Cranes are predominantly used for handling including
lifting, lowering and swing shifting of small to heavy loads. Cranes come in
many types such as crawler-mounted mobile cranes, self-propelled rubber-tyred
wheels, telescopic jib cranes, truck-mounted strut-jib cranes and tower cranes.
Mobile cranes
In wide spread project sites, mobile cranes provide
the best means for lifting and shifting of small to heavy loads. These cranes
can move over level firm surfaces as well as on rough terrains. Mobile cranes
are of the following types:
Crawler-mounted cranes
These cranes spread their dead load over larger area
through their long tracks and as such are useful while working in unprepared
surfaces. The boom of these cranes comes in sections which are joined by pin
connections. The straight boom thus formed can lift loads over a radius of 30
to 40 meters. In order to overcome the ground obstruction to the inclined boom,
a fly-jib (say 18 meter in length) is attached to the top of the end boom. The
fly-jib is generally inclined at 30 degree offset from the main boom and it
acts as its extension. The crawler jib crane can also be converted into a
grabbing crane or dragline carne by fitting appropriate attachments.
Self-propelled rubber-tyred wheels cranes
These cranes have greater mobility over hard surfaces
and are in great demand for shifting and transporting light loads over short
distances and for off-loading of medium to heavy loads. Self-propelled cranes
can be broadly divided into three categories:
- Strut-jib cranes for shifting small loads at a distance, where ground obstruction restricts the utility of the crane.
- Cantilever-jib crane provides greater clearance under the jib for heavy and bulky loads.
- Telescopic-jib crane provides flexibility in adjusting distances and heights of lifts. It has greater mobility on roads than other self-propelled cranes.
Truck-mounted cranes
These cranes are used for lifting medium to heavy
loads over high and wide reaches, such as placing precast concrete slab panels
in a high rise building, or installation of heavy mechanical equipment such as
vessels in production industries. These cranes have a capacity ranging from 10
tons to 100 tons. Cranes of capacity greater than 100 tons are custom-made.
Their main advantage is that they can move on roads, and they take hardly a few
minutes to prepare for the lifting operation. Truck mounted cranes are
available with telescopic-jib and strut-jib. These cranes have hydraulically
operated outriggers, which get stretched out and are made to rest on firm
ground so as to provide a stable base.
