JPH0511739B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a rotating plastic magnet manufacturing apparatus suitable for manufacturing a flat cylindrical rotating plastic magnet used, for example, as an instrument rotor. [Prior Art] Conventionally, vehicle instruments have been equipped with a system for detecting or indicating the rotational speed according to the vehicle speed and engine rotational speed.
As shown in FIG. 4, a rotating plastic magnet b is used which has an axis of rotation a as its center and has north and south poles magnetized in one direction perpendicular to the axis of rotation a. This rotating plastic magnet b has
A characteristic is required in which the surface magnetic flux density distribution on the outer circumferential surface changes sinusoidally with respect to the rotation angle, as shown in FIG. Conventionally, an apparatus having the configuration shown in FIG. 6 has been used to manufacture such rotating plastic magnets. That is, plastic magnet raw material A having plastic as a matrix is transferred from injection device B to multiple cavities E through sprue runner D of a two-plate side gate type mold C.
A yoke F is provided, which is wound with a coil (not shown) that generates a necessary magnetic field so as to sandwich the mold C on a line along the dividing plane C' of the mold C. Therefore, a magnetic field is applied to the raw material in the cavity E from one direction as shown in FIG. 7, and the magnetic powder in the raw material is oriented and magnetized in one direction. [Problems to be Solved by the Invention] As mentioned above, in the conventional device, the mold has a two-plate side gate configuration, so gate marks remain on the outer circumferential surface of the plastic magnet. This disturbs the surface magnetic flux density distribution of the net and prevents desired characteristics from being obtained.
Therefore, when this is used as an instrument rotor, the 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 the gate marks, small pieces generated by the gate mark processing will be attracted to the main body, so it must be demagnetized before the gate processing, and It is necessary to perform re-magnetization processing. As described above, conventional manufacturing equipment requires many troublesome processes after molding, leading to an increase in production costs. A plastic magnet raw material with a synthetic resin matrix and magnetic powder is injected into a mold, molded in a magnetic field that has the ability to orient and magnetize the magnetic powder, and the NS poles are magnetized in the diametrical direction. An object of the present invention is to provide a rotating plastic magnet manufacturing apparatus capable of manufacturing a cylindrical rotating plastic magnet without requiring troublesome treatment of molding marks. [Means for Solving the Problems] In order to solve the above problems, the rotating plastic magnet manufacturing apparatus according to the present invention uses an injection device to produce a raw material for plastic magnets having a synthetic resin matrix and containing magnetic powder. In an apparatus for manufacturing a cylindrical rotating plastic magnet having NS poles magnetized in the diametrical direction by injecting it into a mold and molding it in a magnetic field that has the ability to orient and magnetize magnetic powder, the mold The mold is composed of a three-plate mold having two mold plates forming a plurality of cavities and one runner stripper plate, and a gate for pouring the plastic magnet raw material into the cavities is connected to one side of the rotating plastic magnet. The injection device is constituted by two pin gates connected to a template forming an end face and each located at the same radius from the center of rotation of the rotating plastic magnet, and the injection device is a screw having a screw head with a non-return valve. It is characterized by being constructed with an injection device. [Function] In the apparatus having the above-mentioned configuration, since 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, the pin gate is The gate is automatically cut and the gate mark left by the cut is extremely small. Therefore, there is no need to perform gate cut treatment or gate trace treatment after molding, and there is no need to demagnetize or re-magnetize the molded rotating plastic magnet, resulting in good magnetic properties and a significant reduction in production costs. It is possible to achieve significant reductions. In particular, the gate for pouring the plastic magnet raw material into the cavity is composed of two pin gates, each located at the same radius from the rotation center of the rotating plastic magnet.
If the two pin gates are placed on the same diameter in the magnetizing direction, the pin gate marks will be at symmetrical positions along the magnetizing direction, and the influence on the magnetic properties of the rotating plastic magnet will be minimized. . Further, since the injection device is constituted by a screw injection device having a screw head with a backflow prevention valve, backflow of the raw material can be prevented even if the injection force becomes large due to the use of a pin gate. [Example] Hereinafter, an example of a rotating plastic magnet manufacturing apparatus according to the present invention will be described with reference to 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 a mold dividing surface 1a.
It has two template plates 11 and 12 forming a runner and one runner stripper plate 13 forming a runner removal surface 1b, and the runner removal surface 1b is opened every time the mold is opened to take out the runner. It's getting old. The mold plate 11 and runner stripper plate 13 of the mold 1 are mounting plates 11a and 13a for attaching the mold 1 to a molding machine (not shown).
are attached to each. 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. Furthermore, a sprue 14 is provided through the center of the mounting plate 13a and the runner stripper plate 13 for introducing the raw material into the mounting plate 13a. A runner 15 for flowing the raw material along the surface is further provided in the mold plate 12 from the runner 15 to each cavity 11.
A pin gate 16 for injecting raw material into each of the holes 1 and 1 is formed. The pin gate 16 is connected to a template 1 forming the end face of the rotating plastic magnet, as shown in FIG.
2, two opposing yokes 3 are formed on a straight line along the direction of magnetization by the generated magnetic field, and their positions are 0.5r to 0.8r (r: radius) from the center of rotation of the rotating plastic magnet. Preferably provided. 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 will be small and unnoticeable.
The gate traces are arranged symmetrically along the direction of magnetization so that their influence on the magnetic properties of the rotating plastic magnet is minimized. Reference numeral 2 denotes an injection device for injecting raw materials for plastic magnets 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 and magnetized in one direction. In the above configuration, a plastic mag having a synthetic resin matrix and containing magnetic powder such as ferrite or rare earth metal is supplied from the injection device 2 through the sprue 14, runner 15 and pin gate 16 of the closed mold into the cavity 111. When the net raw material is injected, the magnetic flux flowing through the cavity 111 causes the magnetic powder of the raw material 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, cut, and moves together with the mold plate 12, and is moved inside the cavity of the mold plate 11. The rotating plastic magnet molded into the material remains. The rotating plastic magnet within the cavity is ejected from the cavity by an ejector pin by moving an ejector plate (not shown). The rotating plastic magnet molded as described above and discharged from the cavity is diametrically magnetized, and a small gate mark remains on one end face. Therefore, after molding, gate cut processing,
There is no need for demagnetization and re-magnetization to remove gate marks, and the product can be used immediately after molding and discharge. Although not shown in the figure, the template 12 and the runner stripper plate 13 are separated by the runner removal surface 1b between them, so that the sprue runner can be removed from the template 12. Become. 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 cavity 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 screw head 23 of a screw 22 that rotates and reciprocates within a cylinder 21 and is provided with a backflow type check valve 24. The check valve 24 is used to prevent a 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 figures. During metering, as the screw 22 rotates and retreats as shown in FIG. 2a, the raw material is sent forward through the gap between the screws 22. During injection, as shown in FIG. 2b, the valve 24 is pushed rearward 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 device shown in FIG. 3 shows an example in which a ball check type check valve 26 is provided in the screw head 23.
Valve operation is performed by moving the ball valve 26 within a groove 23a formed in the screw head 23. 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, filling variations can be significantly improved, molding quality and magnetic properties can be improved accordingly, and productivity can also be improved, which is effective. The above-mentioned production equipment uses 12-nylon as a matrix and mainly contains strontium ferrite.
The evaluation results of a rotating plastic magnet with a diameter of 12 mm and a thickness of 3 mm manufactured by injection molding of 53 g per shot using a plastic magnet raw material containing 89% by weight are shown in comparison with those manufactured using conventional equipment. The result will be as shown in the table below.

