Mechanical seal with built-in acoustic emission sensor and state evaluation method

Abstract

The present application belongs to the technical field of mechanical seal design and monitoring, and particularly relates to a mechanical seal with a built-in acoustic emission sensor and a state evaluation method. The mechanical seal comprises an acoustic emission sensor, a static ring seat, a static ring installed on the static ring seat, and an acoustic emission sensor arranged in the static ring seat and matched with the static ring installed on the static ring seat. The present application has the beneficial effect that there is currently a lack of effective monitoring means for the friction and wear state of the dynamic and static friction pair of the mechanical seal, and the seal is usually identified when damage occurs, resulting in an abnormal increase in leakage and equipment shutdown. The present application directly monitors the stress wave signals generated by the contact of the dynamic and static friction pair through the built-in acoustic emission sensor, accurately monitors and judges the contact state and wear state of the mechanical seal friction pair, and provides a basis for mechanical seal failure cause analysis, operation parameter optimization, and reliability improvement.

Description

Technical Field

[0001] This invention belongs to the field of mechanical seal design and monitoring technology, specifically relating to a mechanical seal with a built-in acoustic emission sensor and a method for condition evaluation. Background Technology

[0002] Mechanical seals, as pressure-bearing boundaries, are crucial for the safe operation of large pump equipment. Experience from key nuclear power plant pumps shows that mechanical seals frequently experience abnormal wear, increased leakage, and shortened lifespan during operation. Understanding the contact state of the friction pairs and assessing the operating condition of the mechanical seal is essential for its successful operation. During operation, mechanical seals rely on a liquid film between the dynamic and static rings for cooling and lubrication. However, the state of this liquid film is affected by various factors, and existing methods for monitoring the mechanical seal's condition are limited. They cannot directly monitor abnormal friction states. This hinders timely analysis of the causes of abnormal conditions and, for critical mechanical seals, prevents timely adjustment of operating parameters based on the seal's condition to protect against damage. Summary of the Invention

[0003] The lack of effective monitoring methods for the contact state of dynamic and static friction pairs in key pump mechanical seals makes it impossible to detect abnormal operating conditions of the seal in a timely manner, leading to problems such as unclear causes of seal failure and seal damage. The purpose of this invention is to provide a mechanical seal and condition evaluation method with built-in acoustic emission sensors, which can identify abnormal contact states of mechanical seal friction pairs and achieve accurate monitoring and judgment of abnormal contact and wear of the seal friction pairs.

[0004] The technical solution of the present invention is as follows: a mechanical seal with a built-in acoustic emission sensor, including an acoustic emission sensor, a stationary ring seat, a stationary ring installed on the stationary ring seat, an acoustic emission sensor disposed inside the stationary ring seat, and the acoustic emission sensor cooperating with the stationary ring installed on the stationary ring seat.

[0005] The acoustic emission sensor and the sealing stationary ring are fitted with an interference fit to ensure that the sensor sensing end is in close contact with the mechanical seal stationary ring.

[0006] The acoustic emission sensor has a cable protection sleeve at its end, and the sensor wire of the acoustic emission sensor is built into the cable protection sleeve.

[0007] The protective sleeve is made of a soft and wear-resistant material.

[0008] The acoustic emission sensor is a small acoustic emission sensor with a diameter of 7-8 mm.

[0009] The stationary ring seat has an opening on its side end.

[0010] The acoustic emission sensor is screwed into the hole of the stationary ring seat via a thread.

[0011] A method for evaluating the condition of a mechanical seal with a built-in acoustic emission sensor includes the following steps:

[0012] Step 1: Install the mechanical seal, set the sampling rate Fs for the acoustic emission signal, and obtain the acoustic emission signal sequence X = [x1, x2, x3, ..., x] when the seal is operating normally. i ,...,x N To obtain the waveform of the acoustic emission signal during normal operation, the effective value (RMS) of the acoustic emission signal, and the kurtosis value (KUR) of the acoustic emission signal, the formula for calculating the effective value (RMS) is shown in equation (1):

[0013]

[0014] The formula for calculating the kurtosis value KUR is shown in equation (2):

[0015]

[0016] Where X = [x1, x2, x3, ..., x i ,...,x N [This refers to the sequence of acoustic emission signals acquired within the calculation window.]

[0017] Step 2: After the seal is installed, run it stably for 1 hour and check if the leakage is normal. If the leakage is normal, collect 10 minutes of acoustic emission data. If the leakage is abnormal, it means that the seal is not operating properly. Reinstall and adjust the seal and run it stably for another hour. Observe the leakage to determine if the seal is normal. Repeat the above operation until the acoustic emission signal of the seal is collected during operation.

