Causes and solutions for electric hoist failure
1. The electric hoist does not work after pressing the start switch.
It is mainly because the hoist is not connected to the rated working voltage and cannot work. There are generally 3 situations: ①Whether the power supply system supplies power to the electric hoist. Generally, it is tested with a test pen. If it does not supply power, wait until it is powered on before working. ②If the electrical appliances in the main and control circuits of the hoist are damaged, the circuits are disconnected or the contact is poor, the hoist motor will also be unable to be powered on. In this case, the main and control circuits need to be repaired. During the repair, in order to prevent the main and control circuits from sending the power to the three-phase motor due to phase loss and burning the motor, or the hoist motor suddenly gets power and runs, causing harm, the hoist motor must be disconnected from the power supply line, and only the main and control circuits are powered on, and then the start and stop switches are activated to check and analyze the working conditions of the control electrical appliances and circuits, and the problematic electrical appliances or circuits are repaired or replaced. When it is confirmed that there is no fault in the main and control circuits, the test can be re-run. ③ The voltage at the motor end of the hoist is more than 10% lower than the rated voltage, and the motor starting torque is too small, so that the hoist cannot lift the goods and cannot work. When checking, use a multimeter or voltmeter to measure the voltage at the motor input end. If the motor cannot start due to low voltage, you need to wait until the system voltage returns to normal before using the electric hoist. Sometimes, the voltage of the hoist motor is normal, but the hoist does not work. This requires considering other reasons, such as: the motor is burned, and the motor needs to be replaced during maintenance; the hoist has not been used for a long time, and poor maintenance has caused the brake wheel and the end cover to rust. When starting, the brake wheel cannot be disengaged, and the motor only makes a "hum" sound and cannot rotate, and the hoist cannot work. At this time, the brake wheel should be removed, the rusted surface should be cleaned, and then the test run should be restarted; the motor is seriously swept, which will also make the motor not rotate. If this situation is found, it should be stopped and the motor must be overhauled or replaced to ensure the normal operation of the hoist. In addition, it is strictly forbidden to overload the electric hoist during production. When the goods are overloaded, the hoist cannot lift the goods, and the motor only makes a "humming" sound but does not run. In severe cases, the motor may burn out and even cause an accident. At this time, the machine should be stopped immediately, the goods should be lightened, and the hoist should work at rated power.
2. Abnormal noise occurs when the electric hoist is running.
Many faults of electric hoists, such as faults in control appliances, motors or reducers, are often accompanied by abnormal noises. The location, pitch and tone of these noises vary with the cause of the fault. When repairing, you should listen and watch more. You can use or determine the location of the sound according to the characteristics of the fault sound, find and repair the fault. ① Abnormal noise occurs in the control circuit, and a "hum" noise is emitted. Generally, there is a fault in the contactor (such as poor contact of the AC contactor contacts, inconsistent voltage levels, stuck magnetic cores, etc.). The faulty contactor should be repaired. If it cannot be repaired, it must be replaced. After processing, the noise will disappear by itself.
② If the motor makes abnormal noise, it should be stopped immediately to check whether the motor is running in single phase, or whether the bearing is damaged, the coupling axis is misaligned, or the motor has "sweeping bore" and other faults. These will cause the motor to make abnormal noises. The location, pitch and tone of the noises of different faults are different. When running in single phase, the whole motor makes a regular "buzzing" sound that is sometimes strong and sometimes weak; when the bearing is damaged, a "buzzing" sound accompanied by "click-click" will be emitted near the bearing; when the coupling axis is misaligned, or the motor has a slight sweeping bore, the whole motor will make a very high "buzzing" sound, and it will be accompanied by sharp and piercing sounds from time to time. In short, according to the different noises, the faults should be found, and repaired item by item to restore the normal performance of the motor. When the motor fault is not handled, it is forbidden to use the hoist. ③ Abnormal noise is emitted from the reducer. If the reducer fails (such as lack of lubricating oil in the reducer box or bearing, gear wear or damage, bearing damage, etc.), the machine should be stopped for inspection. First, determine whether the reducer box or bearing of the reducer has been lubricated before use, and whether the lubricating oil is regularly replaced during use. If it is not lubricated as required, the reducer will not only produce excessive "buzzing" sound, but also excessively wear or damage the gears and bearings. Some people think that the reducer can still operate without adding lubricating oil temporarily or adding some lubricating oil casually, and no serious failure will occur. This idea is wrong. When our company installed an electric hoist, the worker forgot to add lubricating oil to the reducer box. After only one day of trial, the reducer made a very high noise. When the reducer box was opened, it was found that the gear was scrapped due to excessive wear. Damage to the reducer bearing is similar to the failure of the motor bearing, and abnormal noise will also be emitted near the bearing. In order to prevent the expansion of the fault, whether the reducer gear is excessively worn or damaged, or the reducer bearing is damaged, it needs to be disassembled, repaired or replaced immediately to eliminate the fault and reduce the noise.
