Vacuum box helium detection device and detection method

Abstract

The present application belongs to the technical field of sealing test of structural parts, and specifically discloses a vacuum box helium detection device and a detection method. The vacuum box helium detection device comprises a vacuum box body unit, a high-pressure nitrogen filling unit, a double-path vacuum pumping unit, a helium mass spectrum leak detection unit, a helium filling and staged recovery unit, an automatic helium cleaning unit and a PLC control unit. High-pressure nitrogen is filled into the inner cavity of the workpiece before leak detection, and the first-stage leakage is screened by monitoring the vacuum degree rising amplitude in the vacuum box body. The qualified workpiece is filled with helium again for helium mass spectrum secondary leakage detection. After leak detection, helium is recovered through the differential pressure recovery of the balance valve, the suction of the recovery pump and the storage of the pressurized compression, and the recovery rate is about 98%. When the background exceeds the standard, nitrogen is automatically filled to clean the helium. The present application can eliminate large-leakage workpieces before secondary leakage detection, reduce helium consumption, shorten the vacuum pumping period and realize the automation of the whole leakage detection process.

Description

Technical Field

[0001] This invention belongs to the field of sealing test technology for structural components. Specifically, it discloses a vacuum chamber helium detection device and detection method, which is suitable for dry leak detection of overall airtightness of various sealed shell components before leaving the factory. It can realize fully automated detection of the entire process, including pre-screening of large leaks, high-precision helium detection of micro leaks, helium circulation and recovery, and automatic helium clearing from the vacuum background. Background Technology

[0002] Vacuum chamber helium mass spectrometry leak detection, as the mainstream process for testing the airtightness of sealed pressure-bearing workpieces, has outstanding advantages such as high detection sensitivity and no residual media in dry detection. However, in industrial mass production scenarios, existing conventional helium detection equipment still has several technical shortcomings, making it difficult to adapt to the needs of efficient and stable mass production testing. Existing equipment generally does not have a pre-screening step for large leaks. When directly performing helium mass spectrometry micro-leak detection, if the workpiece under test has a large leak defect, a large amount of tracer helium will be released into the vacuum chamber instantaneously, causing serious background contamination of the helium in the vacuum chamber. After a single test, the equipment needs to spend a long time evacuating the residual helium before the next round of testing can be carried out, directly lengthening the production cycle. Meanwhile, conventional vacuum chambers are mostly made of ordinary rolled stainless steel plates, and the inner walls are not mirror polished. The micro-unevenness and grain boundary pores on the surface of the plates are very easy to adsorb and retain helium. This not only leads to a high initial helium background value of the equipment, but also causes the vacuum chamber background signal to continue to drift and rise after multiple batches of workpieces are continuously tested, frequently triggering false leak alarms, making it impossible to maintain the leak detection sensitivity stably for a long time.

[0003] Regarding helium recovery and utilization, existing helium detection devices only employ a single-stage pumping recovery mode, resulting in a comprehensive helium recovery rate of less than 80%. High-purity tracer helium is continuously lost, leading to high costs for consumable media under long-term mass production conditions. Furthermore, existing equipment cannot achieve closed-loop recirculation and reuse of low-pressure helium, further exacerbating the waste of helium resources. After workpieces with excessive leakage rates are inspected, a large amount of helium remains inside the vacuum chamber and common vacuum pipeline. Traditional equipment passively reduces background pollution by continuously pumping vacuum for extended periods, lacking an active purification and treatment mechanism for background contamination and an automatic control function for helium purification waiting time. This severely restricts the equipment's continuous automated detection capabilities.

[0004] In addition, the matching degree of the vacuum pumping system is also significantly insufficient. A single vacuum unit simultaneously handles two types of pumping loads: the vacuum chamber and the workpiece cavity. The effective pumping rate in the high vacuum range is insufficient, and it takes a long time for the vacuum chamber and the workpiece cavity to reach the leak detection set vacuum threshold, resulting in a long single inspection cycle for the entire machine. At the same time, the automation integration of most existing equipment is low. Only the leak detection process has achieved semi-automatic control. Processes such as large leak defect judgment, helium recovery, background zeroing, and helium replacement and purification of the vacuum chamber all require manual intervention to perform program reset operations, making it difficult for the production line to achieve unattended continuous inspection. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a vacuum chamber helium detection device and method, integrating functions such as pre-screening for nitrogen leaks, a mirror-finish low-adsorption background vacuum chamber, staged pressurization helium recovery, fully automatic nitrogen replacement and helium removal, and independent vacuum pumping in different zones. It achieves pre-screening for leaks using high-pressure nitrogen, proactively eliminating workpieces with large leaks, preventing excessive helium contamination of the vacuum chamber, reducing helium adsorption, stabilizing the equipment's background value, and achieving a comprehensive helium recovery rate of approximately 98% through a staged recovery and pressurization system with high and low-pressure helium tanks, thus reducing helium consumption. The integrated fully automatic nitrogen helium removal module automatically refills the vacuum chamber with nitrogen and re-vacuums when the background value exceeds the limit, eliminating false alarms. The independent vacuum pumping system in different zones matches the pumping needs of the vacuum chamber and the workpiece's internal cavity, shortening the pumping time. The equipment uses PLC and a touchscreen for fully automated control, automating the entire process from primary leak detection, secondary leak helium detection, helium recovery, helium removal and zeroing, to opening the vacuum chamber, reducing manual intervention and improving production line testing efficiency.

