JPH07249538A - Extrusion molding method of bond magnet - Google Patents

Abstract

PURPOSE:To provide a bond magnet manufacturing method by which the molding speed of an extruder can be increased at the time of manufacturing a bond magnet. CONSTITUTION:In an extrusion molding method which uses an extruder constituted of a hopper 11 which houses a magnet compound, screw 16 which carries, uniformly mixes, and pushes out the compound with a pressure, driving device 17 which rotates the screw 16, a cylinder 12 which houses the screw and heats and cools the compound, and die provided continuously from the cylinder 12 and has a prescribed shape, the magnet compound is solidified by forcibly cooling the exit of the die 20 and its vicinity from the outside on the exit side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for increasing a molding speed by an extrusion molding machine in manufacturing a bonded magnet by extrusion molding.

[0002]

2. Description of the Related Art Bonded magnets, which are composite materials of ferrite magnet powder or rare earth magnet powder and synthetic resin, are inferior in magnetic characteristics to sintered magnets, but have advantages such as ease of mass production and good dimensional accuracy. Therefore, it has been widely put into practical use as a magnet for electronic parts such as devices such as small motors and small generators in the electronics field, sensors, meters, and relays.

Generally, the state before the magnet powder and the synthetic resin are molded into the bond magnet is called a magnet compound, and the bond magnet is molded from this. A compression molding method, an injection molding method, or an extrusion molding method has been mainly used as a method for molding the bond magnet.

[0004]

The compression molding method is so-called press molding in which heat and pressure are applied to a material. This method has an advantage that high magnetic properties can be obtained after forming into a bonded magnet, but it is difficult to form a thin shape,
The compression molding speed is not fast. The injection molding method is a method of filling a fixed amount of material in a mold. Although this method has higher productivity than compression molding, it is inferior in commercialization rate due to the generation of recycled materials, and is also unsuitable for molding thin-walled shapes. Moreover, there is a problem that both the compression molding method and the injection molding method are discontinuous processing.

On the other hand, the extrusion molding method is a method in which a magnet compound is extruded by a screw of a molding machine and is passed through a die having a predetermined die shape to be molded. However, because the structure is such that the magnet compound is solidified in the die and molded and then extruded, the increase in viscosity caused by the solidification of the magnet compound is the extrusion resistance in the die of the extrusion molding machine, As a result, there is a problem that the molding speed cannot be increased. However, unlike the other molding methods, the extrusion molding method is continuous processing. Therefore, if the molding speed is improved, it will greatly contribute to mass productivity. Therefore, a technique for improving the molding speed has been awaited.

From this point of view, a method called in-mold cooling molding 200 as shown in FIG. 5 has been developed.
This uses a heating mold 201 for heating a magnet compound by a heater 213 provided at the rear part of the mold, while an outlet side in the mold uses a cooling mold 202 in which a coolant is circulated through a buried pipe 221. By doing so, the magnet compound is forcibly cooled in the mold and solidified. Although the molding speed was slightly improved by this molding method, the speed was 0.1 to 0.5 m / min.
To further improve productivity, it is necessary to further improve the molding speed.

The reason why the molding speed is slow is that in this molding method, when the molding is carried out from the extrusion side of the die of the extrusion molding machine, it is necessary that the molding is completed by cooling and solidification in the die. Therefore, the solidification on the cooling surface in the mold reduces the viscosity of the molded product, and as a result, the frictional resistance between the molded product and the mold increases, which has an effect. it is conceivable that. The present invention has been made in view of the above problems, and provides a manufacturing method for accelerating the molding speed by an extruder when manufacturing a bonded magnet by extrusion molding.

[0008]

In the present invention, the first point to be noted is that the hopper for containing the magnet compound and the magnet compound introduced from the hopper are transferred and uniformly kneaded, A screw that pressurizes and pushes out, a drive device that rotates the screw, a cylinder that incorporates the screw and that heats and cools the magnet compound, and that is provided continuously to the cylinder and has a predetermined mold shape. In the extrusion molding method using an extruder including a die, the magnet compound is an extrusion molding method of a bond magnet, which is characterized in that the vicinity of a die exit of the die is forcibly cooled and solidified from the outside of the exit side. .

In the present invention, the second point to be noted is that the heat medium is circulated in the die to control the temperature inside the die with high accuracy. By circulating the heat medium through the die in this way, the magnet compound remains melted in a liquid state by heating in the cylinder, is pressed by the screw, and is in a semi-solidified state immediately before solidification near the outlet in the mold. maintain. The heat medium is preferably an oil type, but a granular heat medium such as an alumina type may be used.

The third point to be noted is that the outlet of the die of the extruder is forcibly cooled with air. This forced cooling may be performed by a method of providing an injection nozzle for air-cooling the outlet of the mold or an air curtain method.

The magnet powder used as the raw material for the bonded magnet is
Ferrite magnet systems or rare earth magnet systems can be used. As the rare earth magnet system, Nd-Fe-B system or Sm-Co system can be used. On the other hand, as the synthetic resin, a thermosetting resin or a thermoplastic resin can be used. For example, nylon (polyamide), polycarbonate, polyimide, polysulfone, phenol resin, epoxy resin, melamine resin, silicone resin, polyurethane resin and the like can be used.

