Common Faults and Troubleshooting Methods of Overhead Cranes

The following describes the common faults and troubleshooting methods of bridge cranes from three aspects: mechanical, electrical and metal structures.

Common Faults in Mechanical Transmission

1. The brake does not work well, the braking torque is small, and the hook slips in the lifting mechanism; the car slips in the running mechanism.
(1) There is oil on the surface of the brake wheel, and the friction coefficient decreases, resulting in a decrease in the braking torque, so the car cannot be braked. It can be solved by cleaning the surface oil with kerosene or gasoline.
(2) The brake shoe lining is severely worn and the rivets are exposed. When braking, the rivets are in contact with the surface of the brake wheel, which not only reduces the braking torque and cannot stop the car, but also strains the surface of the brake wheel, which is more harmful. Just replace the brake lining.
(3) Improper adjustment of the main spring and low tension result in a decrease in the braking torque, and the car cannot be braked, resulting in the phenomenon of slipping the car or slipping the hook. Readjust the brakes to increase their main spring tension.
(4) The main spring is fatigued, the material is aged or cracked, there is no elasticity, the tension is significantly reduced and the car cannot be braked. The new spring should be replaced and adjusted.
2. The brake cannot be opened. The reasons and solutions for the brake not opening are as follows:
(1) The tension of the main spring is too high, and the magnetic tension of the electromagnet is lower than the tension of the main spring, so the brake cannot be opened. Readjust the brake to reduce the tension of the main spring.
(2) The brake lever transmission system is stuck, and the brake release force is blocked during transmission, so the brake cannot be opened. Check the transmission system and eliminate the jamming phenomenon.
(3) The brake screw is bent, and the top of the screw cannot touch the moving iron core of the magnet, so the brake shoe cannot be pushed away. Disassemble the brake, remove the screw to straighten it or replace the screw.
(4) The brake shoe liner sticks to the dirty brake wheel running surface.
Removing the dirt on the surface of the brake wheel will solve it.
3. When the brake is working, the brake lining heats up, "smoke", and there is a burning smell, and the lining quickly wears out.
(1) The gap between the brake shoe lining and the brake wheel is improperly adjusted, the gap is too small, and the shoe lining always contacts the working surface of the brake wheel during operation, which is caused by friction and heat generation.
Readjust the gap between the tile lining and the brake wheel to make it even and completely disengaged during work without contacting the brake wheel.
(2) The auxiliary spring of the short-stroke brake fails, and the brake shoe cannot be pushed away, so that the brake shoe is always attached to the surface of the brake wheel to work, which is caused by long-term friction and heat generation.
Replace secondary spring and readjust brake.
(3) The brake frame and the brake wheel are not concentric, and the edge of the brake shoe cannot be separated from the working surface of the brake wheel, resulting in friction and heat generation.
Reinstall the brake to meet the concentric requirements.
(4) The working surface of the brake wheel is rough, the brake shoe lining does not match the brake wheel, and the brake is not good.
Re-finish the brake wheel or replace the brake wheel.

Common Faults in Electrical Transmission

1. Common faults of electrical equipment
(1) The motor overheats uniformly during operation
① The continuous power connection rate of the motor does not match the actual working type of the mechanism, and it generates heat due to overloading.
The motor that matches the actual work type should be replaced.
② The power supply voltage is low.
When the voltage is low, it should stop working to prevent the motor from being burned or accidents.
③ There is a phenomenon of blockage in the mechanical transmission system, and the motor will heat up when the resistance increases.
Check the mechanical transmission system, and eliminate the failure points such as inconcentricity and poor transmission.
(2) The motor vibrates during operation
① The motor shaft is not concentric with the reducer shaft.
Adjust the concentricity of the motor and the reducer to meet the technical standard, and the additional resistance of the transmission will naturally disappear.
② The motor bearing is damaged, causing the motor axis to tilt and increasing the running resistance.
Disassemble the motor and replace with new bearings.
③ The rotor of the motor is deformed, and in severe cases, it contacts the stator, that is, the phenomenon of "bore sweeping" occurs, which causes the motor to heat up and vibrate.
Disassemble and inspect the motor, straighten the rotor or replace the motor rotor.
(3) The controller is stuck during the turning process
① The contacts are in poor contact, and the contacts are welded by ignition.
Flatten the contact surface with a fine file to ensure good contact.
② The positioning mechanism of the controller is faulty.
Check and repair positioning mechanism to turn slider.
2. Electrical circuit failure There are many electrical circuit faults in cranes. In order to quickly eliminate faults and reduce repair time, maintenance personnel and drivers are required to be familiar with the working principle of all circuits of the crane, the performance, function and installation position of electrical equipment and electrical components. When an accident occurs, it should be judged where the fault may occur based on the fault phenomenon, and use electrical instruments and tools to check step by step according to the order of electric transmission, and finally find the faulty part and take limited measures to solve it. Common circuit faults and troubleshooting methods are described below.
(1) Push and close the three-phase knife switch of the protection cabinet, press the start button, and the fuse of the control circuit will be blown. Usually it is caused by a short to ground of a fused phase. Use electrical instruments to find the grounding point and eliminate it.
(2) Push and close the knife switch of the protection cabinet, press the start button, and the main contactor of the crane will not close (commonly known as the brake cannot be started if it is not closed). In any of the following situations, it cannot be started.
① There is no voltage in the circuit;
② Control circuit fuse fuse 1FU or 2FU is blown;
③ The handles of each controller are not placed in zero position;
④ The emergency switch SE, safety interlock switches SQ1 and SQ2 are not closed;
⑤ The normally closed contacts KC1, KC2...KC4 of each overcurrent relay are not closed;
⑥ The KM coil of the main contactor is blown or its wiring is broken.
Check the connection line step by step to find out the reason why the crane cannot start and eliminate it.

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