[0006] The complete technical solution of this invention includes:

[0007] A vacuum chamber helium detection device includes a vacuum chamber unit, a high-pressure nitrogen filling unit, a dual-channel vacuum pumping unit, a helium mass spectrometry leak detection unit, a helium filling and graded recovery unit, an automatic helium cleaning unit, and a PLC control unit.

[0008] The vacuum chamber unit includes a vacuum chamber;

[0009] The high-pressure nitrogen filling unit is used to fill the inner cavity of the workpiece with high-pressure nitrogen at a set pressure before leak detection and to maintain the pressure.

[0010] The PLC control unit collects the pressure changes inside the vacuum chamber in real time, determines whether there is a primary leak in the workpiece based on the increase in vacuum level, and controls whether to enter the vacuum chamber method for helium mass spectrometry secondary leak detection based on the determination result.

[0011] The first-level leakage judgment standard is as follows: if the vacuum degree of the vacuum chamber rises by more than 100Pa within 30 seconds of pressure holding, the PLC control unit determines that the workpiece has a first-level leakage defect and triggers an alarm and a vacuum breaking procedure.

[0012] The dual-channel vacuum pumping unit includes a vacuum chamber pumping unit and a workpiece pumping unit. The vacuum chamber pumping unit is used to pump the vacuum chamber to a high vacuum state required for leak detection, wherein the high vacuum state is no higher than 20 Pa. The workpiece pumping unit is used to pump the inner cavity of the workpiece to a set low vacuum state, wherein the low vacuum state is no higher than 200 Pa.

[0013] The helium filling and graded recovery unit includes a helium filling subunit and a graded recovery subunit. The helium filling subunit is used to fill the inner cavity of the workpiece with tracer helium, and the graded recovery subunit is used to grade and recover the helium in the inner cavity of the workpiece after leak detection. The graded recovery subunit includes a low-pressure helium tank and a high-pressure helium tank. After the workpiece leak detection is completed, the inner cavity of the workpiece is first connected to the low-pressure helium tank to achieve pressure balance, and then the residual helium in the inner cavity of the workpiece is sent into the low-pressure helium tank. Subsequently, the low-pressure helium in the low-pressure helium tank is compressed and stored in the high-pressure helium tank.

[0014] Furthermore, the vacuum chamber pump set consists of a first vacuum chamber pump, a second vacuum chamber pump, and a vacuum chamber Roots pump connected in series; the workpiece pump set is a mechanical vacuum pump; the vacuum chamber pump set and the workpiece pump set are independently controlled.

[0015] Furthermore, the graded recovery subunit also includes a balancing valve, a booster compressor, and a recovery pump, and is equipped with a primary balancing recovery branch, a secondary pump recovery branch, and a tertiary booster storage branch. The primary balancing recovery branch connects the workpiece cavity to the low-pressure helium tank through the balancing valve, relying on the pressure difference to achieve natural pressure relief and recovery. The secondary pump recovery branch extracts residual helium from the workpiece cavity through the recovery pump. The tertiary booster storage branch connects the low-pressure helium tank to the high-pressure helium tank in sequence through a precision filter and a booster compressor, boosting and storing the helium in the high-pressure helium tank for recycling.

[0016] Furthermore, the automatic helium removal unit includes a helium removal pump and a helium removal solenoid valve. The helium removal solenoid valve is connected in parallel to the inner cavity of the vacuum chamber and the common vacuum pipeline in two separate paths. When the background detection of the inner cavity of the vacuum chamber exceeds the standard, the PLC control unit controls the helium removal solenoid valve to open and fill the vacuum chamber and the common vacuum pipeline with high-purity nitrogen to replace the adsorbed helium until the background level reaches the standard before starting leak detection.

[0017] Furthermore, the vacuum chamber is welded from a 304 stainless steel mirror panel, and the internal mirror surface of the 304 stainless steel mirror panel is degreased and cleaned with acid and alkali. The vacuum chamber is equipped with guide rails and a workpiece transfer trolley. The workpiece transfer trolley is equipped with a quick flexible sealing connector for snapping into the workpiece's inflation port.

[0018] Furthermore, when the helium concentration in the high-pressure helium tank is lower than 93%, the helium replenishment solenoid valve of the external high-purity helium source is automatically opened to replenish high-purity helium.

[0019] Furthermore, the detection method using the vacuum chamber helium detection device includes the following steps: loading and sealing the chamber; pre-pressurized nitrogen primary leakage screening; zoned pre-vacuuming; automatic helium clearing and background zeroing; vacuum chamber helium mass spectrometry secondary leakage detection; staged helium recovery; and vacuum breaking and unloading.

[0020] Furthermore, the pre-pressurized nitrogen level 1 leak screening is as follows: 0.4MPa high-pressure nitrogen is injected into the inner cavity of the workpiece and the pressure is maintained for 30 seconds. If the vacuum level of the vacuum chamber rises by more than 100Pa, it is determined that there is a level 1 leak in the workpiece, and an audible and visual alarm is triggered and the vacuum is broken; if the rise is not greater than 100Pa, it is determined that there is no level 1 leak and the process proceeds to the next step.

[0021] Furthermore, the staged helium recovery includes:

[0022] First-level balance recovery: Open the balance valve to connect the inner cavity of the workpiece with the low-pressure helium tank, and rely on the pressure difference to achieve the natural decompression and recovery of some helium.

[0023] Secondary pump recovery: Start the recovery pump to pump the residual helium in the workpiece to the low-pressure helium tank;

[0024] Three-stage pressurization and storage: The pressurization compressor draws helium from the low-pressure helium tank, filters it through a precision filter, and then pressurizes it before sending it to the high-pressure helium tank for storage.

