What do breaking load, usage rate and workload mean?

In the search for the right steel wire rope, you will soon come across the terms: breaking load, usage rate and workload. Find out what these terms mean and take advantage of our tips. 

Breaking load

The breaking load is the maximum load before the steel wire rope breaks. We make a distinction between the “calculated breaking load” and “minimum breaking load”. 

• Calculated breaking load
  This is the theoretical breaking load of the component wires in the steel wire rope. For the calculated breaking load, the material cross section is considered in combination with the average tensile strength of the material. 
   
• Minimum or actual breaking load 
  The minimum or actual breaking load is always lower than the calculated breaking load. This is due to the helical positioning of the wires (double helix): the so-called spinning loss. The difference between the calculated and actual breaking load is determined by the wire construction and the lay length of the strands and wire rope.  

Workload

The workload is the maximum load the steel wire rope may be subjected to in daily use. This may vary depending on the application. 

Usage rate

The ratio between the actual breaking load and the workload is called the usage rate. With a usage rate of 10, the maximum load is one tenth of the minimum breaking load of the wire rope. With an actual breaking load of 50 tons, the wire rope is allowed to pull 5 tons when used.  

How do you determine the usage rate? 

The usage rate of a steel wire rope is laid down in standards. Some of the guidelines include: 

• Steel wire ropes for hoisting
  Usage rate: 5 
  
  The usage rate depends on the rope’s intended purpose. For hoisting purposes, the usage rate for conventional wire ropes is a 5 and a 6 for rotation-resistant ropes. 
   
• Rope slings (up to a diameter of 60 mm)
  Usage rate: 5. 
  
  Do take into account the loss caused by the wire rope fitting: the so-called loss factor.
   
• Lifting 
  Usage rate: 12 (with catch)

Does the breaking load say it all? 

The assumption is often: the higher the breaking load, the better the wire rope. But this doesn’t have to be the case. For example, a high breaking load says nothing about destruction or wear caused by external influences. The course of the steel wire rope and the construction in which the wire rope is applied can strongly influence the life span of a steel wire rope. Frits van Boetzelaer, a steel wire rope expert, discusses this topic in depth.   

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