3. The sliding distance of the machine when braking exceeds the specified requirements. When the electric hoist is out of service for a long time, someone may adjust the brake adjustment nut by mistake, or the brake ring may be worn too much, which may reduce the pressure of the brake spring and the braking force. When the machine is stopped, the brake is unreliable and the sliding distance exceeds the specified requirements. In this case, you only need to readjust the brake nut according to the hoist manual. However, you should pay attention to the following during work: when lifting heavy objects, it is forbidden to adjust, inspect and repair the brake. Sometimes, after adjusting the brake nut, the shutdown sliding distance still exceeds the specified requirements. In such a situation, other reasons should be considered. First, disassemble the brake ring and check whether there is oil on the brake surface. If there is oil, the friction coefficient will be reduced, which will cause slipping during braking and the sliding distance will exceed the specified requirements. It is not very useful to adjust the brake nut alone. At this time, you can only thoroughly clean the brake surface (cleaning with light gasoline) to restore the friction coefficient of the brake surface; secondly, if the brake ring is loose or damaged, the brake ring cannot guarantee effective braking, and you can only replace the brake ring; sometimes it is found that the brake ring is not damaged, but only the brake ring and the conical surface of the rear end cover are in poor contact. When braking, the brake surface contacts too little and the braking force is too small, so that the sliding distance exceeds the specified requirements. During maintenance, in order to increase the braking force, the position of poor contact should be found, and grinding should be carried out to increase the contact surface during braking. When grinding is not possible, the accessories need to be replaced; the hoist motor coupling is not moving or stuck. After shutdown, the brake ring and the conical surface of the rear end cover are in poor contact or cannot be contacted, so that the hoist braking effect is sometimes good and sometimes bad. In this case, the coupling should be repaired or replaced. In addition, the brake pressure spring will become fatigued after long-term use, causing the spring force to decrease. When the machine is stopped, the brake is not firm. In this case, the spring should be replaced and the braking force should be readjusted.
4. The temperature rise of the motor is too high.
First, check whether the hoist is overloaded. Overload causes the motor to heat up. Long-term overload will burn the motor. If the motor is not overloaded but still heats up, check whether the motor bearing is damaged. Also check whether the motor works according to the prescribed working system, which is also one of the reasons for the motor heating up. When using it, it should be strictly operated according to the motor working system. When the motor is running, the brake clearance is too small and not completely disengaged, which generates a lot of friction. While the friction heats up, it is equivalent to adding additional load, which reduces the motor speed, increases the current and heats up. At this time, the work should be stopped and the brake clearance should be readjusted.
5. The heavy object is lifted to the middle of the air, and it cannot be restarted after stopping. Analyze the reasons. First, check whether the system voltage is too low or the fluctuation is too large. If this is the case, you can only start it after the voltage returns to normal. On the other hand, pay attention to the lack of phases in the operation of the three-phase motor, and it cannot be started after stopping. At this time, you need to check the number of power phases. 6. Cannot stop or still does not stop at the limit position. This kind of situation is generally caused by the contactor contact welding. When the stop switch is pressed, the contactor contact cannot be disconnected, the motor is powered on and runs as usual, and the hoist does not stop. When it reaches the limit position, if the limiter fails, the hoist does not stop. In this case, immediately cut off the power supply to force the hoist to stop. After stopping, inspect the contactor or limiter. If it is severely damaged and cannot be repaired, it must be replaced. 7. Reducer oil leakage There are two reasons for reducer oil leakage: ① Between the reducer housing and the cover, the sealing ring is poorly assembled or damaged. The sealing ring should be removed for inspection or replacement. ② The reducer connection screws are not tightened. After stopping, tighten the screws.
8. The motor bore scraping The reasons for the bore scraping are: the support ring on the motor shaft is severely worn, the rotor core is displaced, or the stator core is displaced due to other reasons, resulting in too small a gap between the motor conical rotor and the stator, causing bore scraping. The motor is strictly prohibited from "bore scraping". When bore scraping occurs, the support ring should be removed and replaced, and the gap between the stator and rotor cones should be adjusted to make it uniform, or sent to a maintenance plant for repair. Through the analysis of common faults and treatments of electric hoists, hoist maintenance personnel know where to start when handling faults, which improves maintenance efficiency. In addition, it also provides operators with methods to handle problems on site.
