CN112197916A - Method for detecting air tightness of refrigerating system - Google Patents
Method for detecting air tightness of refrigerating system Download PDFInfo
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- CN112197916A CN112197916A CN202010934568.6A CN202010934568A CN112197916A CN 112197916 A CN112197916 A CN 112197916A CN 202010934568 A CN202010934568 A CN 202010934568A CN 112197916 A CN112197916 A CN 112197916A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
- G01M3/20—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material
- G01M3/202—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material using mass spectrometer detection systems
Abstract
The invention discloses a method for detecting the air tightness of a refrigerating system, which is characterized in that a sample to be detected is subjected to rough detection to detect large leakage, and fine detection is performed after the rough detection is qualified. The invention divides the air tightness detection of the refrigerating system into two flows, avoids the problems of low overall efficiency caused by strict standards and low detection precision caused by loose standards when a unified detection standard is adopted for large leakage and small leakage, and is favorable for considering both the detection precision and the efficiency.
Description
Technical Field
The invention belongs to the technical field of detection of the sealing performance of refrigeration equipment.
Background
Many refrigeration plant spare part and pipe fitting need detect its leakproofness in process of production, prevent to take place to leak, cause the waste of the energy, even produce the potential safety hazard. The traditional leakage detection methods mainly comprise the following methods:
first, a sample to be measured is filled with water or other liquid, and the amount of decrease of the filled medium in a specific time is observed and measured, such as whether the liquid level at a certain position is decreased or not is detected. This is a direct way of measurement.
Secondly, the sample to be detected is filled with gas with certain pressure, usually compressed air, and is placed in water for observation after pressure maintaining, and whether bubbles are generated around the sample to be detected is used as a standard for judging whether leakage exists.
Thirdly, injecting water or other liquid media into the sample to be tested, pressurizing and maintaining pressure, and if the pressure of the sample to be tested does not drop during the test, determining that the sample has no leakage.
The above method has the following disadvantages:
firstly, the method detects whether the sample leaks or not by injecting water, the method is complex to operate and has high requirements on operators, whether the sample leaks or not can be judged only by observing the sample with naked eyes of the operators, the overall detection precision is not high, and specific leakage points cannot be found out;
secondly, gas pressure maintaining is adopted for placing in water for leak detection, the method is high in operation difficulty, pure manual control is achieved, and the error of a measurement result is large;
and thirdly, leak detection is realized by observing pressure change through water injection and pressure maintaining, the method firstly needs to be connected with a water pipe in a butt joint mode, the operation is complex, the precision is not high, a pressurizing device needs to be calibrated frequently, in addition, a refrigerating system after water injection and pressure maintaining is basically scrapped, and the detection cost is high.
In summary, the above three methods can achieve leak detection, but all have the problem of low leak detection precision, and for products with high requirement for air tightness level, the requirements for air tightness test cannot be met, and also all have the disadvantages of high detection cost caused by complex operation, low detection efficiency, and the like.
Disclosure of Invention
The invention aims to provide a refrigerating system air tightness detection method which gives consideration to leakage detection precision and detection efficiency. The refrigerating system in the invention refers to the refrigerating equipment or comprises the refrigerating equipment and a sealing part connected with the refrigerating equipment.
The technical scheme adopted by the invention comprises the following specific contents: a method for detecting the air tightness of a refrigerating system includes such steps as coarse detection of the sample to be detected for higher leakage, and fine detection after the coarse detection is qualified.
The rough detection and the fine detection adopt different methods.
And the rough detection and the fine detection automatically judge whether the parameters pass or not by monitoring whether the change of the test parameters in the set time exceeds a threshold value.
If the detected sample has large leakage, the leakage phenomenon is obvious and the sample can be detected quickly. The invention divides the detection into two flows, and avoids the problems of low overall efficiency caused by strict standard and low detection precision caused by loose standard when a unified detection standard is adopted for large leakage and small leakage.
The rough detection steps are as follows:
and (3) placing the sample to be detected in a vacuum box, adjusting the pressure difference between the sample to be detected and the gas in the vacuum box to ensure that the gas pressure in the sample to be detected is greater than that in the vacuum box, and observing the change of the pressure in the vacuum box so as to judge whether the sample to be detected leaks greatly.
In the rough detection step, the mode of adjusting the pressure difference between the sample to be detected and the gas in the vacuum box is as follows: the vacuum box is vacuumized, and the detected sample is filled with compressed gas, so that a larger pressure difference is formed between the detected sample and the vacuum box, and the inspection precision is improved.
The fine inspection steps are as follows:
and filling tracer gas into the detected sample, enabling the gas pressure in the detected sample to be greater than that in the vacuum box, and detecting the change of the concentration of the tracer gas in the vacuum box by using a leak detector so as to judge whether the detected sample has small leakage.
