JP2011006731A - Core material for divided motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material in which magnetic properties, particularly, core loss is not deteriorated even in the case compressive force is applied, and which is suitable for the divided core of a motor.SOLUTION: The core material has a componential composition comprising, by mass, 2 to 5% Si, ≤0.004% Al, ≤2% Mn, ≤0.005% S, ≤0.004% Ti, ≤0.005% V, ≤0.003% Nb, ≤0.06% Cr, ≤0.005% N, ≤0.005% O, and the balance Fe with inevitable impurities, and in which the number of inclusions with a diameter of ≥5 μm is ≤10 pieces/mm, and also, magnetic flux density and core loss satisfy a prescribed relation.

Description

  The present invention relates to a core material used for a split type motor having a split core.

  Compressor motors for home air conditioners are operated at variable speeds, and the maximum frequency is about 200 to 400 Hz, which is used with a carrier frequency of several hundreds to several kHz superimposed by PWM control. ing. Recently, drive motors and generators of hybrid electric vehicles, which are rapidly spreading, are also driven at a frequency of several kHz from the viewpoint of high output and miniaturization. For non-oriented electrical steel sheets used as the core material of such motors, electrical steel sheets with low high-frequency iron loss are desired, and high grade electrical steel sheets with Si + Al = 3-4% are used. .

  Recently, split cores have been used for these high-efficiency motors. The split core generally constitutes a motor stator by punching the cores and combining them so that the teeth are in the rolling direction of the electromagnetic steel sheet and the back yoke is in the direction perpendicular to the rolling. For this reason, since the material yield is remarkably improved and the rolling direction with excellent magnetic properties can be used as the teeth, the motor efficiency can be expected to be improved.

As an electromagnetic steel sheet for this divided motor, for example, in Patent Document 1, Si + Al is set to 2 to 6% and Al / (Si + Al): 0.3 to 0.9, and the saturation magnetic flux density Bs and the magnetizing force 5000 A / in the rolling direction. A magnetic steel sheet is disclosed in which the ratio of magnetic flux density B _50L (B _50L / Bs) when excited at m is 0.85 or more. However, in a motor using a split core, shrink fitting is performed for core fastening, and therefore, it is used in a state where a compressive force of about 40 to 100 MPa is applied in the circumferential direction of the back yoke of the core. Unless material design is performed in consideration of iron loss deterioration due to shrink fitting, there is a problem that expected characteristics cannot be obtained with an actual motor.

JP 2008-260996 A

  Therefore, an object of the present invention is to provide a material suitable for a split core of a motor, in which magnetic characteristics, particularly iron loss, do not deteriorate even when a compressive force is applied.

The present inventors diligently studied the above-mentioned problems, and reduced the Al content, reduced the amount of inclusions in the steel, and further specified the iron loss after shrink fitting to a range suitable for the split core, thereby shrink fitting. The inventors have found that the deterioration of the magnetic properties is suppressed even when a compressive force is applied by the above method, and have completed the present invention.
That is, the gist of the present invention is as follows.
(1) In mass%, Si: 2 to 5%, Al: 0.004% or less, Mn: 2% or less, S: 0.005% or less, Ti: 0.004% or less, V: 0.005% or less, Nb: 0.003% or less, Cr: 0.06% or less, N: 0.005% or less, and O: 0.005% or less, the composition of the remaining Fe and inevitable impurities, including 10 μm / mm ² or more inclusions with a diameter of 5 μm or more, and magnetic flux density A core material for a divided motor, wherein the iron loss satisfies the following relationship.
B _50L ≧ 1.75T (1)
(W _{10 / 400L} + W _{10 / 400C} ) / 2 ≦ 25W / kg (2)
here,
W _{10 / 400L} : Iron loss in the rolling direction when no stress is applied (frequency: 400 Hz, B = 1.0 T)
W _{10 / 400C} : Iron loss in the direction perpendicular to rolling when the compressive stress is _50MPa (frequency 400Hz, B = 1.0T)

(2) The core material for a split motor according to claim 1, wherein the crystal grain size is 40 to 140 μm.

