JP7091547B1 - Iron core manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an economical method for manufacturing an electromagnetic iron core. SOLUTION: The applicable steel type is industrial pure iron which is easy to mass-produce, the shape of the rolled steel material of the material is set according to the shape of the iron core, and the raw material having the same mass as the iron core is cut out from the rolled steel material, and the raw shape is obtained. The material is heated to 1500 ° C. or higher and 1530 ° C. or lower, and immediately charged into a die of an iron core replica and hermetically pressed. Although it is a kind of hot working, the grain boundaries are melted and pressed into the narrow space of the mold by low pressure lower force to form an iron core of a predetermined shape. Since it is an integral product, induction loss occurs, but magnetic hysteresis loss is not much different from that of high-grade electrical steel sheets. [Selection diagram] Fig. 1

Description

The present invention relates to a method for manufacturing a soft magnetic material and a method for manufacturing an iron core used in an electromagnetic device such as a motor, a transformer, a relay, etc. using the material.

The iron core of an electromagnetic device is usually composed of laminated electromagnetic steel sheets. For electromagnetic steel sheets, the magnetic properties (strengthening of magnetic permeability and minimization of residual magnetism) are improved by appropriate hot rolling and heat treatment of ultra-low carbon silicon steel material, and magnetic hysteresis loss is minimized. The treatment minimizes the induction loss.
Until the invention and manufacture of electrical steel sheets, industrial pure iron (armco iron) was melted in a flat furnace, rolled from the material to steel sheets, and then insulated to form an iron core material.

High-priced electrical steel sheets as materials, processing costs for punching into a predetermined shape using a die, and material yield loss due to punching are recorded in the iron core manufacturing cost, and various methods have been developed to reduce costs. ing.
Patent Document 1 describes that a pure iron powder, which is cheaper than an electromagnetic steel sheet, is used as a raw material and is pressed down in a mold having a predetermined shape to form an iron core.
Even if the electromagnetic performance is inferior to that of the laminated electrical steel sheet, the energy loss is not large for the electromagnetic equipment whose net operating rate is not large, and it is advantageous overall.

The problem is that there are many cases of dust cores, and one-time integral molding is possible, which is cost-effective, but due to the press capacity and the permeability of the rolling pressure, large members are unreasonable and the manufacturable dimensions are limited.

Patent Document 2 describes a method for producing pure iron for industrial use, which is easy to mass-produce. In the case of this method, only a simple decarburization treatment is added in the melting of low carbon steel, and the material cost is further reduced as compared with the powder. Furthermore, it is suggested that an integral iron core is manufactured by appropriate processing (cutting, punching, cold forming) of thick plates, flat steel, and steel bars made of pure iron, and it is expected that the processing cost will be reduced.
Even if the electromagnetic performance is inferior like the dust core, the total cost will be advantageous depending on the application. Since DC equipment is DC, neither hysteresis loss nor induction loss occurs in the main iron core.

The problem is that if the core shape is simple and the dimensions are not large, it can be molded from a massive material by one press hot or cold, but in the case of an electric motor, the core shape is quite complicated and integrally molded. Is not easy. As with the dust core, the manufacturable dimensions are limited by the rolling force. Although it is possible to consider a plurality of assembly methods in which individual members are integrally molded, the superiority is reduced.

Consider a method of molding a member having a complicated shape by a simple process.
1) In the plastic model injection process, the molten resin is press-fitted into the mold. Easy to fill every corner.
2) In thixomolding of Mg alloy, the material is semi-melted and injection molded into a mold. A mobile phone case is manufactured. No case is found in Fe.
3) Cast the molten metal. In fact, the stator of a large DC motor was sometimes manufactured by casting. There is an efficiency problem in small and medium-sized manufacturing.
4) Molding is performed by the hot pressing described above. It is suitable for mass production of simple small items, but it is difficult to fill every corner even if a closed mold is used for complicated shapes, and it is non-uniform for large members as well as powder molding.

5) There is a process of processing semi-molten steel, which is not molding. In the butt welding of rods, the contact surface is preferentially heated by direct energization heating, and when it becomes semi-molten, the contact portion flows and welds with a slight reduction force, and the contact portion rises and is welded.
When the semi-molten part flows plastically, the liquid phase part is extracted and the solid phase part remains. The solid phase portion becomes low carbon, and the discharged liquid phase portion becomes high carbon, and mechanical segregation occurs. If the high carbon part is properly removed, it can withstand wire drawing.
It is conceivable that there is a processing condition in which the above segregation phenomenon does not occur in the molding of semi-molten steel, but it has not been found at present.

