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Impregnation Methods for Electric Motors: The Best Choice for Lasting Performance

motori elettrici stanno per essere impregnati

Impregnating electric motors is a procedure that requires highly specialized professional skills. The impregnation process and methodology are difficult to standardize and vary depending on the specific case.

Only by choosing the optimal impregnation method for the technical and physical characteristics of a specific motor and/or transformer can operational performance be maximized over time.

Below are some of the electric motor impregnation methodologies we offer to our clients. Each is recommended for a specific category of motors and requires different impregnation products.

Immersion and Flow Coating Impregnation

These methods are particularly recommended for low voltage stators and transformers.

The ideal cycle involves preheating the unit to 110-120°C to eliminate moisture from the insulating materials, then cooling it to 40-70°C depending on the impregnation product to be used. Next, the unit is immersed in the impregnation product for 15-40 minutes, followed by a drip period ranging from a minimum of 30 minutes to as long as 6 hours. The process concludes with baking in a static oven for 4-12 hours at 130-170°C.

Flow coating involves a “funnel-shaped cup” installation where the part to be treated is placed. The product is continuously poured over the piece, and the excess is collected at the base of the funnel where a pump recirculates it. The product then cures either in air or through oven baking cycles.

Vacuum and Vacuum/Pressure Impregnation

These methods are recommended for medium/high voltage generators, high-performance motors, and motors and transformers for railway applications.

After eliminating moisture as indicated in the immersion method, the unit is placed in an autoclave in a vacuum atmosphere. The resin is introduced into the autoclave at a rate of 10cm/min from the bottom until the piece is completely immersed. The cycle includes maintaining the vacuum for 20-60 minutes at a residual pressure between 4 and 20 mBar, depending on the product used. After a drip period of 30 minutes to 6 hours, the process concludes with baking in a static oven for 4-12 hours at 130-170°C.

This technique is similar to immersion but is performed at a pressure lower than atmospheric to ensure the process is free of air and moisture. When a pressure cycle (3-6 Bar) is also used, the process is called VPI (vacuum pressure impregnation) to distinguish it from generic vacuum impregnation methods, known as VI (vacuum impregnation) or OVI (only vacuum impregnation).

Drop-by-Drop and Rolling Impregnation

These methods are particularly recommended for stators or small high-speed rotating machines such as power tools (drills, grinders, etc.) and home appliances (washing machine and dishwasher armatures). A uniform distribution of the resin over all parts of the winding is necessary, along with optimal slot filling. This occurs because the centrifugal force from rotation prevents excessive dripping of the liquid resin, unlike static methods (immersion, VPI, VI, or OVI).
The cycle consists of preheating the unit to 80-120°C, followed by resin dripping on rotating pieces or rolling immersion in the resin bath. The process concludes with gelation, still in rotation, for about 10-15 minutes at 120°C, followed by a baking cycle of about 20-40 minutes at 135-160°C.

Joule + UV Impregnation

This method is a hybrid between immersion and drop-by-drop procedures. The unit is immersed in the product connected to a voltage generator to heat the winding by Joule effect. The cycle consists of preheating the winding to 130-150°C by current passage, immersion in resin while continuing to heat the unit (gelation in immersion), and baking for 20-40 minutes at 130-160°C by Joule effect.

The resin is kept in continuous recirculation and cooled to 10-15°C.

Finally, a UV surface cross-linking cycle is performed to harden the resin on metal, cables, tubes, and all other components that have not reached the resin polymerization temperature because they are not sensitive to heating by current passage.

The main advantage of this method is achieving a result similar to drop-by-drop or rolling impregnation on large units (up to 800-1000 kg in weight).

Miotti specializes in offering its clients qualified consulting services regarding products and impregnation methodologies for electric machines. To know which impregnation type is most suitable for your units, contact us.