Ball mill ultrasonic bolt monitoring device and monitoring method

Abstract

The invention relates to the field of equipment state monitoring, in particular to a ball mill ultrasonic bolt monitoring device and method. The device comprises an ultrasonic monitoring module, a signal processing module, a data transmission module, an upper computer monitoring platform and a power supply module. The ultrasonic monitoring module comprises an ultrasonic probe and an EMAT sensor; the signal processing module comprises a filter circuit, an amplification circuit, an algorithm chip and a vibration sound modulation analysis unit; the data transmission module is in communication connection with the signal processing module, and the data transmission module comprises a WIFI / Lora communication module and a data encryption unit; the upper computer monitoring platform is in communication connection with the data transmission module; the power supply module supplies power to the ultrasonic monitoring module, the signal processing module and the data transmission module. According to the invention, on-line monitoring of conventional bolts is realized, the monitoring efficiency is high, the cost is low, ultrasonic signals can be stably transmitted and accurately received, the signal stability is improved, and multi-directional load measurement and loose state monitoring of the bolts can be realized.

Description

TECHNICAL FIELD

[0001] The application relates to the field of equipment state monitoring, in particular to a ball mill ultrasonic bolt monitoring device and a monitoring method. BACKGROUND

[0002] In the mining industry, as a key crushing equipment, the ball mill is prone to wear, looseness and even fracture of the lining bolt under huge pressure and vibration, which directly affects the stable operation of the equipment. The current mainstream bolt monitoring technology has the following problems:

[0003] 1. Manual measurement method: the ball mill needs to be stopped first, and then the inside of the equipment is manually measured after cooling. This method is time-consuming and labor-intensive, and has low measurement efficiency and small data volume.

[0004] 2. Laser three-dimensional scanning method: the measurement accuracy can be improved, but the operation needs to be stopped, and the data post-processing steps are complicated and time-consuming, which affects the equipment operation rate.

[0005] 3. Intelligent bolt online monitoring method: it can be monitored without stopping, but it needs to use customized bolts, and the sensors, signal transmitters and batteries are integrated in the customized bolts. The cost of the customized bolts is high, resulting in high cost for enterprises.

[0006] 4. Traditional ultrasonic offline measurement method: the ball mill needs to be stopped first, and then measured, but in the harsh working conditions of high vibration and complex medium, the ultrasonic signal is prone to attenuation and distortion, resulting in poor monitoring stability. SUMMARY

[0007] The application aims to solve the problems in the background art, and provides a ball mill ultrasonic bolt monitoring device and a monitoring method, which can realize online monitoring of conventional bolts, have high monitoring efficiency and low maintenance cost for enterprises, have good coupling effect of the ultrasonic probe and the bolt nut, can stably transmit and accurately receive the ultrasonic signal, can accurately judge the wear state of the bolt, can inhibit the attenuation and distortion of the ultrasonic signal in harsh working conditions, can improve the signal stability, can realize multi-directional load measurement and looseness state monitoring of the bolt, and fills the blank of the existing technology which can only measure in one direction.

[0008] In one aspect, the application provides a ball mill ultrasonic bolt monitoring device, which comprises an ultrasonic monitoring module, a signal processing module, a data transmission module, an upper computer monitoring platform and a power supply module.

[0009] The ultrasonic monitoring module comprises an ultrasonic probe and an EMAT (Electromagnetic Acoustic Transducer) sensor, the ultrasonic probe is integrated with a temperature sensor, the ultrasonic probe is glued to the top end face of the nut, the ultrasonic probe collects internal longitudinal wave reflection signals of the bolt, three EMAT sensors are evenly distributed in the circumference of the nut, the EMAT sensors are glued to the outer circumferential surface of the nut and have a spacing from the surface of the nut, and the EMAT sensors collect time difference data of the longitudinal wave reflection signals and bolt vibration displacement signals;

[0010] The signal processing module is in communication connection with the ultrasonic monitoring module, the signal processing module comprises a filter circuit, an amplification circuit, an algorithm chip and a vibration sound modulation analysis unit, the filter circuit filters original signals collected by the ultrasonic monitoring module, the amplification circuit enhances the signal strength after filtering, the algorithm chip calculates the bolt wear amount, and the vibration sound modulation analysis unit analyzes the bolt loosening degree;

[0011] The data transmission module is in communication connection with the signal processing module, and the data transmission module comprises a WIFI / Lora communication module and a data encryption unit;

[0012] The upper computer monitoring platform is in communication connection with the data transmission module, the upper computer monitoring platform is loaded with a bolt monitoring software, and the bolt monitoring software comprises a warning module and a data storage unit; the bolt monitoring software displays bolt length, temperature, elongation and load data in real time, generates a trend curve, pre-sets wear and loosening thresholds, and triggers an audible and light alarm when the monitoring result exceeds the thresholds;

[0013] The power supply module supplies power to the ultrasonic monitoring module, the signal processing module and the data transmission module.

