JPH11329877A - Cylindrical ferrite magnet and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise productivity of a cylindrical molded material subjected to extrusion molding, by increasing the efficiency of drying the molded material and the orientation efficiency of the molded material. SOLUTION: A cylindrical extrusion-molded material 2 containing hard ferrite powder as its main component and has 14 to 20 wt.% of moisture is carried in a dryer furnace 3, in a state that the molded material 2 is arranged in a plurality of rows on a transfer means 1 along the transfer direction of the means 1, and microwaves are made to irradiate the molded material 2. As a result, the moisture of the molded material 2 is reduced to 10 wt.% or lower and the molded material is sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical ferrite magnet for improving the productivity of an extruded cylindrical extruded product by improving drying efficiency and improving a construction process, and a method for producing the same.

[0002]

2. Description of the Related Art Cylindrical ferrite magnets having multipolar anisotropy on the surface are frequently used in rotors of stepping motors. This type of ferrite magnet is formed, for example, by extruding a kneaded raw material obtained by mixing a raw material (ferrite particles) with a medium such as water, and imparting multipolar anisotropy to the surface of the obtained cylindrical extruded body. It is manufactured through the steps of drying, sintering, processing and magnetizing. In this production method, it is important to reduce the water content of a cylindrical extruded product (hereinafter referred to as a molded product) in order to increase production efficiency. When a compact having a water content of about 5% or more is sintered, cracks are easily generated and the yield is deteriorated. Means for drying the molded body include natural drying, electric furnace drying, gas furnace drying, and vacuum drying.

However, the natural drying method requires 1 to 5 days for drying depending on weather conditions and product items, and thus requires a large space for drying and storage. In addition, there are variations in the drying time depending on the season and weather conditions, and there is a problem in management. When drying using an electric furnace or gas furnace, the drying time can be shortened, but drying proceeds from the part close to the heat source of the molded body or the surface part exposed to hot air, and the entire molded body is not dried uniformly Uneven drying, cracking, and distortion of the formed body are likely to occur. In the vacuum drying method, it is necessary to warm the molded body with a heater or the like because the molded body temperature is lowered by depriving the molded body of heat of vaporization with drying, and it takes a long time to dry the electric furnace or the gas furnace. As in the case of the drying method used, drying proceeds from a portion near the heat source of the molded body or a surface portion exposed to hot air, and distortion, uneven drying, and dry cracking are likely to occur in the molded body.

In order to solve the above problem, drying a ferrite magnet by using a microwave output is disclosed in Japanese Unexamined Patent Publication No.
No. 226328. The publication describes that irradiating a molded body with microwaves can shorten drying time, improve drying efficiency, firing efficiency, uniformity of drying, quality, yield, and reduce production cost.

[0005]

However, when a cylindrical ferrite magnet is manufactured by an extrusion molding method, the following problems occur. Since the water content is high due to the extrusion molding, and the molded body has a clay-like shape, it is easily deformed when an external force is applied. In practice, handling cannot be performed unless the water content falls below 13.5%. Therefore, it is difficult to transfer the molded body to another drying container or the like and to transport the molded body into the drying furnace, so that drying is difficult. In order to reduce the moisture content of the molded body, it is effective to stay in the drying furnace for a long time, but the molded body cut to a predetermined length is sequentially passed through the drying furnace by a conveying means such as a belt conveyor. Therefore, in order to lengthen the drying time without lowering the productivity, it is necessary to lengthen the drying furnace. It takes too much time for the magnetized orientation of the molded body relative to the molding speed. Therefore, simply using the microwave drying furnace or the like cannot efficiently dry the formed body, and a large amount of time is required for secondary drying.

The present invention solves the above-mentioned problems, and efficiently extrudes and extrudes a cylindrical extruded product having a high moisture content.
It is another object of the present invention to improve productivity by improving the execution process.

[0007]

According to the present invention, a plurality of cylindrical extruded products mainly composed of a hard ferrite powder and having a water content of 14 to 20% by weight are arranged on a conveying means along the conveying direction. The molded product is conveyed in a drying furnace in a state where the molded product is irradiated with microwaves to reduce the water content to 10% or less, and then sintered. That is, conventionally, the extruded molded articles were conveyed to the drying furnace in the order in which they were extruded. However, in the present invention, a plurality of molded articles are conveyed in parallel (for example, n columns: n is an integer of 2 or more). Even if the transport speed is set to 1 / n, the same number of molded bodies can be transported, and can be passed through a drying oven of the same length over a long period of time.

It is preferable to use a belt conveyor as the above-mentioned conveying means, since the molded body can be supplied into the drying furnace without deforming the molded body. In addition, since the molded body with magnetized orientation has magnetic force, if multiple molded bodies are arranged in parallel on a flat conveyor, they will be aggregated due to mutual magnetic repulsion, causing deformation and transporting to the drying oven. In this case, the molded body is not uniformly dried as a whole, and is not sufficiently dried. Therefore, it is desirable that each belt conveyor bends along its moving direction so that the upper surface becomes concave so as to suppress the movement of the molded bodies due to magnetic repulsion.

