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. The effective closure of the brake ensures the reliable and possible stop of the car. Therefore, in the case that the amount of heavy emphasis is greater than the amount of car emphasis, the failure of any link of transmission, traction and braking may lead to the elevator upward speeding, serious will lead to the top. Therefore, there are many reasons for speeding up the elevator:
1 Brake spring relaxation, brake shoe and brake wheel friction cause brake shoe and brake wheel overheating, resulting in brake capacity decline, brake stuck, brake arm, shaft pin fracture and other failures lead to the brake can not be effectively closed;
2. Traction machine spindle, bearing, gear, worm and other mechanical parts are broken or damaged, traction gravity seriously decreased;
3. Traction conditions are damaged, and the traction wheel and wire rope slip.
Overspeed caused by failure of electrical control system, overheating and burning out of motor, abnormal fluctuation of power voltage, etc.
2. There are hidden dangers of overspeed in the elevator
Among the reasons for speeding analyzed above, the upward runaway caused by brake failure is Z common, which is mainly because the brakes used in some elevators are not safety brakes. GB7588-1995 “Elevator manufacturing and installation safety Code” in 12, 4, 2, 1 clearly stipulates that “all involved in the brake wheel (or disk) to apply force brake components should be divided into two assembly set, and has the appropriate size, in order to meet: If a set of components does not work, the brake wheel (or disc) can still obtain enough braking force to slow down the car carrying the rated load.” Originally this is a good rule, it requires that the mechanical parts of the brake must be designed with redundancy, so that when a part fails to work, the brake can still make the elevator stop reliably. Unfortunately, in GB7588-1995, this rule was suspended. As a result of the suspension of this regulation, some elevator brakes in the design of congenital defects, but also for the manufacture and use of non-safety brakes to create conditions.
The use of this non-safety brake in part of the elevator not only brings hidden dangers to the elevator going up out of control, but also greatly reduces the protection effect of all the electrical safety switches in the elevator safety loop, because the electrical safety protection Z of the elevator is ultimately through the reliable stop of the safety clamp to play a role. At present, in the elevator, this kind of non-safety brake is applied in more than a few, as a result of the use of such brake the elevator uplinking accident occurred in many places in our country. More and more attention has been paid to the safety operation of the elevator. This kind of non-safety brake with congenital defects should be paid attention to. Whether to modify the brakes or add upward overspeed protection, or take other measures. This is not only related to the economy and safety, but also involves the different structure of the tractor, and various elevator structure differences, difficult to generalize. But in any case, in the use of the elevator upside speed, especially the use of non-safety brake elevator existing upside speed hidden danger should cause our elevator peers and the relevant departments to pay attention to and seriously.
3. Upward overspeed protection device
It is gratified and fortunate that in the newly promulgated and implemented GB7588-2003, 12, 4, 2, 1 are implemented as mandatory provisions, which will further promote the improvement of the reliability of the brake work. And in the new standard, the upward overspeed protection device as an important safety component is clearly required to be used in the newly installed elevator, which will greatly reduce the newly installed elevator upward out of control accident.
The car overspeed protection device is installed on the traction drive elevator, which is used to make the car stop or slow down effectively when the elevator overspeed to a certain extent. It is generally composed of speed monitoring device and reducer two parts. Two-way speed limiter is usually used as a speed monitoring device to detect whether the car speed is out of control. Reduction devices include safety clamps, rope clamps and safety brakes, which act respectively on the car or counterweight, the wire rope system (suspension rope or compensation rope) and the traction wheel. As an upward overspeed protection device, the safety brake must directly act on the traction wheel or the traction wheel shaft near the traction wheel Z. At present, the permanent magnet synchronous motor in the no-machine room elevator usually uses the brake directly acting on the traction wheel as upward overspeed protection. This kind of brake mechanical structure design redundancy, meet the requirements of safety brake, do not need to consider its failure. At the same time, because it directly acts on the traction wheel, the damage of the main shaft, bearing and other mechanical parts of the traction machine will not affect its effective brake stop. Of course, it can not protect the uplink speed caused by other reasons such as the failure of the traction conditions, the skidding between the traction wheel and the wire rope. This begs the question: What types of upward overdrive do upward overdrives work against? According to the requirements of GB7588-2003 “Safety Code for Elevator Manufacturing and Installation”, the upward overspeed protection device should be used for upward overspeed caused by brake failure and motor transmission failure. Therefore, the current uplink overspeed protection device can not protect all the elevator uplink overspeed