(3) As the component composition, further, in mass%,
Sb: 0.001 to 0.05% and
Sn: 0.002 to 0.1%
The core material for a split motor according to claim 1, comprising one or two of the following.

(4) The core material for a divided motor according to claim 1, 2 or 3, wherein the plate thickness is 0.05 to 0.35 mm.

  According to the present invention, it is possible to provide a material having characteristics suitable for a split core, in which deterioration of magnetic characteristics is suppressed even when compressive force is applied by shrink fitting or the like. Therefore, split-core type air conditioner compressor motor, hybrid EV drive motor, EV drive motor, FCEV drive motor, and high-speed power generation that are shrink-fitted by using this material and compressive force is applied to the core material by resin mold, etc. It is possible to reduce the iron loss of the high-frequency rotating machine.

Is a diagram showing the relationship between the rolling direction of B ₅₀ and torque constant. Is a diagram showing the relationship between the Al content and the rolling direction of B _50. It is a figure which shows the relationship between the iron loss _{WH10 / 400} at the time of shrink fitting, and motor efficiency. It is a figure which shows the relationship between the amount of inclusions 5 micrometers or more in diameter, and motor efficiency.

Hereinafter, the core material for a divided motor of the present invention will be described in detail based on experimental results.
First, in order to investigate the influence of the material characteristics on the torque constant of the split motor, the characteristics were evaluated using various materials having a thickness of 0.35 mm with different Si contents. Here, an 8-pole, 12-slot IPM motor was fabricated using this material. Here, the stator outer diameter is 100 mm, the rotor outer diameter is 70 mm, and the stacking thickness is 60 mm. The stator was made of a split core so that the rolling direction of the material was teeth. In order to fix the core, shrink fitting was performed with a shrinkage allowance of 50 μm. At this time, when the stress in the circumferential direction of the central portion of the core back was measured, the compression was 50 MPa.

FIG. 1 shows the relationship between the magnetic flux density in the rolling direction of the material and the torque constant. Here, the characteristics of the rolling direction are used as the magnetic flux density. Unlike the integrally punched core in the split core, the rolling direction can always be aligned in the teeth direction, and there is a correlation between the magnetic flux density of the teeth and the motor characteristics. This is because it is considered high. FIG. 1 shows that a high torque constant can be obtained when the magnetic flux density in the rolling direction is 1.75 T or more.
The torque constant was obtained by connecting the evaluation motor to the brake motor, measuring the torque when a current of 8 A was passed, and dividing the torque by the current value.

  Next, the conditions for increasing the magnetic flux density in the rolling direction were examined. That is, Si: 3.20%, Al: 0 to 100 ppm, Mn: 0.20%, S: 0.0010%, Ti: 0.0010%, Nb: 0.0010%, V: 0.0015%, Cr: 0.01%, N: 0.0020% and O: A steel containing 0.0030% and the balance of Fe and inevitable impurities was melted in the laboratory to obtain an ingot. After that, hot rolled to a thickness of 2.3 mm and annealed at 1000 ° C. for 30 s, first cold rolled to a thickness of 0.8 mm, and intermediate annealed at 950 ° C. for 30 s, Subsequently, the plate thickness was reduced to 0.25 mm by the second cold rolling, and finish annealing was performed at 900 ° C. × 10 s to produce a single plate sample having a length of 180 mm and a width of 30 mm from the rolling direction.

  For comparison, a single plate sample was also produced under the same conditions except that the plate thickness was changed to 0.25 mm by one cold rolling without intermediate annealing.

  About the obtained single plate sample, the magnetic flux density of the rolling direction was investigated. The result is shown in FIG. 2 in relation to the Al content. Here, the amount of Al indicates acid-soluble Al. FIG. 2 shows that the magnetic flux density is higher in the two-time method when the first-time method cold rolling and the two-time method cold rolling are compared.

Furthermore, in the two-time cold rolling, it can be seen that when the Al content exceeds 40 ppm, the magnetic flux density is lowered. The reason for this is not clear, but it is thought that when Al is present in excess of 40 ppm, the amount of AlN deposited increases, which prevents goth grain growth during finish annealing.
From the above, the Al content is 40 ppm or less. Preferably, it is 20 ppm or less.

