Commutator Mica Sheets are made of natural muscovite mica splittings bonded with a minimum amount of resins in compact, dense and rigid flat plates by means of multiple high temperature pressing primarily for use as insulation between copper segments or bars of commutators used in traction motors as well as other electric motors and turbo-generators. The resin is cured for several hours at high temperature to preclude any oozing or slippage of the mica. The natural cohesive forces between the mica platelets combined with the bonding strength of the rigid thermosetting binder makes these plates adequately resistant to high heat and pressure encountered in the commutators. These plates have high dielectric strength, high thermal stability, good voltage endurance and excellent mechanical and electrical properties. Besides they have extremely low compressibility as is essential in maintaining the commutator's dimensional stability under large centrifugal stresses in operation. Their other properties are smooth surfaces, uniform thickness, great resistance to crushing and excellent machinability. Commutator mica sheets bonded with shellac resins provide excellent overall properties. Epoxy and alkyd yield dimensional stability with ability to withstand extreme compression stress.
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