[0018] Step 3: Using a window of length W, collect the acoustic emission signal X = [x1, x2, x3, ... x] of the mechanical seal during normal operation. i ,,.x. N The sliding motion is performed on the upper part of the mechanical seal, with a sliding length of STEP. The effective value RMS and kurtosis value KUR of the signal within the sliding window are calculated according to (1) and (2), forming a list of effective values ​​when the mechanical seal is operating normally: RMS_L = [RMS1, RMS2, ..., RMS]. k ] and the list of kurtosis values ​​KUR_L = [KUR1, KUR2, ..., KUR k ];

[0019] Step 4: Calculate the effective value list of the mechanical seal during normal operation: RMS_L = [RMS1, RMS2, ..., RMS] k The average value RMS_AVE and standard deviation RMS_σ of the mechanical seal are used to calculate the kurtosis values ​​of the mechanical seal during normal operation. The list of values ​​is KUR_L = [KUR1, KUR2, ..., KUR].k The average value KUR_AVE and standard deviation KUR_σ of the acoustic emission signal during normal operation of the mechanical seal are used to determine the effective value of the acoustic emission signal as [RMS_AVE-3*RMS_σ, RMS_AVE+3*RMS_σ], and the kurtosis value of the acoustic emission signal during normal operation of the mechanical seal is determined as [KUR_AVE-3*KUR_σ, KUR_AVE+3*KUR_σ].

[0020] Step 5: Obtain the acoustic emission signal X_new = [x1, x2, x3, ..., x] obtained from real-time monitoring. i ,...,x N ] Calculate the effective value RMS_new and the kurtosis value KUR_new; determine whether the effective value RMS_new of the real-time acquired acoustic emission signal is within the range of the effective value of acoustic emission during normal operation of the mechanical seal [RMS_AVE-3*RMS_σ, RMS_AVE+3*RMS_σ].

[0021] Step 6: If the effective value RMS_new exceeds the normal signal range, further compare whether the kurtosis value KUR_new is within the range of acoustic emission kurtosis values ​​during normal operation of the mechanical seal [KUR_AVE-3*KUR_σ, KUR_AVE+3*KUR_σ]. When both the effective value and the kurtosis value exceed the normal range, it indicates that abnormal friction has occurred in the friction pair of the mechanical seal. If only the effective value RMS_new of the acoustic emission signal exceeds the normal range, and the kurtosis value KUR_new does not exceed the normal range, it can be determined that there is an abnormal increase in energy in other parts of the equipment. There may be some abnormalities, but they are not caused by abnormal friction of the sealing friction pair.

[0022] In step 3, W takes Fs / 10 data points.

[0023] The beneficial effects of this invention are as follows: Currently, there is a lack of effective monitoring methods for the rubbing and wear state of the dynamic and static friction pairs of mechanical seals. Typically, the problem is only identified when seal damage leads to an abnormal increase in leakage, resulting in equipment downtime. This invention directly monitors the stress wave signal generated by the contact between the dynamic and static friction pairs through a built-in acoustic emission sensor, achieving accurate monitoring and judgment of the contact and wear state of the mechanical seal friction pairs. This provides a basis for analyzing the causes of mechanical seal failure, optimizing operating parameters, and improving reliability. It reduces the attenuation of weak friction signals, making it more effective in capturing abnormal friction between the dynamic and static friction pairs of mechanical seals. It directly monitors the friction state of the dynamic and static friction pairs of mechanical seals through acoustic emission signal monitoring. Abnormal friction of the mechanical seal friction pairs is judged by comparing the effective values ​​and kurtosis values, combined with acoustic emission signal waveform analysis. Attached Figure Description

[0024] Figure 1A schematic diagram of a mechanical seal for a built-in acoustic emission sensor provided by the present invention;

[0025] Figure 2 A flowchart of a mechanical seal condition evaluation method with a built-in acoustic emission sensor provided by the present invention;

[0026] Figure 3 The waveform of acoustic emission signal of the sealing friction pair under normal friction conditions;

[0027] Figure 4 This diagram shows the contact state of the friction pair when there is abnormal friction in the mechanical seal.

[0028] Figure 5 This is a diagram of the mechanical seal condition monitoring device architecture.

[0029] Figure 6 To ensure stable operation, the seal must be used to address any instability in the internal kurtosis value.

[0030] Figure 7 This is a flowchart for the management and application of online monitoring data for mechanical seals.

