Application of Permanent Magnet DC Motors at Republic Steel´s 84-in Hot Strip Mill

Modern magnetic materials of the Alnico® type have made it practical to build dc motors in larger sizes with permanent magnet fields. The motor manufacturers now market motors to 100 hp at 230-V dc with dimensions, speeds, horsepower ratings, and other characteristics equivalent to the Association of Iron and Steel Engineers (AISE) Standard Mill Type Motors. Previously, smaller motors of this type have come into common usage as table motors. The first large-scale industrial application of these larger motors was at Republic Steel´s 84-in hot strip mill in Cleveland, Ohio. This paper reviews the application of these motors on this mill. It discusses application limitations based on design characteristics, the economics of their use, and their performance and service.