non rotating wire rope specifications free sample

Rope Services Direct supplies a variety of anti-spin non rotating wire rope (also called rotation resistant wire-rope). All standard rope wirehas a tendency to develop torque and therefore prone to rotation, whereas non-rotating wire ropes are designed so that the wire-rope outer rotational force naturally counteracts the inner strands rotational force. This is in the event that a rope is subjected to a load.

Rope elongation and rotation occurs on standard ropes when loaded, which can therefore spin the load, quite possibly out of control, which can be dangerous. When the rope rotates in this way the strands will begin to unravel. This causes the rope to lose strength and will undoubtedly fail, which could be catastrophic. It is for these reasons that non rotating wire rope is commonly used for many types of lifting applications including main hoist rope, whip rope,crane rope, off-shore and deck rope and more.

Non rotating wire rope or rotation resistant wire rope has a different construction to standard. as wires and strands are not laid in the same direction like they would be on standard rope. Inner and outer strands of wires are laid in opposite directions. For example the inner may be constructed in left hand lay whilst the outer layer is in right hand lay. The nature of this construction means that torsional forces on the inner and outer wires/strands will counteract each other and therefore minimising the risk of unraveling.

It is worth noting that the number of strand layers will have an effect of the resistance of rotation. A 2 layer rope has less resistance than a 3 layer rope. Therefore the more layers the rope has the greater rotation resistance it will have.

These types of ropes can be classified as spin resistant, rotation resistant or non rotation resistant. Classed on the basis of the number of rotations a certain length of rope does when a force of 20% of the MBF is applied; with 1 turn or less the rope will be classified as non rotating; with rotations between 1 & 4 the rope is classed as low rotation and for rotations between 4 & 10 the rope will be classified as spin resistant, any higher and the rope is NOT rotation resistant at all.

Correct usage and care with handling will prolong the working life. This is due to the friction on the inner wires caused by the strand crossover’s which will eventually cause the inner wires to break up. This is more apparent on non rotating wire rope with two layers. Ropes with 3 or more strand layers will distribute the radial pressures more evenly. Which will reduce friction and stress on the inner wires.

Regular,thorough inspectionsof non rotating rope are essential due to the fact that it is the inner strands that often break first and broken internal wires often go unnoticed as they are difficult to see.Rope Services Direct offer inspectionson all rope with certification issued on completion.

Holding both ends of the rope will prevent unraveling. Correctly fitted terminations will help to prevent damage. Kinking and unraveling may occur and they can also have an effect on the rotational balance if not fitted correctly.

Rotation resistant wire rope refers to a series of steel ropes which minimizes the tendency to spin or rotation under load. These wire ropes boast special design - the outer layer is twisted in the reverse direction of inner layers for counteracting torsional forces generated from multi-layers of strands.

To achieve the resistance against the spin and rotation, all wire ropes are composed of at least two layers of strands. In general, more layers a rotation resistant wire rope has, more resistance it will boast. For example, 2-layer ropes is much easier to spin and rotate than 3-layer ones. Meanwhile, if one end of free rotation is allowed, 2-layer rope can only develop 55% to 75% of its breaking strength comparing with 95% to 100% of 3-layer ropes.

The 3-layer rope with more outer strands is capable to distribute more radial pressure onto inner layers and ideal for larger mobile such as all tower cranes.

Wire ropes with 8 to 10 strands & 2-layer constructions without reversely twisted inner strands have very similar appearance to rotation resistant wire ropes, but they are not.

Rotation resistant wire ropes are considered to be less stable needing to be handled and installed with great care. They must be taken to avoid high loads with small diameter sheaves.

Non-rotating wire ropes are designed so that the wire-rope outer rotational force naturally counteracts the inner strands rotational force in the event of a load applied.

Rather than all wires and strands being laid in the same direction, a rotation resistant wire rope consists of inner strands being laid in the opposite direction to the outer layers, for example the inner may be constructed in left hand lay whilst the outer layer is in right hand lay. This construction means that torsional forces on the inner and outer wires / strands will counteract each other and so minimise the risk of unraveling.

Using an ordinary lifting wire rope for a job or equipment which demand a non-rotating wire rope si very dangerous and it presents the following risks:

Application: For port loading and unloading purposes, for tower crane purpose, lifting and drawing; the rope with steel core can be used under the shock load, heated and squeezed conditions such as excavator.

In a multi-part wire rope system where the blocks have a tendency to twist, or for a single part hoist line which does not require the degree of rotation resistant properties found in a 19 x 7 rope, the 8 x 25 Resistwist rope has found successful application. The rotation resistant characteristic is achieved by laying the eight outer strands around an independent wire rope core so these strands are in the opposite direction to the lay of the core. Thus, when the rope is in tension, opposing rotational forces are created between core and outer strands.

In addition to 8 x 25 Resistwist ropes being more stable than 19 x 7 ropes, several other advantages exist. The 8 x 25 Resistwist has increased resistance to bending fatigue and crushing on drums and sheaves. This is achieved through the use of 8-strand construction with an independent wire rope core.

As with any application where the type of rope on an installation is changed, an 8 x 25 Resistwist rope should be substituted only after carefully comparing specifications and strength requirements.

Rotation resistance ropes frequently can provide the best economical service in specific applications, when selected, handled and used properly. Rotation resistant (contr-helically laid) ropes are different from "standard" construction ropes, because they are required to meet a different set of service requirements. Modes of failure and wear for rotation resistant ropes can vary far more than for standard constructions. The very nature of the construction which allows these ropes to meet their special operational requirements makes certain limitations and special handling which are not encountered with standard constructions.

Tests on rotation resistant ropes show that the length of service life between that point in time where the visible broken wire criteria for removal from service are met, and where actual rope failure occurs, is substantially shorter for rotation resistant ropes than for standard construction ropes. these tests emphasize the need for separate guidelines and criteria for the application, use, inspection and retirement of rotation resistant ropes. Investigation and development work in this area continues.

The use of a swivel at the load hook or in the termination for a rotation resistant rope can result in unpredictable service life. This practice, or any other which allows the rope to rotate while in service, can lead to unbalanced loading between inner and outer layers of strands, which may result in a short length of an operating rope, or there is unevenness of outer strands, the rope should be replaced.

Since rotation resistant ropes are special, applicable industry regulations and standards list separate design, maintenance, inspection and removal criteria for them. Certain inspection techniques for those ropes are different from those required on standard ropes. Assistance in dealing with these special inspection techniques can be obtained by contacting the Company"s Technical Service Engineers.