Care & Use of Wire Rope Slings
Every Lift Uses 1 of 3 Basic Hitches
Choker hitches reduce lifting capability of a sling, since this method of rigging affects the ability of the wire rope components to adjust during the lift, places angular loading on the body of the sling, and creates a small diameter bend in the body at the choke point.
Sling angles have a direct and oftentimes dramatic affect on the rated capacity of a sling. This angle, which is measured between a horizontal line and the sling leg or body, may apply to a single leg sling in an angled vertical or basket hitch, or to a multi-legged bridle sling. Anytime pull is exerted at an angle on a leg, the tension or stress on each leg is increased. To illustrate, each sling leg in a vertical basket hitch absorbs 500 lbs. of stress from a 1,000 lb. load. The same load, when lifted in a 60 degree basket hitch, exerts 577 lbs. of tension on each leg.
It is critical therefore, that rated capacities be reduced to account for sling angles. Angles less than 45 degrees are not recommended and those below 30 degrees should be avoided whenever possible. Use the formula and chart shown below to calculate the reduction in rated capacities caused by various sling angles.
Actual Sling Capacity = Factor x Rated Capacity
|Sling Angles in Degrees||Factor||Sling Angles in Degrees||Factor|
- Rated capacity of a wire rope sling is based upon the nominal or catalog strength of the wire rope and factors affecting the overall strength. These factors include termination efficiencies (see chart), type of hitch, number of rope parts in the sling body, diameter around which the sling is bent, and diameter of the pin or hook over which the sling eye is placed.
- Never force the eye of a sling onto a hook or pin that has a diameter larger than the natural width of the eye. Also avoid placing a sling eye onto a hook or pin whose diameter is less than the diameter of the sling body.
- Rated capacities of fittings and attachments must be equal to or greater than that of the wire rope sling.
- Never "shock load" a sling. The actual force caused by a sudden application of load can easily exceed rated capacities and damage a sling. Abruptly releasing a load can also damage the sling.
- Protect the sling body against sharp edges and corners of loads, protrusions or abrasive surfaces. Sharp bends can distort wire rope and reduce its strength.
- Fiber core wire rope slings should never be exposed to temperatures exceeding 200 degrees F. Avoid using IWRC wire rope slings at temperatures above 400 degrees F or below -60 degrees F.
- Slings are susceptible to damage and strength loss when used in chemically active environments.
- Slings fabricated with a hand tucked splice can unravel and fail if the sling is allowed to rotate during use.
- Do not drag slings across floors or pull from underneath loads.
- Avoid twists, kinks and knots before lifting.
- Store wire rope slings where they will not be subjected to dirt, moisture, extreme heat, corrosion or mechanical damage.
Poured Spelter or Resin
Loop or Thimble