JPH07114173B2 - Green body for flat plate type rotary transformer core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is manufactured by injection molding a mixture of sinterable ferrast powder and a binder, and produces a flat plate rotary transformer core through the steps of degreasing and sintering. In this case, the amount of warpage deformation that occurred during sintering was determined by observing the pin gate marks on the surface of the core, which has excellent mass productivity and is ground and polished on both sides after sintering, and where the coil groove is not provided, The present invention relates to a flat plate type rotary transformer core green body capable of discriminating defective groove depth products.

[Conventional technology]

In the rotary drum device of the rotary head type VTR, a rotary transformer is used as an electric signal transmitting means between the rotating part and the stationary part.

The rotary transformer has a rotary core, which is an annular plate-shaped rotating portion, and a status core, which is a stationary portion, made of a ferrite sintered body.

As shown in FIGS. 9 to 11, these cores are provided with a plurality of concentric coil grooves 2 on one surface of an annular plate-shaped core 1, and the coil grooves 2 are provided with these coil outer circumferences. There is provided a diametrical drawing groove 3 which is connected to.

The rotary core and the status core thus configured have a rotor core 4 and a stator core 5 each having a coil groove 2 on the surface of 20 to 70 μm as shown in the sectional view of FIG.
Are opposed to each other with a gap 6 of each coil groove 2
A rotor coil 7 and a stator coil 8 having a predetermined number of turns are wound around the end, and the ends of the rotor coil 7 and the stator coil 8 are pulled out through the lead-out groove 3 and the
Connected to the R electric circuit.

In the rotary transformer having the above structure, it is necessary to strictly regulate and maintain the relative positional relationship between the rotor core 4 and the stator core 5. Therefore, the groove depth and bottom surface of each groove of the core,
High accuracy is required for the flatness and parallelism of the upper and lower surfaces.

Conventionally, a rotary transformer core (hereinafter referred to as a core) is made by pressing a mixture of sinterable ferrite powder and a binder such as polyvinyl alcohol or methyl cellulose to form a green body, degreasing and sintering the green body. However, since the deformation during sintering is large,
A three-fold sintered body is created and the groove surface and the opposite surface are ground to manufacture. In order to reduce such an amount of grinding, the present inventors have already proposed forming a green body for a rotary transformer core body using a film-shaped ring gate. (Japanese Patent Application No. 62-327101) [Problems to be solved by the invention] However, in order to manufacture a sintered body from a green body for a rotary transformer core body using the film ring gate, first, a film ring gate is used. Need to be removed. The removing step includes a punching step using a punching blade, and a step of processing a portion that remains as a burr after punching. Thus, when the film-shaped ring gate is used, an extra step is required to remove the gate.

Furthermore, even when degreasing and sintering the gate-treated green body, if the temperature inside the furnace fluctuates or if the moving speed of the feed carriage of the continuous furnace fluctuates, harmful warping or deformation of the sintered body occurs, causing grinding. There is a problem that the groove depths of the central part and the outer peripheral part of the later sintered body are different, and waviness occurs in each groove, and a step of removing these defective products is required. In order to remove defective products due to defective groove depth, it is necessary to perform a complicated process of measuring the total depth of each groove in the grinding body and determining the variation, especially in the multi-channel type with multiple grooves. Has a great influence on the transmission characteristics of the rotary transformer, so the accuracy of the groove depth is an important factor.

The inventors of the present invention have made intensive studies to solve the above-mentioned problems by injection-molding a mixture of sinterable ferrite and a binder, and as a result, sintered the resulting green body for a rotary transformer core body into a core. By devising the gate of the core body (hereinafter referred to as the core body green body), the gate cutting step when degreasing and sintering the core body green body is omitted, and the process of inspecting the groove depth of the grinding body is simplified. I found that I could do it.

The present invention has been made based on the above findings, and provides a core green body that can omit the gate cutting step of the green body and can simplify the groove depth inspection step after sintering and grinding. The purpose is to

[Means for Solving the Problems]

The present invention achieves the above-mentioned object, and a factor thereof is a flat body type rotary transformer core green body formed by injection-molding a mixture of a sinterable ferrite powder and a binder. An annular plate-shaped green body for a rotary transformer core with a coil groove is provided with a plurality of pin gates on the surface where the coil groove is not provided, and the pin gate is dented from the plane with the center of the ring symmetrical It is on the green body for the rotary transformer core provided at the position.

