An overhead crane is a device designed to lift and move goods along specially designed tracks, most often inside a building. The scope of these devices is unusually wide, but they are mainly used in various sectors of heavy industry.
Overhead crane construction
Any overhead crane consists of one or more span beams, end beams and a mechanism that lifts and moves cargo along the bridge. Overhead cranes can be classified in many ways. One of the main ones is the number of beams in the bridge. A single-beam crane has one span beam, two-beam - two. To perform various specific tasks - mainly in metallurgy - giant mechanisms of complex construction are created. In the photo - a bridge crane with four span beams.
Depending on the design of the bridge, the layout of the lifting device changes. A special trolley is mounted on a two-girder crane, on which lifting units are fixed. On a single girder crane, instead of a trolley, an electric hoist (hoist) is used.
Lifting device
Stationary hoists are also often equipped with trolleys of double girder cranes. Such an arrangement is called a telpher (or modular) scheme. It is mainly used on cranes of relatively small lifting capacity - up to 50-60 tons. This is due to the fact that telphers of greater carrying capacity are practically never produced anywhere in the world. The exception is China, which produces telphers up to 100 tons, but the products of the Middle Kingdom are not in wide demand outside its borders.
Crane hoist construction are highly maintainable under certain conditions - the unification of equipment at the enterprise and the presence of a certain stock of parts. A lifting mechanism that has failed in a critical area of ​​work is easily replaced by the same mechanism from an adjacent crane, which is temporarily idle. Also, cranes of a modular design are more compact and lightweight.
For large two-girder bridge cranes, the device of the trolley is the so-called expanded scheme. The lifting mechanism consists of the following main parts:
- electric motor;
- gearbox;
- an elastic coupling connecting the motor to the gearbox;
- brakes (mechanical, hydraulic or electromagnetic;
- cable drum.
In the case of a modular layout, all components are “packed” in the hoist body, but in the expanded scheme, they are all located separately from each other in the open air. This makes it somewhat difficult to purchase spare parts in the event of a breakdown. The electric motor is produced by one enterprise, the gearbox is produced by another, etc. If the crane starts to break down in the post-warranty period, you will have to conclude agreements with a dozen different suppliers. But on the other hand, the design of an overhead crane with an unfolded trolley allows you to create mechanisms of very high carrying capacity - 200-300 and more tons.
Movement mechanism
Basic cranes are moved by means of wheels fixed inside the end beams. Suspended crane beams use special movement trolleys fixed to the upper part of the end beams and moving along the lower shelf of the crane track (I-beam).
Currently, there are two main types of drive for the movement of bridge cranes. Jib cranes are moved using gear motors, and overhead cranes are moved by electric motors. A geared motor consists of an engine and a reducer that converts engine torque and transmits it through the shaft to the wheel. On overhead cranes, the torque is transmitted from the motor directly to the wheels of the trolley by means of a gear. This gear is one of the most vulnerable parts of the structure, since it carries a significant load with small dimensions.
Not all wheels and trolleys are equipped with engines. Often the crane has two drive trolleys and two "single". The number of movement electric motors required on a particular crane is calculated based on load capacity, span, operating mode, etc.
How much can a crane lift?
The main technical characteristic of an overhead crane is the weight of the load that it can lift. The largest crane in the world operates in China, with a lifting capacity of 20 thousand tons. He is able to lift such weight at a speed of 10 meters per hour. A crane is used to assemble oil production platforms. A crane is used to assemble oil production platforms. But this is unique equipment.
The most common bridge cranes with a lifting capacity of 1 to 50 tons. This is enough to complete the vast majority of industrial work. However, to carry out various specific tasks, cranes with a lifting capacity of 150, 300, and even 500 tons are manufactured. Most often they are used for installation and maintenance of turbines of hydroelectric power plants, as well as nuclear reactors. In the latter case, cranes are made not only of impressive lifting capacity, but also of circular action - the so-called polar. Such a lifting unit moves along radial rails installed inside the power unit housing, thanks to the special design of the end beams.
Lifting records belong exclusively to the supporting construction of bridge cranes, which can withstand tremendous loads. Suspended crane beams rarely have a carrying capacity of more than 20 tons due to the fact that most global manufacturers do not produce mobile hoists with a higher carrying capacity. In addition, in order for the tracks to withstand the weight of an overhead crane with such a load, they will have to be built too powerful - it is easier and cheaper to install a support crane.
