Ten million fat men step up
Escalators, in common with most other types of public service equipment, have to be thoroughly designed, tested and manufactured to minimise risk of mechanical failure. The consequences of failure of an escalator system could be very serious indeed, and there have been instances where passengers have been injured as a result of a failure in the system.Not surprisingly, there is a relevant British Standard (BS 5656:1983) Safety rules for the construction and installation of passenger conveyors. Among other things, this standard specifies static and fatigue tests for escalator steps, and TWI has carried out these tests on different designs of step for a number of manufacturers.
Static testing involves applying a single download on the top of the step. Elastic deflections under load must be within certain limits, and no permanent distortion is permitted. Fatigue testing involves applying a similar load for a minimum of five million cycles, after which the step must show no signs of fatigue cracking or other damage.
The test loads are very severe, the maximum applied force being 3kN, roughly 300kg or 660lb. This would represent two very large men, plus heavy cases, who would find it most uncomfortable to be squeezed together on the same step! Thus, control of deflection under static load ensures that nothing can jam or seize up, and if a step survives the fatigue test, one may be confident that in service the step will have an infinite fatigue life.
TWI's test facilities are ideal for performing this type of testing and, since one design of escalator step is invariably different from another, a wide variety of test frames are available. Due to this versatility, a testing service with a turnaround time from receipt of a step to delivery of a report of under three weeks is achievable.
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