JP2730961B2 - Cylindrical rotary transformer core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a cylindrical mold manufactured by subjecting a mixture of a sinterable ferrite powder and a binder to a green body by injection molding, followed by degreasing and sintering. The present invention relates to a rotary transformer core, and more particularly, to such a cylindrical rotary transformer core having a shape which enables mass productivity to be improved.

[Conventional technology]

2. Description of the Related Art In a drum device of a ruby type and a small rotary head type VTR (Video Tape Recorder), a rotary transformer is used as an electric signal transmission means between a rotating unit and a stationary unit.

Such rotary transformers include a flat type and a cylindrical type. The cylindrical type has a multiple cylindrical shape formed of a ferrite sintered body, and is a double type having an inner cylinder and an outer cylinder. In, a stator core as a stationary portion is formed by an inner cylinder, and a rotor core as a rotating portion is formed by an outer cylinder.

FIG. 5 is a cross-sectional view of such a conventional stator core. In FIG. 1, reference numeral 1 denotes a stator core made of a cylindrical ferrite, and reference numeral 3 denotes a coil groove for burying a coil for transmitting a signal, which is formed on the outer periphery of a cylindrical shape. Reference numeral 2 denotes a slit shaft formed in a cylindrical axis direction orthogonal to the coil groove 3 for drawing out an end of the coil embedded in the coil groove 3. Note that the depth direction of each slit groove 2 is located radially with respect to the cylindrical axis center K.

FIG. 6 is a cross-sectional view of a conventional rotor core. In the figure, reference numeral 4 denotes a rotor core made of a cylindrical ferrite, and reference numeral 7 denotes a coil groove for burying a coil for transmitting a signal, which is formed on an inner peripheral portion of a cylindrical shape. Reference numeral 6 denotes a slit groove formed in a cylindrical axis direction orthogonal to the coil groove 7 for drawing out an end of the coil embedded in the coil groove 7. Reference numeral 5 denotes a through hole from which an adhesive or the like for attaching the coil to the coil groove 7 is injected. Note that the depth direction of each through hole 5 is located radially with respect to the center K of the cylindrical axis.

FIG. 7 shows the stator coil 1 shown in FIG.
It is a longitudinal cross-sectional view which shows the conventional cylindrical rotary transformer comprised combining the rotor coil 4 shown in the figure.

In FIG. 7, a stator core 13 having a predetermined number of turns is disposed in a coil groove 3 of the stator core 1, and a rotor coil having a predetermined number of turns is provided in a coil groove 7 of the rotor core 4.
It will be noted that a gap 14 is formed between the stator core 1 and the rotor core 4. This gap 14 is a gap of 10 to 70 μm.

The stator core 13 arranged in the coil groove 3 is drawn out through the slit groove 2, and the rotor coil 11 arranged in the coil groove 7 is drawn out through the slit groove 6,
Each is connected to a VTR electric circuit (not shown).

In such a cylindrical rotary transformer,
It is necessary to strictly regulate and maintain the relative positional relationship between the stator core 1 and the rotor core 4. Therefore, high accuracy is required for the groove position and groove depth of each groove of each core, the perpendicularity of the core end face to the cylindrical surface, and the roundness of the inner and outer circumferences.

Examples of a method of manufacturing such a cylindrical rotary transformer core include an example in which only injection molding is performed without firing and limited to Mn-Zn ferrite material as disclosed in JP-A-62-188303, As disclosed in JP-A-63-37606, a method of manufacturing by injection molding and firing without processing is already proposed.

[Problems to be solved by the invention]

However, according to the manufacturing technique disclosed in Japanese Patent Application Laid-Open No. 62-188303, since a core that has been injection-molded without firing is used, the resin component that is a nonmagnetic material remaining in the core is a ferrite material. The ferrite material is distributed around and the ferrite material is not integrated, and a demagnetizing field is generated. As a result, there is a possibility that the effective magnetic permeability is lowered and the material is not suitable for practical use.

In the manufacturing technique disclosed in JP-A-63-37606, advantages such as improvement of dimensional accuracy and no processing such as grinding are recognized, but a simple mold such as a substantially two-part structure is used as a mold. No consideration has been given to enabling the use of a mold having a structure to further reduce costs.

