The crane’s capacity it handle loads from one location to another is given by:
Crane output/Hour = Load/cycle x cycles/hour.
Calculation of the output and cycle time depends upon many variables, and it can best be determined by referring to machinery manuals and sit trials.
It is important that manufacturer’s manuals must be referred to in order to determine the tipping load at a given radius and the safe working load of the crane. Generally the safe working load varies from 67 to 75% of the theoretical crane tipping load.
For initial planning purposes, the cycle time can be computed as outlined below. However, the data indicated is for illustration purpose only:
Sr. No.
|
Activity
|
Time in minutes
(medium-sized crane)
|
1
|
Hooking load at ground level
|
1.0 minute
|
2
|
Raising load from ground level to a height or 30 meters at 60 meters/minute
|
0.5 minute
|
3
|
Slewing through 120 degrees at 60 degree/minutes
|
0.5 minute
|
4
|
Travelling on rails for 45 meters at 30 meters per minute
|
1.5 minute
|
5
|
Moving trolley at jib level for unloading and positioning by 15 meters at 15 meters per minute
|
1.0 minute
|
6
|
Unhooking load
|
1.0 minute
|
7
|
Lowering load by 5 meters at 60 to 100 meters/minute, and resting at the proper place
|
1.0 minute
|
8
|
Raising hook by 5 meters (overlapping)
|
0.0 minute
|
9
|
Moving trolley at jib level loading position
|
1.0 minute
|
10
|
Moving trolley at jib level to loading position
|
0.5 minute
|
11
|
Travelling on rails to original loading position
|
1.5 minute
|
12
|
Lowering hook
|
0.5 minute
|
Total cycle time after disregarding effect of small overlapping activities
|
11.0 minute
|
Therefore, the above crane, operating with job efficiency of 44 mins/h and shifting a 5 Tons load in each cycle, shall handle 5 ton load x cycles in one hour (of 44 minutes).
= 5 x 44min/11min
= 20 tons/h
