Motion System Design
Without a scratch

Without a scratch

Heavy-duty idlers help save galvanized steel strip from damage.

WCI Steel Inc., based in Warren, Ohio, is a flat-rolled steel producer specializing in custom carbon, alloy, and electrical steel products. The company offers approximately 185 grades of high-quality steel used by strip converters, steel service centers, electrical equipment manufacturers, and the automotive and construction industries.

Part of WCI Steel’s coated products facility is a hot-dip galvanizing line, where the steel is coated with zinc for long-lasting corrosion protection. Steel entering the line is first cleaned to ensure a uniform coating before it enters the molten zinc coating bath. After the finish is applied, the strip enters a cooling tower where the coating solidifies. The strip is then flattened and coiled.

The original idlers supporting the steel strip through the hot-dip galvanized line were heavy and hard to turn. The standard ball bearings couldn’t withstand the high loads of the application, and lubrication was difficult. Though replacement would be costly, WCI Steel had to remove the bad rollers, which would often freeze up and scratch the strip.

Rexnord Industries Inc., Milwaukee, suggested permanently lubricated dual-row idlers with roller bearings that provide greater capacity. The new idlers turn freely to prevent product damage. The individual rollers also have lower inertia and turn easier when strip isn’t aligned flat as it comes through the line. In addition, replacement is essentially a drop-in process, reducing downtime. Rexnord designed four different idler sizes and styles, using as many standard components as possible to keep costs down. The designs were developed to fit into the existing galvanizing lines with little modification. In one case, the width of the idler section was split into two rollers for easy replacement and to reduce inertia.

While designing the new replacements, spacing was also revised. Before, they were on 3-ft centers, but with the new idlers, they were moved to 6 to 8-ft centers, reducing the number of rolls required.

For more information: Rexnord Industries Inc.

(414) 643-3000

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