Rope Characteristics

Strength

The published "nominal strength", "catalog strength” or Minimum Breaking Force (MBF) is the calculated strength figure that has been accepted by the wire rope industry. This applies to new, unused rope and is usually measured in tons of 2,000 pounds.

A rope should never operate at or near its minimum breaking force. The minimum breaking force must be divided by the required design factor to determine the working load. During its useful life, a rope gradually loses strength due to factors such as surface wear and metal fatigue.

Because different rope types have different minimum breaking forces, you must check minimum breaking force whenever you consider a change in rope types.

 Crushing resistance is a rope's ability to maintain its round shape when multiple layers of rope spool onto a drum. Because shovel hoists and dragline hoists and drags spool in single layers on grooved drums, this is not a factor in their service life.  It is, however, a factor to consider on boom hoist ropes. In general, 6-strand ropes are more crush resistant than 8-strand ropes. Rope constructions with fewer, larger wires are also more resistant to crushing than those with a greater number of smaller wires.

NOTE: When a decision is made to try a different rope construction, it is normally best to use several sets of the selected rope construction to determine its average service. This way, you can compare the cost per hour (ton or yard) to other construction's cost to determine the best rope construction for your application.