[Action]

Since the core green body according to the present invention has the above-described structure, the mixture injected from the pin gate at the spool tip into the mold has a structure in which the spool portion and the core body green body are in a uniform state when the mold is closed. However, the spool part and the green body are cut at the gate opening as a boundary at the stage when the mold is opened, and the gate processing step after injection molding is omitted. Further, since the plurality of pin gates are installed symmetrically with respect to the center of the annulus on the surface where the coil groove is not provided, and the tips are provided at positions recessed from the flat surface, the groove surface after sintering is Also, even if the sintered body undergoes harmful deformation such as distortion or warpage when the back surface is ground, the groove depth uniformity can be confirmed by visually observing the remaining state of the dents and pin gates on the back surface. It becomes possible to manage, and it is possible to simplify the inspection process of the complicated grinding body.

〔Example〕

1 to 3 are a perspective view, a backside plan view, and a vertical sectional view showing an embodiment of a core green body formed by injection-molding a mixture of sinterable ferrast powder and a binder according to the present invention. Is a ring-shaped green body for the core body.
Two concentric coil grooves 12 are provided on the upper surface of the core body green body, and these coil grooves 12 are provided with diametrically extending grooves 13 that connect the respective grooves to the outer circumference. A pin gate 16 is provided symmetrically with respect to the center of the circular ring at a position 15 recessed from the plane on the surface 14 of the core body green body 11 where the groove surface is not provided. The sinterable ferrite powder used for injection molding the core body green body configured as described above is a nickel-zinc system, magnesium-zinc system, manganese-zinc system ferrite calcined powder, and its average. The particle size can be 0.1 to 200 μm, but 0.1 to 150 μm is preferable, and 0.1 to 100 μm is particularly preferable.
Are preferred. If the average particle size is less than 0.1 μm, it will be difficult to uniformly disperse when kneading, and if it exceeds 200 μm, the shape retention during sintering will be poor and the density after sintering will decrease, resulting in poor magnetic properties and mechanical strength. descend.

Examples of the binder used include styrene-based polymers, ethylene-based polymers, propylene-based polymers, ethylene-vinyl acetate copolymers, alkyls (C6 or less).
A copolymer containing methacrylate as a main component (50 wt% or more) (for example, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate), an alkyl (C6 or less) acrylate as a main component (50 wt% or more) A copolymer (eg polymethyl acrylate,
Examples thereof include polyethyl acrylate and polybutyl acrylate. The number average molecular weight of these synthetic resin binders measured by vapor osmometry is 2000 to 500,000, especially 40
00 to 300,000 is preferable. To form a green body for a core body using the sinterable ferrite powder and the binder, first, a predetermined ratio of the ferrite powder and the binder (usually 5 to 4 parts of the binder with respect to 100 parts by weight of the ferrite powder).
0 parts by weight) and melt-kneaded to form pellets. The pellets are filled in an injection molding machine, melted, and injected into a mold.
The mold used is composed of an intermediate mold 17 having a recessed portion with the green body 11 for the core body as a boundary, a moving mold 18 for molding a groove surface, and a fixed mold 19 for injecting a melt into the mold. And the melt is the first spool 20, runner 21, second
The mold forming the spool 22 is filled, and the spool 22 is pressed into the core body green body molding portion from the pin gate 22 forming the second spool tip. After the injection is completed, the core body green body 11 is released from the intermediate mold 17 and remains in the movable mold 18 by cooling and solidifying and moving the intermediate mold 17 and the moving mold 18.
When the core body green body 11 is released from the intermediate mold 17, it is cut off by the second spool 22 and gated. The first spool 20, the runner 21, and the second spool 22 remain in the stationary mold 19 and are discharged. The core body green body 11 separated together with the moving mold 18 is released by projecting a projecting pin provided on the mold. The separated green body for core body is degreased, sintered, and further ground to obtain a core, and then the one lacking uniformity in groove depth is selected from the balance of the remaining state of the recess on the back surface. The above degreasing and sintering steps may be performed continuously or separately. The thickness of the core body green body 11 according to the present invention is usually 0.5 to 5 m / m, the diameter is 10 to 150 m / m, and the inner diameter is 5 to 50 m / m, although it depends on the performance of the intended rotary transformer. . The dents on the surface without grooves are circular or square with a diameter of 3 to 10 m / m or a side of 3 to 10 m / m, and a depth of 0.5 to 3 m / m, tapered or semicircular and stepped. The above shapes are also included in the present invention. The diameter of the pin gate in the central portion of the recess is 0.5 to 3 m / m, and the number of pin gates is 3 to 8.

