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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:
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 –
These slings are further classified into 3 categories –
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.
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.
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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.
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 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.
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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.
Are you planning your next overhead lifting project and unsure about the best type of lifting sling to use? Or, maybe you’re not getting the service life you would expect out of the slings that you’re currently using? Alloy chain slings, wire rope slings, synthetic slings, and metal mesh slings can all be used to safely and efficiently lift, move, and position a load.
But, choosing the right type of lifting sling is dependent on a complete understanding of the application, the environment it’s being used in, and how the sling will be used to support and lift the load.
In order to have a balanced lift, you need to know the following:
At Mazzella, we provide ideal lifting solutions—offering all styles of lifting slings, rigging hardware, wire rope, overhead cranes and hoists, and engineered lifting devices. Our goal for this article is to help you understand the basics of overhead lifting slings and provide you with the advantages and disadvantages of each type so you can make an informed decision and select the best lifting sling for your particular application.
Wire rope is a preferred lifting device for many reasons. Its unique design consists of multiple steel wires that form individual strands laid in a helical pattern around a fiber or steel core. This structure provides strength, flexibility, and the ability to handle bending stresses.
Wire rope slings are popular in construction, automotive, oil and gas, and general manufacturing industries where a variety of heavy loads and rugged conditions exist. They’re also very popular in steel mills and forging facilities where the durability of the rope is really put to the test.
Different configurations of the material, wire, and strand structure will provide different benefits for the specific lifting application—including abrasion resistance, strength, flexibility, and fatigue resistance. Wire rope slings have a lower initial cost than alloy chain, while remaining fairly lightweight in design.
Wire rope slings are available in single-leg or multi-leg assemblies and can be used in a variety of hitches including vertical, choker, and basket hitches. The Design Factor for wire rope slings is a 5:1 ratio, meaning the breaking strength of the sling is five times higher than the rated Working Load Limit (W.L.L). Per the Wire Rope Users Manual, a design factor is necessary to allow for conditions such as wear, abrasion, damage, and variations in loads which are not readily apparent. Although wire rope slings have a design factor, the user should never exceed the rated Working Load Limit.
When it comes to toughness and dependability—alloy chain slings are the bulldogs of lifting slings. Chain slings can be used to lift very heavy and bulky loads on a regular or repetitive basis. Their flexible design provides strength and durability so they can withstand impact, extreme temperatures, and exposure to chemicals and UV rays.
Chain slings are preferred in high-temperature applications and for lifting heavy-duty loads. Their strength and durability allow them to be used in foundries, steel mills, heavy machine shops, and any other environment where repetitive lifts or harsh conditions would damage or destroy a wire rope sling or synthetic nylon or polyester sling. If any damage does occur on a chain sling, they are completely repairable and can be load tested-and re-certified after the repair.
Alloy chain slings can be heated up to temperatures of 1000°F, however the Working Load Limit must be reduced in accordance with the manufacturer’s recommendations when continually exposed to temperatures above 400°F.
Chain slings can be configured in single-leg, 2-leg, 3-leg, and 4-leg designs. They can be configured for use in vertical, choker, or basket hitches and a variety of different sling hooks, lengths of chain, and master links can be used to create different sling assemblies for different applications.
While there are many different types of chain, alloy steel grades 63, 80, and 100 are normally recommended for overhead lifting. In some applications, chain slings made of material other than alloy steel may be used. These applications involve a corrosive or high-temperature environment. The chain material in these unique applications is often stainless steel or some other special material chain. If non-alloy chain is used for lifting, we recommend that the user document the reason for using chain other than alloy, and also follow all appropriate chain sling standards including sling identification and inspection.
The Design Factor for chain slings is a 4:1 ratio, meaning the breaking strength of the sling is four times higher than the rated Working Load Limit. Although chain slings have a design factor, the user should never exceed the rated Working Load Limit.
