What’re the flame straightening method for crane main girder deformation?
Sometimes ZZHZ will use flame straightening method to correct crane main girder deformation. Flame straightening method refers to that local heating on the metal structure 
produces plastic compression on some places and remained local shrinkage stress can correct the bend after cooling.
As using the flame straightening method of gantry crane, ZZHZ takes detailed deformation condition into consideration and decides size, numbers and position of heating points, some tips below must be considered:
1) the most appropriate heating temperature 700-800℃, over-high or over-slow heating temperature should be avoided.
2) Repeated heating at the same position should be forbidden, or it will cause a bad result as well as a damage to the metallographic structure.
3) Heating point should be located in baffle plate to reduce bending of web plate
4) Heating point should be avoided on the dangerous section. Stress at part around heating point increases after heating correction, so load stress in the dangerous section increases and bending correction will not work.
5) Strengthen the main girder after distortion. Because main girder stress will be large after correction, metal materials get tired with not enough stiffness after many years using. If strengthening the main girder is neglected, the correction effect will lose and the distortion will be more serious.
