JPH04186094A - Manufacture of ring-shaped ferrite core - Google Patents

Abstract

PURPOSE:To restrict warp and deformation of a formed material by a method wherein a casing for use in supporting the firmed material during a baking operation is made into an inverse conical shape and then the casing is positioned while the lower-most lower end peripheral edge of a laminated formed material is abutted against an inner surface of the easing. CONSTITUTION:A casing 2 is formed into an inverse conical shape by hard ceramics with its slant inner surface 2b being expanded at a slant angle of about 45 deg.. A central part of a bottom of the casing is formed with a hole 2a for a thermal convection. Ferrite formed items 1 are piled up in a layered manner while the lower peripheral edge of the lower-most ferrite formed item 1 being abutted against a slant inner surface 2b. With such an arrangement, a friction force during a thermal shrinkage process can be made low and a warp or a deformation of the formed item can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a ferrite core that eliminates problems such as warping and deformation during firing of a ring-shaped ferrite molded body.

(Prior art) Conventionally, in order to sinter a ferrite molded body obtained by press-molding ferrite powder into a ring shape in a sintering furnace,
-In the same way as the flat plate-shaped ferrite molded bodies used in boat fishing, a large number of molded bodies are placed one by one on a flat shaped sagger, or
Alternatively, the molded bodies were manufactured by placing them vertically on a sagger pot, transporting them into a sintering furnace, and firing them.

However, such a manufacturing method has the following technical problems.

(Problem to be Solved by the Invention) In other words, it is known that this type of ferrite molded body undergoes relatively large shrinkage during sintering, but when a ring-shaped molded body is placed on the surface of a flat intermediate needle, When supported, frictional resistance increases on the side of the molded body that contacts the sagger due to shrinkage during sintering, and the shrinkage rate differs between the upper and lower surfaces of the ring during sintering.

For this reason, a difference in shrinkage occurs between the upper and lower surfaces of the molded body, resulting in large deformation and warpage during firing, making manufacturing difficult and resulting in a low yield.

Further, when the molded body is molded in an upright state, it is not possible to prevent deformation of the obtained ferrite core due to the influence of the molded body's own weight in addition to the difference in frictional resistance.

One way to reduce the effects of frictional resistance is to spread alumina or alumina balls on the inner bottom of the sagger, thereby reducing the friction on the installation surface and performing sintering. However, it has been difficult to sufficiently eliminate deformation and warping.

This invention solves the above problems, and by minimizing the contact area of the press-formed body with the sagger, it eliminates the shrinkage difference due to friction during the contraction process of the press-formed body, and eliminates the possibility of warping or deformation. It is an object of the present invention to provide a manufacturing method that allows a small number of ring-shaped ferrite cores to be obtained.

(Means for Solving the Problems) In order to achieve the above object, the manufacturing method of the present invention involves pressing ferrite powder into a ring shape to form a compact, and sintering this press compact in a sintering furnace. In the method for manufacturing a ring-shaped ferrite core, in which a ring-shaped sintered body is obtained, a sagger in which the molded body is supported is shaped like a sagger when the molded body is sintered, and the molded body is formed on the inner surface of the sagger. Characterized by positioning the body.

In the above manufacturing method, a plurality of the molded bodies may be stacked in a stepwise manner on the sagger.

(Function) According to the manufacturing method having the above configuration, the outer periphery of the ring-shaped ferrite molded body is located on the inner surface side of the cradle-shaped sagger, so that it is installed in line contact with the center pillar. In order to
The frictional force in the heat shrinkage process during sintering is small, and the difference in shrinkage between the upper and lower sides due to relative sliding with respect to the sagger can be reduced.

Moreover, if a plurality of molded bodies are stacked in a step-like manner, the contracted state of the upper and lower surfaces of the molded bodies at the intermediate position will be the same, and problems such as deformation can be further avoided.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

1 to 3 show an embodiment of the method for manufacturing a ring-shaped ferrite core according to the present invention, and in the figures, 1 is a ferrite molded body.

This molded body 1 is made by compacting ferrite core powder together with a binder by press molding. For example, for a noise filter, the molded body 1 has a thickness of 121 mm or more, an outer diameter of 154 mm or more, and an inner diameter of 144 mm. It is formed into a ring shape.

A plurality of ferrite molded bodies 1 having the same shape are placed in a stacked state in a sagger 2.

This sagger 2 is made of hard ceramic or the like, and has a hole 2a for heat convection in the center of the bottom, and
For example, they have a bowl shape that expands at an inclination angle of 45°, and are stacked in stages with the lower peripheral edge of the lowermost ferrite molded body l in contact with the inclined inner surface 2b.

The diameter of the inner bottom surface 2c of this sagger 2 is equal to or slightly larger than the final outer diameter when the ferrite molded body 1 is fired and reduced in diameter by heat contraction at this time. is set to .

After performing the above setting, each ferrite molded body 1 is sintered by feeding it into the sintering furnace 3 as shown in FIG.

In this sintering process, the binder contained in each ferrite molded body 1 is volatilized by firing, thermal contraction occurs, and the diameter of each ferrite molded body 1 is sequentially reduced.

As a result of this diameter reduction, the ferrite molded bodies 1 at the bottom tier, due to their own weight in the stacked state, gradually slide down evenly toward the bottom along the slope of the inner surface 2b of the sagger 2, and finally, as shown in FIG. 3. As shown, the lowermost ferrite molded body 1 has an inner bottom surface 2.
c, and a ring-shaped ferrite core is obtained in a state where the laminated state of each ferrite molded body 1 is maintained.

In the above diameter reduction process, the lower peripheral edge of the lowermost ferrite molded body 1 is in annular line contact with the inner surface 2b of the middle column 2, so the frictional force is extremely small and as the contraction progresses, The diameter will shrink as it slides down evenly due to its own weight.

In addition, each ferrite molded body 1 from the second stage onwards has ferrite molded bodies of the same shape in contact with each other on the upper and lower surfaces, so the diameter is reduced under the same conditions, so friction due to relative sliding of the contact parts is taken into consideration. As the heat in the furnace uniformly convects to the inner and outer peripheries of each ferrite molded body 1 as shown by the arrows in Fig. 2, the diameter is reduced without warping or deformation. Sintering is completed in a homogeneous state without any sintering.

(Effects of the Invention) As explained in detail in the examples above, in the method for manufacturing a ring-shaped ferrite core according to the present invention, the ferrite molded body is placed in line contact with the sagger, so it is heated. The frictional force during the shrinkage process is small, and the difference in shrinkage between the upper and lower sides due to relative sliding with respect to the sagger is small, so that factors that reduce yield such as warping and deformation due to the difference in shrinkage can be extremely minimized.

Therefore, the method of the present invention is particularly suitable for manufacturing a ring-shaped ferrite core that is large, thin, and has a small difference between the outer diameter and the inner diameter.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams showing a method of manufacturing a ring-shaped ferrite core according to the present invention. 1... Ferrite molded body 2... Sagger 2b... Inclined inner surface 3... Sintering furnace

Claims (2)

[Claims] (1) In a method for producing a ring-shaped ferrite core, in which a ferrite powder is pressed into a ring shape to obtain a molded body, and this pressed body is sintered in a sintering furnace to obtain a ring-shaped sintered body: 1. A method for manufacturing a ring-shaped ferrite core, characterized in that, when the body is sintered, a sagger in which the molded body is supported is formed into a mortar shape, and the molded body is positioned on the inner surface of the sagger. (2) The method for manufacturing a ring-shaped ferrite core according to claim 1, wherein a plurality of the molded bodies are stacked in a stepwise manner on the sagger.