For highly finished parts or delicate equipment, nothing beats the flexibility, strength, and support that synthetic lifting slings can provide. Synthetic slings can be made from nylon or polyester materials and are lightweight, easy to rig, and extremely flexible. They’re extremely popular in construction and other general industries because they’re fairly inexpensive, come in a variety of standard sizes, and can be replaced easily.
Because they’re so flexible, they can mold to the shape of delicate and irregularly-shaped loads, or be used in a choker hitch to securely grip loads of round bar stock or tubes. The soft materials they’re made from are strong enough to lift heavy loads, but will protect expensive and delicate loads from scratches and crushing. Synthetic slings are extremely versatile, can be used in vertical, choker, and basket hitches and have a Design Factor of 5:1, meaning the breaking strength of the sling is five times higher than the rated Working Load Limit.
Because they’re made of non-sparking and non-conductive fibers, they can be used in explosive atmospheres. However, they’re also more susceptible to cuts, tears, abrasions. Exposure to heat, chemicals, and UV rays can also cause damage and weaken the strength and integrity of the sling.
In most cases, synthetic slings cannot be repaired, so any evidence of damage is cause for removal from service. Best practice is to destroy and dispose of damaged synthetic slings to prevent further use.
Web slings are flat belt straps made of webbing material and most commonly feature fittings, or flat or twisted eyes, on each end. Web slings are the most versatile and widely-used multi-purpose sling. They’re strong, easy to rig, and inexpensive. Compared to alloy chain slings, they’re more flexible and lighter and can be used to help reduce scratching and denting to loads. They can also be fabricated with wide load-bearing surfaces up to 48” to provide significant surface contact for heavy and large loads.
Nylon web sling performance isn’t affected by oil and grease, and they’re resistant to alkaline-based chemicals. However, they should never be used in acidic atmospheres or near chemicals used as bleaching agents. Polyester web slings can be used in acidic environments or near chemicals used as bleaching agents, but should never be used in alkaline environments.
They also have a relatively low heat-resistance and are not to be used in environments that exceed 194°F, or environments where temperatures are below -40°F. For loads with sharp edges, corner protectors or edge guards should be used to protect the sling from cuts and tears. Because there is a difference between abrasion-resistant protection and cut-resistant protection, be sure to identify the type of resistance required for your application.
If used outdoors, they should be stored away in a cool, dark, and dry environment to avoid prolonged exposure to sunlight and UV rays, which can damage and weaken the strength of the sling. When a lift is made at the W.L.L., the user can expect approximately 8-10% stretch when using a nylon web sling and 3% stretch when using a polyester web sling at rated capacity.
Endless roundslings have load-bearing fiber or core yarns that are protected by a woven outer jacket. They are strong, soft and flexible, and protect smooth or polished surfaces from scratches, dents, and crushing. Roundslings can be used in vertical, basket, or choker hitches—which are especially useful for lifting tubes and pipes.
The woven outer jacket is designed to protect the internal load-bearing fibers and core yarns against abrasion, dirt and grease, and UV degradation. Polyester roundslings are suitable for acidic environments, or near chemicals used as bleaching agents, but should not be used in alkaline environments.
Like web slings, roundslings are more susceptible to heat damage and should not be used in environments that exceed 194°F or below -40°F. For loads with sharp edges, corner protectors or edge guards should be used to protect the sling from cuts and tears.
If used outdoors, they should be stored in a cool, dark, and dry environment to avoid prolonged exposure to sunlight and UV rays, which can damage and weaken the strength of the sling. When a lift is made at the W.L.L., the user can expect approximately 3-5% stretch when using a roundsling.
A number of high-performance and lightweight roundslings are available for industrial and heavy lifting applications—including steel, energy, automotive, and manufacturing. Twin-Path® roundslings have the precision and flexibility to perform heavy lifting jobs quickly and safely and only weigh 10% of the total weight of a comparable steel sling. High-performance roundslings come in standard vertical lifting capacities up to 500,000 lbs., and can also be special-ordered to handle larger capacities. These slings have less than 1% stretch at rated capacity.
