Analysis of the Current Situation of Steel Wire Rope Testing at Home and Abroad

Steel wire rope has many advantages such as high strength, light weight, good elasticity, stable and reliable operation, strong ability to withstand dynamic loads and overload, and no noise during operation and winding under high-speed working conditions. Therefore, it is widely used in China's coal industry and is an important component of coal mine main and auxiliary shaft lifting equipment.

However, as an engineering load-bearing component, steel wire rope is often affected by harsh working conditions such as bending fatigue, wear, corrosion, and mechanical impact during operation. It is inevitable that phenomena such as wire breakage, wear, corrosion, and even sudden fracture will occur. Its damage and load-bearing capacity directly affect the life safety of miners and the normal order of production. Only by regularly inspecting the steel wire rope can accidents be avoided to a certain extent and work efficiency be improved.

1. Current situation of steel wire rope inspection in China

Coal is the most important basic energy and important raw material in China. In recent years, with the continuous increase in coal demand, various coal enterprises attach great importance to the safety of the use of mine hoisting steel wire ropes. Realizing accurate and reliable online detection of mine hoisting steel wire ropes is an urgent technical difficulty that needs to be solved. There are two specific issues during the detection process:

(1) Reliability and practicality issues in online detection of steel wire ropes

In the past decade, although various research departments and universities at home and abroad have conducted systematic and in-depth research on quantitative non-destructive testing technology for steel wire ropes, and developed some steel wire rope inspection devices, due to their performance and convenience of use, they cannot meet the requirements of on-site promotion and application. Therefore, only a few important departments use them as auxiliary detection tools to detect the damage of steel wire ropes. More than 95% of the coal mines in China still use the traditional "cloth eye" method to inspect the damage of coal mine lifting steel wire ropes. Dedicated inspectors use cloth, gloves, flashlights, mirrors, etc. to inspect the steel wire ropes in use, and use calipers to measure the rope diameter, and then judge the status based on experience. Artificial visual inspection can only detect external defects in the steel wire rope, while internal defects are powerless. Moreover, in the presence of oil stains on the surface of the steel wire rope, it is difficult to detect the presence of damage with the naked eye. It is obvious that the traditional "cloth eye" method is both time-consuming and labor-intensive, and is influenced by the experience and subjective will of the testing personnel, resulting in low reliability of the test results.

(2) Ineconomical issues in the use of steel wire ropes

Due to the lack of scientific and practical methods for detecting damage to steel wire ropes for a long time, there is a problem of low reliability in manual visual inspection. Therefore, to ensure safety, many domestic steel wire rope usage departments adopt the method of regular replacement, that is, the steel wire rope must be forcibly replaced after running for a certain period of time, running for a certain number of cycles, or accumulating a certain weight, regardless of its damage condition. This method of replacing steel wire ropes not only fails to ensure the safe operation of steel wire ropes during service, but also causes huge waste due to early scrapping.

2 Common methods for detecting steel wire ropes

So far, there are mainly the following types:

(1) Radiographic testing method

The radiographic testing method has been used in the industry for many years, but its ability in detecting defects in steel wire ropes is very limited. This method can detect internal defects in steel wire ropes, but due to the complexity of the wire rope structure, it can only provide clear images of the near surface of the wire rope, and can only inspect a small section of the wire rope at a time.

(2) Eddy current testing method

The principle of eddy current detection method is to set up transmitting and receiving coils near the surface of the steel wire rope. A few kHz to 1MHz currents are applied to the transmitting coils, and eddy currents will be generated in the steel wire rope. Based on the electromagnetic characteristics, the steel wire rope will reflect electromagnetic energy, and the receiving coils will receive electromagnetic energy. Once there is a broken wire on the wire rope, the eddy current in the wire rope will change, causing a change in reflected energy. Based on the reflected energy, the degree of damage to the wire rope can be measured.

(3) Acoustic emission detection method

In 1984, Taylor and Caesy from the UK applied acoustic emission technology to non-destructive testing of steel wire ropes and conducted extensive theoretical and experimental research on steel wire rope testing methods based on acoustic emission technology; In 1998, Wang Shi, Yu Da'an, Shao Yongbo, and others conducted experimental research on acoustic emission technology for detecting steel wire ropes in China, relying on a project funded by the former China National Petroleum Corporation - fatigue damage law and life assessment of steel wire ropes for petroleum use. The research results indicate that this method can effectively detect defects that cause plastic deformation of steel wire rope structures, such as broken wires. However, this method is highly susceptible to noise interference, and different researchers may obtain different results or even opposite conclusions for the same test content, making it difficult to achieve quantification, standardization, and automation. Moreover, from the perspective of detecting defect types, wire breakage and overall damage (plastic deformation, crack cracking, and propagation) can be detected using acoustic emission technology. However, for defects such as rust, acoustic emission methods are powerless, and no relevant reports have been seen so far. So far, only a few countries in the world have conducted intermittent research on acoustic emission detection of steel wire rope damage at different times.

