in the squirrel cage three-phase asynchronous motor, the quality of the cast aluminum rotor directly determines the rotor loss of the motor. combined with some manufacturing design experience, for the cast copper rotor, the additional loss of the rotor is about 0.5% of the rated power, and the additional loss of the cast aluminum rotor accounts for about 1% to 3% of the rated power. therefore, under the current development trend of efficiency and energy saving, it is necessary to control the additional loss of the rotor, some technological measures are taken to reduce the additional loss of the motor. there are many types of additional loss of the motor rotor. for the cast aluminum cast copper rotor, because there is no insulation between the guide bar and the rotor slot, the leakage current between the guide bars through the rotor teeth produces part of the rotor loss, which accounts for about 1% ~ 2% of the rated power. due to the existence of additional losses, the motor efficiency decreases and the temperature increases. in order to reduce the additional loss of cast aluminum rotor and improve the performance index and economic index of motor, it is necessary to improve the quality of cast aluminum rotor so as to reduce the additional loss. the following measures are taken from the process.
1. phosphating treatment of rotor punching
phosphating treatment is to use chemical or electrochemical methods to produce a phosphate film insoluble in water and corrosion-resistant on the metal surface. this surface phosphating film is firmly combined with metal, has high insulation performance, and can withstand high temperature. the thickness of phosphating film on one side of silicon steel sheet after phosphating treatment is between 0.004 ~ 0.008mm. under the pressure of 1 ~ 3mpa, the surface insulation resistance can reach more than 10000 ω· c ㎡, and has high withstand voltage strength (above 240v). the phosphating film of electrical steel sheet can work for a long time at 450 ℃, and can withstand the instantaneous high temperature of 680~720 ℃ of molten aluminum during aluminum casting and the short-term high temperature after aluminum casting. however, due to the poor thermal conductivity of the phosphating film, the temperature rise of the rotor has a certain impact. however, combined with the manufacturing experience, the additional loss of the phosphating treated rotor is reduced, but the phosphating process is relatively complex and the production cost is high, requiring professional equipment to reduce the production cost. the formula and process of phosphating treatment solution are as follows.
1.1 normal method
by using ferromanganese phosphate preparation, the ferromanganese phosphate preparation is a mixed block with the molecular formula of nfe (h, po,) 2mmn (h2po2) 2, in which n and m are the ratio of iron block to manganese block. the main components (mass fraction): p2o3 is 46% ~ 52%, mn is greater than 14%, fe is 0.3%~3%, and h20 is below 19%. ferromanganese phosphate preparation is 27 ~ 30g / l, and the temperature of phosphating solution is 95 ℃. it needs to be degreased after punching and core lamination. it is cleaned with toluene or carbon tetrachloride to clean up the oily waste on its surface, and then immersed in the prepared phosphating solution for 30 ~ 45 minutes. after taking it out, it is washed with 3% soapy water to saponify it, and then acid etched (immersed in 50% concentration of industrial hydrochloric acid for 20 seconds), wash with a large amount of warm water to complete the phosphating treatment of the punching piece and rotor.
1.2 acceleration method
there are many formulas for the accelerated method. the following is the zinc oxide orthophosphate method:
orthophosphoric acid h3po4:40 ~ 50g / 1;
zinc oxide zno: 9 ~ 10g / l;
sodium nitrate nano3:4 ~ 5g / l.
after degreasing, the workpiece shall be immersed in phosphating solution above 95 ℃ for 12 ~ 15min. saponification and cleaning are also required. match
the function of sodium nitrate in the formula is to promote the chemical reaction and make the phosphating film fine. degreasing the workpiece before phosphating is the key process to ensure the phosphating quality. the degreasing method can be cleaned with toluene or carbon tetroxide, or the chemical degreasing solution can be used at the temperature of 70 ~ 80 ℃
lower the treatment for 10 ~ 20min until the oil stain is removed. the formula of chemical degreaser is:
water glass: 250g / l;
op emulsifier: 5 ~ 10g / l.
the phosphating film obtained from phosphating treatment is porous, and generally has good corrosion resistance only after supplementary processing. the phosphating film used as insulation can only be saponified. after saponification, the phosphating film is covered with a very thin water-insoluble film composed of iron soap, manganese soap or zinc soap, which improves the phosphating effect.
the phosphated rotor can increase the contact resistance between the guide bar and the iron core, thus reducing the additional loss, and further improving the temperature rise and efficiency.
2. punching oxidation treatment
the purpose of the oxidation treatment of the punching piece is the same as that of the phosphating treatment of the punching piece, and the process is the same as that of the phosphating treatment of the rotor punching piece, except that the chemical agents used are different, and the process flow is the same.
3. shelling treatment
the shelling treatment uses the characteristics of different expansion coefficients of aluminum and silicon steel sheets to rapidly cool the heated rotor, so as to form a small gap between the iron core and the aluminum strip, increase the contact resistance and reduce additional losses.
the shelling process is as follows; put the cast aluminum rotor in the annealing furnace and heat it to 540 ℃ for 2 ~ 3h, then take it out and cool it in air (or immerse it in water for 7 ~ 10s). when the rotor still has a temperature of about 200 ℃, take it out and use the waste heat to dry the rotor by itself.
4. rotor surface baking
the rotor surface which has been cast aluminum and finished turning is baked with a blowtorch to remove the burrs and aluminum chips on the iron core surface to reduce additional losses. when the aluminum strip is about to melt, it is immediately put into soapy water for rapid cooling to make it shelled.
5. alkaline washing
use strong alkali to remove the aluminum in contact with the rotor slot, increase the contact resistance between the aluminum strip and the iron core, and reduce the additional loss. the method of alkali separation is to immerse the rotor in an alkaline sodium solution with a concentration of 5% and a temperature of 70 ~ 80 ℃ for corrosion for 1min, and then take out clean water for cleaning and drying.
6. insulation treatment of rotor slot
the rotor slot shall be insulated before aluminum casting, and the insulation coating must be high temperature resistant.
to sum up, at the same time, tests have proved that taking any of the above measures has a certain effect on reducing the additional loss of the motor. however, due to the complexity of the manufacturing process, the additional measures will significantly increase the production cost of the motor. therefore, any process measure will cause an increase in the cost. however, due to the advocacy and implementation of national energy conservation and emission reduction, some enterprises have also begun to take measures from the aspects of technology, such as the shelling treatment of rotors rotor surface baking and other processes are used to improve the manufacturing process of motor rotor to reduce the additional loss of rotor.