When gearbox failure
stopped production at the
Omagh Minerals
goldmine in Cavanacaw, Ireland it
initially seemed that repairs would
take weeks if not months. However,
in just over a week, motor control
expert Ralspeed was able to supply a
250kW variable speed drive system
that allowed operations at the mine
to be quickly resumed.

The system has been installed on a
ball mill – essentially a large drum
into which the ore is placed along
with heavy balls. This mill is driven
by a 250kW motor, via a 5.8:1 ratio
gearbox. Problems had, however,
been experienced in the form of
gearbox failures.

In order to use a smaller gearbox
with shorter delivery times, experts
reduced the starting load by
replacing the direct-on-line starter
with a Ralspeed variable speed drive
to give a smooth controlled start up
with greatly reduced peak torque.

With the replacement gearbox and
the Ralspeed variable speed drive
system fitted, the ball mill was back
in operation in less than two weeks
and has been working reliably for
several months without any sign of
distress to the gearbox or other parts
of the drive system.