Load gripping bodies
In accordance with the nature of the transported goods, the cranes are equipped with various lifting devices. Depending on their design, bridge cranes are divided into the following main types:
- Hook. This is the main, most common and universal type of crane. It is equipped with a load gripping hook, usually with an automatic latch. It can lift any loads, but not directly with a hook, but with the help of slings.
- Clamshell - designed for loading and unloading of various bulk materials, as well as scrap metal. There are two types of grabs - in the form of a double bucket for unloading crushed stone, sand, etc., and in the form of a “claw” - for scrap metal or, for example, lumber.
- Magnetic. An electromagnet is installed as a load-gripping device, which can be controlled from the crane operator’s cabin or from the remote control. Used to transport metal sheets.
- Foundries - equipped with special hooks for gripping containers with molten metal.
- Stacker cranes. Equipped with forks to capture pallets with goods. Used in warehouses.
Also on many overhead cranes there are various combinations of lifting devices - for example, magnetic clamshell cranes. On foundries, auxiliary hoists with conventional hooks are often installed.
Overhead and Jib Cranes
Another parameter by which bridge cranes are distinguished is their location on crane tracks. The support crane moves along the rails like a locomotive, the overhead crane is located under the tracks and rests on the lower shelf of the I-beam profile, which serves as crane tracks.
As a rule, one-girder cranes (or beam cranes) are suspended. An overhead double girder crane is an extremely rare occurrence. Its advantage is that, due to the specifics of the design, the cargo can, moving along the bridge, go to the sides outside the crane tracks. To do this, the bridge is equipped with consoles - parts of span beams that extend beyond crane runways. This function is useful when working in a room with a lack of free space, when you need to at least somehow "shove" the load.
State standards
Depending on the type of bridge cranes, there are several regulatory documents governing their manufacture:
- GOST 27584-88 - contains general technical requirements for the production of bridge and gantry cranes, their acceptance, storage, transportation, operation modes, etc.
- GOST for electric bridge cranes single beam support No. 22045-89.
- GOST 25711-83 "Electric bridge cranes for general use with a lifting capacity of 5 to 50 tons."
- GOST for single-girder overhead traveling cranes No. 7890-93.
In addition to these basic standards, each crane must meet the requirements of many other GOSTs - for painting, quality of welded joints, metal hardness, etc.
Mode of operation
The construction of an overhead crane greatly depends on the intensity of its future operation. According to GOST 27584-88, the operating modes of the cranes are designated from 1K to 7K. Depending on this, the technical characteristics of the bridge crane, as well as the power of the metal structure (span and end beams) are calculated.
Modes 1K-3K, as a rule, correspond to cranes designed for insignificant and rare work, mainly for lifting any workshop equipment for the purpose of repair and maintenance. Operation of bridge cranes with one span beam, according to GOSTs, should be carried out in a mode no heavier than 3K.
The average operating mode 4K-5K has the majority of cranes engaged in the technological processes of the main production at various industrial enterprises.
Cranes of heavy (6K) and very heavy (7K) operation are most often found in metallurgical industries. These are real monsters among hoisting mechanisms, they "plow" continuously for days on end, in a polluted atmosphere and at elevated temperatures. In the photo - a bridge crane in the foundry in the process.
Crane control
There are three ways with which you can operate a bridge crane:
- Cabin. A special structure, usually mounted on a crane bridge, in which controls are concentrated. It can be open or closed (glazed). The operator, being in a chair inside the cab, overlooks the work area from above and controls the crane, following the instructions of the slinger.
- Radio control - this method has appeared relatively recently, but is rapidly gaining popularity. Some systems allow you to control the crane at a distance of up to 100 m. This dramatically increases the safety and mobility of the operator.
- Cable remote control. The easiest and cheapest control. It is mainly implemented on single girder cranes.
Often combine two control methods in case of failure of one of them.
Bridge Crane Ways
To move the supporting cranes, railway rails of the “P” type or special crane rails of the “KR” type are used. The latter have a wider base, so that the load from the crane is more evenly distributed over the support. Sometimes, steel bars of square section are used as paths. The rails are mounted on trusses fixed to the walls of the building.
Overhead cranes move along I-beams, leaning on the lower shelf. Beams are attached to the ceiling of the building or on special racks.