As crane experts, we often get the question “what is wire rope?” Many people know that they need it for their lifting application, but don’t know what to ask for when they go to purchase it. Our aim is to provide you with the information you need to feel confident in your purchase and understand what type of wire rope is best for your industrial crane needs.
Moreover, when selecting the right wire rope for your specific industrial lifting application, it is important to consider the wire rope’s material, size, and construction. By understanding the different types of wire rope available, you can make an informed decision about which one is best for your needs.
From wire rope components to strand structure and crane applications, this article will discuss what wire rope is, what different specifications there are for wire ropes, and how they are constructed.
What is Wire Rope?
Wire rope is a popular lifting tool for a variety of reasons. This type of rope comprises many steel wires that are twisted together to form independent strands. Strands then surround a core in a helical pattern.
Commonly used in heavy lifting situations, wire rope is strong, flexible, and able to bear bending strains. However, each type of wire rope has its own strengths and weaknesses. The material, wire, and strand structure utilized may provide distinct advantages, such as strength, flexibility, and resistance to abrasion.
Wire rope key terms to know:
- Length: When wrapped around the spool and delivered, the overall number of feet (cut to size).
- Size: The wire rope’s diameter, in inches or millimeters.
- Strand patterns: The number of strands and their arrangement in the rope.
- Wire rope clip: A type of fastener used to connect wire rope end fittings.
- Wire rope sling: A crucial rigging component in lifting and hoisting operations. Wire rope slings connect the load to the lifting mechanism and are available in a variety of configurations that support a wide range of applications. Single and multi-part slings, such as round braids, flat braids, Tri-Flexes, grommets, single leg slings, and more.
- Single layer: A wire rope in which the strands are all in one layer.
- Lay: The distance between the strands of a rope when they are helically laid or the length of each strand that makes one complete revolution around the core.
- Regular lay: The wires align with the rope’s axis. The strand lay is in the opposite direction of the wire held in the strand.
- Lang lay: The wires are angled with the rope’s axis. The wire lay and the strand lay around the core in the same direction.
- Alternate lay: The wire rope is consists of alternating regular lay and lang lay strands, which are typically for specialized purposes.
- Construction: The rope wraps in a machine that performs several functions to create the rope. The machine twists the strands together and constructs an outer wire sheath around them to protect them from corrosion or wear.
- Filler wire: The two-layer wire construction consists of equally sized wires surrounding a center with an inner layer that is double the number of outer wires.
- Seale: Around the centers, there are two layers of wires with the same number of wires in each layer. The diameter of all wires in each layer is the same. The larger outer strings rest in the valleys between the smaller inner strings.
- Warrington: The center is surrounded by two layers of wires with one wire diameter, and the outer layer has two wire diameters. The larger wires are in the valleys of the outer layer and the smaller ones on the crowns of the inner layer.
- Combination: Consists of two or more different strand patterns that have been combined.
- Preformed: The strands are pre-twisted before being placed around the center.
- Non-preformed: The strands are twisted around the center while they are being formed.
- Finish: The wire rope’s coating or protection.
Wire rope can be made from a variety of different materials. Carbon steel and alloy steels are what most people think of when wire ropes come to mind, but the construction process for each is slightly different. Aluminum, nickel alloy, bronze, copper, and titanium are also a few of the alternative materials available.
The structure of wire rope is critical to its strength and function. The rope’s component strands must be tightly woven together to form a cohesive unit. Wire rope can be composed of various materials, as well as having various strand structures. These include:
Single Layer Strand
A 7-strand strand is the most frequent type of single-layer construction. It features a single wire in the middle with six wires of equal diameter encircling it.
This configuration has two layers of wires around a center with the same number of wires in each layer. The diameter of each wire in each layer is the same. The strand accommodates the larger outer wires, which rest in the valleys between the smaller inner wires.
The center of this structure has two layers of uniform-size wire surrounding it, with the inner layer having half the number of wires as the outer layer. In valleys of the inner layer, little fillers, which are equal in number to the inner layer, are placed.
This design has two layers of wires surrounding a middle with one diameter of wire in the inner layer, and two diameters of wire alternating big and little in the outer layer. The greater outer layer wires rest in the valleys of the inner layer’s larger valleys, while the smaller ones on its crowns.
When a strand is created in a single operation using two or more of the techniques, it is a combined pattern.
Wire Rope Components
A wire rope’s design is made up of four distinct components:
The smallest component of wire rope is the wires. They are placed in a specified pattern around a center in one or more layers to make up a strand.
Strands are what the wires are twisted together to form. The separate strands are wrapped around the rope’s core in a helix. Strands made of larger wire diameter are more resistant to abrasion, while strands made of smaller wire diameter are more flexible.
The core is the structural element that runs down the middle of the rope and supports the strands. It also helps to maintain their relative position under loading and bending strain. Cores are typically constructed from natural or synthetic fibers and steel, although they can also be manufactured from a variety of materials.
