The Relationship between the Number of Broken Wires and the Lay type of Wire Rope in ISO 4309
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Summary
ISO 4309 provides guidelines for the inspection, maintenance, and discard criteria of steel wire ropes used on cranes and hoists. The number of visible broken wires is one of the most important criteria for determining when a rope is no longer safe to use. Under certain operating conditions and within a specific length range (6d, 30d), there is a fixed ratio of approximately 2:1 in the minimum visible number of broken wires required for discard between ordinary lay and Lang lay steel wire ropes of the same classification according to ISO 4309. This paper presents a theoretical analysis of this intriguing relationship.
According to the known concept of the correlation factor n of wire rope parameters, the period formula of the double spiral wire is worked out by analyzing the simulation results. Then using the period formula of the sine function, the concept of the wire rope symmetric correlation factor ω is established, and the physical meaning of ω is explained. The curvature period formula of double spiral steel wire is proved mathematically. In Table 3 of ISO 4309, the ratio of the number of broken wires in ordinary lay to the number of broken wires in Lang lay is equal to the corresponding ω ratio. It has been shown that the ratio of the number of broken wires is only related to the lay type, but not to the lay direction.
Author(s): Z. Shen, W. Qin, Z. Liu and Y. Zhi
Keywords: ISO 4309; broken wire; ordinary lay; Lang lay; lay direction coefficient
