Motors and insulating varnishes are inextricably linked. The composition and manufacturing technology of insulating varnishes are constantly being updated and improved, driving rapid changes and developments in motor design and manufacturing methods, and promoting the widespread application of high-temperature, high-power-density motors that were previously considered off-limits in design.
This shows just how important insulating varnish is to motors, and it's easy to understand why motor enthusiasts always enjoy discussing it so much. Ms. Can will join the discussion today and talk about insulating varnish with everyone.
Motor insulation varnishes can be broadly classified into five categories according to their application: impregnation varnish, wire varnish, coating varnish, silicon steel sheet varnish, and anti-corona varnish. Among them, anti-corona varnish is generally only used on high-voltage motors.
Impregnating paint
Impregnating varnishes are divided into two main categories: solvent-based varnishes and solvent-free varnishes. They are mainly used to impregnate motor windings (stator windings and rotor windings of wound-rotor motors) to fill their gaps and micropores. After curing, they can form a continuous and smooth varnish film on the surface of the windings and solidify into a hard whole.
Impregnation and drying are particularly critical steps in the motor manufacturing process. The viscosity, fluidity, solid content, drying properties, and adhesion of the impregnation varnish directly affect the final performance of the motor.
Enamelled wire paint
Enamelled wire is the most common electromagnetic wire for electric motors, and the enamel coating is mainly used for coating and insulating the wire core. Because the conductor is subjected to heat, chemical forces, and various mechanical forces during winding and embedding, the enamel coating is required to have good coatability (i.e., uniform coating), strong film adhesion, a smooth, soft, and tough surface, certain wear resistance and elasticity, good electrical properties, heat resistance, solvent resistance, and no corrosiveness to the conductor.
Motor manufacturers should pay special attention to the control of enameled wire. Better motor manufacturers are equipped with necessary testing equipment. Tests such as enamel film continuity, twisting and peeling, scratch resistance, and voltage resistance can effectively verify the overall performance of the enamel film.
Cover paint
Topcoat varnish is used to coat impregnated coils and insulating components, forming a uniformly thick insulating protective layer on their surface to prevent mechanical damage to the equipment insulation and corrosion from the atmosphere and chemicals, thereby improving surface insulation strength. Therefore, topcoat varnish is required to have properties such as fast drying, strong adhesion, a hard film, high mechanical strength, moisture resistance, oil resistance, and corrosion resistance.
Silicon steel sheet paint
Silicon steel sheets are also a major raw material for electric motors. Silicon steel sheet paint is used to coat silicon steel sheets to reduce eddy current losses in the iron core and enhance corrosion resistance. After coating, silicon steel sheet paint needs to be dried at high temperature for a short time. Its characteristics include a thin layer, strong adhesion, hardness, smoothness, uniform thickness, oil resistance, moisture resistance, and good electrical properties.
Anti-corona paint
Corona discharge is a discharge phenomenon in which the air in a localized space is ionized at a point of sudden increase in field strength (such as at the sharp point of an electrode) in a highly non-uniform electric field, producing a blue halo.
Anti-corona varnish is generally composed of a mixture of insulating varnish and non-metallic conductor (carbon black, graphite, etc.) powders. It is mainly used as an anti-corona varnish for high-voltage coils, such as at the ends of high-voltage coils in large high-voltage motors. Many motor manufacturers apply anti-corona varnish to the stator and rotor windings and rotor surface by spraying after the windings have been impregnated and baked.
