JP2008001990A - Manufacturing method of iron alloy plate material for hard disk voice coil motor yoke - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a yoke capable of eliminating all leakage magnetic flux and utilizing all the characteristics of high magnetic flux density of a permanent magnet in a magnetic circuit yoke such as a magnetic recording device.
SOLUTION: The composition after casting is C: 0.0001 to 0.02, Si: 0.0001 to less than 0.03, Mn: 0.001 to 0.2, P: 0.0001 or more and 0.05 or less, S: 0.0001 or more and 0.05 or less, Al: 0.0001 or more and 0.1 or less, O: 0.001 or more and 0.1 or less, N: 0.0001 or more and 0. Each master alloy is weighed, melted and cast so that it becomes 03, rolled to a thickness of 0.1 mm or more and 5 mm or less, subjected to plastic working and processed into a yoke shape, and surface treatment is performed as necessary. [Selection figure] None

Description

  The present invention relates to a method of manufacturing a high magnetic flux density iron-based yoke material constituting a magnetic circuit in order to provide a magnetic circuit suitable for a small and thin voice coil motor in a magnetic recording apparatus.

The magnetic circuit of the voice coil motor is composed of a permanent magnet that generates magnetic flux and a yoke that connects them, and is used as an actuator for driving a hard disk head. In recent years, computers tend to be reduced in size and weight in consideration of easiness to carry and carry, and along with this, magnetic recording devices have also become smaller and thinner. Further, this reduction in size and thickness has spread to permanent magnets and yoke material components that constitute a magnetic circuit.
In order to realize the miniaturization and thinning of the magnetic circuit, it has been common in the past to compensate for the decrease in the magnetic flux density between the gaps due to the volume reduction by the high magnetic flux density of the high-performance magnet.

However, the magnetic flux density generated by high-performance magnets increases year by year, while the yoke material uses a rolled steel plate such as SPCC, SPCD, SPCE, etc., so that the saturation magnetization of the yoke material increases as the magnetic flux density of the magnet increases. Cannot be increased. Since the yoke thickness is also limited by the restrictions of the entire device, it is not possible to effectively use all the magnetic flux of the high-performance magnet, resulting in partial saturation or leakage of magnetic flux in the middle of the magnetic circuit. To do.
Such leakage of magnetic flux not only reduces the gap magnetic flux density of the magnetic circuit, but also affects the surrounding magnetic recording media and control equipment. The amount of magnetic flux leakage from the VCM circuit has a certain regulation, and the amount of magnetic flux leakage from the product must be less than this regulation value.

As magnetic materials for magnetic circuit yokes such as magnetic recording devices, cold rolled steel sheets such as SPCC, SPCD, SPCE, etc. have been conventionally excellent in productivity such as punching, die-cutting, drilling and bending, and embossing. Because of the most used. However, since these steel materials do not have sufficient saturation magnetization, it is difficult to avoid magnetic saturation in the partial VCM magnetic circuit due to the above-mentioned miniaturization and thinning, and the permanent magnets having high magnetic flux density are difficult to avoid. The magnetic flux could not be sufficiently guided to the magnetic circuit.
There has been a strong demand for the development and manufacturing method of yokes that can eliminate these leakage magnetic flux amounts and utilize all the characteristics of the high magnetic flux density of permanent magnets.

  As a result of various studies to solve the above-mentioned problems, the composition after casting was C: 0.0001 mass% to 0.02 mass%, Si: 0.0001 mass% to less than 0.03 mass% , Mn: 0.001% to 0.2% by mass, P: 0.0001% to 0.05% by mass, S: 0.0001% to 0.05% by mass, Al: 0.001%. Each master alloy is weighed and dissolved so that it becomes 0001% by mass to 0.1% by mass, O: 0.001% by mass to 0.1% by mass, and N: 0.0001% by mass to 0.03% by mass. -Combined with the composition, characterized by casting, rolling to a thickness of 0.1 mm or more and 5 mm or less, performing plastic processing to process into a yoke shape, and performing surface treatment as necessary Iron alloy sheet for hard disk voice coil motor yoke We have developed a manufacturing method. Magnetic material having a saturation magnetic flux density of 2.07 Tesla or more and 2.2 Tesla or less, a maximum relative magnetic permeability of 1000 or more and 20000 or less, and a coercive force of 10 A / m or more and 400 A / m or less on the plate processed into the yoke shape. It is preferable to perform an adjustment process having characteristics.

