There are two available varnish processes for electric motors: Dip and Bake immerses a motor into a tank of varnish. Vacuum Pressure Impregnation (or VPI) is a process that places the motor into a chamber with a controlled atmosphere.
The dip and bake method develops a hydro static pressure that dissipates many air voids and naturally saturates insulating material. When no bubbles surface, the process is complete.
Vacuum Pressure Impregnation is considered the top-of-the-line varnish processes for electric motor insulation.
VPI is a several-hour process that begins with a pre-bake cycle to remove any moisture. The component is then placed into the varnish chamber, a vacuum is pulled to remove air, varnish is introduced, and the varnish chamber is pressurized. Computerized capacitance monitoring insures a 100% solid fill of the component. A high-grade solvent-less epoxy base varnish is used to impregnate the component, and it will maintain a 100% solid after curing in a bake oven.
The Vacuum Pressure Impregnation process adds significant value to electrical motor windings to ensure longevity that enhances the life of the insulating materials by preventing ingress of contaminates. Additionally, it adds physical strength to secure electrical windings that are subjected to stresses from electrical in-rush currents.