Purpose of motor stator windings dipping and drying
The purpose of drying the electric motor winding dip paint is to drive out the moisture contained in the insulating material and fill all the space air gaps with insulating paint, so as to improve the insulation strength of the winding and moisture-proof performance.
But It also need to improve the heat resistance and heat dissipation of the winding, but also to improve the mechanical properties of the winding insulation, chemical stability, thermal conductivity and heat dissipation effect and delay aging, the quality of the motor dip paint, directly affect the motor .
The quality of motor dipping paint directly affects the temperature rise and service life of the motor.
It is required that the dipping and drying process is carried out in strict accordance with the insulation treatment process to ensure good penetration of the insulation paint, smooth surface of the paint film and high mechanical strength.
The stator windings are bonded into a solid whole.
At present, the processing of the stator windings of electric motors with E and B insulation dipped in lacquer, generally using 1032 melamine alkyd resin lacquer, the solvent is toluene or xylene, the number of dipping lacquer for the second time, will be collectively referred to as the universal second dipping lacquer hot immersion art.
Motor windings dipping and drying process
The process consists of two main processes: pre-baking and lacquer dipping.
I: Pre-drying
1. Purpose of pre-drying
The winding should be pre-drying before dipping paint, in order to drive away the moisture in the winding and improve the temperature of the workpiece when dipping paint, in order to improve the quality of the dipping paint and paint penetration capacity.
2. Pre-drying method
Pre-drying heating to gradually increase the temperature, the speed of temperature rise to not more than 20-30 degrees / h is appropriate.
The pre-drying temperature depends on the insulation grade, the insulation of E grade should be controlled at 120~125 degrees, B grade insulation should reach 125~130 degrees, in the temperature insulation 4~6 hours, then the pre-drying motor windings will be cooled to 60~80 degrees to start dipping paint.
II: Dipping paint
When dipping paint should pay attention to the temperature of the workpiece, the viscosity of the dip and the time of dipping paint for the motor windings in the varnish tank.
1. Immersion temperature
If the workpiece temperature is too high, the solvent in the paint evaporates quickly, so that the surface of the winding prematurely formed paint film, and not easy to dip to the internal winding, also resulting in material waste.
If the temperature is too low, it will lose the role of pre-drying, so that the viscosity of the paint increases, mobility and permeability is poor, also make the dip paint effect is not good.
Practice has proved that the workpiece temperature in 60 ~ 80 degrees dipping paint is appropriate.
2. Viscosity of paint
The viscosity of the paint should be appropriate, the first dip in the paint hope that the paint dip to the motor winding inside, so the requirement of paint mobility is good, so the viscosity of the paint should be low, generally can be 22 ~ 26s (20 degrees, No. 4 viscometer);
the second dip in the paint, the main hope in the winding surface to form a good layer of paint film, so the viscosity of the paint should be larger, generally take 30 ~ 38s is appropriate.
As the temperature of the paint has a great influence on the viscosity, so it is generally stipulated that 20 degrees is the benchmark, so the viscosity should be measured according to the temperature of the paint for appropriate adjustment.
3. Dipping time
The principle of the choice of dipping time:
the first dipping paint, hope that the paint can try to dip into the winding inside, so the dipping time should be longer, about 15 ~ 20min ,
The second dipping paint, mainly to form a better surface paint film, so the dipping time should be shorter, so as not to take too long instead of the paint film damage, so about 10 ~ 15min is appropriate.
But It must be dipped through, until no bubbles, if not ideal to extend the dip time. After each dip paint is completed, the stator winding should be put vertically, drip dry remaining paint, the time should be 30min, and use solvent to wipe other parts of the remaining paint.
Paint dipping method
The main methods of paint dipping are: pouring, immersing and vacuum pressure dipping.
For single repair motor dipping paint, more use of pouring immersion, while immersion and vacuum pressure immersion is usually used for manufacturing motors, for the batch can be considered immersion, high pressure motors only use vacuum pressure immersion.
The common methods of pouring and dipping are:
a) Remove the pre-baked motor, leave it to cool to 60-80 degrees and set it vertically on top of the paint tray.
(b) Fill an empty plastic beverage bottle with solvent-free lacquer in order to grasp the amount of lacquer to be poured.
(c) Holding the plastic bottle with the insulating lacquer, tilt the bottle so that the lacquer flows out of the bottle in a line, pour the lacquer from the upper end of the winding, so that the lacquer penetrates the coil and flows back into the lacquer tray from the lower end of the winding.
(d) When the paint dripping has stopped for about 20-30 minutes, turn the new motor stator over and pour the insulating paint into the upper end of the motor winding (formerly the lower end) until it penetrates.
(e) After stopping the paint dripping for about 30 minutes, use a cloth dipped in paraffin to remove the remaining paint from the inner chamber of the stator and the machine base, and then dry it.
f) If the paint needs to be dipped for the second time, after drying, take it out and cool it to 60~80 degrees and then pour it for the second time.
Vacuum pressure impregnation (abbreviated: VPI) insulation process
The VPI-vacuum pressure impregnation process is to cool the workpiece after pre-baking and de-moistening, and then place it in a vacuum environment to exclude the air and volatiles inside the white coil, relying on the gravity of the paint in the vacuum and the capillary action of the coil, as well as the use of dry compressed air or inert gas to exert a certain pressure on the impregnating paint after lifting the vacuum, so that the paint can quickly penetrate and fill the inner layer of the insulation structure.
