JP3036893B2 - Plastic magnet rotor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic magnet rotor used for a motor, a rotation speed measuring device and the like.

[0002]

2. Description of the Related Art In general, motors and rotational speed measuring instruments, etc.
A rotor having a metal shaft inserted at the center of a cylindrical plastic magnet molded body having a plurality of magnetic poles in the circumferential direction of the surface is used. As the material of the plastic magnet molded body, a polyamide matrix polymer such as nylon 6 or nylon 12 may be used.
Compounds containing a mixture of magnetic powders such as hard magnetic ferrites are often used. For parts used in environments that may be exposed to high temperatures, such as automobiles, PPS (polyphenylene) with high heat resistance has recently been used as a matrix polymer. Sulfide) is increasingly being used.

[0003]

When a compound in which a magnetic material such as hard magnetic ferrite is mixed with polyphenylene sulfide as a matrix polymer is used, an injection-molded rotor having a metal shaft inserted therein is used, for example, at 150 ° C. When subjected to a thermal shock test at 40 ° C., the molded product is generally cracked with a small number of impacts. This is presumed to be a phenomenon that occurs due to the difference in the coefficient of thermal expansion between the plastic magnet molding and the metal shaft, whereby the stress repeatedly generated in the molded body exceeds the limit of the fatigue strength of the molded body. When the rotor is used in a wide temperature range, such as an automobile part, the rotor having a small number of impacts before cracking as described above has low reliability and is hardly put to practical use.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been achieved as a result of intensive studies on compound raw materials in order to stably maintain high thermal shock resistance of a plastic magnet rotor using polyphenylene sulfide.
That is, a substantially linear polyphenylene sulfide having a melt viscosity of 1000 to 4000 poise at 310 ° C. and 1200 / sec is used, and hard magnetic ferrite is mixed as a magnetic material in a range of 70 to 92% by weight. Then, the obtained compound is subjected to injection molding by inserting a metal shaft, or press-fitting the metal shaft after injection molding to obtain a plastic magnet rotor having high thermal shock resistance.

[0005]

The present invention will be described below in detail. Generally, plastic magnet rollers have an outer diameter of 1 to 25 mm and a thickness of 5 to
A metal shaft is inserted at the center of a cylinder of about 15 mm. The circumferential surface of the cylindrical rotor is N.I. The S poles are alternately magnetized into multiple poles such as 12 poles.

The material constituting the molded body is 310 ° C., 12
It is a composite magnetic material in which hard magnetic ferrite is mixed in a range of 70 to 92% by weight with linear polyphenylene sulfide having a melt viscosity of 1000 to 4000 poise at 00 / sec. The magnetic poles on the circumferential surface can be produced by exciting and molding a ferrite by applying a magnetic field to the mold during injection molding, and magnetizing and orienting the ferrite. Also, after taking out the molding,
It is also possible to magnetize by putting it in a magnetized yoke.

When a crosslinked type polyphenylene sulfide having a large number of branched structures is used instead of the linear type as in the present invention, the thermal shock resistance is low. Even in the case of the linear type, the melt viscosity at 310 ° C. and 1200 / sec is 10
If the polymer is less than 00 poise, the desired high thermal shock resistance cannot be obtained. Polymers having a melt viscosity of more than 4000 poise have poor moldability. When the mixing ratio of the hard magnetic ferrite increases, the coefficient of thermal expansion of the compact decreases, and the difference in the coefficient of thermal expansion with the metal shaft decreases, which is preferable.On the other hand, the ductility of the compact itself decreases to absorb stress. It becomes difficult. If the mixing ratio of the hard magnetic ferrite is too low, it becomes impossible to impart necessary magnetic properties. That is, in order to obtain a desired high thermal shock with a magnetic rotor, there is a range of a suitable mixing ratio. The range found by the present inventors as a result of trial and error is 70 to 92% by weight. With a ferrite mixing ratio outside this range, only a rotor having a low thermal shock can be obtained.

[0008]

EXAMPLES Example 1 While stirring 6 kg of strontium ferrite powder with a Henschel mixer, 60 g of a silane coupling agent was sprayed and added, and the mixture was stirred for 120 minutes.
The reaction was completed by heating at 5 ° C. for 5 minutes to obtain surface-treated strontium ferrite.

To this surface-treated strontium ferrite, 1229 g of powdered linear polyphenylene sulfide having a melt viscosity of 1400 poise at 310 ° C. and 1200 / sec was added to make the ferrite content 83% by weight. For 5 minutes.
Then, the mixture was kneaded at 310 ° C. in a twin-screw extruder to produce pellets. Using this pellet, insert injection molding is performed using a φ6.5 cold-forged carbon steel as an insert axis in a mold provided with a magnetic field for polar orientation in a cavity, and a 12-pole plastic magnet in the circumferential direction. One rotor
0 were molded.

As a comparative example, 310 ° C., 1200 / sec
A cross-linked polyphenylene sulfide having a melt viscosity of 1500 poise and a linear polyphenylene sulfide having a melt viscosity of 550 poise at 310 ° C. and 1200 / sec. Co-molded. These molded products were left in a low temperature bath at -40 ° C for 1 hour and immediately transferred to a high temperature bath at 150 ° C and left for 1 hour. This was again transferred to −40 ° C. and 150 ° C., and the thermal shock test was repeated many times.
The number of cracks generated at 100, 150, and 200 times was examined. Number of thermal shocks Linear PPS Crosslinked PPS Linear PPS 1400 poise 1500 poise 550 poise 50 times 0 17 100 0 2 10 150 0 2 200 04 Here, PPS indicates polyphenylene sulfide.

The linear PPS of the present invention (1400 poise)
No cracks were found even in the number of thermal shocks up to 200 times, whereas four out of 10 cracks were found in the crosslinked PPS (1500 poise) in the 200 times thermal shock test. In the case of 550 poise PPS of linear type, 10
Cracks occurred in all 10 pieces in 0 tests. Example 2 6 kg of strontium ferrite surface-treated in the same manner as in Example 1 was added at 310 ° C. for 1200 / sec.
1317 g of powdered linear polyphenylene sulfide having a melt viscosity of 2,200 poise in Example 1 was added to make the ferrite content 82% by weight, kneaded and pelletized as in Example 1, and insert injection-molded to form a plastic magnet rotor. did.

As a comparative example, the same molding was performed with a plastic magnet compound using a linear polyphenylene sulfide having the same melt viscosity (2200 poise) and adjusting the ferrite content to 68% by weight. Each of these 10 molded products was subjected to a thermal shock test at −40 ° C. and 150 ° C. in the same manner as in Example 1 to examine the occurrence of cracks. Number of thermal shocks Ferrite content 82% by weight Ferrite content 68% by weight 100 4 pieces 50 0 8 pieces A ferrite content of 82% by weight showed no crack generation in 100 times of thermal shock tests, but a ferrite content of 68%. In the test of 100% by weight, cracks were observed in 8 out of 10 samples in 100 tests.

[0013]

As described above, the compound for a plastic magnet rotor according to the present invention has excellent thermal stability without cracks in the metal shaft and the molded product even after repeated severe thermal shock tests. It has a special effect of being obtained.

Claims (1)

(57) [Claims] 1. A plastic magnet rotor into which a metal shaft is inserted, at 310 ° C., 1200 / sec.
A plastic magnet rotor characterized in that the rotor is molded from a magnetic compound obtained by mixing 70 to 92% by weight of hard magnetic ferrite with substantially linear polyphenylene sulfide having a melt viscosity of 1,000 to 4,000 poise.