Vacuum Impregnation Varnish for Electric Motors: Best Practices

Precautions for Vacuum Impregnation Varnish in Electric Motors

Quality Management During Use

Solvent-free varnish, a polymerizable resin composition, is prone to self-polymerization during storage and usage. If poorly managed, this can lead to accelerated gelation. In vacuum impregnation equipment, gelled varnish may solidify within 1–2 days, causing severe losses and equipment damage. Therefore, strict quality control measures are necessary to ensure varnish stability:

(1)Regular Quality Monitoring: Perform routine tests such as density, gel time, moisture content, and active diluent levels. Monitoring frequency should align with the varnish type, equipment, and production requirements. If quality indicators exceed limits, adjust immediately by adding fresh varnish or other corrective actions.

(2)Avoid Moisture and Impurities: Both epoxy and polyester solvent-free varnishes are highly moisture-sensitive. Even trace amounts of water can cause a rapid increase in viscosity. Take precautions during transportation, storage, and operation to keep the varnish free from water and contaminants. Use vacuum systems and de-aeration devices to remove moisture, air, and volatiles. Regularly filter varnish to remove sediment and maintain resin purity.

(3)Control Impregnation Temperature: Choose a suitable temperature based on the varnish's viscosity-temperature characteristics, considering the difference between cold and hot impregnation processes. High temperatures destabilize viscosity, while low temperatures reduce impregnation effectiveness.

(4)Circulate and Stir Regularly: Maintain low and uniform varnish temperature in tanks and pipelines to prevent gelation and blockages.

(5)Add Fresh Varnish Periodically: Replenish varnish based on production volume and varnish properties. Regular additions help maintain the long-term usability of the varnish.

(6)Low-Temperature Storage: To slow self-polymerization, store varnish below 10°C, or lower for long-term storage (e.g., -5°C). For solvent-based varnishes, prioritize keeping density and viscosity within controlled ranges.

Impact of Impurities on Vacuum Impregnation

Materials such as copper and phenolic compounds can delay the curing of unsaturated polyester varnishes. Similarly, substances like rubber and oily enameled wires may dissolve or swell in varnish, leaving sticky residues on motor components.

Compatibility with Insulation Systems

Conduct compatibility tests to ensure the varnish works seamlessly with other materials in the motor’s insulation system.

Baking Process Considerations

For solvent-based varnishes, gradual baking with multiple impregnation and heating cycles is recommended to prevent pinholes or voids in the varnish film, thereby enhancing insulation performance and durability. For solvent-free varnishes, avoid excessive varnish flow during baking, and consider rotating baking techniques to reduce resin loss.

Environmental Considerations

Minimize emissions of solvent vapors and styrene during vacuum impregnation and baking. Ensure that emissions are within permissible limits to reduce environmental impact.