JPH01275116A - Manufacturing device for rotary plastic magnet - Google Patents

Abstract

PURPOSE:To reduce production cost, while the gate mark treatment after molding is unnecessary by a method in which the three-plate mold of a pin gate type is used, and the pin gate is formed on the end face of a columnlike rotary plastic magnet. CONSTITUTION:A three-plate mold 1 has two templates 11, 12 forming the parting face 1a of the mold and one runner stripper-plate 13 forming a runner- removing face 1b, and then upon each mold opening, the runner-removing face 1b is opened and the runner is removed. On the template 12, two pin gates 16 injecting raw material into each cavity 111 from the runner 15, are formed in the part of the template 12 forming the end face of a rotary plastic magnet. The pin gate 16 is connected to the cavity 111 at its small point, and the runner may be easily teared off from a molded object by opening the mold, and its gate mark is small. Accordingly, the demagnetization and remagnetization for carrying out gate-cutting treatment and gate mark treatment become unnecessary, and a product is obtained immediately after it has been molded and discharged.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a rotating plastic magnet manufacturing apparatus suitable for manufacturing flat cylindrical rotating plastic magnets used as instrument rotors, for example. be.

(Prior Art) Conventionally, in order to detect or indicate the rotation speed according to the vehicle speed and the engine rotation speed, vehicle instruments have a rotating shaft centered on a rotation axis a as shown in FIG. A rotating plastic magnet b is used in which the north and south poles are magnetized in one direction perpendicular to the rotation axis a.The surface magnetic flux density distribution of the outer peripheral surface of this rotating plastic magnet b is shown in Figure 5. As shown, characteristics that vary sinusoidally with the rotation angle are required.

Conventionally, an apparatus having the configuration shown in FIG. 6 has been used to manufacture such rotating plastic magnets.

That is, a plastic magnet raw material A having a plastic matrix is injected from an injection device B into a plurality of cavities E through a sprue runner D of a two-plate side gate type mold C, and A yoke F wound with a coil (not shown) that generates the necessary magnetic field is arranged so as to sandwich the mold C on a line along the line ′.
As shown in FIG. 7, a magnetic field is applied to the raw material in the cavity E from one direction by the yoke F, and the magnetic powder in the raw material is oriented and magnetized in one direction.

[Problem to be solved by the invention]

As mentioned above, in conventional equipment, the mold has a side gate configuration with two plates, so gate marks remain on the outer circumferential surface of the plastic magnet, which disturbs the surface magnetic flux density distribution of the plastic magnet and prevents the desired prevents obtaining the characteristics of

Therefore, when this is used as an instrument rotor, necessary characteristics cannot be obtained, and therefore, it is necessary to perform deburring treatment after the gate cutting process. In addition, if the plastic magnet is magnetized when processing this gate mark, small pieces generated by the gate mark processing will be attracted to the main body, so it should be demagnetized before gate processing and re-magnetized after gate processing. It is necessary to perform processing. As described above, conventional manufacturing equipment requires many troublesome processes after molding, leading to an increase in production costs.

Therefore, an object of the present invention is to provide an apparatus for manufacturing a rotating plastic magnet that does not require troublesome processing after molding.

[Means for Solving the Problems] In order to solve the above problems, a rotating plastic magnet manufacturing apparatus according to the present invention uses an injection device to inject a plastic magnet raw material having a synthetic resin matrix and containing magnetic powder into a mold. This method produces a cylindrical rotating plastic magnet that is magnetized in the diametrical direction by injecting the magnetic powder into a magnetic field and molding it in a magnetic field that has the ability to orient and magnetize the magnetic powder.The mold is used to form a plurality of cavities. a three-plate mold having two template plates and one runner stripper plate, and a pin gate in which a gate for pouring plastic magnet raw material into the cavity is connected to a template plate forming one end surface of the plastic magnet. It is characterized by being constructed by.

