JPH03145106A - Manufacture of rotary transformer - Google Patents

Abstract

PURPOSE:To obtain a magnetic core which maintains highly precise concentricity in the outside diameter, inside diameter and groove diameter by a method wherein gates are arranged on the position separated from the configuration of manufactured article, it is injection-molded, and a gate trace is treated by plane grinding. CONSTITUTION:When injection operation is conducted, gates 4a and 4b are arranged on the position separated from the configuration of manufactured article. To be more precise, the gates 4a and 4b are provided on the inner wall of the extended section 6 which is formed by extending the inner wall 5a of the positioning hole 5 provided on the center of a magnetic core 3. The ferrite powder, which is kneaded with a binder, is injected into a mold in the above-mentioned state, and after the mixture has been held under pressure to a certain degree, it is cooled down, the mold is opened, and a disc-like magnetic core 3, on one side face 1a of which winding grooves 1 and 2 are concentrically provided, is obtained. Besides, on the above-mentioned bore 3, a spool 7 is formed on the position where the gates 4a and 4b are provided. Then, the extended section 6 is removed by conducting a plane grinding work.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method of manufacturing a rotary transformer used in a rotating magnetic hand device such as a video tape recorder or a digital audio tape recorder. The present invention relates to a method for manufacturing a rotary transformer manufactured by.

[Summary of the Invention] The present invention provides t! When molding a magnetic core with concentric cotton wire grooves by injection molding, the gate is placed at a position apart from the product shape, and the gate marks are removed by surface grinding. This eliminates the need for grinding on the inner diameter surface, which is the positioning part, and makes it possible to manufacture a rotary transformer with high concentricity of the outer diameter, inner diameter, and groove diameter.

[Conventional technology]

Rotary transformers are widely used as a connection means for transmitting signals obtained from a rotating magnetic head installed on the rotating side to circuits on the stationary side in rotating magnetic head devices such as video tape recorders and digital audio recorders. There is.

Generally, a rotary transformer has a rotor formed by fitting annular coils into respective winding grooves provided concentrically on one side of a roughly disk-shaped magnetic core according to the number of channels. These stators are positioned and fixed to the rotating and stationary drums, respectively, and are arranged opposite to each other with a small gap between them. and connecting, for example, a rotating magnetic head connected to the rotor and, for example, a reproduction circuit connected to the stator, by electromagnetic coupling between the coils of the rotor provided on the rotating side and the stator provided on the stationary side, It is designed to transmit video signals, digital audio signals, etc.

By the way, in order to manufacture the rotor and stator of the above-mentioned rotary transformer by injection molding, highly accurate positioning on the drum is required, so a gate is provided in the inner hole drilled in the center and the material is kneaded with the binder. It is desirable to have a ring gate structure made by injecting ferrite powder. In this way, not only high roundness can be obtained, but also the concentricity of the outer diameter, inner diameter, groove diameter, etc. can be controlled with high precision. be done.

However, when a gate is provided in the inner hole drilled in the center as described above, there is a problem in that even if the gate is cut with a mold, the inner diameter at the fractured part becomes smaller than the predetermined inner diameter. There is. This is because cracks and the like occur in the area where the gate was provided. Therefore, it is necessary to grind these gate marks to finish the inner diameter to a predetermined size.

In the grinding process, since it is necessary to perform the process based on the outer diameter or other parts, reliable positioning is required. However, a deviation may occur during positioning, and this deviation may cause the concentricity of the outer diameter, inner diameter, groove diameter, etc. to be distorted. In this way, even if the concentricity of the outer diameter, inner diameter, and groove diameter is controlled with high precision in the mold, if the concentricity is distorted due to the grinding process of the gate group, the merits of injection molding will be lost.
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[Problem to be solved by the invention]

Therefore, the present invention was proposed in view of the conventional situation, and eliminates the grinding process on the inner diameter surface which is the positioning part of the magnetic core on the drum, and improves the concentricity of the outer diameter, inner diameter, and groove diameter. It is an object of the present invention to provide a method for manufacturing a rotary transformer that makes it possible to manufacture a high-quality rotary transformer.

[Means to solve the problem]

In order to achieve the above-mentioned object, the method for manufacturing a rotary transformer of the present invention includes: - When molding a magnetic core having concentric winding grooves on the side surface by injection molding, the gate is placed at a position apart from the product shape; and injection molded.
This method is characterized in that gate marks are treated by surface grinding.

