JPH04245609A - Method for manufacturing synthetic resin magnet with shaft - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention relates to a synthetic resin magnet equipped with a shaft, which is applied to, for example, a rotor of a high-torque motor or an FG magnet for speed control with little reading error. Concerning an advantageous manufacturing method. [0002] This type of synthetic resin magnet is usually molded by injection molding, and a runner is used to guide the molten material for the synthetic resin magnet (hereinafter simply referred to as molten material) from an injection molding machine into a cavity. There are heated hot runners and cold runners that are not heated. With cold runners, the molten material is heated and melted in advance in the injection molding machine, and as it reaches the cavity, it is cooled and its viscosity increases, making it difficult to control the orientation of the magnetic particles in the molten material within the cavity. , it is not possible to obtain a synthetic resin magnet with excellent magnetic properties. Furthermore, spool runners are generated, and if they are discarded, it will be disadvantageous in terms of cost, while if they are recycled, the quality and performance of the obtained magnet will inevitably deteriorate. On the other hand, when a hot runner is used, the molten material is sent into the cavity without being cooled, making it easy to control the orientation of the magnetic particles in the molten material within the cavity. It is possible to obtain magnets. [0003] The molten material is supplied from the hot runner through a nozzle that moves forward and backward into the cavity, and this nozzle is disclosed in, for example, Japanese Patent Application Laid-open Nos. 61-214411 and 61-214411.
A so-called pinpoint gate method, in which the molten material passes through a tapered gate, as shown in Japanese Patent Nos. 1-248406 and 62-30305, is often used. [0004] However, in the pinpoint gate type hot runner, the gate is often exposed to the atmosphere, so cold slag is likely to be generated.
If this cold slag enters the cavity together with the molten material and mixes into the magnet action section, it causes a partial decrease or variation in the degree of orientation of the magnetic particles, causing a decrease or variation in the surface magnetic field. Additionally, when pouring the molten material into the cavity, if the hot runner nozzle is located close to the inner wall of the cavity, so-called weld marks (joint parts of the semi-molten composition) will occur, which will also cause a drop or variation in the surface magnetic field. cause. These problems can be solved by supplying the molten material to the center of the cavity, or if the cavity is cylindrical, on its central axis. However, most of the synthetic resin magnets equipped with shafts for the above-mentioned applications have a shaft passed through the central axis of a cylindrical magnet, and it is extremely difficult to supply the molten material to the center of the cavity. [0005] Therefore, the present invention aims to advantageously produce a synthetic resin magnet with a shaft having excellent magnetic properties by opening a method for supplying molten material to the center of a cavity via a hot runner. [Means for Solving the Problems] This invention provides the following advantages: When molding a synthetic resin magnet integrally with a shaft by injection molding,
When introducing the molten material for synthetic resin magnet into the cavity from the nozzle provided at the tip of the hot runner that advances and retreats with respect to the cavity, the tip of the shaft to be fixed in the cavity is placed in advance so as to protrude from the cavity, and the axis of the shaft is The tip of the shaft is inserted into the gate of the nozzle advanced in a line, the gate valve is opened at the head of the shaft, and the molten material for the synthetic resin magnet is introduced from the gate into the cavity through the shaft. This is a method for manufacturing a synthetic resin magnet having a shaft that FIG. 1 shows a hot runner directly used in the present invention. In the figure, 1 is an injection molding machine nozzle, and a runner 4 is connected to this nozzle 1 via an injection port 2 and a sprue 3. The nozzle 5 provided at the tip of the runner 4 has an inner diameter narrowing into a truncated conical shape toward the gate 6, and extends at a constant inner diameter to reach the opening. Note that the diameter of the gate 6 needs to be larger than the diameter of the shaft attached to the magnet to be molded. Furthermore, a valve 7 made of a combination of a cylinder and a truncated cone is disposed inside the nozzle 5, and this valve 7 is constantly pushed toward the gate 6 by, for example, a spring (not shown) or the supply pressure of the molten material. It plays the role of blocking 6. On the other hand, the cavity 9 to which the molten material 8 from the hot runner is supplied is, for example, in the case of molding a magnet for a motor rotor, formed in the shape of a cylinder with a smaller diameter arranged inside the cylinder, and the center axis of the cylinder. Fix the shaft 10 to. Here, it is important that the shaft 10 is disposed so as to protrude at least the axial length of the gate 6 toward the side of the cavity 8 where the hot runner is disposed. The molten material 8 is supplied by first moving a hot runner along the axis of the shaft 10, as shown in FIG. 2(a). As a result of this movement, the tip of the shaft 10 protruding from the cavity 9 is inserted into the gate 6 of the nozzle 5 as shown in FIG. When the shaft 10 moves until it contacts the surface of the cavity 9, the head of the shaft 10 pushes up the valve 7, and the gate 6 is opened. Molten material 8 flows out from the opened gate 6 and is introduced into the cavity 9 along the shaft 10. [0009] Reference numeral 11 denotes a heater, and although the illustrated hot runner is of an external heating type, an internal heating type may also be used. In addition, known mold materials can be used for the hot runner and cavity, preferably materials with excellent wear resistance such as cemented carbide steel or die steel. , copper-beryllium alloy, stainless steel, high manganese steel, non-magnetic carbide steel, etc. are suitable. [0010] As the magnetic powder in the synthetic resin magnet according to the present invention, any conventionally known magnetic powder may be used, such as ferrite magnetic powder, alnico magnetic powder, and rare earth magnetic powder such as samarium-cobalt magnetic powder or neodymium-iron-boron magnetic powder. can be used, and its particle shape has an average particle size of 1