[0014] Preferably, the spacing between the EMAT sensor and the surface of the nut ranges from 0.5 mm to 0.1 mm.

[0015] Preferably, the periphery of the ultrasonic probe and the periphery of the EMAT sensor are coated with silicone sealant.

[0016] Preferably, the working temperature of the ultrasonic probe ranges from -40 DEG C to 85 DEG C, the load measurement coverage of the EMAT sensor is greater than or equal to 98%, and the signal stability is greater than or equal to 97%.

[0017] Preferably, the transmission frequency of the data transmission module is 42 Hz for a single channel, and is allocated according to 42 Hz / channel number for multiple channels.

[0018] In another aspect, the application provides a ball mill ultrasonic bolt monitoring device.

[0019] S1, preliminary preparation and calibration:

[0020] Bolt calibration: Measure the initial length of the bolt in the shutdown state of the ball mill, send calibration instructions through the host computer monitoring platform, and record the ultrasonic flight time T0 in the free state of the bolt;

[0021] Sensor installation: Install the ultrasonic probe and EMAT sensor on the target position of the nut by adhesive method, and check the coupling state;

[0022] System debugging: Connect the modules in the device, set the warning threshold: wear threshold is 1.5mm, loosening modulation coefficient threshold is 0.8, and pretightening force threshold is 100kN; Test signal transmission stability, adjust the ultrasonic probe gain to 20dB, and ensure that the signal-to-noise ratio is greater than or equal to 30dB;

[0023] S2, Real-time monitoring and signal collection:

[0024] The ultrasonic probe emits 2MHz longitudinal wave signals, and the EMAT sensor synchronously receives the reflected signals at the bottom of the bolt. The temperature sensor collects the environmental temperature every 10s;

[0025] S3, Signal processing and data calculation:

[0026] Temperature compensation: According to the collected temperature t, the sound velocity is corrected by the formula v=v0×(1+α×t), where v0 is the longitudinal wave propagation velocity of ultrasonic wave in 45# steel at 25℃, which is 5900m / s, and α is the thermal expansion coefficient of 45# steel, which is 11.5×10 -6 / ℃;

[0027] Wear calculation: The signal processing module calculates the current flight time T1 of the bolt through the algorithm chip, and the wear is ΔL=(T1-T0)×v / 2;

[0028] Looseness degree judgment: The vibration sound modulation analysis unit inputs 5-50Hz low-frequency vibration signal and 2MHz high-frequency ultrasonic signal, calculates the loosening modulation coefficient β=(A_max-A_min) / (A_max+A_min), and A_max is the maximum amplitude of the mixed signal, and A_min is the minimum amplitude of the mixed signal;

[0029] S4, Data transmission and intelligent early warning:

[0030] Data encryption and transmission: The data transmission module encrypts the monitoring data through AES-128, and uploads it to the host computer monitoring platform at a frequency of 42Hz per channel;

[0031] Warning Trigger: The host computer monitoring platform compares the data with the threshold in real time. If ΔL > 1.5mm or β > 0.8, an audible and visual alarm is immediately triggered, and the warning information is pushed to the central control DCS (Distributed Control System) screen and the mobile phone of maintenance personnel.

[0032] Data storage: The data storage unit automatically stores historical data and supports export in Excel format for fault tracing and maintenance strategy optimization.

[0033] Preferably, the ultrasonic signal acquisition frequency is consistent with the data transmission frequency, and at least 420 data points are acquired every 10 seconds in single-channel mode to ensure measurement stability.

[0034] Preferably, when β∈[0.3,0.5], the bolt is slightly loose; when β∈(0.3,0.5], the bolt is moderately loose; and when β>0.8, the bolt is severely loose.

[0035] Compared with the prior art, the present invention has the following beneficial technical effects:

[0036] This invention enables non-stop online monitoring of conventional bolts on ball mills, providing enterprises with high efficiency and low maintenance costs for monitoring bolt loosening. The ultrasonic probe exhibits excellent coupling with the bolt and nut, ensuring stable transmission and accurate reception of ultrasonic signals. This allows for precise judgment of bolt wear conditions, suppresses ultrasonic signal attenuation and distortion under harsh operating conditions, and improves signal stability. Furthermore, the use of EMAT non-contact measurement and array longitudinal and transverse wave technology enables accurate measurement of bolt strain and multi-directional loads. Integrated temperature compensation and signal noise reduction design adapts to the harsh environment of ball mills and provides real-time warnings of bolt wear and loosening faults, preventing equipment damage or personnel injury caused by bolt breakage and ensuring production safety. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the ultrasonic bolt monitoring device for ball mills according to the present invention. Detailed Implementation

[0038] Example 1

[0039] like Figure 1 As shown in this embodiment, an ultrasonic bolt monitoring device for a ball mill includes an ultrasonic monitoring module, a signal processing module, a data transmission module, a host computer monitoring platform, and a power supply module.

