How to Calculate Wire Rope and Cable Stretch
When designing cable or wire rope systems, the amount of stretch that will occur when a force is applied is an important consideration. Keep the following in mind when you do your calculations:
There are two forms of stretch in cable and wire rope: Structural Stretch and Elastic Stretch.
Structural Stretch
Structural Stretch is the lengthening of the lay in the construction of cable and wire rope as the individual wires adjust under load. Structural Stretch in Loos & Co., Inc. products is less than 1% of the total cable length. This form of stretch can be completely removed by applying a cable or wire rope prestretching operation prior to shipment.
Elastic Stretch
Elastic Stretch is the actual physical elongation of the individual wires under load. The elastic stretch can be calculated by using the following formula*:
E = (W x G) / D2
Where:
E = Elastic Stretch, as a % of Length**
W = Weight of Load, in pounds
D = Diameter of cable, in inches
G = See Chart Below
|
Cable/Wire Rope
|
"G" Factor
|
Cable/Wire Rope
|
"G" Factor
|
|
1x7 302/304 SST
|
.00000735
|
1x7 Galvanized
|
.00000661
|
|
1x19 302/304 SST
|
.00000779
|
1x19 Galvanized
|
.00000698
|
|
7x7 302/304 SST
|
.0000120
|
7x7 Galvanized
|
.0000107
|
|
7x19 302/304 SST
|
.0000162
|
7x19 Galvanized
|
.0000140
|
|
6x19 302/304 SST IWRC
|
.0000157
|
6x19 Galvanized IWRC
|
.0000136
|
|
6x25 302/304 SST IWRC
|
.0000160
|
6x25 Galvanized IWRC
|
.0000144
|
|
19x7 302/304 SST
|
.0000197
|
19x7 Galvanized
|
.0000178
|
*Elastic Stretch derived from this formula is an approximation.
**Remember to keep your units of measure constant. The length of your cable must be calculated in inches to correspond with the diameter measurement, also in inches
For more information, and to download a free stretch calculator from our website, contact a product manager or visit our technical information page.