  In the present invention, any method for increasing the magnetic flux density in the rolling direction may be used. However, as described above, two cold rolling or warm operations in which an intermediate annealing is sandwiched between steels having Al of 40 ppm or less. Rolling is recommended.

  Next, an experiment was conducted to investigate the iron loss during shrink fitting. That is, Si: 3.25%, Al: 0.001%, Mn: 0.20%, S: 0.0010%, Ti: 0.0005%, Nb: 0.0010%, V: 0.0012%, Cr: 0.01%, N: 0.0018% and O: 0.0035 %, And the steel composed of the remaining Fe and the inevitable impurities was melted in the laboratory to form an ingot. After that, hot rolled to a thickness of 2.3 mm, annealed at 1000 ° C for 30 s, and then cold rolled to a thickness of 0.8 mm, followed by intermediate annealing at 950 ° C and 30 s before cooling. The plate thickness was 0.25 mm by hot rolling, and finish annealing was performed at 900 ° C. × 10 s to produce a single plate sample having a length of 180 mm and a width of 30 mm from the direction perpendicular to the rolling. This sample was subjected to magnetic measurement in a stress-free state and in a state where shrink fitting was simulated by applying a compressive stress of 50 MPa in the magnetization direction. The measurement results are shown in Table 1.

From Table 1, it can be seen that the iron loss has deteriorated by about 1.8 times due to the application of compressive force simulating shrink fitting. In order to investigate this cause, the iron loss was separated into the hysteresis loss and the eddy current loss, and both the hysteresis loss and the eddy current loss increased due to the application of compressive stress. It became clear that it was big. As for the cause of the deterioration of hysteresis loss, since the steel plate like the above component has positive magnetostriction, when the steel plate is magnetized, the steel plate will extend in the magnetization direction, but compressive force is applied to the magnetization direction. If this is done, the steel sheet cannot be stretched, magnetization becomes difficult, and iron loss is considered to have increased.
On the other hand, the cause of the increase in eddy current loss is considered to be that the magnetization vector is easily directed in the plate surface direction by applying compressive stress, and the eddy current in the plate surface flows by applying an external magnetic field in this state.

  From the above, the iron loss at the time of shrink fitting is completely different from the stressless iron loss, and it is thought that it is necessary to use a material with low iron loss at the time of shrink fitting in order to improve the motor characteristics. .

Therefore, in order to investigate the relationship between material iron loss and motor efficiency at the time of shrink fitting, a sample of 30 mm x 180 mm was cut from the rolling direction and the direction perpendicular to the rolling, the sample in the rolling direction was no stress, and the direction perpendicular to the rolling was 50 MPa. A magnetic measurement was performed by applying a compressive stress of.
The iron loss _{WH10 / 400} was determined according to the following formula.
_{WH10 / 400} = ( _{W10 / 400L} + _{W10 / 400C} ) / 2
here,
W _{10 / 400L} : Iron loss in the rolling direction when no stress is applied (frequency: 400 Hz, B = 1.0 T)
W _{10 / 400C} : Iron loss in the direction perpendicular to rolling when the compressive stress is _50MPa (frequency 400Hz, B = 1.0T)
An 8-pole, 12-slot IPM motor was manufactured using a material having an iron loss WH10 _{/ 400} of 15 to ₄₀ W / kg determined in this manner. FIG. 3 shows the relationship between material iron loss and motor efficiency. This shows that the motor efficiency is high when the material iron loss _{WH10 / 400} simulating shrink fitting is 25 W / kg or less. Here, the motor efficiency was obtained by rotating the motor at 6000 rpm and dividing the output when the torque was 4 N · m by the input.

In order to set _{WH10 / 400} to 25 W / kg or less, any method may be used, but at least the Si amount needs to be 2% or more. Furthermore, by setting the plate thickness to 0.35 mm or less, more preferably 0.30 mm or less, and the crystal grain size to 40 to 140 μm, it can be stably reduced to 25 W / kg or less.