  The present invention effectively improves the magnetic characteristics of a yoke material having a thickness of 0.5 mm to 5 mm used as a magnetic circuit member for a magnetic recording device voice coil motor, thereby effectively using the magnetic flux input from the magnet to the magnetic circuit to be configured. Therefore, it is possible to provide a magnetic circuit that improves the magnetic flux density between the gaps and that does not magnetically affect the surrounding magnetic recording media and control equipment.

  In order to achieve the above-mentioned object, the present inventors first examined various materials and investigated elements that affect the decrease in magnetic flux density from components such as SPCC materials. For iron, C, Al, Si, P, S, Mn does not have a magnetic moment or the magnetic moment is different from that of the iron matrix, so the presence of these elements reduces the magnetic moment of the surrounding iron. A phenomenon occurs. In particular, P and S adversely affect the corrosion resistance in addition to the decrease in magnetic flux density. However, reducing these elements unnecessarily is disadvantageous from the viewpoint of the production cost of the raw material, and it is satisfactory even if it is contained within a small amount in terms of performance.

From the above viewpoint, first, in terms of composition, C: 0.0001 mass% or more and 0.02 mass% or less, Si: 0.0001 mass% or more and less than 0.03 mass%, Mn: 0.001 mass% or more 0.2% by mass or less, P: 0.0001% by mass to 0.05% by mass, S: 0.0001% by mass to 0.05% by mass, Al: 0.0001% by mass to 0.1% by mass It was confirmed that the following range was possible.
Similarly, O and N also affect the magnetic properties, and it is preferable that O: 0.001% by mass to 0.1% by mass and N: 0.0001% by mass to 0.03% by mass. If so, the saturation magnetic flux density is not particularly deteriorated.
Further, in the present invention, it is preferable that the saturation magnetic flux density is 2.07 Tesla or more and 2.2 Tesla or less from the viewpoint of the performance of the yoke, and even if the saturation magnetic flux density is high, the maximum relative magnetic permeability is small or maintained. If the magnetic force is too large, the magnetic resistance of the magnetic circuit increases and the gap magnetic flux density decreases. Therefore, the maximum relative magnetic permeability is in the range of 1000 to 20000, and the coercive force is in the range of 10 A / m to 400 A / m.

The alloy component is adjusted to the target range depending on the raw material and the steel making method, but the continuous casting method is preferable from the viewpoint of productivity and quality, and the vacuum melting method is suitable for small lot production. After casting, hot rolling, cold rolling, or the like is performed in order to obtain a steel material having a predetermined plate thickness. The iron alloy sheet material obtained in this way is made into a predetermined yoke shape by plastic working such as punching, die-making, drilling, bending, embossing, etc. with a mechanical press, hydraulic press or fine blanking press. After processing, deburring, chamfering, pickling, surface treatment by electroplating of Ni, Cu, Cr, Al, etc., electroless plating, PVD, CVD, ion plating, etc., and used for hard disk voice coil motor It can be manufactured as a yoke material.
Here, when the plate thickness of the yoke material is less than 0.1 mm, even if the saturation magnetization of the plate material is slightly improved, the effect of improving the characteristics of the magnetic circuit is not so much seen. Therefore, there is no problem of saturation of the magnetic circuit without using the present invention.

Examples will be described below, but the present invention is not limited to these examples.
[Example 1]
Steel alloy ingots having the composition shown in Example 1 in Table 1 were melted and continuously cast to obtain alloy ingots having a width of 200 mm, a length of 500 mm, and a plate thickness of 50 mm.
The alloy ingot was heated to 1200 ° C. to start hot rolling, the cumulative rolling reduction was 950 ° C. or less, and the hot rolling was finished at 850 ° C. After the hot rolling was finished, it was air-cooled to room temperature. Then, after cold rolling, finish annealing was performed at 900 ° C., pickling was performed, and a steel sheet having a thickness of 1 mm was obtained.
The obtained steel sheet was punched into a yoke shape with a mechanical punching press to obtain two types of upper and lower yokes.

The obtained yoke was subjected to electroless NiP plating with a coating thickness of about 8 microns. Inside these upper and lower yokes, a permanent magnet having a maximum energy product of 380 kJ / m ³ was bonded to the central position of the yoke to produce a magnetic circuit.
As a comparative example, a general commercially available SPCCSD product and a material with a plate thickness of 1 mm were similarly punched into a yoke shape by a mechanical punching press, and two types of upper and lower yokes were obtained. The obtained yoke was subjected to electroless NiP plating with a coating thickness of about 8 microns, and a permanent magnet having a maximum energy product of 380 kJ / m ³ was adhered to the center of the yoke inside the upper and lower yokes to produce a magnetic circuit.
The produced yoke material of the present invention and the comparative SPCC material were cut into about 4 mm square, and the saturation magnetic flux density was measured with a vibrating sample magnetometer having a maximum magnetic field of 1.9 MA / m.

