JP4028089B2 - Manufacturing method of cage rotor core - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a cage rotor iron core.
[0002]
[Prior art]
In general, a squirrel-cage rotor of an induction motor is formed by casting aluminum into a groove of a rotor core 1 by die-casting to form a secondary conductor 2 and a short-circuit ring 3 at both ends of the rotor core 1, and a shaft of the rotor core 1 It is formed by fitting a rotating shaft into the hole 6 (see FIG. 6). An example of the secondary conductor 2 of the rotor core 1 has a triangular head and a convex shape as shown in FIG. The ratio of the total cross-sectional area of the secondary conductor 2 (the sum of the total number of conductors 2) to the cross-sectional area of the short-circuit ring 3 (doughnut shape) (area in contact with the end surface of the iron core 1) is 1: 2.8 to 1: 3. Therefore, the solidification rate of the cast molten metal (aluminum) is a cooling rate equal to or higher than the reciprocal of the cross-sectional area ratio. Then, in the boundary part 5 of the secondary conductor 2 which becomes a boundary with the short-circuiting ring 3, solidification on the short-circuiting ring 3 side is started later than the secondary conductor 2 already solidified. At that time, the secondary conductor 2 is formed in the boundary portion 5 in a state where the tensile residual stress (about 1.8 to 2.0 kg / mm ² ) is applied (see FIG. 7A).
[0003]
On the other hand, the cross-sectional area of the secondary conductor 2 is determined from the electrical characteristics of the motor, and the length ratio of the secondary conductor 2 and the short-circuit ring 3 in the radial direction at the boundary 5 is about 1: 2 (FIG. 6). Reference). When the electric motor is operated, the total stress of the thermal stress and centrifugal force generated when the motor is operated is applied to the boundary portion 5 in which the secondary conductor 2 is 50% shorter in the radial direction than the short-circuit ring 3 (FIG. 7B). )reference).
[0004]
[Problems to be solved by the invention]
Thus, the total stress of the tensile residual stress, the thermal stress, and the centrifugal force is applied to the boundary portion 5 as a repeated stress. As a result, cracks may occur due to these stresses on the inner periphery side X of the short-circuit ring 3 shown in FIG. 7B (the inner periphery side of the boundary portion 5), and the secondary conductor 2 and the short-circuit ring 3 are separated. Phenomenon occurs (secondary conductor 2 is cut), which causes a reduction in motor characteristics. For this reason, it becomes necessary to keep the residual stress during casting below the load stress during motor operation.
[0005]
The present invention has been made in view of the above circumstances, a phenomenon that expires the secondary conductor does not occur even in a state where the residual stress was phenomena or inherent during casting, to provide a method of manufacturing a cage rotor iron core Objective.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a cage rotor core manufacturing method according to claim 1, wherein a predetermined number of electric iron plates having a plurality of grooves in the circumferential direction are laminated to form a rotor core, and the rotor core is preheated. Inserted into a mold, preheated the rotor core and cast a molten metal into the groove in a temperature ratio with the molten metal of 1.75 to 1.8 to form a secondary conductor and a short circuit ring. And a method for manufacturing a squirrel-cage rotor core in which a squirrel-cage rotor core formed from the mold is taken out after being cooled and held until the temperature of the rotor core and the short-circuit ring reaches 200 ° C. or lower. The stress applied to the boundary 18 can be relieved by cooling and holding until the iron core temperature and the secondary conductor temperature of the mold removal become about 200 ° C. or lower.
[0009]
According to a second aspect of the present invention, there is provided the second electric iron plate which is formed of the first electric iron plate and the second electric iron plate, has the same number of grooves as the first electric iron plate, and has a groove having a cross-sectional area of about 1.5 times. Insert a specified number of rotor cores into the preheated mold on both ends of the specified number of first electric iron plates and insert the molten metal into the two types of grooves to connect the first and second conductors to the short circuit ring. Is a method of manufacturing a squirrel-cage rotor core. By this manufacturing method, the residual stress at the stepped portion and the boundary portion is removed.
[0010]
According to a third aspect of the present invention , the formed cage rotor core is furnace-cooled again by holding the heat treatment temperature at 200 to 300 ° C. for 3 to 6 hours at a heating rate of 20 to 30 ° C./Hr. By this strain relief annealing, residual stress at the stepped portion and the boundary portion can be further removed.
[0011]
In claim 4 , after forming the rotor core by laminating the first electric iron plate and the second electric iron plate, a second arc having a radius of 3 to 10 mm is formed on the arc step portion between the first electric iron plate and the second electric iron plate. It is a manufacturing method in which a molten metal is formed by processing from the groove side of the electric iron plate, and cast into the two types of grooves. With this manufacturing method, an arc step portion is formed at the step portion between the first conductor and the second conductor, and the stress concentrated on the arc step portion is dispersed and relaxed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the main part around the short-circuit ring of the cage rotor core, and FIG. 2 is a cross-sectional view in the II direction of FIG. 3 and 4 are front views showing the electrical punching plates of the rotor core, respectively.
