Electric hoists are widely used in power generation, mainly for equipment maintenance, lifting, and material transportation. The frequency of electric hoist failures is increasing, not only affecting normal production but also potentially causing serious accidents. Preventing accidents and ensuring the safe operation of electric hoists, as well as timely and accurate handling of various malfunctions during operation, has become a crucial aspect of production. Based on maintenance experience, this document analyzes the causes of some common electric hoist malfunctions. 1. The electric hoist does not work after pressing the start switch

This is mainly because the electric hoist is not connected to the rated working voltage and cannot operate. There are generally three situations: (1) Check if the power supply system is supplying power to the electric hoist. Generally, use a test pen. If there is no power, wait for power before operating;

(2) Damage to the electrical appliances in the main and control circuits of the hoist, circuit breaks, or poor contact can also prevent the hoist motor from being energized. In this case, the main and control circuits need to be inspected. During inspection, to prevent the power supply to the three-phase motor in the main and control circuits from being missing a phase and burning out the motor, or the electric hoist motor suddenly starting and causing harm, the electric hoist motor must be disconnected from the power line. Only power is supplied to the main and control circuits. Then, the start and stop switches are actuated to check and analyze the working conditions of the control electrical appliances and circuits. Faulty electrical appliances or circuits are repaired or replaced. Only after confirming that the main and control circuits are fault-free can the test run be restarted; (3) If the motor terminal voltage is more than 10% lower than the rated voltage, the motor starting torque is too small, causing the electric hoist to be unable to lift the goods and thus unable to operate. During inspection, use a multimeter or voltmeter to measure the input voltage of the motor. If the voltage is too low and the motor cannot start, wait for the system voltage to return to normal before using the electric hoist. Sometimes, the voltage of the electric hoist motor is normal, but the electric hoist does not work. This requires consideration of other reasons, such as: the motor is burned out; the brake wheel and end cover are rusted due to long-term disuse and poor maintenance, and the brake wheel cannot be released during startup, the motor only makes a "humming" sound and cannot rotate, and the electric hoist cannot work. At this time, the brake wheel should be removed, the rusted surface cleaned, and then the test run restarted; severe motor scoring will also prevent the motor from rotating. If this situation is found, stop using it and perform major repairs or replace the motor to ensure normal operation of the electric hoist. In addition, it is strictly forbidden to overload the electric hoist during production. When the goods are excessively overloaded, the electric hoist cannot lift the goods, the motor only makes a "humming" sound without rotating, and in severe cases, the motor may burn out or even cause accidents. At this time, stop immediately, reduce the load, and operate the electric hoist at the rated power.

2. Abnormal noise during electric hoist operation

Many faults in electric hoists, such as faults in control electrical appliances, motors, or reducers, are often accompanied by abnormal noise. The location, pitch, and timbre of these noises vary with the cause of the fault. During inspection, listen carefully and observe closely. You can use or identify the characteristics of the fault noise to determine the location of the noise and find and repair the fault.

(1) If the abnormal noise occurs in the control circuit and makes a "humming" noise, it is generally due to a malfunction of the contactor (such as poor contact of the AC contactor contacts, mismatched voltage level, or jammed core, etc.). The faulty contactor should be repaired, and if it cannot be repaired, it must be replaced. After processing, the noise will disappear automatically. (2) If the motor makes an abnormal noise, stop immediately and check whether the motor is running on a single phase, or whether there are faults such as bearing damage, misalignment of the coupling shaft, or "scoring." These will cause the motor to make abnormal noises. The location, pitch, and timbre of the noise vary with different faults. When running on a single phase, the entire motor emits a regular, fluctuating "humming" sound; when the bearing is damaged, a "humming" sound accompanied by "clatter-clatter" will be heard near the bearing; when the coupling shaft is misaligned, or the motor is slightly scored, the entire motor emits a very high "humming" sound, sometimes accompanied by a sharp, piercing sound. In short, according to the different noises, find the fault and repair it item by item to restore the normal performance of the motor. Do not use the electric hoist if the motor fault has not been handled.

(3) If the abnormal noise comes from the reducer, there is a fault in the reducer (such as lack of lubricating oil in the gearbox or bearing, gear wear or damage, bearing damage, etc.). At this time, stop and check. First, determine whether lubricating oil was added to the reducer gearbox or bearing before use, and whether the lubricating oil was changed regularly during use. If the lubrication is not performed as required, the reducer will not only produce a high "humming" sound but also excessively wear or damage the gears and bearings. To prevent the fault from expanding, whether the reducer gear is excessively worn or damaged, or the reducer bearing is damaged, it needs to be immediately disassembled, repaired, or replaced to eliminate the fault and reduce the noise. 3. The braking distance exceeds the specified requirements.

