Causes of elevator overspeed

The traction elevator is driven by the traction machine, and the friction between the traction wheel and the wire rope drives the car to run, and the brake is effectively closed to ensure the car can stop reliably. Therefore, when the weight of the counterweight side is greater than the weight of the car side, any link of transmission, traction and braking will fail, which may lead to the overspeed of the elevator, and in serious cases, it will lead to the jacking. Therefore, there are many reasons for the overspeed of the elevator: the traction elevator is driven by the traction machine, the friction between the traction wheel and the wire rope drives the car to run, and the brake is effectively closed to ensure the car can stop reliably. Therefore, when the weight of the counterweight side is greater than the weight of the car side, any link of transmission, traction and braking will fail, which may lead to the overspeed of the elevator, and in serious cases, it will lead to the jacking. Therefore, there are many reasons for elevator overspeed:

The brake springs of 1 and 1 are loose, and the friction between the brake shoe and the brake wheel causes the brake shoe and the brake wheel to overheat, which leads to the decrease of braking ability, the brake is stuck, and the brake arm and axle pin are broken, which leads to the failure to close the brake effectively.

1 2 mechanical parts such as spindle, bearing, gear and worm of tractor are broken or damaged, and the traction force is seriously reduced;

1 3 traction conditions are broken, and the traction sheave and wire rope slip;

1 4 overspeed caused by electrical control system failure, motor overheating and burning, abnormal fluctuation of power supply voltage, etc.

2. Some elevators in use have hidden dangers of upward overspeed.

Among the overspeed reasons analyzed above, the upward runaway caused by brake failure is the most common, mainly because the brakes used by some elevators before were not safety brakes. Articles 12, 4, 2 and 1 in GB7588- 1995 Safety Code for Elevator Manufacture and Installation clearly stipulate that "all brake components that exert force on the brake wheel (or disc) should be assembled in two groups, and have appropriate dimensions to meet the following requirements: If one group of components does not work, brake. It requires that the mechanical part of the brake must be designed with redundancy, so that when a certain part fails, unfortunately, in GB7588- 1995, this provision is suspended. Due to the suspension of this regulation, some elevator brakes have inherent defects in design, which also creates conditions for the manufacture and application of unsafe brakes.

The application of this unsafe brake in some elevators not only brings hidden dangers to the elevator's upward runaway, but also greatly reduces the protection function of all electrical safety switches in the elevator safety circuit, because the elevator electrical safety protection ultimately plays a role through the reliable braking of safety tongs. At present, this kind of unsafe brake is widely used in elevators in use, and accidents caused by using this kind of brake have occurred in many places in China. Today, more and more attention is paid to the safe operation of elevators, and this kind of unsafe brake with congenital defects should be paid more attention to. Whether to reform the brake or increase the upward overspeed protection device, or take other measures. This involves not only economy and safety, but also the different structures of traction machines and the structural differences of various elevators, so it is difficult to generalize. But in any case, the elevator is speeding up, especially when it is unsafe.

The hidden danger of upward overspeed of fully braking elevator should attract the attention of our elevator peers and related departments.

3. Uplink overspeed protection device

Fortunately, in the newly promulgated GB7588-2003, 12, 4, 2 and 1 are implemented as mandatory provisions, which will further promote the improvement of brake working reliability. Moreover, in the new standard, the upward overspeed protection device, as an important safety component, is clearly required to be used in newly installed elevators, which will greatly reduce the upward runaway accidents of newly installed elevators.

Car overspeed protection device is a kind of safety protection device installed on traction drive elevator, which is used to stop the car or effectively slow down when the elevator overspeed reaches a certain level. It generally consists of two parts: speed monitoring device and deceleration device. Usually, a two-way speed limiter is used as a speed monitoring device to detect whether the speed is out of control. The deceleration device includes safety tongs, rope clamps and safety brakes, which act on the car or counterweight, wire rope system (suspension rope or compensation rope) and traction sheave respectively. As an upward overspeed protection device, the safety brake must directly act on the traction wheel or the traction shaft closest to the traction wheel. At present, on the permanent magnet synchronous motor of the elevator without machine room, the brake directly acting on the traction sheave is usually used as the upward overspeed protection. The mechanical structure design of this brake is redundant, which meets the requirements of safe braking and does not need to consider its failure. At the same time, because it directly acts on the traction wheel, the damage of the main shaft, bearings and other mechanical parts of the traction machine will not affect its effective braking. Of course, it can't protect the upward overspeed caused by other reasons, such as the destruction of traction conditions and the slip between traction sheave and steel wire rope. This leads to a question: in which types should the upstream overspeed protection device play a role? According to GB7588-2003 Safety Code for Elevator Manufacture and Installation, the upward overspeed protection device needs to act on the upward overspeed caused by brake failure and motor transmission failure. Therefore, the current upward overspeed protection device cannot protect all the upward overspeed of the elevator.