JPH0213924B2 - - Google Patents

Description

[Detailed description of the invention]

Application industry field This invention is a wet molding method in which a slurry of magnetic material powder such as ferrite magnet material or soft ferrite material is filtered and compressed and molded into a ring-shaped, disc-shaped, square-shaped or arch-shaped molded body. In particular, by uniformly removing moisture contained in the slurry-like raw material powder filled in the molding space, the density of the molded body is made uniform, and the molded body or sintered body is free from cracks and warpage. The present invention relates to a wet molding method for obtaining a molded product having excellent magnetic properties without any magnetic properties. BACKGROUND ART In the conventional wet molding method, for example, in the case of a die float method for a ring-shaped molded body, a slurry-like raw material powder is filled into a molding space formed by a die, a core, and an upper and lower punch, and the molding device is heated. Due to the pressurizing force of the upper cylinder, the upper punch, water removal plate, and die move down together to perform compression molding, and remove water contained in the slurry raw material powder to the outside through the filter cloth and water removal plate. A molding method was used to remove water. The inventors discovered that in the wet molding method for oxide magnetic materials, the incidence of cracking, peeling, etc. in the molded product changes due to temperature changes in the slurry-like oxide magnetic material filled in the molding space in the die, and It was found that this also has a large effect on molding efficiency. Conventional methods do not consider the above points, and as the ambient temperature changes, the temperature of the slurry-like oxide magnetic material filled in the die also changes, which greatly affects the viscosity of the oxide magnetic material and the water removal rate. It was found that In particular, in winter when the ambient temperature is low, the temperature of the slurry oxide magnetic material is 20℃.
The temperature of the slurry-like oxide magnetic material is about 30°C even in the summer when the ambient temperature is high.
Cracks, peeling, etc. often occur, which, together with molding efficiency, has become a major problem in industrial production. In addition, in the conventional molding method, the water contained in the slurry-like oxide magnetic material is removed from the water drain plate of the conventional device, which has small holes for draining almost uniformly over the entire surface of the plate. For example, if some of the drainage holes become clogged, the water drainage from the drainage plate will become uneven near the center and around the inner and outer peripheries of the ring-shaped molded body. , in the case of a cross-sectional arch-shaped body, the longitudinal direction (axial direction) of the arc end
The water contained in the central part is larger than the central part, and the water removal rate in the water-rich part is slower, resulting in uneven water removal, especially in the magnetic field where a magnetic field is applied to the raw material powder during molding. In the case of molding, density differences occur due to the above-mentioned non-uniform water drainage, which can cause cracks and cracks in the molded product, or warp deformation and cracks in the sintered product. This resulted in a decrease in product yield during polishing to size, and also caused problems such as cracking and cracking, resulting in defective products. Purpose of the Invention The object of the present invention is to provide a wet molding method for oxide magnetic materials that can perform molding with extremely high molding efficiency without causing cracks or peeling of the molded product. This solution solves the problem of water drainage in the molding method.During wet molding, water is drained uniformly from each part of the molded object, eliminating density differences within the molding, and eliminating cracks during molding.
The objective is a wet molding method that prevents cracks, warpage, cracks, and cracks during sintering. Structure and Effects of the Invention The present invention was developed as a result of various studies aimed at preventing cracking and peeling of a molded product and uniformly draining water from each part of the molded product during wet molding. ,, it can reduce the viscosity and increase the water drainage speed, and in addition, instead of the conventional drainage holes that are uniformly spaced over the entire surface of the drainage board,
It has been discovered that by arranging drainage holes of predetermined dimensions at specific positions and widths of the drainage plate, water can be drained uniformly and a molded body with uniform density can be obtained. That is, in this invention, a molding space in a die is filled with a slurry-like oxide magnetic material, water is drained from a filter cloth and a water drain plate interposed between the slurry-like oxide magnetic material and the upper punch, and the oxide magnetic material is In the wet molding method of compression molding into a flat or arched cross-sectional shape, the average particle size of the slurry-like oxide magnetic material filled in the molding space is 0.5 μm to 1.2 μm, and the concentration is
55wt% to 80wt%, and the temperature is maintained at 40℃ to 90℃, and in the case of a flat molded product, the inside or outside of the molding space is similar to and concentric with the cross section of the molding space in the die. In the case of a molded body with a bow-shaped cross section,
This wet molding method is characterized in that water is drained from water drain holes arranged linearly parallel to the axial direction of the molded body, either inside or outside the molding space. In the molding method according to the present invention, the slurry-like oxide magnetic material filled in the molding space in the die is heated, and water is drained from the water drain hole of the water drain plate provided within a specific range, so that the inside of the molded body is heated. Water is removed uniformly and density differences are eliminated, preventing cracks from forming during molding and warping during sintering after forming, improving product appearance and yield. Extremely effective. In addition, the drainage holes in the drainage board are drilled only in a specific range, which reduces the number of holes and is effective in reducing the cost of the drainage board.There are also fewer drainage hole marks on the sintered body, reducing the number of steps required for surface processing. , it has the effect of improving processing quality and reducing processing cost, and also has the effect of uniformizing the magnetic field distribution and improving the orientation of particles by heating the slurry-like oxide magnetic material, improving molding efficiency and improving the sintered body. Effective for improving quality. Limitations of the Invention and Preferred Embodiments In the present invention, the slurry-like oxide magnetic material has an average particle size and concentration that affect the magnetic properties and dehydration rate during molding, and the average particle size is less than 0.5 μm and 1.2 μm. If the concentration exceeds 80 wt%, the magnetic properties will deteriorate significantly, and if the concentration is less than 55 wt%, the water removal rate will decrease, making it unsuitable for industrial mass production. It is desirable that the average particle size is 0.5 μm to 1.2 μm and the concentration is 55 wt% to 80 wt%, since the movement of the particles becomes difficult and the degree of orientation decreases, which also reduces the magnetic properties. The reason why the