Ultra-low temperature liquid nitrogen immersion test device and method

Abstract

The invention provides an ultra-low temperature liquid nitrogen immersion test device and method, comprising a test box, a liquid nitrogen tank, a test bench, a liquid nitrogen circulation pipe system, a temperature adjustment mechanism and a control system. The liquid nitrogen tank and the test bench are both arranged inside the box body. The liquid nitrogen circulation pipe system comprises a connected liquid inlet main pipe and a recovery branch pipe. The liquid inlet main pipe is respectively connected to the liquid nitrogen tank and the liquid nitrogen tank. The temperature adjustment mechanism comprises a thermometer and a vaporization component. The thermometer is arranged on the upper part of the box body and is connected to the control system. The vaporization component comprises a vaporizer, a vaporization inlet pipe and a vaporization outlet pipe. The two ends of the vaporization inlet pipe are respectively connected to the inlet of the vaporizer and the liquid nitrogen tank, and the two ends of the vaporization outlet pipe are respectively connected to the outlet of the vaporizer and the test box. The control system is a PLC industrial control cabinet, which controls the liquid nitrogen to enter and exit the test box and adjust the temperature in the test box. The invention can perform performance tests for special large-scale structures, and can also perform ultra-low temperature performance tests for special new materials, so as to understand the ultra-low temperature comprehensive performance of the materials after manufacturing.

Description

Technical Field

[0001] The invention belongs to the technical field of ultra-low temperature materials and components thereof in ultra-low temperature environment tests and cross-use in aerospace, and in particular relates to an ultra-low temperature liquid nitrogen immersion test device and method. Background Art

[0002] When a spacecraft is flying in space, there is a temperature difference between the sun side and the dark side, and this temperature difference is constantly changing, which makes the spacecraft suffer from the influence of temperature difference stress. To test the tolerance of this alternating stress environment to the spacecraft, it is necessary to conduct alternating tests in ultra-low temperature environment and normal temperature environment to understand the reliability of different materials and different structures under the alternating stress state of thermal cycle. To complete these tests, liquid nitrogen immersion tests are required. The application environment of aerospace products is extremely harsh space and outer space, and the requirements for materials and welding are very high. Various new materials are constantly being used in aerospace and aircraft and their components, and the demand for ultra-low temperature thermal cycle tests below -150℃ is increasing. This test basically uses liquid nitrogen immersion to simulate the alternating stress state of the workpiece alternating between ultra-low temperature and normal temperature. If the structural changes of the liquid nitrogen test box body during the test are not considered, the weld of the box body is easy to tear under the action of alternating stress, resulting in a safety accident of ultra-low temperature liquid nitrogen leakage. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an ultra-low temperature liquid nitrogen immersion test device and method for the above-mentioned problems.

[0004] The technical solution adopted by the present invention to solve the above technical problems is: an ultra-low temperature liquid nitrogen immersion test device, characterized in that it includes a test box, a liquid nitrogen tank, a test bench, a liquid nitrogen circulation pipe system, a temperature adjustment mechanism and a control system, the test box includes a box body and a box cover, the liquid nitrogen tank and the test bench are both arranged inside the box body, the liquid nitrogen circulation pipe system includes a liquid inlet main pipe and a recovery branch pipe, the two ends of the liquid inlet main pipe are respectively connected to the liquid nitrogen tank and the liquid nitrogen tank, the recovery branch pipe is connected to the liquid inlet main pipe, the temperature adjustment mechanism includes a thermometer and a vaporization component, the thermometer is arranged on the upper part of the box body and is connected to the control system, the vaporization component includes a vaporizer, a vaporization inlet pipe and a vaporization outlet pipe, the two ends of the vaporization inlet pipe are respectively connected to the inlet of the vaporizer and the liquid inlet main pipe, the two ends of the vaporization outlet pipe are respectively connected to the outlet of the vaporizer and the test box, the control system is a PLC industrial control cabinet, which controls the liquid nitrogen to enter or discharge the test box and adjust the temperature in the test box.

[0005] According to the above scheme, the test box includes a test inner shell and an insulating outer shell arranged inside and outside, the insulating outer shell includes an insulating inner shell and an insulating outer shell arranged inside and outside, forming an insulating cavity, the insulating cavity is filled with insulating cotton, a vacuum chamber is provided between the test inner shell and the insulating inner shell, the vacuum chamber is connected with a vacuum tube arranged on the insulating outer shell, a vacuum tube cap is provided at the pipe mouth of the vacuum tube, and the vacuum degree of the vacuum chamber is ≥0.005pa.

[0006] According to the above scheme, the liquid inlet main pipe, the recovery branch pipe and the vaporization inlet pipe are respectively provided with a liquid nitrogen input pump, a liquid nitrogen recovery pump and a vaporization delivery pump, which are all connected to the PLC industrial control cabinet.

