JPH07115026A - Manufacture of rotating transformer - Google Patents

Abstract

PURPOSE:To provide a low-cost rotating transformer by manufacturing the inside and outside cores by die molding. CONSTITUTION:An inner metal mold 13 composed of longitudinal groove forming segments 8 and a plurality of lateral groove forming metal molds 10 is covered with an outer metal mold, and the gap between them is filled with magnetic powder. A substance obtained by compression-molding is heated to a high temperature to produce an outside core. Coils are wound around inside and outside cores respectively, and a rotating transformer is produced by combining them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a rotary transformer used for transmitting / receiving a signal to / from a rotating magnetic head such as a video tape recorder, a video camera and a digital audio tape recorder.

[0002]

2. Description of the Related Art Rotary transformers used in magnetic recording / reproducing devices such as video tape recorders, video cameras and digital audio tape recorders are classified into two types, disk type and cylindrical type. The use of cylindrical rotary transformers has increased due to the increase in the number of channels and the increase in the density required for the multi-functionalization.

In the structure of this rotary transformer, both an inner core made of a cylindrical ferrite and an outer core made of a ferrite are coaxially opposed to each other with a certain minimum gap maintained, and the respective surfaces are opposed to each other. Is provided with a coil groove having the required number of channels, and the coil is mounted in the coil groove. In addition, a concave groove for fitting a short ring is provided between each channel of the inner core.

In the rotary transformer having the above structure, it is preferable that the facing gap between the inner core 1 and the outer core 2 is as narrow as possible so long as it does not hinder the rotation in order to minimize the loss of the recording / reproducing signal current. Actually, a rotary transformer used for a video tape recorder or a digital audio tape recorder has a size of 70 μm or less, and particularly for a rotary transformer used for a small video camera. 6
An extremely high precision gap amount of 0 μm or less is required. In order to meet this requirement, it is necessary to accurately control the surface roughness, the circularity, the concentricity, and the assembling accuracy of the inner core and the outer core, which are particularly facing surfaces.

A ferrite core for a rotary transformer is usually manufactured as follows. First, as shown in FIG. 17, a cylindrical ferrite sintered body is manufactured and then finished by special machining to obtain desired dimensional accuracy. In the figure, raw materials are mixed and mixed in a desired composition, and then calcined at a temperature of 1000 ° C. or less. Next, this pre-baked product is pulverized, and an appropriate amount of a binder such as an aqueous solution of polyvinyl alcohol (PVA) is added to the pulverized powder for granulation, and then the granulated powder is uniaxially compression-molded by a cylindrical mold. The cylindrical molded body thus obtained is subjected to main firing at a high temperature of 1000 ° C. or higher to obtain a cylindrical ferrite sintered body, or the above calcinated powder of ferrite calcination is kneaded with a resin and transfer molded into a cylindrical shape, followed by degreasing. There are two methods of obtaining the same ferrite sintered body by carrying out a high temperature main firing at 1000 ° C. or higher after the heat treatment step (see JP-A-61-84006).

However, in either of the above-mentioned methods, the molded body is accompanied by firing shrinkage and deformation of 10% or more during firing, so that the obtained ferrite sintered body is dimensionally and accurately used as a ferrite core for a rotary transformer. It is very difficult to meet the strict requirements of

Therefore, for example, when a cylindrical core is manufactured, it is usually performed as follows. First, prepare a cylindrical ferrite sintered body with an inner and outer diameter having a margin of about 1 mm or more larger than the desired size, and then perform the primary grinding of the outer peripheral surface of this cylindrical ferrite sintered body with a centerless grinder. Roughly grind the inner peripheral surface with an inner surface grinding machine based on the outer peripheral surface, and then finish both the inner and outer peripheral surfaces with a special grinding machine, and then form the groove for the coil of the required number of channels along the inner or outer circumference. Simultaneous grooving with a grinding wheel or continuous rotary blade has achieved dimensional accuracy as the final product of a ferrite core for a cylindrical rotary transformer.