[0025] Furthermore, the vacuum chamber method for helium mass spectrometry secondary leak detection uses a 1.91 × 10⁻ 6 Pa·m³ / s is the leakage rate criterion: if the leakage rate is greater than the criterion threshold, the workpiece is considered to have secondary leakage; if the leakage rate is not greater than the criterion threshold, the workpiece is considered to have qualified sealing.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] 1) Multi-module collaborative pollution reduction and improved detection efficiency: The pre-positioned high-pressure nitrogen primary leak screening eliminates large leaking workpieces at the source, and uses nitrogen as the leak detection medium to avoid large-scale helium leakage and contamination of the vacuum system; combined with the automatic helium cleaning unit to actively replace residual helium, and the low adsorption characteristics of the mirror vacuum chamber, the three work together to increase the vacuum background recovery speed by more than 60%, and the overall detection cycle efficiency is improved by 40% compared with traditional equipment, enabling continuous and uninterrupted mass production testing.

[0028] 2) The dual-path independent pumping architecture significantly shortens the pumping cycle: To meet the different needs of high vacuum in the vacuum chamber and low vacuum in the workpiece, two independent pump sets are used to adapt to each other. The pumping process does not interfere with each other. Compared with the single pump set solution, the vacuuming time is shortened by more than 30%, further reducing the single-cycle inspection time and improving the production line cycle time.

[0029] 3) The three-stage recycling structure significantly improves the utilization rate of helium: by balancing and depressurizing, the potential energy of high-pressure helium is fully utilized, and then residual gas is pumped out and pressurized for storage to form a closed loop. The comprehensive helium recovery rate is stably reached about 98%, reducing the consumption of high-purity helium and lowering the material cost in the long term. The automatic helium replenishment function eliminates the need for frequent manual inspections and replenishment, thus reducing maintenance costs.

[0030] 4) Fully automated closed-loop process with strong detection consistency: From primary leak quantification and judgment, automatic background helium clearing, automatic helium replenishment, to automatic output of test results, the entire process requires no manual intervention, eliminating human error and ensuring stable and reliable test results, making it suitable for automated production line batch testing scenarios. Furthermore, the stable low background characteristics of the mirror vacuum chamber can maintain leak detection accuracy at a high level over a long period, effectively reducing false alarms. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of the vacuum chamber helium detection device provided by the present invention.

[0032] In the diagram, 1 is the vacuum chamber, 2 is the workpiece transfer trolley, 3 is the vacuum chamber pump assembly, 3-1 is the first vacuum chamber pump, 3-2 is the second vacuum chamber pump, 3-3 is the vacuum chamber Roots pump, 4 is the workpiece pump assembly, 5 is the helium mass spectrometer leak detector, 6 is the recovery pump, 7 is the helium cleaning pump, 8 is the staged recovery subunit, 8-1 is the low-pressure helium tank, 8-2 is the booster compressor, 8-3 is the high-pressure helium tank, 9 is the high-pressure nitrogen filling unit, and 10 is the control cabinet. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. However, it should be understood that the embodiments and drawings are merely illustrative of the invention and do not constitute any limitation on the scope of protection of the invention. All reasonable modifications and combinations included within the scope of the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0034] A vacuum chamber helium detection device includes a vacuum chamber unit, a high-pressure nitrogen filling unit, a dual-channel vacuum pumping unit, a helium mass spectrometry leak detection unit, a helium filling and graded recovery unit, an automatic helium cleaning unit, and a PLC (programmable logic controller) control unit.

[0035] The vacuum chamber helium detection device of the present invention is specifically composed as follows: Figure 1 As shown, it includes:

[0036] 1. Vacuum Chamber Unit: Includes Vacuum Chamber 1, which serves as the testing chamber for the equipment. It is constructed from 304 stainless steel mirror-finish panel welded together, with polished weld seams both inside and out. The entire interior of Vacuum Chamber 1 is mirror-polished and has undergone acid-alkali degreasing and cleaning, ensuring a surface free of casting pinholes and unevenness, thus reducing helium adsorption and retention and lowering the equipment's background value. The front of Vacuum Chamber 1 features a manually sealed door equipped with a fluororubber vacuum sealing ring; manual tightening is sufficient for sealing. The interior of Vacuum Chamber 1 accommodates the workpieces to be inspected, featuring guide rails and a separate workpiece transfer trolley 2. The workpiece transfer trolley 2 is equipped with a quick-connect flexible sealing connector, allowing for connection to the inflation ports of various workpieces without requiring additional sealing fixtures. Multiple sets of piping interfaces for vacuuming, inflation, and gas recovery are located on the sides of Vacuum Chamber 1.

[0037] 2. High-Pressure Nitrogen Filling Unit: The high-pressure nitrogen filling unit 9 consists of an external high-pressure nitrogen source, a pressure reducing valve, a nitrogen filling solenoid valve, a pressure sensor, and connecting pipelines. Specifically, the high-pressure nitrogen filling unit 9 is connected to an industrial nitrogen source of 0.6MPa~0.8MPa in the factory area, and a pressure reducing valve, a nitrogen filling solenoid valve, and a pressure sensor are installed at the front end. The pipeline branches only connect to the inner cavity of the workpiece and do not connect to the cavity of vacuum chamber 1. The outlet end connects to the inner cavity of the workpiece and is used to fill the inner cavity of the workpiece with high-pressure nitrogen at a set pressure before leak detection and maintain the pressure.

