Reasons and Treatment Methods for Opening Welding of Container Gantry Crane Trolley Track

The main types of container gantry cranes used in the port are tire cranes and rail cranes. With the increase of the use time of the tire crane and the track crane, the welds between the trolley track and the track pad, the track pad and the top cover of the girder are opened and the trolley track is broken, which has a certain impact on the normal use of the tire crane and the track crane.

1. Trolley track structure form

1.1 Classified according to the connection between the trolley track and the girder

According to the connection between the trolley track and the tire crane, the trolley track can be divided into welded track and platen connected track.

1.2 Classification of welded trolley track

Commonly used welded trolley tracks are mainly A75 I-beam track and square steel track. A75 I-beam rail is composed of rail head, rail waist, rail bottom, etc. The rectangular steel track is formed outside, and the track is perpendicular to the girder when installed.

1.3 Classification according to the welding method of trolley track and girder

The backing plate is a metal flat plate welded between the trolley track and the cover plate on the girder. The material of the backing plate is the same as that of the cover plate on the girder, and Q345B ordinary steel is generally used. According to whether there is a welded plate between the trolley track and the girder, the trolley track can be divided into two types: the plate type I-steel track and the plate type I-steel track.

2. Reasons for opening welding

2.1 The welding process of car track welding does not meet the requirements

The material of the trolley track is high-strength steel, and the carbon equivalent of the high-strength steel used in the typical A75 I-steel track is 1.10, and its weldability is poor. Therefore, when welding the trolley track, there are strict requirements for the flatness between the trolley track, the backing plate and the cover plate on the girder. At the same time, it is necessary to strictly follow the track welding process when welding the trolley track. However, if improper selection of welding materials, insufficient preheating of welding materials, insufficient preheating of welding materials, insufficient thermal insulation after welding, and non-compliance with welding flatness, etc., will cause the weld strength of the trolley track to fail to meet the design requirements, resulting in the opening welding of the trolley track during use.

As the material of the trolley track is high-strength steel, the cover plate and the backing plate on the girder are made of ordinary steel Q345B. Therefore, the welding between the cover plate and the backing plate on the girder is the same material welding, and the welding between the track and the backing plate is the dissimilar material welding. The technical requirements of dissimilar material welding are higher than those of the same material welding.

2.2 The material of the trolley track is different from that of the cover plate on the girder

Because the material of the trolley track is different from that of the cover plate and the backing plate on the girder, the metal rigidity of the trolley track is stronger than that of the cover plate on the girder. When the car is running on the car track, the metal elastic deformation (downtorsion) will occur on the car track and the cover plate of the girder, but because the metal rigidity of the car track is stronger than the cover plate of the girder, the metal elastic deformation of the car track is smaller than the cover plate of the girder, and the welding material between the car track and the cover plate of the girder will bear the tension. With the accumulation of tension, the welding material gradually appears metal fatigue. When the metal fatigue accumulates to a certain extent, the welding material cracks, and finally leads to the opening of the trolley track.

2.3 Track stress release

During the use of trolley track, affected by the change of temperature during the change of seasons, the track will be stretched or contracted. In this process, the stress caused by orbital deformation is released. In the process of stress release, the track will be subjected to a force along the direction of the track. This force is released at the bottom of the thin track, causing the bottom of the track to break perpendicular to the track. This situation will cause the head and bottom of the trolley track to break after a period of time.

In addition to the above conditions, the car track is also affected by the temperature caused by friction during work. The car moves back and forth on the track at high speed, the contact surface of the track head will produce a higher temperature, the middle of the head and the feet are connected by a thin waist, the thermal conductivity of the track and the cross section shape determine its head and feet produce a larger temperature difference, and there is a temperature difference there is stress.

3. Treatment method of opening welding of trolley track

3.1 Processing Methods

At present, the repair welding method is mainly used for the repair of the trolley track with serious welding. The main steps of the repair welding are as follows:

Clean the oil around the weld that needs to be repaired;

Use carbon arc gouging or Angle grinder to remove the raw welding material at the opening welding position, and polish the weld into a V-shaped natural groove;

Preheat the weld at the open welding position, the preheating temperature is controlled at about 450 ℃, and the preheating area is within the range of 50 mm around the weld.

Weld the open welding position, the welding process must be continuous, and ensure that the temperature of the welding layer is not less than 200 ℃;

After the welding is completed, the repair welding area is subjected to post heat treatment, and the post heat temperature is about 450 ℃ and kept for 40 minutes.

Cover the repair welding area with asbestos cloth for heat preservation and slow cooling;

The repair welding position is polished to ensure the smooth transition between the weld and the track base material;

Magnetic particle inspection is carried out in the 200 mm area around the welding position. If it is detected that the trolley track is not fully welded, repair the welding again.

The effect after repair welding

After the repair welding treatment, the trolley track weld will be opened again, the possible reasons are as follows:

Repair welding is only to repair the open welding seam, not completely solve the problem of car track open welding. Therefore, the trolley track weld will be opened again after repair welding.

The welding process of the repair welding fails to meet the requirements of the track welding process during the manufacturing of the equipment, resulting in the low quality of the car track repair welding, which makes the car track weld open again in a short time after the repair welding.