the anticipated ground conditions and the
overall machine architecture.”
As a result, a slewing bearing is always
a highly customised design, created in
close collaboration between the OEM and
bearing supplier. “SKF has developed
specialised design and optimisation
software for such projects, allowing the
modelling and simulation of complete
slewing bearing assemblies, including
rolling elements, cages, raceways, drive
gears and mounting arrangements, and
thus has an accurate calculation of bearing
and gear lifetime under the given load
conditions,” states Dysiewicz. “Special
solutions incorporated into TBM slewing
bearing designs can include spring-loaded
raceway designs to reduce shock loads in
hard rock applications.”
The large size of TBM slewing bearings
presents challenges for transportation,
assembly and maintenance. Depending
on OEM requirements, slewing bearings
can be supplied as single parts or fully
assembled units, including the sealing
system. In some cases, bearings may
be constructed in segments to facilitate
transportation, mounting or replacement,
in case unforeseen events occur, affecting
the machine. Along with the main slewing
bearings, there are also special ranges of
slewing bearings on the market for screw
conveyors and erector systems.
SEALING THE DEAL
“Slewing bearings rely on proper lubrication
and ingress protection to survive,” he
continues. “That means the seals used
to protect these bearings against the
harsh environment in tunnel boring are a
project-critical component. Like the slewing
bearing assemblies themselves, sealing
solutions for TBM main bearings need
to be optimised to suit the needs of
the typical applications, as well as
customised projects with even more
extreme conditions.” SKF retains
“full control of the seal design and
manufacturing process”, formulating
its own proprietary materials and
using in-house manufacturing
processes to ensure precise
control of nished seal geometry,
regardless of the size of the
machine involved. Slewing bearing
seals must achieve multiple
objectives: retaining lubricant within the
bearing assembly, keeping out water,
mud and debris, and accommodating the
signicant misalignment that can occur
during operation. The seal must be able
to full these duties throughout the full
duration of the project, even while subject
to continual abrasion by rock particles.
LIPS ARE SEALED
“To achieve the desired level of
performance, several lip seals in series,
with lubrication in between, are commonly
used. SKF’s TBM seals are designed
by utilising nite element analysis (FEA)
to consider all load cases, such as
misalignments, pressurisation, grease
ushing and even installation behaviour.”
To simplify assembly processes and
facilitate on-site replacement of seals,
where required, SKF has developed
a specialised welding process using
compact, hand-held equipment that
allows engineers to operate in conned
spaces, enabling main seals to be
installed without the need to remove the
cutting head, greatly reducing downtime.
In addition to the highly specialised
components developed specically for
TBM applications, the company provides a
wide range of other components, systems
and solutions for machine manufacturers.
These include standard bearings and
seals used in screw conveyor drives,
erector bearings and other ancillary
equipment, along with sophisticated,
centralised lubrication systems that can
inject oil or grease directly into bearings
in precise quantities to ensure optimum
lubrication with minimal wastage or
environmental contamination, says SKF.
TUNNEL BORING
This 8 tonne bearing was supplied by SKF for
a mining application.
REMANUFACTURING
As operators look to maximise the lifetime
value of their assets, they are increasingly
looking for opportunities to re-use
complete TBMs and key components on
multiple projects. Component re-use can
result in lower costs, less environmental
impact and smaller parts inventories.
“To help manufacturers achieve their
objectives, remanufacturing of TBM
bearings is a good option,” Dysiewicz
concludes. “Used bearings are returned to
specialist facilities or directly on customer
sites around the world, where they are
cleaned, disassembled and inspected.
Worn parts are replaced or reconditioned
and the completed unit is inspected,
documented and returned, ready for
reinstallation.”
Cut-away view, showing integrated SKF
bearings, seals and lubrication systems.
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