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| Mechanical
Considerations |
- Determine
weight of the load.
- Select
sling having suitable characteristics for the type
of load, hitch and environment.
- Slings
shall not be loaded in excess of the rated capacity.
Consideration should be given to sling angles, which
are discussed below.
- Slings
with fittings used in a choker hitch shall be of
sufficient length to assure that the choking action
is on the webbing.
- Slings
used in a basket hitch shall have the load balanced
to prevent slippage.
- Slings
shall not be dragged on the floor or over an abrasive
surface.
- Slings
shall not be twisted or tied into knots, or joined
by knotting.
- Slings
shall not be pulled from under loads when the load
is resting on the sling.
- Slings
shall always be protected from being cut by sharp
corners, sharp edges, protrusions or abrasive surfaces.
- Do
not drop slings equipped with metal fittings.
- The
opening in fittings shall be the proper shape and
size to insure that the fitting will seat properly
in the hook or other attachment.
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| Environmental
Considerations |
- Slings
should be stored in a cool, dry, and dark place, and should
not be exposed to ultra-violet light (sunlight).
- Chemically
active environments can affect the strength of synthetic
web slings in varying degrees ranging from none to total
degradation. The sling manufacturer should be consulted
before using slings in chemically active environments.
- Acids
a) Nylon is subject to degradation in acids, ranging from
none to total degradation.
b) Polyester is resistant to
many acids, but is subject to degradation ranging
from none to moderate in some acids.
- Alkalis
a) Polyester is subject to degradation in alkalis,
ranging from none to total degradation.
b) Nylon is resistant to many
alkalis, but is subject to degradation ranging
from none to moderate in some alkalis.
- See
chart below for effects of other chemicals on web slings.
- Nylon
and polyester slings shall not be used at temperatures
in excess of 194 degree F (90 degree C), however,
they may be used in temperatures as low as -40 degree
F (-40 degree C).
- Slings
incorporating aluminum fittings shall not be used where
fumes, vapors, sprays, mists or liquids of alkalis and/or
acids are present.
- Environments
in which synthetic web slings are continuously exposed
to ultra-violet light (sunlight) can affect the strength
of synthetic webbing in varying degrees, ranging from
slight to total degradation. The degradation is also cumulative.
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| 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
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