The steel shapes are transported through the mill on a series of powered rollers as they move from one production process to another. The rollers and their drive systems are subjected to heat, impact loads, mill scale and water. Under these conditions, maintenance planners look for simple yet rugged mechanical components that are easy to install and maintain. By standardizing on a single family of speed reducers, Nucor-Yamato Steel can replace any one of the hundreds of roll drives in its mill quickly with the exact ratio it needs. Using a few sizes of the same configuration, the company can make fast replacements without the need for extensive alignment, yet the drives last several times longer than the units they replaced.
To power the many roll applications in the Blytheville mill, Nucor-Yamato uses literally hundreds of Rex Planetgear reducers, made by Rexnord Industries, Inc., based in Milwaukee, WI. Rexnord's power-transmission products are also used in food and beverage processing, mining and quarrying, forest, pulp, and paper products, construction equipment, hydrocarbon processing, and cement and bulk material handling. "We've been using the Planetgear drives for as long as seven years in some applications," says maintenance planner Stacy Bullard. "With them, we don't have alignment problems, because they couple up directly between the motor and the driveshaft."
Bullard says the drives are used throughout the mill on caster rolls, both sides of the reheat, the descaler, finishing and many other areas. Bullard says it is easier and faster to change ratios so they can get the ratios they need with the Planetgear design than with conventional gearboxes. With a basic stock, a local distributor can simply change ratios and have the right gearbox there very quickly.
To extend drive-component life under the extreme operating conditions, the company has added driveshafts between some of the rolls and the drives. "We moved a lot of the drives back so they aren't right on the ends of the rolls," says Bullard explains. "They are about 10 feet away now, because we put driveshafts on them so the driveshafts would take the beating."
For some applications, Nucor-Yamato changes the Planetgear drives to a C-face mounting. Bullard says this is done in areas where there is a lot of shock, making a scoop-base mount less reliable. Using a C-face conversion kit supplied by Rexnord simplifies the switch.
Bullard is pleased that the Rexnord drives typically last two to three times as long as the less-rugged units they replaced. "I think the reversing action of the mills is what destroyed some of the old drives," says Bullard, "but the Planetgears hold up to that."
Several Rex Planetgear drives are visible (above, center) during a maintenance shutdown at the Nucor-Yamato steel mill.