JP2881325B2 - Manufacturing method of cage rotor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a cage rotor of an induction motor, and more particularly to an electrical insulation between a secondary conductor formed by aluminum die casting and a rotor core. The present invention relates to a manufacturing method for improving the sound, vibration and electric properties in a good and uniform manner.

[Conventional technology]

In general, a cage rotor of an induction motor is formed by punching a circular thin iron plate having a plurality of slots along a circumference in the vicinity of an outer periphery and a shaft hole at the center, and laminating a predetermined number of the plates to form a rotor core. Then, a good conductor such as aluminum or aluminum alloy is die-cast on the iron core to form a cage-shaped secondary conductor comprising a bar filling each slot and an end ring shorting each bar at both ends in the axial direction. It is manufactured in.

Since the bar of the secondary conductor is in direct contact with the punched surface of the iron core that forms the inner wall of the slot, the eddy current loss increases due to a short circuit between the laminated iron plates, and the current flowing in the secondary conductor flows to the iron core. Leakage causes an increase in stray load loss, resulting in a problem that torque in the acceleration region of the motor decreases. To alleviate this problem, an electrical insulation treatment is generally applied between the secondary conductor and the iron core.
As a general example, there is a method in which an electrically insulating coating is applied to a laminated iron core before die casting, as disclosed in JP-A-60-9351. For this coating, the iron core is placed in a furnace for 500-600
Heated to about ℃ and subjected to steam treatment to produce ferric tetroxide (Fe ₃ O
₄ ) There is a type that forms a film, or a type in which an iron core is immersed in a phosphate solution to form a phosphate film.

As a method for forming electrical insulation after die casting, there is a method disclosed in JP-A-56-83250. In this method, the rotor is heated to about 300 to 500 ° C. in a furnace and then cooled to form a gap between the iron core and the secondary conductor by utilizing the difference in linear expansion coefficient between iron and aluminum.

[Problems to be solved by the invention]

In the case of coating the core before die casting, the heat insulation during the die casting or the impact of the high-temperature and high-pressure molten metal partially destroys the insulation film in the iron core slot, lowering the electrical insulation strength of the slot. There is a problem. This phenomenon is particularly remarkable in a slot near a die-cast type gate or a slot where a relatively large punched burr is present. In this portion, the aluminum is fused to the iron core, and the electrical insulation strength is reduced. Each slot will be formed unevenly.

In the case of performing heat treatment on the rotor after die-casting at the time of forming the electrical insulation, the above-described fused portion of the aluminum to the iron core is not sufficiently separated completely by expansion and contraction, and often is not performed. Insufficient improvement in electrical insulation results, in which case also the electrical insulation strength is partially reduced, and this insulation strength is unevenly formed between the slots. Due to the non-uniformity of the insulation strength, the insulation state of the bars arranged in the circumferential direction of the rotor varies non-uniformly during one rotation of the rotor, and as a result, the insulation state is caused by the stator slot of the motor. The distribution of the ripple of the magnetic flux becomes spatially non-uniform, which causes electromagnetic noise with fluctuation. Further, the distribution of the stator magnetic flux becomes spatially non-uniform, and the magnet pull between the stator and the rotor acts non-uniformly, so that electromagnetic noise accompanied by fluctuations is liable to occur.

In recent years, rotor cores are automatically laminated by a caulking clamp part provided on the core itself to improve the lamination accuracy of the inner and outer diameters, and those that do not cut the inner and outer diameters are often used, but heat treatment is performed before assembling to the shaft. For example, in a rotor of a built-in type motor such as a motor for a refrigerator which needs to be subjected to heat treatment, when heat treatment for insulation is performed on this iron core, deformation is caused in the axial direction and straightness of the inner diameter in the axial direction is caused. Since the degree of deterioration becomes worse, so-called galling occurs when inserting the shaft, resulting in poor insertion, and even after the shaft is inserted, the deflection of the outer diameter of the rotor with respect to the shaft increases, and the air gap between the stator and the rotor is not uniform. However, there have been problems such as an increase in fluctuating noise caused by the deflection.

