Objective
For safe operation, only that part of the contact area rope/wheel can be made use of in which elongation compensation between the higher loaded and the lower loaded hoist tracks takes place. This compensation results in a relative movement (creeping) between rope and wheel in what is called creeping arc (section). Over the rest of the embrace arc (section) of the wheel in contact with rope, the adhesion section, the rope rests without relative movement in its groove. The creeping section therefore develops always towards the run off side of the friction wheel. The order of magnitude of that section depends on the friction parameter of the friction wheel lining. The friction parameter depends on various parameters. The friction coefficient rope/lining decreases with increasing pressure per surface unit and increasing temperature. The influence of lubrication becomes apparent in the following sequence:
u dry > u wet > u lubricated > u wet and lubricated
The friction coefficient with a lang's lay rope is greater than the one of a cross-lay rope. Further parameters are: the shape of the groove, the material and elasticity of the lining, and the creeping rate.
During the passage of the rope over the friction wheel, creeping and slipping effects in the contract section of the rope and the Koepe wheel occur in the following contract areas: friction wheel lining/rope, wire/wire within the strands, wire/wire of neighbouring strand/rope core. Crossing wires are worn by short slip movement causing friction grooves in turn causing wire failure. The attack of friction-induced force has different effects on lang's-lay or cross lay ropes. In case of cross-lay ropes the wires are arranged in approx. tangential direction, and in case of lang's-lay ropes at a greater angle to the tangential direction of the Koepe wheel. Thus, the contact of the wire against the friction wheel lining is of different length and direction. In case of cross-lay ropes this means predominantly tensile, compressive, and flexural stresses, and in case of lang's-lay rope this means torsional stresses. The influence of rope spin has a particularly negative effect if the wires of the strands are arranged in parallel, since torsion results in loosening-up of strands and of the rope. Under the force induction by the friction wheel, loosened-up strands mean more strain in the outer wire layers and destruction of the stands' coherence. Geometrically unfavourable strands may result in squeeze and shiftings within the rope. Observations of damages to ropes and unsafe operation by rope slip can be explained by the phenomena taking place on the friction wheel. Excessive lubricant discharge from the rope or moisture and strong dust exposure resulted in reduced friction, and rope slIp.
Shaft winding systems need to come up to high standards of operational safety and reliability, since manriding as well as product winding and material transport are frequently run in the same shaft. The shaft systems need to be designed with particularly high safety standards and they require regular checks and inspection. A winding rope is subjected to particularly stringent requirements in this context. The exact knowledge of the operational stresses and of the development of rope damages as well as the resulting assessment of the ropes' residual useful life are the basis for reliable inspection/checks and safe operation of the winding ropes.
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44137 Dortmund
Germany