JPH04250015A - Demagnetizing method for product molded with injection molding machine for anisotropic resin magnet - Google Patents

Abstract

PURPOSE:To constitute the above method so that demagnetization can be performed sufficiently by one time demagnetization process. CONSTITUTION:An alternating magnetic field which is constituted so that a positive and negative peak values each are reduced with the lapse of time and the positive and negative peak values are held constantly respectively by a fixed magnetic field holding time tm is added to a molded product of an anisotropic resin magnet.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for demagnetizing molded products using an injection molding machine for molding anisotropic resin magnets.

0002

[Prior art] An injection molding machine for molding anisotropic resin magnets is
Injection molding is performed in a magnetic field, and the magnetic powder contained in the molded product is oriented in the direction of the magnetic field, making the molded product anisotropic. However, since the magnetic particles are magnetized at the same time as they are oriented, the molded product may adhere to the injection molding machine or the ferromagnetic part of the mold, making it impossible for the molded product to fall automatically during the ejection process. , the handling of molded products is inconvenient. Therefore, it is common practice to demagnetize the molded product.

Conventional methods for demagnetizing molded products include, as shown in FIG. 3, applying a magnetic field of strength H2 in the opposite direction to a molded product magnetized to a predetermined magnetization strength B1;
As shown in FIG. 4, there is a method of applying an alternating magnetic field to a molded article, in which the positive and negative peak values simply decrease over time.

0004

[Problems to be Solved by the Invention] Among the above conventional techniques, the one shown in FIG. 3 only applies a magnetic field of a predetermined strength in the opposite direction, so that the coercive force of each magnetic particle is uniform. If not, the demagnetization effect will be different depending on each magnetic particle, and the demagnetization energy may be insufficient or the demagnetization energy may be too strong and magnetize in the opposite direction, making it difficult to perform sufficient demagnetization. Ta. In addition, in the case shown in Fig. 4, the time to apply a strong magnetic field is short, so if a large amount of energy is required for demagnetization due to crystal defects such as vacancies in the crystal of the magnetic powder or impurity atoms, the energy applied to the magnetic particle is Because of the shortage, it was still difficult to perform sufficient demagnetization. For this reason, with all of the above conventional techniques, it is difficult to demagnetize sufficiently, the molded product cannot be automatically dropped reliably, and the air core coil etc. There is a problem in that it is necessary to perform demagnetization again using a separate demagnetization device.

The present invention has been made in view of the problems of the conventional techniques described above, and provides a molded product that can be sufficiently demagnetized in one step and does not require a separate demagnetization device. The purpose is to provide a demagnetization method.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the method for demagnetizing a molded product of the present invention involves performing injection molding in a magnetic field using an injection molding machine for molding anisotropic resin magnets. In a method of demagnetizing the molded product by applying to the molded product an alternating magnetic field whose positive and negative peak values decrease over time after molding a molded product of an orthogonal resin magnet, the positive and negative peak values of the alternating magnetic field are This method is characterized in that each peak value is held constant for a predetermined period of time.

In the molded article demagnetization method of the present invention, it is preferable to demagnetize the molded article before the mold opening step.

[0008]

[Effect] When an alternating magnetic field in which the positive and negative peak values decrease over time is applied to a molded product, the domain wall energy of the domain walls in the magnetic powder contained in the molded product decreases (magnetization becomes weaker). Try to move like this. At this time, if there are defects such as vacancies or impurities in the crystals of the magnetic powder, the amount of energy required to move the domain wall increases, making it difficult for the domain wall to move. However, in the present invention, the alternating magnetic field By holding each positive and negative peak value constant for a predetermined period of time, a sufficient magnetic field is applied to the magnetic particles contained in the molded product, and any domain walls are reliably moved to achieve sufficient demagnetization. .

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be explained based on the drawings.

FIG. 1 shows an example of a mold clamping device of an injection molding machine for molding anisotropic resin magnets used in carrying out the present invention. coil 1
However, each movable platen 4 is provided with an excitation coil 2 for applying a magnetic field to the movable mold 7. The movable platen 4 is guided by a plurality of tie bars 5 fixed to the fixed platen 3, and is arranged to be able to reciprocate in the axial direction of the tie bars 5. The movable platen 4 is slid by a known drive means (not shown) to move the mold. It is configured to open/close and clamp the mold.

The fixed platen 3, the movable platen 4, the tie bar 5, the fixed mold 6 and the movable mold 7 are each mainly composed of a ferromagnetic material, and together with the excitation coils 1 and 2, known anisotropic resin magnets are used. One that constitutes an injection molding machine for molding can be used.

Next, a method of demagnetizing a molded product using the mold clamping device shown in FIG. 1 will be explained.

