The term “sling” covers a wide variety of configurations for synthetic ropes, wire ropes, chains and synthetic webs. Correct application of slings commonly used in construction will be explained here because improper application can be dangerous.
- The use of wire rope slings for lifting materials provides several advantages over other types of slings.
- While not as strong as chain, it has good flexibility with minimum weight.
- Breaking outer wires warn of failure and allow time to react.
- Properly fabricated wire rope slings are very safe for general construction use.
- On smooth surfaces, the basket hitch should be snubbed against a step or change of contour to prevent the rope from slipping as load is applied.
- The angle between the load and the sling should be approximately 60 degrees or greater to avoid slippage.
- On wooden boxes or crates, the rope will dig into the wood sufficiently to prevent slippage.
- On other rectangular loads, the rope should be protected by guards or load protectors at the edges to prevent kinking.
- Loads should not be allowed to turn or slide along the rope during a lift.
- The sling or the load may become scuffed or damaged.
- Chain slings are suited to applications requiring flexibility and resistance to abrasion, cutting and high temperatures.
- Alloy steel chain grade 80 is marked with an 8 or 80 ; grade 100 is marked with a 10 or 100.
- Alloy steel chain is the only type which can be used for overhead lifting.
- As with all slings and associated hardware, chain slings must have a design factor of 5.
- In North America, chain manufacturers usually give working load limits based on a design factor of 3.5 or 4.
- Always check with manufacturers to determine the design factor on which their working load limits are based.
- If the design factor is less than 5, calculate the working load limit of the chain by multiplying the catalogue working load limit by the manufacturer’s design factor and dividing by 5.
Synthetic Web Slings
- Web slings are available in two materials – nylon and polyester.
- Nylon is resistant to many alkalis whereas polyester is resistant to many acids.
- Consult the manufacturer before using web slings in a chemical environment.
- Nylon slings are more common but polyester slings are often recommended where headroom is limited since they stretch only half as much as nylon slings.
- Synthetic web slings offer a number of advantages for rigging purposes.
- Their relative softness and width create much less tendency to mar or scratch finely machined, highly polished or painted surfaces and less tendency to crush fragile objects than wire rope or chain slings .
- Because of their flexibility, they tend to mold themselves to the shape of the load.
- They do not rust and thus will not stain ornamental precast concrete or stone.
- They are non-sparking and can be used safely in explosive atmospheres.
- They minimize twisting and spinning during lifting.
- Their light weight permits ease of rigging, their softness precludes hand cuts, and the danger of harm from a free-swinging sling is minimal.
- They are elastic and stretch under load more than either wire rope or chain and can thus absorb heavy shocks and cushion loads.
- In cases where sling stretching must be minimized, a sling of larger load capacity or a polyester sling should be used.
- Synthetic web slings are available in a number of configurations useful in construction.
Double Jacketed Polyester Round Slings
Hybrid High Performance Round Slings