[0007] According to the above scheme, a liquid level meter is provided in the test box and is connected to the PLC industrial control cabinet.

[0008] According to the above solution, a polytetrafluoroethylene pad is laid between the liquid nitrogen tank and the bottom plate of the test box.

[0009] According to the above scheme, an exhaust pipe is provided on the box cover, and an exhaust pipe cap is provided at the exhaust pipe opening.

[0010] According to the above solution, supporting ribs are provided between the thermal insulation inner shell and the test inner shell.

[0011] According to the above scheme, the volume of the liquid nitrogen tank is 30% to 60% of the volume of the test inner shell.

[0012] According to the above scheme, the test bench is composed of legs and a platform, the platform is higher than the top of the liquid nitrogen tank, and the legs are located in the gap between the liquid nitrogen tank and the inner wall of the test box.

[0013] A method for ultra-low temperature liquid nitrogen immersion test, characterized in that it comprises the following steps:

[0014] S1) Carry out nondestructive testing and dimensional inspection on the welded or machined workpieces to be tested, and record the important dimensions of the workpieces after they pass the test;

[0015] S2) Use a robot arm or crane to open the box cover, place the workpiece to be immersed in liquid nitrogen on the test bench, then close the box cover to make the test box sealed, and open the exhaust pipe cap;

[0016] S3) turning on the PLC industrial control cabinet, starting the liquid nitrogen input program, and allowing the liquid nitrogen to be input into the liquid nitrogen tank through the liquid inlet main pipe;

[0017] S4) The electronic liquid level gauge monitors the liquid level. When the liquid nitrogen reaches 90% of the depth of the liquid nitrogen tank, the PLC industrial control cabinet shuts off the liquid nitrogen input pump;

[0018] S5) Turn on the vaporization delivery pump, let the liquid nitrogen in the liquid nitrogen tank enter the vaporizer through the vaporization inlet pipe to form low-temperature nitrogen, and the vaporization outlet pipe delivers the ultra-low temperature nitrogen to the test box. The thermometer monitors the temperature in the test box. The PLC industrial control cabinet controls the cooling speed inside the test box by controlling the flow of the vaporization delivery pump;

[0019] S6) After the temperature in the test chamber reaches -100°C, turn off the vaporization delivery pump, restart the liquid nitrogen input program, input liquid nitrogen into the liquid nitrogen tank, let the liquid nitrogen overflow from the liquid nitrogen tank, and fill the test chamber with liquid nitrogen until the workpiece to be immersed in the test is submerged. When the workpiece is completely immersed below the liquid nitrogen level and the temperature reaches -196°C±0.5°C, tighten the exhaust pipe cap to carry out the insulation immersion treatment;

[0020] S7) turning on the liquid nitrogen recovery pump to recover the liquid nitrogen to an external liquid nitrogen tank through the recovery pipe;

[0021] S8) simultaneously starting the vaporization delivery pump to vaporize the liquid nitrogen in the liquid nitrogen tank, and controlling the flow rates of the liquid nitrogen recovery pump and the vaporization delivery pump to slowly raise the temperature inside the test chamber;

[0022] S9) When the temperature in the test chamber rises to above -50℃, open the cover and use a blower to purge the liquid nitrogen tank through the liquid inlet main pipe to allow the natural temperature to convect with the low temperature in the test chamber. After the workpiece returns to room temperature, continue the next cycle test or complete the single test. After the test is completed, lift the test workpiece out of the test chamber;

[0023] S10) After the test, re-check the corresponding dimensions of the workpiece to see if there is any dimensional change, and observe whether there is brittle cracking in the weld.