[0013]
In the figure, the rotor core is formed of a first electric iron plate (hereinafter referred to as a first iron plate) 11 and a second electric iron plate (hereinafter referred to as a second iron plate) 11a, which are two types of electric iron plates. The rotor core has a specified thickness L by laminating to a specified thickness l1 and laminating a plurality of second iron plates 11a on both ends of the first iron plate 11 to obtain a specified thickness l2. The specified thickness l2 of the second iron plate 11a is set to 5 to 10% (in consideration of the motor characteristics) of the specified thickness L of the rotor core. As shown in FIG. 3, the first iron plate 11 is formed with a predetermined number of holes 16a having a triangular head 16a and a convex shape in the circumferential direction. Next, the second iron plate 11a has the same number of holes 16 as the grooves 16 of the first iron plate 11, and has a substantially insulator-shaped groove 17 having a cross-sectional area approximately 1.5 times larger than the groove 16 as shown in FIG. The head portion 17a of the groove 17 is formed in the shape of an arc R1 having a radius of 5 to 10 mm, and the head portion 16a of the groove 16 has a substantially outer diameter.
[0014]
This rotor core is inserted into a mold (not shown), preheated to about 400 ° C., molten aluminum at about 700 to 720 ° C. is cast into the respective grooves 16 and 17 by die casting, and the temperature of the core is removed from the mold. Cool and hold until the secondary conductor temperature is about 200 ° C. or less. By this casting, the secondary conductor 12 which is the first conductor is formed in the groove 16 and the secondary conductor 12a which is the second conductor is formed in the groove 17, and the short-circuit ring is connected to the both ends of the rotor core in communication with the secondary conductor 12a. A cage rotor core 15 is formed as shown in FIG. At this time, the ratio of the radial length of the secondary conductor 12a (height of the groove 17) to the radial length of the short-circuit ring 13 (hereinafter referred to as the length of the boundary portion 18) at the end face of the cage rotor core 15 is 0.75. To 1.0 (indicated by about 1.0 in FIG. 1). In addition, as the strain relief annealing for removing the residual stress at the step portion 12c and the boundary portion 18 between the secondary conductor 12 and the secondary conductor 12a, the squirrel-cage rotor core 15 is again heated at a temperature of about 20 to 30 ° C./Hr, You may hold | maintain at the heat processing temperature about 200-355 degreeC for 3 to 6 hours, and furnace-cooling.
[0015]
The effect of the boundary portion thus formed will be described.
By setting the length ratio of the boundary portion 18 to 0.75 to 1.0, the step between the secondary conductor 12a and the short-circuit ring 13 is eliminated or reduced, and the secondary conductor 12a has a cross-sectional area in the form of an insulator. Since there are no corners compared to 12 polygons, there is no problem of stress concentration at the corners, and the cross-sectional area is about 1.5 times larger, and the strength of the secondary conductor 12a on the inner diameter side of the short-circuit ring 13 is increased. . That is, the stress calculation value indicated by the broken line in the modified Goodman diagram at 100 ° C. shown in FIG. 9 is changed from the conventional point a to the point b when the boundary portion 18 length ratio is 0.75. When the ratio is 1.0, it moves to point c and decreases. As a result, the residual stress at the boundary 18 is reduced. In FIG. 9, A represents the fatigue limit at 1.0 * 10 of the SN curve of the fatigue test, and B represents the tensile strength at 100 ° C. FIG. 8 is a stress-strain diagram at 100 ° C.
[0016]
Further, since the head portion 17a of the groove 17 has an arc R1 shape having a radius of 5 to 10 mm, the head portion of the formed secondary conductor 12a also has an arc shape. For this reason, since the conventional head is a triangle, stress concentrates on the apex and there is a risk of cracks occurring at this apex, but in this example, the stress is dispersed by changing from a triangle to an arc. The strength at the top of the head has increased and there is no risk of cracking. Furthermore, the stress applied to the boundary portion 18 can be relieved by cooling and holding until the iron core temperature and the secondary conductor temperature are about 200 ° C. or less. In addition, since the step 12c between the secondary conductor 12a and the secondary conductor 12 is in the rotor core, the centrifugal force of the short-circuit ring 13 due to rotation is protected by the iron core.
[0017]
Due to these synergistic effects, the stress generated in the conventional boundary portion 5 when the motor is operated is relieved, and there is a risk of cracks occurring in the stepped portion X on the inner diameter side of the boundary portion 5 and the outer diameter side head portion. However, it is no longer the boundary 18 in this embodiment. And if the stress relief annealing which removes the residual stress of the level | step-difference part 12c and the boundary part 18 is implemented, this effect will further improve.