[For production]

In the device configured as described above, the pin gate is connected to one of the two templates of the three-plate mold that molds one end face of the cylindrical rotating plastic magnet, so the gate is automatically cut when the mold is opened. Moreover, the gate marks left by the cut are extremely small. Therefore, there is no need to perform gate cutting or gate trace treatment after molding, and there is no need to demagnetize or re-magnetize the molded rotating plastic magnet, resulting in better magnetic properties and a significant reduction in production costs. It is possible to reduce the

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a rotating plastic magnet manufacturing apparatus according to the present invention will be described based on the drawings.

FIG. 1 is a partially cutaway view showing one embodiment of the present invention. In the figure, 1 is a three-plate mold as an injection mold, and the mold 1 has two templates 11 and 12 forming a mold dividing surface 1a, and 1 forming a runner extraction surface 1b. Each time the mold is opened, the runner removal surface 1b is opened to take out the runner. Mounting plates 11a and 13a are attached to the mold plate 11 and runner stripper plate 13 of the mold 1, respectively, for attaching the mold l to a molding machine (not shown).

A plurality of cavities 111 are formed at a predetermined thickness from the mold dividing surface 1a of the template 11 to form the outer peripheral surface and one end surface of the flat cylindrical rotating plastic magnet to be manufactured. In addition, a sprue 14 is provided in the mounting plate 13a and the runner stripper plate 13 through the center thereof to allow the raw material to flow in, and a sprue 14 is provided along the abutting surface between the runner stripper plate 13 and the template 12. A runner 15 for flowing the raw material is further connected to the template 1.
A pin gate 16 for injecting raw material from a runner 15 into each cavity 111 is formed in each of the holes 2 and 2.

Two pin gates 16 are formed on the part of the template 12 that forms the end face of the rotating plastic magnet, and their positions are 0.5r to 0 from the center of rotation of the rotating plastic magnet.
．． It is preferably provided at 8r (r: radius). Since such a pin gate 16 is connected to the cavity 111 at a small point, the runner can be easily torn off from the molded product by opening the mold, and the gate mark is small and unnoticeable.

Reference numeral 2 denotes an injection device for injecting the raw material of the plastic magnet into a mold, and a specific example will be described later.

Reference numeral 3 denotes a yoke around which a coil (not shown) for generating a magnetic field is wound, and is arranged so as to sandwich the mold 1 on a line along the dividing surface 1a of the mold 1. The magnetic field generated by the yoke 3 is applied to the raw material in the cavity 111 from one direction, and the magnetic powder in the raw material is oriented in one direction and becomes E11.

In the above configuration, a plastic magnet having a synthetic resin matrix and containing magnetic powder such as ferrite, rare earth, etc. is inserted into the cavity 111 through the sprue 14, runner 15, and pin gate 16 of the mold in the closed state of the injection device 2. When the raw material is injected, cavity 1
The magnetic flux flowing through the cavity 111 causes the raw magnetic powder in the cavity 111 to be oriented and magnetized in the direction of the magnetic flux.

Once the plastic magnet raw material injected into the cavity 111 has solidified, the mold is opened by a drive mechanism (not shown), and the spool runner is torn off at the pin gate and is cut, moving together with the mold plate 12.
The rotating plastic magnet molded into the cavity of No. 1 remains. The rotating plastic magnet inside the cavity is ejected from the cavity by an ejector bin by moving an ejector plate (not shown).

The rotating plastic magnet molded as described above and discharged from the cavity is magnetized in the diametrical direction, and a small gate mark remains on one end surface. Therefore,
There is no need for demagnetization or re-magnetization to perform gate cut processing or gate trace treatment after molding (it can be used as a product immediately after molding and discharge).

Although not shown in the figure, the template 12 and the runner stripper plate 13 are connected to the runner extraction surface 1b between them.
This allows the sprue runner to be removed from the template 12.

Further, the method of magnetic field orientation is not limited to the above-mentioned example, and an appropriate method may be used depending on the arrangement of the cavities and the like.