[0038] A high-pressure nitrogen filling unit, in conjunction with a dual-channel vacuum pumping unit, evacuates the vacuum chamber 1 to achieve first-level leak screening. Simultaneously, the PLC control unit collects real-time pressure changes within the vacuum chamber 1, determining the presence of a first-level leak defect in the workpiece based on the pressure change rate. The threshold for judgment is set as follows: during the pressure holding phase of the first-level leak screening, if the vacuum level in the vacuum chamber 1 increases by more than 100 Pa, a first-level leak defect is directly determined in the workpiece, triggering an alarm and a vacuum breaking procedure.

[0039] 3. Dual-path vacuum pumping unit: Utilizing two completely independent pumping branches, one for vacuum chamber 1 and the other for the workpiece cavity. The two pumping branches operate synchronously and are independently controlled. The physical piping is completely independent, with no shared valve groups or pumps. They start and stop synchronously without interference. This includes:

[0040] 1) Vacuum box pump group 3: The high vacuum unit is composed of the first vacuum box pump 3-1, the second vacuum box pump 3-2 and the vacuum box pump Roots pump 3-3 connected in series. It is equipped with an independent vacuum gauge and a pneumatic main pump valve. It is responsible for quickly pumping the vacuum box 1 to the high vacuum state required for leak detection. The high vacuum state is not higher than 20Pa.

[0041] 2) Workpiece vacuum pump group 4: A mechanical vacuum pump is used, specifically a single-stage oil vane vacuum pump, which is connected to the inner cavity of the workpiece separately. It is equipped with an independent vacuum gauge and a workpiece vacuum valve to evacuate the inner cavity of the workpiece separately until the required pressure range is reached. The low vacuum state is no higher than 200Pa.

[0042] This unit's dual-channel independent structure can simultaneously meet high and low vacuum requirements, shortening the vacuuming time. Two vacuum gauges upload pressure data to the PLC control unit in real time; the equipment only enters the vacuum chamber 1 background detection process after both gauges have reached the set vacuum threshold.

[0043] 4. Helium Mass Spectrometry Leak Detection Unit: The helium mass spectrometry leak detection unit includes a helium mass spectrometer leak detector 5, a matching leak control valve, and a standard leak calibration assembly. The detector end of the helium mass spectrometer leak detector 5 is connected to the inner cavity of the vacuum chamber 1 and is calibrated before leaving the factory. It collects the helium concentration signal inside the vacuum chamber 1 in real time. The PLC control unit reads the leak rate signal output by the helium mass spectrometer leak detector 5 in real time and automatically determines the qualified workpiece and the unqualified workpiece with secondary leakage according to the preset leak rate threshold. When a secondary leakage failure is detected, an audible and visual alarm signal is output simultaneously.

[0044] 5. Helium Filling and Staged Recovery Unit: This unit includes a helium filling subunit and a staged recovery subunit 8, a balancing valve, a precision filter, a pressure sensor, a helium concentration sensor, and multiple sets of solenoid valves. The staged recovery subunit 8 includes a low-pressure helium tank 8-1, a booster compressor 8-2, a high-pressure helium tank 8-3, and a recovery pump 6. Specifically:

[0045] Helium filling sub-unit: High-purity helium in the high-pressure helium tank 8-3 is injected into the inner cavity of the workpiece via a pressure reducing valve to supply tracer helium. The system monitors the helium pressure in real time. The high-pressure helium tank 8-3 has a built-in helium concentration sensor to monitor the helium purity in real time. When the helium concentration in the high-pressure helium tank 8-3 is lower than 93%, the PLC control unit automatically opens the helium replenishment solenoid valve of the external high-purity helium source to replenish high-purity helium to the standard purity and then closes the valve. The overall helium recovery rate of the entire recovery system is approximately 98%.

[0046] The graded recycling subunit 8 includes a three-stage recycling structure:

[0047] 1) Primary Balance Recovery Branch: The workpiece gas path is connected to the low-pressure helium tank 8-1 via a balance valve. The pressure difference between the high-pressure helium in the workpiece and the low-pressure helium tank 8-1 is used to achieve natural pressure relief and recovery.

[0048] 2) Secondary pump recovery branch: The workpiece gas line is connected to the low-pressure helium tank 8-1 via the recovery pump. After the balance is completed, the recovery pump is started to extract the residual low-pressure helium in the workpiece.

[0049] 3) Three-stage pressurization and storage branch: The low-pressure helium tank 8-1 is connected to the high-pressure helium tank 8-3 in sequence through the precision filter and the pressurization compressor 8-2; the precision filter filters out dust and water vapor in the helium, and the pressurization compressor 8-2 pressurizes the low-pressure helium and stores it in the high-pressure helium tank 8-3 for recycling.

[0050] 6. Automatic Helium Removal Unit: Includes a helium removal pump 7 and a helium removal solenoid valve, connected to a high-purity nitrogen source; the helium removal solenoid valve is connected in parallel with two lines: one connected to the inner cavity of vacuum chamber 1, and the other connected to the common vacuum pipeline. When the background gas level of vacuum chamber 1 exceeds the standard, the helium removal program is triggered. The PLC control unit automatically controls the helium removal solenoid valve to open, filling high-purity nitrogen into vacuum chamber 1 and the common vacuum pipeline to replace the helium adsorbed on the pipeline and the inner wall of vacuum chamber 1; the replacement time can be set on the touch screen, with a default replacement time of 2 minutes under standard operating conditions. After the replacement is completed, the helium removal solenoid valve is closed, the dual-channel vacuum pumping unit re-evacuates and re-measures the background gas level, and the cycle is repeated until the background gas level meets the standard before leak detection is performed.

