All Sling angles as mentioned
in this catalogue are measured 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.
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.
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 wire rope sling size required.
Example:
A 5 ton load has to be lifted with a 2-leg bridle sling. The horizontal sling
angle is 50¾, the slings legs have equal length, and the center of gravity
is in the center of the load (if not, see Center of Gravity).
Solution to find wire rope size:
3.26 tons is the VERTICAL capacity required for each leg. Look up the
table and select the rope size required. In this case you must use a 5/8" diameter
6-strand IWRC wire rope for your 2-leg bridle sling.
.
.
Horizontal
Angle
Angularity
Facotr (AF)
90
1.000
85
1.003
90
1.015
75
1.035
70
1.064
65
1.103
60
1.154
55
1.220
50
1.305
45
1.414
40
1.555
35
1.743
30
2.000
(25)
2.366
(20)
2.924
(15)
3.863
(10)
5.759
Vertical
lifting capacity for
6-strand IWRC wire rope
WLL
tons
Diameter
in
1.3
3/8
1.8
7/16
2.3
1/2
2.8
9/16
3.5
5/8
5.1
3/4
6.9
7/8
8.9
1
11
1-1/8
13
1-1/4
16
1-3/8
19
1-1/2
26
1-3/42
33
2
43
2-1/4
52
2-1/2
NOTE: Remember to
apply additional reduction factors as required; e.g. Choker Hitch & D/d
reduction factors.
(..) Angles below 30° should be avoided.
