Rigging slings are an incredibly significant piece of lifting equipment – even though they are relatively small compared to the large cranes they are used on. Rigging slings help to support material handling equipment by ensuring that items are not damaged as they are hoisted. They are made out of three types of materials:
- Wire ropes
- Alloy Chains
- Synthetic Materials
Using the wrong type of rigging sling can be extremely dangerous, as it could break or the item could slip out of the sling. Therefore, it is incredibly important that you choose the correct type of rigging sling for your application.
If you are in the market to purchase rigging supplies and are wondering which type of sling is best, here are some essential things that you need to know first.
What Exactly Are Rigging Slings?
Essentially, a rigging sling is a part that is attached to or wrapped around the object being lifted and is used in conjunction with a lift or crane.
Since the rigging sling is used for varying weights and sizes, it must be routinely inspected for signs of wear. Over time, the material used in the sling will wear down and must be replaced. It is also generally recommended that slings not be shortened or lengthened by knotting or twisting, as this can wear down the ropes or cables quicker.
Rigging slings are often used with hitches, which are used to connect the object to the sling itself.
There are four types of sling hitches:
A vertical or straight hitch is attached directly to an object (generally by looping around an attached hook) in order to lift it up vertically. A downside to this type of sling hitch is the object can rotate or swing while it is being moved. However, a tagline can be added to help control this rotation and prevent the sling from twisting around.
A basket hitch helps to distribute the weight of an object more evenly by splitting the load and cradling both slides within a sling. It is also typically used in conjunction with a lifting beam or spreader bar to provide additional support.
Now, the angle of the sling does change the load capacity, and both sides need to carry equal weight, otherwise, the object will topple. Therefore, basket hitches are used on longer objects which are of equal weight, such as lumber or pipes.
A choker hitch loops around an object to provide a strong grip with an adjustable knot at the top. This also must be used on evenly balanced loads and must be tightly secured before lighting to ensure that the object does not shift.
A bridle hitch is a term used when two or more slings are needed to lift an object. So, two vertical hitches can be used to create a bridle and distribute the weight more evenly between the sling.
Now the type of material used for a rigging sling is dependent on several factors, such as:
- Application or project
- The load weight, shape, and size
- Center of gravity of the object
- Conditions (wind, clearance, height restrictions)
- Sling and lift angles
So, let’s explain the differences between the three main types of sling materials.
Wire Rope Slings
Wire rope slings are one of the most popular and often preferred lifting sling material due to its strength, flexibility, and fatigue resistance. Wire rope products like rigging slings are made up of strands of wires wrapped around one another to create a bendable yet extremely sturdy rope that can withstand extreme weights. Wire ropes also have a central core, which is made from steel or fibers, to provide additional support when the rope is bent.
Wire rope has numerous other purposes outside of liftings and rigging, such as permanent or temporary attachment securement or material handling.
Wire rope slings have several pattern options:
- Single-layer – typically six strands and one core for lighter lifting applications
- Filler wire – two layers of wire around a core
- Seale – two layers of wire with a smaller inner layer and thicker exterior
- Warrington – two layers of wire. The inner layer has a uniform diameter while the outer layer has different diameters woven in
- Combination – two or more of any patterns woven together to make a single rope
Wire ropes also come in three different finishing types: bright, galvanized, or stainless steel.
A “bright” wire rope means that there is no surface treatment on the metal and are instead lubricated to prevent rust and corrosion. This is generally the least expensive type of wire rope.
Galvanized steel has a zinc coating which also protects from corrosion and increases the breaking strength of the wire. This increases the price point as it offers a higher weight resistance.
Stainless steel wire ropes are the most expensive and are also the most durable. They are highly resistant to corrosion and rust, so they are frequently used on ships or near water.
While wire rope offers numerous benefits, such as strength, flexibility, and resistance to corrosion, there are a few disadvantages. First, wire rope has a fairly low strength-to-weight ratio and the metal core and exterior can wear down faster if it is misused. Wire rope is also non-repairable and must be completely replaced if it breaks.
Common applications for wire ropes include:
- Mining equipment
- Elevator wires
- Crane ropes
- Gas and oilfield equipment
Chain slings are typically made of an alloy mixture of varying grades of steel, making it one of the strongest types of rigging slings available. As it is comprised of chainrings, it is flexible – but does not compromise on strength or durability. The alloy mixture also makes it quite resistant to extreme temperatures and corrosion.
Chain slings can be used repetitively without wearing down as quickly as wire ropes or other materials. Furthermore, chain links can be repaired or replaced if they break.
Chain slings can be extremely heavy, as they have a 4:1 Working Load Limit. So, if an extremely heavy object needs to be lifted, the chain will need to be ¼ of that object’s weight. Alloy chain slings can also be quite expensive compared to wire ropes or synthetic slings and can be easily damaged if they are crushed.
Common applications for chain slings include:
- Heavy-duty lifting
- Foundries, steel mills, heavy machine shops
- Harsh conditions
- Machinery requiring repetitive lifts
Synthetic rigging slings can be made of nylon or polyester fibers woven together to create straps which are extremely lightweight and flexible. Since the material is much softer compared to wire ropes or chain slings, they are often used to protect expensive or sensitive loads that could be damaged from scratches. You will commonly see yachts, vehicles, or décor items lifted with synthetic slings for this reason.
Synthetic slings come in varying styles depending on the application. Synthetic web slings are flat straps that can be used to wrap around an item for lifting. Synthetic round slings are used with vertical, basket, or choker hitches and are best for lifting round objects, like tubes and pipes.
Although synthetic slings are made of fabric fibers as opposed to metal, they are extremely strong and versatile and have a 5:1 Design Factor – meaning that the breaking strength is five times greater than the Working Load Limit of the sling.
However, one of the disadvantages of this type of sling is that it is easily damaged and can be cut or torn during use. The material is also susceptible to damage from heat, chemicals, and UV rays.
Common applications for synthetic slings include:
- Hoists and cranes
- Custom applications
- Light to heavy lifting
Rigging slings are a key component of any lifting application – but you need to have the right material and design. Otherwise, it could compromise the safety and effort of the project. It is crucial that you understand the differences between the types of rigging slings as well as the style of hitch to use. Each comes with its own advantages and disadvantages – but there is a right combination for every application.
If you have any further questions regarding rigging slings or you are ready to place an order, please reach out to Holloway Houston Inc. Our experienced and knowledgeable team would be glad to help you find the exact materials needed for any project at hand.