Vacuum pressure immersion equipment is mainly used for high-voltage (traction, explosion-proof) motor test transformers and other high-quality electrical capacitors and electrical materials for insulation dipping treatment. In this series of equipment, the workpiece to be immersed is placed in a completely sealed container and vacuumed. The dip varnish is injected into the immersion varnish by differential pressure method. After applying a certain pressure, the immersion varnish thoroughly saturates all the gaps of the workpiece to achieve immersion. The best effect of the paint. This series of equipment is equipped with multiple safety protection devices. The cylinder port adopts the lip-tooth method, which is automatically locked. The cylinder head is hydraulically opened and closed automatically. In fact, vacuum pressure equipment is more expensive. Our topic today is why motor manufacturers choose this equipment? Then, the drying after dipping is briefly introduced.

1. vacuum pressure dipping paint introduction

For low-voltage motor windings with high insulation requirements, vacuum, pressure or repeated pressure immersion should be used. After the winding is vacuum dried (or hot air circulating dry), it must be cooled to 60~70 °C in vacuum, then painted, pressurized or repeatedly pressurized. Air can be used as the pressurized gas, and nitrogen should be used for the flammable solvent to avoid explosion. The pressurizing pressure is 0.2 to 0.8 MN/m2. For tightly wound pole coils or higher viscosity paints (such as silicone paints, solventless paints), it is advisable to use repeated pressurization.

Vacuum pressure dipping paint is a better dipping method. It can completely remove moisture and volatiles in the windings; it can avoid the phenomenon of impregnation; at the same time, the viscosity of the paint can be higher to improve the filling performance. Practice has proved that the effect of a vacuum pressure dipping paint is better than that of a second ordinary dipping paint. For some important motor windings, vacuum pressure immersion is necessary. The vacuum pressure immersion equipment is relatively expensive and should be carried out when the coil is not embedded. It is required to use the external pressure-fit structure when vacuum pressure immersion is applied after the welt. This can not only improve the utilization of the immersion equipment, but also avoid the contamination of the impregnating varnish with the dust on the machine base.

2 .drying after dipping

Drying after dipping is more complicated than pre-baking because there are not only physical processes (solvent evaporation) but also chemical processes (oxidation and polymerization of resins and drying oils in the paint base). The drying process is generally carried out in two stages. The first stage is mainly the volatilization of the solvent. At this time, the temperature should be controlled slightly above the volatilization temperature of the solvent, but not higher than the boiling temperature of the solvent, so as to avoid forming more micropores or foaming on the surface of the winding; The surface forms a hard film prematurely, hindering the evaporation of the internal solvent.

At the same time, ventilation should be carried out to prevent the accumulation of solvent gas and cause an explosion accident; and the evaporation of the solvent can be accelerated. The second stage is mainly the polymerization curing of the paint base and the formation of a hard paint film on the surface of the workpiece. For this reason, the drying temperature is generally about 10 ° C higher than the pre-bake temperature, and the rate of temperature rise depends on the impregnating varnish, and is generally about 20 ° C / hour. The drying time is related to the structure and heating method of the impregnated workpiece. Generally determined according to the test. The time of the first stage depends on the volatilization of the solvent, which is generally about 2~3 hours. The time of the second stage should be determined according to the insulation resistance. Generally, the insulation resistance reaches a steady value (about 2~3 hours). . When immersing multiple times, the first few times of baking time should be shorter, so that the paint film is still sticky, so that the paint film formed by the subsequent immersion paint can be well bonded without delamination. The last drying time should be longer to make the film hardened. For rotor or DC armature windings, it should be longer to avoid smearing due to poor hardening and heat during operation.

According to the different process requirements of the two stages, the temperature and air volume are generally controlled in this way. At the beginning, it is dried for a period of time at a temperature slightly higher than the evaporation temperature of the solvent. At this time, the air volume should be larger, and more than 10% of the air should be continuously changed. New, then keep the air volume unchanged, and heat up to the maximum drying temperature at a speed of about 20 ° C / hour. Finally, when it is dry, the amount of air can be smaller. For the polymer paint, since the supply of oxygen is not required, the amount of air exchange should be small.

Rotor or DC armature windings should be placed in a dry position to prevent the paint from flowing to one side and affecting the balance. If it is only flat and dry due to equipment conditions, it should be rotated 180 degrees periodically during the first stage of drying to prevent the paint from flowing to one side; or after the second dipping, the position placed with the first time after drying Instead, the effects of the two flow junctions cancel each other out. But these two methods are not as good as drying.
For windings or coils that require high insulation, vacuum assisted drying. First, at a low temperature of 70~80 °C, use a vacuum pump to assist in pumping out the solvent. Generally, it can be pumped to a water column of 700-730 mm. When there is no solvent condensation in the condenser, the vacuum is released, the temperature is raised, and then the maximum allowable drying temperature is maintained. Dry down.

Reprinted from the network