Lessons and insights from elevator counterweight rope accidents
2025-07-11 12:47
In recent years, there have been frequent incidents of counterweight detachment from the suspension system due to serious counterweight sheave failure, resulting in the falling of the car losing its counterweight traction. Standards and regulations require the suspension device to have more than two redundant components with a safety factor of 12 or more. However, some components in the suspension system are so weak (such as the counterweight sheave guard plate bolts and shaft clamping mechanism) that even after a foreseeable failure (rolling bearing failure is foreseeable and difficult to avoid), the suspension system fails, leading to the car falling. In critical moments of car falls, in these cases, only one speed governor-safety clamp effectively worked, successfully stopping the car; four speed governors triggered the safety clamp, the car decelerated, but failed to effectively stop the car; one speed governor failed to trigger the safety clamp. Is the elevator industry's pride in preventing car falls so unreliable?
The nature of such incidents is extremely serious because it can lead to the fall of a car carrying passengers, causing a major accident with numerous casualties. These incidents expose some design and manufacturing flaws. Preventing such accidents from the design and manufacturing source is clearly more targeted and efficient! During use, maintenance and upkeep also have a great opportunity to discover certain signs before an accident, and also have a responsibility to discover the abnormal working state of the speed governor and safety clamp counterweight sheave rolling bearings, and to maintain these components.
Serious failure of the counterweight sheave detaching from the counterweight frame can lead to serious accidents such as counterweight and car falls. In the technical specifications and standards for special equipment safety, the elevator's suspension system has high requirements. Its suspension device (wire rope or wrapped belt) not only requires multiple redundancies, but also a safety factor greater than 12. However, the shaft support components, shaft guard plates, shaft stop slots, and their fixing bolts included in the current counterweight sheave are quite fragile, and may lead to car falls after a foreseeable serious damage to a single rolling bearing. This should be given high attention by the industry.
It should be noted that when the rolling bearing is seriously damaged, the bearing cage is scattered, and the rolling balls are scattered, the radial and axial swing of the counterweight sheave groove is very large, and the standard-required counterweight sheave anti-detachment device cannot prevent the wire rope from detaching from the groove. The standard-required counterweight sheave anti-detachment device only prevents detachment due to wire rope slack or foreign objects entering.
In addition, in the event of suspension system failure, the main drive brake acting on the traction wheel shaft cannot brake the car. Serious damage to the rolling bearing causes three failure modes of counterweight sheave detachment from the counterweight frame. During this process, maintenance and upkeep have a great opportunity to discover problems and prevent accidents.
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