JP2008017612A - Split core for low frequency motors - Google Patents

Abstract

A conventional electromagnetic steel sheet has been developed for the purpose of greatly reducing iron loss at a commercial frequency such as 50 Hz. As a motor for driving a rolling mill, the rotation speed is 100 rpm, and the frequency of magnetic flux flowing through the steel sheet is as follows. Since it is as small as 1-40 Hz and is not optimized, a split core formed of a magnetic steel sheet designed to reduce hysteresis loss is provided to improve motor efficiency.
SOLUTION: It comprises a split core obtained by processing a grain-oriented electrical steel sheet containing Si of 2.0% by mass or more and 2.8% by mass or less and having an average crystal grain size of 15 mm or more and less than 50 mm. A split core for a low-frequency electric motor in which a material having a different thermal expansion coefficient from that of a steel plate is brought into contact with each other to apply tension to the steel plate.
[Selection] Figure 1

Description

  The present invention relates to a split core for an electric motor that achieves high efficiency, and more specifically, a split core for a low-frequency motor using a magnetic steel sheet with reduced hysteresis loss, that is, a directional magnetic steel sheet. It is about improving.

  Conventional AC motors are generally used for constant speed operation and have a relatively high rated rotational speed. Therefore, even in the case of a large machine, the size of the motor is not so large and light in weight. On the other hand, as a large-sized motor for driving a rolling mill, a DC motor has been conventionally used. For example, the rotational speed is generally low, for example, 6.5 MW / 100 rpm, and for example, 225%, and the normal overload resistance is large. In addition, for example, the split and thick plate mill employs a twin-motor drive type, so the installation space is severely limited. On the other hand, the continuous hot finishing mill has 5 to 7 rolling mills with one stand of 10 to 15 MW in a narrow space. The stand arrangements, and thus the large motor groups that drive them, are also concentrated in a narrow space.

  Recently, AC variable speed motors such as induction motors and synchronous motors, which have been rapidly developed, are going to replace DC motors as main motors for driving rolling mills. In this case, it is necessary to satisfy the same efficiency as a DC motor, a space-saving structure, or at least an equivalent function.

  An AC variable speed motor that replaces a conventional DC motor for driving a rolling mill is provided with at least an equivalent function for installation, disassembly conditions, high efficiency, high controllability, etc. that the conventional DC motor has. Attention has been focused on the necessity, and in this, the need for particularly high efficiency is increasing.

  In particular, there are the following as prior arts in which a tension is applied to the teeth portion in a split core aiming at high efficiency.

  In Japanese Patent Application Laid-Open No. 2005-51941, as shown in FIG. 1, a protrusion is formed at the base portion of the yoke portion, and a gap is formed between the yoke portion and the yoke portion by abutting the protrusion portion without a gap. Thus, it is possible to prevent compressive stress from being generated mainly in the portion where the magnetic flux passes, and thus a technique is disclosed in which iron loss deterioration due to compressive stress can be prevented.

Japanese Patent Application Laid-Open No. 2004-99998 discloses a technique for applying a tensile tension to a steel sheet surface by plating the metal element surface with a metal element Cr, Ni, Cu, Zn or the like due to a difference in expansion coefficient from the steel sheet. ing.
However, these prior arts do not disclose further improving the iron loss at a low frequency.

  The divided core here is a directional electromagnetic steel sheet divided into a yoke part and a tooth part, and the steel sheets are aligned in the direction in which the magnetic flux density is set. No. 67272.

Japanese Patent Laid-Open No. 2005-51941 JP-A-2004-99998 JP-A-7-67272

Conventional electromagnetic steel sheets have been developed mainly for reducing iron loss at commercial frequencies such as 50 Hz. However, since the rotation speed of the large-sized electric motor for driving the rolling mill is about 100 rpm, the frequency of magnetic flux excited in the steel sheet is considerably small as 10-40 Hz. Under such circumstances, there is a need for an electrical steel sheet having a lower iron loss than conventional products at a frequency lower than the commercial frequency from the viewpoint of high efficiency.
An object of the present invention is to provide a split core for a rolling mill drive motor in which a split core is formed of a magnetic steel sheet having a hysteresis loss reduced rather than an eddy current loss in order to improve motor efficiency.

