Discussion on safety performance of crane brake

2003-03-09, Dahua Hydroelectric Power Plant carried out rotating loading according to the work plan in the construction of the maintenance project contracted by Zuojiang Power Plant. After the pre-shift meeting, the work arrangement and safety technology disclosure before the operation are carried out, and the relevant staff are ready to start work. After lifting the drain cone, the whole test lifting runner, 10:28 began to lift to the pit, 10:30 when the runner lifted to the pit and lowered about 3m, the bridge suddenly out of control, the runner accelerated down. In this process, the brake on the bridge burst, the gear of the reduction box cracked, the wire rope broke, and the runner fell to the pit. The accident killed one person and injured two others who were supervising the bridge. The preliminary analysis of the cause of the accident is that the bridge was out of gear when the lifting was lowered, resulting in the bridge out of control.

It is understood that the vast majority of crane brakes, are hub brakes, when the need to open or brake, through the electromagnet suction, put or oil pump starting, stop, the brake spring elastic pressure or release, so that the brake tile left the brake wheel or clamp on the brake wheel, to meet the requirements of opening or braking. And now the lifting work, especially in the lifting of large heavy objects, often equipped with several staff responsible for monitoring the crane, its purpose is to occur in the lifting out of gear, hook accident, must use crowbar and other tools to increase the brake tile on the brake wheel pressure, so as to achieve the purpose of emergency braking, in order to reduce the degree of damage to the accident. In the "3.9" accident, the staff in charge of monitoring on the bridge also took such measures, but they did not achieve corresponding effect. On the contrary, the brake cracked and the brake fragments flew out, resulting in the casualties of the monitoring personnel. Why not reduce the damage at the expense of human life?

First of all, the mechanical staff responsible for monitoring work uses crowbars and other tools to increase the pressure of the brake tile on the brake wheel, so as to achieve the purpose of emergency braking is worth discussing. When the crane is lifting a large weight and out-of-gear, slip hook accident, the starting motor, the transmission shaft will slide with the acceleration of the weight to produce escape speed, and the brake wheel on the transmission shaft will also produce strong radial vibration power. At this time, the crane brake action is closed, the brake tile will be subjected to a huge radial impact, if the brake tile artificially increase the pressure on the brake wheel, the brake tile itself by the huge impact will be greater, the brake tile collapse risk will rise, the risk of the staff before the brake pressure can be imagined. Therefore, the author thinks that it is not advisable to use crowbar and other tools to increase the pressure of brake tile on brake wheel, so as to achieve the purpose of emergency braking. Secondly, the brake only set on the drive shaft is not perfect. Because if there is out-of-gear and the brake is mechanically damaged, there is no way to reduce the loss of the accident.