Analysis of Steel Wire Rope Damage in Tower mounted Multi rope Friction Winder

The Tower mounted multi rope friction hoist is a commonly used equipment for mine hoisting, and the steel wire rope is one of its key components. During operation, the damage to each section of the steel wire rope varies due to different forces. The state of the steel wire rope affects the safety of the hoist, and China has also formulated relevant national and industry standards to control its production, manufacturing, transportation, storage, and use. The author analyzes the stress situation of the steel wire rope and combines it with non-destructive testing data to analyze the damage of different sections, and proposes key areas for daily inspection and maintenance of the steel wire rope to ensure safe operation.

1 Damage analysis

The Tower mounted multi rope friction hoist is divided into two types of hoisting systems: without deflection sheave wheel and with deflection sheave wheel. The principle, structure, and arrangement of the two types of hoists are shown in Figure 1. There is a deflection sheave wheel lifting system, which is located below the friction winder drum . The deflection sheave wheel can adjust the surrounding angle of the steel wire rope on the friction winder drum, and also adjust the distance between the lifting steel wire ropes to ensure that the diameter of the wellbore is not limited by the diameter of the friction winder drum . Therefore, most mines use a multi rope friction lifting system with a deflection sheave wheel.

(a) without deflection sheave wheel (b) with deflection sheave wheel

1、Friction winder drum 2、steel wire rope 3、Shaft lifting container or counterweight 4、tail rope 5、deflection sheave wheel

During operation, the steel wire rope is divided into two sections without guide wheels based on the stress situation: ① the section above the cage only bears tensile force; ② Passing through the friction wheel segment, it is subjected to both tensile and unidirectional bending forces. The guided wheel type is divided into three sections: ① the upper part of the cage is only subjected to tensile force; ② Passing through the friction wheel segment, simultaneously subjected to tensile force and unidirectional bending force; ③ Simultaneously passing through the friction wheel and guide wheel segments, subjected to both tensile and reverse bending forces. According to operating speed, it can be divided into acceleration section, constant speed section, and deceleration section.

1.1 Analysis of Various Forces

(1) The tensile force of the steel wire rope is only affected by the tensile force of the heavy object (see Figure 2), and in this case, the stress variation area of the steel wire rope is the entire cross-section of the steel wire rope (see Figure 3) [1].

(3) During the operation of unidirectional bending force, the steel wire rope undergoes unidirectional bending (see Figure 4). In this case, the steel wire rope is simultaneously affected by the combined stress of tension and bending, and the area with the greatest stress change in the steel wire rope is on one side of the bending section (see Figure 5)

(4) During the operation of reverse bending force, the steel wire rope undergoes two bends in opposite directions (see Figure 6). At this time, the two sides of the cross-section of the steel wire rope are the maximum stress variation area (see Figure 7).

1.2 Damage Analysis of Steel Wire Rope

During the operation of the hoist, the steel wire rope is affected by various stresses such as tension, bending, torsional shear, and contact extrusion, resulting in its damage. The author analyzes the effects of tensile stress, bending stress, and speed on the operation of steel wire ropes as follows.

(1) The damage analysis of the non guided wheel type steel wire rope is only affected by the tensile force when it is above the lifting container, and only suffers from tensile fatigue damage throughout the entire service cycle; During the period of passing through the friction wheel, it is simultaneously affected by tensile and unidirectional bending forces, and is subjected to both tensile fatigue and unidirectional bending fatigue damage throughout the entire service cycle. The steel wire rope passes through the acceleration section, constant speed section, and deceleration section. In the acceleration section, the force on the steel wire rope gradually decreases from the maximum at startup, and the force on the constant speed section is uniform. The force on the deceleration section gradually increases until it stops and unloads [2].

(2) Damage analysis of guided wheel type: Due to the influence of equipment layout, the section of the steel wire rope passing through the friction wheel or guide wheel is very short, which can be simplified into two sections: the upper section of the lifting container and the section passing through the friction wheel and guide wheel. The stress damage situation of a section of steel wire rope above the lifting container is the same as above. After passing through a section of the friction wheel and guide wheel, it is simultaneously affected by tensile and reverse bending forces, and is subjected to both tensile fatigue and repeated bending fatigue damage throughout the entire operating cycle. At the same time, the steel wire rope is also affected by speed during operation.

Based on the above analysis, it can be concluded that the steel wire rope above the container only suffers the smallest damage in the tensile force section. In the section of steel wire rope passing through the friction wheel, due to the influence of speed, the damage in the acceleration and deceleration sections is greater than that in the uniform speed section.

Example analysis of 2 well tower type steel wire rope

A certain mine in northwest China adopts JKM4 × Type 4 hoist with wire rope specification of 6 × 36+FC (14/7+7/7/1) twisted in the same direction, with a nominal diameter of 44mm, is an imported steel wire rope. The rope was hung in November 2013, and in October 2015, four steel wire ropes of the equipment were inspected. The inspection position is below the guide wheel, and the inspection graph is shown in Figure 8. After the inspection, a new steel wire rope was replaced.

The steel wire rope corresponding to area A (sections a and b in Figure 9) in the detection graph is located in a section above the cage of the elevator. During operation, this section of steel wire rope does not pass through the guide wheel and friction wheel, and is only affected by tensile force, resulting in relatively minor damage.

The steel wire ropes corresponding to areas B (Figure 9b, c) and D (Figure 9d, e) in the detection graph are in the acceleration and deceleration operation stage when passing through the guide wheel and friction wheel during operation. They are not only affected by tensile force and reverse bending force, but also have significant changes in the operating speed of the hoist, resulting in relatively serious damage.

The steel wire rope corresponding to the C region (sections c and d in Figure 9) in the graph is already in a constant speed operation stage when passing through the guide wheel and friction wheel during operation. This section is affected by tensile force and reverse bending force, and the impact of speed on it is reduced compared to areas B and C, and its damage is also lighter compared to areas B and C.

From the graph, it can be seen that the steel wire rope is also severely damaged in areas B and D. To verify the practical application of this steel wire rope, three sections were taken from the replaced old steel wire rope, with the cutting positions being: A section, B section, and C section. The appearance and internal condition of the 3-section steel wire rope after dismantling are shown in Figures 10-12.

From the figure, it can be seen that the steel wire rope in area A is coated with grease on the outside (see Figure 10 (a)), and there is a small amount of grease on the inner hemp core (see Figure 10 (b)); There are obvious broken wires in section B (see Figure 11 (a)), and the internal steel wires have obvious wear and indentation, and the hemp core has become loose (see Figure 11 (b)); The C section has a worn section but no broken wire (see Figure 12 (a)), and its interior is also better than the B section. The steel wire rope has wear but no indentation, and the hemp core is still intact (see Figure 12 (b)). Based on the inspection graph and the pictures of rope dismantling, it can be seen that the most severely damaged part is the area B and D where the acceleration and deceleration pass through the guide wheel and friction wheel, followed by the area C where the acceleration passes through the guide wheel and friction wheel, and finally the area A above the cage.

3 Conclusion

Through the above analysis, it can guide the use of steel wire ropes to focus on strengthening the detection and maintenance of severely damaged areas, so as to maximize the energy efficiency of the steel wire rope and ensure the safe operation of the lifting equipment.