  Specific means of the present invention are as follows.

  (1) It is composed of a split core obtained by processing a grain-oriented electrical steel sheet containing 2.0% by mass or more and 2.8% by mass or less of Si and having an average crystal grain size of secondary recrystallization of 15 mm or more and less than 50 mm. A split core for a low-frequency electric motor, wherein a material having a different thermal expansion coefficient from that of a steel plate is brought into contact with a side surface of a tooth portion of the core to apply tension to the steel plate.

  (2) The split core for a low-frequency motor according to (1), wherein the materials having different thermal expansion coefficients are ceramics.

(3) The split core for a low-frequency motor according to (1) or (2) above, wherein the tension range is 0.5 kg / mm ² or more and less than 1.5 kg / mm ² .

The grain-oriented electrical steel sheet as used herein refers to a steel sheet having an iron loss ratio WL _{/ C} of 0.6 or less in the rolling direction L and the direction C perpendicular thereto.

  As already mentioned, to improve the efficiency of the motor, for example, to increase the output torque in the thick plate mill, and to reduce the size to accommodate the narrow space around the continuous hot finishing mill, Iron loss must be further reduced. The inventor of the present invention is a magnetic steel sheet having a low iron loss characteristic at a commercial frequency of 50-60 Hz, which has a low rotational speed of, for example, 100 rpm, such as a rolling mill drive motor used in the steel industry factory. The present invention has been completed on the basis that the assumed use conditions are completely different.

According to the present invention, a grain-oriented electrical steel sheet having a Si content of 2.0% by mass or more and 2.8% by mass or less and a secondary recrystallized grain size of 15 mm or more and less than 50 mm is used, and 0.5 kg in the longitudinal direction of the teeth. / mm ² or more 1.5 kg / mm ² lower than a is to add tension, could be obtained 1~20MW class mill drive motor division cores of conventionally about 1% efficiency.

  First, in the target device of the present invention, since it is often used in the region where the frequency is 10 to 40 Hz rather than the commercial frequency (50, 60 Hz), rather, low frequency iron loss, especially hysteresis loss is used as an evaluation index. We thought it important to develop electrical steel sheets for this target model.

  Conventionally, in the process of improving the efficiency of an electric motor, iron loss at commercial frequencies has been mainly reduced. However, further improvement in efficiency is becoming difficult due to the characteristics of the non-oriented electrical steel sheet. Therefore, a grain-oriented electrical steel sheet with lower hysteresis loss was studied.

  Hereinafter, the reasons for limitation of the present invention according to claims 1 to 3 will be described.

(1) Reason for limiting Si to 2.0% to 2.8% FIG. 1 shows the relationship between the Si content of the grain-oriented electrical steel sheet and hysteresis loss. The sample shape was 60 mm wide × 300 mm long × 0.35 mm, and a sample with a magnetic flux density B8 of 1.90 to 1.91 T at 800 A / m was plotted. The applied magnetic flux density was 1.7 T, and a BH loop was drawn with a slow change of 0.5 Hz or less, and the hysteresis loss was calculated from the area surrounded by the loop.

When no tension is applied to the steel sheet, no significant change in hysteresis loss is observed depending on the amount of Si, but when a tension of 1.2 kg / mm ² is applied in the rolling direction, the hysteresis loss may be reduced when the Si amount is low. It became clear by experiment. The result is shown in FIG. It is considered that the magnetostriction constant is involved in this reduction. The greater the magnetostriction constant, the greater the effect of stress on magnetic properties. For example, it is also empirically known that iron loss is not reduced by applying tension when the magnetostriction constant is 6.5% Si, which is close to zero.

