How much do you know about the impregnation varnish used for motor windings?

How much do you know about the impregnation varnish used for motor windings? Let Germana, the leading manufacturer and supplier of electric motors, tell you about it.

Impregnating varnish is used to impregnate electrical coils and windings, filling the gaps within to bond the wires of the coils and the wires with other insulating materials into a cohesive whole. This improves the electrical strength, mechanical properties, thermal conductivity, and protective performance of the electrical coils. 

1. Basic Requirements for Electrical Coil Impregnation Varnish:

●Low viscosity and high solid content to ensure good penetration and coating application.

●Good stability during storage and use.

●Excellent curing and drying characteristics, with fast curing, low temperature, and good internal drying.

●High bonding strength to allow electrical equipment to withstand higher rotational speeds and mechanical impacts.

●Compatibility with other component materials.

●Good environmental properties.

2. Classification and Characteristics of Impregnating Varnishes

●Solvent-based impregnating varnishes: These varnishes contain solvents, with a solid content (mass fraction) typically ranging from 40% to 70%. Varnishes with a solid content greater than 70% are referred to as low-solvent impregnating varnishes, or high-solid varnishes.

Solvent-based impregnating varnishes offer good storage stability, penetration, and film-forming properties and are relatively inexpensive. However, they require longer impregnation and baking times. Residual solvents can create voids in the impregnated material, and the evaporated solvents contribute to environmental pollution and waste. Their use is limited, primarily applied to impregnate low-voltage motors and electrical windings.

Solvent-based impregnating varnishes are typically applied using immersion methods, but vacuum pressure impregnation and drip impregnation can also be used.

●Solvent-free impregnating varnishes: These varnishes cure quickly, with short impregnation and baking times. They eliminate air gaps in the impregnated insulating parts, offering better cohesion, electrical and mechanical performance. Solvent-free impregnating varnishes have been widely adopted in high-voltage generators, motors, high-volume, fast-paced production lines, and certain special motors and electrical devices, replacing solvent-based varnishes. However, solvent-free varnishes have a shorter storage life.

Solvent-free impregnating varnishes can be applied using immersion, continuous immersion, roll impregnation, drip impregnation, and vacuum pressure impregnation methods.

3. Precautions for Using Impregnating Varnish

●Quality Management of Impregnating Varnish During Use: Solvent-free varnish is a polymerizable resin composition, and various solvent-free impregnating varnishes exhibit varying degrees of self-polymerization during storage and use. Improper management can accelerate this self-polymerization. Once the varnish in the impregnation equipment gels, it can quickly cure and become waste within 1-2 days, leading to significant accidents and losses. Therefore, strict quality management of solvent-free impregnating varnish during use is essential, and measures must be taken to ensure varnish quality stability.

(1) Regularly Monitor the Quality of Impregnating Varnish: Monitor the quality of varnish regularly, with inspection items and intervals based on the varnish used, impregnation equipment, and production tasks. Typical inspection items include density, gel time, moisture content, and active diluent content. If the quality indicators exceed the internal control limits, take immediate corrective actions such as adding new varnish or other measures to adjust.

(2) Prevent Moisture and Contaminants from Entering the Varnish: Both epoxy and polyester solvent-free impregnating varnishes are highly sensitive to moisture. Even a small amount of moisture can rapidly increase the varnish's viscosity. Prevent moisture and contaminants from entering the varnish during transportation, storage, and use. Use vacuum and degassing devices to remove moisture, air, and low molecular weight volatiles from the varnish, and filter the varnish to remove sediment and keep the resin pure.

(3) Properly Select Impregnation Temperature: Adjust the varnish viscosity to the specified value based on the varnish's viscosity-temperature curve, considering differences between cold and hot impregnation workpieces. Excessively high impregnation temperatures can adversely affect the varnish's viscosity stability, while excessively low temperatures can result in high viscosity and poor impregnation results.

(4) Regularly Circulate and Stir the Varnish: Maintain the varnish temperature in the can and pipeline as low as possible to prevent self-polymerization and gelation in the pipeline, which could block the varnish delivery system.

(5) Regularly Add New Varnish: The addition cycle and quantity depend on the production tasks and varnish properties. Adding new varnish under normal production conditions usually helps maintain long-term stability of the varnish in the can.

(6) Store at Low Temperatures: Lowering the storage temperature reduces the varnish's self-polymerization rate. The storage temperature should be controlled below 10°C, and for longer storage or specific conditions, even lower temperatures such as -5°C may be required. For solvent-based varnishes, focus on regularly checking the density and viscosity to ensure they remain within controlled ranges.

●Impact of Impurities on Unsaturated Polyester Varnish Curing: It has been shown that materials like copper and phenolic compounds can delay the curing of unsaturated polyester varnish. Some materials, such as rubber and oil-coated wires, can be dissolved or swollen by the styrene active monomer in the varnish, resulting in a sticky surface on the impregnated workpieces.

●Compatibility Issues: Conduct compatibility tests to ensure that the impregnating varnish is fully compatible with other materials in the insulation system.

●Baking Process Issues: Solvent-based varnishes contain a large amount of solvent and generally require multiple impregnation, baking, and gradual temperature increase processes to prevent pinholes or voids in the varnish film and to improve the insulation performance and lifespan of the coils. For solvent-free varnishes, avoid excessive varnish flow during baking; rotating baking can effectively reduce varnish flow.

●Environmental Pollution Issues: Implement appropriate measures to control the emissions of solvent vapors and styrene from the impregnation and baking process within the permissible limits.

As a leading supplier of Electric Motors, We Germana have the high reputation all over the world. Contact us today to learn more about our products and services. Our team is here to help you find the perfect electric motor solutions for your needs.