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Cableways wire rope detection technology
Cableways wire rope detection technology
The inspection of wire ropes for passenger cableways is clearly stipulated in the international standard (GB9075-88), which is related to the safe operation of the cableways and is an indispensable technical inspection work. The level of its detection accuracy directly affects the service life of the steel wire rope.
In addition to mechanical damage and improper structure selection, the damage methods of steel wire ropes are mainly wear, waste and broken wires and corrosion in normal operation, especially fatigue broken wires and wire rope joint broken wires, which need to be checked frequently. Corrosion is also a problem that cannot be ignored because individual cableways are built in locations with a lot of acid rain and high seawater moisture. There are three types of wire rope detection methods: manual visual inspection, damage detection and non-destructive testing. The manual visual inspection method is a daily inspection, mainly to detect whether there are broken wires, skipped wires and abnormal phenomena in the whole wire rope, and whether there are loose strands and broken wires in the wire rope joints. The key areas should also be stopped for inspection, such as whether there are broken wires, taps and abnormal phenomena at the saddle and the connection of the sleeve, and whether the wire ropes at the anchoring end and the heavy hammer have sliding broken wires and other abnormal phenomena. Periodic inspections need to measure the diameter and lay length of the wire rope. In the process of manual visual inspection, the running speed of the wire rope should not be too fast, and the general requirement is (0(3, 0(5m,s). The length of the wire rope of a ropeway is more than a few meters to several kilometers, the running time is long, and the labor intensity is high. Large, low efficiency, the inspectors are easily fatigued, which affects the inspection accuracy. More importantly, the manual visual inspection can only find the exposed defects of the wire rope, and can do nothing for the invisible internal defects of the wire rope. The influence of human factors (quality and experience) is greater, and its detection accuracy is difficult to guarantee.
The use of damage detection method has great limitations, it is difficult to fully understand and judge the state of the entire wire rope. Because the strength test cannot be carried out without damaging the wire rope, and the wire rope for passenger ropeway is not allowed to take samples from the working section anywhere, it cannot accurately reflect the weakest link of the wire rope or the state of the whole rope. However, the non-destructive testing method can directly inspect the external and internal defects of the wire rope in use without changing the state and performance of the wire rope, thereby improving the detection reliability, overcoming and improving the artificial visual inspection method and Defects in breakage detection methods. Therefore, the research, development, production and promotion of high-performance wire rope flaw detection technology and equipment have become the issues of great concern to the scientific and technological circles of various countries.
Since the birth of the world's first steel wire electromagnetic non-destructive testing device in 1906, domestic and foreign scientific and technological workers have proposed many non-destructive testing methods suitable for steel wire ropes, among which there are several representative ones; (1) Acoustic testing method : (2) mechanical detection method; (3) radiographic detection method; (4) current detection method; (5) optical detection method; (6) eddy current detection method; (7) ultrasonic detection method; (8) vibration detection method ; (9) Acoustic emission detection method; (10) Electromagnetic detection method. Among the above methods, electromagnetic detection is currently recognized as the most reliable non-destructive testing method for steel wire ropes, because most steel wire ropes use magnetic permeability testing, and at the same time, electromagnetic testing methods have the advantages of low cost and easy implementation. The wire rope non-destructive testing technology and equipment are all done using the electromagnetic principle.
Electromagnetic detection method is used to detect broken wires, wear and defects of ropeway wire ropes. The basic principle is: use a magnetic field to magnetize the wire rope axially. When the wire rope passes through this magnetizing magnetic field, once the wire rope is broken, a leakage magnetic field will be generated on the surface of the wire rope, or the magnetic flux of the magnetized wire will be changed. Sensitive elements detect the distortion of these magnetic fields into information about wire rope defects, which are amplified by detection and recorded with images, from which the types, severity and scope of wire rope defects can be analyzed.
