Bergen unveils expert advice: Wire-rope stretch calculations made easy

Wire rope is a key solution available from Bergen.

Bergen Cable has provided great products and unsurpassed expertise for more than 80 years of international success. A leading cable supplier, Bergen offers plenty of resources on its website, including a Cable 101 page, which contains a section about wire-rope stretch – a factor that businesses must take into consideration during product selection.

Customers should also consider the stretching factor when they are inspecting the wire rope that employees use. Bergen recommends checking the stretch regularly when the wire rope is carrying a load, according to most occupational health and safety guidelines.

The two main factors

The term “wire rope” is sometimes used as if it were a synonym for “cable”. But wire rope actually refers to rope with diameters larger than 3/8 of an inch. The two main factors that affect stretch are elastic and structural stretch. According to Bergen, wire elongation causes elastic stretch, while structural stretch results from a blend of lengthening the rope lay, compressing the core, and adjusting the wires and strands to the load that the rope holds.

The variables that affect structural stretch include the ore size, the length of the lays, the rope’s construction, and the loads and amount of bending that the user imposes on the wire rope. The quantitative value of the structural stretch can be estimated by multiplying the length of the rope by 0.005 when it is carrying a medium-weight load, by 0.01 for a heavy load, or by 0.0025 for a light load.

Elastic wire-rope stretch is proportional to load weight and rope length when it holds a load under the elastic limit of the rope. The elastic limit of galvanized wire rope is typically around half of its breaking strength, or about 60 per cent when dealing with stainless steel rope. Elastic stretch is inversely proportional to the wire rope’s metallic area and modulus of elasticity. To calculate the elastic stretch in feet, simply multiply the load weight in pounds by the rope length in feet and then divide the result by the metallic area in square inches multiplied by the modulus.

For more information, contact Bergen.

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