IN FOCUS / EDWARDS HEAVY LIFT
ENSURING THE HOOK AND RIGGING INTERFACE IS CORRECT
In this article Stuart Edwards from Edwards Heavy Lift continues to look at the hook of the crane and other rigging component interfaces. THE TECHNICAL INFORMATION in this article will not be applicable to all manufacturer products and you should always check with the manufacturer and all relevant standards for your particular application. Having said that the items raised in this article might help prompt to know what questions might be worth asking and things to consider. CROWDING Two’s company and three’s a crowd as the saying goes. In the case of a crane hook it’s not the number of slings but whether everything can sit neatly in the hook. In the case of synthetic round slings the best rule to apply is bearing width and contact radius as per AS 4497. Figure 1A & B shows a case where the hook size for the synthetic round slings is probably not the best. For other rigging hardware, these components need to fit with sufficient such that they can find their own line of action and do not crush other slings (as shown in Figure 1C). An alternate arrangement connecting synthetic round slings that would otherwise be crowded is shown in Figure 1D.
1A) Avoid sling crowding. 62 / CAL March 2019
Figure 1B).
UNEVEN LOAD SHARE ON RAMSHORN HOOK Ramshorn hooks might be the original hippies; live life in harmony and balance and everything goes great. Maybe not, but you need to make sure the Ramshorn hook is not unevenly loaded. The maximum recommended uneven load share is 45% to 55%. Outside that, it’s recommended you change over to a single hook, a hook with a hole for a single shackle or another sling arrangement to bring it down to a single point. MAX SLING ANGLE A maximum sling angle from vertical in line with the hook is 45˚ for a number of manufacturers. This is quite generous and some manufacturers reduce this to 30˚. What might catch more people out is the out of plane angle. Out of plane is not the same as “out of body” but you might have that experience if you load a ramshorn hook with a funky out of plane sling angle, the maximum permitted side load of 30˚.
RAMSHORN HOOK ORIENTATION Orienteering is a sport in which runners have to find their way across rough country with the aid of a map and compass. We are not talking about that here but you might find yourself looking for directions north to the nearest airport if the orientation of the hook relative to the load is not correct. The hook is running perpendicular to direction the load is rotated. During the rotation the slings will rotate on the hook till equilibrium is achieved. In the alternative orientation one side of the hook would be loaded up at the start of the lift and depending on the hook configuration could be loading up the sheaves on the heavy side more as well as tilting the hook. This leads to a serious chance of the rope jumping the sheave and cutting the hoist rope. I hope you have found something useful in this article. In the next article we will cover, connection of hardware such as master links and shackles to the crane hook and lift points.
1C) Avoid crushing other slings.
1D) An alternative option.