An object of the present invention is to overcome the problems of the prior art,
Eliminating the danger of becoming unsuitable for practical use, and enabling the use of a mold having a simple structure, such as a substantially two-part structure,
An object of the present invention is to provide a cylindrical rotary transformer core having a shape capable of further reducing costs.

[Means for solving the problem]

As in the conventional stator core shown in FIG. 5 and the conventional rotor core shown in FIG. 6, the slit grooves 2 and 6 or the through holes 5 are arranged radially with respect to the center of the cylindrical axis. It is necessary to make the mold used for injection molding a structure that can be divided by the number of slit grooves or the number of through holes. As a result, it becomes impossible to take a large number of pieces at the time of injection molding. The cost of the mold is increased, and the maintenance and repair of the mold is troublesome, and the molding cycle is lengthened.

Therefore, in the present invention, a core for forming a cylindrical rotary transformer, a coil embedding groove for embedding a signal transmission coil is formed on an outer peripheral portion of the cylindrical core for forming the core, and a sinterable ferrite powder is formed. Injection molding of a mixture with a binder into a green body, and then in a cylindrical rotary transformer core manufactured by degreasing and sintering, in the cylindrical axis direction intersecting with the coil embedding groove, the coil embedding groove A slit groove for drawing out the end of the buried coil is formed, and the depth direction of each slit groove is
In the cross section orthogonal to the cylindrical axis, each slit groove was formed so as to be parallel or orthogonal to each other, and was formed into a shape that could be injection molded by a substantially two-piece mold.

A core forming a cylindrical rotary transformer, wherein a coil burying groove for burying a signal transmission coil is formed in an inner peripheral portion of the cylindrical core forming the core, and a mixture of a sinterable ferrite powder and a binder is formed. After injection molding into a green body, a cylindrical rotary transformer core manufactured by degreasing and sintering, a through hole is formed in a direction orthogonal to the cylindrical axis direction of the cylindrical rotary transformer core, and the through hole is formed. Each through-hole was formed such that the axial directions of the holes were all in the same direction or orthogonal to each other, and the shape was such that injection molding by a substantially two-piece mold was possible.

[Action]

According to the cylindrical rotary transformer core of the present invention, as a mold for directly molding a cylindrical green body,
Since approximately two-part molds can be used, multi-pieces of 4 to 16 pieces can be obtained, and maintenance and repair of the molds are easy, and mass productivity is excellent.

〔Example〕

FIG. 1 is a perspective view showing a stator core of a cylindrical rotary transformer core as one embodiment of the present invention. In the figure, 112 is a stator core, 113, 113-A
Are slit grooves, 114 is a coil groove, and 115 is a pin gate. The pin gate 115 is used when forming a green body by injection molding.

FIG. 2 is a cross-sectional view of the stator core 112 shown in FIG.

In FIG. 2, a straight line Y connecting the center of each of the upper and lower slit grooves 113 and the central axis of the cylinder is defined by each slit groove 113−
It will be appreciated that the straight lines X1, X2 extending in the depth direction of A are both orthogonal. This is a feature of the present invention.

In contrast to the prior art in which the depth direction of each slit groove is directed radially with respect to the center axis of the cylinder, the straight lines X1 and X2 extending in the depth direction of each slit groove 113-A are both relative to the straight line Y. By defining the shape of the slit grooves 113-A so as to be orthogonal to each other, a substantially two-part mold can be used as a mold for directly molding the cylindrical green body part during injection molding of the stator core 112. It becomes.

FIG. 3 is a perspective view showing a rotor core of a cylindrical rotary transformer core as one embodiment of the present invention. In the figure, 121 is a rotor core, 122 is a slit groove, 123 is a coil groove, 124 is a through hole, 125 is a pin gate,
It is. The pin gate 125 is used when forming a green body by injection molding.

FIG. 4 is a cross-sectional view of the rotor core 121 shown in FIG.

In FIG. 4, straight lines K1, K2, and K3 extending in the depth direction of the through holes 124 are both orthogonal to a straight line Y connecting the center of each of the upper and lower slit grooves 122 and the center axis of the cylinder. Will be recognized. This is a feature of the present invention as described above.