[Effect]

In the present invention, when molding the magnetic core by injection molding, the gate is placed at a position separated from the product shape and the gate group is provided in a portion that is not in the product shape. If these gate marks are removed by surface grinding, which is easy to grind, no gate group will be found in the product shape.

Embodiment C] Hereinafter, a specific embodiment of a method for manufacturing a rotary transformer to which the present invention is applied will be described in accordance with the step-by-step process with reference to the drawings.

To make a rotary transformer, first see Figure 1(a).
As shown in Fig. 2, winding grooves (1) and (2) each having a substantially U-shaped cross section are provided in an annular shape, and the number is the same as the number of coils corresponding to the required number of channels (in this example, two channels). The magnetic core (3) is manufactured by injection molding using a mold (not shown) so that the magnetic cores (3) are arranged concentrically.

Injection molding involves, for example, using an injection molding machine with a structure similar to plastic molding to mold ferrite mixed with an appropriate amount of binder (mainly 15 to 20% thermoplastic resin such as polypropylene or low-molecular acrylic) mixed into the mold. This is done by injecting powder.

When injecting, the gels (4a) and (4b) are placed at a position apart from the product shape. That is, the gates (4a) and (4b) have winding grooves <1), (
The inner wall (5a) of the positioning hole (5), which is the other side (3b) side that corresponds to the back side of the surface (3a>) where 2) is formed, and serves as the positioning and fixing part of the magnetic core (3) to the drum.
It is provided on the inner wall of an annular extension part (6) that protrudes to extend. In this way, gate (4a),
The reason why (4b) is provided on the inner wall of the extension part (6) which is an extension of the inner wall (5a) of the positioning hole (5) provided in the center of the magnetic core (3) is because the gate mark is not shaped like the product. This is to provide a ring gate structure in which the roundness and concentricity of the outer diameter, inner diameter, and groove diameter can be controlled with high precision.

In addition, the gates (4a) and (4b) may be provided at the ends of the extending portion (6), as shown in FIG. 2, for example.

Then, in this state, the ferrite powder kneaded with the binder is injected into the mold, kept under pressure to some extent, cooled, and then opened.

As a result, as shown in FIG. 1(a), - side (1a)
A disc-shaped magnetic core (3) is formed in which the winding grooves (1) and (2) are concentrically provided.The magnetic core (3) is provided with the gates (4a) and (4b). ) is formed at the position where the spool (7) is provided.

In the magnetic core (3) obtained in this way, the ferrite powder is evenly pressed in all directions within the mold, so there is little residual stress, and the distribution of packing density is homogeneous. This suppresses the occurrence of cracks, etc. Also,
The magnetic core (3) is molded by injection molding, which enables the production of a 5-ill dense shape, so it has high dimensional accuracy and excellent concentricity of the outer diameter, inner diameter, and groove diameter.

Next, the spool (7) formed in the above process is shown in Figure 1 (
As shown in b), the previous gate (4a), (4b)
Cut at the position.

At this time, a paris (8) is generated in the gates (4a) and (4b) due to cutting, but this paris (8)
Since it is provided in a part that is not directly related to the magnetic core (3) that becomes the product, it does not have any influence.

If firing is required at this stage, as shown in Figure 3, the magnetic core (3
) is placed in the furnace and fired.

At this time, if the other side surface (3b) of the magnetic core (3) and the setter (9) are brought into surface contact, friction with the setter (9) during shrinkage during firing and heat conduction from the atmosphere may occur. Difference in heat conduction from setter (9) or setter (9)
Since the magnetic core (3) may be distorted or deformed due to the reaction with the molded rod of soaked ferrite, the extension portion (6) remaining in the above step should be brought into partial contact with the setter (9). For example, there is less influence from the setter (9) and deformation is suppressed. In addition, the above extension part (6
) alone is not stable, in the above-mentioned injection molding process, add the other side (3b) to the mold in advance near the outer peripheral surface of the magnetic core (3)
It is preferable to provide two or more protrusions (10) and (11) extending from ).
It is desirable to have a shape that reduces the frictional force between the setter (9) and the setter (9), such as a hemispherical shape.

Next, the extending portion (6) is removed by surface grinding.

Then, the gate group (8) remaining at the gates (4a) and (4b) is removed as shown in FIG. 1(c). In this way, surface grinding creates scratches (8).
By removing this, it is not only much easier to work than the conventional method of grinding the positioning hole (5) to the specified inner diameter dimensions, but it is also superior in mass production, and the mold allows for high precision. Controlled concentricity of outer diameter, inner diameter, and groove diameter is maintained.