[0031] In the diagram: 1 Acoustic emission sensor, 2 Cable protection sleeve, 3 Thread, 4 Stationary ring seat, 5 Stationary ring. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] During normal operation, mechanical seals rely on a liquid film for lubrication and cooling between the dynamic and static friction pairs. If the state of the liquid film changes, abnormal friction will occur in the high-speed rotating dynamic and static friction pairs, releasing weak signals of abnormal friction. Acoustic emission monitoring technology, due to its high sensitivity and high-frequency response characteristics, can effectively capture these weak signals released by abnormal friction between the dynamic and static friction pairs. Based on this, this invention provides a mechanical seal with a built-in acoustic emission sensor and a method for condition evaluation.

[0034] This invention discloses a mechanical seal with a built-in acoustic emission sensor. The acoustic emission sensor used has high sensitivity and can detect the signal generated by abnormal friction of the mechanical seal friction pair. However, since the abnormal friction signal is weak and the acoustic emission sensor has high sensitivity, the acoustic emission sensor is miniaturized and built into the stationary ring seat of the mechanical seal. This can effectively reduce the interference of noise signals and collect effective abnormal friction signals of the sealing friction pair.

[0035] like Figure 1As shown, a mechanical seal with a built-in acoustic emission sensor includes an acoustic emission sensor 1, a stationary ring seat 4, and a stationary ring 5 mounted on the stationary ring seat 4. The stationary ring seat 4 has an opening on its side end. The acoustic emission sensor 1 is screwed into the hole of the stationary ring seat via threads. The acoustic emission sensor 1 and the stationary ring 5 mounted on the stationary ring seat are in close contact. The acoustic emission sensor 1 and the sealing stationary ring 5 are in an interference fit to ensure tight contact between the sensor's sensing end and the mechanical seal stationary ring 5. To prevent uneven gaps between the acoustic emission sensor 1 and the stationary ring 5, a coupling agent is applied during sensor installation to fill any potential uneven gaps between the sensor and the stationary ring. Because the stationary ring seat 4 will undergo displacement compensation during the operation of the seal, the positions of the stationary ring seat 4 and the stationary ring 5 will fluctuate, and the gap between the acoustic emission sensor 1 and the mounting structure of the left stationary ring seat 4 will change. The signal cable will experience repeated vibration and bending. To protect the acoustic emission signal cable, a cable protection sleeve 2 is installed at the end of the acoustic emission sensor 1. The sensor wire of the acoustic emission sensor 1 is built into the cable protection sleeve 2. The protection sleeve is made of a soft and wear-resistant material. Through experimental research, the signal frequency range generated by abnormal friction of the mechanical seal is obtained. Based on the frequency range, a small acoustic emission sensor 1 with a diameter of 7-8mm is designed and selected.

[0036] When the dynamic and static friction pairs of a mechanical seal experience abnormal friction, the first sign is an increase in the effective value of the acoustic emission signal. At the same time, because the sampling rate of the acoustic emission signal is very high, reaching 1MHz, and the surface of the friction pair is not a complete plane, an instantaneous impact peak can be seen in the waveform during instantaneous friction, which also manifests as an increase in the kurtosis value.

[0037] like Figure 2 As shown, a method for evaluating the condition of a mechanical seal with a built-in acoustic emission sensor includes the following steps:

[0038] Step 1: Install the mechanical seal, set the sampling rate Fs of the acoustic emission signal (Fs sampling rate is usually 1MHz), and obtain the acoustic emission signal sequence X = [x1, x2, x3, ..., x...] during normal operation of the seal. i ,...,x N To obtain the waveform of the acoustic emission signal during normal operation (e.g.) Figure 3 The effective value (RMS) and kurtosis value (KUR) of the acoustic emission signal are shown in Figure (1). The formula for calculating the effective value (RMS) is shown in Figure (1).

[0039]

[0040] The formula for calculating the kurtosis value KUR is shown in equation (2):

[0041]

[0042] Where X = [x1, x2, x3, ..., xi ,...,x N ] represents the sequence of acoustic emission signals acquired within the calculation window, where i represents the i-th signal value in the signal acquisition list, and N represents the length of the signal list.

[0043] Step 2: According to Figure 2 As stated above, after the seal is installed, it is run stably for 1 hour to check whether parameters such as leakage are normal. If the leakage is normal, acoustic emission data is collected for 10 minutes. If the leakage is abnormal, it means that the seal is not operating properly. The seal is then reinstalled and adjusted, and then run stably for another hour to observe the leakage and determine whether the seal is normal. The above operation is repeated until acoustic emission signals are collected during the operation of the seal.

