JP3114222B2 - Manufacturing method of rotary transformer - Google Patents

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 for transmitting and receiving signals to and from a rotating magnetic head such as a video tape recorder and a digital audio tape recorder.

[0002]

2. Description of the Related Art There are two types of rotary transformers used in magnetic recording / reproducing devices such as video tape recorders and digital audio tape recorders, disc type and cylindrical type. The use of cylindrical rotary transformers has been increasing due to the increase in the number of channels required and the increase in density with the development.

FIG. 13 shows a schematic sectional view of this structure.
As shown in the figure, the structure of the rotary transformer is such that both an inner core 1 made of a cylindrical ferrite and an outer core 2 made of a ferrite are coaxially opposed to each other and kept at a certain minimum gap. A coil groove 3 of a required number of channels is provided on each opposing surface, and a coil 4 is mounted in the coil groove 3. In addition, a concave groove 5 into which a short ring 6 is inserted is provided between each channel of the inner core 1.

In the rotary transformer having the above-described structure, it is preferable that the opposing gap between the inner core 1 and the outer core 2 is as small as possible, so long as the rotation is not hindered in minimizing the loss of the recording / reproducing signal current. Actually 70 μm
An extremely high precision gap amount as follows is required. In order to satisfy this requirement, it is necessary to precisely control the surface roughness, the roundness, the coaxiality, and the assembling accuracy of the inner core 1 and the outer core 2 which are particularly opposed 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 prepared, and then finished by special machining in order to obtain a desired dimensional accuracy. In the figure, after the raw materials are blended and mixed in a desired composition, they are calcined at a temperature of 1000 ° C. or less. Next, the calcined product is pulverized, an appropriate amount of a binder such as an aqueous solution of polyvinyl alcohol (PVA) is added to the pulverized powder and granulated, and then the granulated powder is compression-molded in a mold. The cylindrical molded body obtained in this way was
After firing at a high temperature of 00 ° C. or higher to obtain a cylindrical ferrite sintered body, or kneading the ferrite calcined and crushed powder with a resin, transfer molding into a cylindrical shape, and then performing a heat treatment process for degreasing, There are two methods for obtaining a similar ferrite sintered body by performing high-temperature main firing at 1000 ° C. or higher (see Japanese Patent Application Laid-Open No. 61-84006).

However, the ferrite sintered body obtained by either of the above methods causes a large shrinkage or warpage of 10% or more as compared with the size of the molded body before firing, so that the size and precision of the ferrite sintered body can be improved as it is. However, it is very difficult to meet the strict requirements for a rotary transformer core.

Therefore, for example, when a cylindrical core is manufactured, the following is usually performed. First, a cylindrical ferrite sintered body whose inner and outer diameters have a margin of about 1 mm or more from the desired dimension is prepared, and the outer peripheral surface of the cylindrical core is first ground by a centerless grinder, and then the outer peripheral surface is After roughing the inner peripheral surface with an internal grinding machine as a reference, and then finishing both the inner and outer peripheral surfaces with a special grinder, groove grooves for coil of the required number of channels along the inner or outer circumference Simultaneous groove processing is performed by the rotary continuous blade to obtain dimensional accuracy as the final product of the cylindrical rotary transformer core.

[0008] At this time, the part requiring particularly high precision is the relative gap size between the two cylindrical cores, and the proportion of the groove processing is the highest as the number of processing steps.

[0009]

In such a conventional ferrite sintering technique, a large shrinkage or warping phenomenon of the sintered product is inevitable. Alternatively, a disc-shaped ferrite sintered product is manufactured, and the desired dimensions and accuracy are finally obtained by rough machining from precision grinding, and further, a groove for coil mounting is performed to finish the ferrite core for a rotary transformer. However, this method has a major problem that it is difficult to make it at low cost because of the large number of processing steps, especially grooving, and the poor process yield such as cracking and chipping due to the rigid material. there were.