[0040] The ultrasonic monitoring module comprises an ultrasonic probe and an EMAT sensor, the ultrasonic probe is integrated with a temperature sensor, the working temperature range of the ultrasonic probe is -40 DEG C to 85 DEG C, the ultrasonic probe is glued on the top end face (exposed end face center) of the nut, the position is flat without protrusion, and the longitudinal wave signal coupling efficiency can be maximized. The ultrasonic probe collects the longitudinal wave reflection signal inside the bolt. The load measurement coverage of the EMAT sensor is ≥98%, the signal stability is ≥97%, and the EMAT sensor is uniformly distributed in three positions around the nut, that is, uniformly distributed at an angle interval of 120 DEG along the cylindrical outer side of the nut (corresponding to 0 DEG, 120 DEG and 240 DEG angles respectively). The EMAT sensor is glued on the outer circumferential surface of the nut, and there is a spacing between the EMAT sensor and the nut surface, the spacing range is 0.5mm±0.1mm, and the vibration transmission interference signal is avoided. The EMAT sensor collects time difference data of the longitudinal wave reflection signal and the bolt vibration displacement signal.

[0041] The specific installation mode of the ultrasonic probe and the EMAT sensor is as follows:

[0042] Ultrasonic probe installation: first step, glue layer smearing: evenly smear high-temperature resistant epoxy glue on the center area (diameter 20mm, matched with the ultrasonic probe base) of the top of the nut with a glue scraper, and the glue layer thickness is strictly controlled to be 0.5mm (excessive thickness will cause the probe to tilt, and insufficient thickness will cause poor fitting), and the glue layer is ensured to be free of bubbles and gaps. Second step, probe positioning and pressing: use tweezers to hold the ultrasonic probe, cover the glue layer area with the bottom surface (signal collection surface) of the ultrasonic probe, and gently press the probe for 30 seconds (pressure about 5N, avoid excessive force to cause glue extrusion), ensure that the ultrasonic probe and the top of the nut have no gap, and the fitting degree meets the standard. Third step, preliminary curing and sealing: place for 2 hours to allow the epoxy glue to be preliminarily cured, and then smear silicone sealant around the ultrasonic probe (combined edge with the nut) with a glue scraper to form a 5mm wide and 2mm thick annular protection ring. The protection ring needs to completely wrap the edge of the ultrasonic probe base, and does not block the signal collection surface of the ultrasonic probe. The center 15mm range of the probe is the effective collection area and needs to be exposed. Fourth step, complete curing: stand for 24 hours to allow the epoxy glue and the sealant to be completely cured, and the hardness of the glue layer after curing is ≥80Shore D, avoid touching the probe during the period, and gently pull the probe with your hand after curing, that is, the installation is completed.

[0043] EMAT sensor installation: First step, installation point marking: use a protractor to mark three installation points on the side surface of the nut, with the center of the top end surface of the nut as the reference point. The first point is aligned with the "0° scale line" on the top end surface of the nut, and the other two points are measured 120° to the left and right, respectively. The size of each installation point is 15mm x 10mm (matching the EMAT sensor base), and the marking line must be clear and have an error of ≤±1° to ensure that the multi-directional load measurement has no directional deviation. Second step, glue layer application: Apply Acrylic adhesive (3M DP460) to the edge area (non-central collection area) of each marked point. The glue layer thickness is 0.3mm (only used to fix the sensor, not to support the spacing), and the glue layer range is the four corners of the installation point (glue layer width 2mm). The central 5mm x 5mm area is a "glue-free area" (to avoid the glue layer contacting the sensor collection surface). Third step, spacing control and sensor fixation: Place a 0.5mm thick polytetrafluoroethylene gasket (gasket size 5mm x 5mm, covering the collection area) in the "glue-free area" of each installation point. Use tweezers to hold the EMAT sensor, align the sensor bottom surface (collection surface) with the gasket above, and gently place it on the glue layer. At this time, the sensor is supported by the gasket, maintaining a 0.5mm spacing with the side surface of the nut. Gently press the edge of the sensor (non-collection area) for 10 seconds to ensure that the glue layer adheres to the edge of the sensor. Then remove the gasket, which is only used for positioning and is maintained by the cured glue layer after removal. Fourth step, sealing and curing: Let the Acrylic adhesive cure for 2 hours, then apply silicone sealant to the edge of each sensor (where it meets the nut) to form a 3mm wide, 1mm thick protective layer (covering the glue layer area, not covering the sensor collection surface). Let it stand for 24 hours to fully cure. After curing, use a feeler gauge to measure the spacing between the sensor and the nut to ensure that the spacing between the three sensors and the side surface of the nut is 0.5mm ± 0.1mm. If the spacing is out of tolerance, it needs to be adjusted again.

