BMI-Modified Epoxy Resin and Its Application in an F-Class Simulated Pole Winding Structure

Conventional epoxy adhesives used in motor insulation structures still suffer from insufficient thermal resistance and difficulty in balancing heat resistance with mechanical reliability. In this study, BMI-modified E-51/MeHHPA/EMI-24 epoxy composites were prepared and evaluated as heat-resistant interfacial adhesives for simulated F-class pole windings. BMI/EP composites with different BMI contents were fabricated by melt blending and characterized in terms of curing kinetics, FTIR, mechanical properties, and thermal performance. The optimized formulation was then applied to bond Nomex insulation paper to the upright plate in a simulated pole winding. The results showed that BMI did not alter the main epoxy/anhydride curing pathway, but restricted segmental motion and improved thermal resistance. The 10phr BMI/EP composite exhibited a favorable balance among thermal performance, mechanical properties, and fracture morphology. The simulated winding prepared with this formulation showed no breakdown or flashover under 6800 V/60 s, with an insulation resistance of 64.49 GΩ. A lower-bound apparent temperature index of approximately 157 °C was obtained using the TGA-derived thermal life equation. These results indicate that this system has preliminary application potential as a heat-resistant interfacial adhesive for F-class motor winding insulation, although a complete thermal life assessment is still required.