Case 2: Wire rope breaking accident
1. Time of accident: March 2003
2. Accident unit: a hydropower plant
3.Type of lifting equipment: bridge crane
4.Operating characteristics: Hoisting runner
5.Type of accident: The wire rope is broken and the hanging object falls
6. Degree of accident damage: 1 person died, 1 person was seriously injured, and 1 person was slightly injured.
Introduction to the accident process
On a certain day in March 2003, when a bridge crane was used to hoist a runner in a hydropower plant, a "three lifts and three falls" lifting test was performed and normal lifting was started. At about 10:28, the bridge crane raised the runner from the installation platform to the turn-over platform by about 2m, and then moved the runner to the top of pit # 1, adjusted the center position, and then started to lower the runner. When the runner dropped about 3m, the bridge crane suddenly lost control, the runner accelerated and descended, and the speed reducer made an abnormal sound. The commander immediately issued a stop command, the driver's emergency braking was invalid, and the runner continued to slide. The auxiliary brake brake wheels and brake shoes on the bridge machine emit thick smoke and emit a crackling sound. The brake wheels, brake shoes and other components are smashed and broken, the wire rope is broken, and the runner falls under the runner room. The fall height is about 10m. Due to the entire explosion of the auxiliary brake, its fragments scattered to the corners of the generator layer and the cable layer, hitting 3 staff members in the monitoring operation, causing 1 death, 1 serious injury, 1 minor injury, and hitting the unit control cabinet, etc. . The gearbox is severely damaged, the moving pulley group is deformed, the bottom of the gearbox bearing end of the gearbox below the fixed bearing at the drum is broken, one end of the wire rope is pulled away from the pressure plate, and the other end is broken, and the rotor body blades, pivots and other parts are deformed. Direct economic loss of more than 2.177 million yuan, indirect economic loss of 16 million yuan
Third, the cause of the accident
A deep groove ball bearing of the crane reducer failed, causing the clutch to disengage and disengage automatically during work.The main brake lost its braking effect on the transmission system connected to the hanging object (rotary wheel). Under the pull, the reaction force overcomes the braking force of the auxiliary brake, which causes the hanging object to accelerate to fall, the wire rope is broken, and the hanging object falls into the bottom of the pit.
The brake selection of the main lifting mechanism is smaller than the contract requirements, and the brake wheels have casting defects; there is no reliable mechanical or electrical locking device after the clutch is shifted in place; the clutch tooth angle is processed large, which increases the depth of action on the reducer. Axial force of groove ball bearing; The length of the steel wire rope does not meet the safety requirements, causing one end of the steel wire rope to detach from the fixed pressure plate; the annual inspection has not been performed as required.
3. The main reason
The crane is operating with failure. An out-of-control failure in February aggravated the deformation and damage of deep groove ball bearings, but failed to conduct a detailed inspection and found that its self-locking capacity was reduced, and equipment design and manufacturing were defective.
Fourth, the accident conclusion
The brake selection of the design and manufacturing unit is unreasonable, the brake wheels have casting defects, and the clutch design is irrational.