By: Lia Contesso
Submitted: 2010-02-11 09:22:17 | Word Count: 483
Every time we see a crane in action we remains without words, these machines are sometimes really huge, taking up tons of material hundreds of meters in height. We watch with amazement and a bit of terror, thinking about what would happen if the load comes off or if the movement of the crane was wrong. It is a really fascinating system, surprising both adults and children. These are especially tower cranes, but in reality there are plenty of types and they are in use for centuries. The cranes are formed by one or more machines used to create a mechanical advantage and thus move large loads. Cranes are equipped with a winder, a wire rope or chain and sheaves.
The cranes have been used since ancient times, the chimney or fireplace cranes were used to turn the pots and kettles on the fire, while the height was governed by a trammel hook. It is the same principle of cranes that are now in the harbors. The construction of cranes probably has already begun with the ancient Greeks and were then driven by men or beasts of burden, like donkeys. The cranes were then used for the construction of tall buildings, like temples. Later, cranes were built larger, with the use of tread wheels, which allowed to lift much greater weights.
During the Middle Ages cranes were introduced for lifting, loading and unloading ships in harbors as well as aid in their construction. Some of them were even built into stone towers to increase strength and endurance. Indeed, the first cranes were built in wood, but with the advent of the industrial revolution, cast iron and steel quickly supplanted this material.
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For many centuries, in fact, the cranes were operated by the force of humans or animals, even if the hoists in the windmills and watermills were driven by the forces of natural agents. The first mechanical cranes were operated by steam engines, and came into use in the 18th or 19th century, many remain active even in the 20th century.
Modern cranes usually use internal combustion engines or electric motors and hydraulic systems to provide a much greater capability to lift weights than in the past. Additionally there are the mobile ones, such as hydraulic cranes, mounted on trucks. However manuals cranes are often still used, for example when the provision of power is not considered very profitable.
There are several forms and varieties of cranes to the present day, each created for a specific use. Sizes ranging from the smallest jib cranes, used in workshops, to the highest tower crane used in the construction of the tallest buildings and the larger floating cranes, used to build oil platforms and recover the sunken ships.
