How familiar are you with motor winding varnishing methods? These six impregnating varnishing methods not only affect motor performance but also directly determine its lifespan. This article focuses on six major methods: Pond varnishing, dripping varnishing, roll varnishing, Pouring varnishing, vacuum pressure impregnation (VPI), and spray varnishing.
Pouring Varnishing Method
Process:
Place the stator vertically on a varnish tray with one end of the winding facing upward. Use a varnish pot or brush to pour varnish over the top winding section.
Once varnish fills the winding gaps and begins to seep from the bottom, flip the stator and pour varnish onto the other end. Repeat until fully saturated.
Applications:
This method is suitable for medium to large motors, wind power generators, three-phase asynchronous motors, and diesel generators.
Dripping Varnishing Method
Process:
Heat and rotate the motor stator windings. Varnish is dripped onto the winding ends and penetrates the internal windings and slots under gravity, capillary action, and centrifugal force.
1. Formula: Use 6101 epoxy resin with tung oil and maleic anhydride (50% by mass). Mix fresh before use.
2. Preheating: Electrically heat the windings for about 4 minutes to 100–115°C or place them in a drying oven for approximately 30 minutes.
3. Dripping: Place the stator vertically in a varnish tray. Once the temperature drops to 60–70°C, begin manual dripping. After 10 minutes, flip the stator and repeat on the other side until fully soaked.
4. Curing: Electrically cure the windings at 100–150°C. Alternatively, heat them in an oven for about 2 hours. The process is complete once insulation resistance reaches 20MΩ or exceeds 1.5MΩ for smaller motors.
Applications:
Ideal for small motors such as BLDC motors.
Roll Varnishing Method
Process:
Pour insulating varnish into a tank and place the stator inside. The varnish surface should submerge the windings by at least 200mm.
If the tank is shallow and coverage is insufficient, rotate the stator multiple times or brush varnish while rolling.
Typically, 3 to 5 rotations ensure full varnish penetration.
Applications:
Used for medium and large motors, induction motors (asynchronous), and large wind turbines.
Pond Varnishing Method
Process:
Pour a suitable amount of insulating varnish into a varnish tank. Lower the motor stator into the tank until the varnish covers the windings by more than 200mm.
Allow the varnish to soak into all winding and insulation paper gaps. Then, lift the stator and let excess varnish drip off.
For better results, apply 0.3 to 0.5 MPa pressure during impregnation.
Applications:
Commonly used for small and medium motors, BLDC motors, EV motors, and permanent magnet synchronous motors.
Vacuum Pressure Impregnation (VPI)
Process:
VPI is an advanced insulation treatment method. The process includes preheating, tank loading, vacuum degassing, varnish immersion, draining, unloading, and curing.
Place the stator into a sealed varnish chamber. Use vacuum technology to remove moisture and air.
After varnish application, apply 200 to 700 kPa pressure to drive the varnish into all winding gaps and deep into the insulation paper’s capillaries. This ensures high impregnation quality.
Applications:
Ideal for high voltage motors, large multi-layer yoke coils, and critical applications with strict insulation requirements.
Spraying Varnishing Method
Spray varnish with the proper viscosity onto the winding surface to ensure even coverage. This method works best for large motors with wide exposed windings.
Which varnish impregnation method best suits your motor product?
Understanding how each technique works can help you avoid costly mistakes in design or manufacturing.
If you have specific requirements, feel free to contact us for a tailored solution. Lamnow is a professional electric motor stator winding manufacturer based in China. Our varnishing services include dripping, immersion, and vacuum impregnation. Whether you need prototypes or large-scale production, we can deliver to your specifications.
FAQ – Why Is Varnish Impregnation Necessary?
Improves Heat Resistance and Thermal Conductivity
Before varnishing, winding insulation gaps are filled with air, which poorly conducts heat.
After varnishing, the gaps are fully filled, forming a varnish film that slows oxidation and enhances thermal properties.
Enhances Electrical Insulation
Varnish fills the gaps between turns, phases, and inside insulation materials.
This eliminates air bubbles and forms a strong solid dielectric layer, significantly improving insulation performance.
Boosts Moisture Resistance and Chemical Stability
Before treatment, moisture and water can degrade insulation.
After varnishing, the varnish seals capillaries and gaps, forming a smooth film that blocks moisture, dust, and corrosive gases.
Special varnishes can also resist corona discharge, corrosion, and oil contamination.
Increases Mechanical Strength
The varnish bonds all wires into a solid mass, enhancing mechanical integrity.
This minimizes loosening and abrasion caused by electromagnetic force, vibration, and thermal expansion or contraction.
