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Analysis and preventive measures for the causes of elevator bottom and topping

Jul 27, 2018

The traction elevator is driven by a traction machine and relies on the friction between the traction sheave and the rope to drive the car to run along the vertical track. The safe operation of the elevator is always a topic of concern in the development of the elevator. Although the elevator technology is increasingly updated, although the elevator has been equipped with multiple safety devices such as electrical and mechanical to ensure safety, the effectiveness of the safety device is The safe operation of the elevator has a direct impact.


    Therefore, this paper analyzes the relationship between the effectiveness of safety protection devices and the phenomenon of bottoming and topping, and proposes preventive measures from the perspective of strengthening elevator inspection and maintenance, which improves the efficiency of elevator inspection and maintenance personnel. It is not beneficial to reduce the possibility of elevator bottom and topping.


    1. Reasons for the bottom and top of the elevator

    The bottom of the elevator refers to the phenomenon that the elevator can not effectively stop and crash into the pit when the whole bottom end station of the elevator goes down; the top of the elevator refers to the phenomenon that the elevator can not effectively stop and continue to rush to the top of the hoistway when the elevator is above the upper station. There are several reasons for creating the bottom and top of the elevator:


    1.1 brake failure or insufficient braking force

    The brake mainly plays an effective stop function in the operation of the elevator. According to the requirements of 687588-2003 (Safety Code for Elevator Manufacturing and Installation), when the car is loaded with 155% rated load up and down, the brake can make the car reliable stop. The average deceleration rate is not greater than 9. If the brake fails or the braking force is insufficient, there is a danger of the elevator rolling. The main causes of brake failure or insufficient braking force are as follows:

    (1) The brake is tight and the spring brake is loose and broken;

    (2) The brake electrical contact is stuck or not disconnected, so that the brake solenoid cannot be released.

    (3) The brake gate clearance is too large.

    (4) The brake brake shoe and the brake wheel friction cause the brake brake shoe and the brake wheel to overheat, resulting in a decrease in braking capacity. The brake is stuck, the brake arm and the shaft pin are broken, and the brake can be effectively closed.


    1.2 end station protection switch failure

The end station protection is provided with three kinds of protection switches, such as forced speed change, limit limit and limit switch, also called over-travel protection switch, which is used to prevent the elevator from being over the top or bottom end station due to the failure of the control unit. run. If the car is over-traveled due to slipping of the traction rope, brake failure or insufficient braking force, the end station protection switch is powerless.


    The forced speed change switch is mainly used to control the deceleration of the elevator before the full end of the line; the limit switch is used to cut off the direction relay or contact in the elevator control system when the forced deceleration switch fails to decelerate and stop the elevator. The circuit is released, and the elevator stops running. However, at this time, it is only to prevent the elevator from running in a dangerous direction, and the elevator can still operate in a safe direction; the limit switch is the third protection against over-travel, and when the limit switch is operated, the elevator cannot stop running, then the limit switch is cut off. The drive unit and brake are de-energized and the elevator stops running.


    The failure of the end station protection switch usually manifests as follows:


    (1) The forced speed change switch fails, mainly due to the looseness of the impact wheel mounted on the car or the speed change of the speed change switch and the non-release of the electrical contact.


    (2) The limit switch fails, mainly manifested in the looseness of the touch plate installed on the car frame and the delay or release of the contactor in the contact direction, causing the brake to not brake or the brake lag time, so that the limit switch cannot operate in time.


    (3) Limit switch failure: It is often manifested as the limit switch wheel or the looseness of the touch iron, so that when the speed can not be effectively decelerated and stopped, the limit switch can be disabled and disabled.

If all three protections fail, the elevator will inevitably lead to the consequences of bottoming or topping if the speeding operation is overrun; if the forced deceleration switch fails and the elevator cannot be decelerated, the limit switch will be ineffective after the elevator goes out of the station position. In the case that even if the limit switch is effective, the car cannot stop before reaching the buffer, and the elevator may have a possibility of a bottoming or a topping accident; if the limit switch or the limit switch fails, even if the forced speed change switch is effective, then In the event of a brake failure, the elevator may still be bottomed or topped.


    1.3 insufficient traction ability

The traction elevator is driven by the traction machine. The friction between the traction sheave and the rope is used to drive the car to run along the vertical track. The insufficient traction force can not guarantee the normal lifting of the car and cause the slipping state. Therefore, it is easy to cause the bottom. The main factors of insufficient traction of the elevator are as follows:


    (1) The traction sheave is worn or the diameter of the traction rope is reduced. Since the friction is not a constant during the whole period of use of the elevator, the rope is continuously reduced as the traction rope and the wheel groove are continuously rubbed, and the traction rope gradually approaches the bottom of the groove to cut the traction rope and the rope groove. The point clamping force (for the V-shaped traction rope groove) is also gradually lowered, resulting in insufficient friction, resulting in reduced traction capacity.



    (2) The balance factor does not meet the requirements of the standard. The balance factor is the ratio of the load on the bearing side to balance the load on the car. According to the requirements of GBl0058, the balance coefficient of different types of elevators should be 40% to 50%. The small value of the balance coefficient only affects the quality of the bearing and the small balance load of the elevator, and also affects the tension of the ropes on both sides of the traction sheave. The magnitude of the tension will have an effect on the specific pressure of the traction wire in the rope groove. The larger the tension, the greater the specific pressure, and the greater the traction capacity provided by the traction wire. Therefore, the value of the balance coefficient determines both the unbalanced load and the traction capacity of the elevator. When the maximum unbalanced load is greater than the maximum traction of the elevator, the traction wire will slip in the rope groove, increasing the possibility of the elevator bottoming.