[0051] 7. PLC Control Unit: The control cabinet 10 has a built-in PLC host, a 10-inch touch screen display, and an audible and visual alarm module. It is equipped with a touch screen human-machine interaction module and has a built-in automatic detection program. It can automatically perform the following processes: workpiece loading and closing, high-pressure nitrogen pressurization and first-level leak detection, opening the door and alarming when the first-level leak fails or when the first-level leak passes, zonal vacuuming, automatic nitrogen and helium purging when the background of vacuum chamber 1 is zeroed or exceeds the standard, workpiece helium filling and helium mass spectrometry leak detection in vacuum chamber 1, helium recovery and opening the door with an alarm when the second-level leak fails or when the second-level leak passes, graded helium recovery, and full-process automatic control of vacuum chamber 1 and workpiece opening and removal.

[0052] All pump sets, solenoid valves, pressure sensors, helium mass spectrometer leak detector 5, and helium concentration sensors are connected to the signal port of the PLC control unit; the touch screen can modify all process parameters, including the first-level leakage holding time, vacuum chamber vacuum threshold, workpiece inner cavity vacuum threshold, leak rate judgment value, helium cleaning time, helium recovery termination pressure, and helium replenishment concentration threshold; the equipment is equipped with multi-level alarms, namely first-level leakage alarm, second-level leakage alarm, and helium insufficient or vacuum fault warning. Alarm information is stored in the equipment history record and can be retrieved at any time.

[0053] The operation process of this device includes the following steps:

[0054] (1) Loading and sealing: The shell workpiece is manually hoisted to the workpiece transfer trolley 2, the workpiece inflation port is connected to the quick flexible sealing joint, the workpiece transfer trolley 2 is pushed into the vacuum chamber 1, and the sealing door of the vacuum chamber 1 is manually closed.

[0055] (2) Pre-high pressure nitrogen first-level leakage screening: The system starts synchronously: After the dual-channel vacuum pumping unit evacuates the vacuum chamber 1, it fills the inner cavity of the workpiece with high pressure and maintains the pressure; it monitors the pressure change in the vacuum chamber 1 in real time. If the vacuum degree in the vacuum chamber 1 rises more than the set threshold within the preset time, it is determined that there is a first-level leakage in the workpiece. The system will sound and light alarm, automatically break the vacuum in the vacuum chamber 1 and the workpiece, unlock the sealed door, and manually remove the leaking part; if the vacuum degree in the vacuum chamber 1 rises less than the set threshold, it is determined that there is no first-level leakage and proceeds to the next process.

[0056] During on-site testing, in order to improve screening efficiency, a relatively simplified judgment standard can be adopted, namely: if the vacuum degree of vacuum chamber 1 rises by more than 100Pa within 30 seconds of pressure holding, the workpiece is judged to have a first-level leakage defect, and an alarm and vacuum breaking procedure are triggered.

[0057] Furthermore, to improve screening accuracy, this invention further optimizes the design of the pre-high-pressure nitrogen primary leakage screening system. First, it analyzes the problems found in practical applications, including:

[0058] 1) The transient temperature rise during inflation, the throttling expansion and cooling of leaked gas, the heating of the pump body, and fluctuations in ambient temperature can all affect the pressure reading, which may cause distortion of the pressure rise curve. At the same time, the rate calculation is sensitive to temperature noise. If no compensation is made, the deviation of the rate estimation may be large in some cases, causing jitter at the judgment time and misjudgment or omission of boundary workpieces.

[0059] 2) In some cases, for volumetric leaks (caused by casting defects such as pinholes, cracks, or incomplete weld penetration), the pressure rise can far exceed the set threshold within seconds. Waiting for the full 30 seconds would affect screening efficiency. However, for slow-change leaks (caused by poor sealing or improper clamping), it may take around 30 seconds to detect. Therefore, the fixed time limit for detection cannot meet the sensitivity requirements of different workpieces and standards. Furthermore, there is a lack of refined management in handling workpieces with large volumetric leaks (which should be scrapped immediately) and slow-change leaks (which may pass after resealing or clamping).

[0060] Based on the above problems, the present invention further adopts the following optimized determination method:

[0061] First, a temperature sensor (PT100 platinum resistance thermometer) is installed in the vacuum chamber 1, near the vacuum gauge, with a range of 0~60℃ and an accuracy of ±0.1K. The sensor samples the pressure and temperature simultaneously, with a sampling period of 0.5s. During the pressure holding phase, the main extraction valve is closed, and the chamber is approximately constant-volume and sealed. The gas temperature inside the chamber at the start of the pressure holding phase is set as the reference temperature.

[0062] Temperature compensation is first performed using the following method:

[0063] (1)

[0064] (2)

[0065] In the formula, The pressure inside the vacuum chamber at time t after temperature compensation, in Pa; The measured pressure at time t is in Pa. The reference temperature at the start of the pressure holding process, in Kelvin; This refers to the real-time gas temperature inside the chamber during the pressure holding stage, expressed in Kelvin (K). The cumulative pressure rise at time t after temperature compensation, in Pa; This is the pressure at the start of the pressure holding phase, in Pa (the compensated pressure at this moment is the same as the measured pressure). During the pressure holding phase... Differential pressure is used as the primary leakage screening criterion.