The die may be a sheet die, a pipe die, a plate die or the like depending on the shape of the bond magnet to be manufactured. The cylinder in the extruder may be a single shaft, a twin shaft, a special shaft having three or more shafts, or the like, and the shafts may rotate in the same direction or different directions.

[0013]

[Operation and effect] The magnet powder, which is the material of the bond magnet, and the synthetic resin have a predetermined mixing ratio, and the state before being molded into the bond magnet is generally called a magnet compound. Put into the hopper of the extruder. The charged magnet compound is fed into a cylinder having a heating function, which extends continuously from the hopper, and is pressed forward by a screw rotating by a drive device provided in the cylinder. The magnet compound is kneaded by a screw and is heated to a predetermined temperature by the heating function of the cylinder to be melted.

The melted magnet compound is pressed from the cylinder to a die continuously provided, and is further molded into a predetermined shape by a die inside the die. At this time, by circulating the heat medium through the die, the magnet compound maintains an unstable state in the vicinity of the outlet in the mold, which is on the verge of solidifying from the liquid. As described above, by forcibly cooling the semi-solidified magnet compound at the outlet of the mold, the magnet compound is cooled and solidified just before the outlet, and passes through the outlet while maintaining its shape.

That is, in the present invention, the temperature in the mold is higher than that in the conventional method, as in the case of the conventional cold-molding in the mold in which the material is cooled and solidified in the mold and then pressed and passed from the mold outlet. Since the magnet compound is set and the magnet compound is maintained in a semi-solidified state and forcedly cooled just before the die exit, the viscosity of the magnet compound in the die is low and the frictional resistance to the die can be suppressed. As a result, the molding speed of the extruder can be increased.

[0016]

First Embodiment A first embodiment of the present invention will be described with reference to FIGS. This example was carried out with a single-screw extruder 1 as shown in FIG. The extruder 1 is provided with a hopper 11 in the upper left portion for receiving a magnet compound, and a charging port is opened in the upper portion. Further, as shown in FIG. 2, a cylindrical cylinder 12 is provided below and contiguous to the hopper 11, and a heater 13 for heating the inside of the cylinder is provided in the cylinder 12 in the longitudinal direction of the cylinder 12. A blower 14 for cooling is installed continuously in the lower part of the cylinder in the circumferential direction in the longitudinal direction. Therefore, the cylinder 12 is formed by the heater 13 and the blower 14.
Can be heated or cooled. This keeps the control temperature constant.

As shown in FIG. 1, a screw 16 having spiral irregularities is provided inside the cylinder of the cylinder 12 so as to enable transfer, kneading, and pressurization, and the cylinder 12 is rotated. Therefore, a drive device 17 including a motor 17a and a speed reducer 17b is provided on the left side thereof. The cylinder 12 is fixed by a mount 15.

A die 20 having a predetermined die is continuously provided on the right end of the cylinder 12. This die 20
As shown in FIG. 4, the shape of the die provided in the taper is tapered conically on the outlet side so that the magnet compound extruded and transferred inside the cylinder can be continuously pushed out from the die die in a predetermined shape. It has the shape of.

Further, as shown in FIG. 3 or 4, inside the die 20, two circulation pipes 21 are provided at upper and lower positions so that a heat medium can be circulated in order to accurately control the temperature in the mold. Penetrates. An electric heater 30 for heating the heat medium 100 is provided outside the tank 60,
The heat medium heated to a predetermined temperature by the electric heater 30 is sequentially transferred by the pump 50 to the circulation pipe 21 and the return pipe 211, and is connected so that the heat medium is repeatedly circulated. As the heat medium, a commonly used mineral oil for heat medium was used.

Further, in order to forcibly cool the die outlet of the die 20 of the extrusion molding machine 1 having the above structure from the outside, an injection nozzle 40 is provided so that air can be injected, and the tip of this injection nozzle 40 is It is installed so as to face the mold outlet and be spaced about 20 mm from the outlet.

The magnet compound used was N
d-Fe-B magnet powder and thermoplastic resin (nylon 1
Using the mixture of 2), bonded magnets produced from them are formed into a predetermined shape (height: 0.5 to 3.0 mm, width: 2 to 10 mm).
The cross section of mm was rectangular). The mixing ratio of the magnet powder and the resin was 72% in terms of volume fraction. In Example 1, the shape was formed to have a height of 1 mm and a width of 6 mm.

These functions will be described below. The above magnetic compound is charged into the charging port of the hopper 11. Then, it falls into the cylindrical shape of the cylinder 12. Inside the tubular shape, the screw 16 is rotated by the operation of the drive device 17, so that the spiral unevenness on the outer periphery of the screw 16 transfers the magnetic compound. Further, by rotating the screw 16, the magnetic compound is kneaded.

The inside of the cylinder 12 is heated by the heater 13 for heating at a melting temperature of about 160 ° C. or higher, which is the melting temperature of the magnetic compound, and becomes completely liquid during the transfer by the screw 16. The heating temperature varies depending on the heating zone of the cylinder 12, but the heating is performed at about 200 to 260 ° C. The liquid magnetic compound is transferred to the right side while being pressed by the rotation of the screw 16. The pressing force at this time varies depending on the density in the screw 16, but is pressed at about 400 kg / cm ² .