    (3) Wear of the transmission and reduction mechanism: The transmission mechanism mainly refers to the mechanical components such as the traction machine main shaft, bearings, gears and worms. Due to the long-term use of these moving parts, or excessive lubrication and aging, the traction force is seriously degraded.


    1.4 speed limiter and safety gear failure


    The speed limiter-safety tongs system is a safety device that protects the elevator from the occurrence of downward overspeed and broken rope. The speed limiter is a device that limits the overspeed operation of the elevator. When the elevator overspeed reaches the set electrical speed, it will cut off the safety circuit of the elevator through the electrical switch, thereby cutting off the system power. If the elevator continues to overspeed due to the bearing force or inertia, the mechanical action device of the speed limiter is triggered to stop the speed-limiting wire rope, thereby lifting the safety gear. The safety gear is a mechanical device that stops the car or the opposite bearing. It acts on the guide rail and relies on the friction between the wedge and the guide rail to stop the car.


    (1) The speed limiter does not operate: GB7588-2003 stipulates that the speed limit of the elevator speed limiter should not be less than 115% of the rated speed. If the elevator safety circuit fails or the speed limiter speed does not meet the requirements, the speed limiter does not action. When the elevator is overspeeded, the control circuit will not open and the brake will not be braked.

    (2) Although the speed limiter operates, it cannot operate the car safety gear. The reason is that the speed limiter wheel groove wears and reduces the friction between the rope wheel and the speed limit rope. When the elevator overspeeds, although the speed limiter electrical switch operates, the insufficient tension of the speed limit rope cannot make the safety gear function.


    (3) Car top safety clamp linkage switch failure: At present, the safety clamp switch generally adopts the travel switch, which is easy to cause the electrical contact to stick, so that when the speed limiter rope pulls the safety clamp, the electrical switch fails, and after the elevator overspeed, The control circuit is not open and the brake is not braked.


    (4) The effective operation position cannot be achieved after the safety clamp is installed or repaired. Due to the test and adjustment after the installation and maintenance, the action is not in place, or the side of the safety clamp is not synchronized. That is, there is a sequence between the safety clamp on one side of the car and the safety clamp on the other side of the car, or the clearance between the safety clamp wedge on the side of the car and the side of the guide rail is too large, and the safety clamp on the side is not made. Stopping the car, causing the car to fall.


    (5) The surface friction coefficient of the safety clamp sliding wedge is reduced. If the safety clamp wedge is moved, the actual frictional force on the side of the guide rail is less than the force required to act on the guide rail during the operation of the safety clamp; the dirt on the safety clamp is mechanically corroded. Failure to repair and clean in time caused the machine to jam and could not move. This kind of situation makes the safety clamp small enough to stop the car.


    1.5 elevator overload

    According to GB-7588-2003 "Safety Code for Elevator Manufacturing and Installation", the so-called overload refers to more than 10% of the rated load and at least 75 kg. In the case of overload, the car should have an audio and/or illuminating signal to inform the user. And the power-driven automatic door should remain in the fully open position. When the elevator stops for a long time or because the tidal road and pit environment mix will cause the movable contact of the overload protection device at the bottom of the car to rust, when the elevator is overloaded, the overload device does not operate, so the safety circuit cannot be disconnected, and the car cannot Stop at the bottom and bottom.


    1.6 Uplink protection device is invalid


    GB7588-2003 stipulates that the elevator-driven overspeed protection device shall be installed on the traction drive elevator, and the existing elevators installed before this are installed. At present, there are commonly used rope clamps, speed limiters, a car safety gear, a speed limiter, a pair of safety gears, and a permanent magnet synchronous brake. Among them, a rope clamp, a two-way speed limiter, a car safety gear, and a strong direction. The speed limiter's pair of safety gears is used to monitor the speed of the overspeed protection device. The speed limit of the upstream overspeed protection device is usually the failure of the speed limiter and the safety gear.


    In summary, when the elevator brake fails, the car is overloaded, and the elevator overspeeds. If the speed limiter safety clamp system is over-acting when it returns, the car can still exceed 115% of the rated speed. After the effective stop, however, if the speed limiter safety clamp system fails, the elevator bottom accident cannot be avoided. When the traction capacity of the elevator is insufficient or the control system fails, when the car passes the bottom end station, the end station protection switch will cause the main engine or brake to lose power, and the car will stop; if the end station protection switch fails , it is very easy to cause a bottom accident when the elevator is over the road. When the elevator is lightly loaded upwards, if the brake fails, the elevator will overspeed. For the elevator that fails to install the uplink protection device or the uplink protection device, the ceiling accident will occur. For the uplink protection device, the safety limiter safety force clamp system will be used. The elevator, if the speed limiter safety clamp system fails at this time, will also lead to the top accident. When the elevator ascends close to the top-end end station due to the failure of the control system, if the end station protection switch fails or the elevator top floor space does not meet the requirements, there is a possibility that the car topping occurs.



    Through the above analysis, it can be seen that only the safety components of the elevator and other elevators are reliable and effective, so as to avoid the occurrence of elevator bottom and topping accidents. Therefore, in addition to the daily maintenance and annual inspection of the elevator, the inspection and maintenance measures of the elevator's different safety components should be carried out in accordance with the relevant regulations. It is also necessary to carry out targeted inspections on the components that are likely to cause the elevator bottom and the top. Maintenance to achieve the purpose of preventing accidents.

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