JPH0590052A - Reduction of rotary transformer core - Google Patents

Abstract

PURPOSE:To improve core plane accuracy without deteriorating the characteristics as a rotary transformer core by injection molding ferrite resin manufactured by mixing specific ferrite powder with thermosetting resin or thermoplastic resin. CONSTITUTION:Almost sphere ferrite powder (grain diameter = several mum - several 10mum) is mixed with polymer material such as polypropylene and polyamide by 70-98wt.% and ferrite resin, which is the raw material of a core, is manufactured. Then, the ferrite resin is injection-molded and a rotary transformer core is manufactured. Thus, the core plane accuracy is improved without deteriorating the characteristics as the rotary transformer core, the manufacturing time for the rotary transformer core is shortened and the cost is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a core of a rotary transformer used in, for example, a video tape recorder (VTR) or a digital audio tape recorder (DAT).

[0002]

2. Description of the Related Art Generally, a rotary transformer is used for transmitting an input / output signal of a rotary head in a video tape recorder (VTR), a digital audio tape recorder (DAT), etc., and is composed of a rotor and a stator. It is configured. As this rotary transformer, a flat type (disk type) and a vertical type (cylinder type) are currently known.

The core of the rotary transformer is formed of a material having a high magnetic permeability such as ferrite in order to obtain necessary magnetic characteristics.

As a conventional method for manufacturing a core for a rotary transformer, a compression molding method in which ferrite powder is uniaxially compressed in a mold is generally used.

However, when a rotary transformer core having a complicated shape provided with a coil winding groove is produced by the compression molding method, the filling degree of the raw material charged into the mold becomes uneven, and As a result, there are problems that the core after firing is deformed or warped, and the filling degree of the raw material for each molding shot is non-uniform, so that the reproducibility is low and the individual cores have dimensional variations.

Conventionally, in order to obtain the surface accuracy of the core by eliminating the above deformation, warpage, variation in dimensional accuracy, etc., the core after firing is subjected to polishing treatment. However, in the prior art, since the degree of deformation and warpage is very large, if the thickness of the core after firing is 10 mm, it is necessary to polish it to about half that thickness, which is about 5 mm.

As the recording density of magnetic recording media such as video tapes has increased with the digitization of magnetic recording systems, the core thickness must be increased from about 3 mm (currently) to about 10 mm. In such a tendency, when the surface accuracy is increased only by polishing as described above, it is inevitable that the material is wasted, the polishing time is lengthened, and the manufacturing cost is increased.

Further, conventionally, a binder made of a polymer material is kneaded with ferrite powder and injection molded to form a core for a rotary transformer, after which the binder is degreased for several days and then fired. A technique for obtaining a core has been proposed and has been put to practical use. In this case, the surface accuracy is improved as compared with the conventional manufacturing method described above, and the polishing process can be shortened.

[0009]

However, even in the case of the technique according to the above proposed example, it is necessary to polish the thickness of the core after firing by about 1/4, and there is a limit to the reduction of the manufacturing cost. .

Therefore, recently, a technique of kneading Mn-Zn ferrite powder with polyamide powder to prepare a core raw material, temporarily extruding the core raw material into pellets, and then injection molding to obtain the core. Has been proposed (see JP-A-62-188303).

In this technique, the surface accuracy of the core is dramatically improved, and the subsequent polishing step can be omitted accordingly, and the manufacturing cost can be reduced.

However, the magnetic permeability μ of the core obtained by this method is about 7 to 8 (1 MHz), and the magnetic permeability μ = 20 (1 MHz) required for the rotary transformer core cannot be obtained. If it is desired to obtain a magnetic permeability of about μ = 20, the particle size of the ferrite powder is about 1 mm.
However, when the ferrite powder having a particle diameter of about 1 mm is used for injection molding, the surface accuracy of the core is significantly deteriorated.

In the case of Mn-Zn type ferrite resin, there is a drawback that the contact noise caused by the contact between particles is large and the characteristics with the coil cannot be obtained. This leads to an overall reduction in Q.

The present invention has been made in view of the above problems, and an object thereof is to improve the surface accuracy of the core without deteriorating the characteristics of the core for the rotary transformer. It is to provide a method for manufacturing a transformer core.

[0015]

The present invention provides a rotary transformer core manufacturing method for manufacturing a rotary transformer core by injection molding a ferrite resin obtained by kneading a ferrite powder with a polymer material. The particle diameter is several μm to 200 μm, the weight ratio of the ferrite powder is 70 to 98% by weight, and the polymer material is a thermosetting resin or a thermoplastic resin.

