Analysis of ignitron rectifiers for reversing-mill drives

A REVERSING-MILL DRIVE for rolling-mill service for rolling blooms, slabs, or plates requires application of d-c motors operated under a special load cycle. The motor must be started, accelerated, operated under load, and decelerated many times as the metal which is being rolled is passed back and forth through the rolls. On alternate passes the motor is operated in the reverse direction. The time required for each pass is a few seconds. Typical motor ratings range from about 3,000 hp (horsepower) to about 12,000 hp. The required time for a speed change from base speed in the forward direction to base speed in the reverse direction is about 1 to 2 seconds. Several recent applications of this type have been built with a reversal time of 1 second.