JPS63282974A - Case plate for magnetic shield - Google Patents

Abstract

PURPOSE:To make a magnetic shield characteristic compatible with a lightening in weight by providing a steel plate at a suitable position to the whole thickness of a case plate for the case plate used for a magnetic shield. CONSTITUTION:At the time of constituting a case plate for the magnetic shield of a plate thickness T to use the steel plate of a plate thickness (t), a part to exceed 50% of the thickness of T>1.5t and (T-t) is constituted so as to come to be the thickness of the outside of a steel plate (t). Namely, when the relation of the plate thickness (t) of the steel plate of the case plate of a plate thickness T to combine the steel plate of the plate thickness (t) and absubstance with a a low specific gravity such as a paper, plastic and other foaming substance and the plate thickness T of the case plate is made into suitable conditions, it is advantageous to a case for a magnetic shield. A magnetic flux density in a steel plate is about 1.8 gauss, and thus, when the upper limit is present and it is saturated, a magnetic field leaks even to the side opposite to the magnet. Consequently, the plate may be used in the magnetic field in the scope where a magnetic flux density is not saturated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a case plate used for magnetic shielding cases such as floppy disk cases and magnetic tape cases.

(Prior Art) Storage media using magnetism are widely used, such as floppy disks, magnetic tapes for computers, and compact disks. On the other hand, magnets have also permeated our lives as necklaces, clips, hunt hack caps, etc. In order to protect storage media from these external magnetisms, cases with magnetic shielding functions are becoming necessary, and some cases with magnetic shielding functions are now being seen.

(Invention or problem to be solved) Ferromagnetic materials such as Fe and Ni are used for magnetic shielding.

Is it necessary to use metal such as Go, and considering economic efficiency, F
We will think based on e. In order to improve magnetic shielding performance, it is necessary to increase the thickness of the steel plate. but,
Increasing the thickness of the steel plate increases the weight, making the case inconvenient to handle. In some cases, for example, for storage of computer tapes, the strength of the building must be increased.

(Means for Solving the Problems) The present invention provides a case plate that achieves both magnetic shielding properties and weight reduction. When configuring the case plate for magnetic shielding, T > 1.5t and (T-t)
This is a case plate for magnetic shielding characterized in that the thickness of the outside of the steel plate t exceeds 50% of the thickness of the steel plate t.

In other words, in a case plate with a thickness T, which is a combination of a steel plate with a thickness t and a material with low specific gravity such as paper, plastic, or other foam, the relationship between the thickness t of the steel plate and the thickness T of the case plate is determined appropriately. It was discovered that under these conditions, it is advantageous for case plates for magnetic shielding. There is an upper limit to the magnetic flux density that passes through the steel plate (approximately 1.8 Gauss), and when it reaches saturation, the magnetic field also leaks to the side opposite to the magnet. In the case of iron, we have therefore found that in order to fully demonstrate the shielding performance of steel plates, it is necessary to use them in a magnetic field within a range where the magnetic flux density is not saturated.

Figure 1 shows a Gauss meter 2 placed 2 mm+ away from a bar-shaped electromagnet 1, a steel plate 3 placed between them approximately 1.5 mm away from the magnet, and Gauss meter measurements by changing the magnetic force of the electromagnet. . The horizontal axis is the Gaussmeter measurement value when the plate is placed, and the vertical axis is the measurement value when the steel plate is not placed. This measurement also shows that the magnetic shielding effect is large when a magnetic force within the saturation magnetization range is applied.

It is well known that the strength of the magnetic field becomes weaker with increasing distance from the magnetic pole (however, this state of weakening varies greatly depending on the shape of the magnet).

Therefore, when building a case with a thickness T using a steel plate with a certain thickness t, it is advantageous to place the steel plate in a position far from the external magnetic field, that is, closer to the inside of the case. This point will be explained in detail using FIG. 2.

Figure 2 shows data showing this.When the steel plate is placed on the magnet side (700 Gauss button magnet) of a case plate with a thickness of about 3 mm (A type) and on the Gauss meter side (B type), the Gauss meter The difference in magnetic flux leaking to the sides is significant.

For example, in order to reduce the leakage magnetic flux to 50 Gauss or less, type A requires a steel plate with a thickness of 0.25 m+n, while type B requires a steel plate with a thickness of 0.19 mm to achieve the same effect. For comparison, this was constructed by stacking bare steel plates (t
= T), and in order to make the magnetic flux leaking to the opposite side of the magnet 50 Gauss, a thickness of 0.5 mm is required.

From this example, the combination of lightweight material and steel plate is T〉t,
By placing the steel plate in the appropriate position as described above, weight can be reduced.

(Example) A Gauss meter is placed 3 mm away from an industrial electromagnet (1300 gauss), and the distance (L) from the gauss meter to the 0.3 mm thick steel plate is changed. Figure 3 shows the measurement results of the magnetic flux. (
The parts other than the steel plate were layered with plastic to make a plate with a total thickness of 3 mm. That is, T-t=2.70 mm). As is clear from the figure, the closer the steel plate is to the Gauss meter, the smaller the leakage magnetic flux becomes, and it increases significantly when L exceeds 1.25 mm.

In other words, it is clear that the magnetic shielding effect will be better if the steel plate is placed on the side of the protector from magnetic force rather than at the center of the total plate thickness T, and more than 50% of (T-t) , preferably 60% or more, or on the side where external magnetism is applied.

(Effects of the Invention) According to the present invention, by providing the case plate for magnetic shielding with a steel plate at an appropriate position relative to the total thickness of the case plate,
It becomes possible to achieve both magnetic shielding properties and weight reduction, and the effect is extremely large.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the relationship between the strength of the magnetic field and the presence or absence of a steel plate, Figure 2 is an explanatory diagram showing the relationship between the thickness of the steel plate built into the case plate, the position of the steel plate, and the strength of the magnetic field. The figure is an explanatory diagram showing the distance from the Gaussmeter of the steel plate built into the case plate and the strength of the magnetic field.

Claims (1)

[Claims] When constructing a magnetic shielding case plate with a thickness T using a steel plate with a thickness t, T>1.5t and (T-t)
A case plate for a magnetic shield, characterized in that a portion exceeding 50% of the thickness of the steel plate t has a thickness outside the steel plate t.