temperature of the slurry-like oxide magnetic material in the molding space within the die is limited will be explained below. The relationship between temperature and viscosity of a slurry-like oxide material with an average particle size of 0.75 μm and a concentration of 64 wt% was investigated and is shown in FIG. As is clear from FIG. 1, the lower the temperature of the slurry-like oxide magnetic material, the higher the viscosity, and this tendency increases from about 30°C, and it changes markedly especially when the temperature drops below 20°C. There is a correlation between this viscosity and the water removal rate of the slurry-like oxide magnetic material, and the higher the viscosity, the lower the water removal rate. Therefore, the lower the temperature of the oxide magnetic material, the slower the water removal rate becomes, lengthening the compression molding time and lowering the molding efficiency. Furthermore, if molding is performed without sufficient water removal, the desired density of the molded product cannot be obtained, and cracks, peeling, etc. occur. In this way, the higher the temperature of the slurry-like oxide magnetic material filled in the molding space in the die, the higher the molding efficiency and the lower the incidence of defects such as cracks and peeling of the molded product, but at temperatures exceeding 90℃. The temperature is preferably 90° C. or lower because the cost required to heat the oxide magnetic material increases too much, which is not economical, and also causes various problems in mass production, such as deterioration of workability due to high temperatures. Furthermore, if the temperature is lower than 40°C, the above-mentioned effects will be small, and it cannot be said that this is particularly sufficient to prevent the occurrence of cracking and peeling of the molded product. Therefore, the temperature of the slurry-like oxide magnetic material filling the molding space in the die needs to be 40°C to 90°C. In carrying out this invention, the temperature of the slurry-like oxide magnetic material in the molding space within the die is set at 40°C to
Various methods can be used to maintain the temperature at 90°C, such as directly heating the slurry-like oxide magnetic material in advance with a pipe heater, etc., or indirectly heating the outer surface of the tank with hot water, etc. Alternatively, it is effective to heat the introduction pipe from the injection machine to the die from the outer periphery during automatic injection. In the molding method according to the present invention, it is desirable that the arrangement of the drainage holes be appropriately selected according to the following conditions depending on the shape and dimensions of the molded product. If the molded body is flat, the water drainage plate should be placed concentrically with the cross section of the molding space in the die, within a width of 0.2d or less, with an inner diameter of 1mm to 4mm.
A configuration in which drain holes of mm are arranged at equal intervals. However, in the case of a ring-shaped molded body; d=(D/2)-(D'/2) In the case of a disc-shaped molded body; d=D/2 In the case of a square-shaped molded body; d=L/2 (D : die inner diameter, D′: core outer diameter, L: length of one side inside the die) Alternatively, on the outer periphery of the molding space of the water drainage plate, concentrically with a similar shape to the cross section of the molding space inside the die, with a width of 0.1 d.
A configuration in which drain holes with an inner diameter of 1 mm to 4 mm are arranged at equal intervals within a range of ~1.0 d. However, in the case of a ring-shaped molded body and a disc-shaped molded body; d=D/2; in the case of a square-shaped molded body; d=L/2 (D: inner diameter of the die, L: length of one side inside the die). Next, When the molded body has a bow-shaped cross-section, the length in the chord direction of the curved surface of the molded body with a bow-shaped cross-section is D,
When the axial length is L, in the L direction of the water drainage plate,
A structure in which water drainage holes with a diameter of 1 mm to 4 mm are arranged linearly at equal intervals within a width of 0.2D from the L-direction end face of the die where the water drainage plate and the raw material powder come into contact. Alternatively, if the length in the chordal direction of the curved surface of the bow-shaped molded body is D and the length in the axial direction is L, then in the L direction of the water drainage plate, the width A structure in which drainage holes with a diameter of 1 mm to 4 mm are arranged linearly at equal intervals within a range of 0.2D. In addition, at the entrance of the water drainage hole, that is, the part that contacts the filter cloth, a space for a water reservoir is provided, for example, in a conical, cylindrical, or prismatic shape, or a groove having a similar shape to the cross section of the molding space. By forming this, it is possible to improve the water drainage effect. In the molding method according to the present invention, water is drained in the horizontal direction rather than vertically, so the filter cloth has the fiber direction, the thickness of the fibers and threads, the arrangement and weave of the warp and weft, etc. It is desirable to have a composition suitable for water, such as nylon, Tetron, wool, acrylic, synthetic fibers, silk, felt, metal, etc.
It may be determined as appropriate depending on the material such as metal fiber. In addition, the filter cloth may be composed of one or more sheets, and if it is made of materials other than metal or metal fibers, it may be used during compression molding.
It is desirable to have a thickness of 0.3 mm to 3.0 mm, and most preferably 1.0 mm to 2.0 mm. In addition, if a net-like material made of metal or metal fiber is used for the filter cloth, for example, the roughness of 200 to 400 mesh, 0.05 mm.
~1.0mm thickness is desirable. Examples Example 1 After automatically injecting slurry-like oxide magnetic material 4 with an average particle size of 0.75 μm and a concentration of 64 wt% into the molding space 3 of the die 2 of the wet molding apparatus 1 shown in FIG. 2a,
Molding was carried out in a magnetic field of 10 kOe under conditions of a compression ratio of 2 and a pressing force of 0.5 t/cm ² . During molding, as shown in FIG. 2b, a water drainage plate 5 is used, in which 40 water drainage holes 6 having an inner diameter of 2.0 mm are arranged in a circle at regular intervals in a line relative to the center of the molding space 3 in the radial direction. Water is removed by 60 mm outer diameter x 20 mm inner diameter x height 10
After molding 50 mm-sized molded bodies and drying them naturally for 3 days.
Sintering was performed at 1210°C for 1.5 hours. Note that the water drain plate 5 is provided with a furnace cloth so that it does not come into direct contact with the slurry-like oxide magnetic material 4;
The illustration is omitted in FIG. 2a. Further, the water jet hole 6 of the water drain plate 5 communicates with a water drain passage 8 provided in the upper punch 7 in FIG. 2a. At this time, the temperature of the slurry-like oxide magnetic material in the molding space in the die was varied, and the temperature and molding efficiency of the oxide magnetic material, the occurrence rate of cracking and peeling,
The relationship between warp strain and magnetic properties after sintering was investigated.
The results are shown in Table 1. The molding efficiency is the molding efficiency when the temperature of the slurry-like oxide magnetic material is 20℃.
Evaluation was made using an index set at 100. The one-sided warp strain of the sintered body was measured by measuring the gap between the surfaces of the sintered body placed on a surface plate using a gap gauge.