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

An object of the present invention is to solve the above-mentioned disadvantages of the prior art and to provide 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. is there.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a mold for forming a vertical groove having a vertical groove forming piece protruding in a radial direction on at least a part of the central axis. The inner die is formed by combining a horizontal groove forming die having a plurality of ridges formed on the peripheral surface around the vertical groove forming die and being divided into two or more. The outer periphery of the mold is covered with a cylindrical outer mold, magnetic powder is filled between the outer mold and the inner mold, and the pressing mold is inserted between the inner mold and the outer mold. After compression-molding the magnetic powder, after removing the pressing mold, pull out the vertical groove forming mold of the inner mold,
The lateral groove forming die is moved in the direction of the central axis to be extracted from the molded body, and the molded body extracted from the external mold is subjected to a high temperature treatment to form a cylindrical core, and a coil is assembled in a lateral groove on the inner peripheral surface of the cylindrical core. The present invention relates to a method for manufacturing a rotary transformer in which an outer coil is formed by incorporating an inner coil having a coil formed in a lateral groove on an outer peripheral surface.

As a method of manufacturing the above-mentioned core, first, raw materials are mixed and mixed with a desired composition, and then calcined at a temperature of 1000 ° C. or less. Next, the calcined product is pulverized, an appropriate amount of a binder such as an aqueous solution of polyvinyl alcohol (PVA) is added to the pulverized powder and granulated, and then the granulated powder is filled in an appropriate amount into the mold and compression-molded. To produce a molded body. Next, the molded body having the molding groove obtained in this manner is subjected to main firing at a temperature higher than the pre-baking temperature to obtain a cylindrical core, or if necessary, a portion other than the molding groove is subjected to a minimum amount of machining to form a rotary transformer. This is a method of obtaining a core.

Alternatively, after blending and mixing the raw materials with a desired composition, the mixture is granulated with an aqueous PVA solution, and then subjected to high-temperature firing similar to the main firing, which is then pulverized and sufficiently ferritized. Obtain a crystalline soft ferrite magnetic powder (referred to as main firing powder), then mix and granulate a glass powder having a softening point lower than the firing temperature with the main firing powder, and fill the mold with an appropriate amount. A compression molded article is produced. Next, a method for obtaining a core for a rotary transformer by subjecting the thus obtained molded body having molding grooves to a heat treatment at a temperature not lower than the softening temperature of the glass powder and not higher than the firing temperature of the ferrite powder.

As another method, a glass powder or a glass powder interposed between magnetic powders is heated while molding a mixture of the ferrite magnetic powder and the glass powder or a mixture of the magnetic powder and the resin containing the resin. After the resin is softened and melted and compression-molded to produce a molded body, a heat treatment is similarly performed to obtain a rotary transformer core.

[0016]

The method of manufacturing a rotary transformer according to the present invention is different from the conventional method of forming a groove on the inner peripheral surface of a cylindrical core by machining, so that the groove is formed by molding. Since there is an effect that the groove processing step becomes unnecessary, there is a feature that a far cheaper one can be obtained than the conventional one.

[0017]

Embodiments of the present invention will be described below.

As an example of a method of manufacturing the core for the rotary transformer, as shown in FIG.
In the vicinity of a vertical groove forming die 9 having four plate-like vertical groove forming pieces 8 protruding in the radial direction, it is desirable to have a ridge which is divided into four and has tapered portions at both ends to form a horizontal groove. 3. The lateral groove forming die 10 provided around the number of channels described above is fixed to the periphery of the vertical groove forming die 9 by caps 11 and 12 having a tapered inner cylindrical portion, and fixed. Type 1
Get 3. Next, as shown in FIG. 4, the inner mold 13 is inserted into the downward pressing mold 14, and then, as shown in FIG.
Is covered with a cylindrical outer mold 15 and the outer mold 1
A desired amount of magnetic powder 16 is uniformly filled between the inner mold 5 and the inner mold 13 by a powder supply nozzle 18 or the like, and the lower press mold 14 and the upper mold 14 are interposed between the inner mold 13 and the outer mold 15. The magnetic powder 16 is compression molded as shown in FIG.

