Drying oven application:motor winding dipping and drying

Motor winding dipping paint process: 

The purpose of dipping and drying motor windings is to remove the moisture contained in the insulating materials and fill all the air gaps with insulating paint, which can improve the insulation strength and moisture resistance of the windings, and improve the heat resistance of the windings. It can also improve the mechanical properties, chemical stability, thermal conductivity and heat dissipation effect of winding insulation and delay aging. The quality of motor dipping paint directly affects the temperature rise and service life of the motor. The dipping and drying are required to be carried out in strict accordance with the insulation treatment process to ensure good permeability of the insulation paint, smooth surface of the paint film and high mechanical strength. Make the stator windings bonded into a strong whole.

At present, the treatment of motor stator windings with E and B insulation generally uses 1032 melamine alkyd resin paint, the solvent is toluene or xylene, and the number of dipping times is twice, which is collectively referred to as the universal secondary dipping heat immersion type art.

The process of dipping and drying motor windings is consists of two main steps:pre-drying and dipping.
Step 1: Pre-drying
1. Purpose of pre-drying
The windings should be pre-drying before dipping, in order to drive away the moisture in the windings and increase the temperature of the workpiece during dipping, so as to improve the quality of dipping and the ability to soak the paint.
2. Pre-drying method
The pre-baking heating should gradually increase the temperature, and the temperature rise rate should not exceed 20-30 degrees/h. The pre-drying temperature depends on the insulation grade. The E-class insulation should be controlled at 120-125 degrees, and the B-class insulation should reach 125-130 degrees. Keep it at this temperature for 4-6 hours, and then cool the pre-drying winding to Start to dip paint at 60~80 degrees.

Step 2: Dipping paint
Attention should be paid to the temperature of the workpiece, the viscosity of the dipping, and the time of dipping.
1. Dipping temperature
If the temperature of the workpiece is too high, the solvent in the paint will evaporate quickly, which will make the paint film on the winding surface form prematurely, which will not easily penetrate into the winding and cause material waste; if the temperature is too low, the pre-drying effect will be lost and the viscosity of the paint will increase. , The fluidity and permeability are poor, which also makes the impregnation effect poor. Practice has proved that the temperature of the workpiece is 60~80 degrees for dipping paint.
2. Paint viscosity
The viscosity of the paint should be selected appropriately. When the paint is dipped for the first time, it is hoped that the paint will penetrate into the winding. Therefore, the fluidity of the paint is required to be better. Therefore, the viscosity of the paint should be low, generally 22~26s (20 degrees, No. 4 viscometer) ); During the second dipping, it is mainly hoped to form a better paint film on the winding surface, so the viscosity of the paint should be larger, generally 30~38s is appropriate. Because the paint temperature has a great influence on the viscosity, it is generally stipulated that 20 degrees is used as the benchmark, so when measuring the viscosity, it should be adjusted appropriately according to the temperature of the paint.

3. Dipping time
The selection principle of the dipping time: the first dipping, hope that the paint can penetrate into the winding as much as possible, so the dipping time should be longer, about 15~20min, the second dipping is mainly to form a better surface paint film. Therefore, the dipping time should be shorter, so as not to damage the paint film if the time is too long, so about 10~15min is appropriate. However, it must be soaked until no bubbles appear. If it is not ideal, the dipping time can be appropriately extended. After each dipping is completed, the stator windings should be placed vertically, the remaining paint should be dripped for 30 minutes, and the remaining paint on other parts should be wiped clean with a solvent.
Dipping method
The main methods of dipping paint are: pouring, immersion, and vacuum pressure immersion.
For a single repaired motor, dipping is mostly used. Immersion and vacuum pressure immersion are usually used to manufacture motors. For batches, immersion can be considered, and vacuum pressure immersion is used for high-voltage motors.
The commonly used dipping process methods are:
(A) Take out the pre-baked motor, wait for the temperature to cool to 60~80 degrees, and put it on the paint tray vertically;
(B) Pour solvent-free paint into empty beverage plastic bottles to control the amount of dipping paint;
c) Hold the plastic bottle with insulating paint in your hand, tilt the mouth of the bottle to make the insulating paint flow out of the bottle mouth in a linear shape, pour the insulating paint from the upper end of the winding, so that the paint penetrates the coil and flows back to the paint pan from the lower end of the winding ;
(D) When the paint stops dripping for about 20-30 minutes, turn the motor stator over, and then pour the insulating paint onto the upper end of the winding (original lower end) until it penetrates;
(E) After stopping the dripping of paint for about 30 minutes, dip a cloth in kerosene to remove the remaining paint on the inner bore of the stator and the base, and then dry it;
(F) If the paint needs to be dipped twice, after drying, take it out and cool it to 60-80°C and do the second dipping, the operation is the same as above.

Vacuum pressure impregnation (abbreviation: VPI) insulation process
The VPI-vacuum pressure impregnation process is to pre-bake the workpiece to remove moisture and then cool it, put it in a vacuum environment, remove the air and volatiles inside the white coil, rely on the gravity of the paint in the vacuum and the capillary action of the coil, and use dry compressed air Or inert gas exerts a certain pressure on the impregnating varnish after the vacuum is released, so that the varnish can quickly penetrate and fill the inner layer of the insulating structure. In China, VPI is currently an insulation process for gap operations. The drip-drying process of the workpiece is carried out in the paint dipping tank, and the drying process is generally carried out in a separate container or oven, with methods such as vacuum drying, atmospheric static drying or rotary drying.

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