CONSTRUCTION AND DESIGNATION
CONSTRUCTION AND DESIGNATION
The strand is the simplest construction: it consists of one or more layers of superimposed wires laid spirally around one or more central wires or around a fibre core. The construction of the strand is identified by the number of wires in the individual layers, starting from the outer one (e.g. 12+6+1 or 15+9+FC). FC indicates a fibre core. Distinction is made between strands with cross laid and equal laid wires.
- STRANDS WITH CROSS LAID WIRES
All the wires in this type of strand are of equal diameter and for geometrical reasons the number of wires decreases in each layer, starting from the outermost one, according to an arithmetical progression based on number (18 + 12 + 6 + 1 or 12 + 6). In cross laid constructions each layer of wire is laid up a separate operation with a different length of lay, the result being the crossing of the various layers of wires. Consequently strong pressure occurs between the wires which may break, especially with variable loads. - STRANDS WITH EQUAL LAID WIRES
In these constructions the pitches of the various layers of wires are identical as stranding is carried out in a single operation; therefore, the contacts between wires are lindar. Seale, Warrington and Filler strands belong to this construction. Wires of different diameters are required for these constructions.
As for example:
Seale : 9 + 9 + 1
Warrington : 6/6 + 6 + 1
Filler : 12 + 6F + 6 + 1
SINGLE STRAND ROPES are commonly called strands.
ROUND STRANDED ROPES consist of a number of strands either laid around a fibre core or metallic strand or an independent wire rope core. They can be identified by the number to each strand. A rope with 6 strands, each having 9+9+1wires laid around a central fibre core is designated as; 6 x (9 + 9 + 1) + FC or more concisely 6 x 19 Seale + FC. If this same rope has an independent wire rope core, the designation will be: 6 x (9 + 9 + 1) + IWRC. The IWRC is a metallic rope having for example a construction designated by 7 x (6 + 1) or 7 x 7. Should the strands also contain a fibre core then the rope will be known for example as 6 x (12 + FC) + FC or 6 x 12 + 7FC. Lastly if the rope is formed of two or more layers of strands superimposed around a FC, then it will be known as: 12 x (6 + 1) + 6 x (6 + 1) + FC or 18 x 7 + FC.