[0044] The signal processing module and the ultrasonic monitoring module are communicatively connected, specifically through a shielded cable. The signal processing module includes a filter circuit, an amplification circuit, an algorithm chip, and a vibration acoustic modulation analysis unit. The filter circuit filters the raw signals collected by the ultrasonic monitoring module. The amplification circuit enhances the intensity of the filtered signals. The algorithm chip calculates the bolt wear, by comparing the time difference between the free state (time difference T0) and the fastened state (time difference T1) of the bolt, and combining the mechanical longitudinal wave propagation speed v, the bolt wear ΔL = (T1-T0) x v / 2 is calculated. The vibration acoustic modulation analysis unit inputs low-frequency sinusoidal vibration signals and high-frequency ultrasonic signals to analyze the degree of bolt loosening through signal mixing.

[0045] The algorithm chip and the vibration acoustic modulation analysis unit are welded in the form of "circuit module" on the PCB board of the signal processing module, together with the filter, amplification and other circuits to form an independent signal processing box with an IP65 protection level, suitable for ball mill dust environment.

[0046] The signal processing module is fixed on the rack of the ball mill near the bolt monitoring point, such as within a distance of 1-2 mm from the monitoring bolt, to avoid attenuation caused by excessively long lines during signal transmission. When fixed, the bolt is fixed through a metal bracket, the bracket is insulated from the rack to reduce vibration conduction, and a shock-absorbing pad with a thickness of 5 mm is installed at the bottom of the box, which is made of rubber material and is suitable for high-vibration working conditions of the ball mill.

[0047] The "low-frequency sinusoidal vibration signal (5-50 Hz) and high-frequency ultrasonic signal (2 MHz)" output by the vibration tone modulation analysis unit is not directly acting on the bolt body, but is indirectly coupled to the bolt through the ultrasonic probe and the EMAT sensor. The specific action process and principle are as follows: 1. Signal output and transmission: the double signals (low frequency and high frequency) generated by the unit are first transmitted to the ultrasonic probe (high-frequency signal) and the EMAT sensor array (low-frequency vibration signal) through the "signal output interface" (shielded cable connection) of the signal processing module; during transmission, the "impedance matching circuit" ensures that the signal is not reflected and attenuated (such as high-frequency ultrasonic signal transmission impedance matching to 50Ω, consistent with the impedance of the ultrasonic probe). 2. Signal coupling to the bolt: for high-frequency ultrasonic signals: the piezoelectric ceramic sheet of the ultrasonic probe (fixed on the top of the nut) generates mechanical vibration, which is coupled to the nut through epoxy glue and then transmitted to the inside of the bolt, forming a longitudinal wave propagating along the screw rod; for low-frequency vibration signals: the electromagnetic coil of the EMAT sensor array generates an alternating magnetic field, which induces eddy currents on the surface of the bolt (metal conductor), and the eddy currents interact with the magnetic field to produce low-frequency mechanical vibration, which indirectly acts on the bolt without physical contact; both coupling methods are "non-direct contact / indirect contact", which avoids interference with the state of the bolt when the signal is output (such as directly applying mechanical vibration to change the free state of the bolt, affecting the reference values of T0 and v0), while ensuring that the signal can be effectively transmitted to the inside of the bolt to meet the monitoring requirements. 3. Core target of signal action: the output double signals do not change the state of the bolt, but excite the bolt to produce monitorable signal characteristics, the high-frequency signal is used to measure the speed and length (wear calculation); the low-frequency signal is mixed with the high-frequency signal to extract the loosening characteristics (modulation coefficient β calculation); both of them realize "wear and loosening measurement at the same time with the same sensor", which is fully compatible with the integrated design of the signal processing module.

