JPS6054361B2 - Manufacturing method of porous magnetic plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a porous magnetic plate, particularly a porous sintered magnetic plate suitable for use in electroacoustic transducers.

Conventionally, in order to manufacture the above-mentioned porous magnet plate, a mold consisting of an upper punch with a large number of pins and a lower punch with holes for aligning these pins is used, and powder raw materials for sintered magnets are placed in the mold. The usual method is to fill it with compression molding and then sinter it.

However, such a manufacturing method requires high precision in the mold and molding equipment, which only leads to a rise in manufacturing costs.
Due to molding pressure, pins constituting the mold may be bent or broken, leading to defects. In order to remove these nine colors, as described in Japanese Patent Publication No. 52-33487, a plate-shaped molded body having only one side with a tapered hole that does not completely penetrate to the other side is compression molded, and the above-mentioned A manufacturing method has been proposed in which the other surface is polished until a desired through-hole diameter is obtained.

That is, as shown in FIG. 1, the container 2 is placed on the lower punch 1, and a large number of tapered pins 4 are erected on the upper punch 3.
Sintered magnet powder 5 such as ferrite magnet powder is placed in the container 2.
Fill it with. The upper and lower punches are then moved relative to each other to compress the powder 5 and form a plate-shaped compact 6 as shown in FIG. As shown in FIG. 3, the plate-shaped molded body 6 has a tapered hole 7 formed only on the upper surface, but this hole does not penetrate through the lower surface. After sintering this molded body 6 in a firing furnace, only the lower surface side is ground with a grinder until a predetermined through hole is obtained, thereby obtaining a porous magnet plate 8 as shown in FIG. 4.
However, in the above method, when the powder 5 is compression molded, the molding density is higher in the portion directly under the large number of tapered pins 4 than in other portions.

In other words, since the powder 5 has low fluidity, the compression molding proceeds without being able to maintain a uniform density inside the container 2 during compression molding. Molding density becomes small. Therefore, as shown in FIG. 5, deformation occurs in the subsequent sintering process, which not only increases the polishing allowance in the polishing process and reduces productivity, but also reduces defects such as cracks and breakage caused by the deformation. There are drawbacks that can cause problems and significantly reduce quality. The object of the present invention is to further improve the nine colors described above and to provide a method for manufacturing a porous magnetic plate with high quality and productivity. 6 to 9 are explanatory views showing embodiments of the method of the present invention, and the same parts are designated by the same reference numerals.

In these figures, the upper punch 3 is provided with a tapered pin 4, and the lower punch 1 is also provided with a tapered pin 4, and these pins 4 are arranged in a substantially grid pattern, and the upper and lower pins 4 are connected to each other. The axis line does not match that of the pin 4 on the side. Thus, the container 2 constituting the outer mold is supported slidably on the outer peripheral surface of the lower punch 1. Next, as shown in FIG. 6, a predetermined amount of powder 5 for a sintered magnet is filled into the space formed by the lower punch 1 and the container 2, and then the upper punch 3 is lowered, as shown in FIG. The powder 5 is compression molded in this manner. In this case, the tapered pin 4 provided on the upper punch 3 first enters the powder 5, and then the upper punch 3 compresses the powder 5 while moving the container 2 downward, and forms both the upper and lower surfaces as shown in FIG. A plate-shaped molded body 6 having a tapered hole is molded. The relationship between the axial thickness dimension t of the plate-shaped molded body 6 and the height h of the tapered pin 4 above the punch is determined as follows. After sintering the plate-shaped compact 6 formed in the above manner in a firing furnace, both surfaces thereof are ground with a grinder or the like until a predetermined through hole is obtained, thereby producing a porous magnet as shown in FIG. Thus, plate 8 is obtained. In this case, the plate-shaped molded body 6 tends to slightly increase the powder density directly below or directly above the tapered pin 4 compared to other parts during the molding process;
It has a symmetrical density distribution on both its upper and lower surfaces. Therefore, no deformation occurs during sintering in a firing furnace. In this example, the upper punch and container part are. Although an example of movement has been shown, the present invention is not limited to this, as long as there is relative movement between both the upper and lower punches and/or the container.

Further, the tapered pins to be provided on both the upper and lower punches are not limited to those having a circular cross section, but may have other geometrical shapes, or may be formed by machining or the like integral with the punches. Since the method for manufacturing a porous magnetic plate of the present invention has the configuration as described above, it can achieve the following effects.

(1) Since the plate-shaped molded body serving as the intermediate material has tapered holes on both upper and lower surfaces and has a symmetrical density distribution, deformation during sintering can be prevented. (2) Therefore, there is no occurrence of cracks or damage during the grinding or polishing process, and the yield can be greatly improved. (3) Since the grinding or polishing for penetrating the blind hole is performed from both the upper and lower surfaces, the grinding allowance can be greatly reduced, and continuous machining using a double-headed grinder, for example, is possible, greatly increasing productivity. can be improved.
(4) Since the powder density is uniform throughout the magnet plate,
The variation in magnetic properties is small, and a high-quality magnetic plate can be obtained.

[Brief explanation of the drawing]

1 and 2 are partial sectional views each showing a conventional manufacturing method, FIG. 3 is a sectional view showing a plate-shaped molded body, and FIGS. 4 and 5 are sectional views each showing a porous magnet plate, 6 to 8 are partial cross-sectional views showing embodiments of the present invention, and FIG. 9 is a cross-sectional view showing a porous magnet plate. 1: Lower punch, 3: Upper punch, 4: Tapered pin, 6:
Plate-shaped molded body, 8: Porous magnet plate.

Claims (1)

[Claims] 1 Powder raw material for sintered magnets is compression-molded into a plate-shaped compact with a large number of tapered holes that do not completely penetrate the other side alternately bored in a lattice pattern on both sides, and after sintering this, the desired shape is formed. A method for manufacturing a porous magnet plate, comprising polishing both sides of the plate-shaped molded body until a through-hole diameter of the same size is obtained.