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from the horizontal. As the angle decreases the stress imposed on the leg
of a sling increases. A simple demonstration makes this very clear. Imagine
one carries a weight with one's arm hanging down, and then try lifting the
same weight sideways up and away from your body. When computing sling capacities
always take this most important factor into account. As can be seen from
the table sling stresses increase tremendously with angles smaller than
45°. Only where headroom is a limiting factor should sling angles smaller
than 30° be applied and careful computation made to ensure that a sling
of proper size is used to provide safe working conditions. |
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Which
Angle Applies?
One of the most frequently asked questions. ALWAYS apply the HORIZONTAL
sling angle. If you use slings of unequal length apply the SMALLEST
sling angle. |
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Angularity
Factor (AF)
Although the known trigonometrical functions apply to all stress calculations,
many trade publications and standards give specific sling strength calculation
examples which one can follow.
For a 'day-to-day' practical calculation we found the following method the
easiest way to determine the sling size required. |
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Horizontal
Angle |
Angularity
Facotr (AF) |
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| 90 |
1.000 |
| 85 |
1.003 |
| 80 |
1.015 |
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| 75 |
1.035 |
| 70 |
1.064 |
| 65 |
1.103 |
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| 60 |
1.154 |
| 55 |
1.220 |
| 50 |
1.305 |
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| 45 |
1.414 |
| 40 |
1.555 |
| 35 |
1.743 |
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| 30 |
2.000 |
| (25) |
(2.366) |
| (20) |
(2.924) |
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| (15) |
(3.863) |
| (10) |
(5.759) |
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NOTE: Remember to apply additional
reduction factors as required; e.g. Choker Hitch & D/d reduction factors.
(..) Angles below 30° should be avoided. |
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Example:
A 5 ton load has to be lifted with a two 2-leg bridle sling. The horizontal
sling angle is 50°, the slings legs have equal length, and the center
of gravity is in the center of the load.
Solution to find required capacity (or WLL) for EACH sling leg: |
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3.26 tons is the VERTICAL Rated Capacity
required for each sling leg. Look up the tables in this cataloguge and select
the sling leg size required. |
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Sling-to-Load
Angle
Slings should be long enough so that the Rated Capacity (WLL) is adequate
when the Sling-to-Load Angle is taken into consideration. To avoid edge-loading
(unequal loading over the width of the sling) select the longest possible
sling or use lifting beams and spreader bars. |
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Slings should not be loaded in excess
of their rated capacity. Shock loading, side loading and inadequate consideration
for angular stress adversely affect sling strength. |
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