Steel cable defect detection method

Abstract

The invention relates to a steel cable defect detection method. The method comprises the following steps: step 1, determining parameters of a to-be-detected steel cable; 2, calculating a temperature difference change value of a normal part and a defect part of the steel cable; 3, electrifying and heating the two ends of the to-be-detected steel cable; and 4, detecting the temperature of the steel cable to determine a defect position. After the steel cable is electrified and heated, the defect position of the steel cable is judged by analyzing the temperature distribution condition of the steel cable, the detection is accurate, and the change of local resistance of the steel cable is the resistance of the whole cross section of a damaged part, so that abnormal heating occurs on the whole cross section; according to the method, the original state of the steel cable can not be influenced during detection, the operation is simple and convenient, the defect type can be preliminarily judged, and meanwhile, the normal mechanical property of the steel cable cannot be influenced.

Description

Technical Field

[0001] The invention relates to the technical field of steel cable detection, in particular to a steel cable defect detection method. Background Art

[0002] During long-term use, steel cables may have defects such as broken wires, rust, and local abnormal stretching, so it is necessary to detect the condition of the steel cables in real time. At present, the defect detection methods for steel cables include visual detection, magnetic flux leakage detection, etc., among which visual detection is mainly carried out using equipment such as imagers. For example, the Chinese invention patent with the authorization announcement number CN104034734B discloses a winch steel cable detection device and method thereof, which includes an image acquisition unit installed on the front of the winch steel cable, and the image acquisition unit includes an imager and upper and lower lasers. The device uses the upper and lower lasers to be set at an angle of 45 degrees relative to the steel cable, so that the object behind the steel cable will not produce abnormal light spots, thereby effectively solving the technical problem of the imager misjudgment and misjudgment caused by the abnormal light spots collected. At the same time, due to the use of visible light filtering lenses, only infrared lasers are allowed to pass, completely eliminating the interference of ambient light, so that the image recognition algorithm is simple, efficient and accurate. Good effect. However, the visual detection method cannot detect the damage of the inner layer of the steel cable, and in many working conditions, the steel cable is often covered with heavy oil stains and cannot be visually detected.

[0003] The magnetic leakage method is to generate a stable magnetic field through an excitation device or a permanent magnet to saturate the detected part of the steel cable, and then detect the leakage magnetic flux on the surface of the steel cable through a magnetic sensor and other devices, and judge its damage according to the change of the leakage magnetic flux on the surface of the steel cable. For example, the Chinese invention patent with the authorization announcement number CN114074879B discloses a steel cable inspection method and device. The method uses a flaw detection device using the magnetic leakage flaw detection method for measurement, and performs signal processing for determining broken wires according to the steel strand signal frequency in the measurement waveform output as the main component to the measurement data, and the disclosed invention discloses a method and device for inspecting steel cables. The Chinese invention patent numbered CN114813918A discloses a method and device for detecting defects in steel cables based on a frequency sweeping method. The method includes preliminary detection and secondary detection. During the preliminary detection, AC magnetic field excitation and DC magnetic field excitation at a fixed frequency are applied to the steel cable to be tested, and then the relative position and size information of the defect are output according to the leakage magnetic signal. Under the variable AC magnetic field excitation, the defective part is subjected to secondary detection, and then the data under different frequency excitations are fused through the Kalman filter algorithm to further solve and obtain more accurate defect position and size information. However, the leakage magnetic method usually requires the steel cable to be saturated magnetized before detection, and then the detection device is used to contact and slide with the surface of the steel cable for detection. The operation is relatively cumbersome and will affect the normal use of the steel cable. Summary of the invention

[0004] The object of the present invention is to provide a method for detecting defects in steel cables, which determines the defect location of the steel cable by analyzing the temperature distribution of the steel cable after the steel cable is electrically heated. The method has accurate detection and is simple and convenient to operate.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A wire rope defect detection method comprises the following steps:

[0007] Step 1: Determine the parameters of the steel cable to be tested, including the length L of the steel cable, the cross-sectional area A of the steel cable, the resistivity ε of the steel cable, the density ρ of the steel cable, the resistance R of the steel cable, the mass m of the steel cable, and the specific heat capacity c of the steel cable;

[0008] Step 2: Calculate the temperature difference between the normal and defective parts of the steel cable;

[0009] Assuming that the current I is passed through both ends of the cable and the power-on time is t, the temperature T that rises after the cable is heated at normal position is:

[0010]

[0011] If there is a defect in the steel cable, the cross-sectional area of ​​the defect is reduced to kA, where k is the proportional coefficient. Then the temperature T′ at the defect is:

[0012]

[0013] Therefore, the temperature difference between the normal and defective parts of the cable is ΔT:

[0014]

[0015] Step 3: Electrically heat both ends of the steel cable to be tested;

[0016] Step 4: Test the temperature of the steel cable to determine the defect location.

