Windsor Coal Mine's Downtime Dwindles with Installation of New Drives
 An aging conveyor belt conveyor drive system was proving costly for West Virginia's Windsor
Coal Company. The once reliable controlled-start drives, used to power 6.5 miles of the
mainline conveyor belt system that transports raw coal from underground mining operations to
the preparation plant, had begun to show signs of wear. The dry-brake, planetary-gear drives,
after more than 10 years in operation, were requiring more and more scheduled and unscheduled
maintenance. "This system was originally configured to handle between 1,000- and
1,200-tons-per-hour- capacity. Four years ago, that number jumped up to 2,000 tph when we
incorporated longwall mining operations," reports Steve Wheatley, senior mechanical
engineer for American Electric Power, the utility company that owns the Beech Bottom-based
Windsor Coal. "We've had to put more and more horsepower into these belt-drives to keep up
with the loads, which has only accelerated the wear on them."
In a situation where continuous operations are a goal, any unscheduled shutdowns, due to
equipment failure, can result in significant financial losses. After assessing the
situation, Windsor Coal officials determined they didn't want to spend any more money or
man hours trying to keep up with the failing belt drive system. "We were a little short on
dollars and a lot short on man hours,"Wheatley reported. "We asked ourselves,
'What could we do to help ourselves?' We needed to reallocate manpower and we needed a
solution that could fix the drive problem once and for all, and fast."
Windsor officials approached their problems by developing a few options. Their goal,
according to Wheatley, was to upgrade the conveyor system to ensure highly reliable drive
system operation, thus reducing both scheduled and unscheduled maintenance costs, while
maintaining the current system's "controlled start" capabilities. A repair/rebuild option
was quickly dismissed when officials realized that the cost was just about the same as buying
new, and there were no guarantees that the maintenance problems wouldn't soon return. In the
end, the option selected was to upgrade the belt conveyor system with new drives.
One option, mine officials considered, was to buy the same brand of drives already being
used. Despite the old system's somewhat troublesome nature, engineers liked they way it
consistently provided smooth start-ups (via an electromechanical soft-start device).
"Whatever option we selected, we knew we couldn't afford to have anything less than a soft
start," said Jack Earnest, the mine's maintenance superintendent. "A hard start at these
horsepowers would really tear up these belts and connected drive system equipment."
The electromechanical soft-start employed an electrohydraulic control for actuating a
caliper disc brake within a planetary gear reducer for soft conveyor starts. However, they
are complex and require a considerable amount of scheduled and unscheduled maintenance. Many
electrohydraulic units require diligent maintenance checks on a frequent basis by
highly-skilled maintenance personnel. At Windsor, officials were finding that the excessive
maintenance was sapping manpower and costing the mine more and more money in repairs.
Company officials decided to identify what drive stations needed the most attention. Belt
drives that were most underpowered and drives that had the longest history of maintenance
problems were specified for replacement. The next step was to determine what to replace those
drives with. "In addition to looking at our existing brand, we looked at other drive
suppliers, including the Falk brand," Wheatley said. "We wanted a system that could be relied on and
that would always provide us a smooth start-up. Additionally, we needed a system we could
install with as little downtime and manpower as possible, and something we could afford.
That's what really narrowed it down for us."
An associate of Wheatley's explored competing systems including the Falk Alignment-Free
Drive? system. These right-angled, shaft-mounted drives, Wheatley learned, required no
special shaft alignment or foundation requirements because the gear drive mounted directly
to the conveyor pulley shaft. With simple, bolt-on mounting connections, the alignment-free
drive installations would be easier and take less time than a conventional drive.
Additionally, installation costs would be minimized, since a foundation isn't required.
Conventional conveyor belt drive configurations consist of a foot-mounted motor, gear
drive and shaft couplings, all foundation-mounted on a common bed-plate and aligned with
the conveyor pulley shaft. By its nature, heavy-duty conveying can subject such a system to
operational stresses that can lead to misalignment. Heavy loads, rough starts, the movement
of earth can all affect drive system components. Equipment misalignment is one of the leading
causes of conventional drive system failures.