(4) Optical detection method

In 1987, the Transport Engineering and Materials Technology Research Institute of the Westphalia Mining Federation in Germany manufactured the world's largest steel wire rope inspection equipment, which uses laser scanning method to detect the diameter of steel wire ropes and can detect steel wire ropes with a diameter of up to 175mm. This method uses a laser beam to continuously scan along the axial direction of the steel wire rope to measure the radial size changes of adjacent rope strands, and then calculate the diameter of the steel wire rope in different parts.

(5) Vibration detection method

In 1988, Kwun and Burkhardt from the United States conducted an experimental study on the method of detecting defects in steel wire ropes using transverse excitation vibration waves. When a transverse impact force pulse was applied to a tensioned steel wire rope, the reflected vibration waves generated at the broken wire or reduced cross-sectional area of the wire rope could be detected, and the diffusion speed of the waves followed (F/M) 1/2. Among them, F is the applied excitation load, and M is the mass per unit length of the steel wire rope. The experimental subjects are stainless steel wire rope with a diameter of 2.38mm and twisted nylon rope with a diameter of 6.35mm. This indicates that this method is not limited by materials and is not only suitable for metal ropes, but also for non-metallic ropes. In addition, this method has the characteristics of short detection time and the ability to determine the location of defects. However, from the perspective of detection principle, this method is only suitable for the detection of fixed steel wire ropes (such as steel wire ropes for cable-stayed bridges and suspended roofs), and cannot perform online detection of running steel wire ropes.

(6) Ultrasonic testing method

In 1988, Japanese researchers such as Kiyoshi Suzuki conducted research on the detection of broken wires in bridge suspension cables using ultrasonic technology (with a detection wire diameter of 5-7mm). They studied the propagation characteristics of ultrasonic waves in the length direction of steel wires and the reflection characteristics of broken wire parts through experimental methods based on the theory of sound waves. The research results indicate that this method can detect broken wires at the end of the steel wire rope and its vicinity (the detectable broken wire position is within 5m). However, for damage caused by broken wires in the distance, this method poses certain difficulties. This study has practical significance for solving the problem of detecting end defects of steel wire ropes for static suspension.

(7) Acoustic emission ultrasonic testing method

In recent years, a new detection method called acoustic emission ultrasonic testing has been proposed abroad to quantitatively detect the damage of steel wire ropes. This method is developed based on the advantages of both acoustic emission and ultrasonic methods. Through a set of transducers and coupling agents, ultrasound is introduced into steel wire rope detection to simulate the propagation characteristics of acoustic emission signals in the steel wire rope. Another set of transducers and coupling agents extracts the signal, amplifies it, and sends it to a threshold controller for stress wave coefficient calculation, achieving quantitative identification of steel wire rope defects. The acoustic emission ultrasonic testing method can not only detect defects in steel wire ropes, image defects, and analyze defect characteristics, but also evaluate the inherent properties of steel wire ropes such as fatigue damage, strength, and hardness. It compensates for the shortcomings of the acoustic emission testing method, which can only detect static steel wire ropes and capture instantaneous signals of steel wire fracture, and can detect dynamic steel wire ropes. However, this method is currently in the theoretical research stage.

(8) Electromagnetic detection method

Electromagnetic testing is currently recognized as the simplest, most practical, and reliable method for detecting steel wire ropes. This method has long been highly valued and is also the most mature detection method. The vast majority of steel wire ropes are made of high carbon steel with good magnetic conductivity, which is very suitable for electromagnetic testing; At the same time, electromagnetic detection method has the advantages of low cost and easy implementation, so many practical steel wire rope detection instruments and equipment almost use electromagnetic detection method.

The basic principle of electromagnetic detection method for detecting defects in steel wire ropes (such as breakage, wear, rust, etc.) is to use a magnetic field to uniformly magnetize the steel wire rope section along the axial direction of the steel wire rope. Once there are defects in the steel wire rope, a leakage magnetic field will be generated on the surface of the steel wire rope or cause changes in the magnetic flux inside the magnetized steel wire rope section. By using magnetic sensitive components to detect these magnetic field distortions, information about steel wire rope damage can be obtained.

In summary, existing wire rope detection methods have low accuracy in detecting wire rope defects, especially in quantitative detection, and there is still a certain distance from practical application requirements. Therefore, it is necessary to have a comprehensive understanding of wire rope defects, and based on this, research on defect detection principles and methods, detection signal processing methods, and signal quantitative recognition methods.