[0018]
(Second embodiment)
A second embodiment will be described with reference to FIG. The difference from the first embodiment is that the stepped portion 12c between the secondary conductor 12a and the secondary conductor 12 is formed in the arc-shaped stepped portion 24. This is because, after laminating a plurality of electrical release plates 11a at both ends of the laminated electrical release plate 11, an arc R2 having a radius of 3 to 10 mm is provided by polishing the step portion 12c shown in FIG. An arc step portion 24 is formed in a step portion 12c between 12a and the secondary conductor 12. This is because the expansion and contraction action acts in the axial direction by the thermal stress of the short-circuit ring 13 and the secondary conductor 12a and the secondary conductor 12 generated by the motor operation, and this expansion action and the centrifugal force of the short-circuit ring 13 are applied to the step portion 12c. Concentration is alleviated by supporting in a distributed manner with the circular arc step portion 24. As a result, it is possible to further eliminate the possibility of cutting at the step portion 12c between the secondary conductor 12a and the secondary conductor 12.
[0019]
(Third embodiment)
A third embodiment will be described with reference to FIG. The difference from the first embodiment is that 0.2 to 1.0 weight of the alloy whose composition is Al-10% Ti-B is added to molten pure aluminum cast into the groove of the rotor core. In addition, the electrical conductivity of the formed secondary conductor is set to 57 IACS% or more and the secondary conductor strength is improved. For the electrical conductivity and strength investigation, a sample having the same shape as that of the secondary conductor 12a was manufactured and subjected to a comparative test. The results are shown in FIG.
[0020]
The electrical conductivity of the whole sample of 0.2 to 1.0% by weight added was 57 IACS% or more, and the object was achieved. Further, the addition of Al-10% Ti-B alloy can refine the crystal structure, and the tensile strength is slightly varied, but is improved by 8 to 13%, and the elongation is substantially the same. From this result, it is possible to use a material added with an Al-10% Ti-B alloy as a secondary conductor material with improved strength, and to improve the residual stress resistance of the stepped portion 12c and the boundary portion 18.
[0021]
【The invention's effect】
As described above, according to the present invention, the boundary portion between the secondary conductor and the short-circuit ring at the rotor core end face is reinforced, and cracking at this boundary portion can be prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an essential part of a cage rotor core showing a first embodiment of the present invention;
FIG. 2 is a cross-sectional view in the II direction of FIG.
FIG. 3 is a plan view of a first electric iron plate showing a groove shape;
FIG. 4 is a plan view of a second electric iron plate showing a groove shape;
FIG. 5 is a view corresponding to FIG. 1 showing a second embodiment;
FIG. 6 is a sectional view of a conventional cage rotor core,
FIG. 7 is an explanatory diagram of stress applied to the secondary conductor and the short-circuit ring,
FIG. 8 is a stress-strain diagram,
FIG. 9 is a modified Goodman diagram.
FIG. 10 is a strength comparison diagram by adding Al-10% Ti-B to an aluminum material.
[Explanation of symbols]
11 ... 1st electric iron plate (1st iron plate), 11a ... 2nd electric iron plate (2nd iron plate),
12 ... 1st conductor (secondary conductor), 12a ... 2nd conductor (secondary conductor),
12c ... Step part, 13 ... Short-circuiting ring,
15… Cage rotor core, 16, 17… Groove,
16a, 17a ... head, 5, 18 ... boundary,
24: Arc step, R1, R2 ... Arc.

Claims (5)

A predetermined number of electric iron plates having a plurality of grooves in the circumferential direction are laminated to form a rotor core, and this rotor core is inserted into a preheated mold, and the rotor core is preheated to form a molten metal. The molten metal was cast into the groove in a state where the temperature ratio of 1.75 to 1.8 was formed to form a secondary conductor and a short circuit ring, and cooled and held until the rotor core and the short circuit ring temperature were 200 ° C. or less. A method for manufacturing a cage rotor core, comprising: taking out a cage rotor core formed later from within a mold. The electric iron plate is formed of a first electric iron plate and a second electric iron plate, and a predetermined number of second electric iron plates having grooves arranged in the same number as the grooves of the first electric iron plate and having a cross-sectional area of about 1.5 times are laminated. A rotor core having a predetermined number of layers laminated on both ends of a first electric iron plate is inserted into a preheated mold, and molten metal is cast into the two types of grooves to form a first and second conductors and a short ring. A method for manufacturing the cage rotor core according to 1. The cage rotor according to claim 1 or 2, wherein the formed cage rotor core is furnace-cooled by holding again at a heating rate of 20 to 30 ° C / Hr and a heat treatment temperature of 200 to 300 ° C for 3 to 6 hours. Manufacturing method of iron core. After forming the rotor core by laminating the first electric iron plate and the second electric iron plate, an arc having a radius of 3 to 10 mm is formed at the boundary step between the first electric iron plate and the second electric iron plate on the groove side of the second electric iron plate. The method for manufacturing a cage rotor core according to any one of claims 1 to 3, wherein the cage metal core is formed by machining and molten metal is cast into the two types of grooves . The molten metal is pure aluminum, and an alloy having a composition of Al- 10 % Ti-B is added to the pure aluminum at a 0.2% pitch from 0.2 to 1.0% by weight with respect to the dissolved weight. A manufacturing method of the cage rotor core according to any one of claims 1 to 4 .

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