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E.I. DuPont de Nemours & Co.
in Axis, Alabama had a flow problem, which was slowing
the plant's product packaging line. The plant manufactures
a dry powder surfactant called Alkanol XC(r), used primarily
in the photo processing industry. At the end of the
production line, the product is conveyed by means of
a horizontal screw conveyor to the packaging area. The
conveyor has a 2" diameter shaft, turning at 11 rpm
with a gear reducer, under a maximum 3" head of product.
From the time it was installed in 1985, the seals used
on the conveyor were unsplit MECO conveyor seals, model
# HEAT-200. This seal model, one of the first MECO seals
ever developed, consists of an elastomer wrapped around
the conveyor shaft, secured by a large hose clamp, which
turns two internal rotors against stationary stator
plates. The friction between the rotors and the stator
plates forms the seal faces. The seal is designed to
be used with a nitrogen purge; however, in an effort
to maintain production through the periods after the
seals began to leak, plant workers pumped grease into
the purge chamber to act as a barrier. This worked on
a short-term basis, but ultimately caused more damage
to the seal and shaft. The dry product leakage produced
a gummy substance when exposed to excess moisture in
the atmosphere. This caused safety and housekeeping
problems, including slippery walking surfaces in the
vicinity of the seals.
For a few years, the plant lived with this operating
/ maintaining practice, rebuilding the seals approximately
once per month. "Rebuilding" consists of replacing the
seal's internal rotating elements, i.e. the elastomer
and rotors. With the unsplit seal, this had to be achieved
by removing and replacing the bearing and drive each
time. This job took two workers approximately 4 hours
to complete. As the conveyor was a bottleneck in the
production line, the entire line was being shut down
for a half day per month for seal rebuilds.
The situation was addressed when Reliability Engineer
Joe Del Tosto of DuPont led a team of operators and
mechanics to increase the uptime of the screw conveyor
by reducing seal failures. He had previously used split
MECO seals successfully in a number of applications
at another DuPont plant site, so he proposed them as
part of the solution. Working with Jerry Chevalier of
Mid South Mechanical Seals, the MECO distributor for
the region, the team installed a split EAS model seal
and conducted training on the proper operation and maintenance
of these seals.
The EAS seal was installed in June of 2000. In December
of 2000, the conveyor was shut down for routine cleaning.
The seals had been running without trouble for 6 months,
requiring only occasional monitoring of purge pressure
and external housing adjustment. Nevertheless, Del Tosto
decided to rebuild the seals while the conveyor was
down, as a proactive maintenance measure. The rebuilding
of the split seals took only one hour.
Del Tosto also mentioned that when they rebuilt the
EAS seals, they only did a partial rebuild on one of
the seals. That is, they only replaced the driving elastomer
and left the original rotors in place. "As we move more
toward condition-based maintenance I want to get an
idea how long the seal will last, versus simply replacing
it on a straight time-based preventive maintenance schedule,"
Joe said.
Joe is very pleased with the seal upgrade. "We are at
6X the life now and counting", he said. "Even when we
do rebuild the seals, it only takes one quarter the
time it did before".
Copyright 2005 Woodex Bearing Company, ,Inc. All rights reserved.
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