DC machine and its construction parts

A DC machine is an electromechanical energy converter. As a generator it converts mechanical energy into DC electrical energy; as a motor it converts DC electrical energy into mechanical energy. Construction is the same for both.

   Yoke
  +------------------------------+
  |  Pole core + pole shoe  (N)  |
  |   field winding              |
  |      +---------------+       |
  |      | Armature core |<-shaft|
  |      | + winding     |       |
  |      | Commutator    |-brush |
  |      +---------------+       |
  |  Pole core + pole shoe  (S)  |
  +------------------------------+

Main parts:

1. Yoke (frame): the outer cast-iron or cast-steel ring. It supports the poles, carries the return flux and protects the machine.
2. Poles and pole shoes: laminated steel poles bolted to the yoke carry the field winding. The shoe spreads the flux evenly over the air gap and supports the coils.
3. Field winding: coils of insulated copper on the poles; excited with DC to produce the main flux.
4. Armature core: a cylinder of laminated silicon steel with slots, mounted on the shaft. Lamination reduces eddy-current loss.
5. Armature winding: copper conductors in the slots, connected as lap or wave winding, where the emf is induced.
6. Commutator: copper segments insulated by mica, joined to the armature coils. It converts the alternating emf in the armature to unidirectional output (generator) or reverses the current for continuous torque (motor).
7. Brushes and brush gear: carbon or graphite blocks held by springs against the commutator, to collect or supply current.
8. Shaft, bearings and end covers: carry the rotating parts and keep the air gap uniform.
9. Interpoles (optional) improve commutation, and a fan cools the machine.