An overhead crane is an electromechanical device whose main purpose is to lift a load. The name "bridge" the crane received because of its design. It moves along overhead rails, which are installed in the places of its operation. For example, if this is a factory floor, then rails will pass through the entire room, to which the crane itself is attached.
General device information
It’s easy to operate an overhead crane. This task is usually done by only one person. The control process of the device is carried out either from a special cabin where the stationary control panel is located, or using a special remote control that you can carry with you. The lifting capacity of such cranes begins with small indicators, but can reach significant 800 tons, which further expands the scope of their use.
If we talk about the advantages of bridge overhead cranes, then we can highlight the following few points. Firstly, with their help, you can achieve the rapid collection and delivery of goods to the premises where it is installed. Secondly, the speed of unloading or loading of goods increases significantly. Thirdly, caring for this car is quite simple and does not require much attention.
In addition, such units are characterized in that their fire safety and explosion safety are also very high.
GOST 7890-93 "Single-girder overhead bridge cranes"
On the territory of several countries formerly part of the USSR, including the territory of the Russian Federation, the standard number 7890-93 is in force, which establishes all the requirements and rules of operation, manufacture, etc., concerning bridge cranes.
It should be noted that the document and all the requirements specified therein do not apply to those devices that are operated in places recognized as explosive, fire hazardous, in rooms with a high content of acids or alkalis.
This paper is valid for single-girder manual overhead cranes with a modular design. It also applies to conventional bridge electric single-beam pendant cranes, the operating mode of which refers to 3K, as well as to those with electric hoist and electric movement mechanism.
Main parameters in accordance with GOST
The main types of manufactured cranes in accordance with GOST 7890-93: single-girder overhead traveling cranes single-span or double-span.
If the electrical device has a load capacity of 1; 2; 3.2; 5 t, then the maximum lifting height for it will be 6; 12; 18; 24 and 36 m respectively. Further, if the crane belongs to 8 tons in the capacity class, then its height can be of three types - 12, 24 or 36 meters. Another group of electric machines with a maximum load capacity of 10 tons can have a lifting height of 18, 24, 36 meters. These parameters apply to automatic bridge overhead electric cranes.
If we talk about the main standard sizes for manual drives, then they are as follows: equipment with a carrying capacity of 1; 2; 3.2; 5 tons should have a maximum lifting height of 3, 6, 9 and 12 meters, respectively.
Another important parameter, which is also regulated by the state document, is the speed of movement of the crane. The nominal indicator of this characteristic is from 0.32 m / s to 0.53 m / s.
Basic technical requirements
The interstate standards for overhead cranes, electric or manual, also contain general requirements for their production.
The manufacture of these devices should be carried out in strict accordance with their technical documentation, as well as strictly according to the approved drawings. If the equipment is made to order for export, then the products must be made in accordance with the requirements of the customer. It is worth noting that if GOST 7890-93 bridge overhead cranes are manufactured for delivery to areas characterized by a tropical climate, they must be manufactured in accordance with another state document under the number 15151.
Unit design
A separate paragraph in the document contains all the requirements for the design features of such machines.
- If the customer so requires, the products must be additionally equipped with devices such as a remote control system for equipment over the air. In some cases, a single-wire communication line may be used.
- Another point, which is also fulfilled only if the customer requires it, is the supply of electric cranes with additional systems providing a smooth descent of the mechanism, and will also make it possible to regulate the speed of raising and lowering.
- Another rather important requirement that must always be fulfilled, regardless of the customer’s wishes, is the transportability of the crane components. In other words, the equipment should not be assembled at the factory, but at the installation site, and the manufacturer's task is to produce assembly parts of the structure.
Material and assembly units
If we talk about the requirements for the material, then all the components must be made of steel, the mechanical properties of which, including impact strength, chemical composition, and weldability, will meet the operating requirements specified in GOST. It is also important to note that the design should be ensured in such temperature ranges: from +40 to -40 degrees Celsius, or from +40 to -20 degrees Celsius.
Another important requirement is that cranes can be made only from those steels that have a certificate confirming their quality.
There are several requirements in the document regarding the assembly units from which the crane is assembled. For example, one of the points says that the assembled model of equipment that does not carry cargo should completely touch the paths with the cart wheels. One of the requirements relates to such an assembly unit as a two-piece. Such defects as dents or dents are allowed on the working surface of the lower shelf of this assembly unit, but only if their depth does not exceed 1 mm.
Construction welded joints
In the production process of overhead overhead cranes, it is allowed to use any kind of welding joints, but only if they are met in accordance with all the rules and requirements specified in the regulatory and technical documentation.
However, after the welding work is completed, it is necessary to conduct a quality control, in which it must not be allowed to have the following defects:
- Cracks of any size and direction are not allowed at all.
- Local influx per 1000 mm should not exceed 100 mm.
- A defect is any non-welded crater.
- Burns and fistulas are also unacceptable.
- Pores that are arranged as a solid mesh are not allowed.
If any of the defects are detected, the product must be corrected, and then re-welded and sent back for quality control.
Equipment reliability
According to GOST, single-girder overhead traveling cranes must be operated for at least 20 years. If we talk about MTBF, the equipment must withstand at least 3000 cycles.
When determining the MTBF for such devices, it does not include failures that were caused by minor malfunctions. This category includes, for example, equipment failure due to the operation of the electrical protection apparatus, burnout of electrical warning lamps, etc.