Also, it is possible to easily obtain a plurality of magnets by molding a molded body longer than usual, making a cut in the direction perpendicular to the cylindrical axis, drying, and dividing the cut portion before firing. it can. Usually, since the molded body has a magnetic force at the time of being magnetized and oriented, it is not preferable that a plurality of molded bodies are arranged coaxially and magnetized and oriented to cause repulsion or attraction with each other, which is not stable in the orientation device. However, by making cuts and slightly connecting each other and orienting them at the same time, the movement of each other is suppressed. This has the same effect as aligning a plurality of molded bodies at the same time, and the time required for the alignment can be reduced.
Since some irregularities remain on the surface formed by dividing the cut portion (hereinafter referred to as a cylindrical new surface portion), after sintering, processing for dimensioning mainly by polishing is performed. In particular, if the cut is made to be axially symmetric from the vertical direction of the cylindrical axis of the molded body, cracks in the new cylindrical surface will decrease, and after firing, the new cylindrical surface that will become the fired surface will be damaged to the part required for processing dimensions Alleviate that. The longest depth (h) from the outer peripheral side surface of the cut body
Is 0.23D ≦ h ≦ 0.30, where D is the outer diameter of the molded body.
D is preferred. In the case of 0.23D or less, the probability of causing undesired sintered body cracks at the time of dividing the cut portion before firing increases,
If it is 0.30D or more, the probability of causing undesired cracks also increases due to shrinkage of the molded body due to drying.

[0010]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an overall configuration of a manufacturing apparatus according to an embodiment of the present invention. The kneaded raw material containing 14 to 20% by weight of water is introduced into the extruder 4, and is conveyed to the vacuum chamber 46 by the upper screw. Air bubbles in the kneaded raw material are deaerated in the vacuum chamber 46 and extruded from the extruder 4 by the lower screw. Next, it is cut into a predetermined length by a cutting machine 8. The vicinity of the outlet of the extruder 4 is configured as shown in FIG.
5 is extruded in the direction of the arrow by a lower screw 42 and passes through a base 43 having a cored bar 44 mounted at the end of the case 41, whereby the cylindrical molded body 2 is obtained.

FIG. 3 shows an example of a cutting machine for cutting or cutting a compact. The cutting machine 8 includes a steel wire 81 for cutting the compact and a holding member 82 for stretching the steel wire 81.
And driving means 83 for moving the holding member 82. The driving means 83 includes an optical scale sensor 84, a control device 85, and a pneumatic cylinder 86, and can appropriately change the cutting depth of the molded body.

FIG. 4 shows an example of an orientation device for magnetizing and orienting the compact in a multipolar anisotropic manner. The molded body is carried in from one of the orientation units 51 by conveyance belts 52 and 53 which are substantially parallel to the top and bottom, and carried out from the other after the magnetization orientation. The orientation part 51 contains a cylindrical yoke made of a ferromagnetic material and a coil wound around the magnetic pole part of the yoke, and a ferrite particle of a molded body arranged in the orientation part 51 by applying a pulse current to the coil. Are magnetized. The transport belt is mounted so as to pass through the orientation section while bending along the belt surface in the moving vertical direction, and grips the cylindrical portion outer peripheral surface of the molded body,
The soft molded body is transferred to the orientation unit 51 without being dropped from the belt and without being deformed.

[0013] The magnetized and oriented compacts 2 are respectively placed on four belt conveyors 1 a to 1 d arranged in parallel by a handling device 7 as shown in FIG. Since the belt conveyor passes through the drying furnace 3 for a certain period of time, the conveying speed, the moving distance for each cycle, and the like can be set.

The handling device 7 has a function of transporting the molded product from the molded product discharging portion of the orientation device to the belt conveyor of the microwave drying oven without deforming the molded product, such as the cycle speed and the number of molded products on the belt conveyor. Setting means (eg, control function by control unit)
have.

FIG. 6 is a sectional view of an oven section of a continuous microwave drying furnace used as the above-mentioned drying furnace. The microwave power unit 35 is controlled by the control panel 31,
The microwave output and the selection of the microwave power unit can be set by the operation panel provided on the control panel. The microwave is irradiated from the power unit 35, passes through the waveguide 32, spreads in the applicator 33 while being diffused by the diffusion blades 34, and is absorbed by the molded body 2 while being repeatedly reflected on the inner wall surface of the oven 33.

The temperature of the molded body can be raised in a short time by vibrating water molecules in the molded body by microwave irradiation. In addition, the inside and outside of the molded article can be dried uniformly as compared with natural drying and the like. The microwave drying furnace includes a microwave oven as an irradiation unit, a trap for preventing microwave leakage, and a belt conveyor for transporting a heated object (molded body). Drying is roughly divided into three periods. The first period is preheating the compact, the second period is constant rate drying,
In the third period, drying is performed at a reduced rate, and appropriate conditions are set based on the drying characteristic curve for each type of molded article.