Published Patent Publication 2005-197594 Patent No. 6910523

Iron and Steel Vol.82 (1996) No.12, p.35 ~ p.40 Yamanaka et al., Internal cracking mechanism of continuously cast slabs

The present invention aims at manufacturing an iron core which is slightly inferior in electromagnetic performance to an electromagnetic steel core formed by laminating conventional magnetic steel sheets, but which is significantly advantageous in terms of manufacturing cost, and therefore heat of a low-cost soft magnetic material. It is a problem to be solved to provide a method for forming a core having a complicated shape or a large size from a rolled material.

The first invention is a method of forming an integral electromagnetic core.
When the chemical composition is mass%, C is 0.01% or less, Si is 0.01% or less, Mn is 0.5% or less, P is 0.03% or less, S is 0.03% or less, and O is 0.05% or more and 1.3% or less. When the iron core of a predetermined shape is manufactured by one press molding using rolled steel of industrial pure iron whose balance is unavoidable impurities and Fe and the purity of iron is 99.0% or more, a rod having the above components It is characterized in that a linear, flat or annular raw material is heated to 1500 ° C. or higher and 1530 ° C. or lower, immediately charged in a mold containing the predetermined shape in a state where the grain boundaries are melted, and sealed and pressed. This is a method for manufacturing an integral iron core.

The second invention is
1) For the stator of a motor that has a large number of magnetic poles on the inner circumference, the shape of the element shape is a cylinder.
2) For the rotor of a motor that has a large number of magnetic poles on the outer circumference, the shape of the element shape is a cylinder.
3) The method for manufacturing an integral core according to the first invention, wherein the shape of the raw material is rectangular with respect to the two-pole rotor core or the core having a rectangular cross section.

The first effect of the present invention is that the rolling material used is supplied with the same raw materials and processes as mass-produced ordinary steel, and does not require high-grade and expensive electromagnetic steel sheets.
The molding yield from mass-produced rolled material to the product via the raw material (rolled material divided into the specified core mass) is close to 100%, which is several tens of percent higher than that of punched steel sheet, and the material cost is overwhelming. It is advantageous in terms of.

The processing cost of the raw material itself is only by cutting the rolled steel material or by simply processing it, and the processing from the raw material to the product is also performed by one low pressure pressing hot pressing, from punching and laminating. Is also advantageous.

Comparing the magnetic properties of the industrial pure iron of the present invention and the electrical steel sheet as a soft magnetic material, the former is slightly inferior in magnetic permeability and residual magnetization, but is not definitive. The ultra-high temperature hot working, which is a feature of the present invention, coarsens the crystal grains and improves both of the above properties.
Induction loss due to eddy current, which is an electromagnetic property, is unavoidable, but it can be put to practical use in applications where induction loss is tolerated to some extent.

In a DC motor, the magnetic poles are usually fixed on the stator side, and hysteresis loss and induction loss do not occur. Since the rotor moves in a fixed magnetic field, induction loss occurs.
Many small and medium-sized DC motors are used in automobiles. The utilization rate is small. Since the energy consumption is small, the induction loss can be ignored. The iron core of the present invention can withstand practical use.

The required rolling force of the press for forming the iron core is a fraction of that of the cold press because the processing temperature is hot, and is further lower than the normal hot deformation resistance because the processing is performed immediately below the melting point. Medium-sized iron cores with large dimensions can also be easily manufactured. With a simple shape, it is easy to manufacture a large iron core.

The applicable steel type is high oxygen iron and has excellent corrosion resistance. Even in seawater, it becomes black rust (a magnetite layer is formed on the surface), has excellent corrosion resistance, and is advantageous for use in water.

A method of charging a cylindrical raw material into a closed die and pressing it to form a multi-pole stator core is shown. FIG. A is a view seen from above, and FIG. B is a vertical sectional view. The molding method of a cylindrical raw material is shown. A method of charging a columnar element into a closed die and pressing it to form a multi-pole rotor core is shown. FIG. A is a view seen from above, and FIG. B is a vertical sectional view. In the Fe-C phase diagram, the temperature at which tensile strength develops (ZST) and the temperature at which elongation develops (ZDT) at the time of cooling from the start of solidification are shown. An experimental method of ultra-high temperature machining using a butt welder is shown.