[0016]

According to the above-described production method of the present invention, a ferrite resin having a particle diameter of several μm to 200 μm is kneaded with a thermosetting resin or a thermoplastic resin in a weight ratio of 70 to 98% by weight to obtain a ferrite resin. After that, this ferrite resin is injection-molded to manufacture the core for the rotary transformer, so that the core for the rotary transformer with the facing surface accuracy of about several tens of μm can be obtained, and then it is necessary to perform the polishing treatment. Disappear.

Further, since the core is manufactured by injection molding,
A plurality of cores of the same type or different types can be simultaneously manufactured, and the manufacturing time and the product type switching time can be efficiently shortened.

Further, the ferrite powder having a particle diameter of several μm to 200 μm is kneaded with a thermosetting resin or a thermoplastic resin in a weight ratio of 70 to 98% by weight to obtain a ferrite resin. The magnetic permeability of
22 (1 MHz) can be obtained, and it can sufficiently function as a core for a rotary transformer.

[0019]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3 are cross-sectional views showing the structure of a rotary transformer obtained by the manufacturing method of this embodiment.

FIG. 1A shows a flat rotary transformer 1A for 1ch, and FIG. 1B shows a flat rotary transformer 1B for 3ch. 2A shows a vertical rotary transformer 1C for 3ch, and FIG. 2B shows a double vertical rotary transformer 1D for 4ch. FIG. 3 shows a double flat rotary transformer 1E for 1ch.

In these figures, 2 is a rotor, 3 is a stator, and 4 is a winding coil. 2 is the rotor,
Although 3 is used as the stator, of course, the reverse configuration is also possible.

Next, a method of manufacturing the rotary transformer core constituting the rotor 2 and the stator 3 will be described with reference to FIG.

First, a raw material composition containing iron oxide as a main component is crushed by a ball mill, and an additive (a binder, a defoaming agent, a lubricant, a plasticizer) is added to the material composition to adjust the slurry concentration, and the slurry composition Prepare things. The respective compositions of the raw material composition and the additives are shown below.

Raw material composition Fe ₂ O ₃ 49.72 mol% ZnO 31.70 mol% NiO 9.11 mol% CuO 9.47 mol% additive binder (PVA) 120 liter antifoaming agent 1 liter lubricant 8. 5 kg Plasticizer 1.0 kg Slurry concentration (raw material composition%) 55%

The thus-prepared slurry composition is spray-dried to give a substantially spherical granulated powder. FIG. 5 shows a granulating apparatus 5 for manufacturing the granulated powder used in this example.

The granulating apparatus 5 has a granulating furnace 6 having a conical lower end portion 6a, and a pipe 7 mounted so as to face the inside of the granulating furnace 6. The pipe 7 is configured so that air is blown in from one end 7a by a blower (not shown), and a tank 8 for storing the slurry composition is provided in the middle of the pipe 7.

The other end 7b of the pipe 7 has a nozzle 9
Is rotatably attached. The nozzle 9 has four blowout ports 9a for ejecting the slurry composition in the tangential direction of the rotation direction, and rotates by blowing out the slurry composition from these blowout ports 9a.

In the granulating apparatus 5, the temperature inside the granulating furnace 6 is 1
A tray 11 for recovering the granulated powder 10 dried in the furnace 6 is arranged at a position which is maintained at 20 to 200 ° C. and faces the opening 6b provided in the lower end 6a of the granulation furnace 6. Has been done.

When the granulated powder 10 is manufactured by the granulating apparatus 5 thus constructed, first, the slurry composition is put into the tank 8 and air is sent from one end 7a of the pipe 7. At this time, the slurry composition that has dropped down to the pipe 7 is extruded by the air pressure and ejected from the blowout port 9 a of the nozzle 9 through the pipe 7.

The jetted slurry composition adheres to the inner wall surface of the granulation furnace 6 while forming a substantially spherical shape due to surface tension. The slurry composition adhering to the inner wall surface is dried in the furnace 6 to become a substantially spherical granulated powder 10 which peels off.
It is collected in the tray 11.

The substantially spherical granulated powder 10 thus produced has a particle diameter distributed in the range of 44 to 149 μm, and has a substantially uniform particle diameter as a whole.

The granulating conditions of the granulating device 5 are shown below. Granulation conditions Nozzle diameter 1.7 mmφ Number of nozzles 1 Hot air temperature 300 to 367 ° C. Exhaust air temperature 130 ° C.