[0048] The data processing flow of the signal processing module is branch processing and collaborative calculation:

[0049] First step, signal acquisition and preliminary branch:

[0050] Ultrasonic longitudinal wave probe: collect "bolt internal longitudinal wave reflection signal" (used for calculating wear); integrated temperature sensor collects "environmental temperature data";

[0051] EMAT sensor array: collect "time difference data of longitudinal wave reflection signal" (auxiliary algorithm chip correction multi-directional load effect), "bolt vibration displacement signal" (for vibration acoustic modulation analysis);

[0052] Second step, unified filtering and amplification:

[0053] All original signals (longitudinal wave signal, temperature signal, vibration displacement signal) first enter the filter circuit (second-order Butterworth low-pass filter, cutoff frequency 200Hz), suppress the ball mill motor vibration (50-150Hz) and dust interference noise; The filtered data is then amplified by the amplification circuit (gain 20dB) to enhance the signal strength, ensuring that weak signals (such as small changes in longitudinal wave time difference caused by wear) can be recognized by subsequent modules;

[0054] Third step, branch calculation and processing:

[0055] Wear calculation branch: "longitudinal wave reflection signal" (from ultrasonic probe and EMAT sensor time difference correction) and "temperature data" after filtering and amplification are input into the algorithm chip, and the bolt wear is calculated through the formula ΔL = (T1-T0) x v / 2 (v is modified by temperature compensation) ;

[0056] Looseness judgment branch: the "bolt vibration displacement signal" after filtering and amplification is input into the vibration acoustic modulation analysis unit for separate looseness degree quantitative analysis (parallel processing with the algorithm chip, not in series).

[0057] The core function of the vibration acoustic modulation analysis unit is to quantify the looseness degree of the bolt, filling the monitoring gap of "only measuring wear / load". This unit is a separate analysis module designed specifically for "bolt looseness", which realizes accurate judgment of looseness degree through "active excitation and signal mixed analysis". The specific functions and principles are as follows:

[0058] Core function: distinguish "slight / moderate / severe" looseness, avoid false positives of single threshold, algorithm can only reflect "wear" through bolt length change, EMAT time difference can only reflect "load change", both cannot directly judge "whether the bolt is loose and the looseness degree" (such as the bolt is not worn but the thread engagement gap appears due to vibration, there is no obvious change in existing parameters).

[0059] Working principle: "Dual signal mixing and modulation coefficient calculation", the unit realizes looseness judgment through two key steps: 1, active excitation: input two signals to the bolt-nut system, low-frequency sinusoidal vibration signal (5-50Hz, simulate the actual vibration of the ball mill, high-frequency ultrasonic signal 2MHz, match the frequency of the ultrasonic probe to ensure signal compatibility); 2, signal analysis: collect the mixed "modulation signal", calculate its amplitude maximum (A_max) and minimum (A_min), and get the modulation coefficient through the formula β=(A_max-A_min) / (A_max+A_min); 3, logical association: bolt looseness will cause the increase of thread engagement gap, the amplitude fluctuation (A_max and A_min difference) of mixed signal will increase accordingly, and the value of β will also increase, so the looseness degree can be judged reversely through the numerical interval of β (experimental verification: when the bolt is from fastening to severe looseness, the value of β increases from 0.2 to 1.0, and the linear correlation reaches 95%).

[0060] Coordination with other modules: the "looseness modulation coefficient β" output by the unit will be transmitted to the upper computer together with the "wear amount ΔL" output by the algorithm and the "load data" output by the EMAT, and the bolt state will be judged comprehensively through the three, for example: when ΔL does not exceed the threshold value (no obvious wear) but β>0.8 (severe looseness), the system will still trigger an early warning to avoid bolt fracture accidents caused by misjudgment of a single parameter.

[0061] The data transmission module is in communication connection with the signal processing module, and is connected through an SPI interface in particular. The data transmission module includes a WIFI / Lora communication module and a data encryption unit, supports wireless / wired transmission, and can customize communication protocols. The transmission frequency of the data transmission module is 42Hz per single channel, and when multiple channels are used, the frequency is allocated as 42Hz per channel number. Real-time transmission data values are monitored on a host computer monitoring platform.

[0062] The host computer monitoring platform is in communication connection with the data transmission module, and is connected wirelessly / wiredly in particular. The host computer monitoring platform is equipped with a bolt monitoring software including an early warning module and a data storage unit. The bolt monitoring software displays bolt length, temperature, elongation and load data in real time, and generates a trend curve. The wear and looseness thresholds are set in advance, and when the monitoring results exceed the thresholds, an audible and visual alarm is triggered and pushed to a central control DCS or a mobile phone. The data storage unit stores historical data, supports data export and fault tracing.

[0063] The power supply module supplies power to the ultrasonic monitoring module (3.3V), the signal processing module (5V) and the data transmission module (5V) through a DC-DC voltage stabilizing circuit. In normal working conditions, an external power supply is used for power supply, and when there is no external power supply, a lithium battery is used for power supply.

