The choice of the lay type must consider the specific use of the rope, the rope construction, crane components and the expected wear factors in use, which determine the lifetime of the rope substantially.
The aim of the rope choice is a high rope lifetime ensuring a high safety factor at the same time, which means the operator can recognize the secure operating condition of the rope reliably at any time, considering the discard criteria of the specific application. Therefore a general statement about the use of regular or lang’s lay ropes is not possible or not useful without knowledge of the specific case/application.
Ordinary (regular) lay ropes
Ordinary lay ropes are widespread which are therefore presumably considered as universally applicable. Ordinary lay ropes have a very good structural stability due to the opposing stranding of the wires and strands which make them more resistant against external twist. The rope torque is lower than the one of lang’s lay ropes. Ordinary lay ropes also offer a good wear-resistance. Construction wise the externally visible wire breaks appear earlier of ordinary ropes than of lang’s lay ropes due to the higher pressure between wire and rope groove and a stronger wire bend within the strand, which makes it easier to recognize wire breaks and thus the rope state, making it easier to evaluate the discard criteria. Ordinary lay ropes are still no universal ropes for all applications under the abovementioned aims of the rope choice.
Lang’s lay ropes
Lang’s lay ropes are more demanding not only in the production process, but also with the application, beginning with the installation. The reason for this lies in the stranding of wires and strands in the same direction, which raises the rope torque and makes lang’s lay ropes substantially more sensitively against every kind of external twist.
Lang’s lay ropes reach very high bending cycles until break because of the geometrically more favorable contact conditions between wire and rope groove which leads to the reduction of the pressure in the contact areas. This reduction of pressure is advantageous to the lifetime of the crane components and the rope itself.
However, it must also to be mentioned that in comparison to ordinary lay ropes the development of the externally visible wire breaks occurs more slowly. Therefore the recognition of the discard criteria due to externally visible wire breaks can be complvicated. For this reason the numbers of wire breaks until discard are clearly lower for lang’s lay ropes than for ordinary ropes with identical rope construction. Therefore also lang’s lay ropes are no universal ropes for all application under the abovementioned criteria of rope choice.
Important: As described in the “Lang’s Lay ropes” paragraph, these ropes can have an increased amount of internal wire breaks, which are not visible on the outside. This is expecially the case with rotation-resistant ropes in Lang Lay under bending cycle usage. This should always be clarified with a rope expert.
Crane components and crane geometry
Besides the rope itself crane components and crane geometry are important criteria for the right rope choice. The applied drum system and the crane geometry constructively selected fleet angles are to mentioned particularly.
While on single-layer drums the rope gets stressed due to tensile load and substantially due to bend and lateral deflection and thus twists, dominates on multi-layer drums mechanical wear and lateral pressure stress between the touching ropes.
The crane geometry constructively selected fleet angle is a very important characteristic for a reliable rope spooling and the degree of rope wear. For multi-layer spooling a maximum fleet angle of 1,5° is recommended, while single-layer drums can work with higher fleet angels like for example up to 4°.
Consequently the right rope choice is to be matched with these operating-/wear conditions.
The following basic rules for the correct choice of rope lay types for ropes that spool on drums have proved themselves and therefore are also recommended by us:
- single-layer drums = ordinary lay ropes
- multi-layer drums = lang’s lay ropes
On single-layer drums the ordinary lay ropes have clear advantages, because it can usually compensate the bigger fleet angle. Also the easier recognition of externally visible wire breaks is an important argument for the use of ordinary lay ropes on single-layer drums where strong mechanical rope wear, which also leads to wire breaks, does not or not substantially exist.
On multi-layer drums the bending fatigue resistance of the rope is not decisive for the rope lifetime but its resistance to mechanical impact is. Ordinary lay ropes are less suitable for multi-layer drum spooling because the wires of the neighboring ropes can rub with each other. This leads to high mechanical wear. The touch of the neighboring ropes during the spooling process is also well “audible”. The results are premature wire breaks. Lang’s lay ropes have proved themselves in the multi-layer spooling because neighboring ropes can not rub into each other, which raises the lifetime of the rope significantly.
The use of ropes with compacted outer strands and/or rotary swaged rope constructions can
clearly raise the rope lifetime due to the very smooth surface and the high resistance to abrasion.
The abovementioned statements have proved themselves in practice. Customer desired, occasionally divergences should therefore be analyzed thoroughly with regard to:
- specific operating conditions of the rope
- the chosen rope construction
- the customer-sided rope supervision concerning discard criteria before a divergent decision can be made