Then, the granulated powder 10 obtained as described above is fired while being stirred at a temperature of about 1050 to 1100 ° C. using, for example, a known rotary kiln with stirring blades, and a substantially spherical ferrite powder (particle diameter) is obtained. = Several μm to several 1
0 μm) is obtained.

Next, the ferrite powder is kneaded with a polymer material in a weight ratio of about 70 to 98% by weight to obtain a ferrite resin as a raw material for the core.

As the polymer material, in this example, polypropylene, polyamide, polyphenylene sulfide, polyethylene, polystyrene, ethylene vinyl acetate copolymer, ethylene ethyl acrylate, 6-nylon, 6,6-nylon, 6,10- A thermoplastic resin such as nylon, 11-nylon, 12-nylon, polyethylene terephthalate or polybutylene terephthalate is used.

Next, the ferrite resin is injection-molded to obtain a rotary transformer core. Then, the coil is wound around the winding groove formed in the core to obtain the rotor 2 and the stator 3 shown in FIGS.

At the time of this injection molding, for example, a coil is arranged in the cavity of an injection molding die, and ferrite resin is injection molded in this state, and a rotor in which a part or all of the coil is embedded in the ferrite resin. 2 and the stator 3 may be directly obtained.

As described above, according to this example, the ferrite powder having a particle size of several μm to several tens μm is kneaded with the thermoplastic resin in a weight ratio of 70 to 98% by weight to obtain a ferrite resin. Since the ferrite transformer is injection-molded to manufacture the rotary transformer core, it is possible to obtain the rotary transformer core having a facing surface accuracy of about 50 μm.

At present, the facing surface accuracy of the rotary transformer is about 20 μm to 50 μm, and it can be sufficiently used without polishing treatment thereafter. Therefore, according to the manufacturing method of this example, the time required for the polishing process can be omitted, and the number of steps and the manufacturing cost can be reduced. In addition, when it is desired to set the facing surface accuracy to 20 μm, it can be achieved by slightly performing a polishing process thereafter.

Further, since the core is manufactured by injection molding,
A plurality of cores of the same type or different types can be simultaneously manufactured, and the manufacturing time and the product type switching time can be efficiently shortened.

Since ferrite powder having a particle size of several μm to several tens of μm is kneaded with a thermoplastic resin in a weight ratio of 70 to 98% by weight, a ferrite resin is obtained.
18 to 22 (1MHz) as magnetic permeability μ of completed core
Can be obtained and can sufficiently function as a core for a rotary transformer.

As a raw material for the ferrite resin, Mn
Since the Ni—Zn type ferrite is used instead of the —Zn type ferrite, the occurrence of contact noise due to the contact between the particles is small, and it is possible to avoid the deterioration of the overall Q.

In the above example, the particle size of the ferrite powder is several μm to several tens of μm, but the particle size is several μm to 2 μm.
Even if it is 00 μm, the same effect as described above can be obtained. Although the thermoplastic resin is used as the polymer material, other thermosetting resins such as phenol resin, epoxy resin, diallyl phthalate resin can be used. in this case,
It has excellent heat resistance, moisture resistance, cold resistance, and oil resistance.

[0044]

According to the method of manufacturing a rotary transformer core according to the present invention, the surface accuracy of the core can be improved without deteriorating the characteristics of the rotary transformer core. The time and cost can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view (No. 1) showing a rotary transformer obtained by a method of manufacturing a rotary transformer core according to an embodiment.

FIG. 2 is a sectional view (No. 2) showing the rotary transformer obtained by the method for manufacturing the core for a rotary transformer according to the present embodiment.

FIG. 3 is a sectional view (No. 3) showing the rotary transformer obtained by the method for manufacturing the core for a rotary transformer according to the present embodiment.

FIG. 4 is a process block diagram showing a method of manufacturing a rotary transformer core according to the embodiment.

FIG. 5 is a configuration diagram showing a granulating apparatus used in the method for manufacturing a rotary transformer core according to the present embodiment.

[Explanation of symbols]

 1A to 1E Rotary transformer 2 Rotor 3 Stator 4 Winding coil

Claims (1)

[Claims] 1. A method for producing a core for a rotary transformer, comprising producing a core for a rotary transformer by injection-molding a ferrite resin obtained by kneading a ferrite powder with a polymer material, wherein the ferrite powder has a particle diameter of several μm to 200 μm. The weight ratio of the ferrite powder is 70 to 98% by weight, and the polymer material is a thermosetting resin or a thermoplastic resin.