Yates hoist bushing change done in a day

Giving ourselves a little license for hyperbole, we could argue that our entire project is held together with 12 bolts.

Those 12 bolts fasten a large steel component called a ?spider? to the clutch in the cage hoist the Yates Shaft. Without the clutch, the hoist won?t operate, and without the secondary access afforded by the Yates Shaft, work must stop underground.

Work did stop today, but only because of planned maintenance. An Operations Department crew is replacing the drum bushings in the Yates hoist. Facilities Technician Kevin Becker, who has 30 years? experience working on these hoists, explained the work.

The bushings, three per drum, are part of the complex drive trains on both the Ross and Yates hoists, Becker said. The bushings, lined with a smooth tin and lead alloy called ?babbitt,? allow the hoist?s shaft to rotate freely, absorbing the wear and tear that would otherwise be inflicted on the rotating shaft. Bushing have to be replaced from time to time, and it?s a big job. Each bushing weights more than 500 pounds. ?Everything?s big on these hoists?even the tools,? Becker said. The crew used an electric hoist to remove the old bushings and lower new ones into place, then they used a 50-ton hydraulic ram to slide them into place. 

The ?spiders??so named because of their radiating steel arms?also are part of the drive train, which converts energy from two 1,250 horsepower DC motors into the turning power to raise and lower the cage hoist.

The two motors turn pinion gears that, in turn, rotate the shafts inside the large over-wind and under-wind drums, each capable of spooling more than 5,000 feet of steel rope. When the hoist is operating, the shafts are always turning, inside those bushings. Large clutches in the drums can disengage the turning shafts from either or both drums. The clutch pinches a steel ring called a ?brake band.? Becker described the mechanism as similar to a disk brake on a car. ?These two clutches do all the work,? Becker said. ?Without them, this is all just junk.? And without the twelve bolts the clutches won?t work.

The hoist also has brakes,  which are lined with spongy basswood. They operate like a car?s drum brakes, except they squeeze in instead of push out. The brakes also are weight-activated, so if the power fails the brakes automatically engage.

Facilities Technician Jeff Essink  led the bushing change this week. Others on the crew included  hoist operators Kelly Bauer and Chris Huber; infrastructure technicians Bill Heisinger, Loren Larson and Derek Lucero; facilities technicians Kevin Ennis, Jason Rath and Richard Reif; and Rope Technician Mike Dropulich. 

Bushings can last for many years. Measurements of wear determine when they must be changed, and the changes can take three days or more. However, as Deep Thoughts is going to press, the crew is finishing the job in a single day. (Underground access will remain restricted Tuesday and Wednesday while other maintenance is performed.)