Quantitative – analysis of specific rope loading in traction drives*

Service life is severely reduced when ropes are used on traction elevators incorporating drive sheaves fitted with so called form grooves (vee or semicircular grooves with undercut). This is the case when compared with rope drives where the ropes run in round grooves with no traction loading. Literature presumes that several different factors are influencing this reduction of the service life. In addition to the increased pressure loading when using undercut or vee grooves it is assumed that other factors play a role in degradation, including alternating stresses that cause the rope to adopt an oval cross section when it runs over sheaves with differing groove geometries. Yet another factor is the rope slip present in drives with a traction sheave.

In efforts to take account of this ancillary damage when designing sheave drives for traction lifts the calculation method put forth by [1] is applied to reduce the calculated service life of the rope running in round grooves; this reduction is taken into account the correction factor fN3 and depends on the shape of the groove. Individual loading parameters resulting from the particulars of the traction drive are considered only in a generalised manner in the calculation method after Feyrer. A further limitation of this design methodology is found in the fact that the correction factors worked out by [2] were based on a statistical survey of real-world elevators incorporating only 8×19 Warrington rope designs with fibre cores. For want of findings on other rope designs, the correction factors (determined exclusively with fibre-core ropes) were adopted in 1998 as generally valid rules by inclusion in the applicable [3] standard.

Author(s): Berner, O.R. & Wehking, K-H.