[0066] By employing the above methods, the distortion of the pressure rise curve caused by the inflation transient and throttling cooling is eliminated, the relative error of rate estimation and the boundary misjudgment rate are significantly reduced, and a reliable input signal is provided for segmented pressure holding determination.

[0067] Secondly, the distinction between volumetric leakage and slowly varying leakage is made as follows:

[0068] 1) Divide the pressure holding period into a first part and a second part according to the time ratio: first part duration Under a 30-second pressure holding time =10s, the second part is 20s long.

[0069] 2) Set the threshold value at the end of the previous segment. ; Subsequent incremental judgment threshold ,in The sum of the two thresholds is always equal to the total threshold for determining a first-level leak. .

[0070] 3) Sliding window speed: , is the average pressure rise rate of the sliding window at time t, in Pa / s, used for real-time prediction and process monitoring in the early stage; The sliding window duration is set to 5 seconds (sampling period 0.5 seconds, 10 sampling points within the window). When not at the sampling time, take the most recent sampled value or linear interpolation.

[0071] 4) Reference line for the initial judgment: It is used for the preliminary prediction of volumetric leakage in the early stage.

[0072] In the formula, The duration of the preceding segment is in seconds (s). The duration of pressure holding is measured in seconds (s). The total threshold for determining a first-level leak is preferably 100 Pa. , These are the final judgment threshold for the first segment and the incremental judgment threshold for the second segment, preferably set to 60Pa and 40Pa respectively. The reference pressure rise for the previous stage is measured in Pa. The average pressure rise rate of the sliding window at time t is expressed in Pa / s. The duration of the sliding window is set to 5 seconds.

[0073] 1) Prediction within the first segment: t < At that time, if This indicates a volumetric Class I leak; an early warning is issued and monitoring continues.

[0074] 2) End check at the beginning: t= At that time, if The workpiece was determined to have a volumetric Class I leak, and the screening was terminated.

[0075] 3) Cumulative checks in the later stage: t= At that time, if and The workpiece was determined to have a slow-changing Class I leak, and the screening was terminated.

[0076] 4) If none of them are triggered, then there is no Level 1 leakage.

[0077] By adopting the above screening method, the classification and determination of volumetric / gradually changing large leaks (level 1 leaks) of workpieces can be realized, thereby enabling subsequent production line diversion and disposal (direct scrapping or resealing) and reducing the false scrap rate.

[0078] (3) Pre-vacuuming in zones: After passing the first-level leak screening, the inner cavity of the workpiece is automatically emptied. The workpiece pump group 4 pumps the inner cavity of the workpiece to the set low vacuum pressure. The vacuum box pump group 3 continues to pump air until the vacuum box 1 reaches the high vacuum pressure required for leak detection. After completion, the background test of the vacuum box 1 is performed.

[0079] (4) Automatic helium clearing and background zeroing: Collect the helium background signal of vacuum chamber 1. When the background value exceeds the standard, start the automatic helium clearing unit: fill the vacuum chamber 1 and the common vacuum pipeline with high-purity nitrogen to replace the helium. After the replacement is completed, re-evacuate the vacuum and repeat the cycle until the background meets the standard. After the background is qualified, the helium mass spectrometer leak detector 5 performs background zeroing operation.

[0080] (5) Vacuum chamber method helium mass spectrometry secondary leakage detection: After the background is suppressed to zero, the helium filling solenoid valve is opened to fill the inner cavity of the workpiece with tracer helium at a set pressure; the helium mass spectrometer leak detector 5 continuously collects the helium signal in the vacuum chamber 1 and compares it with the set leakage rate to determine the workpiece sealing performance: if it is not qualified, the system will sound and light alarm and start the helium recovery process; if it is qualified, it will directly enter the graded helium recovery process.

[0081] (6) Graded helium recovery: Regardless of whether the workpiece is qualified or not, the helium in the inner cavity of the workpiece is automatically recovered: the balance valve is opened to balance the pressure between the inner cavity of the workpiece and the low-pressure helium tank 8-1, and the recovery pump pumps the residual helium to the low-pressure helium tank 8-1; the booster compressor 8-2 continuously boosts the low-pressure helium to the high-pressure helium tank 8-3 for storage, and the overall helium recovery rate is about 98%; if the helium concentration in the high-pressure helium tank 8-3 is lower than 93%, the system automatically replenishes high-purity helium.

[0082] (7) Emptying and unloading: After the helium is recovered, the vacuum chamber 1 and the inner cavity of the workpiece are filled with air to empty the vacuum chamber. The touch screen of the control cabinet 10 indicates that the test is completed. Manually open the sealed box door, manually disconnect the quick flexible sealing joint, pull out the workpiece transfer trolley 2 to take out the workpiece, and the single test process ends. Wait for the next piece to be loaded.

[0083] Example 1

[0084] Taking the aluminum alloy casting housing of a high-voltage switch as an example, the complete single-test implementation steps of this device are as follows:

[0085] Step 1: Manual loading and closing of the sealed chamber door: The operator uses an overhead crane to hoist the shell workpiece to the workpiece transfer trolley 2, and clamps and seals the workpiece inflation port with the quick flexible sealing joint of the workpiece transfer trolley 2; the operator manually pushes the workpiece transfer trolley 2 along the guide rail into the vacuum chamber 1, manually presses the sealed chamber door, and clicks to start the test on the touch screen of the control cabinet 10, and the equipment automatically enters the fully automatic process.