[0064] Example two

[0065] The embodiment provides a ball mill ultrasonic bolt monitoring method, which is implemented through the ball mill ultrasonic bolt monitoring device in embodiment one as shown in the figure. Figure 1 The method comprises the following steps S1-S4.

[0066] S1, preliminary preparation and calibration:

[0067] Bolt calibration: in the shutdown state of the ball mill, the initial length (such as 150 mm) of the bolt is measured, a calibration instruction is sent through the upper computer monitoring platform, and the ultrasonic flight time T0 in the free state of the bolt is recorded, for example, 2000 ns; the propagation speed v0 of the ultrasonic wave in 45# steel is 5900 m / s; 45# steel is a commonly used material for ball mill bolts, which is a high-quality carbon structural steel with moderate strength and good machinability.

[0068] Sensor installation: the ultrasonic probe and the EMAT sensor are installed on the target position on the nut through the adhesive method, and the coupling state is checked.

[0069] System debugging: connect the modules in the device, set the early warning threshold value: the wear amount threshold value is 1.5 mm, the loosening modulation coefficient threshold value is 0.8, and the pretightening force threshold value is 100 kN; test the signal transmission stability, adjust the ultrasonic probe gain to 20 dB, and ensure that the signal-to-noise ratio is greater than or equal to 30 dB.

[0070] S2, real-time monitoring and signal collection:

[0071] The ultrasonic probe emits a 2 MHz longitudinal wave signal, the collection frequency of the ultrasonic signal is consistent with the data transmission frequency, at least 420 data points are collected per 10 s in a single channel, and the measurement stability is ensured. The EMAT sensor synchronously receives the reflected signal at the bottom of the bolt. The bottom refers to the end position of the screw rod away from the bolt head. When the bolt and the nut are assembled and installed on the ball mill device, the bolt passes through the device base (for example, a liner, a rack), and the bottom of the bolt is in contact with the inner side surface of the device base or a gasket. The end face is the key position of the ultrasonic signal reflection. The temperature sensor collects the environmental temperature (in the range of-40℃-85℃) once per 10 s.

[0072] S3, signal processing and data calculation:

[0073] Temperature compensation: according to the collected temperature t, the sound speed is corrected through the formula v=v0× (1+α×t), wherein v0 is the longitudinal wave propagation speed of the ultrasonic wave in 45# steel at 25℃, which is 5900 m / s, and α is the thermal expansion coefficient of 45# steel, which is 11.5×10 -6 / ℃.

[0074] Wear amount calculation: the signal processing module calculates the current flight time T1 of the bolt through an algorithm chip, and the wear amount is ΔL=(T1-T0)×v / 2.

[0075] Looseness degree judgment: the vibration sound modulation analysis unit inputs 5-50Hz low-frequency vibration signal and 2MHz high-frequency ultrasonic signal, and calculates the looseness modulation coefficient β=(A_max-A_min) / (A_max+A_min), wherein A_max is the maximum value of the amplitude of the mixed signal, and A_min is the minimum value of the amplitude of the mixed signal; the preprocessed modulation signal can clearly reflect the amplitude fluctuation, and A_max and A_min are extracted through the following steps A1-A3:

[0076] A1, amplitude calculation: the instantaneous amplitude is calculated according to the voltage amplitude of each sampling point for the preprocessed digital signal, because the signal is a sine wave, the instantaneous amplitude = √(u(t) 2 +i(t) 2 ), wherein u(t) is the real part of the voltage, and i(t) is the imaginary part, which is obtained by Hilbert transform, to obtain a "time-amplitude" curve (the horizontal coordinate is time, and the vertical coordinate is amplitude, unit: mV);

[0077] A2, extreme value identification: in the "time-amplitude" curve, all amplitude peak values are identified and recorded by traversing the entire acquisition period (100ms) through the "sliding window extreme value detection algorithm" (the window size is set to 100 sampling points, about 0.01ms, to avoid missing detection), in the traversal process, if the amplitude of a sampling point is greater than the amplitudes of the previous and subsequent 50 sampling points, it is determined as a "local maximum value"; if the amplitude of a sampling point is less than the amplitudes of the previous and subsequent 50 sampling points, it is determined as a "local minimum value";

[0078] A3, determination of A_max and A_min: the "maximum value" is selected from all local maximum values, which is A_max; the "minimum value" is selected from all local minimum values, which is A_min, for example: the local maximum values of the preprocessed signal are 5mV, 5.2mV and 4.9mV, and the local minimum values are 1.8mV, 1.9mV and 1.7mV, then A_max=5.2mV and A_min=1.7mV;

[0079] S4, data transmission and intelligent early warning:

[0080] Data encryption and transmission: the data transmission module transmits the monitoring data by AES-128 encryption, and uploads to the upper computer monitoring platform at a frequency of 42Hz single channel;

[0081] Early warning triggering: the upper computer monitoring platform compares the data with the threshold value in real time, if ΔL>1.5mm or β>0.8, the sound and light alarm is triggered immediately, and the early warning information is pushed to the central control DCS picture and the maintenance personnel's mobile terminal;

[0082] Data storage: The data storage unit automatically stores historical data, with a storage period of ≥1 year, and supports Excel format export for fault tracing and maintenance strategy optimization.

