Contact Pressure Between Reeving Components

When the rope is bent over a component, it generates pressure which is dependent on its diameter, the diameter of the component over which the rope is bent and the applied tension.

The nominal average pressure can be calculate using the following formula:

Multistrand and non rotating ropes ensure a better pressure distribution than six strand ropes, as the higher number of outer strands generates a wider contact surface (see figures below).

Compacted strands and Lang’s lay ropes further extend the contact surface.

In order to ensure proper performance, the groove material should ensure a smooth and hard contact: in case of inadequate hardness, the steel will be locally hardened, with consequent embrittlement and detachment of steel flakes, which can damage both the rope and the component itself. The typical recommendation is to use hardened steel with approximate 300 HB value.

In case of synthetic sheaves, the yield point of the material should be higher than the exerted pressure, calculated using the formula above.

A good groove dimension is also important to achieve a reduced pressure. The diagram below shows different configurations depending on various groove oversize: narrow, well dimensioned and large groove.