Jib cranes use a mounted boom to lift and move material and can rotate about a central axis. They have been used since ancient Greece and incorporate pulleys and other machinery to increase lifting capacity. Modern jib cranes use strong metal wiring and can be mounted on a mobile frame.
A jib crane is a type of crane that uses a mounted boom to lift, move and lower material. The arm, mounted perpendicular or at an acute angle upwards from a pillar or wall, can rotate about its central axis through a limited arc or a complete circle. A jib crane is often used in industrial settings, such as warehouses and docks, to load and unload containers.
The history of the jib crane dates back to ancient Greece, where the concept of using a mechanical arm to lift objects first came into wide use. The Romans later embraced the technology and applied it to building roads, aqueducts, and other engineering projects. Cranes were perfected, but remained largely identical in nature to classic designs until the Industrial Revolution and the introduction of the steam engine in the 19th century. With ever larger construction projects on land and sea, as well as increasing demands from increasingly complex factories and shipping companies, cranes too developed in size and complexity during this time.
The fundamental basis of the crane arises from the concept of mechanical advantage. Mechanical advantage is the idea that a machine, such as a pulley, can multiply the force applied to it by a certain factor. This is why it is possible, for example, for a single man using a pulley to lift the same heavy crate that it would require a team of men to lift directly. Cranes incorporate a variety of pulleys with other simple machinery, such as gears and levers, to greatly increase lifting capacity.
In a modern jib crane, strong metal wiring is wound around the ends of the boom post, with the hoist end usually connected to a hook or electromagnet and the other end connected to a winch. When the winch is activated, the pulleys provide a lifting force equal to the actual force applied by the winch, multiplied by the number of lengths of wire wrapped around the pulleys. In many jib cranes, the hoist may be able to move outward and inward along the length of the jib, providing even greater flexibility of movement.
Jib cranes are not limited to fixed locations and can be mounted on a mobile frame for use on temporary construction sites or in military operations. Such cranes generally sacrifice lifting capacity for mobility. Outriggers are essential for a mobile jib crane to maintain stability under load, unlike fixed ones which are firmly anchored in place.
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