Kurt Schmidsberger explains how plastification of a lubricated steel core increases the service life of ropes.
Text: Plastified lubricated steel cores generally increase the life span of offshore crane ropes. That is the reason why the product portfolios of all major manufacturers of high-performance steel wire ropes also feature ropes that incorporate this technology.
Steel wire rope specialist Teufelberger has already been using plastic-covered steel cores for several years.
Plastification has a positive impact on a rope's life span in two different ways. Firstly, the compact plastic cover acts like a cushion between the rope's inner portion and its outer strands. Secondly, this technology effectively blocks the ingress of water into the core.
When the rope is tensioned, all strands will be stretched accordingly. As the helix of the outer strands gets longer, their diameter decreases. Hence, the rope's inner portion is subjected to lateral compression.
This is where the Plastfill core comes in. It causes punctiform pressures to be distributed across larger areas and, in this way, eases the contact pressure per unit area exerted on the wire. This reduces stress concentration and, as a result, enhances the rope's service life.
In use, ropes are not only tensioned but also exposed, on a daily basis, to repeated bending stresses while running over sheaves or subjected to high lateral pressures in multilayer spooling.
In this connection, Plastfill cores offer another advantage: when running over sheaves, there is relative movement of the wires and strands. Internal wear frequently results in fretting corrosion that shortens the rope's service life accordingly. Lubricating the steel core and surrounding it with a compact plastic cover in order to keep the lubrication intact helps to reduce fretting corrosion in the rope's inner portion. Furthermore, by embedding the outer strands in the plastic cover, it is possible to position the strands accurately, which in turn ensures the consistent spacing of the strands in a vault-like configuration. This is of particular importance for multilayer spooling where ropes are exposed to high lateral pressures.
This optimised construction features the stabilized strand structure ensured by the Plastfill core. It helps distribute the pressure evenly onto all strands and, as a consequence, enhances the stability to lateral pressures of the high-performance steel wire rope made by Teufelberger.
Prevention of ingress of water
Another important aspect for use in offshore environments is water-induced corrosion. Teufelberger Plastfill technology relies on special plastic materials that do not absorb water. This helps to reduce the risk of internal corrosion and minimizes the risk potential in the area that cannot be inspected visually.
As has already been mentioned above, Teufelberger's Plastfill technology optimises the frictional situation. Therefore, it achieves greater breaking strength than comparable steel wire ropes without plastic covers, in both Q-ropes (non-rotation-resistant ropes) and TK-ropes (rotation-resistant ropes).
Plastfill is a technology where the steel core is surrounded by a compact plastic cover. Not only does this technology increase the rope's service life, but it also enhances its breaking strength.
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Kurt Schmidsberger, Product Manager Steel Wire Ropes, Teufelberger Seil GmbH, Wels, Austria. www.teufelberger.com
Fig. 1. Schematic view of the lateral compression.
Fig 2. A cross-section of EVOLUTION Q 8 rope.
Fig. 3. A sample of QS 816V rope.
Fig. 4. A sample of EVOLUTION TK 18.