Paper Tiger
Drive standardization pays off at pulp
mill
By converting most of its mechanical equipment drives to C-face
motor-mounted planetary reducers, a major Southern paper mill
has reduced downtime, improved maintenance procedures, and
lowered spare parts inventories. Standardizing on a simpler
drive configuration has eliminated most V-belt and right-angle
drives. In service at the mill are Planetgear speed reducers,
manufactured by Rexnord Corp., Milwaukee, WI, which have made
repair and replacement easier and have reduced downtime, compared
to previous drives.
At the large pulp mill, more than one million cords per year
of whole log or short wood trees are cut and chipped, then
treated in a digester before being processed into pulp. At
every stage of the process, from chip handling through final
processing, speed reducers play a key role in mechanical power
transmission and control.
Originally, equipment at the mill included a variety of drives
from several different manufacturers. In-line reducers were
driven through V-belts and pulleys, while others incorporated
right-angle drives. The complexity of some of the gearboxes
and the variety of manufacturers that supplied them made it
difficult to complete unscheduled repairs quickly and minimize
downtime. A company spokesman explains, "When some of
the OEM gearboxes started failing prematurely, we found they
were already obsolete, and we couldn't get parts. Other equipment
had drives that came from overseas, and spare components were
either too expensive or unavailable when it came time to repair
or rebuild them."
To solve the problem, the company worked with Rexnord Corporation
on redesigning many of the existing mountings to eliminate
most belts and pulleys. Some equipment in the mill already
was equipped with the company's Planetgear drives, which had
proved to be reliable under the mill's service conditions.
The spokesperson notes, "We asked them to design us something
that would work in other applications, and their standard
Rex Planetgear reducers fit right in place."
Whenever possible, the motors are installed using an integral
C-face input mount to the reducers. This generally takes less
space than other approaches and eliminates the need for components
such as V-belts, pulleys and guards. It also makes alignment
procedures unnecessary. As an added benefit,the drives can
be mounted in any orientation, making it easy to apply them
to a broad range of applications and confined spaces. The
spokesman points out, "We can turn them around and stand
them on end if necessary. Otherwise we'd have to deal with
right-angle gearboxes in a lot of applications."
Planetgear speed reducers are available in single, double,
triple and quadruple reductions, with a broad range of ratios
and torque ratings. The planetary gear train is self-aligning,
with carrier modules that float radially and axially to distribute
all loads. Gearing is carried entirely on roller bearings,
and loading is distributed over at least three points of contact
(minimum six teeth), instead of at a single point, as in conventional
reducers.
The modular design simplifies assembly and minimizes downtime.
Additionally, modules are shared amongst reducer sizes, keeping
spare parts to a minimum while maximizing flexibility for
ratio changes. The company spokesperson comments, "I
have close to 60 distinct ratios in the reducers at this facility,
and for under $100,000 I can stock spares to cover all but
two of the largest ones in the woodyard."
To further improve throughput and keep downtime at a minimum,
the mill has instituted a predictive maintenance plan that
is based on taking regular vibration analysis readings for
all rotating equipment. The spokesperson notes, "We are
building in greater reliability with the Planetgear drives,
but we're also tracking mean time between repairs so we can
plan ahead of time when to replace the reducers. We actually
schedule our downtime around this vibration analysis data."
Currently, several hundred Planetgear drives are installed
at the mill, on everything from log and chip conveyors in
the woodyard to agitator drives in the mill and precipitator
chains in the power plant. Most are mid-size Planetgear drives,
typically Earth, Venus and Neptune series. The spokesperson
reports that Rexnord recently conducted a complete mill survey
to determine what other applications would be suitable for
conversion to the new drive configuration. He says, "We
can take just about any application and put these drives on
it. From a maintenance and reliability standpoint, they're
the best speed reducers in this facility."
--RM
For more information:
Circle 445 - Rexnord Corp., or connect directly
to their website via the Online Reader Service Program
at http://www.OneRS.net/103df-445
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