In the fine detection step, before the trace gas is filled into the detected sample, the vacuum box and the detected sample are respectively vacuumized, and the step is also beneficial to improving the detection precision.
In the fine detection step, the detection accuracy is ensured through repeated recheck.
The invention is applicable to the detection standard: ISO 14903-2017, IEC 60335-2-40: 2018.
Has the advantages that:
1) the invention divides the air tightness detection of the refrigerating system into two flows, avoids the problems of low overall efficiency caused by strict standards and low detection precision caused by loose standards when a unified detection standard is adopted for large leakage and small leakage, and is beneficial to considering both the detection precision and the efficiency by the arrangement;
2) the method comprises the steps of placing a sample to be detected in a vacuum box, adjusting the pressure difference between the sample to be detected and the vacuum box, judging whether the sample to be detected has large leakage or not by detecting the pressure change in the vacuum box, and if the sample to be detected has large leakage, performing rough detection by the method can completely meet the requirements on precision and efficiency; different from a coarse detection method, the fine detection is realized by detecting whether the detected sample has trace gas leakage, and the method can realize higher detection precision and detection efficiency under the condition that the sample only has fine leakage. And only adopt the tracer gas representation method in the accurate detection environment, can effectively avoid tracer gas's waste. Compared with the prior art, the detection method can better meet the air tightness test requirement of products with high air tightness grade requirements, is simple to operate and high in efficiency, does not damage the detected samples, and can obviously reduce the detection cost.
Drawings
FIG. 1 is a schematic diagram of a detection device used in a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of the overall structure of a detecting device used in the preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of the connection of some modules of the detecting device used in the preferred embodiment of the present invention;
FIG. 4 is a diagram of the control loop of the detecting device used in the preferred embodiment of the present invention.
Detailed Description
The method for detecting the air tightness of the refrigerating system comprises the following main steps: during detection, firstly, filling high-pressure nitrogen into a detected sample (positioned in a vacuum box), and then detecting leakage by monitoring the change of the pressure in the vacuum box; and then, according to the basic leak detection principle of helium leak detection, helium is used as tracer gas, the helium is filled into the detected sample, and then the helium leak detector is used for detecting whether the tracer gas exists in the vacuum box or not, so that the precise detection of the detected sample is realized. The method can judge the leakage condition of the detected sample rapidly and accurately with high precision.
The following is a detailed description of the method of this embodiment.
Fig. 1 is a schematic diagram of the detecting device of the present embodiment. The following detailed description of the method according to this embodiment is provided with reference to schematic diagrams:
1. coarse inspection
After the vacuum box door is closed, the control system opens the electromagnetic valve V6, simultaneously starts the vacuum pump 1, and performs rough pumping and fine pumping on the vacuum box in sequence until the vacuum degree in the box reaches the set leak detection pressure, such as 50 Pa. When the vacuum box is vacuumized, the control system opens the electromagnetic valve V1, high-pressure nitrogen gas of 2.0MPa (adjustable range: 0.5-2 MPa) is filled into a detected sample in the box, then pressure maintaining is carried out, and after a set time, the control system judges whether large leakage exists according to a detection result of a pressure gauge (used for monitoring the air pressure in the vacuum box). If the sample has large leakage, the control system exhausts the high-pressure gas in the sample, simultaneously closes an air exhaust valve V6 of the vacuum box, terminates the rough detection program, and opens a V7 to fill the vacuum box with the atmosphere. The operator presses the confirmation button on the touch screen of the control system, the vacuum box door is automatically opened, the sample is taken out, and the sample is placed in the to-be-treated area after being marked. And if the control system does not find the sample leakage, automatically entering the next step of leakage detection program.
In this embodiment, after maintaining the pressure for a period of time, the value of the pressure gauge is observed, and whether the rough inspection of the detected sample passes or not is judged. In other embodiments, whether to end the rough inspection may also be controlled by time-matching a pressure change threshold. If the set time is up or the pressure increment exceeds the pressure change threshold, the rough detection of the detected sample is judged to be unqualified. Compared with the two control modes, the former is simple, and the latter is generally more efficient.
2. Precision inspection
2-1) evacuating the sample: if no sample leakage is found, the control system opens the V3, the V4 and the vacuum pump 2 to discharge high-pressure gas in the sample, then closes the V4, vacuumizes the interior of the sample, stops vacuuming after the vacuum degree in the sample reaches a set pressure value, and waits for the completion of the vacuumizing process of the vacuum box. The set value of the vacuum degree in the sample is set according to the accuracy which needs to be achieved by the sample needing to be subjected to leak detection, namely the air tightness grade which needs to be tested, and the higher the vacuum degree is, the higher the air tightness grade which can be tested is. Generally, 1500Pa is set as the low detection pressure setting value, 200Pa is set as the medium detection pressure setting value, and 20Pa is set as the fine detection pressure setting value.
