JPH06267750A - Manufacture of rotary transformer core by injection molding - Google Patents

Abstract

PURPOSE:To obtain a rotary transformer core having small warpage and good yield by injection molding. CONSTITUTION:A binder mainly composed of a thermal plastic resin is added to ferrite powder, which is heated and kneaded to produce a raw material in a slurry form. This slurry of raw material is injected into a mold. After cooling, a formed material 1 comprising the ferrite powder and the binder in a flat disk shape, one side 1a of which contains a plurality of concentric circular grooves 2a and 2b, and the other side 1b of which is flat, is taken out of the mold. In a method of manufacturing a rotary transformer core according to injection molding in which this formed material 1 is placed on a setter 3 for degreasing and baking through heat treatment, the formed material 1 is so placed that the side 1a having the concentric circular grooves 2a and 2b faces the setter 3 for degreasing and baking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a rotary transformer core by injection molding.

[0002]

2. Description of the Related Art Generally, a rotary transformer is used in a rotary head device of a VTR. Conventionally, as a manufacturing method of this rotary transformer core, for example, a ferrite powder to which a binder (polyvinyl alcohol) is added is used as a raw material, and a flat disc shape is formed by a compression molding method in which uniaxial compression is performed in a mold. A molded body having a plurality of concentric circular grooves on one surface and a flat surface on the other surface is formed and then fired.

In this compression molding method, since the raw material to be put into the mold is powder, friction between the raw materials or friction between the mold and the raw material causes non-uniform filling degree, and as a result, the rotary after firing is rotated. There is a disadvantage that the transformer core is deformed or warped, and the reproducibility is low due to the non-uniform filling degree of the raw material for each molding lot, and there is a disadvantage that dimensional variations occur in individual rotary transformer cores.

Therefore, various methods for manufacturing a rotary transformer using an injection molding method have been studied as a method for manufacturing the rotary transformer core. With regard to injection-molded injection-molded articles, the fluidity of the slurry during injection molding is investigated. Is low, and defects are likely to occur, resulting in poor yield. Regarding degreased products and calcined products, when the amount of the binder added is increased in order to increase the fluidity of the slurry, degreasing becomes difficult or the degreasing time becomes very long, resulting in poor productivity. . In addition, there is a problem that the initial magnetic permeability decreases as the amount of binder added increases.

Since the warpage after firing is relatively large,
The grinding thickness is large, for example, about three times the thickness of the product is required, and there is a disadvantage that the raw material cost is increased, and the grinding man-hour is large, and the grinding wheel is abraded severely.

In view of the above point, the present invention proposes a method of manufacturing a rotary transformer core by injection molding, which can obtain a rotary transformer core having a small warp and a good yield.

[0007]

A method of manufacturing a rotary transformer core by injection molding according to the present invention will be described with reference to, for example, FIGS.
As shown in Fig. 2, a binder containing a thermoplastic resin as a main component is added to ferrite powder, and the mixture is heated and kneaded to obtain a slurry-like raw material. The slurry-like raw material is injected into a mold, and after cooling, this mold is used. From a ferrite powder and a binder, a flat disk-shaped molded body 1 having a plurality of concentric circular grooves 2a and 2b on one surface 1a and a flat other surface 1b is taken out.
In a method for manufacturing a rotary transformer core by degreasing and firing by heat treatment on a setter 3 such that the surface 1a having the concentric grooves 2a and 2b faces the setter 3. It is placed and degreased and baked.

The method of manufacturing a rotary transformer core by injection molding according to the present invention is as described above, for example, as shown in FIGS. 1, 2 and 3, in which the mixing weight ratio of the ferrite powder (P) and the binder (B) (B / P) 0.06 to 0.15
And the degreasing heat treatment is performed at a predetermined temperature, for example, from 80 ° C to 20 ° C.
The heating rate is 4 ° C. to 8 ° C./hour up to 0 ° C. or higher.

[0009]

According to the present invention, the injection molded body 1 is placed so that the surface 1a having the concentric grooves 2a and 2b faces the setter 3, and degreasing and firing are performed. Can be very small.