  By the way, when the motor evaluation was repeated, a material with low motor efficiency was found although the iron loss value of the material was 25 W / kg or less. In order to investigate this cause, the end face of the back yoke of the split core was observed, and it was revealed that the fracture surface ratio was high in the material with low efficiency. Furthermore, many coarse inclusions were observed in the material having a high fracture surface ratio. This was thought to be due to the fact that the amount of inclusions increased due to insufficient deoxidation because the amount of Al was reduced to improve the magnetic flux density. The cause of motor efficiency degradation due to an increase in fracture surface ratio is not clear, but is considered as follows.

  That is, in the split core, the shearing surface of the yoke is pressed so as not to generate a gap by shrink fitting, but the fracture surface is a gap and is in a high magnetic resistance state. For this reason, the magnetic flux of the yoke is concentrated on the shearing surface. When the shearing surface ratio is small, the magnetic flux leaks from the core surface, and the magnetic flux enters the upper and lower cores from the plate surface direction. As a result, it is thought that the plate surface eddy current loss increased and the efficiency decreased.

Therefore, attention was focused on inclusions having a diameter of 5 μm or more that significantly increase the fracture surface ratio. This is because if the inclusion diameter is 5 μm or more, cracking occurs from the inclusion as the starting point during punching, and the fracture surface ratio increases. Then, the relationship between the amount of inclusions having a diameter of 5 μm or more and the motor efficiency was investigated. The result of the investigation is shown in FIG. 4 as the relationship between the amount of inclusions and the motor efficiency. From the figure, it can be seen that the motor efficiency decreases when the amount of inclusions exceeds 10 / mm ² .
From the above, the amount of inclusions with a diameter of 5 μm or more is 10 pieces / mm ² or less.

Next, the reasons for limiting other components will be described.
Si: 2 to 5%
Since Si can increase the specific resistance and reduce the iron loss, it is contained at 2% or more, preferably 25% or more. On the other hand, if it exceeds 5%, the magnetic flux density decreases due to a decrease in saturation magnetization, so the upper limit is made 5%.

Mn: 2% or less
When Mn exceeds 2%, the upper limit is set to 2% because the magnetic flux density decreases due to the decrease in saturation magnetization.

S: 0.005% or less Since S forms a sulfide when the content is large and the iron loss increases, the upper limit is made 0.005%.

Ti: 0.004% or less
Ti forms Ti-based nitrides, but in general high-grade electrical steel sheets containing a large amount of Al, most of the nitrogen precipitates as AlN, so a small amount of Ti affects the growth behavior of goth grains. There are few things. However, in steel with Al of 40 ppm or less, the grain growth behavior is affected by the presence of a small amount of TiN, and the accumulation of goth grains during finish annealing is reduced, so the upper limit is made 0.004%.

V: 0.005% or less
Nb: 0.003% or less
Cr: 0.06% or less V, Nb and Cr, like Ti, form nitrides and reduce the accumulation of goth grains, so the upper limits are made 0.005%, 0.003% and 0.06%, respectively.

N: 0.005% or less If N exceeds 0.005%, the amount of nitride increases, so the iron loss increases. For this reason, the upper limit is made 0.005%.

O: 0.005% or less O is contained in an amount of 0.01% or less because the inclusion increases when the content is large and the material is easily cracked.

(Production method)
In the present invention, it is important that the components, the amount of inclusions, and the magnetic properties are within a predetermined range. For example, the molten metal is blown in a converter and the molten steel is degassed to obtain a predetermined value. The amount of inclusion and the amount of inclusions are adjusted, and casting is continued to form a slab. Here, since Al is 0.004% or less in the steel according to the present invention, the amount of coarse Si-based inclusions is increased as compared with a normal Al-deoxidized electromagnetic steel sheet. Therefore, it is necessary to sufficiently reduce the amount of inclusions in the steel within a predetermined range by performing the vacuum degassing treatment for 20 minutes or more. Thereafter, the steel sheet of the present invention is subjected to finish annealing after hot rolling by a normal method, followed by two or more cold or warm rolling sandwiching the intermediate annealing to a predetermined thickness. Can be obtained.