Next, as shown in FIG. 7, the fixing caps 11, 12 of the four lateral groove forming dies 10 are removed, and then the vertical groove forming dies 9 are removed as shown in FIG.

Next, as shown in FIG. 8, a center rod 30 having oppositely threaded portions at upper and lower ends is inserted into a vertical groove forming mold 9.
Into the space from which the upper and lower ends of the threaded portions are tapered.
The horizontal groove forming die 10 is screwed down to just before the tapered portion.
Then, as shown in FIG.
2 are rotated in the direction in which they approach each other, so that the blanking dies 31 and 32 are moved at the same speed. The mold 10 is moved in the direction of the central axis to extract the molded body 19 from the molded body 19 as shown in FIG. 11, and finally, the molded body 19 is extracted from the external mold 15 by the extraction mold 20 as shown in FIG.

At this time, the order of taking out the molded body is not limited to this example. First, the molded body 19 is pulled out from the outer die 15 and then the vertical groove forming die 9 of the inner die 13 is pulled out.
The lateral groove forming die 10 may be moved in the central axis direction in the same manner as described above, and may be extracted from the molded body 19.

Next, the molded body 19 thus obtained is subjected to a high-temperature treatment to form a cylindrical core. As shown in FIG.
To form an outer coil. In the inner core, a coil 4 is formed in a lateral groove on the outer peripheral surface of the outer coil to form an inner coil, and this is incorporated in the outer coil to produce a rotary transformer.

Here, an example in which the number of vertical grooves is four has been described. However, the present invention is not limited to this. Basically, a vertical groove forming mold having two or more vertical grooves, It suffices that the horizontal groove forming die divided into the predetermined number is combined with the die.

The magnetic powder may be a preliminarily baked powder of ferrite, a mixture of a highly crystalline ferrite magnetic powder which has been sufficiently ferritized by firing at a high temperature and a glass powder, or a mixture of these and a resin.

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

Hereinafter, specific embodiments will be described. (Example 1) Fe ₂ O ₃ as shown in FIG. 1 48 mol%,
NiO 14mol%, ZnO 34mol%, CuO 4mo
1% of a starting material is blended and mixed, and a 5 wt% aqueous solution of polyvinyl alcohol (PVA) is added to the mixture at 5 wt%.
In addition, what was granulated and fired at 1250 ° C. for 6 hours was crushed to obtain a Ni—Zn—C having an average particle diameter of 50 μm.
A u-based soft ferrite main firing powder was prepared. As a result of X-ray analysis of this powder, a sharp spinel structure diffraction line peculiar to soft ferrite was obtained, and it was confirmed that the powder was a magnetic powder having extremely high crystallinity. Next, 3 wt% of a non-alkali lead borosilicate glass powder having a softening point (Td) of 370 ° C. and an average particle size of 1 μm is added to the highly crystalline ferrite magnetic powder, and the mixture is granulated.

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

Further, in the case of the inner core, in order to form a concave groove on the outer peripheral surface, as shown in FIGS.
Each of the split molds 22 is filled with a desired amount of the above-mentioned granulated powder, and pressed and formed with upper and lower pressing dies 23 and 24 at a pressure of 3 ton / cm ^{2 in} the same manner as described above to form a coil groove and a short ring groove. Further, a cylindrical molded body 25 for the inner core having a vertical groove was produced.

These compacts were individually placed in an electric furnace and heated at 1200 ° C. for 60 minutes in air to obtain a glass-bound ferrite core for a cylindrical rotary transformer.

Next, as shown in FIG.
, A coil 4 or a short ring 6 was wound thereon, 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 core shrinkage was 0.1% or less, and almost no core shrinkage due to heat treatment resulted in a mold having the same dimensions as the mold. The gap between the outer core and the inner core was 70%.
An extremely high precision cylindrical rotary transformer of less than μm could be realized, and a magnetic and transformer with excellent characteristics were obtained.

