JPH0281364A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To prevent the flowing-out of a magnetic fluid due to the temperature and pressure change by minimizing the inner diameter of at least one ring yoke out of the magnetic circuits of the ring yoke and a ring magnet. CONSTITUTION:As the internal construction of the spindle motor of a magnetic disk device, 3 ring magnets 12 are sandwiched between 4 ring yokes 11, a magnetic fluid seal main body 7, in which 2 inner diameter of the vertical directioned of the ring yokes 11 are composed of the diameter smaller than one central inner diameter, is distributed in the upper and lower directions of a spindle motor hub 1. Namely, for the diameter of vertical magnetic fluid sealing main body 7, the diameter of an upper side shaft 9 is smaller than the lower side and the upper side sealing main body inner diameter is also smaller than the lower side. Consequently, when the magnetic fluid flows from the magnetic circuit in the initial condition due to the temperature change and the pressure change, a ring yoke 11a with small vertical inner diameter become a flow preventing wall and the flowing to the external part and the internal part of a spindle motor hub is prevented. Thus, at the time of rapid pressure changes on the like, the flow-out and the dispersion of the magnetic fluid can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to dust prevention inside a spindle motor hub of a magnetic disk device, and particularly to prevention of outflow of magnetic fluid due to changes in temperature and pressure.

[Conventional technology]

In conventional magnetic disk drives, magnetic fluid leaks due to changes in temperature and pressure.In order to prevent this magnetic fluid from flowing out, we have developed a structure that prevents the magnetic fluid from being affected by changes in pressure, etc., and a structure that prevents it from scattering after it flows out. However, in the latter method, JP-A No. 62-73480 discloses that a scattering prevention cap is provided separately to prevent scattering due to outflow.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into consideration the outflow of the magnetic fluid before it is scattered, and only protects against the case where the outflow liquid is scattered due to centrifugal force. For this reason, when a force or pressure other than centrifugal force is applied, the outflow liquid is not contained within the protective wall, but scatters and adheres to the inside and outside of the spindle motor, causing damage to the magnetic disk, etc.

In other words, in the outflow before scattering, there are cases where a gradual pressure change is applied and oozes out, and there are cases where a sudden pressure change is applied and the outflow breaks down, and in the latter case, a spill prevention structure in front of the protective wall is required. It will become.

An object of the present invention is to prevent the magnetic fluid from flowing out and scattering even in the event of sudden pressure changes.

[Means to solve the problem]

In order to achieve the above object, the present invention prevents sudden pressure changes from being applied to the magnetic fluid or prevents it from flowing out within the magnetic circuit consisting of the magnetic fluid seal body, the magnetic fluid, and the spindle motor shaft. In view of this, in the latter case, the inner diameter of at least one of the annular yokes of the magnetic fluid seal body is made smaller than the gap between the inner diameter of the other annular yokes and the outer diameter of the spindle motor shaft.

[For production]

The magnetic circuit consists of the annular yoke of the magnetic fluid seal body, the annular magnet, the magnetic fluid, and the motor shirt I. The magnetic flux emitted from the N pole of the annular magnet flows through the annular yoke, the magnetic fluid, and the magnetic circuit.
It flows into the south pole through the shaft. On this occasion,
The strength of the coupling of the magnetic fluid with the annular yoke and the shaft becomes stronger as the gap between the inner diameter of the annular yoke and the outer diameter of the shaft is smaller, and the magnetic fluid becomes less likely to flow out of the magnetic circuit.

Here, magnetic fluid is not injected into at least one of the annular yokes outside or close to the inside of the spindle motor hub, and the inner diameter of the annular yoke is made small to serve as a protective wall for the outflow of magnetic fluid. 0 For example, even in the worst case of magnetic fluid rupture, the gap between the annular yoke and the shaft is captured before it flows out of the motor hub, and a new magnetic circuit is constructed.

At this time, the gap between the annular yoke and the shaft becomes smaller than before the destruction, and the coupling of the magnetic fluid with the shaft, etc. increases, resulting in an increase in the withstand pressure from the initial state.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is an internal structural diagram of a spindle motor of a magnetic disk device, in which three annular magnets 12 are sandwiched between four annular yokes 11, and the two inner diameters of the upper and lower annular yokes 11 are centered. Consisting of one piece smaller than the inner diameter,
Magnetic fluid seal bodies 7 are arranged above and below the spindle motor hub 1. As shown in FIG. 2, since the diameter of the upper shaft 9 is smaller than that of the lower side, the inner diameter of the upper and lower magnetic fluid seal bodies 7 is also smaller than that of the lower side.

The magnetic fluid seal body 7 is bonded to the spindle motor hub 1 via a non-magnetic material 8.

The inner diameter forms a magnetic circuit via the outer diameter of the shaft 9 and the magnetic fluid 13.

This allows it to function as a dustproof seal.

Here, to explain the initial state of the magnetic circuit consisting of the annular yoke 11, annular magnet 12, magnetic fluid 13, and spindle motor shaft 9, in the initial state,
The two central annular yokes of the four annular yokes llb
A magnetic fluid is injected into the core to form a magnetic circuit, which provides a dustproof function.

In this state, if the magnetic fluid flows out of the magnetic circuit in the initial state due to a temperature change or pressure change, the upper and lower annular yokes lla with small inner diameters act as outflow protection walls to prevent outflow to the outside and inside of the spindle motor hub.

The presence of the annular yoke as a protective wall is intended to trap the outflowing magnetic fluid through the gap between the inner diameter of the yoke and the outer diameter of the shaft, even under the worst conditions such as an explosive outflow of magnetic fluid. It is used to construct a magnetic circuit together with the captured magnetic fluid.

According to this embodiment, in addition to the dust-proof operation by the conventional magnetic circuit, the annular yoke lla with a small diameter at the top and bottom of the magnetic fluid seal body 7 prevents the magnetic fluid 13 from flowing out due to temperature changes, pressure changes, etc. operation is also possible, and is also effective in preventing damage to magnetic heads and magnetic disks resulting from leakage.

〔Effect of the invention〕

According to the present invention, it is effective to prevent the magnetic fluid from flowing out due to temperature changes and pressure changes.

Specifically, in the magnetic fluid that constitutes the magnetic circuit together with the annular yoke and annular magnet that constitute the magnetic fluid seal body, and the spindle motor shaft, the inner diameter of at least one of the annular yokes near the inside and outside of the spindle motor is reduced. In order to prevent the magnetic fluid from leaking to the outside and inside of the spindle motor hub from the initial magnetic circuit, and to separate the magnetic fluid caught in the worst case of leakage such as a magnetic fluid rupture, this magnetic circuit is It also has the effect of increasing the withstand voltage of the magnetic circuit.

[Brief explanation of the drawing]

FIG. 1 is a structural sectional view showing one embodiment of the present invention, and FIG. 2 is a sectional view of the magnetic fluid seal main body showing details of the present invention. 7... Magnetic fluid seal body, 8... Non-magnetic material, 9
... Spindle motor shaft, 11a... Annular yoke, llb... Annular yoke, 12
...To the annular magnet 1, 13...Magnetic fluid.

Claims (1)

[Claims] (1) In a magnetic disk drive having a dustproof mechanism for a spindle motor consisting of a spindle motor hub, a spindle motor shaft, an annular magnet, a magnetic fluid, etc., the inner diameter of at least one annular yoke among the annular yoke and the magnetic circuit of the annular magnet A magnetic disk device characterized by making it smaller.