Rexnord® Omega™ Couplings Keep Coeurs Mine Crushers Operating
CASE STUDY
The Coeur Rochester, Inc. precious metals mine near Lovelock, Nevada, has almost eliminated downtime for coupling replacement and minimized wear on speed reducer bearings and seals by replacing jaw-type couplings with Omega split bonded elastomer couplings. The Omega couplings absorb vibration and misalignment and make it easier to install or replace the equipment they connect.
The mine is about two hours northeast of Reno, at an altitude approaching 6,000 feet. Silver and gold ore go through a series of crushers that reduces material size from 8-inch at the primary crusher to 3/8" in four tertiary crushers. Temperatures can drop to -20º F in winter and soar as high as 120º F in summer, with a climate that can range from bone dry to very wet.
All crushers are Symons cone crushers, including one 7-ft. standard and four 7-ft. shortheads. Because proper lubrication is essential to keep them running under heavy loads and difficult operating conditions, a positive-displacement pump supplies lubricant to each crusher and provides instant pressure during operation. A 5 hp electric motor drives each pump through a 25:1 in-line speed reducer. One coupling connects the 1775 rpm motor to the input side of the speed reducer with one coupling, while another joins the reducer to the pump. On the output end, speed is reduced to about 70 rpm with a corresponding increase in torque, so a higher capacity coupling and larger diameter shaft are used.
Aerial view of the Coeur Rochester mine near Lovelock, NV
The original metal jaw-type couplings accommodated up to 1º angular misalignment and absorbed some vibration when new. However, they only lasted four to five months until their rubber spiders failed or disintegrated, according to John Murphy, mobile equipment/crusher superintendent. Then, Murphy says, the resulting metal-to-metal contact created excessive vibration that damaged several speed reducers, pumps, and motors.
Downtime costs were excessive. “In a low-grade, high-tonnage operation like this, we lose thousands of dollars an hour on each system if we’re down,” explains Murphy. “You can’t run the crusher without lubrication, and if we have to replace a coupling every four months, it adds up to thousands of dollars very quickly.”
Instead, Murphy replaced the jaw couplings with Rexnord Omega couplings, which combine flexibility with strength and durability. These split-in-half flexible polyurethane couplings consist of only two hubs and two half-elements. The non-lubricated, material-flexing couplings incorporate torsionally soft flex elements to protect connected equipment by cushioning shock loads, reducing torsional vibration, and absorbing up to 4º of angular misalignment.
Omega couplings shown on this 5 hp electric motor
through an in-line reducer to the lubrication pump
At last report, the original Omega units were running more than three years after installation without incident, compared to the four-month average life of the previous couplings. In case of a mishap, the Omega coupling would protect the connected equipment by a “soft” failure in which the coupling element separates instead of transmitting damaging forces.
Savings have been dramatic. “It’s a maintenance item that’s been eliminated,” Murphy says. Savings also extend to lower failure rates on pumps, reducers and motors. Murphy has seen a reduced level of problems with these components and their bearings and seals.
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4-104CP/8-17-2000
4-154-104CS/9-27-03
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