Wire Rope Slings & Lifting Angle Requirements
What are Wire Rope Slings?
Wire rope slings are lifting accessories made from processed wire rope, used for hoisting, pulling, tensioning, and load bearing. They offer high strength, light weight, stable operation, and resist sudden breakage, acting as a flexible link between lifting equipment and the load. They are value-added products derived from wire rope.
Practical Applications
These slings are widely used in hoisting operations across industries like ports, mining, metallurgy, petrochemicals, shipping, bridge construction, and aerospace. Notably, in lifting and port operations, over half of all wire rope used is processed into slings.
Common Classifications
Pressed Slings: Feature modern design, advanced manufacturing, high efficiency, strong safety reliability, high load capacity, and smooth, secure fittings. Ideal for various professional settings.
Spliced Slings: Made by interweaving rope ends into loops. They are more cumbersome to produce, use more material (higher cost), and have lower splice strength than pressed slings. Often used in specific sectors like steel and chemicals.
Endless Slings (Grommets): Known for excellent flexibility, multiple lifting points, high strength, and minimal space requirements. Perfect for confined spaces or large projects like transformer installation or shipbuilding.
Cast Slings: Involve a complex casting process requiring trained operators. Manufacturing is time-consuming, inefficient, and costly, but results in very high consolidation strength. Used for critical applications, often assembled on-site, and require pre-use proof testing.
Usage Specifications
Do not use slings without identification and certification.
Perform daily pre-use inspections. Do not use if the wire rope or metal fittings are excessively damaged.
Strictly prohibit exceeding the Working Load Limit (WLL).
The included angle between sling legs must not exceed 120 degrees.
Match the rated capacities of all components (hooks, shackles, etc.).
Lift smoothly and avoid shock loads.
Protect slings from bending over sharp edges or colliding with the load.
Do not drag slings or throw them from heights.
Operating temperature range is -40°C to 100°C.
Do not use in corrosive environments.
Slings stored over two years require sample tensile testing before use.
Inspection
Regular inspection is crucial due to inevitable wear.
Rules: Check for broken wires, wear, corrosion, lubrication status, deformation, kinks, crushing, or other damage. Inspect terminations for tightness, rope slippage, and thimble condition (deformation, wear, corrosion, cracks).
Intervals: Perform monthly inspections by qualified personnel. Shorten the interval for frequently used slings.
Impact of Sling Angle
The sling angle critically affects load stability, position, and forces on the slings.
Why ≥60° is critical: Angles exceeding 60 degrees significantly reduce the safety factor. The rated load is multiplied by a higher factor, decreasing the maximum safe working load. Excessively large angles generate high horizontal forces on the load, potentially causing damage.
Solution for large angles: If space constraints create angles over 60°, use two slings or a four-leg assembly with webbing slings and a spreader beam to mitigate risks.
Load Calculation: The load on each leg is calculated as: Load per Leg = (Load Weight / Number of legs) / cos(θ) where 'θ' is the angle between the sling leg and the horizontal. A larger angle increases the load on each leg.
Lifting Rope Angle in Practice
Definition: The angle between the sling leg and the horizontal plane.
Application & Control: The angle is vital for load stability and equipment forces. It should be controlled and adjusted for safety, ideally between 45° and 60°, and not less than 30°.
Key Precautions
Determine the angle based on load weight and characteristics (heavier loads often need smaller angles).
Monitor rope tension. Large angles increase tension, reducing rope life; very small angles can overload and risk breakage.
Use proper support and inspection points.
For large angles, consider using multiple slings to distribute load safely.
