JPS636823A - Manufacture of plastic magnet - Google Patents

Abstract

PURPOSE:To enhance the axial magnetic characteristic of a plastic magnet without loss of the radial magnetic characteristic of the magnet by disposing a conical ferromagnetic core and a ringlike ferromagnetic unit above a molding space to concentrate the leakage magnetic flux from the core at the ringlike ferromagnetic unit. CONSTITUTION:A metal mold is formed of a pole core 1 made or a conical ferromagnetic unit, a ringlike ferromagnetic unit 11 above a molding space 2, other ferromagnetic unit indicated by shaded part, and nonmagnetic units 4, 5, 6, and so composed that the magnetic flux induced by an electromagnet coil 3 becomes a magnetic path of direction of an arrow. Since the core 1 has a conical structure, the line of magnetic flux of the high magnetic force can be fed radially of the space 2, a leakage magnetic flux axially of the space from the core 1 can be easily generated by the unit 11, and the leakage magnetic flux is concentrated at the unit 11 to be axially disposed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a ring-shaped plastic magnet used in motors used in various electronic industrial equipment, and the magnet is shown in Fig. 1. As shown in the figure, the ring body has magnetic properties in two directions: the radial direction and the axial direction.

[Prior art]

Conventionally, in order to improve the accuracy of motor characteristics, a ring-shaped motor drive magnet with magnetic properties in the radial direction and a ring-shaped FG detection magnet with magnetic properties in the axial direction were separately manufactured, and the two The method used was to glue magnets together.

However, this method has the disadvantage that two magnets are required in advance, the number of parts increases, and an adhesion process is required, resulting in high manufacturing costs.

In addition, by using a mold structure that combines ferromagnetism and non-magnetism as shown in Figure 3, magnetic paths are created in the radial and axial directions, and lines of magnetic force are forced in the radial and axial directions when a magnetic field is applied. A method of integrally molding the driving magnet and the FG detection magnet by flowing them is also known.

However, with this method, a large number of magnetic lines of force enter the magnet in the axial direction due to the magnetic path created in the axial direction, so that sufficient lines of magnetic force do not flow in the radial direction within the magnet, and the ferromagnetic powder is uniformly distributed in the radial direction. Since the ferromagnetic powder cannot be oriented in the radial direction, the magnetic properties in the radial direction are lower than that when the ferromagnetic powder is oriented only in the radial direction.

[Object of the Invention] The present invention was developed as a result of research aimed at obtaining a plastic magnet that has sufficient magnetic properties for detecting rotation in the axial direction without deteriorating its magnetic properties in the radial direction. By concentrating the leakage magnetic flux from the circular ferromagnetic material of the mold onto the ring-shaped ferromagnetic material placed above the molding space,
We found that this can be obtained by orienting ferromagnetic powder in the axial direction, and based on this knowledge, we conducted further research and completed the present invention.

C) Structure of the Invention) The present invention involves injection molding a molding material containing ferromagnetic powder in a thermoplastic resin into a chitobite part of a mold placed in a magnetic field that can orient the ferromagnetic powder. When obtaining a ring-shaped magnet, in a mold that combines ferromagnetic and non-magnetic materials, a conical columnar ferromagnetic core is placed in one part of the mold, and a ring-shaped ferromagnetic material is placed above the molding space. This not only orients the ferromagnetic material in the radial direction of the magnet, but also concentrates the leakage magnetic flux from the conical columnar ferromagnetic core inside the mold, which occurs during the application of a magnetic field, on the ring-shaped ferromagnetic material. The present invention relates to a method for producing a plastic magnet characterized in that it has two easy magnetization directions in which ferromagnetic powder is oriented also in the direction perpendicular to the direction (hereinafter referred to as the axial direction).

