They may look simple, but wire rope slings play a critical role in various industries, including construction, shipping, material handling, and rigging.
You can use them to make permanent or temporary attachments. You can attach a wire rope sling to a hoist or crane to move large loads.
The unique physical properties and resistance to abrasion make it easier to use these slings with shackles, hooks, and swivels for a variety of material handling applications. They also provide strength, durability, and resistance to abrasion or elements.
However, this seemingly simple lifting device comes with a unique structure and functional properties. Let’s take a look at the complete anatomy of wire rope slings.
1. What Is a Wire Rope Sling?
A typical wire rope sling consists of a wire rope made from small individual steel wires twisted together. Both ends of the wire rope are looped together individually to form a sling. The wire rope is the fundamental component of a sling.
These slings come in a variety of sizes, shapes, and tensile strengths. The most common ones are those with an eye loop swaged on both ends of the sling.
Let’s take a look at the structure and mechanics of a wire rope in the next point.
2. Understanding the Anatomy of a Wire Rope
A typical heavy-duty wire rope has multiple small twisted strands made from various grades of steel. The configuration and number of these strands changes, depending on how complicated the pattern is.
Usually, a typical rope comes with hundreds of outer wire strands covering the core strand. All these strands move together as well as independently, providing the wire rope with the necessary strength and flexibility. The mechanics of this movement are quite complex.
A. Parts of the Wire Rope
The typical wire rope consists of the following three components:
A wire is the smallest part of a wire rope. You can use different types of metals, including stainless steel, iron, steel, and bronze to make the wires. The grade of the material used for making the wire depends on strength, abrasion resistance, and durability required for the intended application.
You can create a strand by twisting two or more wires together tightly in a precise pattern. Again, the weaving pattern will be determined by the end-application of the rope.
It is made from steel or natural and sometimes synthetic fibers. The strands go around the core, which offers support when the rope bends or is attached to the load.
B. Common Strand Patterns
As mentioned, strand patterns are critical as they determine the strength, durability, and abrasion resistance of the rope. Usually, the strand consists of the number of wires per layer, the number of layers of wires, and the size (diameter) of the wires in each layer.
Here are the few most commonly used strand patterns.
- Single Layer
As the name suggests, this type of pattern consists of only one layer of wires around the core, all having the same size or diameter. There are usually six strands covering a core, totaling the number to seven.
- Filler Wires
It comprises two layers of wires wrapped around the core. The inner layer usually has six wires, while the outer layer has twelve with equal diameter. Six filler wires with a smaller diameter are used to fill the gap between the two layers of strands.
Like the filler pattern, this one also has two layers of wires surrounding the core. However, wires in the inner layer have a smaller diameter compared to the ones in the outer layer. The outer wires rest in the troughs of inner smaller wires.
This pattern also consists of two layers of wires. However, only the inner layer has wires with a uniform diameter. The ones in the outer layer have two sets of wires, one with a bigger diameter and the other with a smaller one.
In the outer layer, the bigger wires rest in the troughs of the inner layer, while the smaller ones rest on the crests on the wires in the inner layer.
In this type of wire rope structure, manufacturers use two or more of any of these patterns to build the rope.
C. Common Layering Patterns
Layering is the next level of structure in a wire rope sling. It is different ways in which:
- You can lay the wires to create strands
- You can lay the strands to create the wire rope
There are three common ways to lay down the wire ropes.
- Regular Layering
This is one of the most common types of layering patterns. In this, the strand layering and the wire layering are in opposite directions. This arrangement provides the wire rope slings with exceptional resistance to crushing forces and offers better spooling.
- Lang Layering
In this type of structure, the wire layering and the core layering are in the same direction. However, the wires form an angle with the rope axis. This arrangement provides a higher resistance to fatigue and abrasion.
- Alternate Layering
In this type of structure, manufacturers use both regular and lag layering in a suitable combination. However, alternate layering is designed for specialized applications only.
3. Common Types of Wire Rope Sling Terminations
Different types of slings are available in the market, depending on the type of end-fittings or loops.
Here are a few common ones.
A. Flemish Eye Splice
This is the most popular wire rope sling. In this type of loop, the spliced end of the rope is tied around the body of wire rope slings using a metal sleeve. The Flemish eye splice is best suited for six-strand ropes.
However, if you are using these loops with other types of wire ropes, you need to use aluminum or loop-back (turn-back) steel sleeves. The regular sleeves often cause an electrochemical reaction, which speeds up the deterioration process.
B. Aluminum Sleeve Loop-Back Splice
In this loop, an aluminum sleeve is pressed using fabrication over both rope parts. The integrity of the pressed sleeve solely determines the strength of these wire rope slings. You can also add thimbles to these slings.
C. Steel Sleeve Loop-Back Splice
This is similar to aluminum sleeve loop-back splice. However, it uses steel sleeves with a slightly smaller diameter. It can also be used for making stainless steel rope slings of a larger rope diameter.
D. Swaged Fittings
The rope gets inserted into the fitting bore, and it then gets swagged onto the rope. With this method, you can attach open and closed sockets, buttons, threaded studs, and load hooks directly to the rope. The process results in a high-efficiency bond.
E. Spelter Sockets
This is a type of socket that is attached to one or both ends of a wire rope to form a sling. The strength of these sockets is the actual rope strength.
As you can see, wire rope slings are a complex piece of lifting device, although they look simple. Hopefully, understanding their structure will help you know how they can offer the required strength, flexibility, and resistance to abrasion, crushing, and fatigue. It will also help you choose the right sling suitable for your application. Do tell us why and how you use these slings in your industry in the comments section.