2-2) vacuum helium testing: when the evacuation of the vacuum box reaches the set leak detection pressure and is usually set to be 40Pa, and meanwhile, the evacuation of a sample in the box is finished, the control system firstly opens the V5 and the vacuum pump 3, detects the concentration of helium in the vacuum box through the leak detector, inhibits zero of the signal, then opens the V2, fills helium of 2.0Mpa (adjustable range: 0.5-2 MPa) into the sample, and after the pressure of the helium in the sample reaches the set value, the leak detector carries out leak detection on the sample again. If the leak detector finds that the helium signal exceeds the set value, the sample in the box leaks slightly, the control system automatically carries out circulating detection on the sample, namely the current helium signal is suppressed to zero again, the above detection is repeated, and after 1-3 times of repeated detection (each time lasts for 3-8 minutes), if the problem still exists, the sample is judged to have the leakage, and the signal lamp displays reminding. And opening the V7, automatically opening the vacuum box after the vacuum box is filled with the atmosphere, and taking out and marking the sample after an operator can separate the quick connector from the sample. If the leak detector does not detect a helium signal exceeding the set value, it indicates that the sample to be tested is not leaking, and the control system sends a signal that the test is passed. The leak detector adopted in this embodiment is of the following instrument type: 231B, manufacturer: and (5) a Wan instrument.
2-3) helium gas emission: after the sample detection is passed, the V3, the V4 and the vacuum pump 2 are started again, helium in the sample is automatically discharged, meanwhile, the control system starts the V7 to fill air into the vacuum box, when the pressure of the vacuum box rises to the atmospheric pressure, the door of the vacuum box is automatically opened, the detection procedure is completed, and the product is manually taken down.
The gas storage tank in fig. 1 is used for buffering and stabilizing pressure so as to stabilize the gas pressure in the sample. The detection device monitors the pressure of the gas in the vacuum box and the sample through the pressure gauge, monitors the vacuum degree of the gas in the vacuum box and the sample through the vacuum gauge, and the specific installation positions of the gas and the vacuum gauge, and a person skilled in the art can select a proper position to install according to the detection process in the embodiment. In this embodiment, the pressure gauge is mainly used for detecting the pressure of the high-pressure (higher than atmospheric pressure) gas to make up for the deficiency of the vacuum gauge in detecting the high-pressure gas.
In the embodiment, helium is used as the tracer gas, and the detection cost is substantially as follows: one bottle of helium with the volume of 40L and the pressure of 15MPa and the purity of 99.9 percent is about 2000 yuan. The volume converted to one atmosphere is: 40Lx150 ═ 6000L. 5000L can be used by removing the residual factors in the bottle, so that the unit volume cost of helium is 0.4 yuan/L. Therefore, when helium is used as the tracer gas, the test cost can be well controlled.
Fig. 2 is a schematic view of the overall structure of the detection device used in the method of the present embodiment. As shown in fig. 2, the detection device is designed as a rectangular box. The front of this box is equipped with a plurality of lattice structures, and left side below is vacuum box 11, and the upper left side is the sample and places district 12, and the upper right side is electrical control cabinet 13, and touch display screen 131 and a plurality of control button 132 set up on electrical control cabinet 13's cabinet door, and leak detector 2 places in instrument cabinet 14 of electrical control cabinet 13 below. Other structures are all arranged in the box body. The detection device of the structure has the following characteristics:
1) the vacuum box is reasonable in position, and a large detected sample can be conveniently tested;
2) the electrical socket of the leak detector 2 is directly inserted into the instrument cabinet 14 and is fixed to the cabinet wall of the instrument cabinet 14. The leak detector 2 is arranged in the instrument cabinet 14, can be conveniently connected with electricity to form a part of the detection device of the embodiment, and can also be taken out at any time for independent use;
3) the integrity of the device is better.
The connection of the tubing system to the vacuum box and sample in fig. 1 is as follows:
the pipeline system is communicated with the inner side of the vacuum box through a joint which is hermetically arranged on the wall of the vacuum box, and the pipeline system used for being connected with the sample is further communicated with a quick joint through a high-pressure-resistant flexible pipe (the pressure resistance is up to 6Mpa) which is easy to bend so as to be conveniently and quickly connected with the sample through the quick joint. The quick connector interface pipe diameter adopted in the embodiment is provided with 5/8-turn 3/8, 1/4, 1/2 and 3/4 copper pipe connectors which are respectively provided with two sets. Is provided with a digital display torque wrench set.