After more than years of continuous exploration, research, manufacture and practical use of ropeway wire rope detection technology, it has affirmed the advanced nature and reliability of electromagnetic element damage detection technology. This has attracted great attention from many countries, and some countries have established special research institutions to design and manufacture corresponding instruments and equipment, the so-called wire rope electromagnetic flaw detectors. For example, the "MTC-9AB Type Wire Rope Quantitative Detector" successfully developed by Chinese scientist Yang Shuzi and his student Dr. Kang Yihua belongs to this type. These instruments and equipment have been greatly improved in terms of volume, weight, structural principle and performance, and the accuracy of detecting wire rope breakage, wear, corrosion, and cross-sectional area has been improved accordingly. However, due to the principle structure of the instrument itself,
Factors such as testing environmental conditions and human operating experience lead to differences in testing results, which cannot correctly reflect the actual state of the tested wire rope. Let's talk about how this error occurs and how to make up for it?
1. In terms of construction principle, electromagnetic flaw detectors can be divided into several methods: such as the impedance method using the self-inductance of the excitation coil; the method using the mutual inductance of the excitation coil and the detection coil; the power generation method using the movement of the magnetized wire rope (static magnetic field method), etc. Wait.
In terms of construction principle, when the magnetic permeability is different, the impedance method is not suitable for detecting the cross-sectional area of the wire rope. Strictly speaking, some new samples of the steel wire rope to be tested must be retained. From the time of the new sample, the problem of electromagnetic flaw detection and even life judgment has begun. It can be saved as an archive data for testing and comparison during the use of the steel wire rope, so as to prevent the judgment. error.
However, in actual operation, because the steel wire to be detected is carried out at a certain speed and the detection points are different, the change of its tensile force is unavoidable. The change of the pulling force causes the change of the magnetic permeability, which is the so-called magnetostriction phenomenon. The increase or decrease of the magnetic permeability (the magnetic induction also changes accordingly, and the instrument reflects the error. If the magnetization state of the detected wire rope maintains a high magnetic flux density, the influence of the magnetic permeability can be avoided, but large power is required, which is detected on site. environment is difficult to do.
2. When applying the impedance method to keep the magnetization state at a low magnetic flux density, in order to increase the change of impedance, the frequency is generally increased, but it is easily affected by the skin effect at this time. In addition, when the wire rope passes through the coil, as the wire rope deviates from the center, its impedance also changes (although it is a wire rope with the same cross-sectional area), which causes an eccentricity error, and the deviation t2, value is changeable.
3. Generally, the broken wire is detected by the electrostatic magnetic field method. As far as the principle is concerned, the broken wires within the pitch of the wire rope should also be recorded one by one, that is, the actual situation of the internal broken wires cannot be detected.
4. In order to improve the detection accuracy of the electromagnetic flaw detector, you can use large power or increase the magnification of the amplifier. However, if the vibration of the wire rope is not controlled in the process of being tested at the same time, errors will be generated due to signal amplification, resulting in misjudgment of the test results.
5. The use of electromagnetic flaw detectors to detect steel wire ropes should have such a full understanding that during the detection process, the vibration generated may be mistaken for broken wires; if the specified voltage is not used, it is entirely possible to miss the detection of internal broken wires and other problems .
6. The electromagnetic flaw detector measures the cross-sectional area of the wire rope, and the cross-sectional area of the wire rope varies - it must be proportional to the diameter. This is also the characteristic of different types of wire ropes, so it should be noted. Measuring the cross-sectional area of the wire rope can more accurately estimate the strength of the wire rope than measuring its diameter. At present, the development of passenger cableways at home and abroad is rapid, and more than 30,000 cableways of different forms have been built, with a total length of tens of thousands of kilometers. my country has built nearly 300 passenger cableways in recent years. In order to ensure the safe operation of the cableway and the personal safety of tourists, it is necessary to carry out regular non-destructive testing on the wire ropes of each cableway to accurately judge the remaining strength of the wire ropes and determine its service life. In view of the continuous development of cableways wire rope detection technology, various types of detection instruments and equipment have been continuously updated and transformed, and this detection task has been basically completed. Although there are still some problems in the structure of the instrument, the actual operating environment and the quality of personnel, it is believed that modern scientific and technological means can be solved quickly, so that the detection technology of steel wire ropes will develop faster and more perfect, and the detection accuracy will be higher.
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