In contrast to the prior art in which the depth direction of each through hole is directed radially with respect to the center axis of the cylinder, the straight lines K1, K2, and K3 extending in the depth direction of each through hole 124 in this way are both By defining the shape of the through-holes 124 so as to be orthogonal to each other, it is possible to use a substantially two-part mold as a mold for directly molding the cylindrical green body part during the injection molding of the rotor core 121. It is.

As described above, the cylindrical rotary transformer core having the shape as described with reference to FIGS. 1 to 4 is molded by an injection molding method to be a green body, and then degreased and sintered.
Thereafter, the inner and outer peripheral surfaces and both end surfaces are ground and polished to obtain a product.

The sinterable ferrite powder used to form a green body by injection molding is a nickel-zinc-based, magnesium-zinc-based, manganese-zinc-based calcined ferrite powder, the average particle size of which is 0.1 to 200 μm. Can be used, but 0.1
The thickness is preferably from 150 to 150 μm, particularly preferably from 0.1 to 100 μm.

If the average particle size is less than 0.1 μm, uniform dispersion during kneading becomes difficult, the density after sintering decreases, and the magnetic properties and mechanical strength decrease.

As the binder to be used, for example, a styrene-based polymer, an ethylene-based polymer, a propylene-based polymer, an ethylene-vinyl acetate copolymer, an alkyl (having 6 or more carbon atoms)
Copolymers containing methacrylate as a main component (50 wt% or more) (eg, polymethyl methacrylate, polyethyl methacrylate), and copolymers containing alkyl (having 6 or less carbon atoms) acrylate as a main component (50 wt% or more) ( For example, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate) can be mentioned.

The number average molecular weight of these synthetic resin binders measured by the vapor osmotic pressure method is preferably 2000 to 500,000, particularly preferably 4000 to 300,000.

In order to form a core green body using the sinterable ferrite powder and the binder, first, the ferrite powder and the binder are melt-kneaded at a predetermined ratio (usually 5 to 40 parts by weight of the binder with respect to 100 parts by weight of the ferrite powder). And form into pellets. The pellets are filled and melted in an injection molding machine and injected into a mold.

FIG. 8 is a longitudinal sectional view showing the positional relationship between the spool, the runner and the green body for the stator core when the mold for injection molding the green body of the stator core is in a closed state.

As can be seen in the figure, the green body for the stator core
The mold used for injection molding 112-A is substantially three molds that can be separated from the core green body 112-A, that is, an intermediate mold 35 having a gate portion 115.
And a movable mold 36 for forming the groove surface, and a fixed mold 34 for injecting the molten material into the movable mold 36. In addition, 30 is a first spool, 31 is a runner, and 32 is a second spool.

FIG. 9 is a cross-sectional view of the movable mold 36 of FIG. Ninth
As can be seen from the figure, the moving mold 36, which is a mold for directly molding the cylindrical green body, is a green mold 112-.
In order to form the coil groove 12 and the slit groove 113A on the outer peripheral portion of A, split molds 36-A and 36-B that can be divided into approximately two right and left, and a slit mold 37 for forming the slit groove 113 therein.
Consists of

The melt fills the molds forming the first spool 30, the runner 31, and the second spool 32, and is pressed into the core green body molding portion from the pin gate 115 forming the tip of the second spool 32.

After the injection is completed, the intermediate mold 35 and the movable mold 36 are moved after being cooled and solidified.
A is released from the intermediate mold 35, and at this time, the second spool
Separated from 32 and gated. When the moving mold 36 moves, the slit mold 37 slides, and then the split mold 36 is divided into two by the slit mold portion.
-A and 36-B are slit grooves 113, 113A and coil groove 1
The core green body 112-A formed with 2 is protruded by a protruding pin provided on the mold and released.

FIG. 10 is a longitudinal sectional view showing a positional relationship between a spool, a runner, and a green body for a rotor core when a mold for injection molding the green body of the rotor core is in a closed state. FIG. 11 is a cross-sectional view of the movable mold 40 of FIG.

As can be seen from these figures, the mold used for injection molding the rotor core green body 121-A has approximately four molds that can be separated at the core green body 121-A. That is, the intermediate mold 35 having the gate portion
And a movable mold 40 for forming a through-hole 124, a collapsible core 41 for forming a slit groove and a coil groove in a peripheral portion of the green body, and a fixed mold 34 for injecting a melt into the core. It is molded in the same manner as the green body for use.