[0044] Step 3: Using a window of length W (W can be Fs / 10 data points), measure the acoustic emission signal X = [x1, x2, x3, ..., x] acquired during normal operation of the mechanical seal. i ,...,x N The sliding motion is performed on the surface, with a sliding length of STEP (STEP can be FS / 40). The effective value RMS and kurtosis value KUR of the signal within the sliding window are calculated according to (1) and (2), forming a list of effective values ​​for normal operation of the mechanical seal: RMS_L = [RMS1, RMS2, ..., RMS]. k ] and the list of kurtosis values ​​KUR_L = [KUR1, KUR2, ..., KUR k ];

[0045] Step 4: Calculate the effective value list of the mechanical seal during normal operation: RMS_L = [RMS1, RMS2, ..., RMS] k The average value RMS_AVE and standard deviation RMS_σ of the mechanical seal are used to calculate the kurtosis values ​​of the mechanical seal during normal operation. The list of values ​​is KUR_L = [KUR1, KUR2, ..., KUR]. k The average value KUR_AVE and standard deviation KUR_σ of the acoustic emission signal during normal operation of the mechanical seal are used to determine the effective value of the acoustic emission signal as [RMS_AVE-3*RMS_σ, RMS_AVE+3*RMS_σ], and the kurtosis value of the acoustic emission signal during normal operation of the mechanical seal is determined as [KUR_AVE-3*KUR_σ, KUR_AVE+3*KUR_σ].

[0046] Step 3: Obtain the acoustic emission signal X_new = [x1, x2, x3, ..., x] obtained from real-time monitoring. i ,...,x N] Calculate the effective value RMS_new and the kurtosis value KUR_new; determine whether the effective value RMS_new of the real-time acquired acoustic emission signal is within the range of the effective value of acoustic emission during normal operation of the mechanical seal [RMS_AVE-3*RMS_σ, RMS_AVE+3*RMS_σ].

[0047] Step 3: If the effective value RMS_new exceeds the normal signal range, further compare whether the kurtosis value KUR_new is within the range of acoustic emission kurtosis values ​​during normal operation of the mechanical seal [KUR_AVE-3*KUR_σ, KUR_AVE+3*KUR_σ]. When both the effective value and the kurtosis value exceed the normal range, it indicates that abnormal friction has occurred in the friction pair of the mechanical seal. If only the effective value RMS_new of the acoustic emission signal exceeds the normal range, and the kurtosis value KUR_new does not exceed the normal range, it can be determined that there is an abnormal increase in energy in other parts of the equipment. There may be some abnormalities, but they are not caused by abnormal friction of the sealing friction pair.

[0048] When monitoring the condition of mechanical seals, the sampling rate of acoustic emission signals reaches 1MHz, resulting in a massive amount of monitoring data. This data transmission, management, and storage present certain challenges. Furthermore, because the operating state of mechanical seals is unstable and unpredictable, continuous online monitoring is necessary to understand their health status throughout their entire service life. To effectively manage and utilize this massive amount of monitoring data, this invention proposes a distributed deployment, edge node data processing online monitoring system architecture for mechanical seals. The monitoring data for each mechanical seal is placed on its respective edge computer for feature calculation. The calculated features are then transmitted to a data server for storage and management. Terminals can then access the data server via a wireless network to understand the seal's operating status.

[0049] like Figure 5 As shown, the present invention also relates to a mechanical seal condition monitoring data acquisition and processing device and a distributed monitoring and processing system. The device comprises an acoustic emission sensor, a data acquisition and edge computing node, a data server, and an access terminal, as shown below. Figure 5 As shown, acoustic emission sensors are installed inside the mechanical seals, with one sensor installed inside each mechanical seal. Data acquisition and edge computing nodes are installed in the field, directly performing feature value calculations and anomaly detection on the acoustic emission sensor signals collected from multiple field locations. If the mechanical seal is in normal condition, only the feature values ​​per second are saved and transmitted to the data server. If the mechanical seal is in abnormal condition, raw waveform data for at least 10 minutes before and after the abnormality is collected and transmitted to the data server. The data server is deployed in a computer room for the storage and management of feature values ​​during normal operation, the storage and analysis of raw waveform data during abnormal alarms, and the application of mechanical seal condition monitoring and evaluation methods developed based on the data server.

[0050] The usage process of a mechanical seal condition monitoring data acquisition and processing device is as follows: Figure 7 As shown.

[0051] The computations and processing performed by the edge computing nodes are as follows:

[0052] (1) Acquire real-time acoustic emission data at a sampling rate of 1MHz, and divide the data of this second according to the rotation speed N. In order to reduce the amount of data and speed up the data processing, retain the friction data of 4 rotations of relative motion of the dynamic and static friction pairs. Therefore, the 2-second data is divided into N / 240 parts, one part is retained, and the remaining data is discarded.