In this case, the portion requiring particularly high precision is the relative gap size between the two cylindrical cores, and the groove machining occupies the highest proportion as the number of machining steps. After that, the coil is wound in the groove for the coil, and the inner core and the outer core are assembled to complete the rotary transformer.

[0009]

As described above, in the conventional ferrite core for a cylindrical rotary transformer, it is inevitable that the sintered product is significantly shrunk and the central part of the sintered product is warped. Prepare a cylinder-type or disc-type ferrite sintered product with a margin that allows for advance, and finally obtain the desired size and precision from rough grinding to precision machining.
In addition, the ferrite core for rotary transformers is finished by performing groove processing for coil mounting. However, this method has a big problem that it is difficult to manufacture at low cost because the manufacturing yield is bad, especially because the number of processing steps such as groove processing is large, and because the material is hard, cracks and chips occur during processing. It was

Further, in the conventional method, there is no method of forming the groove on the inner peripheral surface of the outer core by molding, and all the groove processing is a method of machining.

The present invention solves the above-mentioned drawbacks of the prior art and provides a method for manufacturing a cylindrical rotary transformer at low cost by forming a groove on the inner peripheral surface of an outer core by molding.

[0012]

In order to solve the above-mentioned problems, the present invention is directed to the periphery of the central axis of a vertical groove forming die having a vertical groove forming piece projecting in at least a part of the central axis in the radial direction. An internal mold is formed by combining a lateral groove forming mold having a plurality of concave grooves formed on the peripheral surface of the vertical groove forming mold and forming a lateral groove around the vertical groove forming mold. The outer circumference of the is covered with a cylindrical outer mold, magnetic powder is filled between the outer mold and the inner mold, and a pressing mold is inserted between the inner mold and the outer mold to make the magnetic After compression molding the powder, first remove the vertical groove forming mold of the inner mold, move the horizontal groove forming mold in the direction of the central axis and extract it from the molded body, and then remove the push mold, The molded body extracted from the mold is treated at high temperature to form a cylindrical core, and the coil is installed in the lateral groove of the inner peripheral surface of this cylindrical core. Constitutes an outer coil and the inner coil to form a coil on the lateral grooves of the outer circumferential surface to a method of manufacturing a rotary transformer incorporated within said outer coil.

[0013]

The method of manufacturing a rotary transformer according to the present invention is different from the conventional method of forming the groove on the inner peripheral surface of the cylindrical core by machining, so that the method is performed up to now. There is an effect that the groove processing step is unnecessary, and a much cheaper one than the conventional one can be obtained.

[0014]

EXAMPLE As a manufacturing method of the core for a rotary transformer, as shown in FIG. 2 as an example, first, a vertical groove having four plate-shaped vertical groove forming pieces 8 protruding radially from a central shaft 7 is formed. A lateral groove forming die 10 is provided around the forming die 9 in which a desired number of channels are provided with a plurality of recessed grooves 10b which are divided into four and have tapered portions 10a at both ends to form lateral grooves.
Is combined and fixed around the vertical groove forming die 9 with caps 11 and 12 having a taper on the inner cylindrical portion to obtain an inner die 13 as shown in FIG. Next, as shown in FIG. 4, after inserting the inner mold 13 into the downward pressing mold 14, as shown in FIG. 5, the outer circumference of the inner mold 13 is covered with a cylindrical outer mold 15, and the outer mold is A desired amount of magnetic powder is filled between the die 15 and the inner die 13, and the lower pressing die 14 and the upper pushing die 17 are inserted between the inner die 13 and the outer die 15 and pressed. The machine performs compression molding as shown in FIG.

