New Shaft-Mounted Drive Technology
Solves Old Installation/Removal
Headaches
BIRMINGHAM, AL -- A new shaft-mount speed reducer design gave
Vulcan Materials-Dolcito a time-saving option recently when a
twin-tapered shaft-mounted drive needed to be replaced on a
conveyor feeding one of the company's crushers. A shaft-mounted
speed reducer was installed in half the time due to a unique
single-tapered bushing design.
"With the tapered bushing, all we had to do was slide the
bushing onto the shaft," says Maintenance Manager Jerry Champion.
With the bushing in place on the shaft, the speed reducer's
tapered bore was moved into place over the bushing and a threaded
nut and set screw tightened. The bushing design provides a uniform
draw of the speed reducer onto the shaft.
The torque assist TA Taper® bushing is a feature of the
Quadrive®, the newest
Falk shaft-mounted speed reducer. A 7.5 hp motor powers Vulcan Material's Quadrive. The low
speed shaft turns at 70 rpm processing a maximum capacity of 220
tons per hour (tph) while operating at 330 feet per minute on
Vulcan's conveyor with 18-foot pulley shaft centers.
"The Quadrive, with the torque assist taper bushing, is easy
to put on since there is only one key to line up and fewer parts
than a twin-taper design," notes Champion.
"With twin-taper shaft-mounted drives, you have two bushings
and the gear box to line up in one keyway," he adds. "And, there
are six to eight bolts to tighten and line up. This can be very
difficult, especially if you're in a tight spot on an above-ground
platform and pressed for room."
Problems With Straight-Bore Design
Straight bore designs offer no simple solutions, either,
since the shaft has to be in near perfect condition. Says
Champion: "Straight bore drives are difficult to install as well
because you have to be sure that the shaft is clean. And even
then, straight-bore speed reducers, often times, don't go on the
shaft easily."
Vulcan Materials-Dolcito is a subsidiary of Vulcan Materials
Corp., a 36-year-old company with 122 plants across the United
States and Mexico and 1991 sales of $1.7 billion.
Up to 30 conveyors (two of which have pulley shaft centers of
272 feet) move material throughout Vulcan Material-Dolcito. More
than 1.5 million tons of limestone, sand and gravel, and other
lightweight material are processed yearly.
Installing and maintaining quality equipment helps Vulcan
Materials meet its annual production goals. That is why at first
sign a leakage problem was developing, the old shaft-mounted drive
was replaced with the Quadrive.
And, while installation of the unit saved some time, removal
of the shaft-mounted drive with the new bushing is expected to
take far less time compared to other drive designs. The TA Taper
bushing design marks an end to the need for hammering and the
damaging results.
Simplified Removal
The threaded nut set screw is loosened and an optional
removal tool is attached to lock the bushing
nut (standard tools can also be used). When the high-speed shaft
is turned, the drive's mechanical advantage powers the unit free
from the bushing taper.
This will come as welcome relief to Champion who confronted a
host of problems during removal of the twin-taper shaft mounted
drive. While the drive was located in an easily accessible
location (10 feet off the ground), the conveyor hindered
Champion's ability to free the unit from the shaft through
pounding, a common method of drive removal.
"It took us well over an hour to pound off the old unit from
the shaft. It would have taken us much longer if we were higher
up," Champion remembers. "The biggest problem with the twin-taper
design is that you have to wedge the drive off. If you can get the
bushings to move, you've got it. But, a lot of times the bushings
are frozen to the shaft."
In some cases, he adds, a portable power source is required
to push the shaft-mounted drives free. "It's a lot more time
consuming, especially if you are up in the air," Champion notes.
Additionally, the result of pounding or forcing the drive
from the shaft often leads to damaged or ruined equipment, which
doesn't exactly meet the Vulcan Material philosophy of maintaining
equipment.
"The bushings are often ruined. Sometimes the oil seals are
cracked. And, in extreme situations, the speed reducer is damaged
beyond repair," Champion notes.
The Quadrive shaft-mounted drive solved other problems for
Vulcan Materials as well.
"With the Falk unit, we didn't have to worry about shaft
length," adds Champion."The bushing mounts on the back of the
drive, so we had some shaft to play with. With the twin-taper
design, you have to make sure you have enough shaft for both
bushings."
Welcome Change
Plant Manager Welton Hawkins, a 29-year veteran of the
aggregate industry, is impressed with this latest bushing
technology. "I'm amazed at the developments to shaft-mounted speed
reducers within the past 10 years," Hawkins says. "In the past,
every shaft-mounted drive was straight bore. There were no
tapered-bushing designs available for removing a unit economically
and without damage. Now, the time involved in installation and
removal has been greatly reduced."
Champion agrees. "Straight bore shaft-mounted drives make you
struggle to get the drive all the way off the shaft. With the
tapered bushing design, once you get the drive loose from the
bushing taper, it'll pop right off," he says.
As a result of the simplified installation and removal,
Hawkins plans to specify the single-tapered bushing type shaft-
mounted speed reducers on any drives that need to be replaced in
the future.
"My first selection criteria is the single-taper type," he
notes. "I also look for the easiest shaft-mounted drives to
install and remove. And, of course, the drive needs to be the
right size for the application."
Prolonging Equipment Life
In addition, Hawkins studies the service factors of all the
equipment in the plant. In fact, to safeguard against unplanned
downtime, Hawkins frequently orders equipment with capacity up to
20 percent more than required. "If I'm running at close to 220
tph, I know that my equipment can go faster if needed," Hawkins
notes.
He combines this cushion with a rigorous continuous
predictive maintenance program to combat equipment failures. Speed
reducer oil is changed twice a year and oil samples are tested for
any premature bearing wear. Monthly grease purges are also
conducted.
"You could have the best speed reducer in the world and the
bearings could drag it to death due to poor lubrication habits,"
Hawkins says.
Hawkins also follows strict rules for loading the equipment.
"The feed controller has a lot to do with the life of a speed
reducer. Not properly regulating the workload, or splurging, can
ruin a drive," he says.
To date, after six months of operation, the Quadrive single-
taper shaft mounted drive with TA Taper bushings has performed
above expectations. "We haven't had any problems with leaking or
wobbles," says Champion. "The seals are designed well since they
aren't exposed to the elements. This should prolong the life of
the drive."
In fact, the Quadrive design features an "inboard" bushing
design complemented with severe-duty grease purged seals to
protect the high-speed bearings.
Simplified installation and removal play a critical role in
the life of a shaft-mounted speed reducer. Forcing the drive on or
off the shaft can cause undue stresses to the equipment, not to
mention wasted time and energy. This latest technological
development in the design of shaft-mounted speed reducers will
give Vulcan Materials maintenance crews a time-saving advantage
during future changeouts.
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