Core wires are identified as:
- Fiber Core (FC) — Natural or manufactured polypropylene fibers can be used to make a fiber core. FC have greater elasticity than a steel core but are more susceptible to crushing and aren’t suited for high-temperature atmospheres.
- Independent Wire Rope Core (IWRC) — IWRC provides strength, better resistance, and can handle extreme heat. It is best for severe loads on ropes running over sheaves or on wound drums.
- Wire Strand Core (WSC) — WSC is a strand made of wires. Strand cores are most frequently utilized in utility wires and applications where severe crushing is expected.
During the manufacturing process, lubrication is applied throughout and to the core. Wire rope lubrication has two primary advantages:
- Reducing friction as the wires and strands pass over one another
- Corrosion protection and lubrication in the core, interior wires, and exterior surface
Wire Rope Construction
The four steps in the construction process are as follows:
- First, the wire is manufactured to precise specifications and then cleaned.
- Second, the wires are formed into strands that will make up the rope’s core.
- Third, each strand is helically wound around the core.
- Fourth, the lubricant is applied, and the rope is heat-treated to set the final properties.
Types of Wire Rope
There are three main types of wire ropes.
The most popular alloy for rope and cable is stainless steel. Its corrosion resistance is greater than that of galvanized and coated ropes, but its strength is identical.
Stainless steel wire rope is a highly utilized material to produce precision instruments, automobiles, and other goods due to its resistance to corrosion, heat and cold. Moreover, it is resistant to chemicals from industries like food processing or waste treatment.
Galvanized Wire Rope
Galvanizing is a coating that is applied to the wire rope’s surface to protect it from corrosion. The zinc layer reacts with the atmosphere and forms a protective layer of zinc carbonate.
The main reason for galvanizing wire rope is to produce resistance from corrosive conditions like seawater, salt spray, etc.
Galvanized steel has less tensile strength than stainless steel, but it is more flexible in cold temperatures which makes it especially useful when lifting things on an icy surface.
Coated Wire Rope
Coating is a process that is applied to the wire rope’s surface to protect it from wear and tear. The coating can be rubber, plastic, nylon, or vinyl.
The most common type of coated wire rope is PVC (polyvinyl chloride). It has good resistance to abrasion, oil, weathering, and chemicals which makes it ideal for marine applications.
Wire Rope Classification
The variety of wire rope classifications includes the total number of strands, as well as a nominal or precise number of wires in each strand. Classification by the number of wires is, however, a broad generalization that may or may not reflect the strand’s actual construction. However, every category has the same strength and weight limits.
Below are some of the most common wire rope configurations arranged in specific classifications.
Other types of wire rope exist for particular lifting applications and unique construction including:
Rotation Resistant Wire Rope
Under high loads, certain wire rope varieties are more prone to rotation. As a result, rotation-resistant wire rope is designed to resist any twisting or spinning. It may be utilized in a single-line or multi-part configuration.
Compact Strand Wire Rope
Compact strand wire rope is produced by compressing strands through a die or rollers, resulting in a strand with a smaller overall diameter. This procedure flattens the surface of the outside strands while also increasing the density of the strand. The result is a wire rope that has increased resistance to wear and fatigue.
Compact / Swaged Wire Rope
Compact wire rope (also known as swaged) is the result of a process that permanently compresses together alternating wires to form what appears like one solid core strand. After the wire rope has been closed, a rotary swager machine compacts or shrinks the diameter of a swaged wire rope. The configuration reduces weight and increases wire rope strength due to increased density in all strands.
Plastic Coated Wire Rope
As the name suggests, plastic-coated wire rope has a layer of extruded plastic that covers the entire wire rope. This coating provides abrasion resistance and helps to protect the wire from weathering, chemicals, and other harsh environments.
Plastic Impregnated (PI) Wire Rope
Like plastic-coated wire rope, PI Wire Rope has an extruded layer of plastic that covers the entire wire rope. Plastic-filled wire ropes are filled with a matrix of plastic within the internal gaps between the strands and wires. The internal and external wear are reduced by the plastic filling, which aids in the reduction of bending fatigue.
Plastic Filled IWRC Wire Rope
Plastic-filled IWRC wire rope is a unique construction that combines the advantages of an individual wire rope core (IWRC) with the benefits of plastic filling. The internal wires are protected by extruded plastic, while the external wires serve as a wear surface. This configuration increases fatigue resistance and helps to minimize distortion.
Wire Rope Applications
Wire rope is used to lift and pull heavy objects. It has a high tensile strength that allows it to withstand substantial amounts of force while also being lightweight, flexible, relatively easy to install and affordable.
Wire rope is ideal for several different industries, including the following:
Wire rope is for lifting and lowering heavy equipment. It can also be of use to move construction materials, such as concrete blocks, pipes, lumber, and other building materials high above the ground.
