JPH04284605A - Formation of ferrite segment magnet - Google Patents

Abstract

PURPOSE:To prevent a firing break such as a top break, a side break or the like and to prevent a defect such as a leg chip or the like by a method wherein the surface roughness of a slurry injection passage at a metal mold used to form many segment magnets is made smaller than the average particle size of magnetic powders. CONSTITUTION:When many segments are manufactured by a wet system by making two or more segments at one shot, the surface roughness of a slurry flow passage at a metal mold is made smaller than the average particle size of magnetic powders of a Ba-Sr ferrite or the like. Thereby, a slurry can be fed uniformly into individual cavities at the metal mold, and a firing break such as a top break, a side break or the like and a defect such as a leg chip or the like can be eliminated.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to Ba-ferrite and S-ferrite.
The present invention relates to a wet manufacturing method for anisotropic segment magnets used in small motors, generators, etc., using magnetic powder such as r-ferrite as a raw material.

0002

[Prior art] Ferrite magnets are made from raw material calcined powder of 20 to
It is manufactured by mixing it with 50% water to form a slurry, sending it to a press molding machine, dehydrating it while press-molding it under an applied magnetic field, and molding it into a predetermined size, followed by firing it at 1200-1300°C for several hours. . Segmented magnets are typically several centimeters long and have a curved shape, as shown in FIG. In recent years, the number of pieces produced has increased dramatically as they are frequently used in automotive electrical motors, etc., and in many cases, several pieces or more are manufactured in one press molding process, that is, "multi-piece molding". Cracks occur vertically in the length direction (top cracks), cracks from the sides (horizontal cracks), or chips in the legs, and top cracks occur particularly frequently. Such defects can amount to several 10% of the products.

[0003] Segment magnets are prone to cracks, and in order to avoid this, it is necessary to uniformly fill the slurry in the cavity, as disclosed in, for example, Japanese Patent Application Laid-Open No.
-91799 publication. The mold used for molding is manufactured by precision machining, but the flow path is usually milled, and the surface roughness (center line average roughness R
a) has a size of several μm or more. When molding is performed using an as-machined mold, if the amount of slurry filled into the cavity becomes uneven, the mold can be removed from the molding machine and the slurry injection channel cleaned. The symmetry of the path is restored and the magnetic particle deposits described above can be removed. However, a multi-cavity mold weighs several tens to hundreds of kilograms, and it takes a lot of time and effort to take it down from the molding machine, disassemble it, clean it, and then load it back into the molding machine. It is extremely difficult to carry out production.

0004

[Problems to be Solved by the Invention] The present invention addresses such non-uniform filling within the cavity, and at the same time, when molding segments using multiple moldings, it is necessary to eliminate variations in the amount of filling between cavities. Therefore, the object of the present invention is to provide a method for forming segments without firing cracks.

[0005]

[Means for Solving the Problems] That is, the present invention aims to improve the surface roughness (Ra
) is smaller than the average particle diameter of magnetic powder.

[0006]

[Function] The inventors of the present invention have conducted extensive studies on the causes of the above-mentioned defects that occur when segments are produced in large numbers. As a result, since the slurry fed into the molding machine is a solid-liquid dispersion system, if there are irregularities on the surface of the flow path of the mold, the flow of magnetic particles will be disrupted, and magnetic particles with low water content will accumulate on the irregularities. Therefore, as shown in Figure 2, even if the mold is designed in such a way that the flow paths are symmetrical on the left and right, and the length of the flow paths to each cavity are all equal, the flow rate of the slurry will be different in each part of the flow path. If pressurization is performed under these conditions, a cavity filled with enough slurry will be sufficiently pressurized, but a cavity with a small amount of slurry will be pressurized sufficiently. Pressurization becomes insufficient in the cavity entered,
It has been discovered that the non-uniformity of pressure between cavities is the root cause of defects.

Incidentally, FIG. 3 shows the fact that when molding is performed using multiple cavities, the smaller the variation in the amount of slurry filled between cavities, the fewer the number of cavities. In order to improve this current situation, the present inventors investigated smoothing the flow path of the mold and found that if the surface roughness of the flow path is smaller than the average particle size of the magnetic powder, the water content will be low. It was confirmed that magnetic particles were difficult to accumulate.

Ba, Sr used in segment production
-The average particle size of magnetic powder such as ferrite is JP-A-55-15
As disclosed in Publication No. 0209 etc., usually 0
．． It is 8 to 1.5 μm. According to the present invention, the average roughness Ra of the flow path may be made smaller than the average particle diameter of the magnetic powder of the slurry used, but the smaller the roughness, the better. Any technique such as metal plating such as chromium plating, plasma treatment such as ion plating, or mechanical polishing may be used to smooth such a flow path. Further, the mold constituting the injection channel can be made of metal or a combination of metal and ceramics or the like.

[0009]

[Example] Average particle size 0.85, 1.0 and 1.5
Slurries with a moisture content of 38% were made using μm Sr-ferrite powder, and each mold was made with 16 holes: A: Slurry injection channel remained milled; Ra
~6 μm, B: Cr plating on the channel of A; Ra ~0.45
μm, C: The flow path of A was lapped by wet polishing;
The segment of FIG. 1 was molded with Ra ~ 0.6 μm. and 1240℃
Firing was performed for 6 hours. Table 1 shows the average number of cracks per molding unit shot in the segment after firing of the molded product after 10,000 shots.

It can be seen that when molds B and C, in which the surface roughness of the slurry channel is smaller than the average particle diameter of the magnetic powder, are used, the number of ceiling cracks is smaller than when molding is performed using mold A. Incidentally, in this case, the number 1 showing the fluctuation of the filling amount in Fig. 3
The value has decreased to nearly 0.7.

[0011]

[Math 1]

0012

[Table 1]

[0013]

Effects of the Invention The present invention is applied to a mold for wet-manufacturing segment magnets by molding multiple pieces of two or more pieces in one shot. In other words, the surface roughness value (Ra) of the flow path of the mold as it is produced by machining such as milling is the average particle diameter of the magnetic powder used for manufacturing the segment magnets, which is 0.8 to 1.
．． Because the diameter is larger than 5 μm, slurry made of magnetic particles tends to accumulate in the flow path in a finished mold, making it difficult to feed the slurry evenly into each cavity of the mold, resulting in defects such as ceiling cracks or horizontal cracks. It is the cause of inducing. The present invention has made it possible to significantly prevent the occurrence of such defects.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the positions of defects that occur in an example of a segment targeted by the present invention.

FIG. 2 is a diagram showing an injection flow path and a location where slurry is deposited in the flow path for a 16-cavity mold as an example of a multi-cavity mold.

FIG. 3 is a diagram showing the filling amount between cavities and the number of defects (top cracks) for each shot.

Claims (1)

[Claims] 1. A ferrite segment characterized in that, in wet pressure molding of ferrite magnetic powder, the surface roughness (Ra) of a slurry injection channel of a multi-cavity mold of the segment magnet is made smaller than the average particle diameter of the magnetic powder. How to form magnets.