An apparatus and a working method for carrying out the stator core forming method of the present invention will be described with reference to FIG.
The outer die 1 for sealing pressing has a bottomed cylindrical inner wall 2. The inner wall 2 is the outer circumference of the target stator 6. Reference numeral 3 is a concentric columnar core, and the lower portion is a cylinder, but the upper portion is provided with a groove 5 forming a magnetic pole 4 inward from the wall surface of the cylinder. The shape of the groove 5 is the same as that of the stator 6 (the shape of the white portion in the figure).

The cylindrical element 7 having the same volume as the stator 6 and having a predetermined component is preheated to 1500 ° C. or higher, and is charged into the annular space 8 formed in the gap between the outer mold 1 and the core 3. To. An annular lower mold 9 is provided at the bottom of the annular space 8, and an upper mold 10 is provided above the annular space 8. After charging, the upper mold 10 is pushed down to close the upper surface of the annular space 8. Next, the lower mold 9 is pushed up by the piston 11 penetrating the bottom of the outer mold 1, the raw material 7 is pushed into the closed space and flows into the groove 5, and the stator 6 is formed. Next, the upper mold 10 is retracted, the lower mold 9 is pushed up further, and the stator 6 is taken out from the outer mold 1.

A method of preparing a cylindrical raw material will be described with reference to FIG. In the figure, A is a pipe material having appropriate dimensions.
B is formed by winding a plate material into a tubular shape. C is formed by winding a rod in a coil shape to form a tubular shape. In the case of the latter two, forge welding progresses during the processing to the stator core, and they can be used together like a pipe material.

A method of forming the rotor core will be described with reference to FIG. Reference numeral 21 is an outer die for sealing and pressing, and a replica space 23 (black part in the figure) having the same shape as the target rotor 22 is engraved inside the outer die 21 like a sand mold in casting. ing. Below the replica space 23, a bottomed cylindrical charging space 24 is provided coaxially with the space.

The columnar raw material 25 having the same volume as the rotor space is preheated to 1500 ° C. or higher and charged into the charging space 24. A disk-shaped lower mold 26 is provided at the bottom of the charging space 24, and a disk-shaped upper mold 27 is provided above the charging space 24. After charging, the upper mold 27 is pushed down to close the upper surface of the replica space 23. Next, the lower mold 26 is pushed up by the piston 28 penetrating the bottom of the outer mold 21, and the raw material 25 is pushed into the closed space and flows into the groove portion which becomes the magnetic pole, and the rotor 22 is formed. Next, the upper mold 27 is retracted, the lower mold 26 is pushed up further, and the rotor 22 is taken out from the outer mold 21.

The iron core material will be described.
Suitable conditions for a soft magnetic material are high magnetic permeability, low residual magnetization (holding force), and high electrical resistance. The former reduces the magnetic hysteresis loss, and the latter reduces the induction loss. Laminated iron cores using electrical steel sheets of ultra-low carbon high silicon steel with an insulating coating are the best. An insulating film is added to control not only the components but also the crystal grains to improve the magnetic properties and to improve the electrical properties.

Until the invention of the above steel grade, pure iron called armco iron was used as the core material.
The present invention inherits that trend. Comparing the magnetic properties of the above steel types with pure iron, there is no great difference in magnetic permeability and residual magnetization. No hysteresis loss itself occurs in DC magnetization. Pure iron is sufficient for low operating rate electromagnetic equipment.
In the present invention, the steel grade described in Cited Document 2 is used. The chemical composition is in mass%
C is 0.01% or less, O is 0.05% or more and 0.13% or less, Si is 0.01% or less, Mn is 0.5% or less, P and S are 0.03% or less, and the balance is inevitable. It is an impurity and Fe, and the Fe purity is 99.0% or more.
The characteristic of this steel grade is not only the magnetic property but also the action of O to form black rust (magnetite) even in a corroded environment and suppress the subsequent corrosion. It becomes a rust-resistant iron core.

The processing temperature will be described.
In ordinary hot forging or hot pressing, it is difficult to integrally form a stator and a rotor having a large number of magnetic poles, and the larger the size, the more difficult it is. Even with excessive pressure, the plastic flow does not spread in a narrow space.
As described above, if it is semi-melted, it can be press-fitted into a closed mold. It is also easy to connect and weld the wires. Each is performed with a much smaller pressing force than hot working.