[0032]

[Table 1]

EXAMPLE 2 The same ferrite main powder used in Example 1 was mixed with 3 wt% of the same glass powder and 5 wt% of epoxy powder as a resin, and then mixed. Heat kneading at 90 ° C for 2 minutes
After granulation, a desired amount of the granulated powder was filled in the same mold as in Example 1, and the mold temperature was 180 ° C. for 30 seconds, and 1 ton / c.
By compression molding with m ² , ^two cylindrical molded bodies were produced.

Next, these compacts were individually placed in an electric furnace, subjected to a degreasing step, and heat-treated in air at 1200 ° C. for 60 minutes to obtain a glass-bound ferrite core for a cylindrical rotary transformer. Then, a rotary transformer was manufactured in the same manner as in Example 1.

In Example 2 in which the material properties of Example 2 are shown in (Table 1), the contraction rate of the core is 0.1% or less, and there is almost no core shrinkage due to heat treatment. As a result, an extremely high precision cylindrical rotary transformer having a gap between the outer and inner cores of 70 μm or less was realized, and a magnetic rotary transformer having excellent transformer characteristics was obtained.

Example 3 A 5 wt% aqueous solution of PVA was added to a mixture of starting materials having the same composition as in Example 1 to obtain a mixture of 5 wt%.
In addition, the granulated powder is calcined at 1000 ° C. for 2 hours, finely pulverized to 2 to 5 μm, and the granulated powder is divided into two cylindrical compacts in the same manner as in Examples 1 and 2. Produced.

This molded product was placed in an electric furnace, and 1200
After sintering in air at 3 ° C. for 3 hours, the temperature was lowered while cooling down to obtain a Ni—Zn—Cu ferrite sintered type cylindrical core.

The material properties of Example 3 are shown in (Table 1). In Example 3, the core shrinkage was 10%, but the inner core and the outer core were easily machined to a high precision cylindrical mold simply by subjecting the inner and outer peripheral surfaces other than the molding grooves to minimum dimensions. A rotary transformer was obtained, and a magnetic transformer and a transformer having excellent characteristics were obtained.

Example 4 The same ferrite main powder used in Example 1 was mixed with 10 wt% of the same glass powder, mixed, and then granulated with an aqueous PVA solution. Next, the granulated powder is uniformly filled in a desired amount in the same mold made of stellite in the same manner as in Example 2. At this time, a heater is attached to the outer mold around the mold as shown in FIG.
The mold was pressed up and down at a temperature of 1 ° C. for 1 minute at a pressure of 1 ton / cm ² , and molding was performed while softening and melting the glass powder interposed between the magnetic powders. After the completion of the molding, the mold was cooled, and the core was taken out in the same manner as in Example 2 to produce two cylindrical molded bodies.

Next, these compacts were individually placed in an electric furnace, and heat-treated in air at 1200 ° C. for 60 minutes to obtain a glass-bound type ferrite core for a cylindrical rotary transformer. To produce a rotary transformer.

The material properties of Example 4 are shown in (Table 1). In Example 4, the core shrinkage was 1% and the core shrinkage due to the heat treatment was small, so that a size close to the mold size was obtained. The gap between the outer and inner cores was a very high precision cylindrical rotary transformer of 70 μm or less. Can be realized, and the magnetic characteristics,
Excellent transformer characteristics were obtained.

In the first, second, third and fourth embodiments, the powder was charged into the mold by the method of filling the granulated powder. And a cylindrical core may be produced in the same manner as described below.

[0043]

As described above, in the method of manufacturing a rotary transformer according to the present invention, the core is obtained by machining in the conventional method, but the manufacturing process is very simple because the core is manufactured by molding. Since the cost can be significantly reduced, a rotary transformer that is far less expensive than the conventional one can be obtained.

