The Cause Of The Bottom Or Topping Accident That Occurs When The Elevator Is In Normal Operation.
1. Electrical safety device failure
A. The forced deceleration device fails. When the elevator runs out of control to the top or bottom of the hoistway, the first is the forced deceleration switch. If the switch fails or the deceleration relay sticks out and does not release, the elevator cannot decelerate before reaching the end station, that is, the car still runs at a constant speed until 蹲Bottom or topping;
B. The position switch is out of order. If the forced deceleration switch fails to slow down and stop the elevator, especially when the elevator goes down to the bottom position with full load, the lower limit switch fails, and the control circuit cannot be opened to brake the brake. Even if the limit switch is valid, the elevator will occur. Bottom accident. Therefore, after the elevator reaches the limit switch position, the distance between the car striker and the top surface of the buffer is only 150mm~200mm.
Can the car be smoothly stopped within this limited distance? From the kinematics point of view, the stopping distance is mainly determined by the braking force of the inertia of the moving object, and the braking force is constant. Therefore, the greater the inertia, the slower the braking deceleration and the longer the braking distance. For an elevator that is fully loaded and has not been decelerated, it is impossible to stop the car without stopping the accident.
C, the switch is out of order. Under the condition that the forced deceleration switch and the limit switch fail, if the limit switch fails, the bottom or top accident will be inevitable;
D. The direction contactor is stuck or released slowly, causing the brake to not brake or the brake time lag.
2, insufficient braking torque
The braking performance of the brake is an important indicator of the safe operation of the elevator. GB10060 stipulates that “brake reliability” is required in the performance of the traction capacity test or in the operation test and overload test.
A, the brake release clearance is too large;
B. The brake shoe is adjusted in time after the brake shoe is worn, that is, the spring force is too small;
C. There is oil on the brake wheel and brake shoe surface.
These factors have different effects on the dangerous situation of the elevator. If one of these factors is serious, and the elevator is in the state of full load down or no load up, the bottom may be generated with or without electrical or mechanical safety devices. Or topping.
3. Insufficient gravity
One of the important guarantees for the safe operation of the traction type elevator is the friction between the traction rope groove and the traction rope. If the friction is insufficient, even if the brake is reliable, the car cannot be reliably stopped. The safety device simply prevents accidental car fall and dangerously ascending and accelerating.
Reasons for insufficient traction:
A. The groove is worn or the diameter of the hoisting rope is reduced. Since the friction is not a constant throughout the life of the elevator. As the rope groove wears and the rope diameter decreases, the hoisting rope gradually approaches the bottom of the groove, so that the clamping force between the hoisting rope and the rope groove is gradually reduced (to the V-shaped rope groove), resulting in friction. insufficient;
B. The diameter of the traction wheel pitch circle is not equal. During the ascent process, the car is wound on a wheel groove with a larger pitch diameter, and its circumferential speed is larger than that of the hoisting rope wound on the wheel groove with a smaller pitch circle diameter, thus causing an increase in tensile force due to The pulling force of each traction rope is uneven, so that the contact pressure between the traction rope and the wheel groove is different, that is, the tension ratio of each traction rope is too large, and the sliding amount of the traction rope is also increased;
C. The wrap angle of the traction rope on the rope groove of the traction sheave is smaller than the design requirement;
D. The rework of the newly replaced hoisting rope and the hoisting rope groove does not match the original design.
4, the balance coefficient does not meet the requirements of the standard provisions of Gb10058: the balance coefficient of various types of elevators is 40% to 50%. That is, when the elevator is moving up and down, the counterweight and the car should work in a balanced state as much as possible. Otherwise, the load of the motor will increase, and the heating and damage of the motor coil will be caused, and the safety performance of the car's leveling or operation will also be affected. It is well known that the hoisting rope of an elevator must be larger than the difference between the load of the car and the counterweight to enable the elevator to operate normally.
4, the speed limiter fails
A. The speed limiter electrical safety switch fails. After the elevator overspeeds, the control circuit is not disconnected and the brake is not braked;
B. The speed limiter mechanical switch fails;
C. Although the speed limiter operates, it cannot operate the car safety gear. The reason is that the speed limiter groove wears and reduces the friction between the rope wheel and the speed limiter rope. When the elevator overspeeds, although the speed limiter moves , but the tension of the speed limiter does not allow the safety gear to function;
D. The speed limit of the speed limiter's movement speed adjustment is loose. This phenomenon does not generally occur.
6, the safety gear failed
A. After the safety clamp is installed or repaired, no test or adjustment is made, resulting in failure to achieve an effective action position, or the safety clamps on both sides cannot be 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. Stopping the car, causing the car to fall;
B. The surface friction coefficient of the safety wedge sliding wedge is reduced. If the safety clamp wedge is actuated, the actual frictional force is less than the force required to act on the guide rail during the operation of the safety clamp;
C. The dirt on the safety clamp mechanical and rust is not repaired and cleaned in time; the selection of the safety clamp and the elevator speed do not meet the national standards;
In addition, the failure to comply with the rated load capacity (number of members) of the elevator is seriously overloaded; the deviation of the estimated weight of the cargo is large and the overload is delayed, which may cause the dangerous situation of the elevator.