The problems of the semi-melt press-fitting method will be described. Carbon steel becomes semi-molten at the temperature between the liquid phase line and the solid phase line. When pressurized in this state, it is easily deformed, but the low carbon solid phase hardly moves, the high carbon liquid phase preferentially flows, and mechanical segregation occurs. It's like squeezing a lemon. There may be theoretical conditions in which both phases flow in a homogeneous state, but there are no studies. This is the reason why there are no examples of semi-melt press-fitting in steel.

Since the component of the present invention is almost pure iron,
1) The temperature range between the liquid phase line and the solid phase line is extremely narrow.
2) The component difference between the two phases is extremely small.
Therefore, even if the segregation phenomenon can be reduced, the working temperature range is narrow and it is difficult to apply it.

In Cited Document 3, the tensile strength and elongation behavior in the solidification process are studied in detail in order to prevent cracking in the continuous steel casting process. according to it,
1) There is no tensile strength or elongation between the liquid phase line and the solid phase line during cooling, and the tensile action easily induces cracking.
2) When the solidification is completed, there is no elongation, but a tensile strength close to the hot strength develops. The temperature is referred to as ZST (Zero-Strength Temperature). It is lower than the solidus temperature.
3) Further cooling causes elongation. This temperature is referred to as ZDT (Zero-Ductile Temperature).
4) If the limit strain (quite small) is exceeded between both temperatures, cracking will occur. The limit strain became clear from the experiment.
5) Hot working is possible below ZDT.

FIG. 4 accurately cites the data described in the above document and superimposes ZST and ZDT on the Fe—C system phase diagram. Both ZST (solid phase ratio 0.8) and ZDT (0.99) lines are located below the solid phase line (low temperature side), and appropriate or inappropriate processing (strain) regions correspond to the amount of C. I understand.
It can also be seen that there is no strength or elongation between ZST and the solid phase line even if the shape is maintained.

The above studies have elucidated the development of strength and stretchability during the cooling process. It is presumed that the same phenomenon occurs in the heating process, if not equivalent. It is well known that cracks are likely to occur on the surface of hot working when it enters the overheated region in both temperature and time, and it is said that it is caused by grain boundary melting.

Plastic working is possible even if there is no elongation. Tensile tests on clay show that it is easily torn off and has low elongation. Under the pressure of clay, it easily becomes a plastic flow while generating cracks, and a part of it is pressed and the cracks disappear.
In the plastic working between ZST and ZDT, cracks occur at the same time, but the working is possible. Since the strength is exhibited, the deformation resistance is close to that of normal hot working, so a rolling force to resist it is required.
Although it has not been examined in the literature, it is reasonably presumed that it is possible to deform it with a low-pressure lower force without considering cracking because there is no strength or elongation in processing above ZST.

The melting point, liquidus temperature, and solidus temperature of pure industrial iron, which is the material used in the present invention, are close to each other. However, it is presumed that the plastic deformation of the low deformation resistance generated in the low carbon steel described later is the coexistence of the liquid phase and the solid phase, or the state where the grain boundary is the liquid phase and the inside of the grain is the solid phase. On the one hand, it is supposed to resemble the fluidized state of sand.
In the present invention, this state is applied, and the main purpose is to perform plastic working above (high temperature side) of ZST, which is considered to be inappropriate.
ZST is directly below the solid phase line, and in the case of pure iron, it is about 1500 ° C. The temperature is affected by the amount of C, impurities P, S, residual amounts of unavoidable impurities and the like.

The lower limit of the processing temperature of the present invention will be described.
The appropriate processing temperature is ZST or higher. As can be seen from FIG. 3, ZST is about 20 ° C. below the solid phase line. The solid phase line of the steel grade of the present invention is at about 20 ° C. below the melting point. Therefore, it is considered to be about 40 ° C. below the melting point.
Approximate the solidus temperature of the steel type. From the phase diagram of the Fe binary alloy, the melting point depression is
-4 ° C with 0.01% C, -3 ° C with 0.5% Mn, -3 ° C with 0.03% P,
With 0.03% S, it becomes -24 ° C, and the total becomes -34 ° C. That is, the solid phase temperature is about 1500 ° C. In reality, S, which has a prominent effect, binds to Mn and diminishes its action, and is estimated to be 1510 to 1520 ° C. ZST is estimated to be 1490-1500 ° C. This is the reason why the specific temperature is 1500 ° C or higher.

