What material is used as insulation between the commutator and the armature shaft?

Mica is commonly used as insulation between the commutator and the armature shaft due to its excellent electrical insulating properties and thermal stability. It can withstand high temperatures and has low electrical conductivity, which is essential in preventing short circuits and ensuring the efficient operation of the motor. Mica is also durable and can handle the mechanical stresses that occur in electric machines, making it an ideal choice for this application.

While materials like copper, rubber, and plastic have their own uses in electrical and mechanical contexts, they do not provide the specific combination of high insulation resistance and thermal endurance necessary for the insulation between a commutator and an armature shaft. Copper, for instance, is a conductor used in windings rather than insulators, and rubber and plastic may not withstand the same operational temperature ranges or mechanical stresses as mica does in this particular application.