[Means for solving the problem]

The present invention is to form a cage-shaped secondary conductor composed of bars and end rings by die-casting aluminum on a laminated rotor core, and then immersing the entire cage rotor in an alkaline solution for treatment. It is.

As the alkaline solution, an aqueous solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH) is arbitrarily selected and used. The immersion time is such that the corrosion of the bar by the alkali slightly progresses and the corrosion of the iron core portion. Is set in a range where almost no occurrence occurs, and is appropriately set in relation to the concentration and temperature of the alkaline solution. If the immersion time is set to be long, a stable product can be obtained in terms of quality. However, from the viewpoint of productivity, short-time treatment is preferable.

[Action]

When the cage rotor is immersed in the alkaline solution, the aluminum constituting the cage secondary conductor of the rotor is corroded by the alkali. This action proceeds, for example, when the alkali is sodium hydroxide, by a reaction represented by the following formula, and as a result of the reaction, aluminum is corroded to produce aluminate and hydrogen.

On the other hand, the iron constituting the rotor core is also corroded by a similar reaction, but the reaction requires a high temperature and a high concentration of alkali, so that the reaction speed is slow at room temperature.
On the other hand, the reaction of aluminum as shown in the formula (1) has a large tendency to ionize aluminum and proceeds rapidly even at room temperature. Only the secondary conductor is corroded with almost no dimensional change on the inner wall and the like.

At the bar portion of the secondary conductor, corrosion occurs from the outer peripheral surface of the bar due to the alkaline solution that has permeated between the laminations from the outer or inner diameter portion of the iron core, and since this corrosion is a chemical reaction, Progresses uniformly and reliably at As a result, a minute gap is surely formed between the outer peripheral portion of each bar and the iron core slot as well as the portion where aluminum is firmly fused with the iron core, and the electrical insulation strength between each bar and the iron core is the same. As the level is improved, it becomes uniform among the slots.

〔Example〕

FIG. 1 shows an example of the result of frequency analysis of the noise of an induction motor in a 1/3 octave band.
(B) shows the case where the rotor according to the present invention subjected to the immersion treatment in the alkali solution after the die casting is used, and (b) shows the case where the rotor manufactured by the conventional method subjected to the heat treatment after the die casting is used. It should be noted that the rotor in which the iron core is coated before die-casting also shows a tendency substantially equal to the noise characteristic shown in FIG. 1 (b), and therefore FIG. 1 (b) is generally common to the conventional rotor. Noise characteristics. In addition, the stator used is the same one in (a) and (b). The output is 76 W, the number of pole pairs is 1, the number of slots is 20, and 2892 rpm (slip = 3.6
%).

As shown in FIG. 1 (b), it can be seen that when a rotor manufactured by the conventional method is used, a fluctuating sound is generated in the frequency range of 500 Hz and 1000 Hz. In this case, the 500Hz sound is
The vibration source of the even harmonic component of the power supply and the natural frequency of the shaft system are generated by resonance, and the sound of 1000 Hz is
This is an electromagnetic sound due to the ripple of the magnetic flux caused by the stator slot. Generally, when the number of pole pairs is P, the number of stator slots is Ns, the slip is S, the power supply frequency is fo, and k = 1, 2, 3,..., The frequency f of the electromagnetic force wave caused by the stator slots is , When this equation (2) is calculated using the above-mentioned values, f = 916 Hz and 1012 Hz, and the sound has a component of 1000 Hz.

It can be seen that when the rotor according to the present invention shown in FIG. 1A is used with respect to the rotor according to the above-mentioned conventional manufacturing method, the fluctuation sound in the frequency range of 500 Hz and 1000 Hz is greatly reduced. This is because the insulated state of the bars arranged in the circumferential direction of the rotor is uniformly formed,
During the rotation, the fluctuation of the insulation state becomes uniform, so that the spatial distribution of the even harmonic components of the power supply becomes uniform, and the diagonal components of the magnet pull between the stator and the rotor are canceled out to work uniformly. On the other hand, the electromagnetic force wave resulting from the combination of the magnetic flux due to the stator slot ripple and the fundamental wave magnetic flux also becomes spatially uniform, and these results make it difficult to generate electromagnetic noise with fluctuation. is there.

