This post will cover the Rope Category Number, it's purpose, and how to determine it's value.
The RCN or Rope Category Number is ISO 4309's attempt to categorise wire rope by the number of load bearing wires in the outer strands. The RCN is used to determine the maximum permissible number of random broken wires during an inspection.
The maximum number of broken wires before a rope becomes dangerous is dependent on the construction. As new wire rope constructions reach the market all the time, if the construction was used in ISO 4309 to determine the safe number of broken wires, it would be necessary to publish a new version of the standard several times a year to keep up!
As the safe number of broken wires depends on the number of load-bearing wires, categorising ropes by load-bearing wires is logical, and future-proofs ISO 4309.
There are several ways of finding the Rope Category Number.
Look-up table for determining the RCN of Single-Layer and Parallel-Closed Ropes. (Seale constructions with 19 wires or less e.g. 6x19 Seale are placed 2 rows above where they would normally be placed. Where a wire rope has Filler wires, these are not regarded as load bearing wires)
Look-up table for determining the RCN of Rotation-Resistant Ropes. (Seale constructions with 19 wires or less e.g. 6x19 Seale are placed 2 rows above where they would normally be placed. Where a wire rope has Filler wires, these are not regarded as load bearing wires)
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The Rope Category Number is a useful classification for wire rope inspectors and is an essential component of ISO 4309. Without the RCN, determining the maximum number of permissible broken would be an arduous process.
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