After clamping the fixed mold 6 and the movable mold 7, a predetermined current (DC) is applied to each exciting coil 1, 2.
When a current flows, a magnetic field corresponding to this current is generated. In this magnetic field, when molten resin containing magnetic particles is injected into the cavity formed by the fixed mold 6 and the movable mold 7, a molded product 8 in which the magnetic particles are oriented in the direction of the magnetic field is formed, and the fixed plate 3. A magnetic circuit is formed by the movable platen 4, the tie bar 5, the fixed mold 6, the movable mold 7, and the molded product 8. Next, after the molded product 8 reaches a temperature at which it can be taken out through the cooling process,
A demagnetization process is performed before the mold opening process.

In the demagnetization process, as shown in FIG. 2(a), an alternating current is used in which the positive and negative peak values decrease over time, and each of these positive and negative peak values is kept constant for a predetermined current holding time ta. An alternating current that is maintained at a constant value is applied to each of the excitation coils 1 and 2, respectively.

As a result, the molded product 8 has the shape shown in FIG. 2(b).
As shown in Fig. 2(a), the alternating magnetic field is proportional to the alternating current, and the positive and negative peak values decrease over time, and these positive and negative peak values are maintained for a predetermined magnetic field holding time. An alternating magnetic field is applied that is kept constant by tm. The above-mentioned positive and negative peak values may decrease linearly or may decrease curved, for example, like a quadratic function.

When the alternating magnetic field shown in FIG. 2(b) is applied to the molded product 8, even if there are defects such as holes or impurities in the crystals of the magnetic powder contained in the molded product 8, the domain wall of the magnetic powder moves reliably, the domain wall energy is minimized, and sufficient demagnetization occurs.

Since the alternating current and alternating magnetic field shown in FIGS. 2A and 2B are proportional to each other, the current holding time ta and the magnetic field holding time tm are approximately equal. Further, if the magnetic field holding time tm is too short, there will be no difference from the conventional example shown in FIG. 4, and if it is too long, the demagnetization process will take too much time, so it is preferably about 0.1 μs to 500 ms.

Next, experimental examples and comparative examples of the present invention will be shown.

Experimental Examples 1 to 3 and Comparative Examples 1 to 3 A fixed mold 6 and a movable mold 7 having a disc-shaped cavity with a volume of 0.9 cm 3 were used in the mold clamping device shown in FIG. An anisotropic resin magnet molded article was molded using the polyamide as shown in Table 1 and the magnetic powder shown in Table 1.

Table 1 Next, this molded article was demagnetized under the conditions shown in Table 2. However, in Table 2, the number of repetitions is the number of times each positive or negative peak value appears, and for example, in Figure 2
(b) and the alternating magnetic field shown in FIG. 4 each have five times. In addition, in each of the experimental examples and comparative examples, the alternating magnetic fields are such that after repeating the above number of repetitions, the positive and negative peak values linearly decrease so that the magnetic field strength becomes 0 in the next cycle. shall be.

Table 2 Table 3 shows the residual surface magnetic flux densities of the molded products of each experimental example and comparative example after completion of demagnetization.

Table 3 As is clear from Table 3, sufficient demagnetization was achieved in each experimental example compared to each comparative example.

[0023]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following effects.

[0024] Sufficient demagnetization can be performed in a single demagnetization process, and it is easy to automate automatic dropping, transportation, assembly, etc. of molded products. There is no need to perform demagnetization again using the device. Therefore, in addition to improving productivity, it is possible to reduce the cost of a separate demagnetizing device.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing an example of a mold drawing device of an injection molding machine for molding an anisotropic resin magnet used in carrying out the present invention.

FIG. 2 is a diagram for explaining the demagnetization method of this example;
2A is a waveform diagram showing alternating currents flowing through each excitation coil shown in the figure, and FIG. 2B is a waveform diagram showing an alternating magnetic field applied to the molded product shown in FIG. 1. FIG.

FIG. 3 is an HB curve diagram for explaining a conventional example of a demagnetization method.

FIG. 4 is a waveform diagram of an alternating magnetic field for explaining a conventional example of a demagnetization method.

[Explanation of symbols]

1 Excitation coil 2 Excitation coil 3 Fixed plate 4 Movable plate 5 Tie bar 6 Fixed mold 7 Movable mold 8 Molded products ta Current holding time tm Magnetic field holding time

Claims (2)

[Claims] Claim 1: Injection molding is performed in a magnetic field using an injection molding machine for molding anisotropic resin magnets, and after molding an anisotropic resin magnet molded product, positive and negative peak values change over time. In the method of demagnetizing the molded article by applying an alternating magnetic field that decreases with time to the molded article, each of the positive and negative peak values of the alternating magnetic field is held constant for a predetermined time (tm). magnetic method. 2. The demagnetization method according to claim 1, wherein the molded product is demagnetized before the mold opening step.