Bergen Cable offers advice on how to calculate wire-rope stretch

The Bergen website offers info on wire rope.

There are two important factors that go into Bergen Cable and its 80 years of international success: great products, and unsurpassed expertise. The company provides plentiful cable resources on its website, including a Cable 101 page, which includes a section about wire-rope stretch, a trait customers should consider during product selection.

Businesses should also consider the stretching factor when inspecting the wire rope that workers are using. Bergen suggests checking the stretch on a regular basis, according to most occupational health and safety standards, when the wire rope is carrying a load.

The variables that affect stretch

Many people use the term “wire rope” as if it is a synonym for “cable”. But the former refers to rope with diameters higher than 3/8 of an inch. The two main factors that affect stretch are structural and elastic stretch, according to Bergen. Wire elongation causes elastic stretch, while stretch results from a mix of lengthening the rope lay, compressing the core, and adjusting the wires and strands to the load that the rope holds.

Among the variables that affect structural stretch are the ore size, the length of the lays, the rope construction, and the loads and amount of bending that users impose 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 usually 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 answer by the metallic area in square inches multiplied by the modulus.

To learn more, contact Bergen.

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