[0086] Step 2: Pre-high-pressure nitrogen level 1 leak screening: The equipment simultaneously performs two sets of actions: the high-pressure nitrogen filling unit 9 opens the nitrogen filling solenoid valve, fills the inner cavity of the workpiece with 0.4MPa high-pressure nitrogen and maintains the pressure; the vacuum box pump group 3 starts and continuously evacuates the vacuum box 1; the PLC control unit collects the pressure value of the vacuum gauge in the vacuum box 1 in real time and continuously monitors the pressure change within 30 seconds of maintaining the pressure: if the vacuum degree of the vacuum box 1 rises by more than 100Pa, it is determined that there is a level 1 leak in the workpiece, the equipment alarms with sound and light, and automatically opens the venting solenoid valve to simultaneously fill the vacuum box 1 and the workpiece with gas to ventilate; after venting is completed, the sealed box door is unlocked, and the workpiece transfer trolley 2 is manually pulled out to remove the leaking part, and this test ends; if the vacuum degree of the vacuum box 1 rises by no more than 100Pa, it is determined that there is no level 1 leak, the nitrogen filling solenoid valve is automatically closed, and the inner cavity of the workpiece is opened to ventilate and release pressure.

[0087] Step 3: Zoned pre-vacuuming: After the workpiece cavity is depressurized, the dual-channel vacuum pumping unit starts simultaneously: the workpiece pumping pump group 4 evacuates the workpiece cavity separately until the pressure inside the workpiece cavity is not higher than 200Pa; the vacuum chamber pumping pump group 3 continuously evacuates the vacuum chamber 1 until the pressure inside the vacuum chamber 1 is not higher than 20Pa; the two vacuum gauges provide real-time feedback of pressure data, and after both channels reach the set vacuum threshold, the process of background testing of vacuum chamber 1 begins.

[0088] Step 4: Automatic Helium Clearing and Background Zeroing: The helium mass spectrometer leak detector 5 collects the helium background value of the vacuum chamber 1. If the background value meets the standard, the helium mass spectrometer leak detector 5 automatically performs background zeroing and directly enters the helium filling and leak detection process. If the background value exceeds the standard, the PLC control unit starts the automatic helium clearing process, the helium clearing solenoid valve opens, and high-purity nitrogen is introduced into the vacuum chamber 1 and the common vacuum pipeline for 2 minutes of purging. After the purging is completed, the helium clearing solenoid valve is closed, the dual-channel vacuum pumping unit re-evacuates the vacuum, and the background is detected again. This process is repeated until the background is qualified, and then the background zeroing operation is performed.

[0089] Step 5: Secondary Leak Detection by Vacuum Chamber Helium Mass Spectrometry: After the background is reduced to zero, the helium filling solenoid valve is opened. High-purity helium gas from the high-pressure helium tank 8-3 is injected into the workpiece cavity after being stabilized by the pressure reducing valve. After reaching the set helium filling pressure, the helium filling solenoid valve is closed. The helium mass spectrometer leak detector 5 continuously collects the helium concentration signal in the vacuum chamber 1 at a rate of 1.91 × 10⁻⁻⁶. 6 The criterion is Pa·m³ / s: if the leakage rate is greater than the threshold, the workpiece is determined to have a secondary leakage, the equipment will sound an audible and visual alarm, and the process will proceed to the graded helium recovery process; if the leakage rate is not greater than the threshold, the workpiece is determined to be airtight and the process will proceed to the graded helium recovery process.

[0090] Step 6: Staged Helium Recovery: Regardless of whether the workpiece is qualified or not, a complete helium recovery process is executed: First-stage balancing recovery: The balancing valve is opened to connect the workpiece's inner cavity to the low-pressure helium tank 8-1, relying on the pressure difference to complete the natural recovery of most of the helium; Second-stage pump recovery: After balancing, the recovery pump is started to pump the remaining low-pressure helium in the workpiece to the low-pressure helium tank 8-1; Third-stage pressurization and storage: The pressurization compressor 8-2 continuously extracts helium from the low-pressure helium tank 8-1, filters impurities through a precision filter, and then pressurizes and sends it to the high-pressure helium tank 8-3 for storage, to be used for helium refilling of the next batch of workpieces; The recovery process ends when the pressure inside the workpiece drops to no more than 200 Pa. If the helium concentration in the high-pressure helium tank 8-3 is lower than 93%, the equipment automatically opens the helium replenishment solenoid valve of the external high-purity helium source to replenish high-purity helium.

[0091] Step 7: Vacuum chamber and workpiece venting and manual unloading: After helium recovery is completed, the venting solenoid valve opens synchronously, and air is injected into the vacuum chamber 1 and the workpiece cavity to restore normal pressure; the touch screen of the control cabinet 10 displays a "Detection complete" prompt; the sealed door of the vacuum chamber 1 is opened manually, the workpiece transfer trolley 2 is pulled out, the quick flexible sealing joint is disconnected, the shell workpiece is removed, and the single complete detection process is completed, and the next workpiece can be loaded and detected directly.

