Several of the shafts were rebuilt using a wire thermal spray gun before being machined back to the
design tolerance
RAPID GEARBOX REPAIR RESOLVES
DESIGN FAULTS FOR STEEL MILL
eeping lost production
time to a minimum
requires a combination
of in-house engineering
skills and a partnership
with a well-resourced, specialist repair
provider. This became evident for one
steel mill when a bearing failure caused
a production line to stop and an urgent
repair was required. Calling on Sulzer
engineers, the plant initiated a round-the-
clock repair procedure that minimized
downtime and delivered a cost effective
and long-lasting solution.
K
Any time invested in maintenance needs
to be minimized and repairs need to be
completed on time, but dealing with
‘enclosed’ pieces of equipment such as
pumps and gearboxes can often reveal
unexpected damage. What may appear
as a simple repair can quickly develop
into a much larger concern once the
covers have been removed and the initial
investigations are carried out. The extent
of the issues found may be beyond the
technical capabilities of a customer’s
in-house maintenance department. In
such situations, entrusting the repair to
a proven, multi-disciplined maintenance
provider may be the most cost-effective
solution.
120
PECM Issue 26
In this particular case, a 15-shaft gearbox
on a steel coil levelling line had suffered
from a failed bearing and the maintenance
manager immediately asked the local
Sulzer engineer to attend site and discuss
possible options. Having been reassured
that the local service center could
complete the inspection and repair, field
engineers started to prepare the gearbox
for shipment.
Sulzer took delivery of the gearbox at
2am the next morning and the process
of disassembly and detailed inspection
began. From the outset, a list of issues was
drawn up and the customer was frequently
advised on progress. Even with all of the
securing bolts removed, the casing was
difficult to open; this was potentially a
problem caused by excessive sealant use.
In fact, it appeared the sealant may have
also blocked the oil galleries lubricating
the shaft bearings and was a likely
contributing factor to the bearing failure.
As the inspection progressed, the
customer was informed on all of the
findings which were likely to have
contributed in the failure of the gearbox;
the bearings themselves were not uniform
as they varied in dimensions both in
diameter and width, despite their critical
need to be identical. This discrepancy in
the dimensions had a knock-on effect to
the spacers on each shaft as they, too,
were all different, each one a bespoke
size to accommodate the variation in the
bearing dimensions.
Aneil Hanafiah, Mechanical Engineer
explains: “It soon became apparent
that the gearbox was an original design
that had been copied. We measured
several dimensions repeatedly because
they seemed to be so far out from what
we were expecting. We invited the
customer to come and inspect the various
components in order to gain a better
understanding of the scale of the final
repair.”
Almost every component within the
gearbox had to be remanufactured or
repaired in some form, either due to poor
original manufacturing or through wear
caused by inaccurate assembly. Even the
keyways on the shafts that held the gears
in position were off-center both radially
and axially. This would soon be resolved
by slightly enlarging the keyways
so that the new position could be
aligned on each shaft; and the new
keys were manufactured so that
the gears could locate into the
correct positions.