In constant rate drying, the moisture content starts to decrease in proportion to time, and when the rate of drying starts, the balance between the amount of water movement from the inside of the molded body to the surface and the amount of evaporation from the molded body surface is lost, and the molding is performed. Dryness of the body surface becomes noticeable. Further, since the energy by the microwave is consumed by the latent heat of water evaporation and the sensible heat by heating the compact, the drying speed gradually decreases. The molded body dried as described above is divided at the cut portion, sintered at a temperature of 1000 to 1200 ° C. in a sintering furnace, and a cylindrical new surface portion and the like are processed to predetermined dimensions and then magnetized by a magnetizing device. To obtain a cylindrical ferrite magnet.

[0018]

EXAMPLE A cylindrical ferrite magnet was manufactured using the apparatus shown in FIG. 1 under the following conditions. 18% by weight of water and 0.65% by weight of methylcellulose as a binder were kneaded with an Sr ferrite powder having an average particle diameter of 0.8 μm to obtain an extruded raw material, which was then charged into an extruder. 0.5 mm, length 84 mm, water content 18% by weight, weight 1
14.3 g of a cylindrical molded body was molded at an interval of about 10 seconds / piece. In addition, a notch is made at the position of 42 mm in the central part of the length with a maximum depth of 7.5 mm from both sides.

The above compact is supplied to an orientation device, and 3 kO
After applying a pulse magnetic field of e or more to impart 12-pole surface anisotropy, drying is performed using the microwave drying furnace, sintering is performed at 1200 ° C., 12-pole magnetization is applied, and surface magnetic flux is applied. A ferrite magnet having a density of 1.7 kG was obtained. In the present embodiment, the cycle time was set to 40 seconds and the pitch feed movement distance was set to 160 mm for the molded body. The conveying means 1 conveys the compact from the carry-in port to the carry-out port, and the total length of the microwave oven, which is a drying function part of the drying furnace, is about 6 m.

The molded product having a reduced water content by the drying method of the present invention is further reduced to a water content of 5% by weight which can be calcined by secondary drying. In this case, the secondary drying was performed in the atmosphere at about 40 ° C. near the firing furnace.

FIG. 6 shows the relationship between the drying time, the temperature and the water content when the compact is dried in a microwave drying oven. 4
Since the microwave oven is conveyed in a row, the microwave oven is about 6 m in length, which is the same as that of the conventional machine, but can be kept in the atmosphere in the drying furnace for about 23 minutes. Accordingly, as shown in FIG. 6, the water content finally decreases by about 10% by weight as compared with the water content before drying of 18% by weight, and the time for secondary drying can be greatly reduced.

FIG. 7 shows the relationship between the drying time, the temperature, and the water content under the same conditions as described above except that a conventional drying furnace was used. In this case, the drying is performed by preheating the molded body for about 2 minutes, raising the temperature to about 80 ° C., and then maintaining constant drying at about 80 ° C. for about 3 minutes. The length of the conventional microwave oven is about 6 m, and when the extruder of the present embodiment is set in the same molding speed and loaded in a row in a drying furnace, it is discharged from the drying furnace in about 8 minutes. 7, it can be seen that the moisture content is reduced only to 13% by weight from 18% by weight before drying, and the degree of drying is insufficient.

[0023]

As described above, by greatly drying the cylindrical extruded product by the method unique to the present invention, and by improving the process, it is possible to obtain much higher productivity than in the past.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a manufacturing method of the present invention.

FIG. 2 is a sectional view showing a main part of the extrusion molding machine of the present invention.

FIG. 3 is a view showing a cutting machine according to the present invention.

FIG. 4 is a view showing an orientation device according to the present invention.

FIG. 5 is a view showing a carry-in portion of the drying furnace of the present invention.

FIG. 6 is a sectional view showing a microwave drying furnace of the present invention.

FIG. 7 is a diagram showing the relationship between the drying time, temperature, and moisture content of a compact in a drying furnace of the present invention.

FIG. 8 is a diagram showing the relationship between the drying time, temperature, and moisture content of a compact in a conventional drying furnace.

[Explanation of symbols]

1: belt conveyor, 2: molded body, 3: drying oven, 4: extrusion molding machine 5, orientation device, 8: cutting machine,

Claims (4)

[Claims] 1. A cylindrical extruded product mainly composed of hard ferrite powder and having a water content of 14 to 20% by weight is conveyed into a drying furnace in a state of being arranged in plural rows along a conveying direction on a conveying means. A method for producing a cylindrical ferrite magnet, which comprises irradiating the compact with microwaves to reduce the water content to 10% or less and then sintering the compact. 2. The apparatus according to claim 1, wherein a plurality of belt conveyors arranged in parallel are used as the conveying means, and the belt conveyor is curved so that an upper portion thereof is concave along a moving direction of the belt. Manufacturing method of cylindrical ferrite magnet. 3. A cylindrical ferrite magnet which is divided from a cut portion made in a direction perpendicular to a cylindrical axis before firing. 4. A cylindrical ferrite magnet, characterized in that at least one new cylindrical surface is a surface obtained by polishing a fired surface.