  Therefore, in the present invention, in order to obtain the effect of reducing the hysteresis loss, the hysteresis loss in the rolling direction is reduced by 10% in anticipation of the tension application effect with respect to the Si amount of about 3.2% in the normal grain-oriented electrical steel sheet. The Si content was regulated to 2.8% or less, which is the magnetostriction constant. If Si is less than 2.0%, there is no effect of reducing hysteresis loss, so the lower limit was made 2.0% or more.

(2) Reason why the average crystal grain size is limited to 15 mm or more and less than 50 mm B8 is a sample of 1.90 to 1.91 T, and the relationship between the hysteresis loss in the rolling direction and the secondary recrystallization average grain size is shown in FIG. . The secondary recrystallization average particle size was obtained by counting the number of intersections between the straight line drawn in the sample and the crystal grain boundary, and dividing the number of intersections from the linear distance.

  Hysteresis loss decreased as the secondary recrystallization average grain size increased. This is presumably because the domain boundary is reduced, the domain wall movement is not hindered, and the magnetization is easily performed. On the other hand, eddy current loss increases as the crystal grain size increases. This is considered to be because the domain wall spacing increases, the domain wall travel distance per unit time when an alternating magnetic field is applied increases, the domain wall travel speed increases, and eddy current loss increases.

  In considering only the reduction of hysteresis loss, it is better to increase the secondary recrystallization average grain size. The reason for limiting the secondary recrystallization average particle size to 15 mm or more and less than 50 mm is that the grain size of the grain-oriented electrical steel sheet used in the conventional large generator is about 6 mm, and this hysteresis loss is reduced. This is because in order to reduce by 20%, it is necessary to make it 15 mm or more and less than 50 mm, preferably 15 mm or more and less than 20 mm.

(3) Reason why the tensile tension is limited to 0.5 or more and less than 1.5 kg / mm ^{2 The} effect described above is an influence on hysteresis loss focusing on the rolling direction. However, the direction in which the magnetic flux flows in the teeth portion of the large electric motor is perpendicular to the rolling direction. In the direction perpendicular to the rolling direction, the absolute value of the hysteresis loss is about twice as large as that in the rolling direction, and the lowering margin due to tension is rather larger than that in the rolling direction. Therefore, the iron loss reduction effect when tension is applied in the direction perpendicular to the rolling direction is greater than in the rolling direction.

  If the width of the magnetic steel sheet is about 1 m and the outer diameter is larger than this, the core is formed by combining the divided blocks. Moreover, since the main body of the magnetic flux which flows into a core is a circumferential direction, the rolling direction of a normal-oriented electrical steel sheet is arrange | positioned in the circumferential direction, and a split core is formed. However, at this time, the tooth portion of the core does not have desirable magnetic characteristics because the direction of magnetic flux is perpendicular to the rolling direction.

Therefore, when a tension of 0.5 kg / mm ² or more and less than 1.5 kg / mm ² is applied in the same direction as the magnetic flux in the teeth direction, the iron loss of the tooth portion is reduced. The reason for setting it to 0.5 kg / mm ² or more is that the hysteresis loss is reduced by almost 20%. The reason why it is less than 1.5 kg / mm ² is that the reduction of iron loss is almost saturated in this region.

  Next, means for applying a tensile tension to the teeth portion will be described.

  FIG. 3 shows a specific structure for applying tensile tension. In a state where the teeth 1 were heated to several hundred degrees in advance, both sides thereof were pressed by the ceramic plate 2, and the longitudinal direction of the tooth portion was fixed by the wedge 3. When the tooth portion returns to normal temperature, the steel plate contracts, while the ceramic plate hardly contracts and does not bend by the stator winding 4, so that tension is applied to the steel plate. It was found that the iron loss can be further reduced by this tension. The external tension in the tooth direction was obtained from Young's modulus using a strain gauge for high temperature measurement.

  Here, the material to be brought into contact with the side surface of the tooth portion is not limited to ceramics, and any material having a smaller thermal expansion coefficient than that of the electromagnetic steel sheet may be used. Further, specifically, ceramics are preferably silicon carbide (silicon carbide), silicon nitride (silicon nitride), or alumina.

