Genstar Stone Products Upgrades Key Conveyor Drive System
Baltimore, Maryland in the United States -- Replacing the drive system
on a critical plant conveyor is often seen as time consuming and expensive
downtime. Genstar Stone Products Co., the top producer of stone and
gravel in the Baltimore-metro area, embraced the scheduled downtime
as an opportunity to improve its future uptime.
A new, more durable gear drive with more than double the service factor
was installed on Genstar's C1 conveyor after predictive maintenance
tests forecast impending failure of the existing unit. Motor horsepower
rating and conveyor speed also received a boost during the changeover.
Genstar's new drive system powers a vital conveyor -- the only conveyor
hauling stone out of the pit. The 1,000 ft, 42-in. wide C1 conveyor
moves 3 million tons of stone per year from the quarry at a rate of
2,000 tons per hour. It feeds 50 additional conveyors and three crushers
that produce stone products from minus 7 inch to trap sand (10 mesh).
Key components of the drive system include a Falk right angle, hollow
shaft triple reduction gear drive with 34.47:1 ratio and 1,317 hp capacity;
a Ringfedder shrink disc shaft-hub locking device; and a 500 horsepower,
1,750 rpm General Electric motor.
The Falk gear drive produces an output speed of 50.77 rpm and delivers
621,000 in. lbs. torque. Other components include a Falk fluid coupling
and a Falk True Hold low-speed backstop, from the original system.
"We could probably double the size of the conveyor and still use the
new drive," says Maintenance Foreman Steve Killon. "The gear drive was
sized with present and future demands in mind."
Components of the old system, on the other hand, could not meet growth
expectations. The drive package was installed in 1987 as part of a project
to extend the C1 conveyor length. It replaced a drive system, with a
parallel shaft gear drive, that had been in operation since 1953. The
goal of the upgrade was to increase hourly tonnage from 1,200 tph to
2,000 tph.
"When we extended the conveyor in 1987, we went with a right angle
drive for a more compact package," Killon remembers. "But it didn't
meet the tonnage we were trying to bring up the hill."
The 1987 conveyor system struggled to pull 1,200 tons per hour from
the pit, and a low 1.25 service factor on the gear drive prevented any
significant increases in production rates.
Damaging Failure
Less than two years after the system was installed, the backstop failed,
allowing the belt to run backwards. Operating in reverse, the gear drive
became a speed increaser.
As the reverse speed increased, the fluid coupling exploded, sending
softball-sized pieces of the coupling through the roof, some landing
300 yards from the building. The shaft of the 400 hp Westinghouse motor
was bent beyond repair.
A new 400 hp motor, a Falk fluid coupling and True Hold backstop were
installed on the old gear drive. However, Dan Connell, Genstar vice-president
of engineering, was already working to find a more suitable, long-term
replacement since consistent operating temperature over 200 degrees
F gave warning of impending problems.
"Through our experience, we knew that anything that runs that hot eventually
lays down," says Killon of the ailing gear drive.
Eventually, the new drive system, including reducer, bedplate with
torque arm, motor, fluid coupling, pulley, headshaft, and bearings were
brought together at Genstar and preassembled on the ground. A crane
hoisted the entire 15-ton system 100 feet into place. The Falk True
Hold backstop from the old system was incorporated into the new package.
"Without cutting the conveyor belt, the new system was installed and
operational within five days," Killon says of the changeover which was
completed in January during a slow production period. More importantly,
it solved several old headaches and allows for significant expansion. "Engineering
wanted a long-term fix," Killon adds.
Meeting Future Goals
The hollow shaft right angle drive met several key long-term goals,
including accommodating future conveyor expansion.
First, a high 2.63 service factor provides a comfortable margin that
will permit the gear drive to be utilized in expanding the conveyor
to more than double its size.
"We could retrofit the system with a 1,000 hp motor and still use this
new gear drive," notes Killon. "We specified it with such a high service
factor because we want to utilize the drive in the future when we run
a longer conveyor out of the quarry."
Secondly, the keyless fit and use of a Ringfedder shrink disc shaft-hub
locking device will make future change outs and upgrades faster and easier.
"When the time comes to take the drive off to replace the bearings
or pulley, it will be a matter of letting the Ringfedder loose and moving
the drive off the shaft," says Killon. "In terms of downtime, this could
mean a significant savings."
The shrink disc is an external shaft hub locking device installed over
a turned down hub shank. By tightening the locking screws, the locking
collars exert clamping force on the tapered inner ring and hub, creating
a mechanical shrink fit connection.
Such an arrangement comes as a welcome change to Genstar crews, who
are used to struggling to remove gear drives with keyed shafts.
Notes Killon: "With a keyed unit, you literally end up disassembling
the unit right on the shaft. In some cases, you end up totaling the
unit."
Other features of the system include a thermostatically controlled
cooling fan. Also, temperature gauges allow crews to closely monitor
the operating temperature of the gear drive.
Finally, Genstar expects parts availability to save time during downtime.
"One of the reasons we chose this drive system is parts availability,"
Killon notes. "With some manufactures, a model might only take ½ a
day to rebuild but 13 weeks to get parts!"
Meeting Expansion Goals
All of the modifications to the drive system come as the company is
poised to expand its production. A new rail system at Genstar runs aggregate
to their recently acquired concrete and blacktop plant in Waldorf, MD.
In the past, Genstar would move stone using 18-ton capacity trucks.
Railcars hold up to 100 tons per car and can usually complete the shipment
in less time and expense.
"Our concern is about meeting the demands of our new shipping capacity.
We'll need increased conveyor capacity to move that additional 5,000
tons of stone per week," Killon says.
By upgrading its system during scheduled downtime, Genstar's conveyor
system should see the company through this latest expansion and any
more in the years to come.
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