FIGS. 2 and 3 show a specific example of the injection device 2 preferably used in the embodiment described above. The apparatus shown in FIG. 2 includes a backflow IJ type check valve 24 provided on a screw head 23 of a screw 22 that rotates and reciprocates within a cylinder 21. The check valve 24 is used to prevent part of the raw material from flowing backward through the screw groove due to the reaction force of the injection force applied to the raw material when the raw material is injected from the nozzle. The outline of the operation will be explained with reference to the drawings. During metering, as the screw 22 rotates and retreats as shown in FIG. 2(a), the raw material is sent forward through the gap between the screws 22. During injection, as shown in FIG. 2(b), the valve 24 is pushed backward by the reaction force of the raw material and comes into close contact with the valve seat 25 on the screw 22 side, closing the gap and preventing backflow of the raw material.

The apparatus shown in FIG. 3 shows an example in which a pole check type non-return valve 26 is provided in the screw head 23, and the ball valve 26 is moved within a groove 23a formed in the screw head 23 to perform valve operation.

The above-described injection device 2 uses a pin gate 16, so in the above-described embodiment where it is necessary to apply a large injection force to the raw material with high viscosity and low fluidity, it prevents the raw material from flowing backward due to the reaction force of the injection force. Since the injection force can be ensured, the filling variation has been reduced to one major problem.
This is effective because molding quality and magnetic properties are improved and productivity is also improved.

Diameter 12III manufactured by injection molding of 53g per shot using the above-mentioned manufacturing equipment using a plastic magnet raw material containing 12-nylon as a matrix and mainly containing 89% by weight of strontium ferrite.
The evaluation results of a rotating plastic magnet of I11 and thickness of 3 m [Il] are shown in the table below in comparison with those manufactured using conventional equipment.

In addition, although the above-mentioned embodiment does not mention the rotating shaft of the rotating plastic magnet, the rotating shaft can be attached by insert molding.

〔effect〕

As explained above, according to the present invention, a pin gate type three-plate mold is used, and pin gate marks are formed on the end face of a cylindrical rotating plastic magnet. It does not disturb the density distribution characteristics, eliminates the need for gate cut treatment and gate trace treatment after molding, and also eliminates the need for detachment and re-magnetization treatment. Therefore, productivity is improved and production costs can be significantly reduced.

In particular, since the injection device uses a screw injection device with a scree head with a backflow prevention valve, it is possible to prevent material from flowing back during injection even if the injection force increases due to the use of a pin gate. By ensuring the sufficient amount, the variation in the filling of raw materials within the cavity can be significantly improved, thereby improving molding quality and magnetic properties.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway view showing one embodiment of the apparatus of the present invention, FIGS. 2 and 3 are cross-sectional views each showing a preferred example of the injection device, and FIG. 4 is a rotating body produced by the apparatus of the present invention. FIG. 5 is a waveform diagram showing the ideal waveform of the surface magnetic flux density distribution characteristics of the rotating plastic magnet shown in FIG. 4. FIGS. 6 and 7 are cross-sectional views and diagrams showing an example of a conventional device. FIG. ■... Mold, 1a... Mold dividing surface, 1b... Runner extraction surface, 11, 12... Mold plate, 13... Runner stripper plate, 111... Cavity, 16
... bin gate, 2 ... injection device, 24 ... backflow type backflow prevention valve, 26 ... ball check type backflow prevention valve, 3 ... magnetic field generation coil. Figure 1 Figure 3 (G) Figure 2 Figure 4 Figure 5

Claims (2)

[Claims] (1) An injection device injects a plastic magnet raw material with a synthetic resin matrix and magnetic powder into a mold, and molds it in a magnetic field that has the ability to orient and magnetize the magnetic powder. In an apparatus for manufacturing a magnetized rotating plastic magnet, the mold is divided into two templates forming a plurality of cavities and one
A three-plate mold having two runner stripper plates, and a gate for pouring the plastic magnet raw material into the cavity is a pin gate connected to a template forming one end surface of the plastic magnet. Manufacturing equipment for rotating plastic magnets. (2) The rotating plastic magnet manufacturing apparatus according to claim 1, wherein the injection device is a screw injection device having a screw head with a check valve.