Unlike string, line, or thread, rope is a twisted or braided length of fibers that exhibits increased strength. Rope is made from natural and synthetic fibers as well as from steel. Synthetic rope enjoys widespread popularity for its many advantages.
Rope is formed by either twisting or braiding individual strands of fibers. The two methods are shown below:
Uses And Limitations
Compared to steel wire rope, synthetic rope by its very nature is limited to light load lifting applications and for strapping and tethering, as in a tag line.
OSHA defines a tag line as “a rope (usually fiber) attached to a lifted load for purposes of controlling load spinning and pendular motions or used to stabilize a bucket or magnet during material handling operations . . . the end of which is held by an employee who controls the load's motion.”
Rope Material Comparisons
If a natural fiber, say manila, is considered as a basis for strength comparison, then a three-strand nylon rope has 21⁄2 times greater strength and a 2-in-1 braided nylon rope has 3 times greater strength.
Synthetic Rope Advantages
- Superior lifting/pulling strength versus natural fiber rope
- Outstanding strength to weight ratio (ease of handling)
- Pliant and grips the load well without marring surfaces
- Electrically non-conductive (eliminates potential for electrocution when used as tag line)
- Inherently safer than wire rope with a breakage due to lighter weight
- Safe, cost-efficient alternative to wire rope for some applications
Synthetic Rope Disadvantages
- Limited to light load applications
- Exhibits substantial elongation under load
- Looses strength when subjected to temperatures greater that 150° F
- Melts when subjected to temperatures exceeding 300° F, friction points for example
The potential of rope constructed of ultra high molecular weight polyethylene fibers (UHMPWE) to replace wire rope in logging applications is proving to be successful. UHMPWE rope's strength is similar to steel wire rope of the same nominal diameter but it weighs only about 1/9th as much. (Reference: http://www.orosha.org/pdf/grants/osu/synthropeusewinch.pdf).