A lifting sling is a flexible piece of equipment used to connect a heavy or awkward load to a lifting machine, such as a crane or hoist. Their primary function is to enable the safe and efficient movement of materials within industrial, construction, or maritime environments. Because these devices bear the full weight of the object being moved, improper use can lead to equipment failure, property damage, or serious injury. Understanding the correct procedures for selecting, inspecting, and applying a lifting sling is paramount to operational safety.
Selecting the Appropriate Sling
The choice of sling material must align with the specific demands of the load and the working environment. Synthetic webbing and roundslings are chosen when lifting objects with delicate surfaces because their pliable nature prevents scratching or marring. Chain slings offer superior resistance to high temperatures and sharp edges, making them suitable for abrasive environments like foundries or steel mills. Wire rope slings provide a balance of strength and flexibility, often used in general construction applications where durability is required.
After selecting the material, determining the appropriate capacity is the next step in safe operation. Every sling possesses a specific Working Load Limit (WLL), which represents the maximum weight it can safely bear. Users must consult the sling’s identification tag or the manufacturer’s load charts to verify the WLL before every lift. Exceeding the WLL compromises the sling’s integrity and increases the risk of failure.
Pre-Lift Inspection and Setup
Before a sling is attached to a load, a thorough visual inspection is necessary to confirm its readiness for service. For synthetic slings, users must look for signs of damage like cuts, snags, broken stitching, or evidence of chemical exposure that could weaken the fibers. Chain slings require examination for cracked welds, bent links, or excessive stretching, which indicates permanent deformation. Any sling exhibiting these defects must be immediately removed from service to comply with safety standards.
Proper preparation requires a precise assessment of the load itself, starting with accurately determining its weight. Misjudging the weight can lead to selecting an undersized sling, resulting in an overload situation. Identifying the load’s center of gravity is paramount, as the sling must be positioned directly over this point to ensure the load remains level and stable once lifted. If the sling is placed incorrectly, the load will tilt or shift unpredictably, creating a hazard during the movement phase.
Rigging Techniques and Hitch Selection
The simplest configuration is the vertical hitch, where the sling is attached directly between the lift point and the load for a straight, single-leg pull. This method provides the least stability and is reserved for loads with inherent balance or those being guided precisely. The vertical hitch allows the sling to utilize its full rated capacity, as the force is applied directly along the axis of the material.
When handling loads that are prone to shifting or have no dedicated attachment points, the choker hitch is employed. This method involves passing the sling around the load and then through one of its own end fittings, which creates a gripping action as tension is applied. Using this method reduces the sling’s Working Load Limit (WLL), which typically drops to 80% of its straight-pull capacity due to the compressive forces and bending radius at the choke point.
The basket hitch is used to maximize stability and distribute the load’s weight across two separate legs, similar to cradling the object. This technique is preferred for long or oddly shaped items because it prevents tipping and provides superior balance throughout the lift. The capacity of the sling is greatly increased when used in a basket configuration, assuming the sling angle remains favorable.
The angle formed between the sling legs and the horizontal plane influences the tension and usable capacity. As the angle decreases, the tension on each leg dramatically increases. A sling rated for a certain weight vertically can only lift a fraction of that weight at a very shallow angle. Riggers must strive to maintain angles of 60 degrees or greater, as angles less than 30 degrees impose excessive stress on the sling material.
To prevent premature wear and failure, it is necessary to protect the sling from contact with sharp corners or abrasive surfaces on the load. Corner pads, sleeves, or blocks should be placed at all points where the sling makes contact with an edge. This step prevents cuts and tears, especially in synthetic materials, which can compromise the integrity and strength of the sling system.
Executing the Lift and Post-Use Care
Once the load is rigged, the lifting process must begin slowly and deliberately. The operator should apply tension gradually, lifting the load only a few inches off the ground initially to confirm that it is balanced and the rigging is secure. Throughout the movement, operators must maintain control, preventing sudden stops, starts, or swinging motions that could dynamically increase the forces on the sling. Clear communication, often utilizing standardized hand signals, must be maintained between the rigger and the operator to ensure a coordinated movement path, keeping all personnel clear of the load’s trajectory.
After the lift is completed and the sling is removed, proper maintenance is necessary to ensure its long-term reliability. Slings should be inspected again for any damage sustained during the lift, cleaned if necessary, and then stored correctly. They should be kept in a dry environment away from direct sunlight, corrosive chemicals, or heat, which can degrade materials, especially synthetics.