Further, according to the present invention, ferrite powder (P)
And mixing ratio (B / P) of binder (B) is 0.06
Since it is set to be ~ 0.15, the fluidity of the slurry is high in the injection-molded body, and no defects occur. Also, regarding degreased products and baked products, since the heating rate for degreasing heat treatment from the predetermined temperature to 200 ° C. or higher is 4 ° C. to 8 ° C./hour, defects such as cracks and breaks do not occur during degreasing and baking.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a rotary transformer core by injection molding of the present invention will be described below with reference to the drawings. In this example, as shown in FIG. 2, a ferrite powder as a raw material (for example, Fe ₂ O ₃ having a composition of 49.
5 mol%, ZnO 31.5 mol%, NiO 9.
5 mol% and CuO (9.5 mol) were prepared (step 11) and a binder was prepared (step 12), and the ferrite powder and the binder were premixed (step 13).
Then, the mixture is heated and kneaded to obtain a slurry for injection molding (Step 1
4). An example of the composition of this binder is as follows.

[0012]

At this time, the addition amount of the binder is set to 0.06 to 0.15 as a weight ratio of the binder and the ferrite powder (binder weight B / ferrite powder weight P). In this case, if the amount of the binder is too small, the binding force between the ferrite powder and the binder will be lost, and a slurry will not be obtained, or the fluidity of the slurry will be reduced, making injection molding difficult.

If the amount of this binder is too large, degreasing will become difficult, or the initial magnetic permeability of ferrite will suddenly deteriorate. Further, even if the addition amount of this binder is increased, the fluidity of the slurry is saturated and it is not effective.

The slurry thus obtained is injected into a mold and then cooled to obtain an injection molded article 1 (step 15). This injection-molded product 1 is made of ferrite powder and a binder as shown in FIG. 1A and FIG.
A has two concentric grooves 2a and 2b, and the other surface 1b is flat. At this time, the injection-molded product had no defects because the fluidity of the slurry was good.

Next, since this injection-molded product contains a large amount of binder, the binder is degreased by raising the temperature from 200 ° C. to 600 ° C. at a slow heating rate of 4 ° C. to 8 ° C./hour ( Step 16).

In this case, the degreasing treatment pattern as shown in FIG. 3 was examined. This pattern is heated up to a predetermined temperature, for example 80 ° C., at a heating rate of 80 ° C./hour,
Then, the temperature is raised to 200 ° C at a rate of 16 ° C / hour, then raised to 350 ° C at a rate of 30 ° C / hour, and then raised to 420 ° C at a rate of 70 ° C / hour. Then, the temperature was decreased to room temperature at a temperature decrease rate of 100 ° C./hour. In this degreasing treatment pattern, after degreasing, 100 for every 100 population
The individual pieces were cracked and cracked.

The pattern and the predetermined temperature are, for example, 8
The temperature is raised to 0 ° C. at a heating rate of 80 ° C./hour, then 200
Up to 8 ° C./hour and 4 ° C./hour at temperature rising rates, then to 350 ° C. at a temperature rising rate of 30 ° C./hour, and then to 420 ° C. at a temperature rising rate of 70 ° C./hour. Raise the temperature, then 1
The temperature was decreased to room temperature at a temperature decrease rate of 00 ° C./hour. With this degreasing treatment pattern and after degreasing,
No cracks or breaks were found.

Therefore, in this example, this degreasing step 16
In the above, in a temperature range of 80 ° C. to 200 ° C., the rate of temperature rise is 4 ° C. to 8 ° C./hour. In this case, if the temperature rising rate is set to be lower than 4 ° C./hour, degreasing takes too much time.

The degreased product after this degreasing is treated at a peak temperature of 1000.
C. to 1400.degree. C. and a keeping time of 3 hours to 5 hours to obtain a sintered body (step 17). Since the sintered body thus obtained has good degreasing conditions, no defects occur in the sintered body. The sintered body is subjected to grinding or the like to obtain a rotary transformer core (step 18).

Further, in this example, an injection molded product 1 for obtaining a rotary transformer core in the degreasing step 16 and the firing step 17 has a concentric groove 2 as shown in FIGS. 1A and 1B.
The surface 1a having a and 2b is placed so as to face the setter 3.

