Analysis and prevention of sliding rope of steel wire rope of multi rope friction hoist

Multi rope friction hoist relies on the friction between steel wire rope and friction pad to transmit power. Its friction has an extremely important impact on the normal and reliable operation of multi rope friction hoist. During abnormal lifting, when the running speed of the hoist wire rope exceeds the rotating linear speed of the main drum, the rope sliding accident occurs. When the sliding distance is close, the harm is generally small, which will damage the crown wheel or the friction pad of the main drive drum; When the sliding distance of the steel wire rope is long and the sliding speed is large, the crown wheel and the main drum liner are seriously worn and even the friction liner melts, resulting in serious malignant shutdown accidents such as over rolling or falling of the skip, damage to the shaft equipment, and incalculable economic losses to the mine. In view of this situation, through theoretical analysis, the external force braking mode to meet the system safety is proposed to ensure the safe operation of the mine main hoisting system.

1. Cause analysis of wire rope sliding

In recent years, in the process of mine hoisting, by taking some measures, there are few major malignant sliding rope accidents, but they have not been completely eliminated. The main reasons are as follows: ① excessive braking force causes the braking deceleration to be greater than the limit acceleration, resulting in sliding rope. ② The lifting container is seriously overloaded, causing the dynamic tension ratio of steel wire rope to be greater than the constant of friction wheel, resulting in sliding rope. ③ The quality of friction pad is poor, the friction coefficient is low, and the pressure resistance and heat resistance are poor; The surface of steel wire rope is coated with lubricating grease or friction increasing grease with poor performance, which greatly reduces the friction coefficient, which leads to too small friction and sliding rope. ④ Illegal operation, such as sliding rope caused by excessive speed lowering of heavy skip and then emergency braking. ⑤ Extreme bad weather, such as severe cold weather in winter, no heating facilities or heating equipment failure, resulting in wire rope icing and crown wheel icing, etc

2 Analysis of sliding rope of hoisting wire rope

Heavy load emergency braking rope slipping

Under the action of braking torque MZ, the friction wheel rotates over the angle φ When, the friction wheel brake stops. At this time, the sliding distance between the steel wire rope and the pad is h, and the corresponding sliding speed of the steel wire rope is ve. According to the kinetic energy theorem, the motion equation of the two parts is equation (1):

MZ is the dynamic moment of the lifting mechanism; φ Is the angle turned by the hoist during braking; M1 is the total mass at heavy load side; M2 is the total mass of light load side; FH is the friction resistance between the rope and the lining when slipping; H is the slip distance between the rope and the lining; Ve is the sliding speed of the rope when the sliding distance is h [2-3]. Equation (1) shows that when the hoisting heavy-duty emergency braking wire rope slips, the work done by the braking torque only overcomes the kinetic energy of the rotating part of the hoist and motor; The friction resistance between the rope and the lining, the thermal energy generated in the sliding process and the potential energy of the sliding system overcome the kinetic energy of the sliding system. Therefore, the kinetic energy of the system is quickly overcome and the sliding speed will be quickly reduced to 0. At this time, the thermal energy generated by friction resistance is less, which generally will not cause excessive damage to the rope lining, but only scratch or slightly damage the friction pad. Therefore, in the sliding process, the friction coefficient changes little. When the sliding speed is 0, the friction resistance is enough to overcome the reverse sliding of the steel wire rope. This phenomenon has been confirmed in the test of hoist in many mines, but it must be emphasized that due to the heat generated by friction, the liner will be damaged and invalidated to some extent.

3.2 when the wire rope slips during the emergency braking of the idle operation, it can be seen from the kinetic energy theorem that the equation of the two parts when the emergency braking of the idle operation slips,

(2) equation (2) shows that when the emergency braking wire rope slips in the empty operation, the kinetic energy of the sliding system is overcome by the heat energy generated by the friction resistance in the sliding process, and the sliding speed gradually decreases to 0. The rope lining may be scratched and damaged during sliding, but it will not cause long-distance sliding of the steel wire rope. This phenomenon has also been verified in many mine hoist tests.

