Twisted rope is the simplest and the oldest type.
It’s made in essentially the same way today as it was thousands of years ago - by twisting a bunch of fibers or yarns together to form a strand, then taking three or so of these strands and twisting them together in the opposite direction.
When long lengths of twisted rope were required for a tall mast or to hoist a load to a high place, they were formed - by hand or later with machines - in a 'rope walk' as long as the finished dimension, in order to avoid splices. To the same end, abandoned chicken coops are sometimes converted into rope making factories.
Natural fiber cordage for general use - mostly made from manila or cotton was the ‘state-of-the-art’ until the mid-twentieth century, when nylon rope was introduced. With it's superior strength, rot resistance, chemical resistance and ability to absorb shock loads, nylon twisted rope was soon replacing manila and cotton in farm, industrial, and military cordage applications. Since that time, polyester and other synthetic fibers have been developed and used to produce a variety of specialty products, matching the strengths of the individual - and in some cases multiple - fibers to the needs of the work to be done.
Manila, the previously 'state of the art' working rope, is now - with few exceptions - recommended just for decorative use. Manila should not be used for overhead lifting or when failure could lead to damage to people or property.
As far as long term use, especially outdoors, Manila and any other natural fiber ropes will eventually rot. If it is stored wet, or if it does not dry out completely after getting wet, the fibers will rot - not visibly, but on the inside - and the rope will break without warning.
Properties of 3 Strand Twisted Ropes
|Diameter (inches)||Circum- ference (Inches)||New Rope Breaking Strength Lbs||Working Load Limit Range Lbs||New Rope Breaking Strength Lbs||Working Load Limit Range Lbs||New Rope Breaking Strength Lbs||Working Load Limit Range Lbs||New Rope Breaking Strength Lbs||Working Load Limit Range Lbs||New Rope Breaking Strength Lbs||Working Load Limit Range Lbs|
WORKING LOAD LIMITS
The Working Load is the weight or force applied to a rope in a given application.
Working Load Limits (WLL) are guidelines for the maximum weight or force capacity of a given rope in general use.
Working Load Limits are calculated, using an application based Design Factor, as a percentage of the breaking strength of new, unused rope.
Again – the Working Load Limits shown are guidelines, not specifications, and are for non-critical applications. They do not apply if the rope is to be used for overhead lifting, or if life, limb, or property is at risk. In these cases - or for more complete information on determination of Design Factor and WLL - please refer to the Cordage Institute "Safer Use of Fiber Rope".
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