Failure of an inclined elevator

The failure and crash of an inclined passenger lift are examined and the pr obable cause together with a likely sequence of events is arrived at. This failure was in two parts, initially the gearbox output shaft suffered a fat igue failure, freeing the winch drum from the motor and normal brake. This was followed more importantly by the malfunctioning of the emergency brakes on the lift, allowing the lift to roll to the bottom of the run. The lift had been upgraded prior to its failure. Calculations show that the gearbox output shaft that failed was more than adequate for the loads imposed on it by the new controlled motor, whereas the original direct-on-line motor pro bably had overstressed the shaft. The steel lifting rope exhibited three se vere kinks about 1 1/2 m from its attachment to the trolley. The search for the causes of these kinks led to the discovery that a lever mounted on the emergency brake shaft had been damaged and bent. Evidence came to light th at the whipping action of the rope, following the release of the winch drum after the shaft failed, relocated the lifting rope under the lift cabin an d over the safety equipment on the trolley. This abnormal location of the r ope placed it in a position where it interfered with the movement of the le ver and hence with the rotation of the emergency brake shaft. With this sha ft restricted in its rotation the emergency brakes failed to apply properly .