In addition, a ring sample having an outer diameter of 45 mm and an inner diameter of 33 mm is produced from the remaining plate material punched into a yoke shape, and the above-described ring sample is placed between the paper samples according to the method described in JIS C 2531 (1999). 2 layers, wound with insulating tape, and then wound with 0.26mmφ copper wire for 50 turns each as an exciting coil and a magnetization detecting coil, DC magnetic characteristics automatic recording device with maximum magnetic field ± 1.6kA / m The magnetic hysteresis curve was drawn at, and the maximum relative permeability and coercive force were measured.
Further, in order to investigate the performance of the magnetic circuit for the voice coil motor thus produced, the total magnetic flux between the magnetic circuit gaps was measured using a magnetometer (480Fluxmeter manufactured by Lakeshore) using a planar coil used in an actual magnetic recording apparatus. The amount was measured.
The above experimental results are shown in Table 1.

From Table 1, it can be seen that the alloy of Example 1 increased in saturation magnetic flux density with respect to SPCC, and correspondingly increased the total magnetic flux in the magnetic circuit gap.
The ratios in Table 1 are expressed as relative ratios with the gap magnetic flux amount of the comparative example as 100.

[Example 2]
Similarly, a steel ingot having the composition shown in Example 2 of Table 1 was melted and cast through an electric furnace, converter-degassing, and continuous casting process to obtain a slab having a thickness of 200 mm. The hot metal was purified by RH degassing and VOD method (vacuum-oxygen decarburization method).
The obtained slab having a thickness of 200 mm was heated and soaked to 1100 to 1200 ° C., and rolled with a hot rolling mill to a plate temperature of about 10 mm at a finishing temperature of 850 to 950 ° C. After recrystallization annealing (850 to 900 ° C.), the thickness was about 4 mm by pickling and cold rolling. Thereafter, it was pickled after finishing annealing at about 850 ° C. to obtain a test steel plate. The obtained steel sheet was punched into a yoke shape with a mechanical punching press to obtain two types of upper and lower yokes. The obtained yoke was subjected to electroless NiP plating with a coating thickness of about 6 microns.

Inside these upper and lower yokes, a permanent magnet having a maximum energy product of 400 kJ / m ³ was bonded to the central position of the yoke to produce a magnetic circuit.
The magnetic characteristics of the produced yoke plate material were measured by the method shown in Example 1.
In addition, in order to investigate the performance of the magnetic circuit for the voice coil motor, the planar coil used in the actual magnetic recording device is used to run the range on the permanent magnet between the magnetic circuit gaps, and the total magnetic flux amount is calculated. It was measured.
The above experimental results are also shown in Table 1.
As a result, the steel plate having the composition of Example 2 improved the saturation magnetic flux density with respect to SPCC, and correspondingly increased the total magnetic flux in the magnetic circuit gap.

  According to the present invention, a magnetic circuit that improves the magnetic flux density between gaps by effectively using the magnetic flux input from the magnet to the magnetic circuit and that does not magnetically affect the surrounding magnetic recording media and control equipment. Since it is provided, it is a tremendous advantage in the technical field using a magnetic recording device voice coil motor.

Claims (2)

The composition after casting is C: 0.0001 mass% or more and 0.02 mass% or less, Si: 0.0001 mass% or more and less than 0.03 mass%, Mn: 0.001 mass% or more and 0.2 mass% or less, P: 0.0001 mass% to 0.05 mass%, S: 0.0001 mass% to 0.05 mass%, Al: 0.0001 mass% to 0.1 mass%, O: 0.001 Each mother alloy is weighed, melted, and cast so that the thickness is 0.101 mass% or more and N: 0.0001 mass% or more and 0.03 mass%, until the thickness becomes 0.1 mm or more and 5 mm or less. A method for producing an iron alloy plate material for a hard disk voice coil motor yoke, comprising rolling, plastic processing to form a yoke, and performing surface treatment as necessary. Magnetic properties of a plate material processed into a yoke shape having a saturation magnetic flux density of 2.07 Tesla to 2.2 Tesla, a maximum relative permeability of 1000 to 20000, and a coercive force of 10 A / m to 400 A / m. A method for manufacturing an iron alloy plate material for a hard disk voice coil motor yoke according to claim 1, wherein the magnetizing process is performed so as to include a magnetic disk.