[0053] (2) Based on the retained data fragments, calculate the effective value and kurtosis value, and confirm whether either exceeds the normal operating range. If not, transmit the calculated effective value and kurtosis value to the data server, while high-frequency raw data fragments are cached at the edge nodes.

[0054] (3) When either the valid value or the kurtosis value exceeds the normal range, the valid value and the kurtosis value are transmitted to the data management server. In addition, the cached original data fragments of the first 10 minutes and the data fragments of the next 10 minutes are also transmitted to the data server to record the original data under abnormal conditions.

[0055] The tasks performed by the data processing server include:

[0056] (1) Classify, store, and manage the data transmitted from the edge for users to access.

[0057] (2) Based on the degree of excess of effective value and kurtosis value, the friction state of the sealing friction pair is judged and classified, the abnormal operation time of the seal is counted, and on this basis, the wear of the seal is judged by continuous monitoring.

Claims

1. A method for evaluating the condition of a mechanical seal with a built-in acoustic emission sensor, characterized in that, Includes the following steps: Step 1: Install the mechanical seal, set the sampling rate Fs for the acoustic emission signal, and obtain the acoustic emission signal sequence during normal operation of the seal. To obtain the waveform of the acoustic emission signal during normal operation, the effective value (RMS) of the acoustic emission signal, and the kurtosis value (KUR) of the acoustic emission signal, the formula for calculating the effective value (RMS) is shown in equation (1): （1）， The formula for calculating the kurtosis value KUR is shown in equation (2): （2）， in, To calculate the sequence of acoustic emission signals acquired within the calculation window, Step 2: After the seal is installed, run it stably for 1 hour and check if the leakage is normal. If the leakage is normal, collect 10 minutes of acoustic emission data. If the leakage is abnormal, it means that the seal is not operating properly. Reinstall and adjust the seal and run it stably for another hour. Observe the leakage to determine if the seal is normal. Repeat the above operation until the acoustic emission signal of the seal is collected during operation. Step 3: Using a window of length W, collect the acoustic emission signals during normal operation of the mechanical seal. The slide is performed with a length of STEP. The effective value RMS and kurtosis value KUR of the signal within the sliding window are calculated according to (1) and (2) to form a list of effective values ​​when the mechanical seal is operating normally: RMS_L=[RMS1,RMS2,…,RMS k ] and the list of kurtosis values ​​KUR_L=[KUR1,KUR2,…,KUR k ]; Step 4: Calculate the effective value list of the mechanical seal during normal operation: RMS_L = [RMS1, RMS2, ..., RMS k The average value RMS_AVE and standard deviation RMS_σ of the mechanical seal are used to calculate the kurtosis values ​​of the mechanical seal during normal operation. The list of values ​​is KUR_L=[KUR1,KUR2,…,KUR]. k The average value KUR_AVE and standard deviation KUR_σ of the acoustic emission signal during normal operation of the mechanical seal are used to determine the effective value of the acoustic emission signal as [RMS_AVE-3*RMS_σ, RMS_AVE+3*RMS_σ], and the kurtosis value of the acoustic emission signal during normal operation of the mechanical seal is determined as [KUR_AVE-3*KUR_σ, KUR_AVE+3*KUR_σ]. Step 5: Acquire the acoustic emission signal obtained from real-time monitoring Calculate the effective value RMS_new and the kurtosis value KUR_new; determine whether the effective value RMS_new of the real-time acquired acoustic emission signal is within the range of the effective value of acoustic emission during normal operation of the mechanical seal [RMS_AVE-3*RMS_σ, RMS_AVE+3*RMS_σ]. Step 6: If the effective value RMS_new exceeds the normal signal range, further compare whether the kurtosis value KUR_new is within the range of acoustic emission kurtosis values ​​during normal operation of the mechanical seal [KUR_AVE-3*KUR_σ, KUR_AVE+3*KUR_σ]. When both the effective value and the kurtosis value exceed the normal range, it indicates that abnormal friction has occurred in the friction pair of the mechanical seal. If only the effective value RMS_new of the acoustic emission signal exceeds the normal range, and the kurtosis value KUR_new does not exceed the normal range, it can be determined that there is an abnormal increase in energy in other parts of the equipment. There may be some abnormalities, but they are not caused by abnormal friction of the sealing friction pair.

2. The method for evaluating the condition of a mechanical seal with a built-in acoustic emission sensor as described in claim 1, characterized in that: In step 3, W takes Fs / 10 data points.

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