．． A thickness of about 5 μm is preferable. [0011] As for the synthetic resin, any conventionally known synthetic resin can be used, and representative examples thereof are as follows. Polyamide-based synthetic resins such as polyamide-6 and polyamide-12. Single or copolymerized vinyl-based synthetic resins such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polymethyl methacrylate, polystyrene, polyethylene, and polypropylene. Synthetic resins such as polyurethane, silicone, polycarbonate, PBT, PET, polyetheretherketone, chlorinated polyethylene and Hypalon. Rubbers such as propylene, neoprene, styrene butadiene and acrylonitrile butadiene. Epoxy resin. Phenolic synthetic resin. [0012] Furthermore, it is desirable that the mixing ratio of the magnetic powder and the synthetic resin as the binder is approximately 90% magnetic powder to 10% synthetic resin. In addition, it goes without saying that conventionally used plasticizers, antioxidants, surface treatment agents, etc. can be used in appropriate amounts depending on the purpose. [Operation] Even if it is necessary to introduce the molten material into the cavity after placing the shaft in the center of the cavity, the molten material can be guided into the cavity along the shaft as described above. This makes it possible to feed the molten material to the center of the cavity. Therefore, the supply of molten material to the vicinity of the inner wall of the cavity can be avoided, so weld marks can be prevented, and even if cold slag inevitably gets mixed in, the slag remains around the shaft without affecting the magnet action section. [Example] Using the hot runner A shown in FIG. 1, the synthetic resin magnet for rotor shown in FIG.
It was manufactured using molds A and B under the following conditions. For comparison, similar synthetic resin magnets for rotors were manufactured using the above-mentioned pinpoint gate type hot runner B and cold runner under the same conditions as described below. In FIGS. 4 and 5, reference numeral 12 denotes an ejector rod that pushes out the molded magnet from the cavity 9, 13 an ejector plate that pushes the ejector rod 12, and 14 an ejector pin that pushes the ejector plate 13. The mold shown in FIG. 4 is made entirely of ferromagnetic material and the orientation of the magnetic particles is controlled by an excitation coil (not shown), while the mold shown in FIG. 15 to control the orientation of the magnetic particles. (1) Ferrite magnetic powder mixed with melting agent (average particle size 1.5 μm): 66
vol% polyamide 12:33 vol% isopropyl triisostearoyl titanate: 1vo
l % (2) Molding conditions Mold temperature: 100°C Injection cylinder temperature: 300°C Injection pressure: 1.8 tons/cm2 [0016] The results of investigating the magnetic properties of each synthetic resin magnet thus obtained are shown in the table below. Shown in 1. [0017] As shown in the same table, the magnet obtained according to the present invention had a high surface magnetic field and no weld marks were observed, but in the comparative example, the molten material was placed in the cavity. Since it was forced to supply the material off-center, the surface magnetic field was low and weld marks were observed. [0019] According to the present invention, even when manufacturing a magnet having a shaft on its central axis, such as a rotor magnet, the molten material can be supplied to the center of the cavity through the hot runner. Therefore, the intrusion of foreign matter into the working part and the generation of weld marks due to the supply of molten material at an eccentric position of the cavity are avoided, and a synthetic resin magnet with a high and uniform surface magnetic field can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a hot runner used in the present invention.

FIG. 2 is a schematic diagram showing a procedure for supplying molten material from a hot runner.

FIG. 3 is a schematic diagram showing a rotor magnet.

FIG. 4 is a schematic diagram showing a mold for molding a magnet.

FIG. 5 is a schematic diagram showing a mold for molding a magnet.

[Explanation of symbols]

1 Injection molding machine nozzle 2 Inlet 3 Sprue 4 Runner 5 Nozzle 6 Gate 7 Valve 8 Melting material 9 Cavity 10 Shaft 11 Heater 12. Protruding rod 13　Protruding plate 14 Ejection pin 15 Permanent magnet

Claims (1)

[Claims] Claim 1: When molding a synthetic resin magnet integrally with a shaft by injection molding, a molten material for the synthetic resin magnet is guided into the cavity from a nozzle provided at the tip of a hot runner that moves forward and backward into the cavity. The tip of a shaft to be fixed in advance in the cavity is arranged so as to protrude from the cavity, the tip of the shaft is inserted into the gate of a nozzle advanced on the axis of the shaft, and the gate valve is opened at the head of the shaft, A method for manufacturing a synthetic resin magnet equipped with a shaft, characterized by introducing a molten material for a synthetic resin magnet into a cavity from a gate through the shaft.