The role of the contactor, ac contactor and the characteristics of the dc contactor

What is the role of the contactor? According to the structure characteristics of how to distinguish between ac and dc contactor? Contactor's role is to control the motor start-stop, positive &negative, braking and speed adjustment, etc. Ac contactor core with silicon steel sheet pile of riveting, and its excitation coil with skeleton, isolation and will make iron core and coil type coil made short and thick stout, this is advantageous to the core and coil heat dissipation. Core of dc contactor usually use whole piece of pure iron into steel or engineering, and its high excitation coil is made of tall and thin, and do not set the coil skeleton, so direct contact with the coil and iron core, easy to heat dissipation.