Other variables of a conventional drive system are also problematic. For example, the cost
of constructing a foundation can account for 10 to 15 percent of the initial cost of a drive
system. And, in many applications, this cost will be repeated as operations shift and
conveyors are relocated, requiring new foundations. "We also looked at maintenance
requirements and factored them into overall 'lifetime' system costs," Wheatley said.
Because the Falk drives are alignment-free, they are unaffected by ground movement and
shifts. This eliminates the leading cause of drive system downtime. Companies don't have to
conduct scheduled or unscheduled maintenance due to alignment problems. Recommended
periodic maintenance is limited to checking oil levels, lubrication of grease-purged seals
and torque-arm bearings, and occasional oil analysis. Another appealing feature of the
alignment-free drive was the exclusive Magnum™ Seal, which also plays a role in reducing maintenance costs and downtime, by keeping the oil in and the contaminants out. That's an important consideration because oil leaks are a major source of drive failures. And with Falk fluid
couplings as accessory components in the drive system, Windsor's soft-start requirements were
met. A dependable conveyor soft-start control device is critical to preserving optimum
conveyor system performance. Without a controlled acceleration at startup, belts are
susceptible to breakage and shock loads, which can carry through the system and affect all
connected equipment.
To fulfill the soft-start requirements of the conveyor, a Falk True
Torque series extended-start
fluid coupling was specified for Windsor. Fluid couplings offer the same soft-start
capabilities as the more complex, Talk's soft-start devices, but without the
maintenance and safety concerns. There is practically no maintenance involved. With fluid
couplings, the mine gets soft starts, higher availability on its conveyors, less maintenance
time, and less cleanup. Fluid couplings effectively control torque during equipment startup.
The coupling's extended delay-fill chamber and improved circuit design provides a softer
start by applying initial starting torques as low as 40 percent of full-load power and
lengthening the torque build-up time. Typical no-load starts range from 10 to 20 seconds, and
full-load starts range from 20 to 50 seconds. With a fluid coupling, the torque delivered to
the driven machine starts at zero and gradually increases as the coupling's runner is
accelerated by the impeller.
Fluid couplings are a low-maintenance, reliable alternative to fulfill soft-start
requirements. In addition to reliability and less maintenance, there also is a safety
advantage with fluid couplings. With the fixed-fill fluid coupling, the caliper brake, a
possible heat source on the Talk's unit, is eliminated.
With a need for a reliable and cost-effective drive, Windsor Coal ordered 10 of the Falk
Alignment-Free Drive systems (nine to replace existing drives and one for reserve -- a
spare). Each of the drives is powered by a 300-hp (224 kW) Reliance AC electric motor. The
1750- rpm motor is flange-mounted to the Alignment-Free drive package and connected to the
drive through fluid coupling. With an output shaft speed at 82.2 rpm, the drive's reduction
ratio is 21.28:1. Each drive produces 230,018 lb.-in. (25,990 Nm) output torque. All but
three drive stations on the mainline conveyor system include two of the 300-hp Alignment-Free
Drive configurations (the remaining three are single-drive stations).
The motor is flange-mounted directly to create an inherent equipment alignment. The gear
drive output connection to the conveyor system is made via a flange-moment coupling. The gear
drive output shaft and the conveyor shaft are brought into alignment as the bolts on the
register fit are tightened. The entire drive assembly is supported by the conveyor
pulley-shaft and torque-arm reaction point. Because the drives were installed over a series
of weekends (from January to June), no production was lost. "We began at the end of the
Friday evening shift -- just after midnight -- and finished the job in time to begin
production again that Sunday at midnight," Wheatley said. "Three shifts on Saturday, three
shifts on Sunday was all it took for each drive station.
The installation is as easy as hanging the entire drive system on the pulley, wiring the
motor and pinning the torque arm. No alignment procedures were necessary. The drives were
alignment-free in two respects. The drives did not require motor-to-gear drive or gear
drive-to-conveyor alignment. In each case, an articulating arm was the only foundation
attachment that was needed. Wheatley estimated that by installing the alignment-free drives,
the company shaved about 40 percent off the typical installation time. For the past year,
each Falk Alignment-Free Gear Drive System has worked problem-free. "This has enabled us to
reallocate our maintenance NM and increase our belt availability by at least 10
percent," Wheatley said.
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