Lifting gear - Synthetic Wire ropes , Construction and defects

SYNTHETIC WIRE ROPE

Rules of thumb to check if Tag showing WLL (SWL)  is correct for a Synthetic Wire Rope if used for lifting

                                      SWL (WLL) = D²

                             D is the  Diameter in mm

 Note: If unknown, the formula for fiber rope stitching should apply or be accepted.

Certification of Breaking load is issued in case of Ropes for heavy service , such as mooring ropes.

Examples :

 (i) 12 mm diameter unidentified Synthetic rope      : 12mm = 12x12 = 144 kg WLL.

(ii) 15 mm diameter unidentified Synthetic rope      : 15mm = 15x15 = 225 kg WLL       

Minimum Allowable diameter for handling Purposes: 12 mm

Maximum allowable handling temperature : 65 °C (limited due to material )

Smallest size diameter fibre rope allowed for use as a hand-held tagline: 16mm

Types of Ropes and construction

The twist direction is indicated by the capital letters “S” and “Z”. When the rope is held vertically, the twist spires in the consecutive rope parts are in the same diagonal direction as indicated with the letter “S” (left hand) or “Z” (right hand). The most common final twist for cabled ropes is “Z”.

The opposite twists result in a “balanced” rope. Varying the number of twists results in a more soft- or hard-laid rope - according to the customer's preference. Without extra specifications, the rope is always produced as “medium” lay. The lay-length is then between 2,8 and 3,5 times the diameter.

Composition of a right hand twisted rope:

• Single yarn: bundle of filaments twisted “Z” (right)
• Cabled yarn: composed of “S”-twisted yarns subsequently twisted together in the “Z” (right) direction
• Strand: assembly of yarns twisted “S” (left)
• Rope: assembly of strands “Z”-twisted together - for specific use cabled rope also exists in “S” lay

To avoid kinking it is recommended to uncoil “Z” twisted rope
by pulling out the inner end of the coil counterclockwise. 

3-strand

Most common construction especially in northern Europe. Standard diameter 1-40mm. 

4-strand with or without central core

The core can be a rope or a strand. Often used in southern Europe. Standard diameter 6-52mm. 

6-strand + central core

Only used for speciality ropes such as compound steel wire/textile ropes, mooring ropes as Superwinchline or combination rope. Standard diameter 12-96mm according to products. 

For narrow ropes:

Braided rope without core

8 or 16 plait - only narrow ropes (1-16mm diameter).

Braided rope with core

8-,16- or 24-plait around a central core; the core itself can be composed of a bundle of single yarns, cabled yarns, strands, braided or cabled ropes. In order to obtain a torque-free final construction half of the twisted core elements need to be “S”, the other half “Z” twisted. The outer braid as well as the inner core contributes to the breaking strength of the rope.
Mostly used for rope diameter from 2 to 24mm. 

For thicker ropes – mooring ropes (up to 220mm):

Double braided ropes (braidline - coaxial - braid on braid)

Double-braided ropes are composed of 2 concentric braided elements. Both braided parts contribute ±50% to the final breaking strength. The central core is mostly a 8- or 16-plait rope, the outer braid 24-, 32- or 48-plait.
Often used as mooring rope and for offshore applications.

 

8-strand plaited rope – square line

Composed of 4 pairs of twisted strands; 2 pairs of strands “S”-twisted, 2 pairs “Z”-twisted; then plaited pair by pair.
Most popular construction for mooring ropes.

12-strand plaited rope

Same system as 8-strand but 6 pairs of strands. Rounder shape construction.

Superline

This construction is different from the above. The outer braided cover is only meant to protect and compact the load-bearing central core. The advantage is a higher breaking load for a smaller size than the above constructions. The reason for this is that there is less processing of the core. The core can be an assembly of twisted or braided ropes. The rope is utilized for heavy duty applications.

Strands are fraying, 

Strands are cut, Rope chafed inside or outside,

Rope rotted by acid or alkali, 

Rope affected by mildew, /heat, sun rot, - minor or major snags