Following our previous edition, a number of quarry managers asked us to look at their plant to provide a critical opinion of machinery hazards, guarding, emergency stops and access for maintenance.
Some of the interest was sparked by a recent serious injury with a conveyor. Other inquiries came from people who were contemplating plant modifications or had just completed them.
On inspection we found a range of approaches to guarding. Some complied with AS 1755 Conveyors – Safety Requirements, others were practical but require some work to bring them up to a reasonable standard.
This edition gives us a valuable opportunity to share some of the better examples.
Picture one (above) shows new guards on new or upgraded plant. It shows some good thinking and construction by the Southern Quarries people involved. The guards are made with a complying, lightweight welded mesh mounted on solid bar to be reasonably light and well supported. Clearance from nip points has been set at more than 200mm as the mesh has 50mm square openings. This size was selected because none of the products of this plant are large enough to be caught in the guard.
All guards are bolted in place and belt tension adjustment can be done without removing the guards. (Note the emergency stop lanyard switch with an internal balance spring - pulling the wire or cutting it will stop the conveyor.)
The second example is from Rocla Quarries at Maslins Beach (picture 2, above.) It shows guarding on a trommel screen. The hinged guards are bolted shut and the remote grease nipples minimise the need to isolate and lock out the plant for regular maintenance. It is sturdily constructed and mounted with surface treatments specifically chosen to resist the wet conditions of the washing plant.
Emergency stop switches are required for all conveyors, and in mining applications (yes - quarries are mines) they are required to be of the lanyard or pull-wire type. When installed along all accessible parts of the conveyor, they provide continuous emergency stop capability.
There are a couple of types of emergency stop switch available that meet the requirement for stopping the conveyor if the wire is pulled or cut.
On many older plants, the type shown in picture 3 is common, and is still widely available. It is mounted in or near the middle of the wire run and the end mounts of the wire are spring tensioned to achieve a balance of wire tension at the switch.
Another type shown above in picture 4 has an internal tensioning device and is mounted at the end of the wire run.
Please note that we are not recommending the particular brand switches shown here; rather we are using the photographs to illustrate the types of switches available.
Regardless of the type of emergency stop switch, the Australian Standard requires signs to be installed showing the location of the pull wire. There is always a need to periodically check the proper functioning of the emergency stops for all plant.
If you require an inspection of your plant and conveyor please contact the Operations Manager, Wayne Hooper on 8204 9500 or 0427 011 648.
Conveyor guarding at Rocla Quarries