When comparing the detailed data of FIGS. 1 (a) and 1 (b), when the rotor according to the present invention was used, the noise level itself was lower than that of the conventional rotor, and the value was 50%.
A reduction of about 5 dB at 0 Hz and about 10 dB at 1000 Hz was achieved.

FIG. 2 shows the rotation speed-torque characteristics of the induction motor as the measurement target of the noise characteristics shown in FIG. In the figure, a solid line T1 indicates the case where the rotor according to the present invention is used, and a broken line T2 indicates the case where the rotor manufactured by the conventional method is used. As is clear from this figure, when the rotor according to the present invention is used, a phenomenon of an increase in the torque appears remarkably, and in particular, the torque in the acceleration region greatly increases, and the area of the region surrounded by the curves T1 and T2 increases. A new proportional amount of acceleration energy is obtained. This is because the insulation according to the present invention ensures the insulation of each of the bars of the rotor, and as a result, the overall insulation level is improved without a partial decrease in the insulation strength. .

The improvement in the insulation level also appears remarkably as motor characteristics. For example, the characteristics of the motor described in FIGS. 1 and 2 are as shown in the table below, and the input and current are reduced, and the motor efficiency is improved. ing.

Further, as another embodiment of the present invention, a coating is formed on a laminated iron core or a thin iron plate before lamination by a conventional manufacturing method such as triiron tetroxide, and aluminum is die-coated on the iron core. The cage may be cast to form a cage rotor, and then the entire cage rotor may be treated by dipping in an alkaline solution. In this case, the aluminum fused at the location where the insulating film was partially destroyed by die casting is corroded by alkali, improving the level of electrical insulation strength between the bar and the iron core and improving the insulation strength between each slot. Uniformity is achieved. In particular, in this case, since the purpose is to repair a portion where the insulation strength has been deteriorated by die casting, the processing time with alkali is reduced.

〔The invention's effect〕

According to the present invention, an electromagnetic wave of an even harmonic component of a power supply,
The spatial distribution of each electromagnetic force wave due to the combination of the magnetic flux due to the stator slot ripple and the fundamental wave magnetic flux becomes uniform, and the diagonal component of the magnet pull between the stator and rotor is canceled out and acts uniformly. Therefore, the fluctuating noise is reduced, and the noise of the electric motor is greatly reduced. Further, by increasing the torque in the acceleration region, shortening of the acceleration time and improvement of durability and quality are achieved. At the same time, a motor with excellent motor efficiency can be manufactured.

Furthermore, since no heat treatment is involved, there is no deformation of the iron core, eliminating problems with shaft insertion failure and outer diameter runout in rotors that do not cut the inner and outer diameters, and at the same time, generating fluctuating noise caused by this runout Can also be prevented.

On the other hand, in terms of production, the time required for the treatment is greatly reduced as compared with the conventional method such as a heat treatment, and the productivity is improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an example of frequency analysis of noise of an induction motor, wherein (a) is a noise characteristic diagram when a rotor according to the present invention is used, and (b) is a rotor manufactured by a conventional method. FIG. 2 is a characteristic diagram showing the rotational speed-torque characteristic of the induction motor.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-81955 (JP, A) JP-A-57-138851 (JP, A) JP-A-1-131571 (JP, A) JP-A 63-81955 258674 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H02K 17/16

Claims (1)

(57) [Claims] An iron core is formed by laminating thin iron plates having a plurality of slots, and then aluminum is die-cast on the iron core to form a cage rotor. A method for manufacturing a cage rotor, wherein the cage-shaped rotor is immersed in an alkali solution.