Electric control for rolling-mill motors

Much has been said regarding the remarkable electrical applications during the last few years in connection with the iron and steel industry, but only those directly interested in this work realize how much impetus has been given to it by the development of suitable controlling apparatus. When A. C. Dinkey, then chief electrician of the Carnegie Steel Homestead works, installed the first electric motor for roll-table service in 1893, he naturally used the standard apparatus of the day, and quite naturally it failed. He immediately sought for something better, especially in controlling apparatus. At that time the only service comparing in severity with that encountered in rolling mills was in electric railway practice; accordingly, the railway motor was rewound for 250 volts and placed in service. In controllers not even temporary satisfaction was found in the devices available, so Mr. Dinkey developed a simple rheostatic controller of the face-plate type. This controller, or one similar to it, together with the rewound railway motor, supplied the demands for about 12 years. Meantime, however, it was found that mill service was much more severe than railway service — more severe in the number of starts and stops per hour, in continuity of service, in lack of intelligent handling, and in the initial temperature of the surrounding atmosphere. It should be said, too, that the penalties of delay in the mill are much higher. If a car in a traction system is put out of service, it can, at the worst, wait and be taken to the car-barn by the following one, without causing essential money loss. But a steel works is unusual in being a manufacturing plant in which there is no reservoir: the material must pass through in an uninterrupted stream; for a delay at any point breaks up the process all along the line, resulting in the derangement of the entire system, much spoiled steel, and consequent loss.