Dual Motor Drives & Housings
The main advantage of a dual motor drive is that each work roll is individually driven. If one roll gets damaged and needs to be ground down, the other roll does not have to be ground down to the same diameter. This allows each motor drive to compensate for the different diameters. If they are geared together in a pinion stand with one motor, and one roll is damaged, both rolls must be ground down to the same diameter; otherwise, one roll will rotate faster than the other. This is a big advantage because rolls that have to be ground in pairs increase the maintenance cost. Also, with a pinion stand, if the roll sets get mixed up in inventory, you will have a different peripheral speed and this creates a tremendous load on the universals or spindles and gears.
Housings
Housings can be made from forged steel and 100% welded. Housings can be made quickly without waiting for patterns and castings. Many old cast iron housings were extremely heavy, as they were not forged, and due to inherent imperfections during the casting process, had to be twice as large as a superior forged housing. The housings had to be made very heavy because of the possibility of cracking. This is very common with large cast housing. In my 60 years of building rolling mills, I have never heard of a cast housing breaking. The stresses the housings are under are extremely low, especially on older rolling mills. Also, old mills did not have automatic gauge control. They tried to make the housings extremely stiff to prevent elongation to get a uniform thickness coming out of the rolling mill. Older rolling mills have mechanical screwdowns where today we use hydraulic screwdowns.