For this reason, as shown in FIGS. 4A and 4B, the injection molded product 1 for obtaining the rotary transformer core is placed so that the flat surface 1b faces the setter 3, and the degreasing step 16 is performed.
And when the firing step 17 is performed, the maximum value is 20 after firing.
A large warp occurs with 0 μm, the minimum value of 100 μm, and the average value of 170 μm.

However, as shown in FIGS. 1A and 1B, the injection molded product 1 for obtaining the rotary transformer core is placed so that the surface 1a having the concentric grooves 2a and 2b faces the setter 3, and the above-described degreasing process 16 and firing process are performed. When the test No. 17 was carried out, after firing, only a very small warp occurred with a maximum value of 30 μm, a minimum value of 20 μm and an average value of 28 μm.

As described above, the injection-molded product 1 for obtaining the rotary transformer core is formed on the surface 1 having the concentric grooves 2a, 2b.
Since a is placed so as to face the setter 3 and degreasing and firing are performed, the warp of this sintered body can be made extremely small, the grinding thickness can be made small, and the raw materials can be reduced. Therefore, there is an advantage that the number of grinding steps can be reduced and the number of grinding wheels to be replaced can be reduced.

Further, according to this example, since the mixing weight ratio (B / P) of the ferrite powder (P) and the binder (B) as the raw materials is set to 0.06 to 0.15, the fluidity of the slurry is high and the injection molding is performed. The product has the benefit of not being defective.

As for the degreased product and the baked product, the degreasing heat treatment is performed at a predetermined temperature, for example, a temperature rising rate from 80 ° C. to 200 ° C. is 4 ° C. to 8 ° C./hour, so that defects such as cracks and cracks are generated during degreasing and baking. There are benefits that do not arise. Therefore, according to this example, there is an advantage that the rotary transformer core can be obtained with good yield.

The present invention is not limited to the above embodiment,
Of course, other types of configurations can be adopted without departing from the scope of the present invention.

[0028]

As described above, according to the present invention, the injection molded product 1 for obtaining the rotary transformer core is provided with the concentric groove 2.
Since the surface 1a having a and 2b is placed so as to face the setter 3 and degreasing and firing are performed, the warp of this sintered body can be made extremely small, the grinding thickness can be made small, and the raw material There is a profit that can be reduced. Therefore, there is an advantage that the number of grinding steps can be reduced and the number of replacements of the grinding wheel can be reduced.

According to the present invention, the mixing weight ratio (B / P) of the ferrite powder (P) as the raw material and the binder (B) is set to 0.06 to 0.15, so that the slurry has high fluidity and is injection molded. The product has the benefit of not being defective.

As for the degreased product and the baked product, the degreasing heat treatment is performed at a predetermined temperature, for example, from 80 ° C. to 200 ° C. at a heating rate of 4 ° C. to 8 ° C./hour. There are benefits that do not arise. Therefore, according to the present invention, a rotary transformer core can be obtained with good yield.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an example of a method for manufacturing a rotary transformer core by injection molding of the present invention.

FIG. 2 is a diagram showing a process example of a method for manufacturing a rotary transformer core by injection molding of the present invention.

FIG. 3 is a diagram showing a degreasing treatment pattern.

FIG. 4 is a diagram for explaining a comparative example.

[Explanation of symbols]

 1 Injection molded product 2a, 2b Groove 3 Setter

Claims (2)

[Claims] 1. A ferrite powder containing a binder containing a thermoplastic resin as a main component is kneaded by heating to obtain a slurry-like raw material. The slurry-like raw material is injected into a mold, and after cooling,
From the mold, a ferrite disk and a binder, a flat disk shape, having a plurality of concentric grooves on one surface, the other surface is taken out of the molded body, put the molded body on a setter, In a method of manufacturing a rotary transformer core by injection molding in which degreasing is performed by heat treatment and then firing, the molded body is placed so that the surface having concentric grooves faces the setter, and the degreasing and firing are performed. A method for manufacturing a rotary transformer core by injection molding, which is characterized in that 2. The method for producing a rotary transformer core by injection molding according to claim 1, wherein the mixing weight ratio (B / P) of the ferrite powder (P) and the binder (B) is 0.06 to 0.15. The method for producing a rotary transformer core by injection molding, wherein the degreasing heat treatment is performed from a predetermined temperature to 200 ° C. or higher at a temperature rising rate of 4 ° C. to 8 ° C./hour.