  Here, the finishing temperature and the coiling temperature at the time of hot rolling need not be specified, and may be normal conditions. Moreover, although hot-rolled sheet annealing after hot rolling may be performed, it is not essential. Next, the finish annealing is preferably controlled so that the crystal grain size is 40 to 140 μm. In particular, if the rate of temperature increase during finish annealing is slowed, crystal grains become coarse, and therefore a rate of temperature increase of 10 ° C./s or more is preferable.

  The plate thickness is preferably 0.35 mm or less, and more preferably 0.30 mm or less from the viewpoint of reducing iron loss during shrink fitting. The lower limit is preferably 0.05 mm or more from the viewpoint of productivity.

  Steels having compositions shown in Table 2 were used, and after defoaming in a converter, degassing treatment was performed for a predetermined time to adjust to predetermined components, and then cast into slabs. The slab was heated at 1140 ° C. for 1 h, and then hot-rolled to the plate thickness shown in Table 2. The hot rolling finishing temperature was 800 ° C. The coiling temperature was 610 ° C., and after coiling, hot rolled sheet annealing at 900 ° C. × 30 s was performed. Thereafter, pickling was performed, cold rolling (primary cold rolling) was performed to 0.8 to 1.2 mm, and intermediate annealing at 1000 ° C. × 30 s was performed. Some samples were finished to the final plate thickness by primary cold rolling without intermediate annealing. Then, cold rolling (secondary cold rolling) was performed to the plate thickness shown in Table 2, and annealing was performed under the finish annealing conditions shown in Table 2.

From the sample thus obtained, a single plate sample having a length of 180 mm was cut out from the rolling direction, a single plate magnetic measurement was performed under no stress, and a single plate sample having a length of 180 mm was cut from the direction perpendicular to the rolling direction, and 50 MPa in the longitudinal direction. The compressive force was applied, and the magnetic characteristics in the compressive force applying direction were measured.
Inclusions were observed by SEM at 10 magnifications at 10 fields, and the presence frequency of inclusions having a diameter of 5 μm or more was determined. The crystal grain size was determined by the line segment method of JIS G 0552.
As these measurement results are also shown in Table 2, it is possible to obtain a split core having excellent motor characteristics by setting the components, magnetic characteristics, and amounts of inclusions within the scope of the present invention.
On the other hand, the comparative example of No. 1 performs cold rolling at once and is inferior in motor characteristics. In the comparative examples of Nos. 6, 7, 21, 27, 28, 29, 30, 35 and 36, the component composition is out of the scope of the present invention, and sufficient magnetic properties are not obtained. The comparative examples of No. 13 and No. 14 are inferior in motor characteristics due to the large amount of inclusions.

Claims (4)

In mass%, Si: 2 to 5%, Al: 0.004% or less, Mn: 2% or less, S: 0.005% or less, Ti: 0.004% or less, V: 0.005% or less, Nb: 0.003% or less, Cr: 0.06 %, N: 0.005% or less, and O: 0.005% or less, with the composition of the remaining Fe and inevitable impurities, 10 inclusions / mm ² or more inclusions with a diameter of 5 μm or more, and magnetic flux density and iron loss. A core material for a split motor characterized by satisfying the following relationship.
B _50L ≧ 1.75T (1)
(W _{10 / 400L} + W _{10 / 400C} ) / 2 ≦ 25W / kg (2)
here,
W _{10 / 400L} : Iron loss in the rolling direction when no stress is applied (frequency: 400 Hz, B = 1.0 T)
W _{10 / 400C} : Iron loss in the direction perpendicular to rolling when the compressive stress is _50MPa (frequency 400Hz, B = 1.0T)   The core material for a divided motor according to claim 1, wherein the crystal grain size is 40 to 140 µm. As the component composition, further, in mass%,
Sb: 0.001 to 0.05% and
Sn: 0.002 to 0.1%
The core material for a split motor according to claim 1, comprising one or two of the following.   The core material for a split motor according to claim 1, 2 or 3, wherein the plate thickness is 0.05 to 0.35 mm.

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