Tackle Block Warning,
Use & Maintenance Information.
Tackle Block Information Continued:
Loads
on Blocks
The
Working Load Limit (WLL) for Crosby Group blocks indicates the
maximum load that should be exerted on the block and its
connecting fitting. This total load value may be different from
the weight being lifted or pulled by a hoisting or hauling
system. It is necessary to determine the total load being imposed
on each block in the system to properly determine the rated
capacity block to be used. A single sheave block used to change
load line direction can be subjected to total loads greatly
different from the weight being lifted or pulled. The total load
value varies with the angle between the incoming and departing
lines to the block.
The following chart indicates the factor to be
multiplied by the line pull to obtain the total load on the
block.
| Angle
Factor Multipliers |
| Angle |
Factor |
Angle |
Factor |
| 0° |
2.00 |
100° |
1.29 |
| 10° |
1.99 |
110° |
1.15 |
| 20° |
1.97 |
120° |
1.00 |
| 30° |
1.93 |
130° |
.84 |
| 40° |
1.87 |
135° |
.76 |
| 45° |
1.84 |
140° |
.68 |
| 50° |
1.81 |
150° |
.52 |
| 60° |
1.73 |
160° |
.35 |
| 70° |
1.64 |
170° |
.17 |
| 80° |
1.53 |
180° |
.00 |
| 90° |
1.41 |
- |
- |
Example A
(Calculations for determining total load value
on single line system.)
A gin pole truck lifting 1,000 lbs.
There is no mechanical advantage to a single
part load line system, so winch line pull is equal to 1,000 lbs.
or the weight being lifted.
To determine total load on snatch block A:
| A = |
1,000lbs. |
x |
1.81 |
= 1,810 lbs. |
| |
(line pull) |
(factor
50° angle) |
|
|
|
To determine total load on toggle block B:
| A = |
1,000lbs. |
x |
.76 |
= 760 lbs. |
| |
(line pull) |
(factor
135° angle) |
|
|
|
Example B
(Calculation for determining total load value for mechanical
advantage system.)
Hoisting system lifting 1000 lbs. using a traveling block. The
mechanical advantage of traveling block C is 2.00 because two (2)
parts of load line support the 1,000 lb. weight. (To determine
single line pull for various bearing efficiency see "How to
Figure Line Parts").
To Determine Line Pull:
LinePull = 1000 lbs. / 2.00 = 500 lbs.
To determine total load on traveling block C:
| C = |
500 lbs. |
x |
2.0 |
= 1000 lbs. |
| |
(line pull) |
(factor 0°
angle) |
|
|
|
To determine total load on stationary block D:
| D =
|
500 lbs. |
x |
1.87 |
/ 500 lbs. |
= 1,435 lbs. |
| |
(line pull) |
|
(factor 40° angle) |
(dead end
load) |
|
|
|
To determine total load on block E:
| E = |
500 lbs. |
x |
.84 |
= 420 lbs. |
| |
(line pull) |
(factor
130° angle) |
|
|
|
To determine total load on block F:
| F = |
500 lbs. |
x |
1.41 |
= 705 lbs. |
| |
(line pull) |
(factor
90° angle) |
|
|
|