[0017] In step 1, the cable resistance R is determined according to the following formula (1):

[0018]

[0019] The volume of the steel cable V = LA, and the mass of the steel cable m is determined according to the following formula (2):

[0020] m=ρLA (2).

[0021] In step 2, assuming that all electrical energy is converted into thermal energy for heating the steel cable, the thermal energy E of the heating steel cable is calculated according to the following formula (3):

[0022]

[0023] When the temperature of the steel cable rises to T at normal temperature, the required heat energy E is:

[0024] E = mcT = ρLAcT (4);

[0025] Combining equations (3) and (4), the temperature T of the cable after being heated at normal position is:

[0026]

[0027] In step three, both ends of the steel cable to be tested are energized and heated by a current generator 2, and the current generator 2 controls the magnitude of the heating current according to the T and T' values ​​calculated in step two.

[0028] In step 4, the temperature distribution detection device is used to detect the steel cable and obtain the temperature distribution. During analysis, the ΔT value calculated in step 3 is combined with the temperature distribution obtained by the temperature distribution detection device to obtain the position of the defect in the steel cable.

[0029] Before the test, the temperature rise of different defect types of the steel cable is obtained through experiments, where the proportional coefficient k of different defect types of the steel cable is different. Then, in step 4, the defect type of the steel cable defect is preliminarily determined in combination with the temperature distribution obtained by the temperature distribution detection device.

[0030] The detection lens of the temperature distribution detection device is aimed at the steel cable and a distance is left between the steel cable and the steel cable.

[0031] The temperature distribution detection device is a thermal imager.

[0032] The advantages and positive effects of the present invention are:

[0033] 1. The present invention determines the defective position of the steel cable by electrically heating the steel cable and analyzing the temperature distribution of the steel cable. Defective parts of the steel cable, such as broken wires, rust and abnormal stretching, will cause the local resistance of the steel cable to increase, while the current passing through all cross sections of the steel cable is equal. It can be seen from Ohm's law that the increase in the local resistance of the steel cable will increase the thermal power generated by the current at that location, thereby causing the temperature at that location to be significantly higher than other locations. Therefore, by analyzing the collected temperature distribution data of the steel cable, the defective points can be easily found, and the detection can be accurate.

[0034] 2. During detection by the present invention, since the change in the local resistance of the steel cable is the resistance of the entire cross section at the damaged part, the abnormal heating occurs on the entire cross section. Therefore, even if the damaged part is away from the lens of the temperature distribution detection device, the temperature distribution detection device can still capture the temperature anomaly at this place. Therefore, the detection operation is simple and convenient, and there is a certain distance between the temperature distribution detection device and the steel cable. The original state of the steel cable can be not affected during detection, such as there is no need to interrupt the normal use of the steel cable, and detection can also be performed when the steel cable is covered with oil or a protective layer.

[0035] 3. When detecting, the present invention can determine the temperature rise of different defect types of steel cables (broken wires, rust, abnormal stretching and other defect types have different cross-sectional areas, that is, different k values) through experiments in advance. In this way, when analyzing the temperature distribution of the steel cable later, the type of defect can be preliminarily judged based on the specific temperature rise.

[0036] 4. Considering that excessively high temperature of the steel cable may have an adverse effect on the mechanical properties of the steel cable, the present invention can obtain the temperature values ​​T and T′ of the normal and defective parts of the steel cable to be tested through calculation and analysis before testing, and can control the heating temperature of the steel cable accordingly, thereby ensuring that the test will not affect the performance of the steel cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram of the process of the present invention,

[0038] Figure 2 This is a schematic diagram of an embodiment of the system for detecting the temperature of a steel cable according to the present invention.

[0039] Figure 3 This is a schematic diagram of the temperature distribution of a steel cable obtained according to an embodiment of the present invention.

[0040] Among them, 1 is a steel cable, 2 is a current generator, 3 is a processor, and 4 is a temperature distribution detection device. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings.

