JPH03230814A - Hot correcting method for magnetic disk base plate of titanium - Google Patents

Abstract

PURPOSE:To obtain a magnetic disk base plate of titanium of excellent flatness by specifying the relation of a surface plate and a fastening tool, also limiting a flatness of this surface plate, a pressure of this fastening tool, a heating temperature and a heating time, and heat-treating this base plate. CONSTITUTION:On the case of inserting the magnetic disk base plate of titanium 1 between the surface plates 21, 22, fastening it with the fastening tools 31, 32, heat-treating and hot-correcting, the relation of the coefficient of linear expansion (a) of the surface plates 21, 22 and the coefficient of linear expansion (b) of the fastening tools 31, 32 is made to a>=b, and the flatness of the surface plates 21, 22 is made to <=100mum, also the fastening pressure is made to >=0.03 kgf/mm<2> to <1kgf/mm<2>, and more, the heating temperature is made to >=500 deg.C, the heating time is made to >=1 hour and then the heat-treating is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for hot straightening magnetic disk substrates made of titanium and titanium alloys (hereinafter simply referred to as titanium).

[Conventional technology]

The titanium magnetic disk substrate has 1. A titanium plate with a thickness of about 100 nm is used, but since it is produced by punching a cold-rolled plate, distortion usually occurs as a result of punching. Also, since the material is a cold-rolled plate, distortions from cold-rolling remain. However, the flatness required for a magnetic disk substrate (here, flatness refers to the maximum displacement per 100 mm) is 20
Because the flatness is at a high level of less than μm, if the substrate material does not have sufficient flatness, the yield will decrease due to polishing, so the degree of flatness of the material is This was one of the constraints on its use.

On the other hand, titanium magnetic disk substrates are polished by sandwiching them between upper and lower grinding wheels that have a high level of flatness. Due to the unavoidably applied pressure, a certain level of flattening is achieved. However, when the pressure is removed after polishing, titanium has a large springback, so if the material has low flatness, it will deform into a shape that reflects this.

Therefore, a method of improving flatness using the creep phenomenon of titanium plates has been implemented. i.e. 50-200 kg
A weight made of iron or the like is placed on a titanium magnetic disk held between a surface plate, and the material is charged into a heating furnace or the like while being pressurized to perform pressure annealing and straightening.

[Problem that the invention seeks to solve]

In order to obtain a sufficient straightening effect by such pressure annealing straightening, it is necessary to increase the pressing force.

However, even if an attempt is made to increase the pressing force by increasing the number of weights, there are limitations in the load capacity and processing capacity of the heating furnace, and a sufficient straightening effect cannot currently be obtained.

The present invention has been devised in view of the above-mentioned problems of the prior art, and provides optimal processing conditions for hot straightening of a titanium magnetic disk substrate, which can improve the flatness of the titanium plate by utilizing the creep phenomenon of the titanium plate. The purpose is to clarify the following.

[Means for solving problems]

3- Therefore, the present invention, as shown in the attached drawings, involves sandwiching a titanium magnetic disk substrate (1) between surface plates (21) and (22), tightening them with fasteners (31 and 32), and then subjecting them to heat treatment. In the hot straightening method for titanium magnetic disk substrates, the function of the linear expansion coefficient a of the surface plate (21) (22) and the linear expansion coefficient s of the fasteners (31) (32) is defined as a≧
b, and the flatness of the surface plates (21) and (22) is 10
0μm or less and tightening pressure of 0.03kg
The basic feature is that the heat treatment is performed at f/llN112 or more, 1 kgf/or more, 500° C. or more, and heating time of 1 hour or more.

With the above configuration, it is possible to perform high-temperature heat treatment under optimal compressive stress, and this makes it possible to utilize the creep phenomenon of only the titanium magnetic disk substrate (1). It becomes possible to obtain a manufactured magnetic disk substrate (1).

The reason for limiting each condition in the structure of the present invention will be explained below.

First, the surface plate (21) (22) and the tightening tool (31) (
32) respectively 4- linear expansion coefficient a. The reason why the function of b is defined as a≧b is because if the linear expansion coefficient function is a < b, the compressive stress will be unloaded with heating, and a sufficient leap flattening effect will not be obtained. This is because there is no Furthermore, if this linear expansion coefficient ratio a/b is sufficiently large, it is expected that compressive stress will increase during hot straightening and that uneven plate thickness will occur due to severe creep deformation.
The difference in linear expansion coefficient at 0°C is at most 10 μm per 1 mm of plate thickness of the titanium magnetic disk substrate (1), and this degree of non-uniformity in plate thickness does not pose a practical problem, so a /
There is no upper limit for b.

Furthermore, the flatness of the surface plates (21) and (22) was limited for the following reasons. Constant II used in the present invention (21)
(22) plays the role of providing excellent flatness to the titanium magnetic disk substrate (1), and therefore the surface plate (21)
) (22) is greater than 100 μm, hot straightening will transfer the low flatness of the surface plates (21) and (22) to the titanium magnetic disk substrate (1), reducing the flatness. This is because you will no longer be able to obtain superior products.

