Repair method for deformation of main beam of bridge crane
When the main girder of the bridge crane is deformed, we should repair it. The repair methods are mainly: flame correction method, prestress method, repeated welding method, cutting method, etc.
1. Flame correction method
The principle of the flame correction method is to locally heat the main beam to cause plastic deformation in some parts of the metal structure. After cooling, the residual local shrinkage stress can achieve the purpose of correction. Pay attention to the following points when using flame correction method for correction:
1.1 The heating temperature should be 700 ℃ 800 ℃, at this time the steel plate appears pink, the heating temperature should not be too high or too low. At this time, the yield limit of the metal is close to zero, and it is in the state of "hot carbon steel", and the correction effect is achieved.
1.2 In order to reduce the wave degree of the web, the heating point should be at the partition. The heating point should avoid the dangerous section of the main beam. After heating correction, the stress of the roasting point increases, so the load stress of the dangerous section is also increased, which is easy to make the correction deformation invalid.
1.3 The same position can not be heated repeatedly, not only the effect is not good, but also the metallographic structure of the metal is damaged.
1.4 The main beam should be strengthened after the deformation of the main beam is corrected. Because the main beam has great stress after correction, and after years of use, the fatigue of the metal material increases and the rigidity is insufficient. If it is not reinforced, not only the correction effect will not be maintained, but also the deformation will be aggravated. The general reinforcement method is to use channel steel as webs on both sides of the lower cover in the span of the main girder, and add a layer of lower cover to increase the section of the main girder.
The flame correction method has a better correction effect, simple construction process, and strong flexibility. However, when flame correction, the correction part of the main beam is jacked up (to put the baking area under compressive stress), which increases the difficulty of construction and technical requirements; flame After correction, the main beam still needs to be reinforced with channel steel, otherwise it will produce more serious plastic deformation. Under normal circumstances (except for local correction of hard bends), flame correction is not recommended.
2. Prestress method
The pre-stress method to correct the deflection of the main girder is to pass through fixed supports at both ends of the lower cover of the main girder, and stretch multiple steel bars or wire ropes with prestress to make the main girder subject to a bending moment (the upper half of the main girder is under tensile stress). , The lower half is under compressive stress), under the action of this bending moment, the main girder resumes arching. When the main girder is under load, the working pressure is just opposite to the prestress of the steel bar, so that the prestress of the steel bar can offset part of the working compressive stress, thereby improving the bearing capacity of the main girder.
The prestress method is an effective method to correct the downward deflection of the main beam. The upward arch value after correction is accurate and stable, and can be adjusted at any time according to the changes in daily use; the strength and rigidity of the main beam will be strengthened after the correction; the correction is simple and reliable, Easy and accurate control, short construction period, low correction cost, etc. However, the prestressing method is not suitable for the horizontal bending and local deformation of the main beam, and is only suitable for the correction of the bow deflection of the box-shaped main beam of the bridge crane; the corrected appearance is not beautiful, etc. If the bridge crane has been used for many years, long-term full-load operation, insufficient main beam rigidity, poor carrying capacity, long-term full-load operation, poor working environment, etc., it is suitable to adopt the prestress method.