How many types of insulating varnishes are used on a motor?

Motors and insulating varnishes are closely intertwined. The components and manufacturing techniques of insulating varnishes have been continuously updated and improved, driving changes and advancements in motor design and manufacturing methods, thereby promoting the widespread application of high-temperature, high-power density motors that were previously confined to the design phase.

So, how many types of insulating varnishes can be used on a motor?

1.Impregnation Varnish:

Impregnation varnishes are divided into two main categories: solvent varnishes and solvent-free varnishes. They are mainly used for impregnating coils of motors and electrical appliances to fill their gaps and micropores. After curing, they form a continuous and smooth varnish film on the surface of the impregnated material, bonding it into a solid whole. The basic requirements for impregnation varnishes include low viscosity, good flowability, high solid content for easy penetration and filling of the impregnated material. They should cure quickly, have good drying properties, strong adhesion, thermal elasticity, and be able to withstand centrifugal forces during motor rotation. They possess excellent electrical properties and chemical stability, as well as resistance to moisture, heat, and oil, and exhibit good compatibility with conductors and other materials.

2.Enamel Wire Varnish:

Enamel wire varnish is mainly used for insulating coating of enamel wire cores. Since conductors undergo heating, chemical, and various mechanical stresses during processes like winding coils and embedding wires, enamel wire varnishes are required to have good coating properties (i.e., uniform coating), strong film adhesion, smooth and flexible surface, some degree of abrasion resistance and elasticity, good electrical properties, heat resistance, solvent resistance, and no corrosion to conductors.

3.Coating Varnish:

Coating varnishes are used to coat impregnated coils and insulated components to form a uniform insulation protective layer on their surfaces, preventing mechanical damage and corrosion from atmosphere and chemical agents, and enhancing surface insulation strength. Therefore, coating varnishes are required to have fast drying, strong adhesion, hard varnish film, high mechanical strength, moisture resistance, oil resistance, corrosion resistance, etc. Coating varnishes are classified into alkyd varnishes, epoxy varnishes, and organosilicon varnishes based on resin types. Epoxy varnishes have better moisture resistance, mold resistance, internal drying properties, and adhesion than alkyd varnishes, with high varnish film hardness, and are widely used for surface coating of motor and electrical equipment components in humid and hot regions. Organosilicon varnishes have high heat resistance and can be used as H-class motor and electrical insulation varnishes.

4.Silicon Steel Varnish: 

Silicon steel varnish is used to coat silicon steel sheets to reduce eddy current losses and enhance corrosion resistance of the iron core. After coating, silicon steel varnish needs to be dried at high temperature for a short time. Its characteristics include thin layer, strong adhesion, hardness, smoothness, uniform thickness, oil resistance, moisture resistance, and good electrical properties.

5.Corona-Resistant Varnish: 

Corona discharge is a discharge phenomenon that occurs in extremely non-uniform electric fields, where blue corona glow is generated due to local space ionization at sharp points (such as electrode tips). Corona-resistant varnish is generally composed of insulating varnish and non-metallic conductive (such as carbon black, graphite, etc.) powder, mainly used as corona-resistant varnish for high-voltage coils, such as those used at the ends of high-voltage coils in large high-voltage motors. Industrial requirements for corona-resistant varnishes include stable surface resistivity, strong adhesion, good abrasion resistance, fast drying speed, storage stability. Corona-resistant varnish can be applied directly to the coil surface, coated on asbestos tape, glass tape on the outer layer of the coil, or coated on glass cloth for one-time molding with the main insulation.

6.Surface and Anticorrosive Varnish: 

Insulating varnishes are mainly composed of varnish base (i.e., film-forming substance) and solvents, diluents, fillers, etc. The varnish base is synthetic resin or natural resin, which is a liquid or solid with high viscosity at room temperature. Solvents or diluents are used to dissolve the varnish base, gradually evaporating or becoming part of the insulator during the film-forming and curing process. Insulating varnishes can be divided into several types according to their uses, such as impregnation varnish, enamel wire varnish, coating varnish, silicon steel varnish, and corona-resistant varnish. It is evident that insulating varnishes are crucial for motors, as they influence the performance and lifespan of machines. A stable electrical insulation system can protect electrical motors from damage caused by high temperature, chemicals, moisture, etc., enabling efficient and smooth operation.

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