Electrical Power Distribution
Wire ropes are used in electrical power distribution systems that transmit a significant amount of electricity via high voltage transmission lines. Wire ropes can handle high loads at great heights and must be able to endure the elements.
Dockyards & Ports
Wire rope is used to secure and raise/lower cargo in a safe, efficient manner. The wire ropes are attached directly to the cranes on-site or through overhead lifting frames for safety reasons.
Energy (Oil/Gas) Industry
Wire rope is used to drill, complete and workover rigs. It can also be utilized for support when drilling oil or gas wells.
Wire ropes are a key component in the production of large steel structures where heavy loads must be lifted into place on top of cranes & buildings during construction. Additionally, wire ropes may attach directly to the crane or to a lifting beam.
It is also used in a number of other applications, including:
- Winches: to pull or move heavy objects.
- Cranes and hoists: to lift and lower heavy objects.
- Draglines: to move copious amounts of earth.
- Conveyors: to transport materials over a distance.
- Lifts: to transport people or heavy objects vertically.
As you can see, wire rope is an extremely versatile piece of equipment that has a million different uses for the industrial and construction industries.
How to Choose the Right Wire Rope for Your Crane Project
When choosing a wire rope for your crane project, there are several factors to consider. The most important thing to keep in mind is the weight of the object being lifted. You also need to consider the working radius and what type of environment the wire rope is in. Moreover, ropes have a variety of qualities that affect their performance capabilities. Therefore, it’s worth taking a closer look at each rope’s distinct features before making a selection.
Wire rope is engineered with a variety of qualities in mind:
Generally, wire rope strength is measured in tons of 2,000 lbs. The breaking strength of wire rope is stated in terms of minimum breaking force (MBF) or nominal (catalog) strength. These represent predicted strengths that have been accepted by the wire rope industry.
The minimum breaking force is the force at which a sample wire rope will break when tested under laboratory conditions, while the nominal strength is what the manufacturer guarantees the wire rope will withstand.
When subjected to tension a new rope should break at the same or greater force than the one specified for that rope. Moreover, a wire rope should never be operated at the minimum breaking force. This value is used as a guide to select the correct wire rope for new installations.
Wire ropes are also engineered to resist fatigue. Fatigue resistance is the ability of a wire rope to withstand multiple cycles of flexing without breaking. The number of cycles a wire rope can endure before failure depends on a variety of factors, including the type and size of wire rope, the severity of the stress, and the ambient temperature.
A large number of wires are used in rope construction to improve fatigue resistance. It factors in wire diameters as well as basic metallurgy. For example, a rope made of many smaller wires will have better fatigue resistance than the same-size rope constructed of fewer larger wires. Smaller wires are more flexible and can bend farther as the rope passes over sheaves or around drums.
To counteract the effects of fatigue, ropes must never bend over small sheaves or drums with wire diameters that might kink or strain them. Sheave and drum dimensions are strictly regulated to accommodate all sizes, types, and brands of ropes.
External pressure has a direct effect on a rope’s cross-section shape, strands, or core by distorting the rope’s cross-section. The crushing force applied to the rope by any object can cause the wire strands and core to be squeezed together.
This, in turn, reduces the diameter of the rope and its breaking strength. When a rope is crushed, the wires, strands, and core are kept from moving and adjusting normally throughout use.
To help prevent this from happening, wire ropes are manufactured with a high degree of crushing resistance. The number of wires per strand, as well as the size and type of wire, are all key factors in providing crushing resistance.
Metal Loss and Deformation Resistance
In addition to the above-mentioned qualities, wire ropes are also engineered to resist metal loss and deformation. Metal loss is a result of the wires in a rope rubbing against each other as the rope moves. This can cause the individual wires to wear down, thinning the diameter of the rope over time.
Deformation is what happens when the shape of the rope’s cross-section is changed because of external pressure. This can cause the wire strands and core to be squeezed together, reducing the diameter of the rope. The most typical kind of metal deformation is peening, which occurs when ropes are stretched, and the exposed wires appear to have been hammered across them.
Both metal loss and deformation reduce the breaking strength and fatigue resistance of a wire rope. To combat these effects, manufacturers add extra wires to the strand and use larger-diameter wires in the construction of a rope.
When a wire rope is subjected to rotation, the wires, and strands inside it will attempt to straighten out, which causes torque to generate throughout the rope.
However, this load-induced torque can be reduced via specifically designed rotation resistant ropes. In rotation-resistant ropes, the lay of the outer strands is in the opposite direction from that of the inner strands, resulting in torques that are in opposite directions and cancel each other out.
Wire Rope and Wire Rope Slings for Overhead Cranes
Wire rope is a vital component in overhead crane applications. The wire rope’s strength and fatigue resistance are what determine how much weight the crane can lift.
In addition, the rotation resistance of the wire rope helps to prevent the torque generated as the wire rope rotates from affecting the lift. Overall, wire rope is an essential part of any overhead crane system.