The magnet according to the present invention is manufactured using a mold shown in FIG. This mold consists of a magnetic pole core 1 made of a conical columnar ferromagnetic material.
, a ring-shaped ferromagnetic material 11 above the molding space 2, and other ferromagnetic and non-magnetic materials 4,5,6 in the shaded area, and the magnetic flux induced by the electromagnetic coil 3 is directed in the direction of the arrow shown in the figure. It is configured to form a magnetic path of

This mold has a cylindrical structure of the ferromagnetic material 8 shown in the mold diagram of FIG. 4, which is used to have an axis of easy magnetization only in the radial direction since the ferromagnetic core 1 has a conical columnar structure. Compared to the ferromagnetic material 7 and the ring-shaped ferromagnetic material 11, it has the effect of concentrating and dispersing the magnetic flux read by the electromagnetic coil 3, and allows high magnetic flux lines to flow in the radial direction of the molding space 2. As the distance between
As a result, leakage magnetic flux from the ferromagnetic core 1 in the axial direction of the molding space is likely to occur, and by concentrating this leakage flux on the ring-shaped ferromagnetic body 11, the ferromagnetic powder is It can also be oriented in any direction. In the case of a mold structure without the ring-shaped ferromagnetic material 8, the leakage magnetic flux from the ferromagnetic core 1 of the conical column cannot be concentrated in the axial direction of the molding space 2, and the magnetic properties in the axial direction will decrease. Further, the taper angle α of the conical ferromagnetic material shown in FIG. 2 is preferably from 45° to 80'. If the taper angle α is 80' or more, the effect is almost the same as that of the cylindrical structure shown in FIG. 4, and the magnetic properties in the axial direction are deteriorated. Also, if the taper angle α is less than 45°, the second
Since the distance between the ferromagnetic material 7 and the ring-shaped ferromagnetic material 11 shown in the figure is too close, the leakage magnetic flux from the ferromagnetic material core 1 becomes too large. This results in a decrease in magnetic properties. The dimensions of the ring-shaped ferromagnetic body 8 are not particularly limited as long as the non-magnetic portion between the ferromagnetic body 8 and the conical column-shaped ferromagnetic body 1 is 1M or more. If the non-magnetic part between the ferromagnetic material 8 and the ferromagnetic material is less than 1M, the leakage magnetic flux will become too large and the mold (M
As with the structure, a large number of magnetic lines of force enter in the axial direction, reducing the magnetic properties in the radial direction.

[Effects of the Invention] According to the method of the present invention, it is possible to obtain a magnet that has sufficient magnetic properties for detecting rotation in the axial direction without damaging the magnetic properties in the radial direction of the magnet.Moreover, since it is molded as a negative body, it is easy to manufacture. The cost is also low and it is suitable as a method for manufacturing plastic magnets that have axes of easy magnetization in two directions.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a ring-shaped magnet with easy magnetization axes in two directions, Fig. 2 is a cross-sectional view of the mold structure used in the present invention, and Fig. 3 is a longitudinal cross-sectional view of a ring-shaped magnet with easy magnetization axes in two directions. FIG. 4 is a cross-sectional view of a mold conventionally used to provide an axis of easy magnetization only in the radial direction. The shaded area indicates the ferromagnetic material, and the arrow indicates the magnetic path. Patent Applicant: Sumitomo Bakelite Co., Ltd. 1st Ward 11 L-shaped 5-piece A + Plain wood 2nd drawing

Claims (1)

[Claims] When obtaining a ring-shaped magnet by injection molding a molding material containing ferromagnetic powder in a thermoplastic resin into the cavity of a mold placed in a magnetic field that can orient the ferromagnetic powder, In a mold that combines a magnetic material and a non-magnetic material, by arranging a conical column-shaped ferromagnetic core in one part and a ring-shaped ferromagnetic material above the molding space, the ferromagnetic material is placed in the radial direction of the magnet. In addition to orienting the powder, by concentrating the leakage magnetic flux from the conical column-shaped ferromagnetic core inside the mold into the ring-shaped ferromagnetic body, which is generated during the application of a magnetic field, ferromagnetism can be achieved in the radial and perpendicular directions as well. A method for producing a plastic magnet characterized by having two directions of easy magnetization in which body powder is oriented.