[0042] In order to simplify the calculation model, the present invention simplifies the steel cable into a solid steel rod and assumes that no heat exchange is performed with the air during electric heating.

[0043] like Figure 1 As shown, the method of the present invention comprises the following steps:

[0044] Step 1: Determine the parameters of the steel cable to be tested, including the length L of the steel cable, the cross-sectional area A of the steel cable, the resistivity ε of the steel cable, and the density ρ of the steel cable, and determine the resistance R of the steel cable according to the following formula (1):

[0045]

[0046] The volume of the steel cable V = LA, and the mass of the steel cable m is determined according to the following formula (2):

[0047] m = ρLA (2);

[0048] Step 2: Calculate the temperature difference between the normal and defective parts of the steel cable. Assume that the current I is passed through both ends of the steel cable for a power-on time of t, and assume that all electrical energy will be converted into heat energy for heating the steel cable. Calculate the heat energy E of the heating steel cable according to the following formula (3):

[0049]

[0050] Assuming that the temperature of the cable rises by T when it is electrically heated, and the specific heat capacity is c, the heat energy E required for the temperature rise of the cable at normal location is:

[0051] E = mcT = ρLAcT (4);

[0052] Combining equations (3) and (4), the temperature T of the cable after being heated at normal position is:

[0053]

[0054] If there is a defect in the steel cable, so that its cross-sectional area is reduced to kA, k is the proportional coefficient, then the temperature T' at the defect of the steel cable is:

[0055]

[0056] Therefore, the temperature difference change value ΔT between the normal and defective parts of the cable is:

[0057]

[0058] Assume that the resistivity of the steel cable is 7.2×10 -7 Ωm, density is 7.85g / cm 3 , the specific heat capacity is 500J / kg℃, if the cable heating current is 30A, the heating time is 6 minutes, and the cable diameter is 10mm, the cross-sectional area is 78.5mm 2 When the cross-sectional area of ​​the defective part of the steel cable becomes 4 / 5 of the original (k=4 / 5), it is calculated that the temperature rise of the normal part of the steel cable is 9.6°C, the temperature rise of the defective part is 15.0°C, and the temperature difference ΔT is 5.4°C. The existing temperature measurement equipment can easily identify this temperature difference.

[0059] Step 3: Heat both ends of the steel cable to be tested. Figure 2As shown, in one embodiment of the present invention, a current generator 2 is used to heat the steel cable 1 to be tested, and the two ends of the current generator 2 are respectively connected to the two ends of the steel cable 1 through wires. The current generator 2 can adjust the control current size according to actual needs (mainly according to the temperature of the steel cable). The current generator 2 is a well-known technology in the art and is a commercially available product.

[0060] Step 4: Test the temperature of the steel cable to determine the defect location.

[0061] In one embodiment of the present invention, the temperature distribution detection device 4 can be used to detect the steel cable 1. Figure 2 As shown, the temperature distribution detection device 4 and the current generator 2 are connected to the processor 3 through lines respectively, the detection lens of the temperature distribution detection device 4 is aimed at the steel cable 1, and the temperature distribution detection device 4 is driven by a moving mechanism (or a person holding it) to move along the length direction of the steel cable 1 for detection. Since the change of the local resistance of the steel cable 1 is the resistance of the entire cross section of the damaged part, the abnormal heating occurs on the entire cross section. Therefore, even if the damaged part is away from the lens of the temperature distribution detection device 4, the temperature distribution detection device 4 can still capture the temperature anomaly. After the temperature distribution detection device 4 completes the temperature data acquisition, it is processed by the processor 3 to obtain Figure 3 In the temperature distribution diagram shown, an abnormal temperature peak can be clearly seen at A, which is the defect of the steel cable 1. In this embodiment, the data ΔT obtained in the above step 3 is combined with the detection result of the temperature distribution detection device 4 to obtain the accurate defect position of the steel cable 1, and the temperature rise of different defect types (different k values) of the steel cable 1 obtained in advance can also be combined. Figure 3 The type of defect at that location is preliminarily determined. In addition, considering that too high a temperature of the steel cable may have an adverse effect on the mechanical properties of the steel cable, the present invention first obtains the temperature difference T and T′ between the normal location and the defect location of the steel cable 1 to be tested through calculation and analysis of the above steps one to three before testing. The heating temperature of the steel cable 1 can then be controlled accordingly to ensure that the test will not affect the performance of the steel cable.