〔effect〕

As explained above, according to the present invention, a pin gate type three plate mold is used, and the two pin gate marks are located at the same radius from the rotation center of the rotating plastic magnet on the end face of the cylindrical rotating plastic magnet. As a result, gate marks do not disturb the surface magnetic flux density distribution characteristics of the rotating plastic magnet, there is no need for gate cut processing or gate mark processing after molding, and along with this, demagnetization and re-magnetization are possible. Processing is no longer necessary. Therefore, productivity is improved and production costs can be significantly reduced. If the above two pin gates are located on the same diameter in the magnetization direction, the influence of the pin gate marks on the magnetic properties can be minimized, and the magnetic properties can be further improved. . In particular, since the injection device uses a screw head with a backflow prevention valve, it is possible to prevent the backflow of material during injection even if the injection force increases due to the use of a pin gate. In order to secure the amount, it is possible to significantly improve the dispersion in the filling of raw materials within the cavity, thereby improving the 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 manufactured by the apparatus of the present invention. 5 is a waveform diagram showing an ideal waveform of the surface magnetic flux density distribution characteristic of the rotating plastic magnet shown in FIG. 4; FIGS. 6 and 7 are sectional views showing an example of a conventional device; and FIG. It is a partial plan view. DESCRIPTION OF SYMBOLS 1... Mold, 1a... Mold dividing surface, 1b... Runner ejection surface, 11, 12... Mold plate, 13... Runner stripper plate, 111... Cavity, 16... Pin gate, 2... Injection device, 24... Back flooring type check valve, 26...ball check type check valve, 3...magnetic field generating coil.

Claims (1)

[Scope of Claims] 1. A plastic magnet raw material having a synthetic resin matrix and containing magnetic powder is injected into a mold by an injection device, and molded in a magnetic field that has the ability to orient and magnetize the magnetic powder. and diametrically
In an apparatus for manufacturing a cylindrical rotating plastic magnet magnetized with NS poles, the mold is a three-plate mold having two mold plates forming a plurality of cabinets and one runner stripper plate. The gate for pouring the plastic magnet raw material into the cavity is connected to a mold plate forming one end face of the rotating plastic magnet, and each of the gates is connected to a mold plate forming one end face of the rotating plastic magnet, and each of the gates is located at the same radius from the center of rotation of the rotating plastic magnet. 1. An apparatus for manufacturing a rotating plastic magnet, comprising a pin gate, and wherein the injection device is a screw injection device having a screw head with a check valve.