JPS6354711A - Manufacture of plastic magnet - Google Patents

Abstract

PURPOSE:To obtain a method through which ferromagnetic body powder is dispersed uniformly and productivity is also improved, by using a mold undercut in the spool lock bush section and the disk gate section and a rotor yoke undercut in the outer circumference, when the rotor yoke is insert-molded through a disk gate system. CONSTITUTION:When a rotor yoke 1 is insert-molded through a disk gate system by employing a molding material in which ferromagnetic body powder is contained in a thermoplastic resin, a mold, undercut in the spool lock bush section 2 and the disk gate section 4 and a rotor yoke 1 undercut in the outer circumference of which are used. When the molding material into which ferromagnetic body powder is contained is filled through the disk gate system, and cooled for a fixed time and the mold is opened from a parting line, a spool section 3 is pulled in the direction of the arrow by the undercut of the spool lock bush section 2, and the disk gate section 4 is drawn in the direction of the arrow by the undercut of the disk gate section. Accordingly, a gate port 5 is cut by force working in two opposite directions, thus separating the disk gate section and a product section.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of manufacturing a plastic magnet, which performs insert molding of a rotor yoke using a disc gate method using a molding material containing ferromagnetic powder.

<Prior Art> Conventionally, in the manufacturing method of plastic magnets, side gate method, pinpoint gate method, etc. have been widely used because the mold structure is easy and productivity is high. However, if the plastic magnet obtained after molding is magnetized into multiple poles, the magnetic force in the gate and weld parts of the molded product will be disturbed, so it cannot be used in magnetic encoders etc. that require a high degree of magnetization accuracy. There wasn't. Furthermore, by using the disk gate method in which resin is filled from the inside of the inserted rotor yoke, it is possible to obtain a molded product in which ferromagnetic powder is uniformly dispersed without disturbance of magnetic force in the gate and weld areas after various magnetization. This is also known. However, when using the disc gate method, if the conventional mold structure shown in Fig. 3 is used, the molded product taken out from the mold after molding will have a disc gate part 7 and a product part as shown in Fig. 4. Since the parts 8 are integrated, post-processing is required to separate the disgate part 7 and the product part 8 as shown in Part 5, which has the disadvantage of extremely poor productivity and a significant increase in product cost. there were.

<Purpose of the Invention> The present invention uses a molding material containing ferromagnetic powder in a thermoplastic resin, and provides a method for separating the disk gate portion and the product portion when performing insert molding of a rotor yoke using the disk gate method. After careful consideration, we found that by providing undercuts on the outer periphery of the rotor yoke and part of the disc gate type mold, it will be possible to easily separate the disc gate part from the product part after molding without any post-processing. After obtaining this knowledge, we proceeded with various studies based on this knowledge and completed the present invention. The objective is to provide a method for manufacturing plastic magnets using a disk gate method, in which the ferromagnetic powder in the molded product is uniformly dispersed and the productivity is good.

<Structure of the Invention> The present invention provides undercuts in the sprue lock bushing portion and the disk gate portion when insert molding a rotor yoke using a disc gate method using a molding material containing ferromagnetic powder in a thermoplastic resin. The present invention relates to a method of manufacturing a plastic magnet characterized by using a mold having a rotor yoke provided with an undercant on its outer periphery.

The ferromagnetic powder used in the present invention is not limited in any way as long as it forms a permanent magnet, such as ferrite-based powders such as strontheim and barium, and rare earth-based powders.

Schematic diagrams of a rotor yoke with an undercut on its outer periphery and a mold used in the present invention are shown in FIGS. 1 and 2.

After filling the molding material containing ferromagnetic powder using the disk gate method and cooling it for a certain period of time, the mold is opened from the paring line, and the spool part 3 is formed by the undercut of the Sublu Rotta push part 20 as shown in Figure 2. The disk gate portion 4 is pulled in the direction of the arrow shown in FIG. 2 due to the undercant of the disk gate portion.

As a result, the gate opening 5 is cut by two forces acting in opposite directions, and the disk gate part and the product part are separated. If there is no undercut on the outer periphery of the rotor yoke, the adhesive force between the rotor yoke and the molding material will be weak, and the product part 6 will come off the rotor yoke due to the force generated by the undercut at the disk gate part.

The arrows shown in FIG. 2 indicate the direction of the force applied to the molding material when the mold begins to open at the parting line.

<Effects of the Invention> According to the present invention, when insert molding of the rotor yoke is performed using the disc gate method, it is possible to separate the disc gate part from the product part, which was a drawback of the disc gate method, without post-processing. This improves performance and reduces the cost of each product.

In addition, the resulting plastic magnets are uniformly filled with ferromagnetic powder using the disk gate method, so compared to conventional molded products using the side gate method or pinpoint gate method.
When the θ1 stone is multipolarized, the magnetic force becomes uniform, and this method is suitable as an industrial method for manufacturing plastic magnets.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a rotor yoke with an undercut on its outer periphery. FIG. 2 is a schematic sectional view of a mold having a disk gate type structure according to the present invention. FIG. 3 is a schematic cross-sectional view of a mold having a conventionally used disk gate type structure. Figure 4 is a cross-sectional view of a plastic (one stone) in which the disc gate part and the product part are integrated, taken out from a mold with a conventional disc gate structure. Figure 5 is a cross-sectional view of the disc gate part and the product part. FIG.

Claims (1)

[Claims] When insert molding a rotor yoke using a disc gate method using a molding material containing ferromagnetic powder in a thermoplastic resin, a mold with undercuts in the spool lock push part and disc gate part and an undercut on the outer periphery are used. A method of manufacturing a plastic magnet characterized by using a rotor yoke provided with cuts.