We’ve read all about how it is extremely crucial for industrial workers to select the right slings when moving a suspended load. Wire rope suppliers churn out the best and the most hi-tech and innovative slings from time to time, with a view of bringing about safe equipment handling and lifting of loads.
Broadly speaking, the selection of the right sling is based on the following few factors:
- The size of the load
- The weight of the load
- The shape of the load
- The temperature and sensitivity of the material being moved
- Environmental conditions
- Outcome of the visual inspection (This is to be done before each use to ensure safety and effectiveness)
Slings are also used in hoisting equipment. Apart from overloading, incorrect use of hoisting equipment (including slings) may lead to either an accelerated speed or a slowdown.
There are 6 types of slings –
- Chain sling
- Wire rope
- Metal mesh
- Natural fiber rope
- Synthetic fiber rope
- Synthetic web
These slings are further classified into 3 categories –
- Wire rope and mesh
- Fiber rope/ synthetic web
The following pointers may be useful in the selection of the right kind of sling –
The right chain will, typically, be strong, sturdy and devoid of incisions. Before using it, you might want to check it for stretches, scratches, cavities and wear exceeding that which is allowed by the manufacturer. Should you come across any of these signs, you can consider the slings unsafe for use and have them discarded from service immediately.
Alloy steel chains are most commonly used in heavy lifting equipment because not only are they strong, they can also adapt to the shape of the load. Proper care needs to be taken, however, when using chain slings because they are not resistant to sudden shocks, which may lead to a sling failure, damage to the load, and injury to the workers.
To make a wire rope, a collection of wires is compiled with individual wires twisted together to form strands. These strands are further twisted together, which results in the formation of a wire rope. Wire ropes which are made of fiber strands tend to be more ductile, but are less resistant to adverse environmental conditions. On the other hand, wire ropes made of wire strands are generally associated with greater strength and higher endurance to heat.
Selecting a good quality and long-lasting wire rope entails looking for 4 chief features that make it reliable: strength, wear resistance (bending without distortion), the ability to endure abrasion, and the ability to withstand abuse.
To determine the strength of the rope, you need to take its size (diameter), grade, and construction into account. The main purpose of doing so is to ensure that the wire rope is strong enough to bear the maximum applied load.
- Wear Resistance
One of the key factors to consider in wire rope selection is its ability to withstand fatigue. Fatigue failure is caused when small cracks develop in the rope when it is bent at a small radius. The most common method of preventing the occurrence of such cracks is by blocking or padding the wire rope to increase the bend radius.
- Endurance to Abrasions
This factor is determined by the size and number of wires assembled together to make the rope. It has been observed that smaller wires bend more easily, thereby offering greater flexibility. They do not, however, offer much resistance to abrasions. On the contrary, larger wires are less flexible, but endure abrasions better.
- Withstanding Abuse
This is one of the common causes of rope failure. Misusing or mishandling wire rope slings can bring about serious structural damage which can result in kinks and/or bird caging, which in turn may lead to injuries to those handling the slings. In order to prevent such circumstances and increase the longevity of the sling, it is important to strictly adhere to the safety procedures related to its proper use.
Fiber Rope and Synthetic Web
- Fiber Rope
Fiber rope and synthetic web slings are best for short-term use, for example, work such as construction and painting. They are considered most reliable for handling delicate and expensive loads, especially fragile equipment.
A major drawback of fiber rope slings, however, is that they fail on contact with acids and caustics. Care needs to be taken, therefore, to store these ropes away from such substances. Furthermore, slings should be inspected for cuts, gouges, worn-out surfaces, brittle or discolored fiber, melting, or charring. Should such defects be discovered, the sling should be discarded immediately.
An important sign to watch out for is the build-up of powder-like sawdust on the inside of the fiber rope, which indicates extreme internal wear. Additionally, if merely scratching the rope fibers with a fingernail causes them to split easily, it implies that the sling has suffered chemical damage. Such ropes are unsafe for use and should be discarded.
- Synthetic Web Slings
These slings are made of nylon, polyester or polypropylene. They easily adjust themselves around the load and hold it with a snug, anti-slip grip. They can withstand loads of up to 300,000 pounds (depending on their size). They can also absorb heavy shocks without damage and are less likely to scar polished surfaces. They have low initial costs and are long-lasting as they are unaffected by mildew, decay, or bacteria, can resist chemical action, and have outstanding abrasion resistance.
It is always advisable to adhere to manufacturer’s specifications and inspect synthetic web slings before use and remove them from service if found to have suffered burns, melting or charring, snags, tears, or cuts, broken stitches, distorted fittings, or wear or elongation beyond safety.
Proper use and maintenance of a sling can ensure not only its own safety, but also that of those working with it. The above mentioned tips should be helpful in familiarizing you with its important aspects.