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ROTATION RESISTANCE

In certain instances the use of rotation-resistant wire rope is necessary to provide rotational stability to the lifted load. In general, the use of these wire ropes is limited to those situations where it is impractical to:

1. Use a tag line

2. Relocate rope dead end.

3. Increase sheave sizes.

4. Eliminate “odd-part” reeving.

5. Significantly reduce rope loading and rope fall length.

Rotation-resistant wire ropes have less of a tendency to unlay when loaded than do conventional wire ropes. This results in improved rotational stability to the lifted load. Rotation-resistant wire ropes are designed in such a way that the rotational force of the outer strands is partially counteracted by the rotational force of the inner strands or core when the rope is subjected to a load.

The chart compares the rotational properties of rotation-resistant ropes with a standard 6×25 wire rope. The rotation-resistant ropes far surpass the rotational stability of a conventional 6×25 IWRC wire rope on both short and long falls.

SAFETY DESIGN FACTORS

BS 302/BS EN 12385 specifies that rotation-resistant ropes have a safety design factor of five or greater. The required strength design factor of rotation-resistant rope becomes very important from the standpoint of maintaining the inherent low rotation of the rope and eliminating any tendency to overload the inner core, thereby causing a reduction in rope strength.

HANDLING & INSTALLATION

Precautions should be followed when using rotation-resistant wire rope. The rope ends must be properly seized and secured (refer to Handling and Installation: Seizing Wire Rope) and cut with a saw or impact hammer to prevent unlaying of the strands.
Attachment of end fittings must be done with care to prevent kinking or unlaying of rope, which harms the rotational balance of the rope.
Operation of rotation-resistant wire ropes (excluding SFP 35™) with a swivel is generally not recommended. The use of a swivel allows the inner core to twist tighter, resulting in a significant reduction in rope strength, possibly leading to premature rope failure. A swivel may be used as a temporary device only during the initial installation period to help eliminate any installation-induced twisting or cabling.

The swivel must be removed from the reeving after the rope installation is completed and before the crane begins operation.
Due to the opposite lay direction of the inner core and outer strand layers in rotation-resistant ropes, care should be taken to avoid shock loading. Shock loading will result in distortion of the rope structure, causing birdcaging, core protru-sion, etc. Due to the potential for complete rope failure, shock loaded wire ropes must be immediately removed from service.

Strands: 8
Wires per strand: 19
Core: IWRC
Standard grade(s): EIPS
Lay: Regular
Finish: Bright
Strands: 8
Wires per strand: 19
Core: IWRC
Standard grade(s): EIPS
Lay: Regular
Finish: Bright

19×7 is recommended for hoisting unguided loads with a single-part line.

The rotation-resistant properties of this rope are secured by two layers of strands. The inner strands are left lay, while the 12 outer strands are right lay, which enables one layer to counteract the other layer’s rotation.

The rotation-resistant characteristics of the 19×7 wire ropes are superior to those of the 8×19 Class wire ropes.

The 8×19 Classification rotation-resistant ropes are recommended for hoisting unguided loads with a single-part or multi-part line.

The eight outer strands are manufactured in right lay, with the inner strands being left lay.

These ropes are slightly stronger and signifi-cantly more rugged than the 19×7 construction. However, the rotation-resistant properties of the 8×19 rotation- resistant ropes are much less than those of the 19×7 construction.

These ropes are manufactured in right regu-lar lay in the 8×19 Seale and 8×25 Filler Wire constructions.