  Hereinafter, the present invention will be described based on examples.

  C: 0.06%, Si: 2.4%, Mn: 0.1%, S: 0.01%, N: 0.01%, Sn: 0.03% Steel is used as an inhibitor. In the process using AlN as an inhibitor, in this example, in order to align the crystal orientation of the electrical steel sheet and promote grain growth, an inhibitor that is a precipitate that suppresses the growth of crystal grains having no easy axis in the rolling direction is used. It strengthened with the following process conditions.

At the stage of slab, Si = 2.4%, N = 0.050 to 0.0100%, acid-soluble Al = 0.02 to 0.03%, and the slab is hot rolled. The plate was cooled to 550 ° C. at 70 ° C./second to obtain a hot-rolled sheet having a thickness of 1.6 mm. Thereafter, the hot-rolled sheet was annealed at 1100 ° C. for 30 seconds, then cooled and pickled at 35 ° C./second, and further cold-rolled to a sheet thickness of 0.30 mm. Decarburization annealing was performed in a wet hydrogen and nitrogen atmosphere with a dew point of 65 ° C. for 830 ° C. × 70 seconds. Subsequently, nitriding was performed at 750 ° C. for 30 seconds in an atmosphere gas in which ammonia was added to dry nitrogen and hydrogen mixed gas, so that the nitriding amount of the steel sheet after nitriding was 0.02%. Thereafter, a slurry mainly composed of MgO and TiO ₂ was applied and dried, and then finish annealing was performed at 1200 ° C. for 20 hours.

The obtained secondary recrystallized grain size was 16.4 mm. The manufactured electrical steel sheet was punched into large electric motor pieces and laminated to make a block. When a ceramic plate was fitted by shrink fitting as shown in FIG. 3 in order to apply tension in the tooth direction, the result of calculating the tension by Young's modulus from the elongation obtained from the strain gauge was 1.2 kg / mm ^2. Met.

  An induction motor having an output of 9,000 kW, the number of poles: 6 poles, and 18 divisions was manufactured and tested using the above-described electromagnetic steel sheet. The efficiency of the induction motor at this time was 97.8% in the split core of the present invention compared to 96.3% when a general material was used, and the total iron loss was reduced to about 20%.

  C: 0.05%, Si: 2.2%, Mn: 0.1%, S: 0.01%, N: 0.008%, Sn: 0.05% of steel, and inhibitor In this example, in order to increase the crystal grain size, the following process conditions were applied.

An electromagnetic steel slab using the above steel was rapidly cooled after completion of finish hot rolling, and wound at a low temperature to obtain a 1.6 mm thick hot rolled sheet. When the winding coil was water-cooled within a short time, carbides were finely deposited on the crystal grains of the hot-rolled sheet, and solid solution C also increased. Thereafter, the hot-rolled sheet was annealed at 1100 ° C. for 30 seconds, then cooled at 35 ° C./second and pickled. In pre-cold rolling, fine carbides hinder the movement of dislocations, and a large amount of processing strain accumulates in the hot-rolled steel sheet due to coarsened grains during slab heating. It became fine sized. The inhibitor was finely dispersed and precipitated, and further cold rolled to a plate thickness of 0.30 mm. Decarburization annealing was performed in a wet hydrogen and nitrogen atmosphere with a dew point of 65 ° C. for 830 ° C. × 70 seconds. Subsequently, nitriding was performed at 750 ° C. for 30 seconds in an atmosphere gas in which ammonia was added to dry nitrogen and hydrogen mixed gas, so that the nitriding amount of the steel sheet after nitriding was 0.02%. Thereafter, a slurry mainly composed of MgO and TiO ₂ was applied and dried, and then finish annealing was performed at 1200 ° C. for 20 hours.