Next, as shown in FIG. 7, after removing the caps 11 and 12 for fixing the four lateral groove forming molds 10,
As shown in FIG. 8, the vertical groove forming die 9 is extracted. Next, as shown in FIG. 9, the center rod 30 having screw parts at the upper and lower ends which are opposite to each other is inserted into the space where the vertical groove forming die 9 is removed, and the screw parts at the upper and lower ends are tapered to the inner cylindrical part. The punching dies 31 and 32 having the above are screwed in from the vertical direction to just before the taper portions of the four lateral groove forming dies 10. Then, as shown in FIG. 10, by rotating the center rod 30 in a direction in which the punching dies 31 and 32 approach each other, the punching dies 31 and 32 are operated at the same speed, and the punching die and the lateral groove forming die 10 are moved. By utilizing the mutual taper, four lateral groove forming dies 10 are formed.
Is moved in the direction of the central axis to extract the molded body 18 from the molded body 18 as shown in FIG. 11, and finally, as shown in FIG.

At this time, the order of taking out the molded body 18 is not limited to this example. First, the outer mold 15 is moved to the molded body 18 first.
It is also possible to remove the vertical groove forming mold 9 of the inner mold 13 after removing, and to remove the horizontal groove forming mold 10 in the central axis direction in the same manner as described above, and then to remove from the molded body 18.

Next, the molded body 18 thus obtained is subjected to a high temperature treatment to form a cylindrical core, and as shown in FIG. 13, this cylindrical core is used as an outer core 2 and the coil 4 is incorporated in a lateral groove on its inner peripheral surface. The outer coil is formed, and in the inner core, the coil 4 is formed in the lateral groove of the outer peripheral surface of the inner coil to form the inner coil, which is incorporated into the outer coil to manufacture the rotary transformer.

Here, an example in which the number of vertical grooves is four has been described, but the number of vertical grooves is not limited to this.
It suffices that a vertical groove forming die having a number of vertical grooves equal to or more than a number and a lateral groove forming die divided into a corresponding number are combined.

Further, the magnetic powder may be a calcined powder of ferrite, a mixture of highly crystalline ferrite magnetic powder which has been sufficiently made into ferrite by high temperature firing and glass powder, or a mixture of these and a resin.

Further, in the case of compression molding, in the case of a mixture of the above glass powder or resin, it can be carried out in a heated state at a temperature at which the glass powder or resin is melted. The resin may be either thermosetting or thermoplastic.

Specific examples will be described below. (Example 1) As shown in FIG. 1, Fe ₂ O ₃ 48.1mo
1%, NiO 14.2 mol%, ZnO 34.0 m
ol% and CuO 3.7 mol% are mixed and mixed, and 5 wt% of a 5 wt% aqueous solution of polyvinyl alcohol (hereinafter referred to as PVA) is added to this mixture.
The granulated product was calcined at 1250 ° C. for 6 hours and pulverized to prepare a Ni—Zn—Cu based soft ferrite main calcined powder having an average particle size of 50 μm. As a result of X-ray diffraction of this powder, a sharp spinel structure diffraction line peculiar to soft ferrite was obtained, and it was confirmed to be a magnetic powder having extremely high crystallinity. Next, 3 wt% of an alkali-free lead borosilicate glass powder having a softening point (Td) of 370 ° C. and an average particle diameter of 1 μm is added to the above highly crystalline ferrite magnetic powder and mixed, and then granulated.

Next, in order to form the concave groove and the vertical groove for winding the coil on the opposite surfaces of the two cylindrical cores by molding, the outer core molding is shown in FIGS. A mold is filled with a desired amount of granulated powder by the manufacturing method shown below, and main molding is performed at a pressure of 3 ton / cm ² to obtain a cylindrical molded body for outer core having lateral grooves and vertical grooves.

Further, in the case of the inner core, since the concave groove is formed on the outer peripheral surface, the concave groove is provided as shown in FIGS.
A desired amount of the above-mentioned granulated powder is filled in each split mold 21, and the upper and lower push molds 22, 23 are pressed at a pressure of 3 ton / cm ² as above.
The inner core cylindrical molded body 24 having a groove for coil, a groove for short ring, and a vertical groove formed by pressure molding with
Was produced. The obtained molded body is placed in an electric furnace and
Heat treatment was performed in air at 00 ° C. for 60 minutes to prepare a glass binding type ferrite core for a rotary transformer.

