Fibre rope returns to the mainstream28 September 2017
The potential benefits of fibre rope, versus the steel wire rope routinely used in the industry, have for a long time been a focus for crane manufacturers and rope experts. When I started on this magazine, a little over ten years ago, crane engineers were considering ways to overcome problems with how rope would (or rather, would not easily) spool on the drum. Today, those issues appear to have largely been fixed, not by major changes to crane design as we then thought, but by new ropes that can largely be used in the same way as steel wire rope.
This represented an important change in rope technology. This month though, with the launch of the FEM's guidelines FEM 5.024— Safe Use of High Performance Fibre Ropes in Mobile Crane Applications, we've seen the conclusion of a process that marks the return of fibre rope to mainstream use in the lifting industry. The guidance was developed by major mobile crane manufacturers and rope manufacturers, with the support of the University of Stuttgart.
The document notes that, in fact, fibre rope is not so much a new technology as a very old one. Its introduction provides examples of the use of fibre rope in heavy lifting dating as far back as the pyramids. It cites work by University of Tübingen archaeologists on a mammoth bone tool, dating back 40,000 years, that appears to have been used to construct fibre ropes.
Fibre rope then is as much a 'proven' technology as any technology could be. For as long people have built and lifted or pulled things, they've used fibre rope successfully. In recent years, in climbing and in offshore applications, fibre rope has found applications.
In my time on the magazine, there have been two main obstacles raised to its adoption on mobile cranes. Firstly, it had not until recently been possible to spool fibre rope in the same way as steel wire rope. Initial attempts to solve this problem had looked at finding new ways to store the rope. These would have added weight and bulk to the crane, potentially countering all the benefits of the lighter material. In recent years though, starting with Samson's launch of fibre rope on Manitowoc cranes (now offered for all cranes), and then with Teufelberger's development with Liebherr of its own approach to fibre rope construction, this technological issue looks to have been solved. Both solutions are, I understand, essentially interchangeable with steel wire rope.
The other obstacle is operational rather than technological. How do you tell if a rope is safe to use, without clearly established discard criteria to show when it is not? It is this issue that the FEM guidance addresses. The document is not yet part of any standard, but aims to lay the basis for an EN or ISO standard. While it focuses on mobile cranes, and notes that further work would be needed for its adoption on stationary cranes, it lays the groundwork for this sector too.
The document opens with a discussion on how rope and crane manufacturers should work together to develop a failure mode effect analysis for each rope and crane system, demonstrating how the rope will perform. It explains some of the key differences between fibre rope performance in a rope system, compared to steel wire rope. This includes guidance on the substitution of fibre for steel wire on existing cranes, highlighting that some crane owners may be able to increase the effective capacity of their existing cranes.
The guidelines then explain how rope will be 'qualified', or shown to be suitable for use, and how discard criteria should be developed. It notes that, with different approaches to fibre rope already launched (and, I would expect, further designs under development) no single set of criteria is possible. Instead, a method for developing criteria is explained, and two current examples given.
As the crane industry continues to find new ways to increase capacity and optimise mobile cranes, fibre rope will clearly be a technology of interest. It is a reassuring sign that so much attention has been paid to its safe development and use. The guidance is available now via the VDMA's online store.