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Road and workshop
Page 77
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Loads and forces (25)
• With mechanical handling and palletization going hand on hand, thoughts have naturally turned to parcelling anything and everything that is on the move, and the range can now stretch from bricks, steel plates, to a load of caged and palletized live poultry.
However, I am here considering the more dangerous types of load—steel plate, strip, sheet, rod and bricks held by steel bands.
Whereas bricks have a fairly high co-efficient of friction even under light tension, steel plates or sheets quite often have a protective coating of oil— dangerous if there should be a weak or overloaded band, as it only needs one band to ease or snap and the next strain may send the stack cascading off the platform.
Recently, one of six stacks of steel plates each weighing 3 tons and banded with steel, came apart at a roundabout, showering sheet steel on stationary vehicles waiting to enter the island. Prior to the incident, the vehicle, an artic, had been running along a clearway for 13 miles, and had negotiated four roundabouts before meeting trouble at the fifth.
This accident, because of a third-party involvement and subsequent claims, merited close investigation to determine just why one banded stack had broken loose while the remaining five stacks stayed put. The method of lashing had been soft ropes with each run Placed on sacking over the steel plate, and each run also tensioned by a normal rope hitch, no mechanical aids being used. As the front stack was tight up against the headboard no fore and aft lashings had been considered necessary. However, the stack that burst apart was the rearmost stack on the nearside. no doubt subjected to greater centrifugal force than the rest.
Further investigation disclosed one stack with two wooden wedges driven between the steel bands and the plates. Questioned about this, the driver said that in his opinion this had been necessary, as the bands on this stack and one other had been "easy", and the plates could be moved within the bands. He indicated that one other stack had four wedges driven in, and a further check confirmed that this was the burst one.
There is no doubt that the initial nip placed on the bands was normal. That would have been the measured nip given by the clenching tool and although it appears that the bands had either stretched or eased during that process, what is important is that in driving in slim wedges there was no way of assessing the amount of tension then being applied, which could well have brought the strapping close to breaking point.
It was accepted that in this instance the driver had been observant and taken the obvious steps if the straps or bands are slack, then tighten them), the only point being that there is a difference between tapping in wedges to take up slack, and "belting them home solid".