Next, as shown in FIG. 13, these concave grooves 3 and 5 are formed.
A coil 4 or a short ring 6 was wound around the core, and two cores 1 and 2 were combined to produce a rotary transformer.

The material properties of Example 1 are shown in (Table 1). In Example 1, the shrinkage rate of the core was 0.1% or less, there was almost no core shrinkage due to heat treatment, and the roundness of the central part of the core was almost 8 μm or less, so that the mold dimension was obtained and the outside was obtained. The gap between the core and the inner core was 70 μm or less, which made it possible to realize a highly accurate cylindrical rotary transformer and also to obtain excellent magnetic characteristics and transformer characteristics.

(Example 2) 3 wt% of the same glass powder and 5 wt% of epoxy powder as a resin were added to and mixed with the same ferrite main baked powder used in Example 1, and the mixture was heated to a temperature not lower than the softening temperature of the resin. After heat kneading at 90 ° C. for 2 minutes, crushing and granulating this, the desired amount of this granulated powder was filled in the same mold as in Example 1, and the mold temperature was 180 ° C. for 30 seconds for 1 t.
Compression molding is performed at on / cm ² to obtain a cylindrical molded body for the outer core having lateral grooves and vertical grooves.

Further, in the case of the inner core, since the concave groove is formed on the outer peripheral surface, the concave groove is provided as shown in FIGS. 15 and 16.
A desired amount of the above-mentioned granulated powder is filled in each split mold 21, and pressure molding is performed by the upper and lower pressing molds 22 and 23 at a mold temperature of 180 ° C. for 30 seconds at a pressure of 1 ton / cm ² as described above, A cylindrical molded body 24 for an inner core having a groove for a coil, a groove for a short ring, and a vertical groove was produced.

Next, these molded bodies were individually placed in an electric furnace, and after undergoing a degreasing step, they were heat treated in air at 1200 ° C. for 60 minutes to obtain a glass-bonding type ferrite core for a cylindrical rotary transformer, Then, a rotary transformer was produced in the same manner as in Example 1.

The material properties of Example 2 are shown in (Table 1). In Example 2, the shrinkage ratio of the core was 0.1% or less, there was almost no core shrinkage due to heat treatment, and the roundness of the central part of the core was almost 6 μm or less, so that the mold dimension was obtained and the outside was obtained. The gap between the core and the inner core was 70 μm or less, which made it possible to realize a highly accurate cylindrical rotary transformer and also to obtain excellent magnetic characteristics and transformer characteristics.

(Comparative Example 1) A mixed powder of starting materials having the same composition as in Example 1 is pre-baked at 1000 ° C for 2 hours. Next, the pre-baked powder is finely pulverized to 2 to 5 μm, and 5 wt% of a 5 wt% PVA aqueous solution is added to the pulverized powder for mixing and granulation. After the desired amount of the obtained granulated powder was filled in the same mold as in Example 1, the mixture was compression-molded with a press at a pressure of 3 ton / cm ² to form a cylindrical molded body for the outer core having lateral grooves and vertical grooves. Was produced.

Further, in the case of the inner core, since the concave groove is formed on the outer peripheral surface, the concave groove is provided as shown in FIGS.
A desired amount of the above-mentioned granulated powder is filled in each split mold 21, and the upper and lower push molds 22, 23 are pressed at a pressure of 3 ton / cm ² as above.
The inner core cylindrical molded body 24 having a groove for coil, a groove for short ring, and a vertical groove formed by pressure molding with
Was produced.

