The pins in new escalator chains were observed to have drifted laterally out of the chain side plates within a few hours of startup. The force driving this movement was sufficient to overcome a light interference fit and retaining rings intended to restrain the pins. Neither pins with heavy interference fit nor connector pins with sliding fits exhibited this tendency to drift. A failure analysis showed that even if the pins and side plates had been manufactured with a heavy interference fit, the sharp edge of the retaining ring groove acted as a broaching tool during assembly, shaving out and enlarging the side plate hole, and destroying the intended fit. The driving force for pin drift was traced to the hysteretic force and rotation sequence as the chain traveled around the escalator sprockets, which led to a walking mechanism that imparted a lateral force sufficient to move the pins and overcome the retaining rings.

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