In the mining industry, nothing about it is small – not the machines, parts or costs of a recurring problem in the operation.
When asked to identify a significant problem at the mine site, Kelvin Kennedy, dragline & shovel maintenance coordinator for Kennecott Energy, took Timken associates two stories deep to the belly of a dragline at Cordero Rojo mine. What he showed them was one of six lower swing bearings supporting the swing shaft pinions that pivot the 15 million pound dragline. The bearing in each position is critical to the dragline’s ability to remove tons of earth covering the vein of coal running through Kennecott ’s Powder River Basin operation.
Plagued with a problem of leaking lubrication, Kennecott’s problem with the lower swing bearings was three-fold: premature bearing failure, potential damage risks to the swing rack, and excess grease usage and disposal costs.
“Multiple and premature bearing failures of the lower swing shaft bearings were an ongoing cost and maintenance problem at the mine,” Kennedy said. “So we turned to Timken for its innovative designs to improve the product.”
PROBLEMATIC DESIGN
The life of the standard lower swing bearings ranged from 5,000 to 40,000 hours, based on 6,000 hours of usage per year. With such a wide range, the unexpected failures were detrimental to production. The cause was improper and inadequate lubrication for the slow, reversing rotation and high loads placed on this vertical shaft bearing position.
Repairs on the dragline are not only costly, but detrimental to production. Kennecott reported costs up to $12,000 per hour for loss of production cost when a dragline needed to be shut down for repairs.
In addition to frequent bearing replacement costs, the purged lubricant would leak onto the pinion, swing rack and tub. This bearing grease leaked onto an important swing rack gear of the dragline, wiping off the open gear lube and causing damage to a costly gear nearly 50 feet in diameter. Finally, the leakage resulted in additional grease clean up and disposal costs. Considering that each of the six swing shaft bearings may use up to 50 gallons of lubrication each year, the sealed bearing solution provides thousands of dollars in savings in grease replenishing and disposal costs each year compared to the standard lower swing bearings.
FINDING A SOLUTION
To address the problems with this application, Timken designed a sealed lower swing assembly – complete with a spherical roller bearing, seals and grease.
Each bearing assembly weighs 1,600 pounds and has an outside diameter of nearly three feet and a width of nearly two feet. Designed specifically for the lower swing position of the Marion 8750 dragline, it fits into the space of the standard bearing and labyrinth seals without any retro-fitting.
The new seals and bearing are integrated in a single unit and use a special-purpose grease. This patented technology keeps the lubrication in the bearing cavity without requiring frequent lubrication.
“They were aggressive in the redesign and delivery schedule,” said Kennedy. “Not only has this work improved installation and operations, but our relationship with Timken has also led to better handling and assembly techniques overall.”
Now in place on two draglines at Kennecott, the sealed lower swing assembly provides piece of mind. The new design eliminates the need to grease, eliminates grease clean up and disposal, and has reduced surprise failures. Kennecott says they are a long term customer thanks to the superior customer service and quality provided by the Timken team.
Kennecott Energy Company, headquartered in Gillette, Wyo., provides approximately six percent of the nation’s electricity and is one of the largest low sulfur coal producers in the United States. Affiliated with the Rio Tinto group of companies who are leaders in finding, extracting and processing mineral resources, Kennecott Energy is among the safest and most efficient energy producers in the world and operates five western U.S. coal mines: Antelope, Cordero Rojo, Jacobs Ranch, Spring Creek in the Powder River Basin of Wyoming and Montana, as well as the Colowyo Mine in Colorado.