Next, these compacts were individually placed in an electric furnace and subjected to main firing in air at 1200 ° C. for 3 hours to obtain Ni--Zn.
A -Cu-based cylindrical ferrite core was obtained. Since the obtained cylindrical ferrite core contracted by 10% or more during firing and had a large roundness of 50 μm or more, the dimensional specifications required could not be satisfied.

The material properties of Comparative Example 1 are shown in (Table 1).

[0034]

[Table 1]

[0035]

As described above, in the rotary transformer manufacturing method of the present invention, the cores are all machined by the conventional methods, but the manufacturing process is very simple because the cores are manufactured by die molding. Since the cost can be significantly reduced, a rotary transformer that is much cheaper than the conventional one can be obtained.

[Brief description of drawings]

FIG. 1 is a process drawing of a manufacturing process showing an embodiment of a method for manufacturing a rotary transformer of the present invention.

FIG. 2 is an exploded perspective view of an inner die used in the method.

FIG. 3 is a perspective view of the internal mold.

FIG. 4 is a perspective view showing a state where the internal mold is assembled into a downward pressing mold.

FIG. 5 is a perspective view showing a state in which an outer die is incorporated into the inner die and magnetic powder is supplied.

FIG. 6 is a perspective view of the molding die during molding.

FIG. 7 is a partially cutaway perspective view showing a state where the cap is removed after the molding.

FIG. 8 is a partially cutaway perspective view showing a state in which the vertical groove forming die is removed.

FIG. 9 is a partially cutaway perspective view showing a state in which the same punching die is assembled.

FIG. 10 is a partially cutaway perspective view showing a state where the same punching die is incorporated.

FIG. 11 is a perspective view showing a state in which the lateral groove forming die is removed.

FIG. 12 is a partially cutaway perspective view showing a state where the molded body is taken out.

FIG. 13 is a sectional view of a rotary transformer formed by the same method.

FIG. 14 is a perspective view of a molding die of another embodiment.

FIG. 15 is a sectional view showing molding of the inner core in the present invention.

FIG. 16 is an explanatory diagram of the same.

FIG. 17 is a process diagram showing a manufacturing process of a conventional rotary transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 inner core 2 outer core 3 groove for coil 4 coil 5 groove for short ring 6 short ring 7 center axis 8 vertical groove forming piece 9 vertical groove forming die 10 lateral groove forming die 10a taper portion 10b concave groove 11 , 12 Cap 13 Inner mold 14 Lower push mold 15 External mold 16 Magnetic powder 17 Top push mold 18 Molded body 19 Punching die 20 Heater 21 Split mold 22 Top push mold 23 Bottom push mold 24 Molded body 30 Center Rod 31, 32 punching type

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Atsushi Inuzuka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Hiroshi Fujii 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A vertical groove forming die having a vertical groove forming piece which projects in a radial direction on at least a part of the central axis. The vertical groove forming die is divided into two or more parts around the central axis. An inner mold is formed by combining lateral groove forming dies having a plurality of concave grooves for forming lateral grooves on the peripheral surface, and the outer periphery of the inner mold is covered with a cylindrical outer mold. After filling the magnetic powder between the mold and the inner mold and inserting the pressing mold between the inner mold and the outer mold to compress and mold the magnetic powder, first the vertical groove of the inner mold. Extract the forming die, move the lateral groove forming die in the direction of the central axis to extract it from the compact, remove the push mold, and then subject the compact extracted from the outer mold to a high temperature to form a cylindrical core. , The outer coil is formed by incorporating the coil in the lateral groove of the inner peripheral surface of this cylindrical core, and the coil is formed in the lateral groove of the outer peripheral surface. A method for manufacturing a rotary transformer, wherein the formed inner coil is incorporated into the outer coil. 2. A magnetic powder comprising a mixture of highly crystalline ferrite magnetic powder, which has been sufficiently ferritized by high temperature firing, and glass powder, or the magnetic powder or a mixture thereof containing a resin. Item 1. A method for manufacturing a rotary transformer according to Item 1.