[Table] As is clear from Table 1, the present invention maintains the temperature of the slurry-like oxide magnetic material filled in the molding space in the die at a predetermined temperature, and drains water from a predetermined water drain hole. It can be seen that this wet molding method is extremely effective in improving magnetic properties and molding efficiency, and preventing cracking, peeling, warping, etc., and is extremely advantageous for industrial production. Example 2 Composition of 10% SrO, 90% Fe ₂ O ₃ , average particle size 0.75μ
m, slurry-like oxide magnetic material 1 with a concentration of 64 wt%
3 was automatically injected into the molding space ¹² of the die 11 of the wet molding apparatus 10 shown in FIG. During molding, as shown in Fig. 3b, drain holes 15 with an inner diameter of 2.0 mm are placed at positions 4 mm outside the end surface of the molding space 12 of the die 11, and 6 holes are placed at equal intervals in a straight line in the L direction, for a total of 12 holes. The water was drained by the water drain plate 14 arranged with the water drain plate 14, and 50 molded bodies 18 having dimensions of D65 mm x L40 mm x T10 mm as shown in Fig. 3c were molded, and after natural drying for 3 days.
Sintering was performed at 1210°C for 1.5 hours. Note that a filter cloth is interposed between the water drain plate 14 and the slurry-like oxide magnetic material 13 so that it does not come into direct contact with the slurry-like oxide magnetic material 13.
The illustration is omitted in FIG. 3a. Further, the water injection hole 15 of the water drainage plate 14 communicates with a water injection passage 17 provided in the upper bunch 16 in FIG. 3a. At this time, the temperature of the slurry-like oxide magnetic material in the molding space in the die was varied, and the relationship between the temperature of the oxide magnetic material, molding efficiency, cracking and peeling occurrence rate, and magnetic alignment characteristics was investigated. The results are shown in Table 2. The molding efficiency was evaluated using an index with the molding efficiency when the temperature of the slurry-like oxide magnetic material was 20° C. as 100. As is clear from Table 2, the present invention maintains the temperature of the slurry-like oxide magnetic material filled in the molding space in the die at a predetermined temperature, and drains water from a predetermined drainage hole, thereby improving the magnetic properties. It can be seen that this wet molding method is extremely effective in improving molding efficiency and preventing cracking and peeling, and is extremely advantageous for industrial production.