[0083] In this monitoring method, for the judgment of the degree of bolt loosening, when β ∈ [0.3, 0.5], the bolt is slightly loose, still more than 80% engaged, and does not need to be handled immediately; when β ∈ (0.3, 0.5], the bolt is moderately loose, the engagement is reduced to 50%-80%, and needs to be checked during planned shutdown; when β > 0.8, the bolt is severely loose, the engagement is < 50%, and may break at any time, triggering an emergency warning.

[0084] The preload threshold value needs to be < 100 kN, which is a key verification condition to avoid false reporting of the β value due to interference (such as dust blocking the sensor). The preload (axial tightening force of the bolt) is derived through the multidirectional load monitoring function of the EMAT sensor array: EMAT sensors are distributed at an angle interval of 120° on the side of the nut, collecting the time difference of ultrasonic wave propagation in different directions (axial, radial, tangential) of the bolt. The signal processing module converts the "axial time difference change" collected by the EMAT sensor into an axial force value through the "ultrasonic guided wave load inversion algorithm" (parallel to the UBLV algorithm), as the bolt will produce a small axial deformation when subjected to preload, causing the propagation time of ultrasonic waves in the axial direction to be prolonged, and the deformation is linearly related to the preload (experimental data of 45# steel bolt: for every 10 kN increase in preload, the axial time difference increases by 0.2 ns), thereby inversely deducing the real-time preload.

[0085] The threshold value of preload < 100 kN is not a "single loosening determination standard", but is used to verify the authenticity of "loosening modulation coefficient β > 0.8", forming a "double condition triggering warning", the specific logic is as follows:

[0086] Simulate loosening, gradually loosen the bolts;

[0087] 1. When the preload decreases from 200 kN to 150 kN and β increases from 0.3 to 0.6, only record the data, and do not warn.

[0088] 2. When the preload decreases to 120 kN and β increases to 0.8, push the "moderate loosening reminder", and do not trigger the sound and light alarm.

[0089] 3. When the preload decreases to 95 kN (< 100 kN) and β increases to 0.82, both "preload < 100 kN" and "β > 0.8" are met, triggering an emergency warning.

[0090] The application realizes on-line monitoring of conventional bolts on the ball mill without stopping, avoids off-line measurement affecting the equipment operation rate, and has high monitoring efficiency and low maintenance cost for the ball mill bolt loosening state of the enterprise, without using high-cost intelligent bolts, only installing ultrasonic probes on conventional bolts, reducing monitoring cost by more than 60%, reducing downtime maintenance frequency, reducing equipment downtime loss, and improving enterprise economic benefits. The coupling effect of the ultrasonic probe and the bolt nut is good, the ultrasonic signal can be stably transmitted and accurately received, the accurate judgment of the bolt wear state can be realized, the attenuation and distortion of the ultrasonic signal under harsh working conditions can be inhibited, the signal stability is improved, and the EMAT non-contact measurement and array longitudinal and transverse wave technology are used, the bolt strain and multidirectional load can be accurately measured, and the blank of the prior art that can only measure in one direction is filled. The integrated temperature compensation and signal noise reduction design still maintains 1 mu m elongation accuracy, ±3% pre-tightening force accuracy (more than 50% rated pre-tightening force) under-40℃-85℃ working conditions, and is suitable for the harsh environment of the ball mill. The application can also real-time early warning of bolt wear and loosening failure, avoid equipment damage or personnel casualties caused by bolt fracture, and ensure production safety.

[0091] The embodiments of the application are described in detail above in combination with the drawings, but the application is not limited thereto, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the application.