2.3 when lowering heavy load emergency braking, the steel wire rope slips. According to the kinetic energy theorem, the equation of two parts when lowering heavy load emergency braking slips

The results show that when the lowering heavy-duty emergency braking wire rope slips, the heat energy generated by friction resistance should overcome not only the kinetic energy of the sliding system, but also the potential energy of the sliding system. If the work done by the friction resistance in the sliding process can gradually overcome the kinetic energy and potential energy of the sliding system, it is possible to gradually reduce the sliding speed to 0. Before the failure of the friction pad, the friction coefficient increases. If the sliding distance is short, the sliding of lowering heavy load can be stopped.

For example: ① during the emergency braking test of the floor type friction wheel hoist in the auxiliary shaft of Zhangshuanglou mine of xukuang group, the lifting heavy load, empty operation and lowering heavy load all slide, but they all stop. The reason is that the oil pressure is too low and the braking torque is too large. ② The sliding problem of lowering heavy load emergency braking occurred many times in the commissioning stage of the floor friction wheel hoist in Dongfeng well of jinmeisihe mine, but they all stopped because the cage quality was small and did not meet the design requirements. This happens when the lifting speed is very small, the kinetic energy of the system is small, and the friction heat generation is not enough to make the gasket seriously invalid. Therefore, slow lifting can be adopted when the heavy skip is accidentally lowered or large pieces are lowered. The above two mine sliding rope accidents occurred during the commissioning of the hoist, without the participation of external factors, and the accident did not cause adverse effects.

If the work done by the friction resistance in the sliding process can not overcome the potential energy of the sliding system, and with the increase of the sliding distance, the heat energy generated by the friction resistance will gradually increase the surface temperature of the rope lining and promote the failure of the friction lining, so as to reduce the friction coefficient of the lining and reduce the friction resistance. Then, the relative sliding speed between the steel wire rope and the rope lining is bound to be greater and greater, which will lead to long-distance sliding of the steel wire rope and malignant rope sliding accident.

① At the end of December 2009, the skip in the main shaft of a coking coal company was seriously overloaded and the crown wheel was frozen. After the driver found it, he immediately made emergency braking. Due to the excessive braking force, the main drive drum soon stopped running, and the steel wire rope and skip were still running, resulting in the slip accident of the steel wire rope. After the sliding rope accident, the crown wheel and the main shaft device pad were seriously worn out of limit, the skip was over rolled, and the coding program was chaotic. After nearly 24 hours of treatment, the production was resumed, causing great economic losses to the mine. ② The skip of a coal mine of coking coal company was seriously overloaded, and the motor driving force was insufficient when lifting to the midway, so it was forced to lower the heavy skip. A serious steel wire rope slip accident occurred. The heat generated by the friction resistance during the steel wire rope sliding melted the friction liner, and the high pressure between the friction interfaces made the rope liner stick to the steel wire rope. The liner was torn and damaged like rags, resulting in a serious skip fall accident, Caused great losses to the coal mine.

3 measures to prevent sliding of friction lifting (1) a pulse encoder is installed at the guide wheel. When the steel wire rope slips, the number of pulses sent by the guide axle encoder and the main axle encoder is different. At this time, the control system acts to make the hoist brake reliably. (2) the impact limit theory is adopted in the design to effectively limit or eliminate the elastic vibration of steel wire rope during emergency braking and improve the safety and reliability of friction hoisting system. (3) reasonably select the hydraulic braking system, and try to use the constant deceleration hydraulic braking system with limiting system vibration. (4) reasonably set the oil pressure of the hydraulic braking system to make the dynamic torque of the lifting mechanism meet the requirements, so that there is no slip in the emergency braking under various conditions. (5) the static tension ratio of steel wire rope shall be strictly limited to prevent overload of lifting container and sliding rope caused by overload or excessive tension ratio. (6) high performance friction pads shall be used, and pads with good friction coefficient, pressure resistance and heat resistance shall be selected to prevent sliding rope caused by too small friction. (7) adopt high-quality galvanized steel wire rope, and do not apply lubricating grease or antifriction grease on the surface of the steel wire rope (antifriction grease will reduce the friction coefficient between the steel wire rope and the liner), so as to prevent sliding rope caused by too small friction. (8) improve the performance of the control system, strictly prevent overload operation and illegal operation, and reduce rope sliding accidents.

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