【table】 [Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between temperature and viscosity of a slurry-like oxide magnetic material. FIG. 2a is a longitudinal sectional view of the main part of the wet molding apparatus, and FIG. 2b is an explanatory view showing the positional relationship between the molding space and the water drainage hole of the water drainage plate. Figure 3a is a longitudinal sectional view of the main parts of the wet molding device;
Figure b is an explanatory view showing the positional relationship between the molding space and the water drain hole of the water drain plate, and figure c is a perspective view of the molded body. 1,10...Wet molding device, 2,11...Dice, 3,12...Molding space, 4,13...Slurry oxide magnetic material, 5,14...Drain plate, 6,
15...Drain hole, 7,16...Upper punch, 8,1
7... Water drainage passage, 18... Molded body.

Claims (1)

[Claims] 1. A molding space in a die is filled with a slurry-like oxide magnetic material, and water is drained from a filter cloth and a water-draining plate interposed between the slurry-like oxide magnetic material and the upper punch.
In a wet molding method of compression molding an oxide magnetic material into a flat shape, the average particle size of the slurry-like oxide magnetic material filled in the molding space is 0.5 μm to 1.2 μm,
The concentration is 55wt% to 80wt% and the temperature is 40℃ to
A wet molding method characterized by maintaining the temperature at 90°C and draining water through drainage holes arranged inside or outside the molding space in a shape similar to and concentrically with the cross section of the molding space in the die. 2 Fill the molding space in the die with a slurry-like oxide magnetic material, and drain water through a filter cloth and a water-draining plate interposed between the slurry-like oxide magnetic material and the upper punch,
In a wet molding method of compression molding an oxide magnetic material into a bow-shaped cross section, the average particle size of the slurry-like oxide magnetic material filled in the molding space is set to 0.5 μm to 1.2 μm.
m, the concentration was 55wt% to 80wt%, and the temperature was 40%.
A wet molding method characterized by maintaining the temperature at a temperature of 90° C. to 90° C. and draining water through drainage holes arranged in a straight line parallel to the axial direction of the molding space inside or outside the molding space.