[0062] In this embodiment, it is only necessary to energize both ends of the steel cable 1, and then use the temperature distribution detection device 4 to perform the detection. The entire operation is simple and convenient, and there is a certain distance between the temperature distribution detection device 4 and the steel cable 1. The detection can be carried out without affecting the original state of the steel cable 1, such as without interrupting the normal use of the steel cable 1, and the detection can also be carried out when the steel cable 1 is covered with oil or a protective layer (not heat-insulated). The temperature distribution detection device 4 is a well-known technology in the art and is a commercially available product, such as a thermal imager purchased on the market. In addition, the calculation and analysis of steps one to three can be achieved through relevant software or programming, which is a well-known technology in the art.

[0063] In another embodiment of the present invention, the temperature of the steel cable 1 can also be detected using a temperature measuring optical fiber. Specifically, the temperature measuring optical fiber is bonded to the surface of the steel cable 1 using a thermal conductive adhesive, and the optical fiber and the steel cable 1 are sheathed together using a protective sleeve. The temperature distribution measurement of the entire length of the temperature measuring optical fiber is performed using the Raman or Brillouin distributed temperature detection principle, and the temperature mutation point is detected and located. This is a well-known technology in the art. For example, a Chinese invention patent with authorization announcement number CN101532973B discloses a method for detection using a temperature measuring optical fiber. However, this method is for the protective jacket of the steel cable, and the principle of temperature mutation is as follows: when a damage point of the protective jacket appears, the temperature isolation effect of the protective layer is destroyed, and aqueous substances invade the interior of the cable. The aqueous substances evaporate under the sun, and the temperature at the damage point of the protective jacket will change significantly, thereby generating a temperature mutation point.

Claims

1. A wire rope defect detection method, characterized in that: The steps include: Step 1: Determine the parameters of the steel cable to be tested, including the length L of the steel cable, the cross-sectional area A of the steel cable, the resistivity ε of the steel cable, the density ρ of the steel cable, the resistance R of the steel cable, the mass m of the steel cable, and the specific heat capacity c of the steel cable; Step 2: Calculate the temperature difference between the normal and defective parts of the steel cable; Assuming that the current I is passed through both ends of the cable and the power-on time is t, the temperature T that rises after the cable is heated at normal position is: If there is a defect in the steel cable, the cross-sectional area of ​​the defect is reduced to kA, where k is the proportional coefficient. Then the temperature T′ at the defect is: Therefore, the temperature difference between the normal and defective parts of the cable is ΔT: Step 3: Electrically heat both ends of the steel cable to be tested; Step 4: Test the temperature of the steel cable to determine the defect location.

2. The wire rope defect detection method according to claim 1, characterized in that: In step 1, the cable resistance R is determined according to the following formula (1): The volume of the steel cable V = LA, and the mass of the steel cable m is determined according to the following formula (2): m=ρLA (2).

3. The wire rope defect detection method according to claim 1, characterized in that: In step 2, assuming that all electrical energy is converted into thermal energy for heating the steel cable, the thermal energy E of the heating steel cable is calculated according to the following formula (3): When the temperature of the steel cable rises to T at normal temperature, the required heat energy E is: E = mcT = ρLAcT (4); Combining equations (3) and (4), the temperature T of the cable after being heated at normal position is:

4. The wire rope defect detection method according to claim 1, characterized in that: In step three, both ends of the steel cable to be tested are energized and heated by a current generator 2, and the current generator 2 controls the magnitude of the heating current according to the T and T' values ​​calculated in step two.

5. The wire rope defect detection method according to claim 1, characterized in that: In step 4, the temperature distribution detection device is used to detect the steel cable and obtain the temperature distribution. During analysis, the ΔT value calculated in step 3 is combined with the temperature distribution obtained by the temperature distribution detection device to obtain the location of the steel cable defect.

6. The wire rope defect detection method according to claim 5, characterized in that: Before the test, the temperature rise of different defect types of the steel cable is obtained through experiments, where the proportional coefficient k of different defect types of the steel cable is different. Then, in step 4, the defect type of the steel cable defect is preliminarily determined based on the temperature distribution obtained by the temperature distribution detection device.

7. The wire rope defect detection method according to claim 5, characterized in that: The detection lens of the temperature distribution detection device is aimed at the steel cable and a distance is left between the steel cable and the steel cable.

8. The wire rope defect detection method according to claim 5, characterized in that: The temperature distribution detection device is a thermal imager.

Images