Analysis of Vacuum Pressure Immersion Coating Process for Hengli Motors
A student from the Department of Electrical Engineering at a university visited a factory for an internship, and based on their knowledge and on-site discussions with the company, most of them showed great interest in the VPI equipment of the enterprise.
Vacuum pressure coating is a highly effective coating method, and standardized motor companies have adopted the vacuum pressure coating process. Vacuum pressure coating can thoroughly remove moisture and volatile substances inside the winding; It can also avoid the phenomenon of incomplete immersion; At the same time, the viscosity of the paint can be higher to improve the filling performance. Ms., today I will have a brief exchange with you on the vacuum pressure coating process and equipment.
Advantages of vacuum pressure coating
Practice has proven that the effect of a single vacuum pressure coating is better than that of a second ordinary coating. For some important motor windings, it is necessary to use vacuum pressure coating. The cost of vacuum pressure impregnation equipment is relatively high, and it should be carried out as much as possible when the coil is not embedded; When vacuum pressure coating is required after wire embedding, an external pressure mounting structure should be used as much as possible. This can improve the utilization rate of the coating equipment and avoid the contamination of the coating by dust particles brought into the machine base.
For low-voltage motor windings with high insulation treatment requirements, it is advisable to use vacuum, pressurized, or repeatedly pressurized immersion methods. After vacuum drying (or hot air circulation drying), the winding must be cooled to 60-70 ℃ in vacuum; Then apply paint, apply pressure or repeatedly apply pressure. The pressurized gas can be air, and for flammable solvents, argon gas should be used to avoid explosion. The pressurization pressure is 0.2~0.8MN/m2. For tightly wound magnetic pole coils or paints with high viscosity (such as silicone paint, solvent-free paint), repeated pressure should be applied
Introduction to Vacuum Pressure Immersion Coating Equipment
The composition of vacuum pressure impregnation equipment mainly includes: vacuum drying furnace, impregnation cylinder, paint storage cylinder, vacuum pump, etc.
● Vacuum drying furnace
A sealed metal box that is circular or elliptical in shape. It is required to be able to withstand high temperature and high pressure, usually made into a double-layer structure, with high-pressure steam heating introduced into the interlayer. When there is a lack of high-pressure steam, hot oil heating or electric induction heating methods can be used. But it is not as safe as high-pressure steam. The outer surface of the cylinder is covered with insulation layer, and there are vacuum gauges, thermometers, and safety valves installed on top of the cylinder. In addition, lead out porcelain columns should be installed to measure the insulation resistance of the coil.
● Immersion paint cylinder
It is circular and made of thick steel plate. The cylinder must be equipped with a pressure gauge, vacuum gauge, observation window, and safety valve. There are also those that integrate the dipping tube with the drying oven.
● Paint storage container
Similar to the immersion tube, but with lower mechanical strength requirements and larger volume. And a mixer must be installed, driven by an explosion-proof motor. Connected to the immersion tank through a paint filter and controlled by a valve. For impregnating paints (epoxy solvent-free paints) that require low-temperature storage, they should be placed in an adjustable refrigeration room.
● Paint filter
Paint may contain impurities after use, and in order to ensure impregnation quality, it must be filtered through a filter when reused.
● Air heater
The air that is blown in is heated and enters the drying furnace. Generally, steam, hot oil, or electric heating wire is used for heating.
● Vacuum cleaner and moisture absorber
Compressed air must be filtered to remove moisture and dust, usually using silica gel as a desiccant and fiberglass to filter dust.
● Condenser
A condenser must be installed before the vacuum pump to condense the solvents, moisture, oils, etc. in the gas pumped into the vacuum pump, in order to avoid damaging the vacuum pump. At the same time, by checking the condensation amount, the dryness level of the processed winding can be inferred. The condenser is generally made of salt water. The condensation capacity of the condenser must adapt to the exhaust speed. If the condensation capacity is too small, the exposed condensate is often drawn into the vacuum pump together, which affects the service life of the vacuum pump. When the condenser is stopped, be careful to drain all the cold water to avoid the formation of scale or freezing.
● Vacuum pump
The quality of the vacuum pump determines the quality of the immersion paint, and it must be carefully selected and maintained. It is best to have two sets of vacuum pumps, one set for establishing vacuum with a larger capacity, and the other set for maintaining high vacuum with a smaller volume.
