In preparation for the manufacture of 'modules' for
the Mozal Aluminium Smelter in Mozambique, an
engineering fabrication works in Durban, South Africa,
had to refurbish their cranes to prevent downtime
during the fabrication phase of the project.
The
plant engineer did not hesitate to use PDL Electronics
variable speed motor controllers on the refurbishment
program as he had successfully used the range on other
fabrication equipment.
An
Xtravert controls the cross travel and a Microdrive
Elite controls the long travel and hoist. This meant
that the old wound rotor resistance starters could be
scrapped and variable speed motor control technology
introduced, producing "operator proof"
control that eliminated downtime due to operators
overdriving the cranes.
The
end result has been that travel speeds are selectable
within limits, hoist control is far smoother and
positioning better controlled, and the programmable
start/stop ramp has eliminated wheel-spin when
starting and skidding when stopping when the crane is
unloaded - all reducing long term maintenance on the
crane.
The
use of a load limiter has been introduced to prevent
excessive travel speeds when loaded.
As
the cranes are typically rated at 15 and 25 ton
capacity, it is common for the works to use two cranes
in tandem to move loads heavier than a crane's rating.
The use of the Microdrive Elite has introduced the
concept of 'master / slave' control of tandem cranes
for long travel and hoist using only one pendant
controller.
At
the time of writing, the fabrication phase is
half-complete and to date there has been no downtime
due to any upgraded crane failure.
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