In order to ensure the safe and normal operation of the bridge crane , the company must regularly organize technical personnel to conduct safety inspections on the crane. If the main girder of the bridge crane is found to be deflection, it must be resolved in time. The editor briefly introduces the causes, hazards and treatment measures of the deflection of the main girder of the general overhead crane.
Through previous experience analysis, the main reasons for the deflection of the main girder of the bridge crane are as follows:
The high temperature working environment has a great influence on the main beam of the crane. This is because the main girder of the bridge crane used in the thermal processing workshop has been in a high-temperature baking state for a long time, thereby reducing the yield limit of the metal material and generating temperature stress. On the one hand, the temperature stress and other stresses may exceed the yield of the material after being superimposed Limit; on the other hand, due to uneven heating of the upper and lower cover plates of the main beam, the temperature of the lower cover plate is much higher than that of the upper cover plate, and the lower cover plate elongates more, which finally causes the main beam to deflection.
Overloading, overtime and unreasonable use of cranes are another important reason for the deflection of the main beam. In some companies, the weight of a single piece of the crane exceeds the rated load of the crane, causing the crane to be overloaded for a long time; and some companies adopt the method of "resting people without stopping the machine" in order to catch up with the construction period and rush the time, and use it beyond the working level . The crane keeps the crane in a long-term fatigue state. The above two unscientific use methods will cause the local stress of the main beam to be at or even exceed the yield limit, resulting in deformation and deflection of the main beam. What's more, individual operators use cranes to drag heavy objects, which is an important reason for the deflection of the main beam.
Because the crane bridge is a long and large structure, it has large elasticity, and unreasonable storage, lifting and installation will cause the bridge to deform. We learned that some new cranes were not installed in time due to various reasons and were put away everywhere before installation, and no measures were taken to prevent the bridge from being deformed; while some new cranes were not based on the center of gravity of the bridge during the hoisting and installation process. The hoisting plan is designed according to the stress situation, and the bridge frame is deformed due to the rough hoisting. This is also one of the reasons for the deflection of the main beam of the crane.
The congenital deficiencies in the design and manufacture of cranes produced by some unqualified manufacturers are also one of the reasons for the deflection of the main girder. One is that the design and manufacturing quality of the purchased crane does not meet the standard requirements, and the rigidity of the main girder is not fully guaranteed, and the main girder deflection occurs during use; the other is due to the tension and compression in different directions caused by forced assembly during the manufacturing process. Stress and residual internal stress caused by welding, and during use, these stresses gradually homogenize or even disappear, causing permanent deformation of the main beam, and also causing the main beam to deflection.
The deflection of the main beam will seriously affect the safe operation of the crane. If it is not repaired or scrapped in time, it may cause serious equipment and personal accidents. The main hazards are summarized in the following aspects.
When the main girder is permanently deformed, the downward deflection will be more serious after the load, causing the trolley track to slope and the trolley cannot work normally. When the trolley runs from the center to one end, it will be difficult to run due to climbing slopes . In severe cases, the resistance will increase. The motor is too large and burned out. When the trolley moves from the ladder to the middle, the phenomenon of "slipping", speeding up, and inaccurate parking will occur, and even cause accidents.
Especially for bridge cranes with a centralized drive type, due to the downward deflection of the main girder, the drive shaft support and structure of the cart operating mechanism will move down together, and the drive shaft will bend. When the drive shaft is severely bent, it will damage the journal, or even cause the teeth of the coupling to break, and the connecting bolts to break. In severe cases, the shaft may be cut and the motor may even be burned.
When the degree of deflection of the two main beams is different, the four wheels of the trolley cannot be in contact with the track at the same time, resulting in the phenomenon of "three legs" of the trolley . At the same time, as the main beam is deflected, it causes the horizontal bending of the main beam. The main girder is bent inward to reduce the trolley gauge. When the gauge decreases to a certain value, the double-rim trolley will have a running rail, and the outer single-rim trolley will cause derailment.
From the above analysis, it can be seen that the deflection of the main girder has a major impact on the safe operation of the crane. The degree of deflection of the main girder of the crane is not allowed to be used. At present, the country has no clear regulations. If all deflection cranes are repaired, it will inevitably cause waste. According to the relevant regulations in GB6067-85 "Crane Safety Regulations", the deflection s of the main girder under the rated load (s is the span of the crane) is taken as the reference value. For cranes whose downward deflection is small and far less than the reference value will not be repaired for the time being, they will be degraded and used for a limited time, strengthen safety technology management, and increase the number of recheck safety precautions; for the downward deflection far exceeding the reference value, the service life will be longer. Long cranes with no maintenance value should be resolutely scrapped and renewed; for cranes whose downward deflection is close to or reach the reference value, two methods of prestressing or flame heating are adopted for main girder correction and maintenance as appropriate. After maintenance, the camber of the main girder meets the requirements of the national standard. After long-term use and testing, the camber is stable and the effect is good, thus effectively ensuring the safe operation of the crane.
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