After the injection is completed, the intermediate mold 35 and the movable mold 40 are moved after being cooled and solidified, and the core green body 121-A is released from the intermediate mold 35, and is separated from the second spool 32 at that time. And gated. When the movable mold 40, which is a mold for directly molding the cylindrical green body, moves, the two divided molds 40-A and 40-B open right and left, and the collapsible core 41 is centered. Part, the slit groove and coil groove in the inner peripheral part, and the through hole 12
The core green body 121-A formed with 4 is released.
The configuration of the collapsible core is not shown.

The stator green body and the rotor green body released as described above are degreased and sintered, and then ground and polished to obtain a cylindrical rotary transformer core. This degreasing / sintering step may be performed continuously or separately.

The thickness of the thus-produced cylindrical rotary transformer core according to the present invention varies depending on the desired performance of the rotary transformer, but is usually 0.5 to 5 mm, and the outer diameter is 10 to 20 mm for the stator, and the rotor is In case of 11-30
mm, the height is 10 to 30 mm, the pin gate portion provided on the end face has a diameter of 0.5 to 3 mm, the number is 3 to 8, and the pin gate portion may be provided at a position recessed from the plane.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide a stable cylindrical rotary transformer core that does not require secondary processing such as groove processing, is excellent in mass productivity, and is low in cost and stable. There are advantages.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a stator core of a cylindrical rotary transformer core as one embodiment of the present invention.
FIG. 3 is a cross-sectional view of the stator core shown in FIG. 1, FIG. 3 is a perspective view showing a rotor core of a cylindrical rotary transformer core as one embodiment of the present invention, and FIG. 4 is a view shown in FIG. FIG. 5 is a cross-sectional view of a conventional stator core, FIG. 6 is a cross-sectional view of a conventional rotor core, FIG. 7 is a vertical cross-sectional view showing a cylindrical rotary transformer, and FIG. The figure is a longitudinal sectional view when the mold for injection molding the green body of the stator core is in a closed state, FIG. 9 is a transverse sectional view of the mold shown in FIG. 8, and FIG. 10 is the green body of the rotor core. A longitudinal sectional view when the mold for injection molding is in a closed state, FIG. 11 is a transverse sectional view of the mold shown in FIG. 10,
It is. Description of the symbols 30, 32 ... spool, 31 ... runner, 34 ... fixed mold, 35 ... intermediate mold, 36 ... moving mold, 112 ... stator core, 113, 113A ... slit groove, 114 …… Coil groove, 115, 125 …… Pin gate, 121 …… Rotor core, 1
22: slit groove, 123: coil groove, 124: through hole

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Jiro Ishikawa 2-10-12 Shibadaimon, Minato-ku, Tokyo Showa Denko KK (56) References JP-A-63-37606 (JP, A) JP-A Sho 62-188303 (JP, A) JP-A-61-176106 (JP, A)

Claims (2)

(57) [Claims] 1. A core constituting a cylindrical rotary transformer, wherein a coil embedding groove for embedding a signal transmission coil is formed on an outer peripheral portion of the cylindrical core constituting the core, and a sintered ferrite powder and a binder are formed. Injection molding of the mixture with the above into a green body, and then degreased and sintered, the cylindrical rotary transformer core is buried in the coil burying groove in a cylindrical axis direction crossing the coil burying groove. Slit grooves for drawing out end portions of the formed coil are formed, and each slit groove is formed such that the depth direction of each slit groove is parallel or orthogonal to each other in a cross section orthogonal to the cylindrical axis. A cylindrical rotary transformer core characterized by the following. 2. A core forming a cylindrical rotary transformer, wherein a coil burying groove for burying a signal transmission coil is formed in an inner peripheral portion of the cylindrical core forming the core, and a sinterable ferrite powder is formed. After injection molding a mixture with a binder into a green body, a cylindrical rotary transformer core manufactured by degreasing and sintering, a through hole is formed in a direction orthogonal to the cylindrical axis direction of the cylindrical rotary transformer core. A cylindrical rotary transformer core, wherein each through-hole is formed such that the axial directions of the through-holes are all in the same direction or are orthogonal to each other.