Elevator chain wheel shaft break analysis

Abstract

Shafts are rotatingmechanical elements intended to transfer power of a driving device to a desired place.Most often, they are equipped with gears or pulleys tightly fixed by wedges or fitting keys. During operation, the shaft is subjected to both torsional (due to torque) and bending stresses (due to its ownweight andweight of built-in elements) [1,2] causing dynamic, alternating tensile–compressive stresses in surface layer of the shaft [3]. Generally, the shaft is always made of different diameters, and the transitions between them, depending on their rounding-up, represent smaller or greater local stress concentrators [2]. The contact of the hub edge and the shaft surface can represent a stress concentrator as well. This is why the shafts, due to its shape, are quite sensitive to the formation of fatigue cracks while their susceptibility to cracking is additionally increased by inadequate surface treatment of the shaft (rough surface and inappropriate microstructure of the surface part of the shaft). The elevator buyer delivered into analysis a broken shaft of a D = 135mm diameter whereto a chain wheel was fixed by a wedge. Even though the warranty period has already expired, the buyer wanted to verify the shaft material conformity with technical documentation and identify the cause of the resulting break in order to be able to file a potential claim.