ROPE

assemblage of fibres, filaments, or wires compacted by twisting or braiding (plaiting) into a long, flexible line. Wire rope is often referred to as cable (q.v.). The basic requirement for service is that the rope remain firmly compacted and structurally stable, even while the rope is bent, twisted, and pulled. The prime property of a rope is its tensile strength. The texture and the nature of a rope is determined by the colour, fineness, stiffness, strength, and stretchability of the fibres or filaments used in its construction. Cotton ropes, for example, are softer, weaker, and stretchier than manila or sisal ropes. Manila ropes are stronger, for a given size, than hemp or jute ropes. Since even short fibres can be spun into long flexible yarns, practically any fibre can be made into a rope. Ropes made of filaments drawn from ductile metals or synthetic polymers differ from natural-fibre ropes in that any particular filament contributing to the rope form runs throughout the entire length of the rope. A thick filament or wire is stiffer than a fine one of the same material; its use results in a stiffer rope for a given size. In the basic twisted rope structure, alternate stages are twisted in opposite directions to give torsional stability. When the rope twist is seen to spiral in direction upward to the right as the rope is held vertically, it is designated as right-laid or Z-twist; if upward to the left, as left-laid (S-twist). The braided or plaited rope structure provides torsional balance by crossing and recrossing rope components in maypole fashion. Natural-fibre, man-made filament, and wire ropes ordinarily range upward from a diameter of 3/16 in. (about 5 mm). Smaller ropes are designated cords; similar assemblages in which torsional balance is of no consequence are called twine or yarn. Cables are torsionally balanced structures formed by twisting several ropes together. Compared with organic-fibre ropes, wire ropes are stronger, stiffer, heavier, and less extensible. Man-made filament ropes are stronger than natural-fibre ropes but are generally stretchier.