Ropes and winches: switching designs
By Katherine Weir29 February 2016
When changing the type of rope used in hoisting operations a number of points have to be taken into consideration. As Helene Leitner, head of marketing at German rope manufacturer Teufelberger explains, if someone wants to switch from wire rope to fibre rope the requirements of the specific application have to be checked.
Jason Wormald, Bridon International group product development and technology centre manager, points out, “It is important to refer to the standards for specific applications. Each situation is different and design standards for synthetic rope often differ from wire rope, so a qualified person should be consulted in each case. As a general rule, when considering using synthetic ropes on equipment which has previously used a steel option, wear points should be inspected and freed from conditions such as burrs, sharp edges, damage, or anything which may compromise the integrity of the synthetic rope.
“Typically synthetic ropes require bespoke equipment designed to suit the material and construction of the rope being used, unlike our hybrid ropes which have the weight saving properties of fibre and the robustness of steel, allowing them to be deployed on existing steel rope equipment,” Wormald adds.
Helene Leitner adds, “For winch applications, you can normally choose the same diameter as you would for a wire rope (including the cover) which makes it extremely comfortable to the customer to change from wire to synthetic rope without adaptation of the machine.”
Another factor that can be overlooked is lubrication, as Wormald points out, “Lubrication is one of the key parameters often overlooked when selecting wire rope. The correct lubrication can have a huge impact on extending rope life. Bridon has recently developed a new range of wire rope lubricants and service dressings which outperform existing benchmark products and also address the Ecolabel certification requirements of some environmental protection agencies.”
One of the main advantages of switching from steel to synthetic rope is the reduction in weight. According to rope manufacturers, synthetic rope makes installation and replacement easier and, in addition, they do not corrode with exposure to moisture. They can, however, degrade in other ways, for example from UV and heat.
“They are generally non-conductive if clean and dry (a consideration when working with or around utility lines), can have excellent bending and tension-tension fatigue properties and can often be terminated, repaired or replaced in the field without heavy equipment,” Jason Wormald says. “Steel wire ropes offer better abrasion resistance, are not susceptible to UV light, and have better axial stiffness and creep characteristics (tendency for the rope to stretch and continue to elongate under load). Hybrid ropes can offer the best of both materials where improved endurance in fatigue and weight saving is combined with the robustness of steel and ability to be deployed on existing systems. Wire rope can also be inspected with traditional NDT methods and has clearly defined and tested discard criteria.”
Not having fully regulated discard criteria is a disadvantages of synthetic ropes. As mentioned in previous articles, replacement criteria for ropes vary depending on whether it is steel or synthetic. Wormald says, “Bridon recommends users should follow standards that are applicable to their specific application. For general winch applications refer to ASME B30.7, which defines inspection and offers wire rope retirement criteria.
Other references governing winch operation in specific applications include OSHA 1917.47, ISO 6115, 3730, and 3078. “For synthetic ropes, refer to Cordage Institute spec CI 2001-04 for inspection criteria,” Wormald adds.
German rope manufacturer Teufelberger also develops and manufactures both steel and synthetic ropes, including steel and synthetic ropes designed for winch applications. Helene Leitner says, “In case of fibre ropes, the criteria for replacement are quite simple: as long as the cover is ok, the core is mostly ok too. So a careful visual inspection of a fibre rope is obligatory. If the cover is damaged and you can see the core in any way you must refrain from using the rope further.
“For steel wire ropes there is a standard in place for discard criteria,” Leitner continues. “For special ropes Teufelberger developed the Teufelberger Damage Ratio Calculator (TDRC). Experience has shown that ropes are often discarded either too early or sometimes discarded too late, and that the real performance of an MRT rope cannot be assessed by the use of tonne-cycle calculations. The TDRC is based on a theoretical model that calculates the damage ratio as a degree for rope degradation and determines the earliest possible moment of rope failure. The calculation combined with a practical inspection results in an ideal rope lifetime. This leads to increased safety due to daily rope condition monitoring, pre scheduled rope changes and decreased cost because of less downtime.”
Casar, part of the WireCo World Group, produces tailor-made steel wire ropes. The manufacturer recommends its customers to follow instructions according to ISO 4309. The standard defines exact discard criteria, including visible broken wires, decrease in rope diameter, fracture of strands, corrosion, deformation and damage as well as general discard criteria.
Markus Klinck, Casar product manager and industrial engineer, says, “To be able to ensure that our ropes will have the best performance and longest lifetime on the drum, they are produced within very tight diameter tolerances. The design of our ropes fits to all of the well-known drum and winch manufacturers in the market. Due to the compaction and swaging technology of Casar, we are also able to supply our ropes as OEM for the big crane manufacturers. Casar also produce especially designed ropes for multi-layer spooling drums, where highest performance, breaking loads and the best spooling behaviour are required.”
DSM Dyneema supplies HMPE fibre to rope manufacturers to produce high performance synthetic ropes. “Ropes based on Dyneema fibres give equal strength to diameter performance as existing steel wire ropes,” the manufacturer says. “We have developed a portfolio of Dyneema grades specifically designed for these types of dynamic applications of running ropes, which have, for example, very good bending and abrasion properties. Examples are Dyneema SK78 XBO and Max Technology DM20 XBO. Next to full synthetic ropes, also hybrid rope developments are based on Dyneema fibre products.”
Maud Roeters, DSM Dyneema business development manager, adds, “Overall, industry organisations, such a, ISO, FEM, ASME and the WSTDA, are working on new standards and guidelines enabling the use of synthetic fibre rope and sling technologies for hoisting applications.”