JPS59117205A - Formation of plastic magnet - Google Patents

Abstract

PURPOSE:To enable to take out automatically a plastic magnet from a metal mold by executing surely demagnetization of the molded product, a sprue and a runner, and to obtain the plastic magnet of superior quality by a method wherein a pulse current to present plus and minus alternately, and moreover reducing amplitude gradually is flowed to an orientating coil during cooling of the molded product. CONSTITUTION:Molten plastics containing magnetic powder are injected into a metal mold 2 from an injection molder 1, the magnetic powder is orientated by flowing a current to an orientating coil 3 provided outside of the metal mold 2, and then during cooling of a molded product, demagnetization is performed by flowing in the orientating coil 3 a pulse current 4 to present the plus direction and the minus direction alternately as blocks, and moreover having a waveform reducing amplitude gradually. The molded product demagnetized in such a way has extremely small residual magnetism, automatic taking out of the molded product, a sprue and a runner from the metal mold becomes to possible, and moreover, redemagnetization of the molded product becomes unnecessary, and when magnetization is performed, the product of uniform and superior quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently molding resin magnets of excellent quality.

Conventionally, when manufacturing anisotropic resin magnets, molten resin containing magnetic powder is injected into a mold, and an electric current is applied to an orientation coil provided inside or outside the mold to inject the magnetic powder. The molded product is oriented, demagnetized during cooling, and taken out of the mold, and then magnetized in a subsequent process.

For example, if a current with a waveform whose amplitude gradually decreases as shown in Figure 1 is passed through an orientation coil to cause orientation, the demagnetization method is to run a current in the opposite direction to the orientation fill. It has the following drawbacks:

(1) Since the magnetic energy of the molded product, sprue, and run j is different, if you demagnetize according to the molded product,
The sprue and runners are either insufficiently demagnetized or have a strong diamagnetic force. Therefore, the molded product, sprue, and runner remain attracted to the mold, making it difficult to take them out automatically.

(2) Magnetism remains in the mold, making it easy for foreign objects to be attracted to it.
This can easily cause mold damage.

(3) Furthermore, in the conventional method, sufficient demagnetization is not performed and the residual magnetism of the molded product is large, so re-magnetization is required and the magnetic performance when magnetized varies. One object of the present invention is to reliably demagnetize molded products, sprues, and runners to enable automatic removal from molds, and to mold resin magnets of excellent quality.

That is, in the present invention, a molten resin containing magnetic powder is injected into a mold, an electric current is applied to an orientation coil to orient the magnetic powder, and while the molded product is being cooled, positive and negative waves alternately appear and the amplitude increases. The method is characterized in that demagnetization is carried out by passing a gradually decreasing pulse current through the orienting coil.

An embodiment of the present invention will be described.

Molten resin containing magnetic powder is injected into a mold 2 from an injection molding machine 1, and a first
A current with the waveform shown in the figure was applied to orient the magnetic powder. Next, while the molded product is being cooled, a pulsed current having a waveform in which positive and negative directions alternately appear as blocks and whose amplitude gradually decreases as shown in FIG. 3 is applied to the orienting coil 3.
Demagnetization was performed by flowing the

The surface roughness of the molded product demagnetized in this way (product of the present invention) is as shown in Table 1, and it can be seen that the residual magnetism is extremely lower than that of the molded product demagnetized by the conventional method (conventional product). .

Table 1 As mentioned above, the present invention can reliably demagnetize the molded product while it is being cooled, and (1) it is only possible to automatically remove the mold parts of the molded product, sprue, and runner.

(2) Since no magnetism remains in the mold, there is less adhesion of foreign matter and damage to the mold can be prevented.

(3) There is no need to re-magnetize the molded product, and when magnetized, it is possible to obtain a product with uniform quality and excellent quality.

Its industrial value is extremely great.

[Brief explanation of drawings]

FIG. 1 is a curve diagram showing the waveform of the orientation current, FIG. 2 is an explanatory diagram showing the outline of a resin magnet molding machine, and FIG. 3 is a curve diagram showing an example of the waveform of the demagnetizing current in the present invention. . 1 is an injection molding machine, 2 is a mold, and 3 is an orientation coil patent applicant.

Claims (1)

[Claims] In a resin magnet molding method in which molten resin containing magnetic powder is injected into a mold and an electric current is applied to the mold or an orientation coil provided in the mold to orient the magnetic powder, cooling of the molded product is performed. 1. A method for molding a resin magnet, which comprises demagnetizing the orienting coil by passing a pulse current in which positive and negative currents alternately appear and whose amplitude gradually decreases.