〔effect〕

As described above, since the core body green body according to the present invention has the above-mentioned configuration, it does not require gate treatment,
When degreasing / sintering causes warping or bending, and there is a problem with groove depth uniformity after grinding, it is easy to select, does not require a complicated selection process, and does not require groove depth in transmission characteristics. Compared to the multi-groove type, which is likely to be affected, it has many advantages such as cheaper stable products.

[Brief description of drawings]

1 to 3 show an embodiment of a green body for a rotary transformer core according to the present invention. FIG. 1 is a perspective view, FIG. 2 is a rear plan view of FIG. 1, and FIG. FIG. 3 is a vertical sectional view of FIG. 4 to 6 show the shape of the recess of the gate portion according to the present invention. FIGS. 4 (b) and 4 (c) are plan views of the stepped recess, and FIG. 4 (a) is the stepped recess. 5B and 5C are plan views of the tapered concave portion, FIG. 5A is a vertical sectional view of the tapered concave portion, and FIG. 6B is a semicircular concave portion. Plan view, FIG. 6 (a)
FIG. 4 is a vertical cross-sectional view of a semicircular recess. 7 and 8 are vertical cross-sectional views showing the positional relationship between the core body green body, the spool, and the runner when the mold is closed and when the mold is open. 9 to 11 are plan views of the core grinding body. FIG. 9 is a plan view of the core grinding body having two grooves, FIG. 10 is four grooves, and FIG. FIG. 12 is a vertical sectional view showing an example of a rotary transformer. FIGS. 13 to 18 are plan views showing the back surface of the core grinding body, respectively. FIG. 13 shows a non-defective product with a uniform groove depth, and FIGS. 14 to 18 show a defective product with a non-uniform groove depth. It is a top view which shows an example. 1 ... Core grinding body, 2 ... Coil groove, 3 ... Drawing groove, 4
...... Rotor core, 5 ... Stator core, 6 ... Cap, 7 ... Rotor coil, 8 ... Starter coil,
11 …… Rotary transformer Green body for core body (green body for core body), 12 …… Green body coil groove, 13…
… Green body pull-out groove, 14 …… Green body back surface, 15 …… Pin gate recess, 16 …… Pin gate, 17 …… Intermediate mold, 18
...... Movable mold, 19 …… Fixed mold, 20 …… First spool,
21 …… Runner, 22 …… Second spool.

Claims (4)

[Claims] 1. A green body for a flat plate type rotary transformer core obtained by injection molding a mixture of a sinterable ferast powder and a binder, which is an annular plate shape having a plurality of concentric coil grooves on one surface. A flat plate having a plurality of pin gates symmetrical with respect to the center of the ring on the surface of the green body for the rotary transformer core body on which the coil groove is not provided, and the pin gates are provided at positions recessed from the plane. Type green body for rotary transformer core. 2. The vertical cross-sectional shape of the recess in which the pin gate is provided is
The flat body type rotary transformer core green body according to claim 1, wherein the green body has a stepped shape, a tapered shape, or a semicircular shape. 3. The flat plate type rotary transformer according to claim 1 or 2, wherein the green body is degreased and sintered, and then both sides are ground to leave a concave portion provided with a pin gate. 4. When a flat body for a rotary transformer core is injection-molded, a boundary of a surface of the core green body on which a plurality of concentric coil grooves is not provided is defined as a boundary.
Fixed with at least three or more pin gates symmetrical about the center of the ring and an intermediate mold for forming recesses in the vicinity thereof, a moving mold for forming coil grooves, and a spool part for injecting a melt into the mold. The green body for a flat plate type rotary transformer core according to claim 1 or 2, which is molded by using a mold having a mold structure.