Claims

1. An ultrasonic bolt monitoring device for a ball mill, characterized in that, include: The ultrasonic monitoring module includes an ultrasonic probe and an EMAT sensor. The ultrasonic probe integrates a temperature sensor and is glued to the top end face of the nut. The ultrasonic probe collects longitudinal wave reflection signals inside the bolt. Three EMAT sensors are evenly distributed around the nut and are glued to the outer circumference of the nut with a gap between them and the nut surface. The EMAT sensors collect the time difference data of the longitudinal wave reflection signals and the bolt vibration displacement signal. The signal processing module, which communicates with the ultrasonic monitoring module, includes a filtering circuit, an amplification circuit, an algorithm chip, and a vibration sound modulation analysis unit. The filtering circuit filters the raw signal acquired by the ultrasonic monitoring module, the amplification circuit enhances the strength of the filtered signal, the algorithm chip calculates the bolt wear, and the vibration sound modulation analysis unit analyzes the degree of bolt loosening. The data transmission module communicates with the signal processing module, including a WIFI / LoRa communication module and a data encryption unit; The host computer monitoring platform communicates with the data transmission module and is equipped with bolt monitoring software, including an early warning module and a data storage unit. The bolt monitoring software displays bolt length, temperature, elongation and load data in real time, generates trend curves, and presets wear and loosening thresholds. When the monitoring results exceed the thresholds, an audible and visual alarm is triggered. The power supply module provides power to the ultrasonic monitoring module, signal processing module, and data transmission module.

2. The ultrasonic bolt monitoring device for ball mills according to claim 1, characterized in that, The distance between the EMAT sensor and the nut surface is 0.5mm ± 0.1mm.

3. The ultrasonic bolt monitoring device for ball mills according to claim 1, characterized in that, Silicone sealant was applied to the outer periphery of both the ultrasonic probe and the EMAT sensor.

4. The ultrasonic bolt monitoring device for ball mills according to claim 1, characterized in that, The ultrasonic probe operates in a temperature range of -40℃ to 85℃, and the EMAT sensor has a load measurement coverage of ≥98% and a signal stability of ≥97%.

5. The ultrasonic bolt monitoring device for ball mills according to claim 1, characterized in that, The data transmission module has a transmission frequency of 42Hz for a single channel, and for multiple channels, the frequency is allocated as 42Hz / number of channels.

6. A method for monitoring ultrasonic bolts in a ball mill, implemented using the ultrasonic bolt monitoring device for a ball mill as described in claim 1, characterized in that... The method includes the following steps: S1. Preliminary preparations and calibration: Bolt calibration: With the ball mill stopped, measure the initial length of the bolt, send a calibration command through the host computer monitoring platform, and record the ultrasonic flight time T0 of the bolt in its free state; Sensor installation: Install the ultrasonic probe and EMAT sensor onto the target position on the nut using adhesive, and check the coupling status; System debugging: Connect the modules in the device and set the warning thresholds: wear threshold is 1.5mm, loosening modulation coefficient threshold is 0.8, and preload threshold is 100kN; test the stability of signal transmission. S2. Real-time monitoring and signal acquisition: The ultrasonic probe emits a 2MHz longitudinal wave signal, the EMAT sensor synchronously receives the reflected signal from the bottom of the bolt, and the temperature sensor collects the ambient temperature every 10 seconds. S3, Signal Processing and Data Computation: Temperature compensation: Based on the collected temperature t, the velocity of sound is corrected using the formula v = v0 × (1 + α × t), where v0 is the longitudinal wave propagation velocity of ultrasound in 45# steel at 25℃, which is 5900 m / s, and α is the thermal expansion coefficient of 45# steel, which is 11.5 × 10⁻⁶ m / s. -6 / ℃; Wear calculation: The signal processing module calculates the bolt's current flight time T1 through the algorithm chip, and the wear amount is: ΔL=(T1-T0)×v / 2; Looseness assessment: The vibration and sound modulation analysis unit inputs a 5-50Hz low-frequency vibration signal and a 2MHz high-frequency ultrasonic signal to calculate the loosening modulation coefficient β=(A_max-A_min) / (A_max+A_min), where A_max is the maximum amplitude of the mixed signal and A_min is the minimum amplitude of the mixed signal. S4. Data transmission and intelligent early warning: Data encryption and transmission: The data transmission module encrypts the monitoring data using AES-128 and uploads it to the host computer monitoring platform at a single channel frequency of 42Hz; Warning Trigger: The host computer monitoring platform compares the data with the threshold in real time. If ΔL > 1.5mm or β > 0.8, an audible and visual alarm is immediately triggered, and the warning information is pushed to the central control DCS screen and the mobile phone of the maintenance personnel. Data storage: The data storage unit automatically stores historical data.

7. The ultrasonic bolt monitoring method for ball mills according to claim 6, characterized in that, The acquisition frequency of the ultrasound signal is consistent with the data transmission frequency. In single-channel mode, at least 420 data points are acquired every 10 seconds to ensure measurement stability.

8. The ultrasonic bolt monitoring method for ball mills according to claim 6, characterized in that, When β∈[0.3,0.5], the bolt is slightly loose; when β∈(0.3,0.5], the bolt is moderately loose; and when β>0.8, the bolt is severely loose.

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