Overhead crane girder is the main supporting part of the lifting system and the loads, which requires high rigidity, strength, and stability to ensure safety. Besides, in order to ensure the high crane usability, crane girder is designed with certain camber to avoid trolley climbing and gliding.
Crane girder camber makes the trolley from travel up or down on the main girder.
Below the yield strength of crane girder steel, the girder will spring back to its original shape after unloading. The girder camber of overhead crane is shown just like the following diagram:
However when the loads exceed the yield strength by more than about 10%, the girder camber will lose. Then when it is loaded again with the loads ≤ rated capacity, it will deflect the normal incremental amount and the stress will be at the normal level except that the starting point for the deflection increment will be at a lower elevation due to the lost camber. The girder camber will be lost each time the girder is loaded past the yield strength and the permanent deformation is produced, shown in the following diagram:
Normal crane camber deflection vs. Permanent deformed crane camber. In severe conditions, overhead crane girder may have a “kink” around the center of crane span. If you have any questions or needs, you can الاتصال بنا by البريد الإلكتروني: sales010@cranesdq.com
Overhead crane camber deformation are resulted from various reasons, generally involved with the crane design, manufacturing, transporting, installation and usage, etc.
1) Unreasonable design.
It is the inborn problem of the crane which could be avoided with the professional overhead crane manufacturers.
2) Internal Residual Stress.
During crane girder fabrication, the spot heat produced will result in metal shrinkage and the internal residual stress produced will cause the deformation of the overhead crane girder.
3) Crane girder camber formation.
The formation of the crane girder camber may result in the loss of the girder camber, which can be minimized due to the development of the technology.
4) Crane overload.
Overhead crane load exceeds the rated capacity will result in the girder deformation and the possible crane accidents.
5) Mis-operation of overhead crane.
Girder camber deformation also may be caused by the mal-operation of overhead crane, such as, the lifting loads suddenly without straining the wire rope, sudden braking, vastly braking, suddenly braking heavy loads vertically, etc.
6) Web plate deformation.
The web plate is the main supporting part of the crane girder. Usually, the web plate deformation casts little influence to the deformation of crane girder camber however when the web plat deformation becomes larger and the influence to the camber will get larger which will eventually get the camber deformed.
7) High temperature.
Huge amount of heat radiation will cause the temperature difference between the upper and lower plates of the crane girder, and the lower plate will get expanded and resulting in camber loss.
8) Incorrect storage, transporting, lifting, and installation.
Overhead crane girder is the long thin metal part with large internal Residual Stress inside which is vulnerable to the damage. Therefore the improper storage, transporting, lifting, and installation will cause the overhead crane camber deformation.
9) Improper maintenances.
During maintenance, the heat produced by cutting and welding on crane girder will result in the crane girder camber deformation.
The overhead crane camber deformation will cause bad influence to the whole crane and may cause crane accidents. Generally, it will influence in the overhead crane in the following ways:
1) To trolley travelling.
The sever deformation of overhead crane girder will make the crane trolley to climb and slide and may cause crane accidents.
2) To crane travelling mechanism.
The sever deformation of crane girder camber will damage the transmission shaft, and even broke the coupling tooth, or the coupling bolt, etc.
3) To crane girder.
The camber deformation will cause the crane girder bending which will cause the trolley track deformation and eventually result in gnawing track.
4) To cover plate or web plate.
Camber deformation will result in the cover plate or web plate broken and increase the likability of server crane accidents.
Once the overhead crane girder camber is deformed, the repairing is required unless you have adequate budget, you can replace the old piece of lifting equipment with a set of new overhead crane. There are two ways to restore the deformed crane girder, the traditional Flame Correction Method and Prestress Correction Method.
Flame Correction Method
The principle of flame correction method is to heat the three sides of the girder and cool it down to reform the girder camber. It is difficult to control the heating temperature and time, thus, it is also very difficult to guarantee the reformation of the girder camber.
Prestress Correction Method
Prestress correction method is to install two prestressed tensioners on the both sides of the flange-slabs of the overhead crane girder and use the tensioners to produce tensioning forces evenly and simultaneously to restore the crane girder camber. The advantages of this approach are:
When overhead crane camber deformation happened, professional crane restoration engineer is needed and advices, technique support and services from the overhead crane manufacturer are important. Free consultation are provided from Dongqi Crane whenever needed.
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