Text 2. Mobile Cranes

The function of a crane is to hoist or lower, a load suspended, from its jib. Various types of cranes are available, the type and size best suited for a specific operation being influenced by the following factors:

1. The nature of the work on which it is to operate.

2. The weight of load it has to handle.

Mobile cranes have a wide range of uses on building and civil engineering works of construction. Cranes of this type usually take the form of a frame carrying a jib, a winch, and other necessary hoisting and controlling equipment, the whole being mounted on a cast-iron bed plate fitted with road wheels of the pneumatic type. One may also have, them mounted on caterpillar tracks or on a lorry chassis if desired.

At present rope-operated mobile cranes are being superseded by hydraulically operated ones, in which all working operations, but traveling, are performed with the help of hydraulic rams. The jib of the mobile crane can be of the solid or latticed type, the latter being preferred now because of its lower weight.

1. Complete the table.

2. Read the statements below and decide if they are true or false according to the text ‘Mobile Crane’.

1. The most basic type of mobile crane consists of a steel truss or telescopic boom mounted on a mobile platform, which may be rail, wheeled (including ‘truck’ carriers) or caterpillar tracks. ( )

2. The boom is hinged at the bottom, and can be raised and lowered by cables or

by hydraulic cylinders. ( )

3. A hook is suspended from the top of the boom by wire rope and sheaves. ( )

4. The wire ropes are operated by whatever prime movers the designers have available, operating through a variety of transmissions. ( )

5. Steam engines, electric motors and internal combustion engines (IC) have all been used. ( )

6. The operational advantages of this arrangement can now be achieved by electronic control of hydrostatic drives, which for size and other considerations is becoming standard. ( )