Apr 01, 2021
The main girder of overhead crane is welded as box type by high strength carbon steel plate.
And rail track for trolley is welded at top of main girder.
Because of self-weight of main girder and trolley, the main girder will sink as trolley moves to middle-span. To help trolley move smoothly along the rail track, one upper camber value is pre-set to offset the deflection of main girder.
Then how we ensure the camber in fabrication?
1.Pre-set the upper camber of web plate
Before fabricating, self-weight of main girder and deformation from welding have to be fully considered. Usually the pre-setting upper camber value for web plate shall be greater than that required by technical documents.
Before fabricating, the pre-setting upper camber value shall be （3~4)S/1000（S=Span）
After fabricating, the finished upper camber value shall be (0.9/1000~1.4/1000) /S (S=Span)
2.Welding technology to control suitable deformation of main girder and rail after welding
To prevent camber reducing caused by welding deformation from 4 long welding joints in main girder, 2 long welding joints at bottom of main girder shall be welded firstly with small current.
As welding rail track at top of main girder, we shall weld it from middle-span part to two ends.
Strict inspection on main girder has to be done after finishing welding. If the upper chamber value is smaller than expected, flame heating on large reinforced plate part at web plate lower chord area shall be conducted.
The heating temperature shall be <700 celcius degree;
Three should have more points for flame heating;
The bottom side of the triangular heating zone should be narrow or close to a straight line, which ensures uniform change of upper camber.
4.Welding technology on butt weld
To ensure bearing capacity,the splicing joints of the wing plate and the web cannot be arranged on the same section, and the staggered distance shall not be less than 200mm. At the same time, the joints should not be arranged 2m position near the mid-beam.
CO2 gas protection welding, single-sided welding and double-sided forming
Above 4 measures help us ensure the camber of main girder in fabrication. And we also have many other technology in production. For more details, please visit our website: www.kevino-crane.com