[0092] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A vacuum chamber helium detection device, characterized in that, It includes a vacuum chamber unit, a high-pressure nitrogen filling unit, a dual-channel vacuum pumping unit, a helium mass spectrometry leak detection unit, a helium filling and graded recovery unit, an automatic helium removal unit, and a PLC control unit; The vacuum chamber unit includes a vacuum chamber; The high-pressure nitrogen filling unit is used to fill the inner cavity of the workpiece with high-pressure nitrogen at a set pressure before leak detection and to maintain the pressure. The PLC control unit collects the pressure changes inside the vacuum chamber in real time, determines whether there is a primary leak in the workpiece based on the increase in vacuum level, and controls whether to enter the vacuum chamber method for helium mass spectrometry secondary leak detection based on the determination result. The first-level leakage judgment standard is as follows: if the vacuum degree of the vacuum chamber rises by more than 100Pa within 30 seconds of pressure holding, the PLC control unit determines that the workpiece has a first-level leakage defect and triggers an alarm and a vacuum breaking procedure. The dual-channel vacuum pumping unit includes a vacuum chamber pumping unit and a workpiece pumping unit. The vacuum chamber pumping unit is used to pump the vacuum chamber to a high vacuum state required for leak detection, wherein the high vacuum state is no higher than 20 Pa. The workpiece pumping unit is used to pump the inner cavity of the workpiece to a set low vacuum state, wherein the low vacuum state is no higher than 200 Pa. The helium filling and graded recovery unit includes a helium filling subunit and a graded recovery subunit. The helium filling subunit is used to fill the inner cavity of the workpiece with tracer helium, and the graded recovery subunit is used to grade and recover the helium in the inner cavity of the workpiece after leak detection. The graded recovery subunit includes a low-pressure helium tank and a high-pressure helium tank. After the workpiece leak detection is completed, the inner cavity of the workpiece is first connected to the low-pressure helium tank to achieve pressure balance, and then the residual helium in the inner cavity of the workpiece is sent into the low-pressure helium tank. Subsequently, the low-pressure helium in the low-pressure helium tank is compressed and stored in the high-pressure helium tank.

2. The vacuum chamber helium detection device according to claim 1, characterized in that, The vacuum chamber pump set consists of a first vacuum chamber pump, a second vacuum chamber pump, and a vacuum chamber Roots pump connected in series; the workpiece pump set is a mechanical vacuum pump; the vacuum chamber pump set and the workpiece pump set are independently controlled.

3. The vacuum chamber helium detection device according to claim 2, characterized in that, The graded recovery subunit also includes a balancing valve, a booster compressor, and a recovery pump, and is equipped with a primary balancing recovery branch, a secondary pump extraction recovery branch, and a tertiary pressurization and storage branch. The primary balancing recovery branch connects the workpiece cavity to the low-pressure helium tank through the balancing valve, relying on the pressure difference to achieve natural pressure relief and recovery. The secondary pump extraction recovery branch extracts residual helium from the workpiece cavity through the recovery pump. The tertiary pressurization and storage branch connects the low-pressure helium tank to the high-pressure helium tank in sequence through a precision filter and a booster compressor, pressurizing and storing the helium in the high-pressure helium tank for recycling.

4. The vacuum chamber helium detection device according to claim 1, characterized in that, The automatic helium removal unit includes a helium removal pump and a helium removal solenoid valve. The helium removal solenoid valve is connected in parallel to the inner cavity of the vacuum chamber and the common vacuum pipeline. When the background detection of the inner cavity of the vacuum chamber exceeds the standard, the PLC control unit controls the helium removal solenoid valve to open and fill the vacuum chamber and the common vacuum pipeline with high-purity nitrogen to replace the adsorbed helium until the background meets the standard before starting leak detection.

5. A vacuum chamber helium detection device according to claim 1, characterized in that, The vacuum chamber is welded from a 304 stainless steel mirror panel, and the internal mirror surface of the 304 stainless steel mirror panel is degreased and cleaned with acid and alkali. The vacuum chamber is equipped with guide rails and a workpiece transfer trolley. The workpiece transfer trolley is equipped with a quick flexible sealing connector for snapping into the workpiece's inflation port.

6. A vacuum chamber helium detection device according to claim 3, characterized in that, When the helium concentration in the high-pressure helium tank is below 93%, the helium replenishment solenoid valve of the external high-purity helium source will automatically open to replenish high-purity helium.

7. A detection method using the vacuum chamber helium detection device according to any one of claims 1 to 6, characterized in that, The process includes the following steps: loading and sealing; pre-pressurized nitrogen primary leak screening; zoned pre-vacuuming; automatic helium clearing and background zeroing; vacuum chamber helium mass spectrometry secondary leak detection; staged helium recovery; and venting and unloading.

8. The detection method according to claim 7, characterized in that, The pre-pressurized nitrogen level 1 leak screening is as follows: 0.4MPa high-pressure nitrogen is injected into the inner cavity of the workpiece and the pressure is maintained for 30 seconds. If the vacuum level of the vacuum chamber rises by more than 100Pa, it is determined that there is a level 1 leak in the workpiece, and an audible and visual alarm is triggered and the vacuum is broken. If the rise is not greater than 100Pa, it is determined that there is no level 1 leak and the process proceeds to the next step.

9. The detection method according to claim 8, characterized in that, The staged helium recovery includes: First-level balance recovery: Open the balance valve to connect the inner cavity of the workpiece with the low-pressure helium tank, and rely on the pressure difference to achieve the natural decompression and recovery of some helium. Secondary pump recovery: Start the recovery pump to pump the residual helium in the workpiece to the low-pressure helium tank; Three-stage pressurization and storage: The pressurization compressor draws helium from the low-pressure helium tank, filters it through a precision filter, and then pressurizes it before sending it to the high-pressure helium tank for storage.

10. The detection method according to claim 9, characterized in that, The vacuum chamber method for helium mass spectrometry secondary leak detection uses 1.91 × 10⁻ 6 Pa·m³ / s is the leakage rate criterion: if the leakage rate is greater than the criterion threshold, the workpiece is considered to have secondary leakage; if the leakage rate is not greater than the criterion threshold, the workpiece is considered to have qualified sealing.

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