-pressure gas molding The pressure obtained by the above-mentioned methods a) to c) is usually several hundred atmospheric pressure on the surface of the workpiece, and 1500 atmospheric pressure at the maximum. And the yield stress of the magnetic disk substrate is 15 kgf / mm ² (= 1500
Since it is difficult to exceed the atmospheric pressure), a sufficient correction effect cannot be obtained.

Further, in a) to c), the cycle time is long, and it is difficult to realize the correction within a few seconds. Although the method of b) can realize a cycle time of several seconds, it cannot generate a working force by causing an electromagnetic force action on an aluminum alloy having no magnetism. Therefore, the conventional impact processing method is not suitable for straightening the magnetic disk substrate.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a vertical sectional view of a first embodiment device of the present invention. The apparatus of the present embodiment has a combustion chamber 1, and the combustion chamber 1 has an inverted conical shape that narrows downward, and the passage cross-sectional area in the cross section is maximum at the upper end 1A and minimum at the lower end 1B. It is designed to form a converging portion.

The inner wall of the upper end 1A of the combustion chamber 1 is curved slightly upward, and a plurality of hole-shaped guide passages 2 communicate therewith. The plurality of guide paths 2 are converged at the upper side into a disk-shaped dispersion chamber 3. An ignition chamber 4 extending upward is connected to the dispersion chamber 3 so as to communicate therewith. An ignition plug 5 which is operated by an ignition device 6 is provided above the ignition chamber 4, and a fuel supply source 9 and an oxidant supply source 10 are connected via flowmeters 7 and 8, respectively. . Reference numeral 11 denotes a pressure gauge for checking the pressure in the ignition chamber 4.

A lower end portion 1B of the combustion chamber 1 is opened, a pressure chamber 12 is connected to the lower end portion 1B, and a working / forming device 13 using an impact pressure is provided immediately below the pressure chamber 12.
A liquid or a rubber-like elastic body as a pressure medium is housed in the pressure chamber 12, and a viscoplastic body (a rubber plate in this embodiment) 19 is housed in the surface in contact with the plate material P as a workpiece. . The upper end surface of the pressure medium may directly face the lower end portion 1B of the combustion chamber 1 as shown in the figure, or the interface may be formed by a tough and deformable film body.

As shown in FIG. 2, a surface plate 16 for mounting a magnetic disk substrate on its upper surface is replaceably housed inside the processing and molding apparatus 13. The upper surface of the surface plate 16 is finished with high precision, and the flatness is 2 μm or less. A vacuum pump device 17 is connected to the work forming device 13 so as to penetrate the platen 16 and communicate with an upper space thereof to create a vacuum in the space. The vacuum pump device 17 is also connected to the ignition chamber 4 described above.

In the apparatus of this embodiment, the generation of high-pressure elastic pressure and the correction of the magnetic disk substrate using this are performed as follows.

First, the magnetic disk substrate P to be corrected is set on the surface plate 16.

Then, the vacuum pump device 17 brings the ignition chamber 4, the dispersion chamber 3, the guide passage 2 and the combustion chamber 1 to a predetermined vacuum degree. At the same time, the space between the surface plate 16 and the plate P is also sucked so as to have a predetermined degree of vacuum.

After that, the pressure chamber 12 is filled with a liquid or an elastic body, and in the ignition chamber 4, the dispersion chamber 3, the guide passage 2 and the combustion chamber 1, a combustible gas having a substantially theoretical mixing ratio is supplied as a fuel supply source. 9, filled with the oxidant supply source 10.

After the setting is completed, the ignition devices 6 simultaneously activate the spark plugs 5. A detonation occurs in the ignition chamber 4 due to the ignition, and the flame is propagated to the upper end 1A of the combustion chamber 1 through the dispersion chamber 3 and the guide path 2. At this time, since the path lengths of the plurality of taxiways 2 are set equal to each other, the flames of the plurality of taxiways 2 are simultaneously set at the upper end portion 1
Reach A.

In the combustion chamber 1, the flame progresses from the upper end portion 1A to the lower end portion 1B, but since the cross-sectional area of the combustion chamber 1 gradually decreases downward, its pressure rises and at the lower end portion 1B. It becomes extremely high pressure.