In this step, secondary recrystallization was good and the particle size was 17.0 mm. The manufactured electrical steel sheet was punched into large electric motor pieces and laminated to make a block. When a ceramic plate was fitted by fitting as shown in FIG. 3 in order to apply tension in the tooth direction, the stress was calculated from Young's modulus from the elongation obtained from the strain gauge, and the result was 1.0 kg / mm ^2. Became.

  An induction motor having an output of 4,000 kW, the number of poles: 6 poles, and 9 divisions was manufactured from the above magnetic steel sheet and tested. The efficiency of the induction motor at this time was 97.1% for the split core of the present invention compared to 96.1% when a general material was used, and the total iron loss was reduced to about 19%.

  C: 0.06%, Si: 2.1%, Mn: 0.1%, S: 0.01%, Al: 0.03%, N: 0.008%, Sn: 0.05% In this example, the following process conditions were applied to increase the crystal grain size in a process using AlN, CuS, and MnS as inhibitors.

An electromagnetic steel slab using the above steel was hot-rolled into a 1.6 mm thick hot rolled sheet. Then, after promoting the decomposition of Si ₃ N _{4 in} the temperature rising stage of the hot-rolled sheet annealing, CuxS was sufficiently solutionized by holding the primary soaking time of 1000 ° C. or more for 20 to 120 seconds. Thereafter, by controlling the secondary cooling rate after performing primary cooling and predetermined secondary soaking to 20 to 100 ° C./second decooling, SasCuxS is precipitated finely by 70 to 140 ppm, and the SasMnS / SasCuxS ratio is determined. 0.3-2.5, cooled and pickled. Further, the sheet was finally cold-rolled to a thickness of 0.30 mm. Decarburization annealing was performed in a wet hydrogen and nitrogen atmosphere with a dew point of 65 ° C. for 830 ° C. × 70 seconds. Subsequently, nitriding was performed at 750 ° C. for 30 seconds in an atmosphere gas in which ammonia was added to dry nitrogen and hydrogen mixed gas, so that the nitriding amount of the steel sheet after nitriding was 0.02%. Thereafter, a slurry mainly composed of MgO and TiO ₂ was applied and dried, and then finish annealing was performed at 1200 ° C. for 20 hours. At this time, the average particle size was 18.3 mm.

The manufactured electrical steel sheet was punched into large electric motor pieces and laminated to make a block. When a ceramic plate was fitted by fitting as shown in FIG. 3 in order to apply a tension in the tooth direction, the stress was calculated from Young's modulus from the elongation obtained from the strain gauge, and the result was 0.9 kg / mm ^2. Became.

  An induction motor having an output of 15,000 kW, the number of poles: 4 poles, and 18 divisions was manufactured from the above-described electromagnetic steel sheet and tested. The efficiency of the induction motor at this time was 96.3% in the case of using a general material, whereas it was 98.3% in the split core of the present invention, and the total iron loss was reduced to about 19%.

  As described above, according to the present invention, it is possible to reduce the total iron loss and realize an electric motor with high efficiency.

It is the figure which measured Si amount and hysteresis loss of an electromagnetic steel plate. It is the figure which measured the secondary recrystallization average particle diameter and loss of the electrical steel sheet. It is the figure which showed the split core using the electromagnetic steel plate of this invention.

Explanation of symbols

1 Teeth 2 Ceramic plate 3 Wedge 4 Stator winding

Claims (3)

  It consists of a split core obtained by processing a grain-oriented electrical steel sheet containing Si in an amount of 2.0% by mass to 2.8% by mass and having an average crystal grain size of secondary recrystallization of 15 mm or more and less than 50 mm. A split core for a low-frequency motor, characterized in that a material having a different thermal expansion coefficient from that of a steel plate is brought into contact with a side surface to apply tension to the steel plate.   The split core for a low-frequency motor according to claim 1, wherein the materials having different thermal expansion coefficients are ceramics. The split core for a low-frequency motor according to claim 1 or 2, wherein the tension range is 0.5 kg / mm ² or more and less than 1.5 kg / mm ² .

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