Unlike standard roundslings, Twin-Path® roundslings utilize two paths of K-Spec® load-bearing fibers. The Twin-Path® patented design provides the rigger with two connections between the hook and the load for redundant back-up protection. They also feature other technologies like a Check-Fast® inspection system and an External Warning Indicator (EWI) that can provide visual indications of overloading, UV damage and degradation, or damage to the internal core fibers.
Twin-Path® slings are susceptible to cuts and tears to the jacket when used to support loads with sharp corners or edges. The specially-designed Covermax® Cover provides the best ultraviolet (UV) protection and the best abrasion protection of any commercially available synthetic lifting sling. CornerMax® Pads and CornerMax® sleeves are extremely cut resistant and can be used to protect the Twin-Path® slings in applications where cutting is a concern. If the outer jacket is cut or torn, and the load bearing fibers are not cut, Twin-Path® slings are repairable by applying a patch and proof-testing the sling after the repair is performed.
Standard Twin-Path® slings are also susceptible to heat damage, and should not be used in high heat environments above 180°F. Specially-designed slings are available with high-temperature core yarns and a high temperature cover that is resistant to temperatures up to 300°F.
Although synthetic rope slings have been in use for over sixty years, the advancement of high-performance fibers has recently improved the perception of using rope slings for overhead lifting applications. These high-performance fibers are characterized by their light weight, strength, flexibility, and versatility. Not only are they becoming more widely-accepted, but are preferred in certain lifting applications in the construction, shipyard, and offshore and deepwater industries. Because there are various types of synthetic rope material, it’s critical to know the specific fiber that a rope is made from to help understand its environmental characteristics.
Diameter to diameter, a synthetic rope sling is approximately 1/8 the weight of a steel wire rope sling with similar specifications, and compared to chain slings, they offer even more significant weight-savings.
Another major benefit of synthetic rope slings, is that if a break or failure occurs, there is no whipping motion of the sling or projectiles that could injure nearby workers. When a steel rope or chain breaks, the reaction is often violent and explosive and can potentially injure workers or damage nearby equipment.
Synthetic rope slings are more prone to damage from abrasion or cutting when lifting loads with sharp corners or edges. Additional edge protection and abrasion protection is available, but can add significant costs to the slings to try and equal the durability and resistance that more traditional steel slings offer.
Metal mesh slings are made from high-tensile carbon, alloy, or stainless steel wire mesh and are used primarily in metalworking and other industries where the loads can be hot, abrasive, or have the tendency to cut through softer synthetic slings. They’re resistant to corrosion and they’re designed to last in demanding and rugged operating environments.
Metal mesh slings are flexible and have a wide bearing surface that can be used to firmly grip an irregular load without extensive stretching and can be used in vertical, basket, or choker hitches. They’re extremely resistant to abrasion and cutting, however if there is evidence of even one broken wire in the sling, the entire sling needs to be removed from service. The Design Factor for wire rope slings is a 5:1 ratio, meaning the breaking strength of the sling is five times higher than the rated Working Load Limit. Although metal mesh slings have a design factor, the user should never exceed the rated Working Load Limit.
As you can see, there are many different options when it comes to selecting the proper lifting sling for the job at hand. Many factors should be considered to ensure that the lifting sling you select will provide consistent performance over many safe and reliable lifts:
At Mazzella, we provide rigging equipment, rigging inspection services, and rigging/operator training to workers in all types of industries. We have locations scattered throughout the country that provide specialized lifting and rigging services to industries like energy, construction, automotive, steel, naval and maritime, and mining.
If you have questions about the proper type of lifting sling you should be using for your application, or you want to get better service life out of the slings you’re currently using, contact a Lifting Specialist at a location nearest you.
Are you looking for lifting slings, including chain, wire rope, synthetic flat web, metal mesh, cordage, and single-path / high-performance roundslings? We can help provide the right sling for your needs!
Additionally, if you need sling assemblies—both large and small, we can manufacture bridge cables, crane cables, steel mill cables, and thousands of OEM assemblies.
Contact us today to get the lifting slings and assemblies you need!
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