Since the upper end surface of the pressure medium in the pressure chamber 12 faces the opening of the lower end portion 1B of the combustion chamber 1, the high pressure is propagated to the pressure medium and is passed through the membrane or directly. Then, the magnetic disk substrate P is pressed with a constant pressure against the surface plate 16 of the processing and forming apparatus 13 to perform corrective forming.

Thereafter, the magnetic disk substrate P as a product is taken out, and the steps 1 to 3 are repeated, so that the magnetic disk substrates can be corrected one after another.

Next, an example of the method of straightening the magnetic disk substrate in this embodiment will be shown with specific numerical values.

Outer diameter 95 mm, inner diameter 25 mm, thickness 1.5
A 5086 mm aluminum alloy hollow disk made of A5086 was used as a material for the magnetic disk substrate. The flatness of this material is 45 μm
Met.

The material of this magnetic disk substrate was placed on a surface plate having a flatness of 2 μm in the working and molding apparatus by the detonation pressure of this embodiment, and was pressed and corrected by the liquid pressure or elastic pressure generated by the detonation. .

The flatness after the straightening process by the apparatus of this embodiment was 2 μm, and the pattern shape was concentric. Thus, a magnetic disk substrate having a very high flatness was obtained.

Next, a second embodiment device of the present invention will be described with reference to FIG. In the figure, the same parts as those of the apparatus of the previous embodiment shown in FIG.

In the present embodiment, the combustion chamber 1'is formed in a horizontal shape that expands in the radial direction. The combustion chamber 1'has a shape in which the cross-sectional area decreases toward the center by the upper wall surface of a part of a substantially spherical surface which bulges downward.

According to the apparatus of this embodiment, it is convenient when the size of the apparatus cannot be increased. The operation is the same as in the case of the previous embodiment, and after the flame reaches the peripheral portion 1′A which is one end of the combustion chamber 1 ′ from the guide passage 2, the flame moves toward the central portion 1′B which is the other end. proceed. In the process, the pressure becomes extremely high as the cross-sectional area decreases. Then, the high pressure is propagated to the pressure medium in the pressure chamber 12, and the working / forming apparatus 13 causes the magnetic disk substrate P to move into the concave portion 16A of the surface plate 16.
Press to correct.

[0039]

As described above, according to the present invention, a very large pressing force is applied to the material of the magnetic disk substrate by the detonation, so that it is plastically processed into a flat shape and the residual stress is extremely reduced. Small level, eg 1kgf / mm ²
If the platen has a flatness of 2 μm or less, the flatness of 2 μm or less can be obtained, and a material for a magnetic disk substrate having a concentric circular pattern can be obtained. As a result, a magnetic disk substrate suitable for high density and high capacity can be realized.

Conventionally, no matter how high the precision of the surface plate was finished, a sufficient pressing force could not be obtained, so that the magnetic disk substrate could not be corrected with high precision accordingly.
The present invention has solved that problem.

Moreover, the cycle time for detonation correction according to the present invention can be shortened to a few seconds if the magnetic disk substrate is quickly loaded / unloaded to / from the processing / molding apparatus, so that the productivity can be improved. It also brings the effect.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a first embodiment device of the present invention.

FIG. 2 is an enlarged view of a work molding apparatus portion of the apparatus shown in FIG.

FIG. 3 is a vertical sectional view of a second embodiment device.

FIG. 4 is a pattern shape that can occur after the correction of the magnetic disk substrate.

[Explanation of symbols]

 1 Combustion Chamber 4 Ignition Chamber 12 Pressure Chamber 13 Processing Room 16 Surface Plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Moriichi Abe 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A detonation wave generated by igniting a combustible air-fuel mixture in a combustion chamber is converged with its progress, and the high pressure obtained at the converging portion is formed of a liquid or an elastic body directly or through a medium capable of exchange. By transmitting it to a pressure medium to convert it into hydraulic pressure or elastic pressure, and pressing the magnetic disk substrate through a film body or directly by the hydraulic pressure or elastic pressure onto a metal-based or ceramic-based surface plate having a flatness of 2 μm or less. Method of correcting magnetic disk substrate by detonation.