The history of hoisting devices is long. Mechanisms similar to cranes were used by the ancient Greeks. The name itself comes from the German word kranich (crane). This is due to the fact that the first cranes were similar to those that are now called portal. They were used for loading and unloading ships in ports. Overhead cranes appeared later.
History of creation
The first mechanism, similar to a modern bridge crane, appeared at the end of the 19th century in the capital of France. It was mainly made of wood, set in motion by hand and required tremendous effort to operate, but people saw its potential. Soon, cranes began to be made all-metal, and in the 30s of the XIX century they began to be equipped with mechanical drives.
The first electric double girder overhead crane was built in Germany in 1880. He had only one electric motor, but after 10 years a crane with three electric drives appeared in the USA. The evolution of these mechanisms does not stop to this day.
Cranes in Russia
In the USSR, the peak of crane construction occurred in the 70s of the XX century. At that time, about 7 thousand double-girder bridge cranes a year were produced around the country. The development was conducted by the All-Union Scientific Research Institute of Hoisting and Transport Engineering (VNIIPTMASH). The institute was founded in 1930 at the time of the beginning of industrialization, but it still works. The development of the institution was very useful in the formation of Soviet industry.
After the collapse of the Soviet Union, the volume of industry in Russia fell sharply, and accordingly, the need for bridge cranes also decreased. However, their production remains relevant, because in recent years, industry in the country has been reviving. In addition, Soviet-made cranes that have served their time must be replaced with more modern designs.
The device of an electric bridge double girder crane
The overall construction of the bridge crane has not changed since the very beginning of the production of these mechanisms. The changes concerned mainly electricians, drives and the method of connecting parts. The first cranes were riveted, and subsequently welding began to be applied. The main components of the crane:
- Bridge. It consists of two span beams along which a trolley with load-lifting mechanisms moves.
- End beams - are used to move the crane along the paths along the span. Connect to the bridge with bolts. Most often equipped with platforms for servicing drives.
- Crane truck - moves cargo along the crane bridge. Walks on rails located on span beams. Hoisting mechanisms are installed on it . The design of the trolley can be of two types - detailed and modular or telpher scheme. In the first case, all the components of the lifting device (engine, drum, gearbox, brake, etc.) are located separately from each other and are connected by shafts and couplings. With a modular layout, a stationary electric hoist is installed on the trolley - a ready-made hoist assembly.
- Crane operator's cab. Not always present, recently cranes have been massively transferred to radio control from the floor.
Supporting structure
The vast majority of electric double girder overhead cranes are basic. This means that the crane is placed on rails fixed along the walls of the workshop, and moves along them like a train. With this design, the crane has an optimal lifting height. In addition, crane tracks withstand heavy loads, which can significantly increase the carrying capacity. With the supporting structure of the crane under it, more free space remains in the span, which is important when installing high-altitude equipment in the workshop.
Outboard version
A much rarer phenomenon is a double-girder overhead crane. He loses reference in all the basic parameters and the overall reliability of the design. As a rule, such cranes are manufactured with a lifting capacity of not more than 20 tons. Jib cranes can lift both 300 and 500 tons of cargo. The only advantage of a double-girder overhead bridge crane is the ability to extend the load-lifting member beyond the span.
Atomic cranes
In a separate category, it is worth highlighting polar cranes or cranes of circular action. These are real monsters among hoisting machines. The average carrying capacity is 350-400 tons, the purpose is the installation and maintenance of reactors in nuclear power plants. Such double-girder overhead traveling cranes are carried out with special care and pass a multi-stage control system. The price of such a giant sometimes exceeds one billion rubles. A design feature of polar cranes is that they drive along circular paths inside the building of a nuclear reactor, while all other double-girder bridge cranes move in a straight line.
Appointment of cranes
The design of double girder bridge cranes varies depending on the purpose. Basically, the cargo handling body is undergoing changes. The following types are distinguished:
- Hook crane - cast iron hooks on which slings are worn are used to capture the load. This type of crane is found most often, since it is capable of lifting a wide variety of loads.
- Clamshell crane. As a load-gripping device, a kind of βclawβ (grab) is used, which consists of either several narrow paws or two buckets interconnected. The first type of grab is used when moving scrap metal, lumber and other similar materials, the second type is used to capture bulk cargo (sand, gravel, etc.).
- Magnetic tap - equipped with an electromagnet. It is mainly used for overloading metal sheets.
- Foundry cranes. They are used in the metallurgical industry and have many varieties - a pratzen crane, multi-magnetic, water well, etc. Depending on their purpose, they are equipped with various devices for lifting loads.
- The stacker crane is significantly different in design from the rest of the types. For all other cranes, the load-lifting member is raised and lowered using a steel cable passed through a block system. The stacker is equipped with a rigid metal mast with a pitchfork at the end. With the help of them, he captures the cargo, which is on europallets. Such cranes are used in warehouses.
Separately, it is worth mentioning explosion-proof equipment that is supplied to explosive industries: oil and gas refineries, chemical enterprises and fertilizer factories. Electrics and drives of such double-girder bridge cranes are carried out in a special explosion-proof casing. When sparking inside and detonating an explosive atmosphere, such a shell will extinguish the energy of the explosion and prevent it from spreading out. A possible explosion in the room will be prevented.