The Yoke in a DC machine
The function of a Yoke in a DC machine is twofold. The yoke acts as path for the magnetic flux. It also provides mechanical support and shape to the dc machine.
As it is a path for the magnetic flux, the yoke should be made only of a magnetic material.
The Yoke is usually made of cast iron, forged steel or cast steel. In certain large machines, the yoke is made of two pieces which are bolted together.