Stieber backstop used
for controlled back
running of inclined
conveyors
I
n established industries
there are tried and
trusted solutions for most
engineering requirements;
however, sometimes we must look
beyond the ‘standard’ to find new
improvements. By starting a design
project from the very basics – defining
system requirements and looking at
all potential approaches – it is often
possible to challenge conventional
practices and find better solutions.
An example can be found in a coal
mining company based in Pennsylvania
which required a new inclined coal
conveyor in one of its mines. Instead
of commissioning a replica of its
existing conveyors, it took the time to
re-evaluate the requirements of the
mine and the demands that would be
placed on the conveyor. It then sought
alternative solutions to see if they
could offer greater returns in terms of
reliability, productivity and efficiency.
Normally inclined conveyors have a
backstop arrangement that prevents
them from running backwards under
load. This is particularly important
in coal mines, where the load on a
conveyor can be truly enormous, made
up of coal and rock over the whole
length of the conveyor. This is a vital
feature that prevents tonnes of rock
accelerating backwards and offloading
at the end of the conveyor – which
could lead to many hours of lost
Allowing the conveyor to run
backwards makes it possible to
quickly clear blockages and undertake
maintenance when required
production and would have a risk of
causing further damage.
However, the Pennsylvanian engineers
soon realised that in their case, if
the conveyor had the ability to run
backwards in a controlled manner,
even if only a short distance, there
would be considerable advantages
when it came to clearing blockages and
undertaking maintenance.
With this thought in mind, a search
was launched to find a suitable clutch,
or other mechanical mechanism, that
would meet the project’s requirements.
The RDBK high-speed backstop
from Stieber Clutch, part of Altra
Industrial Motion was quickly identified
as probably the best match to the
conveyor’s needs. The supplier was
contacted and technical discussions
and tests followed soon afterwards.
The RDBK is a centrifugally operated,
lift-off sprag, high-speed backstop,
equipped with integral torque limiter.
The latter limits the backstop’s
transmissible torque to a value that
is factory set, according to user
specification.
The backstop is often specified on
multi-drive systems, such as large
inclined conveyors, where two or more
backstops share the reverse load. The
torque limiting function is performed
through a multi-disc brake working in
oil. This solution not only provides for
The RDBK is a centrifugally
operated, lift-off sprag, highspeed backstop which can
perform multiple reverse
rotations when required for
maintenance purposes
a high torque density of the complete
unit, but also ensures that the set
slip torque remains constant over
extended periods, regardless of the
environmental conditions, even in
the rigours of a coal mine. Similarly,
the friction linings work in an oil bath
to make sure that the unit remains
functional even if there are periods of
inaction.
With the RDBK fitted the mine’s
operators are confident that in the
event of a failure the conveyor will be
held in position. However, offloading
the conveyor is now a much simpler
process which allows maintenance
work to be carried out quickly and
downtime to be reduced greatly.
The RDBK is designed so that the
sub-assembly which rotates backwards
under overload is fully bearingsupported. This means it is capable
of performing as many reverse
rotations as may be required (within
the limits of energy dissipation) to
completely unload the conveyor prior
to maintenance work being carried out.
Stieber can build each RDBK with the
release function manually, hydraulically
or mechanically controlled; with the
last generally being preferred in mines.
This easy-to-use release function
helps reduce downtime by making the
clearing of blockages, belt jams or
overloads fast and efficient.
The RDBK range is available with
torque capacities from 5,500Nm up to
180,000Nm, it is able to offer up to 3.5
times more torque capacity than other
backstops of similar size, with up to 15
times more energy dissipation.
www.stieber.de
Issue 15 PECM
93