Cables experience inevitable fatigue during their working life. While some environmental factors contribute to expedited wear, such as exposure to corrosive salts or acids, pulleys also play a significant role in this lifespan. One specific engineering concept, called the D:d ratio, helps extend this cycle life by matching the ideal pulley diameter to a corresponding cable diameter. Here is a closer look at how the D:d ratio functions.

What is the D:d Ratio?
The D:d ratio describes the relationship between pulley diameter and cable diameter, and it is used to maximize cable service life. D indicates the pulley diameter, while d refers to the diameter of the cable, including any jacketing. Simply put, the larger the pulley, the higher the D:d ratio. In general, the larger the D:d ratio, the longer the service life of the cable. It should be noted that the D:d ratio is just one of many factors contributing to cable longevity, and that other aspects of your system should also be evaluated and considered if you are experiencing issues with cable fatigue.

What does this mean?
Pulleys that are too small for a given cable diameter place excess strain on the system by requiring the cable to bend around too small of a radius. This generates fatigue in the cable that will result in eventual failure if not properly addressed. Simply putting the same size cable back on the same size pulley will just repeat the same issue. You can resolve this by adjusting the size of either the cable or the pulleys.

What are the solutions?
Consider selecting a smaller diameter cable for your existing pulleys, as smaller cables are able to bend around tighter radii. Alternatively, you can upgrade your pulleys with the help of QSheaves, Process Sheaves, and eSheaves from Loos & Co., Inc. Cableware Division. QSheaves provides quick turnaround on customizable lifting sheaves, so you no longer have to wait for long lead times from other manufacturers. ESheaves has the OEM replacements you need from Crosby McKissick, and Process Sheaves offers plastic sheaves for processing linear products.

Begin comparing your options at https://www.esheaves.com, or contact our sales department with any questions.