What is the primary material commonly used for the yoke in a DC machine?

The primary material commonly used for the yoke in a DC machine is steel. The yoke serves as the outer frame of the machine and provides structural support, while also forming part of the magnetic circuit. Steel is favored due to its excellent magnetic properties, which enhance the machine's efficiency by reducing magnetic losses. Moreover, steel is robust and can withstand the mechanical stresses present in the machine during operation.

In contrast, aluminum is lighter but does not have the same magnetic permeability as steel, making it less effective for this application. Copper, while having great electrical conductivity, is not suitable for the yoke since it is not magnetic and would not effectively contribute to the magnetic circuit. Iron, although a magnetic material, is often less desirable compared to steel due to its susceptibility to rust and lower tensile strength. Thus, steel combines the necessary magnetic properties and durability, making it the material of choice for the yoke in DC machines.