Rexnord® Omega™ Couplings Absorb Tunnel-furnace Shocks at Nucor Steel
CASE STUDY
At Nucor Steel’s mill in Crawfordsville, Indiana, routine downtime has been cut and maintenance expenses have been reduced by using Rexnord Omega couplings to connect roller shafts and gears along the facility’s tunnel furnace. The mini-mill produces up to 20,000 tons/week of premium steel from scrap. The heart of the facility’s thin-slab process is a continuous caster and tunnel furnace made in Germany. Temperatures inside the furnace reach as high as 2000° F, while temperatures on motors and couplings outside the furnace can go up to 150° F.
During the mill’s regular, 12-hour weekly maintenance shutdown, it isn’t unusual to replace as many as 20 of the 169 rollers in the tunnel furnace. The changeover could be time-consuming if not for the Rexnord Omega E-40 couplings between the drive motors and rollers, according to Von L. Baum, maintenance supervisor at Nucor. He says the couplings are so easy to disconnect and reconnect that roller changes are a snap, rarely requiring more than 45 minutes per roller.
To replace a roller, cap screws are first removed to free the roller shaft. On the opposite side of the furnace, water hoses are disconnected, the bearing block loosened, and furnace insulation is removed. Then the roller is pulled out and a new or rebuilt one is pushed into place. The procedure is reversed for installation. The crew simply bolts the two coupling half elements to hubs on the drive and driven shafts, with almost no alignment required.
The couplings include reversible hubs, premium-grade cap screws, and a flex element consisting of two half-elements of tough polyurethane material bonded to steel shoes that fit directly over the hub on each shaft. The torsionally soft urethane flex element not only accepts misalignment but also reduces shock loads, vibration and noise.
The real test of the coupling occurs when the operator puts the roll table into the oscillating mode, slowly moving the slab back and forth near the end of the tunnel to raise its temperature. During this procedure, the 3/4 HP and 1 HP motors, which normally run at 1,175 RPM, are reduced to about 300 RPM, placing a great deal of torque on the couplings when they reverse. Although the operation can be tough on gearboxes, the flexible couplings absorb most of the shock, and the gearboxes survive very well.
There is no need to disassemble the couplings for inspections, which can be performed visually. The elements can even be inspected on the fly using a strobe light. Since no lubrication is required, maintenance costs are low. Also, by reducing vibration, the Omega couplings save wear and tear on the entire system. The flexible polyurethane element cushions shock loads and accommodates up to 4-degree angular or 1/8-inch parallel misalignment, which protects connected equipment.
Nearly 170 Rexnord Omega couplings join motor/gearbox
units to roller shafts on the tunnel furnace at
Nucor’s Crawfordsville, Indiana mini-mill
“These are relatively inexpensive couplings,” says Baum, “but their great value to us is in time saved through fast disconnect/reconnect for roller replacements. They are perfect for our application because they contribute to production uptime.”
NOTE: This application has been featured in articles that appeared in Iron Age, Industrial Maintenance & Plant Operation, and New Steel
CAPTION INFORMATION:
4-154-NucorCS/12-11-03
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