What is the calculation required to determine the safe working load (SWL) of a sling, given its breaking strength and design factor?

The safe working load (SWL) of a sling is calculated by dividing the sling's minimum breaking strength (MBS) by the design factor. The minimum breaking strength, also known as the ultimate tensile strength (UTS), is the force at which the sling is expected to fail under a static load. The design factor, also known as the safety factor, is a multiplier that accounts for uncertainties in loading conditions, sling wear, and other factors. The formula for calculating SWL is: SWL = MBS / Design Factor. The design factor varies depending on the type of sling and the application. For example, wire rope slings typically have a design factor of 5:1, meaning the MBS is divided by 5 to determine the SWL. Synthetic web slings often have a design factor of 5:1 or higher, while alloy steel chain slings typically have a design factor of 4:1. It is crucial to use the correct design factor as specified by the sling manufacturer and applicable standards, such as ASME B30.9. For example, if a wire rope sling has a minimum breaking strength of 20,000 pounds and a design factor of 5:1, the SWL would be 20,000 pounds / 5 = 4,000 pounds. Exceeding the SWL of a sling can lead to sling failure, dropped loads, and serious injuries. The SWL must be clearly marked on the sling's identification tag, and users must never exceed this limit.