terminals must be prooftested before placing the sling
in initial service.
The COMSECOND/COMTHIRDNCBINST
11200.11 has rated capacity charts enclosed for
numerous wire rope classifications. You must know
the diameter, rope construction, type core, grade, and
splice on the wire rope sling before referring to the
charts. The charts provide you the verticalrated
capacity for the sling. The test weight for singleleg
bridle slings and endless slings is the verticalrated
capacity (V. R. C.) multiplied by two or (V.R.C. x 2 =
sling test weight).
The test load for multilegged bridle slings must
be applied to the individual legs and must be two times
the verticalrated capacity of a singleleg sling of the
same size, grade, and wire rope construction. When
slings and rigging are broken out of the TOA for field
use, they must be prooftested and tagged&fore being
returned to CTR for storage.
Check fiber line slings for signs of deterioration
caused by exposure to the weather. Ensure none of
the fibers have been broken or cut by sharpedged
objects.
SLING SAFE WORKING LOADS
There are formulas for estimating the loads in
most sling configurations. These formulas are based
on the safe working load of the singlevertical hitch of
a particular sling. The efficiencies of the end fittings
used also have to be considered when determining the
capacity of the combination.
The formula used to compute the safe working
load (SWL) for a BRIDLE HITCH with two, three,
or four legs (fig. 617) is SWL (of singlevertical
hitch) times H (Height) divided by L (Length)
times 2 = SWL. When the sling legs are not of equal
length, use the smallest H/L measurement. This
formula is for a twoleg bridle hitch, but it is strongly
recommended it also be used for the three and
fourleg hitches.
NOTE: Do NOT forget it is wrong to assume that
a three or fourleg hitch can safely lift a load equal to
the safe load on one leg multiplied by the number of
legs.
Other formulas are as follows:
Singlebasket hitch (fig. 618):
For vertical legs:
SWL = SWL (of singlevertical hitch) x 2.
For inclined legs:
SWL = SWL (of singlevertical hitch) x H divided
by L x 4.
Doublebasket hitch (fig. 619):
For vertical legs:
SWL = SWL (of singlevertical hitch) x 4.
For inclined legs:
SWL = SWL (of singlevertical hitch) x H divided
by L x 4.
Singlechoker hitch (fig. 620):
For sling angles of 45 degrees or more:
SWL = SWL (of singlevertical hitch) x 3/4 (or
.75).
Sling angles of less than 45 degrees are not
recommended; however, if they are used, the formula
is as follows:
SWL = SWL (of singlevertical hitch) x A/B.
Doublechoker hitch (fig. 621):
For sling angle of 45 degrees or more:
SWL = SWL (of singlevertical hitch) x 3 divided
by 4 x H divided by L x 2.
Sling angles of less than 45 degrees:
SWL = SWL (of singlevertical hitch) x A divided
by B x H divided by L x 2.
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 comers of a load.
Pieces of wood or old rubber tires are fine for padding.
SLING ANGLE
When using slings, remember that the greater the
angle from vertical, the greater the stress on the sling
legs. This factor is shown in figure 622.
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