Mining in focus
A mine needs to have enough weighbridges on site to
prevent any serious bottlenecks and delays
Donovan Pye,
director at Richter Scale
How many weighbridges
should a mine install to prevent
unnecessary bottlenecks?
It depends on volume. Once a
mine or quarry needs more than
around 75 trucks weighed each
day, a second weighbridge should
be considered due to the time
constraints involved in weighing
each truck in and out every day.
Avoiding bottlenecks is essential
to move product in or out, so if
volumes are higher, then the mine
would need to consider a dedicated
inbound and outbound weighbridge.
In extreme cases, the volume
might justify multiple incoming
and outgoing weighbridges on one
property. These are normally always
installed at the entrance/exit of the
property for control purposes.
[32] MINING MIRROR JULY 2018
What should mining companies
consider when installing a
weighbridge at a new mine?
Firstly, the strength and reliability
of material and equipment are very
important. Many of the imported
weighbridges are simply not built to
withstand the robust South African
mining environment. Many are poorly
manufactured, and this will become an
issue when the volumes increase and the
unit needs to perform. We have replaced
many collapsed or bent imported decks.
Secondly, make sure that the
company supplying it is SANAS
accredited and has the equipment,
experience, and NRCS authority to
certify and repair the equipment they
are offering. Many companies either
use third parties or do not have their
own weighbridges NRCS type approved
and thus mix and match decks, loadcells,
and instruments from various suppliers
and pass these off as their own products.
Many decks have never even been tested
by the NRCS type-approval department.
Lastly, if they are based in South
Africa and are moving more than 500t
per month from their mine, they need
to comply with the National Road
Traffic Act, which puts the onus on the
company loading the trucks on their
premises to check the load distribution
and total GVM of each outgoing truck.
They then need to provide the driver with
the evidence (printout) that the truck is
loaded correctly. For this they need to
install a multi-deck weighbridge. Which
means the 22 or 24m-long weighbridge
is broken up into four separate platforms
to enable the truck axle groups to be
checked instantly. Standard weighbridge
tickets/slips will also be produced by such
a weighbridge.
Do different mines require
different weighbridges?
Some mines need weighbridges
for checking loads closer to the
supply/pit before they pass over the
legal-for-trade and SANAS-verified
weighbridges. Cleaning can be a big
issue, so pit-mount weighbridges
are in the minority due to extra
maintenance needed.
What does the site preparation
for weighbridges entail?
This is soil and condition dependent.
Remember, close to 60t (80t for
non-South African operations) will
be going over the scale every hour of
every day, so preparation is critical. Any
bad soil or turf needs to be removed,
backfilled, and compacted.
What does the construction of
weighbridges entail?
The civil work is crucial to get an
accurate weighing at the end of the day.
One cannot expect basic slapdash civils
to be good enough for a high-volume
site. Ramps on and off the weighbridge
are also critical. They need to be built
well to avoid the hammering they take
every day from heavy trucks destroying
the ramp in a short period of time. They
also need to be wide enough for drivers
to comfortably drive on and off and to
avoid accidents by trucks driving off the
sides of the ramps.
Side barriers are also essential on a
weighbridge to prevent accidents caused
by trucks driving over the side of it —
the barriers are there to prevent this.
One recovered truck will more than pay
for the additional costs of the barriers.
Concrete needs to cure sufficiently
before the unit is tested or used. Once