Feature Article
Minimum Hook Block Weights Article contributed by JOHN HUMPHRIES - CICA
Incidents involving the failure of lifting wire ropes are often attributed to rope deterioration, poor quality end termination fitting or process, improper installation, or exceeding the rope’s actual capacity or line-pull. Whilst these are serious safety concerns, there are lesser known causes that can also pose risk of injury, damage, or fatality. Wire ropes can be seriously damaged if they are used with insufficient tension or hook weight. Unwanted compressive loads causing a ‘birdcage’ effect or partial unravelling of the many strands that make up a rope can damage the rope to the point that a replacement is required. A crane winch is designed to feed a rope out under tension, however, when the tension is not maintained between the winch and boom head due to insufficient hook weight or load, slack rope can accumulate at the winch. 6
LIFTING MATTERS
ISSUE Q3 2020
Another effect of insufficient hook weight is that the hook can be pulled up on one side, particularly if the operator is not smooth with the controls or winches up too fast before the multiple line parts can pass through the sheaves. In some cases, the hook block can strike the boom head causing considerable damage. When winching down with insufficient force to pull all the rope through the sheaves, the hook block may not lower initially, but instead drop suddenly creating a serious hazard for anyone underneath. So, how do we know how much weight is required on the hook? That depends on your crane configuration and the manufacturer’s recommendation first and foremost. Basically, the longer the boom and more line pull required for a lift, the more reeving of the rope required which effectively increases the dependence on
