Steel Wire Rope Constructions

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A steel wire rope is defined not only by its basic elements (wires, strands, core), but also by how these elements are laid together to create a strand and how the strands are laid around the core. The construction of steel wire rope is defined when the following criteria are determined:

• Number of wires in a strand
• Type of strand (strand design)
• Number of strands
• Type of core
• Lay direction (steel wire rope and strand)
• Pre-forming

The steel wire rope is designated according to the number of strands, the number of wires in each strand, the design (type) of the strand, and the type of core.

• 6x7 Standard with FC (fiber core)
• 8x19 Standard with WSC (steel core)
• 8x19 Seale with IWRC (steel core)
• 6x36 Warrington Seale with FC (fiber core)

Number of Wires in a Strand

The number of wires in a strand varies between three and approximately 139, although 7, 19, 24, or 36 wires are most common. The number of wires and their thickness depend on the design of the strand and affect the characteristics of the steel wire rope.

Types of Strand (Strand Construction)

The type of strand is characterized by how the wires in the strand are arranged. There are four basic types of strand design used in all steel wire ropes, either in their original form or as a combination of two or more types. The four basic types are:

• Standard
• Seale
• Filler
• Warrington

Standard

The Standard construction features wires of equal thickness, although the core wire may be thicker. The wires are laid together such that all except the center wire are of equal length, ensuring equal load distribution when pulled straight.

The geometric wire distribution consists of a center wire, onto which one or more layers are laid. Each layer is produced in a separate operation. If there are several layers, the number of wires increases by six for each layer.

The designation for a Standard strand with seven wires is (1-6), meaning one center wire with six external wires in one operation. For 37 wires, it is (1-6/12/18), meaning one center wire with six external wires from the first operation, 12 from the second, and 18 from the third.

The center wire may be replaced by several wires or a fiber core.

Seale

The Seale construction consists of two layers of wire produced in one operation, with identical numbers of wires in both layers. This construction is stiffer than a comparable Standard construction because the outer wires are considerably thicker.

A Seale strand with 19 wires is (1-9-9), meaning one center wire with nine wires in the first layer and nine in the second. The center wire may be replaced by several wires or a fiber core.

Filler

The Filler construction features two layers of wires produced in one operation, with the second layer containing twice the number of wires as the first. Filler wires are inserted between the first and second layers to prevent a hexagonal shape.

This construction is more flexible than a comparable Standard construction and much more flexible than a comparable Seale construction. A Filler strand with 25 wires (including 6 filler wires) is (1-6+6F-12), meaning one center wire with six wires in the first layer and 12 in the second, with six filler wires between them.

The center wire may be replaced by several wires or a fiber core.

Warrington

The Warrington construction features two layers of wire produced in one operation. The second layer contains wires of two dimensions, with the number of wires in the second layer twice that of the first.

This construction is very compact and flexible. A Warrington strand with 19 wires is (1-6-6+6), meaning one center wire with six wires in the first layer and 12 wires of two dimensions in the second layer. The center wire may be replaced by several wires or a fiber core.

Other Types of Strand

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Other strands combine one or more of the basic types mentioned above. One such combination is the Warrington-Seale. This construction is one of the most widely used and most flexible compared to the four basic types.

The Warrington-Seale construction consists of three layers of wire produced in one operation, where the number of wires in the third layer matches that of the second. The layers below the outer layer are built as a Warrington construction.

A Warrington-Seale strand with 36 wires is (1-7-7+7-14), meaning one center wire with seven wires in the first layer, 14 wires of two dimensions in the second layer, and 14 wires in the third. The strands and wires do not necessarily have to be round and can be designed to meet specific requirements.

Number of Strands

The number of strands in a steel wire rope varies between three and approximately 36, with six strands being most common. More strands result in a more rounded and flexible rope, although the wires in the strands will be thinner and less durable.

Types of Core

There are two types of core for steel wire ropes:

• Fiber core (natural or man-made)
• Steel core (WSC or IWRC)

Fiber Core

Fiber cores, usually made of polypropylene (PP) or sisal, are the most commonly used. They provide an elastic base and allow lubrication from the inside by adding oil or grease during production, reducing internal rust. PP is resistant to weak acids and alkalis and does not rot, while sisal absorbs oil/grease better for internal lubrication.

Steel Core

A steel core can be a strand (WSC) or an independent steel wire rope (IWRC). Steel cores are recommended when the fiber core may not provide adequate support for the strands, such as when spooling onto a drum under heavy load or at high temperatures. A steel core increases the tensile strength of the rope by approximately 10%.

Lay Directions (Steel Wire Rope and Strand)

The term “lay” describes both the process of interweaving wires and strands and the appearance of the finished rope. Common terms for lay include:

Right Hand Regular Lay - Wires in the strand are laid in the opposite direction to the strands in the rope (helically left wires, helically right strands).

Left Hand Regular Lay - Wires in the strand are laid helically right, and strands helically left.

Right Hand Lang Lay - Wires and strands are laid in the same direction (helically right).

Left Hand Lang Lay - Wires and strands are laid helically left.

Other Terms

• Multi-layer steel wire rope (low rotation/rotation resistant) - Usually has two layers of strands, the inner layer being left hand Lang lay, and the outer layer right hand regular lay.
• Alternate lay steel wire rope - A combination of regular lay and Lang lay.
• Cable laid steel wire rope - Strands are normally 6-lay steel wire rope with a fiber or steel core, with the core as a fiber core or a 6-lay steel wire rope with a fiber or steel core.
• Square braided steel wire rope - Square braided from strands or steel wire ropes.
• Flat braided steel wire rope - Flat braided from strands or consists of parallel strands or steel wire ropes bound together (belt strap).

Right hand lay steel wire rope is also known as Z-lay, left hand as S-lay. Similarly, right hand lay strand is z-lay and left hand is s-lay. Right hand regular lay is the most common type.

Preforming

“Preformed” refers to steel wire ropes where strands are permanently formed during laying, making them stress-free within the rope. If a strand is removed, it retains its helical shape.

Advantages of Preformed Steel Wire Rope

• Rope will not untwist during cutting
• Easier installation, stress-free, no tendency to form kinks
• Can run over smaller sheaves
• Less tendency to turn on its own axis
• Reduced wear and tear
• Better load distribution between strands and wires
• Less tendency for broken wires to protrude or damage adjacent wires and sheaves

In general, preformed steel wire ropes offer longer life expectancy than non-preformed ropes. All Randers Reb steel wire ropes are supplied preformed, except for certain special constructions.

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