The magnet compand that has been further pressed and transferred is pushed into a predetermined mold provided inside the die 20 provided at the right end of the cylinder 12. This die 2
0 is provided with a circulation pipe 21 in which the heat medium oil heated to a predetermined temperature (190 ° C.) by the electric heater 30 is circulated, and can be kept within ± 1 ° C. of the predetermined temperature. As a result, the magnetic compound is kept in a semi-solidified state (semi-molten state) immediately before solidifying from the liquid, and is extruded and transferred by the screw 16 to the vicinity of the die exit of the die 20 in this state.

In the semi-solidified state of the magnet compound, after being extruded and transferred to the die outlet of the die 20, the vicinity of the die outlet is forcibly air-cooled by the injection nozzle 40 with air at a flow rate of 50 L / min. About 10 than temperature
Cool at ℃. Therefore, the semi-solidified magnet compound is solidified in the shape of the mold in the vicinity of the mold outlet and is molded and extruded.

The effects will be described in detail below. As described above, according to the present invention, the magnet compound is not solidified in the mold of the die, but is forcibly cooled and solidified in the vicinity of the mold while being maintained in a semi-solidified state until just before the mold exit. Since the viscosity of the magnet compound is low, the frictional resistance between the mold and the magnet compound can be reduced. As a result, the molding speed can be increased.

In Example 1, the molding speed was 4.0.
Since extrusion molding was possible at m / min, the molding speed could be more than doubled compared with the conventional one. In addition, since the maximum energy product (BHmax) of the molded bond magnet was about 8 MGOe, it was found that the bond magnet can be molded with the quality characteristics being almost the same as those of general ones. In addition, since it is possible to continuously form the magnet compound by continuously charging it into the hopper, there is no doubt that this method can greatly contribute to the improvement of productivity.

[0028]

Second Embodiment A second embodiment of the present invention will be described below. The components of the magnet powder and the resin and the mixing ratio thereof are the same as the conditions of the above-described first embodiment. However, the shape of the die was changed so that the molding dimensions were 0.5 mm in height and 2 mm in width as a small article. Further, the same equipment as in Example 1 was used, and the heating temperature, pressing force, heat medium temperature, and forced cooling air flow rate were also set under the same conditions. As a result, extrusion molding was possible at a molding speed of 2.5 m / min. That is, the cross-sectional area of the molding dimension is about 1/6 of that of the first embodiment.
That is, although it leads to the speed of forced cooling, on the contrary, the extrusion resistance between the magnetic compound and the mold increases, so that the molding speed becomes slow. This is because the extrusion resistance related to the cross-sectional area of the bonded magnet increases during molding. However, it was confirmed that the extrusion molding speed can be improved as compared with the conventional method.

Third Embodiment A third embodiment of the present invention will be described below. The components of the magnet powder and the resin and the mixing ratio thereof are the same as the conditions of the above-described first embodiment. However, the shape of the die was changed so that the molding dimensions were slightly larger, with a height of 3.0 mm and a width of 10 mm. Further, the same equipment as in Example 1 was used, and the heating temperature, pressing force, heat medium temperature, and forced cooling air flow rate were also set under the same conditions. As a result, extrusion molding was possible at a molding speed of 5.0 m / min.
That is, although the cross-sectional area of the molding dimension was about 5 times that of Example 1, the cooling rate was hardly decreased and the molding rate was improved. This is because the extrusion resistance related to the cross-sectional area of the bonded magnet decreases during molding. Therefore,
It was confirmed that the extrusion molding speed could be increased several times faster than the conventional method.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an extrusion molding machine according to an embodiment.

FIG. 2 is a partial view of an extrusion molding machine according to an embodiment.

FIG. 3 is an explanatory diagram of a heat medium circulation path according to the embodiment.

FIG. 4 is a detailed explanatory diagram around a die according to an embodiment.

FIG. 5 is an explanatory view of a conventional die.

[Explanation of symbols]

 1 Extrusion Molding Machine 11 Hopper 12 Cylinder 13 Heater 14 Blower 15 Stand 16 Screw 17 Drive Device 20 Die 21 Circulation Pipe 30 Electric Heater 40 Injection Nozzle

Claims (3)

[Claims] 1. A hopper for containing a magnet compound, a screw for transferring the magnet compound from the hopper and kneading the mixture uniformly, and pushing it out, a drive device for rotating the screw, and the screw. In the extrusion molding method by an extruder, which comprises a cylinder for heating and cooling the magnet compound, and a die having a predetermined die shape, which is continuously provided in the cylinder, the magnet compound is the die. The method for extruding a bonded magnet, comprising: forcibly cooling the vicinity of the die exit from the outside on the exit side to solidify. 2. The extrusion molding method for a bond magnet according to claim 1, wherein the die is temperature-controlled by circulating a heating medium. 3. A method of extrusion molding a bonded magnet according to claim 1, wherein the forced cooling method is a cooling method using air.