Exploring the Safety Performance of Overhead Crane Brakes

2003-03-09 The Dahua Hydropower Plant, while undertaking the maintenance and overhaul work at the Zuojiang Power Station, proceeded with the reinstallation of the turbine rotor according to the scheduled plan. After holding a pre-shift meeting to finalize task arrangements and conduct safety and technical briefings, the relevant personnel were fully prepared and began their work. Once the water discharge cone was successfully lifted into place and the overall test lift of the rotor confirmed no abnormalities, 10：28 Starting the lifting operation into the machine pit, 10：30 When the rotor crane is lowered into the machine pit and released by about 3m At that moment, the bridge crane suddenly lost control, and the rotating wheel began to accelerate downward. During this process, the brake on the crane burst, the gearbox gears shattered, the steel cable snapped, and the rotating wheel plummeted into the machine pit. The accident resulted in injuries to the staff member who was responsible for monitoring the crane. 1 A person has died, 2 People were injured. Preliminary analysis of the accident indicates that the bridge crane lost control after its gear disengaged while lowering a load.

It is understood that the vast majority of crane brakes currently used are hub-type brakes. When it’s time to release or apply the brake, an electromagnet either pulls in or releases its armature, while a pump starts or stops—both actions adjust the tension of the brake spring, either pressing it firmly against the brake wheel or letting it relax. This mechanism causes the brake shoes to either move away from the wheel or clamp tightly onto it, thus achieving either the release or application of the brake. In modern crane operations, especially when lifting large and heavy objects, cranes are often equipped with several crew members specifically tasked with monitoring the process. Their primary role is to intervene promptly in case of unexpected incidents such as gear disengagement or cable slippage. In such emergencies, these workers use tools like pry bars to increase the pressure exerted by the brake shoes on the brake wheel, enabling rapid emergency braking and minimizing damage caused by accidents. 3.9 "In the accident, the staff member supervising the bridge crane also took similar measures—but these efforts failed to produce the desired effect. Instead, a brake component unexpectedly cracked, sending fragments flying and tragically injuring or killing the supervisor. Why, despite this devastating human cost, were the overall damages of the accident not reduced at all?" ?

First of all, the method employed by mechanical staff responsible for monitoring—using tools like crowbars to increase the pressure exerted by brake shoes on the brake wheel in order to achieve emergency braking—is questionable. When a crane lifts large, heavy objects and an accidental gear disengagement or cable slippage occurs, the hoisting motor and transmission shaft may rapidly accelerate downward along with the load, leading to runaway speeds. This, in turn, generates intense radial vibrations on the brake wheel mounted on the transmission shaft. At this critical moment, if the crane’s brake system engages, the brake shoes will experience a massive radial impact force. If workers then artificially amplify the pressure applied by the brake shoes against the brake wheel, the already substantial impact on the shoes themselves will only grow even larger, significantly increasing the risk of brake shoe failure—and consequently raising the danger faced by personnel applying pressure directly in front of the brake mechanism. Therefore, the author believes that using tools such as crowbars to forcibly increase the pressure of brake shoes on the brake wheel for emergency braking is an impractical and unsafe approach. Secondly, relying solely on brakes installed on the transmission shaft is insufficient. After all, if a gear disengagement occurs and the brake mechanism itself suffers mechanical damage at the same time, there would be no effective way to mitigate the resulting accident and its associated losses.