Furthermore, regarding the tightening pressure by the tightening tools (31) (32), the pressure is 0.03 kg f / rm2
This is because if the temperature is less than 1 kg f/n, creep deformation will not occur at the hot straightening temperature, making it impossible to improve the flatness by hot straightening, and the tightening pressure is 1 kg f/n.
If it is more than u2, strong creep deformation occurs, and although the flatness can be improved by hot straightening, the plate thickness becomes non-uniform, making it unsuitable for use as a magnetic disk substrate.

On the other hand, the lower limit temperature for hot straightening was set at 500°C, and the hot straightening time was set at 1 hour or more because both conditions are sufficient to prevent leap deformation and provide excellent flatness for titanium magnetic disks. This is because the substrate (1) cannot be obtained.

The upper limit of temperature and upper limit of time for hot straightening is set on the surface plate (21).
(22) It depends on the creep strength of the fasteners (31) and (32), and there is no upper limit condition specific to the hot straightening conditions for titanium, but the ease of mirror finishing of the titanium magnetic disk (1) (The fine grain structure is easy to mirror finish), so the upper limit of hot straightening temperature is 650℃, and the upper limit of hot straightening time is 1
0 hours is desirable.

〔Example〕

An annular pure titanium plate with an outer diameter of 95 mm, an inner diameter of 25 mm, and a plate thickness of 1.5 mm was prepared as a test material, and as shown in the drawing, 30 test materials were placed on a surface plate (21) (22). Sandwich.

Next, it was tightened with tightening tools (31) and (32) to apply the required tightening pressure, and hot straightening was performed.

The plate thickness accuracy of the above pure titanium material is 1.5mm±lOμpus,
The flatness is 150 μm. Also, upper wire fitting tool (31)
(32) has SKD 61 (linear expansion coefficient 14.2X1
0'/°C), Ti-6AI-4V alloy (linear expansion coefficient 18.7 x IF'/°C), alumina (linear expansion coefficient 7.8 x IO-'/°C) and silicon carbide (linear expansion coefficient 4. OX 10-''/''C) was used, while the surface plates (21) and (22) had a flatness of 200 μm to 10 μm. In addition, the tightening pressure is adjusted between 0.01 kg f/rm2 and 5 kg f/an2, the hot straightening temperature varies from 400℃ to 700℃, and the hot straightening time varies from 0.5 hours to 20 hours. I let it happen.

After each test, 5 test materials were selected at random from among the 30 test materials, and the thickness accuracy and flatness were measured for each test material.
The average value of each was determined. The results are summarized in the table below along with these hot straightening conditions.

As is clear from this table, the coefficient of linear expansion is the surface plate (21)
(22) is the same as or lower than the linear expansion coefficient (i.e., a
≧b) Made of titanium with excellent flatness and plate thickness accuracy, only when hot straightening is performed using tightening tools (31) (32) of the material and the tightening pressure is 0.03 to 1 kg f / wn2. A magnetic disk substrate (1) has been obtained.

On the contrary, the fastener (3) is made of a material with a linear expansion coefficient higher than that of the surface plates (21) (22) (i.e., a < b).
1) When (32) is used (comparative example Nα29), good flatness is not obtained even if the tightening pressure conditions are within the range defined by the present invention. Also, surface plate (21) (
Even if the linear expansion coefficient of 22) is the same as or larger than that of the fasteners (31) and (32) (a≧b),
Good flatness cannot be obtained when the tightening pressure is smaller than the lower limit specified by the present invention (Comparative Example No. 19), and when the tightening pressure is larger than the upper limit (Comparative Example No. 2
To &22), the plate thickness accuracy is decreased.

From the above results, it has become clear that as long as the conditions of the present invention are adhered to, a titanium magnetic disk substrate material with excellent plate thickness accuracy and flatness can be manufactured.

In addition, using the titanium magnetic disk substrate material (plate thickness accuracy of 10 μm, flatness of 83 μm or less) obtained in the example of the present invention,
When double-sided mirror polishing was performed, a highly accurate titanium magnetic disk substrate with a plate thickness accuracy of ±5 μm or less and a flatness of 15 μm or less, which could not be obtained by conventional methods, was obtained.

〔Effect of the invention〕

As described above, according to the hot straightening method of the present invention, a titanium magnetic disk substrate is 0.0
3kg f/wn” or more 1kg f/rrt
By performing heat treatment at a temperature of 500° C. or higher for 1 hour or more while applying a tightening pressure of less than n'', a titanium magnetic disk substrate material with excellent flatness can be obtained.

[Brief explanation of drawings]

The accompanying drawing is an explanatory view showing an example of a state in which a titanium magnetic disk substrate is sandwiched between surface plates and tightened with a tightening tool. In the figure, (1) is a titanium magnetic disk substrate, (21) (2
2) shows the surface plate, and (31) and (32) show the tightening tools.

Claims (1)

[Claims] In a hot straightening method for titanium magnetic disk substrates, which involves sandwiching a titanium magnetic disk substrate between surface plates, tightening it with a fastener, and then subjecting it to heat treatment, the linear expansion coefficient a of the surface plate and the linear expansion coefficient b of the fastener are determined. The relationship is a≧b, and the flatness of the surface plate is 100 μm or less, and the tightening pressure is 0.03 kgf/mm^2 or more and 1 kgf/mm^
A method for hot straightening a titanium magnetic disk substrate, characterized in that the heat treatment is carried out at a heating temperature of 500° C. or higher and a heating time of 1 hour or longer.