Apparatus for identification of need to replace synthetic...

Measuring and testing – Hoisting cable and rope

Reexamination Certificate

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Reexamination Certificate

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06247359

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to an apparatus for identifying the need to replace ropes constructed of synthetic fibers, preferably of ropes of aromatic polyamide.
From the European patent document EP 0 731 209 A1 a device for identifying the need to replace a stranded fiber rope is known. The stranded rope consists of several layers of high-tensile synthetic fibers, the layers being laid over each other and surrounded by a firmly bonding rope sheath. To make identification of the maximum allowable internal rope wear possible, the extruded sheath of the rope has different colors arranged coaxially. The rope sheath indicates abrasive wear that occurs on driving, or driven, ropes as a result of the slipping that occurs on the traction sheave due to differences in force. Experimental values are used to correlate the abrasive wear of the sheath, by reference to the defined running surface of the ropes in the traction sheave, to the state of wear in the interior of the ropes. Accordingly, as soon as the underlying color is visible, this is taken to indicate that the interior of the rope is worn to the maximum allowable extent, and that the rope must be replaced within a specified remaining period of time.
With the device for identifying the need to replace synthetic fiber ropes described so far, the state of the rope can be easily assessed by means of a simple visual check of the rope sheath. However, the indication obtained in this indirect manner depends on experimental values; it does not allow a statement to be made concerning the precise internal condition of the rope. Rope wear due to, for example, such factors as premature material fatigue, short-term overloading, or external influences is not taken into consideration.
The problem underlying the present invention is that of proposing a device for identifying the need to replace ropes which reliably indicates the true state of wear.
SUMMARY OF THE INVENTION
As a solution to the problem, the present invention has been developed. In essence, the present invention consists of a rope construction with outwardly neutral torsion properties, between whose individual layers of strands a reactive torque ratio ensures that the rope takes up a position of unstable torsional equilibrium. The relationship between torques in the rope acting in opposition to each other is set in such a way that weakening of the layers of strands by abrasive wear or other influences disturbs the internal torsional equilibrium, so that when the worn rope is loaded during operation it twists about its longitudinal axis until it takes up a new position of equilibrium corresponding to the changed conditions of torque. Twisting of the rope is therefore an indication of wear in the interior of the rope, which has caused a change in the specific characteristics of the rope, such as loss of breaking strength. Correspondingly, the change in structure of the rope is detected by means of a suitable device, and taken as an indication of the need to replace the rope, with even simple distortion of the rope being an indicator of an unacceptable amount of rope wear.
This makes it possible to achieve the advantage that the load-bearing synthetic strands, which are present in any case, simply by being laid in the manner specified according to the invention, can indicate any type of wear of the rope very simply as a twisting of the rope as soon as the weakening of the load-bearing structure of the rope due to wear exceeds a certain definable amount. Twisting of the rope, and therefore the need to replace it, can be detected without costly additional devices. In particular, by applying a reference mark, it becomes possible to check the condition of the rope visually.
In a further development of the invention, between the adjacent concentric layers of strands which are laid in opposite directions there is an intersheath to reduce friction. This has the advantage that the choice of materials and the dimensions of the intersheath can be used to determine the radial distance of the layers of strands from each other, and thereby the torsional equilibrium. Furthermore, the fatigue strength of the intersheath can be used to obtain a desired service life of the rope. As soon as the intersheath becomes worn through by the longitudinal displacement of the outer layers of strands which occurs due to relative movement when bending, points of contact occur with the strands laid in the opposite direction. Due to the rubbing of the strands against each other, the constricting force under tension, and the pressure on the sheave which arises as the rope passes over it, the lateral stress ultimately causes strands to fracture. Due to the causal relationships described above, the rope twists and thereby indicates that the rope is in need of replacement.
In a preferred embodiment of the invention the outermost layer of strands of a multi-layered stranded rope is systematically wound round, and in the opposition direction to, a multi-layer parallel-laid rope core. This has the advantage that the layer of the rope core which is adjacent to and carries the outermost layer of strands is subject to the greatest lateral stress as a result of which the filaments or strands of this layer of strands display points of damage before any others. Only this selected layer of strands is weakened, whereas all other layers of strands remain undamaged and ensure that the remaining load-bearing capacity of the synthetic fiber rope is adequate.
In a preferred embodiment of the invention there is a mark running along the length of the external surface of the unworn rope which indicates twisting of the rope in that the marking winds helically around the longitudinal axis of the rope.


REFERENCES:
patent: 5015859 (1991-05-01), Uejio
patent: 5834942 (1998-11-01), De Angelis
patent: 6080982 (2000-06-01), Cohen
patent: 0 731 209 (1996-09-01), None

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