Next, each winding groove (1), (2
) are fitted with annular coils (not shown) produced in separate steps and fixed with an adhesive or the like to produce a rotor or stator.

A rotary transformer is constructed by positioning and fixing the rotor and stator to the drums on the rotating side and the stationary side, respectively, and arranging them facing each other with a small gap. A rotary transformer configured in this way generates video signals and digital audio signals through electromagnetic coupling between the coils of the magnetic core (rotor) placed on the rotating side and the magnetic core (stator) placed on the stationary side. etc. will be transmitted.

In the above, in the method for manufacturing a rotary transformer to which the present invention is applied, a so-called flat rotary transformer in which disk-shaped magnetic cores are arranged facing each other with a minute gap has been described. It can also be applied to a so-called vertical rotary transformer which is arranged coaxially and facing each other in close proximity to the inside and outside.

For example, as shown in FIG. 4, the number of coils corresponding to the number of channels required for the inner wall surface (12a) of the cylindrical magnetic core (12) provided on the outside (in this example, two
The winding groove (13), which has a substantially U-shaped cross section (channel), (1
4) are provided in an annular shape and are arranged at predetermined intervals in the height direction. When forming the bottom shape of the magnetic cores (12) using a mold (not shown), the gates (1
5a) and (15b) may be provided on the inner wall of an annular extending portion (16) that protrudes from one end surface (12b) in the axial direction so as to extend the inner wall surface (12a).

On the other hand, when manufacturing a cylindrical magnetic core (17) provided on the inside, as shown in FIG. Windings vA1 (1B) and (1
When forming the bottom shape of the magnetic core (17) formed by providing the gate (9) in an annular shape using a mold (not shown), the gate (2
0a) and (20b) from one end surface (17b) in the axial direction to the inner wall surface (17c) which is the back surface of the outer wall surface (17a).
) may be provided on the inner wall of an annular extending portion (21) that protrudes to extend.

Then, the binder and kneaded ferrite powder were injected into these molds to obtain magnetic cores (12),
Spools (22), (23) provided in (17)
to the previous gate (15a), (15b), (20
a) Cut at position (20b).

If firing is required at this stage, the magnetic cores (12) and (17) are placed on a setter using the annular extensions (16) and (21) as contact parts. In particular, in this case, the firing is carried out in a furnace, and only the above-mentioned extension parts (16) and (21) are used to stably place the I on the setter.
Therefore, there is no need to provide a protrusion at another location to alleviate the influence of the setter.

Finally, by removing the extending portions (16) and (17) by surface grinding, the magnetic cores (12) and (17), which have no gate group in the product shape, are removed with high precision by the mold in the step. The concentricity of the diameter, inner diameter, and groove diameter is maintained.

〔Effect of the invention〕

As is clear from the above explanation, according to the method of the present invention, since the gate is arranged at a position apart from the product shape, no gate group is formed on the inner diameter surface of the drum. There is no need to grind the inner diameter surface which is the positioning part, and the injection molding makes it possible to obtain a magnetic core in which the concentricity of the outer diameter and inner groove diameter is maintained with high precision.

Further, according to the method of the present invention, the gate a is removed by surface grinding, which is easy to grind, so the workability and workability are much improved compared to the conventional method in which the inner diameter surface is ground to a predetermined size. A significant improvement in mass productivity can be achieved, and an inexpensive rotary transformer can be provided.

[Brief explanation of the drawing]

1141(a) to FIG. 1(c) are enlarged sectional views showing the manufacturing process of a rotary transformer manufactured by applying the method of the present invention according to the process order, and FIG. 1(a) shows the injection process, Figure 1 (b) shows the spool removal process, Figure 1 (
c) is a surface grinding process. FIG. 2 is an enlarged sectional view showing another example of the arrangement position of the gate,
FIG. 3 is an enlarged sectional view showing the firing process when firing is required. 4 and 5 respectively show the gate arrangement positions when the method of the present invention is applied to a vertical rotary transformer. FIG. 4 is an enlarged sectional view of the magnetic core disposed outside, The figure is an enlarged sectional view of the magnetic core disposed inside. 1.2, 13.14.18.19 ... Winding groove 3.
12.17 ...Magnetic core

Claims (1)

[Claims] When molding a magnetic core with concentric winding grooves on one side by injection molding, injection molding is performed with the gate placed at a distance from the product shape, and gate marks are treated by surface grinding. A method for manufacturing a rotary transformer.