Common Faults and Solutions of Double Girder Bridge Cranes

In the process of companies using double-girder bridge cranes, some problems may occur that are not equipment but cannot be operated. For new users and maintenance personnel with less work experience, they need to be aware of some common false faults of general double-girder bridge cranes, and they can be dealt with immediately when encountered to avoid affecting production. I will use the following examples to tell you about the common faults and solutions of double-girder bridge cranes.

Example 1: safety door switch of double girder bridge cranes

A company has a double-beam bridge crane. Its indicator light is on and the display light on the control linkage station is on, but it cannot be started. After maintenance personnel went to the site for inspection, they found that the protective door from the driver's cab to the walkway was not closed. When the maintenance personnel close the protective door tightly, all operations of the lifting equipment are normal. This is a false fault. In the safety maintenance of the lifting equipment, there is a door switch next to the hatch door, driver's access door and maintenance door. When the lifting equipment driver or maintenance personnel go to the lifting equipment to perform maintenance, they must be turned on. When the hatch door reaches the lifting equipment platform, or the maintenance door opens to the main beam of the lifting equipment rail, the normally closed point of the electrical switch next to the opened door is disconnected, and the main AC contactor of the electrical equipment box is released, thus disconnect the power supply of the lifting equipment so that the lifting equipment cannot be started. At the same time, this kind of maintenance protects maintenance workers from the danger of cars on the bridge rack sliding and electrifying, and also prevents others from starting to drive and injuring maintenance workers. It can be seen that the protection function of the safety door switch is very necessary.

Example 2: zero position maintenance function of bridge cranes

The power distribution of a double-girder bridge hoisting equipment is normal, and the protective doors are closed and intact, but they cannot be started. After on-site inspection by maintenance personnel, it was found that the lifting control camshaft did not return to zero effectively. That is, although the zero point mark of the camshaft was at the zero position, the zero position maintenance contact point did not touch. Because it is a lifting equipment that has been used for many years, the elasticity of its contact points has weakened, causing false failures that sometimes cannot be reached. Replace the contact points with new ones and the non-startup problem is solved. It is known from the structure of the cam controller that the zero position circuit breaker of the crane, car and truck control panels is closed only when the rocker of each control panel is placed in the zero position. In any other working position (that is, non-zero position), it is in the broken position. Therefore, when all the control panel rockers are not in the zero position (or the zero contact point is not closed), the main control loop of the lifting equipment cannot be connected, and the lifting equipment cannot be started. This avoids the dangerous accident of sudden movement of the mechanism when restarting after placing the working position due to the rocker not returning to the zero position for various reasons. This is the zero position maintenance function of lifting equipment.

Example 3: start button and pause button connected wrong of double girder bridge crane equipment

For a double-girder bridge hoisting equipment, its power supply, protective door and control rocker are all normal, but it cannot be started by pressing the start button. Maintenance personnel went to the site to inspect and forced the main AC contactor to start, and everything was operating normally. However, the AC contactor cannot be disconnected when the stop button is pressed, but the AC contactor is disconnected when the start button is pressed. Press the stop button again, and the main AC contactor starts normally, indicating that the start button and pause button are connected incorrectly. This is a false fault caused by the maintenance personnel not explaining clearly.

Example 4: the capacity of 32/5-ton double-girder bridge-type lifting equipment reduced

A 32/5-ton double-girder bridge-type lifting equipment has reduced hoisting capacity, and the main hook can only lift more than 20 tons of suspended objects. After several inspections, it was thought that it was caused by the aging of part of the electrical equipment. However, check the electrical equipment part, from the entrance of the switching power supply to the control panel, the cable diameter size meets the requirements; the contact points of each AC contactor are intact; the main contact points of the cam controller are also intact; the main hook resistor wiring is accurate, the wiring is good; the main hook motor wiring is correct, the rotor brush is good, and the motor rotation sound is normal, indicating that the fault is not in the electrical equipment part. When inspecting part of the mechanical equipment, it was found that the galvanized steel wire rope of the main hook was relatively damaged. When I opened the pulley cover on the car frame, I saw that the galvanized steel wire rope was not on the roller, but had fallen on the pulley shaft. It was also found that there was a gap on the edge of the roller. A new roller was replaced, and a new galvanized steel wire rope was replaced at the same time. As a result, the trial operation of hoisting a 10t load was normal.

Regarding this common fault situation, the general maintenance experience is mostly in the electrical equipment part. For example, insufficient cable diameter, poor main contact point contact, incorrect wiring of resistors, etc. will all lead to a reduction in hoisting capacity, so multiple repairs will fail. The work started on the electrical part, but this false fault was blocked by the pulley block protective cover, making the repair out of the way.

Managers and maintenance personnel who actually operate bridge cranes must follow the operating procedures of the lifting equipment and have sufficient knowledge of the equipment when using the lifting equipment. When an abnormal condition is found in the double-girder bridge hoisting equipment, the cause must be analyzed based on the problem. As long as careful inspection and comprehensive observation are required, some false faults can be identified.

If you have any questions about double girder bridge cranes, please feel free to contact us.