Sling Angle

Equipment Operator Basic - Beginning construction equipment operators manual
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determined to ensure that the individual legs are not overloaded. Figure 13-32.—Multi-legged bridle slings. The single-leg sling may be used as a choker hitch (fig. 13-31, view A) in hoisting by passing one eye through the other eye and over the hoisting hook. The single-leg sling is also useful as a double-anchor hitch (fig. 13-31, view B). The double-anchor hitch works well for hoisting drums or other cylindrical objects where a sling must tighten itself under strain and lift by friction against the sides of the object. Single-leg slings can be used to make various types of bridles. Three common uses of bridles are shown in figure 13-32. Either two or more single slings may be used for a given combination. The bridle hitch provides excellent load stability when the load ia distributed equally among each sling leg. The load hook is directly over the center of gravity of the load, and the load is raised level. The use of bridle slings requires that the sling angles be carefully NOTE: It is wrong to conclude that a three- or four-leg bridle will safely lift a load equal to the safe load on one leg multiplied by the number of legs. This is because there is no way of knowing that each leg is carrying its share of the load. With a four-legged bridle sling lifting a rigid load, it is possible for two of the legs to support practically the full load while the other two legs only balance it. COMSECOND/COMTHIRDNCB strongly recom- mend that the rated capacity for two-leg bridle slings listed in the COMSECOND/COMTHIRDNCBINST 11200.11 be used also as the safe working load for three- or four-leg bridle hitches. When lifting heavy loads, you should ensure that the bottom of the sling legs is fastened to the load to prevent damage to the load. Many pieces of equipment have eyes fastened to them during the process of manufacture to aid in lifting. With some loads, though, fastening a hook to the eye on one end of each sling leg suffices to secure the sling to the load. Use a protective pad when a fiber line or wire rope sling is exposed to sharp edges at the corners of a load. Pieces of wood or old rubber tires are fine for padding. Sling Angle When you are using slings, remember that the greater the angle from vertical, the greater the stress on the sling legs. This point is shown in figure 13-33. The rated capacity of any sling depends on the size, the configuration, and the angles formed by the legs of the sling and the horizontal. A sling with two legs used to lift a 1,000-pound object will have 500 pounds of the load on each leg when the sling angle is 90 degrees. The load stress on each leg increases as the angle decreases; for example, if the sling angle is 30 degrees when lifting the same 1,000-pound object, the load is 1,000 pounds on each leg. Try to keep all sling angles greater than 45 degrees; sling angles approaching 30 degrees are considered extremely hazardous and must be avoided. Figure 13-33.-Stress on slings at various vertical angles. 13-17

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