The Causes of the Damage to the Bearing Rope – The Failureanalysis

Abstract

In our laboratory we quite often experience problems with the operation of steel ropes. There is a range of causes related to lifetime problems of ropes. These problems are related to poor quality of input material used for wire production, mixing of different wire strengths in the rope construction, improper roping of the rope into the hoist system, improper rope operation, improper rope design for a particular type of operation as well as unfair practices of vendors. The subject of the article is the analysis of the rope showing the combination of a large number of the above factors leading to the damage of the rope. During the operation of the cargo cableway, the hauling ropes were damaged in a very short time. The Z wires from the surface layer of the rope started to release from the rope. Subsequently, the wires were unwinding from the layer, they created visible protuberant waves, they were braking and dropping out from the rope. The hauling rope had to be replaced. Than the samples were taken from the rope in order to find out the cause of the rope damage. Mechanical, metallographic and fractographic measurements were performed on the rope. The metallographic and fractographic measurements revealed the material defects of the wires of the rope caused during manufacturing of the Z wires from the surface layer of the hauling rope. The mechanical tests revealed differences in the tensile strength grade the operator required compering to the tensile strength grade the vendor declared. The above mentioned problems unambiguously show that it is appropriate to introduce a mechanical control of the rope properties in advance to its deployment. Checks must be performed by an independent testing laboratory. This procedure overprices inputs needed for the rope replacement. On the other hand, it can reduce the costs when a poor quality rope is deployed. Some of our customers have already adopted this approach. It helped to the increase in the safety of the operation of the mechanisms and it eliminated the problems with exchange and climes on bad quality ropes.

Prognosis methods of stress corrosion cracking under harsh environmental conditions

“…To evaluate the stress corrosion cracking resistance of metallic alloys, fracture mechanics principles, and pre-cracked specimens have been used successfully in recent years [ 37 ]. These pre-cracked specimens can be produced by fatigue, which creates compressive residual stresses in the vicinity of the crack tip [ 38 ]. In addition, Li has pointed out that stress-corrosion cracking occurs when the corrosion product occupies a larger volume than the volume of metal destroyed [ 39 ].…”