Equality among the classes28 August 2015
Over recent years, the ISO committee responsible for cranes, TC96, has been trying to bring classification of crane structures and ropes in line. After a series of false starts, Gerhard Wagner, chairman of the crane design subcommitee, will propose a new approach to the problem at aplenary meeting of TC96 in Sydney this September.
At the heart of the split between ISO members are two standards. The original ISO 4301-1 established a general classification for crane components, known as 'M-classes', using a calculation of working life based on operating hours. ISO 16625, Cranes and hoists -- Selection of wire ropes, drums and sheaves, draws on this, using the M-classes taken from the original ISO 4301-1. ISO technical committee TC96 sets standards for cranes around the world. TC96 is split into sub-committees, covering a range of related issues. TC96 SC10 is responsible for design principles and requirements.
Wagner has chaired SC10 since 2003. After being awarded his doctorate in engineering at Darmstadt Technical University in 1980, he worked in the design departments of Donges (now part of Konecranes), Demag (now Terex), and MAN (former owner of Wolff). Since 1989, he has worked in academia, and on standards.
Wagner has recently prepared a paper, Classification of cranes and components: Why there is no need for M-Classes, which he intends to present to ISO TC96 members at a plenary session in Sydney, Australia, in September.
Talking to Cranes Today, Wagner explains why the approach he proposes in the paper is needed: "ISO TC96 has subcommittees that are crane-type linked. Then some that are more horizontal: design (SC10), maintenance (SC5), and one (SC3) that is just for wire rope. SC3 is the only subcommittee focussed on just one component.
"Design general (SC10) covers everything from classification, loads and load cases, limit states, proof of competence, steel structure. Complete, all way up to proof of competence, up to crane structure. But, ropes are not included." In his paper, he explains why classification is important to crane buyers: "Cranes move loads the mass of which is within their rated capacity. However there are wide variations in their duty. The crane design has to take into account the duty in terms of conditions of service, in order to reach an appropriate level of safety and useful life which is in line with the purchaser's requirements.
"Classification serves as a reference framework between purchaser and manufacturer, by which a particular appliance can be matched to the intended service. It is also used to specify the service conditions of cranes or components which are designed for serial manufacture, and allows items to be selected in accordance with their intended use."
Importantly, Wagner says, M-classes are calculated in a way that focusses on operating time, rather than the actual load cycles undergone by the crane. As shown in the illustration, two identical factory cranes working at different lifting heights and speeds may go through wildly different loading in terms of cycles (by a factor of 10) over the same operating time.
Wagner says, "The operating time [used in the M-class definition] is not a measure of fatigue." Wagner's design group, SC10, abandoned references to M-classes in its revision of ISO 4301-1, published earlier this year. The work on the revision had been going on for many years before. At a plenary session in Warsaw, in 2013, it has been agreed that SC10 and SC3 would work together to develop a new standard, Proof of competence of wire ropes.
Tasks like this are assigned by ISO technical committees as work items. When the TC96 committee voted in 2014 on whether to assign a work item to the new standard, it was split 7:7, meaning work on the standard was not adopted.. The result is that, with no new standard under development, ISO 16625 refers still to the old M-classes in the original, unrevised, ISO 4301..
With his paper, available via our sister magazine at www.cranestodaymagazine. com/content/Wagner.pdf, Wagner hopes to convince SC3 rope committee members to join SC10 in dropping M-classes altogether.