The upper limit temperature is naturally below the melting point. If it exceeds the melting point, it becomes a mere casting. The melting point depends on the amount of impurities and is calculated to be about 1530 ° C.

Naturally, cracking easily occurs during processing, but since it is pure iron, it is also easy to join because of grain boundary melting, and cracking and joining occur in parallel during processing. Even if the streaks of the joint remain, it does not pose a problem due to the nature of the product.
Since it has low deformation resistance, it is machined with lower power than ordinary hot working machines (rolling machines, forgings, presses), and the plastic flow easily penetrates into every corner of the die.

A low carbon steel close to pure iron was used as a substitute, and a confirmation test was conducted to see if it would be easily deformed with lower stress than hot working when heated and approached the solidus temperature.
The steel type is a carbon dioxide gas welding rod, which is 0.05% C, 1.5% Si, 1.0% Mn, 0.01% P, 0.01% S. The melting point depression per 1% of each element is 400 ° C, 6 ° C, 7 ° C, 100 ° C,
It is 800 ° C. S is the largest factor, but it is almost ignored due to coexistence with Mn. The melting point depression of the steel grade is about 30 ° C. The solidus temperature is estimated to be about 1500 ° C.
In the steel grade of the present invention, 0.01% C has a large effect, and the drop is about 10 ° C. The solidus temperature will be between 1520 and 1530 ° C. Since ZST is about 20 ° C lower than the solidus temperature, it is presumed that both strength and elongation disappear at about 1500 ° C or higher. It is presumed that softening occurs below that in the experimental steel grade.

The possibility of low stress deformation was reexamined using the above-mentioned wire butt welding.
As shown in FIG. 5, the welding machine includes a power supply 51, two electrode clamps 52 and 53, and a pressurizing device 54 that presses one side of the clamp against the clamp side of the other pole. In butt welding, it is observed that the butt portion rapidly rises due to energization, partially melts, and is welded through a plastic flow due to pressure. Since it is partially melted, the required pressing force is not large. It can be dealt with with a normal pneumatic cylinder.
When one wire 55 of the above steel type was clamped and energized, the temperature of the central portion was preferentially raised in the same manner as in the case of abutting, and the bulge 56 was generated without melting and falling. Vertical warpage (in the linear axis direction) may occur on the outer periphery of the bulge 56. It can be considered that the invention steel grades close to the experimental steel grades show almost the same behavior. This is because we cannot find a factor that does not.
What is important here is that the rolling force generated by the plastic flow (= the pressing force of the pneumatic cylinder) is overwhelmingly smaller than the product of the normal hot deformation resistance and the cross-sectional area. The possibility of low stress and high strain machining of the present invention is supported.
The above experiment can be said to be a phenomenon similar to the thixomolding of Mg alloys or the melt forging method of non-iron alloys.

The iron core manufacturing method of the present invention can be easily carried out at low cost.

1; outer mold 2; inner wall 3; core 4; magnetic pole 5; groove 6; stator 7; element shape material 8: annular space 9: lower mold 10; upper mold 11; piston 21; outer mold 22 Rotator 23; Replica space 24; Charge space 25; Base material 26; Lower mold 27; Upper mold 51; Power supply 52, 53; Electrode clamp 54; Pressurizing device 55; Wire rod 56; Balge

Claims (2)

It is a method of forming an integral electromagnetic core, and the chemical composition is C 0.01% or less, Si 0.01% or less, Mn 0.5% or less, P 0.03% or less, S 0.03% or less in mass%. Once using rolled steel material with a predetermined cross-sectional shape of industrial pure iron having O of 0.05% or more and 1.3% or less, the balance being unavoidable impurities and Fe, and iron purity of 99.0% or more. In order to produce an iron core having a predetermined shape by the press forming of the above, a rod-shaped or flat-shaped or annular raw material cut out from the rolled steel material is heated to a range of 1500 ° C. or higher and 1530 ° C. or lower immediately below the solid phase line temperature . A method for manufacturing an integral iron core, which comprises immediately charging the iron core into a replica mold in a molten state and pressing the iron core in a sealed manner. For the stator of the motor with many magnetic poles on the inner circumference, the shape of the base material is a cylinder, and for the rotor of the motor with many poles on the outer circumference, the shape of the base material is a cylinder. The method for manufacturing an integral core according to claim 1, wherein the shape of the raw material is rectangular with respect to the pole rotor core or the core having a rectangular cross section.

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