When the electric hoist is left unused for a long time, if someone mistakenly adjusts the brake adjusting nut, or the brake ring is excessively worn, the brake spring pressure will decrease, and the braking force will be reduced. When the machine stops, the braking is unreliable, and the sliding distance exceeds the specified requirement. In this case, simply readjust the brake nut according to the instructions of the electric hoist. However, during operation, it should be noted that adjusting, inspecting, and repairing the brake is prohibited when lifting heavy objects. Sometimes, after adjusting the brake nut, the sliding distance when the machine stops still exceeds the specified requirement. If this happens, other reasons should be considered. First, disassemble the brake ring and check whether there is oil stain on the brake surface. If there is oil stain, the friction coefficient will be reduced, causing slippage during braking, and the sliding distance will exceed the specified requirement. Simply adjusting the brake nut will not help much. At this time, only the brake surface should be thoroughly cleaned (light gasoline can be used for cleaning) to restore the friction coefficient of the brake surface; secondly, if the brake ring is loose or damaged, the brake ring cannot ensure effective braking, and the brake ring must be replaced; sometimes it is found that the brake ring is not damaged, only the brake ring and the rear cover cone surface are in poor contact. During braking, the brake surface contact is too small, and the braking force is too small, causing the sliding distance to exceed the specified requirement. During inspection and repair, in order to increase the braking force, the position of poor contact should be found and repaired to increase the contact surface during braking. If it cannot be repaired, the parts need to be replaced; the electric hoist motor coupling is not flexible or is stuck. After stopping, the brake ring and the rear cover cone surface are in poor contact or cannot contact, causing the braking effect of the electric hoist to be sometimes good and sometimes bad. In this case, the coupling should be inspected or replaced. In addition, the brake pressure spring will fatigue after long-term use, causing the spring force to decrease. When the machine stops, the braking is not firm, so the spring should be replaced and the braking force should be readjusted.

4. Motor overheating First, check whether the electric hoist is overloaded. Overloading causes the motor to overheat, and long-term overloading will burn out the motor; if the motor is not overloaded but still overheats, check whether the motor bearings are damaged; also check whether the motor is working according to the specified working system, which is also one of the reasons for motor overheating. During use, the motor should strictly follow the working system. When the motor is running, if the brake clearance is too small and not fully disengaged, it will generate a large frictional force, generating frictional heat and increasing the additional load at the same time, reducing the motor speed, increasing the current, and causing overheating. In this case, the work should be stopped, and the brake clearance should be readjusted. 5. The heavy object cannot be started again after stopping in mid-air Analyzing the reason, first check whether the system voltage is too low or the fluctuation is too large. If this is the case, wait until the voltage returns to normal before starting; on the other hand, pay attention to the phase loss of the three-phase motor during operation. After stopping, it cannot be started. At this time, the number of power supply phases needs to be checked.

6. Cannot stop or still cannot stop at the limit position

This situation is generally caused by the welding of the contactor contacts. When the stop switch is pressed, the contactor contacts cannot be disconnected, and the motor continues to be energized and runs, and the electric hoist does not stop; if the limit switch fails at the limit position, the electric hoist does not stop. In this case, immediately cut off the power to force the electric hoist to stop. After stopping, repair the contactor or limit switch. If it is severely damaged and cannot be repaired, it must be replaced.

7. Gearbox oil leakage The reasons for gearbox oil leakage are:

(1) The sealing ring between the gearbox body and the cover is poorly installed or damaged and failed. It should be disassembled for inspection or replacement of the sealing ring;

(2) The connecting screws of the gearbox are not tightened. After stopping, the screws should be tightened.

(3) Motor rubbing

The reason for rubbing is: the supporting ring on the motor shaft is severely worn, the rotor core is displaced, or the stator core is displaced due to other reasons, causing the conical rotor and stator of the motor to have too small a gap and rubbing occurs. The motor is strictly prohibited from "rubbing". When rubbing occurs, the supporting ring should be removed and replaced, the gap between the stator and rotor cone surfaces should be adjusted to be uniform, or it should be sent to a repair shop for repair. Through the analysis of common faults and handling of electric hoists, electric hoist maintenance personnel know where to start checking when handling faults, improving maintenance efficiency, and also providing on-site problem-solving methods for operators.