Wire rope is an essential component of air winch systems, as it is used to pull a load horizontally from one area to another. This rope is made of metal wire and consists of three primary components: the core, strands and the outer wire. These components are designed to work together to give wire rope its strength, flexibility and long term durability.
The core of the wire is the foundation of the strands, giving them a solid base to wrap around. The inner strands make up the majority of the strength of the wire rope, providing the brunt of its holding capacity. The outer layer of wire primarily functions as an abrasion barrier to protect the rest of the wire and add to its durability.
It is important to understand the specific characteristics of wire rope in order to ensure its safe usage. This will allow operators and those responsible for specifying winch and load handling equipment to be able to maximize workplace safety. When this is taken into consideration along with other factors such as safety warning lighting, issuance of appropriate personal protective equipment and physical barriers to prevent injury, accidents can be dramatically reduced, safety improved and operational downtime minimized.
Characteristics of Wire Rope
There are several specific characteristics of wire rope that determine its appropriateness for each application and performance requirements. The six primary characteristics are listed below:
Size – One of the most basic ways in which to differentiate types of wire rope, size refers to the outside diameter of the rope. It is always measured at the rope’s widest point. The general rule of thumb for wire ropes is that their load carrying capacity will increase as their diameter gets larger, with the same style of materials and construction.
Classification – This is the primary way in which different wire ropes are differentiated. Classification specifically includes two numbers – the number of strands and number of individual wires that makes up the wire rope. For example, a 6×37 refers to a rope with 6 strands each made up of 37 wires. Higher wire and strand counts produce more flexible, but less durable ropes.
Rope Lay – This describes not only the direction that the wires and strands spiral around the core, but also the style of wrap. Generally speaking, this will be a right or left hand lay, with the wrap style being regular or lang. Regular lay ropes are less likely to experience kinking or untwisting, whereas lang lay ropes are more flexible and have better abrasion resistance. The lay style chosen is based on which of these characteristics the end user prefers.
Grade of Steel – Wire rope will be constructed of one of three primary grades of steel: Improved Plow Steel (IPS), Extra Improved Plow Steel (EIPS or XPIS), which is the most commonly used and manufactured grade, or Extra Extra Improved Plow Steel (EEIPS or XXIPS). The grade chosen is entirely dependent on the application requirements, with certain types of applications requiring higher grades in critical environments.
Type of Core – There are three common options for wire rope cores: Fiber Core (FC), Wire Strand Core (WSC), and Independent Wire Rope Core (IWRC). Fiber core (FC) is made of synthetic material, is the most flexible and elastic, but is susceptible to crushing. Wire strand core (WSC) is made up of an additional strand of wire, is used in smaller ropes, and is ideal for suspension and tensioning. Independent Wire Rope Core (IWRC) contains a smaller wire rope to serve as the core, is highly durable in all environments, and is preferred in offshore and construction environments.
Nominal Strength – This is one of the most straightforward yet important characteristics of wire rope. Normal strength describes the minimum breaking strength of a new, unused rope. It is important to ensure that wire ropes have enough strength to withstand the loads they are bearing, and it is therefore important that wire rope have a nominal strength that is considerably higher than the load it will be handling. This gives it a capacity cushion in order to ensure safe operation, especially as wire rope ages and potentially loses some of its strength.