In China, VPI is currently still a gap-working insulation process.
The drip-drying of the workpiece is carried out in the dipping tank and the drying process is usually carried out in a separate container or oven.
The methods are vacuum drying, atmospheric pressure static drying or rotary drying.
VPI-process flow: ⊙ → pre-drying and dehumidification → into the tank → vacuum exhaust → vacuum dipping paint → pressure impregnation → pressure discharge paint → unloading pressure drip paint → out of the tank → curing and drying → ⊙.
Comparison: It is clear that VPI is far superior to other dipping processes in terms of lacquer penetration and impregnation. In terms of application, VPI is more suitable for large high-voltage coils, multilayer flush-wound yoke coils and demanding large windings, as well as other high-voltage coils.
With regard to pressure, in principle the pressure is applied to make it easier for the lacquer to enter and fill the voids, and there is in fact an atmospheric pressure in the process.
If the capillary wettability of the insulation structure is already balanced, then increasing the pressure has no significant effect on the filling of the entire insulation structure, unless the increased pressure is maintained throughout the curing process.
So the effective way to increase the filling is to reduce the viscosity of the lacquer and reduce the void in the insulation structure, increasing the capillary effect, rather than increasing the pressure.
The data from the “Viscosity and pressure on penetration rate” test shows that when the viscosity of the lacquer is high, increasing the pressure has a greater effect on the filling rate, while when the viscosity of the lacquer is low, the effect of increasing the pressure on the filling rate is not significant.
However, the viscosity of the lacquer has a very significant effect on the filling rate, which is inversely proportional to each other.
It can be seen that in the application of the VPI process, a one-sided emphasis and the simple pursuit of high vacuum or high pressure is blind and unhelpful.
The result can affect the efficiency of the impregnation and can even spoil the quality of the impregnation.
The actual process parameters of a process vary for different insulation structures as well as for different technical requirements.
For example, VPI has four process parameters, i.e. vacuum Vi, pressure Pi, temperature Ti, time ti, where i is 1, 2, 3, ……. The four process parameters are, for example, vacuum Vi, pressure Pi, temperature Ti and time ti, where i is 1, 2, 3, and n (n is the total number of VP process steps and i is the sequence of steps).
The insulation structure (W), the technical specifications (A) and the lacquer characteristics (E) are the basic function elements of these four process parameters.
Insulation treatment of motor and transformer windings with dipping paint
From immersion, i.e. ordinary impregnation, to multiple impregnation, to dip, roll impregnation and vacuum impregnation, vacuum pressure impregnation has developed into a continuous process of ordinary immersion, dip and roll impregnation, and finally to the integration of vacuum impregnation and drying, forming a series of diverse mechanised continuous operations.
Application of modern computer technology and PLC technology automatic control of the impregnation process, which is constantly through technological innovation, production needs and social development of the promotion, the gradual evolution of development, it is this promotion, and produced a new generation of vacuum dipping paint dryer, energy saving, environmental protection into an integrated high-tech products, brand-name products, nearly 600 users at home and abroad use.
The new generation vacuum paint dipping and drying machine is a mechanical insulation process in which the workpiece is put into the dipping and drying cylinder for pre-drying.
The air and volatiles inside the coil are excluded in the vacuum environment, and then the paint is dipped under vacuum conditions relying on the gravity of the paint and the capillary action in the coil, so that the paint quickly penetrates and fills the inner layer of the insulation structure.
FGH process: put into the workpiece → white pre-baking → vacuum de-wetting → vacuum dipping paint → back to paint → drip paint → cleaning → back to the cleaning agent → low temperature drying to high temperature curing → insulation → out of the oven the whole process, fully sealed without environmental pollution in one go.
The advantages of the role of FGH: In the scope of application of the FGH process, the advantages of its role are mainly in the following areas.
(1) Improve the integrity, as the vacuum dipping paint makes the insulation paint almost completely filled inside the insulation, strengthening the integrity of the entire winding, the winding in operation each part will not move separately, reducing the failure caused by mobile wear.
(2) Improved environmental conditions, due to the vacuum dipping paint, the whole dipping process, including paint delivery and paint dipping and drying, is carried out and completed under completely sealed container conditions.
The whole drying process is heated by hot air circulation, and the waste gas generated is recycled and re-emitted through the A and B two groups of condensers, improving the working environment and meeting environmental requirements.
(3) Reduce the operating temperature and temperature rise, due to the vacuum dipping paint and drying into one completely filled, a good substitute for the internal air gap, improve the thermal conductivity of the motor, transformers can generally reduce 5-10 ℃.
(4) improve the performance of the workpiece, as a result of vacuum dipping paint drying the entire winding is impregnated with paint tightly encapsulated, soaked, smooth and bright surface paint film, so that pollutants, moisture and chemical gases can not enter the inner layer, eliminating the fault caused by the conductive medium bridging.
(5) Energy saving and cost reduction, due to vacuum dipping lacquer, drying into one, drying time than the oven to shorten two fifths, drying temperature than the oven to reduce 10-20 ℃, to further achieve increased production and energy saving and cost reduction.
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