[Brief description of the drawings]

FIG. 1 is a process diagram of a manufacturing process showing one embodiment of a method for manufacturing a rotary transformer according to the present invention.

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

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

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

FIG. 5 is a perspective view showing a state in which an outer mold is incorporated into the inner mold 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 in which a cap is removed after the molding.

FIG. 8 is a partially cutaway perspective view showing a state where the vertical groove forming mold is removed.

FIG. 9 is a partially cutaway perspective view showing a state where the punching die is incorporated.

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

FIG. 11 is a perspective view of a state where the lateral groove forming mold is removed.

FIG. 12 is a partially cutaway perspective view showing a state in which 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 according to another embodiment.

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

FIG. 16 is an explanatory view of the same.

FIG. 17 is a process chart showing steps of a conventional method for manufacturing a rotary transformer.

[Explanation of symbols]

 Reference Signs List 1 inner core 2 outer core 3 concave groove for coil 4 coil 5 concave groove for short ring 6 short ring 7 center axis 8 vertical groove forming piece 9 vertical groove forming die 10 horizontal groove forming die 11, 12 cap 13 inner shape Mold 14 Lower die 15 External die 16 Magnetic powder 17 Upper die 18 Powder supply nozzle 19 Mold 20 Molding die 21 Heater 22 Split mold 23 Upper die 24 Lower die 25 Mold 30 Center rod 31, 32 punching die

────────────────────────────────────────────────── ─── Continuation of the front page (72) Michio Ohba, Inventor 1006 Odaka, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-61-84006 (JP, A) JP-A-63 JP-A-3-289106 (JP, A) JP-A-3-289112 (JP, A) JP-A-3-289113 (JP, A) JP-A-5-47575 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01F 23/00 H01F 41/02

Claims (4)

(57) [Claims] 1. At least a part of a longitudinal axis forming die having a longitudinal groove forming piece protruding in a radial direction on at least a part of a central axis.
One or more divided horizontal groove forming dies are combined with the periphery of the vertical groove forming die with a fixing cap to form an inner die, and a down-pressing die is inserted into the lower surface of the inner die, and A cylindrical outer mold is placed over the outer periphery of the mold, magnetic powder is filled between the outer mold and the inner mold, and an upward pressing mold is inserted into the open surface of the outer mold. After the magnetic powder is compression-molded, the fixing cap is withdrawn, and the vertical groove forming mold is withdrawn. The center rod having opposing screw portions at upper and lower ends in the space from which the vertical groove forming mold is removed. , And the punching die is screwed to the vicinity of the horizontal groove forming die, and the horizontal groove forming die, the upper pressing die, the lower pressing die and the punching die are moved in the central axis direction by rotating the center rod. And then withdrawn from the compact and molded out of the outer mold Into a cylindrical core by high-temperature treatment, a coil is incorporated in a lateral groove on the inner peripheral surface of the core to form an outer coil, and an inner coil having a coil formed in a lateral groove on the outer peripheral surface is incorporated into the outer coil. Manufacturing method of rotary transformer. 2. A lateral groove is formed by rotating a center rod.
Center axis for dies, up-press dies, down-press dies and punching dies
Direction, remove from the molded body, and remove from the external mold.
Process of processing the extruded compact at high temperature to form a cylindrical core
Instead, pull out the molded body from the outer mold and rotate the center rod to press the upper mold
Move the die, down-press die and punch die in the direction of the center axis.
And remove the molded body from the
2. The method for producing a rotary transformer according to claim 1 , wherein said step is a step of forming a cylindrical core . 3. A magnetic powder comprising a mixture of a highly crystalline ferrite magnetic powder and a glass powder whose ferrite has been sufficiently formed by firing at a high temperature, or a resin containing the magnetic powder or a mixture thereof. Item 7. A method for producing a rotary transformer according to Item 1. 4. The method for producing a rotary transformer according to claim 3, wherein the compression molding is performed in a heated state in which the glass powder or the resin is melted.