Tuesday, April 28, 2015

Coupling Failures on Steel Mill Tables

The failure

A leading Midwest steel mill plant was constantly replacing tire couplings on runout tables. Needless to say, the amount of time required for maintenance was becoming unmanageable.

The equipment and environment

This particular hot strip mill plant produces a coiled steel rolls commonly used to form large kitchen appliances and automobiles.  Runout tables, containing hundredths of rollers, move steel slabs along the shaping process. Each roller uses a tire coupling that attached to a motor, which turns the roll.

High misalignment and a lower service factor between motor and roll can cause high failure rates on the tire couplings.  In addition, each tire coupling has several component fasteners that require tools to change the element. The design of the tire coupling makes it susceptible to corrosion from the heat, water, and slag associated with a runout table application.

The steel mill plant had a dedicated maintenance team to replace the large quantities of tire couplings every month. The high replacement part cost, increased maintenance time and resources required to maintain the tire couplings was prohibitive.

The solution

After a fact-finding visit to the hot strip mill plant, the Lovejoy Engineering Team analyzed the situation and presented an effective solution.

The team addressed three core runout table failures:
1) Tire coupling slipping
2) Heat, water, and slag damages
3) Inefficient inspection process.

The recommended solution was to replace all tire couplings with the Lovejoy’s Jaw In-Shear 6 Pin (JIS) couplings.  The Jaw In-Shear 6 Pin coupling is made up of a standard L-type jaw coupling, a radially assembled element, and stainless steel locking ring.

With its effective locking mechanism, the JIS coupling eliminated the slipping issue.  The stainless steel locking ring provided the element with protection from heat, water, and slag. Lastly, the ease of simple visual inspection and quick change-out, made the JIS the most effective solution.

In the end, failures were reduced to a minimum.  The dedicated plant maintenance team could now refocus its attention on other critical areas in the mill.  Furthermore, this solution brought in a 33% cost savings per coupling.

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