JPH0727832B2 - Manufacturing method for plastic magnets - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a plastic magnet in which a rotor yoke is insert-molded by a disc gate method using a molding material containing a ferromagnetic powder.

<Prior Art> Conventionally, in a method of manufacturing a plastic magnet, a side gate method, a pinpoint gate method, and the like have been widely used because of easy mold structure and high productivity. However, if the plastic magnet obtained after molding is magnetized into multiple poles, the magnetic force of the gate and weld parts of the molded product will be disturbed, and it cannot be used for magnetic encoders that require a high degree of magnetization accuracy. There wasn't. In addition, by using the disk gate method in which resin is filled from the inside of the inserted rotor yoke, after multi-pole magnetization, there is obtained a molded product in which ferromagnetic powder is uniformly dispersed without disturbing the magnetic force in the gate part and the weld part. It is also known to be. However, in the case of the disc gate method, if the conventionally used mold structure as shown in FIG. 3 is used, the molded product taken out from the mold after molding is, as shown in FIG. Since 8 is integrated, post-processing is required to separate the disassembling part 7 and the product part 8 as shown in FIG. 5, which results in extremely poor productivity and a large increase in product cost. there were.

<Purpose of the Invention> The present invention provides a method for separating a disc gate portion and a product portion when insert molding of a rotor yoke is performed by a disc gate method using a molding material containing a ferromagnetic powder in a thermoplastic resin. As a result of intensive studies, it is possible to easily separate the disk gate part and the product part without post-processing after molding by providing an undercut on the outer peripheral part of the rotor yoke and a part of the disk gate type mold. The present invention has been completed by obtaining knowledge and further conducting various researches based on this knowledge. The object is a method for producing a plastic magnet by a disc gate method, in which the dispersion of the ferromagnetic powder in the molded product is uniform and the productivity is good.

<Structure of the Invention> When the rotor yoke insert molding is performed by the disc gate method using the molding material in which the ferromagnetic powder is contained in the thermoplastic resin, the sprue lock bush portion and the disc gate portion are undercut. The present invention relates to a method for manufacturing a plastic magnet, characterized by using a provided die and a rotor yoke having an undercut provided on the outer periphery.

The ferromagnetic powder used in the present invention is not limited as long as it is a permanent magnet such as strontium, barium or other ferrite-based or rare earth-based permanent magnet.

A schematic view of a rotor yoke having an undercut provided on its outer periphery and a mold used in the present invention is shown in FIGS.

When the mold is opened from the padding line after filling the molding material containing the ferromagnetic powder by the disc gate method and cooling it for a certain time, the spool portion 3 is shown in FIG. 2 due to the undercut of the sprue lock bush portion 2. The disc gate portion 4 is pulled in the direction of the arrow, and the disc gate portion 4 is pulled in the direction of the arrow shown in FIG. 2 due to the undercut of the disc gate portion.

As a result, the gate opening 5 separates the disc gate portion and the product portion, which are cut by the forces acting in two opposite directions. Here, if there is no undercut on the outer periphery of the rotor yoke, the adhesive force between the rotor yoke and the molding material is weakened, and the product portion 6 is displaced from the rotor yoke due to the force generated by the undercut of the disc gate portion.

The arrow shown in FIG. 2 indicates the direction of the force applied to the molding material when the mold begins to open on the parting line.

<Effects of the Invention> According to the present invention, when the insert molding of the rotor yoke is performed by using the disc gate method, the disc gate portion and the product portion, which are the drawbacks of the disc gate method, can be separated without post-processing. It is possible to improve the productivity and reduce the cost of the product unit.

In addition, the obtained plastic magnet is filled uniformly with the ferromagnetic powder by the disk gate method, so compared to the conventional side gate method or pinpoint gate method molded product.
The magnetic force becomes uniform when the magnet has multiple poles, which is suitable as an industrial plastic magnet manufacturing method.

[Brief description of drawings]

FIG. 1 is a sectional view of a rotor yoke using an undercut on the outer circumference. FIG. 2 is a schematic cross-sectional view of a mold having a disc gate type structure of the present invention. FIG. 3 is a schematic cross-sectional view of a mold having a disk gate type structure which has been conventionally used. FIG. 4 is a cross-sectional view of a plastic magnet in which a disc gate portion and a product portion, which are taken out from a mold having a conventional disc gate system structure, are integrated. FIG. 5 is a sectional view showing a state in which the disc gate portion and the product portion are separated.

Claims (1)

[Claims] Claim: What is claimed is: 1. Gold for which an undercut is provided in the spool lock bush portion and the disc gate portion when insert molding of the rotor yoke is performed by the disc gate method using a molding material in which a ferromagnetic powder is contained in a thermoplastic resin. A method of manufacturing a plastic magnet, characterized in that a rotor yoke having an undercut provided on a mold and an outer periphery thereof is used.