The control system of the above detection device is mainly composed of a PLC, a switching value expansion module FBs-8YR, an analog value expansion module FBs-4A2D, and a touch panel, as shown in fig. 3 and 4. The touch screen and the leak detector are respectively connected with the PLC, and the PLC is also respectively connected with a switching value expansion module FBs-8YR and an analog value expansion module FBs-4A2D which are respectively used for expanding a switching value contact and an analog value contact of the PLC. Various data acquisition devices in the detection device mainly refer to a pressure gauge, a vacuum gauge, a leak detector and the like, various indicator lamps and electromagnetic valves are respectively connected with a control system, and the connection relationship between the indicator lamps and the electromagnetic valves and the control system is specifically shown in fig. 4. The pressure gauge is used for detecting the pressure during inflation so as to judge whether the inflated pressure meets, and the vacuum gauge is used for detecting during vacuum pumping so as to judge whether the vacuum in the vacuum box and the vacuum in the sample reach a set value. The pressure gauge, the vacuum gauge and the leak detector are connected with the analog quantity expansion module FBs-4A2D, and the acquired real-time value is output to the PLC so that the PLC can make a judgment.
Different from the prior art, the leak detector of the embodiment is additionally provided with an analog quantity monitoring end besides finishing information interaction (transmitting various information including leakage rate) by connecting with the PLC through a 485 bus. The communication connection through the 485 bus can inevitably have some delay conditions, and the connection between the added leak detector and the analog quantity expansion module FBs-4A2D feeds back the real-time leakage rate of the leak detector to the analog quantity input of the PLC through the analog quantity signal output so as to improve the control precision of the control system.
The main technical parameters of the detection device are as follows:
minimum detectable leak rate: 5X 10-12Pa·m3/s；
Leak rate display range: 1X 10-3～1×10-12Pa·m3Start-up time (referring to the time required for the device to perform a self-test process before each power-on): less than or equal to 5min
Response time (time for the leaked helium molecules to undergo signal conversion by molecular pumping to the helium mass spectrometer chamber): <1S leak detection port maximum pressure (leak detector maximum pressure to evacuate): 1300Pa
Ultimate vacuum (ultimate pressure that the vacuum box can withstand): 5X 10-1Pa
The device adopts a process flow automation technology, combines process equipment with an electric automatic control technology, automatically controls the whole sample detection process flow by the PLC and the touch screen, and an operator only needs to install and uninstall a sample without judging the result of each process flow, and automatically judges the result of the previous step and completes the execution of the next step by the PLC according to preset conditions.
The detection device has the characteristics of simplicity in operation, high automation degree, safety, high efficiency, high leakage detection precision and the like.
The method is suitable for testing the sealing performance of all parts and the whole machine of the refrigeration system, has wide measuring range and high precision, and has wide application range.
Claims (8)
1. The method for detecting the air tightness of the refrigerating system is characterized in that a sample to be detected is subjected to rough detection to detect large leakage, and fine detection is performed after the rough detection is qualified.
2. The method for detecting the airtightness of a refrigerating system according to claim 1, wherein the rough inspection and the fine inspection are performed by different methods.
3. The method for detecting the airtightness of the refrigerating system according to claim 2, wherein the rough inspection and the fine inspection are performed by monitoring whether the variation of the test parameter within a set time exceeds a threshold value, so as to automatically determine whether the variation passes or not.
4. A method for detecting the airtightness of a refrigerating system according to claim 3, wherein the rough detection step is as follows:
and (3) placing the sample to be detected in a vacuum box, adjusting the pressure difference between the sample to be detected and the gas in the vacuum box to ensure that the gas pressure in the sample to be detected is greater than that in the vacuum box, and observing the change of the pressure in the vacuum box so as to judge whether the sample to be detected leaks greatly.
5. The method for detecting the airtightness of a refrigerating system according to claim 4, wherein in the rough detection step, the pressure difference between the sample to be detected and the gas in the vacuum box is adjusted in a manner that: and vacuumizing the vacuum box, and filling compressed gas into the detected sample.
6. A refrigerating system airtightness detection method according to any one of claims 1 to 5, wherein the fine inspection step is as follows:
and filling tracer gas into the detected sample, enabling the gas pressure in the detected sample to be greater than that in the vacuum box, and detecting the change of the concentration of the tracer gas in the vacuum box by using a leak detector so as to judge whether the detected sample has small leakage.
7. The method as claimed in claim 6, wherein in the fine inspection step, before the trace gas is filled into the sample to be inspected, the vacuum box and the sample to be inspected are respectively vacuumized.
8. The method for detecting the airtightness of the refrigerating system according to claim 7, wherein in the fine inspection step, the detection accuracy is ensured by repeating the re-inspection.
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| CN202010934568.6A CN112197916A (en) | 2020-09-08 | 2020-09-08 | Method for detecting air tightness of refrigerating system |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114486104A (en) * | 2022-01-26 | 2022-05-13 | 中家院（北京）检测认证有限公司 | System and method for detecting sealing performance of refrigerating device and storage medium |
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