[0024] The beneficial effects of the present invention are as follows: providing an ultra-low temperature liquid nitrogen immersion test device and method, using a separate liquid nitrogen tank to fill liquid nitrogen, and using a vaporizer to vaporize part of the liquid nitrogen to gradually reduce the temperature inside the test box, so that the temperature drops to a low temperature of -100°C, and then all the liquid nitrogen is slowly filled into the interior of the test box, allowing the liquid nitrogen to overflow the liquid nitrogen tank with part number 17 and immerse the test workpiece, the heating and cooling requirements during the test are preset by the PLC industrial control cabinet, and the flow of all pumps and valves is automatically controlled by the servo motor to receive the instructions of the PLC to meet the requirements of technical regulations, the test device can be large or small, and can be used for performance tests of special large structures, and can also be used for ultra-low temperature performance tests of special new materials, such as ultra-low temperature immersion tests after the material is welded, and then dissected for microscopic inspection to see whether there are microcracks, and the normal temperature impact value and ultra-low temperature impact value of the weld and the heat-affected zone are tested to understand the ultra-low temperature comprehensive performance of the material after manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1It is a schematic structural diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0027] like Figure 1 As shown, the ultra-low temperature liquid nitrogen immersion test device includes a test box 1, a liquid nitrogen tank 2, a test bench 3, a liquid nitrogen circulation pipe system, a temperature control mechanism and a control system. The test box includes a box body and a box cover. The liquid nitrogen tank and the test bench are both arranged inside the box body. The liquid nitrogen circulation pipe system includes a liquid inlet main pipe 4 and a recovery branch pipe 5. The two ends of the liquid inlet main pipe are respectively connected to the liquid nitrogen tank and the liquid nitrogen tank, and the recovery branch pipe is connected to the liquid inlet main pipe. The temperature control mechanism includes a thermometer 6 and a vaporization component. The thermometer is arranged on the upper part of the box body and is connected to the control system. The vaporization component includes a vaporizer 7, a vaporization inlet pipe 8 and a vaporization outlet pipe 9. The two ends of the vaporization inlet pipe are respectively connected to the inlet of the vaporizer and the liquid inlet main pipe, and the two ends of the vaporization outlet pipe are respectively connected to the outlet of the vaporizer and the test box. The control system is a PLC industrial control cabinet 10, which controls the liquid nitrogen to enter or discharge the test box and adjust the temperature in the test box.

[0028] The test box includes an inner test shell 11 and an outer insulation shell, the outer insulation shell includes an inner insulation shell 12 and an outer insulation shell 13, forming an insulation cavity, the insulation cavity is filled with insulation cotton 14, a vacuum chamber 15 is provided between the test inner shell and the insulation inner shell, the vacuum chamber is connected to the vacuum tube provided on the insulation shell, the mouth of the vacuum tube is provided with a vacuum tube cap, and the vacuum degree of the vacuum chamber is ≥0.005pa. In order to ensure the insulation effect of the liquid nitrogen test box, a double-layer insulation scheme is adopted, the inside is vacuumed for insulation, and the outside is insulated with insulation cotton. A support rib spot welding support is provided between the insulation inner shell and the test inner shell, and the outside of the vacuum chamber is completely sealed and welded.

[0029] The box cover of the test box is made of austenitic stainless steel, and the middle is filled with thickened thermal insulation asbestos to play a role in heat preservation. A slot and an asbestos pad are set between the box cover and the box body. After the box cover is closed, the box cover and the box body are fastened with a clamp or bolt to play a sealing role to prevent nitrogen from escaping. An exhaust pipe 16 is provided on the box cover, and an exhaust pipe cap 17 is provided at the exhaust pipe mouth.

[0030] The liquid inlet main pipe, recovery branch pipe and vaporization inlet pipe are respectively provided with liquid nitrogen input pump 18, liquid nitrogen recovery pump 19 and vaporization delivery pump 20, all of which are connected to the PLC industrial control cabinet. The PLC industrial control cabinet controls the opening and closing of the above pumps and valves, thereby controlling the flow direction of the liquid nitrogen.

[0031] A liquid level meter 21 is provided in the test box, which is connected to the PLC industrial control cabinet to monitor the temperature in the test box in real time and feed back to the PLC industrial control cabinet.

[0032] A polytetrafluoroethylene pad 22 is laid between the liquid nitrogen tank and the bottom plate of the test box, and the volume of the liquid nitrogen tank is 30% to 60% of the volume of the test inner shell. When liquid nitrogen is directly filled, rapid cooling will cause a large temperature difference stress. The liquid nitrogen tank and the bottom plate of the test box are isolated by a polytetrafluoroethylene pad to ensure that the liquid nitrogen tank can shrink and expand freely, and prevent structural stress instability and cracks caused by temperature imbalance.

[0033] The test bench consists of legs and a platform. The platform is higher than the top of the liquid nitrogen tank. The legs are located in the gap between the liquid nitrogen tank and the inner wall of the test chamber, and a dimensional spacing of more than 20 mm should be left with the outer wall of the liquid nitrogen tank to ensure that the liquid nitrogen tank does not interfere with the legs of the test bench when it is reduced in size during the initial stage of filling with liquid nitrogen.

[0034] The test chamber, liquid nitrogen tank, piping, pumps, valves and other components are all made of 304, 304L or 316L austenitic stainless steel. The vaporizer can be made of austenitic stainless steel or aluminum alloy.

[0035] The heating and cooling requirements during the test are preset by the PLC industrial control cabinet, and the flow of all pumps and valves is automatically controlled by the servo motor receiving the instructions of the PLC industrial control cabinet. When the heating or cooling speed exceeds the technical requirements, the PLC industrial control cabinet sensing system automatically adjusts the vaporizer flow and liquid nitrogen input flow to meet the requirements of the technical requirements.

[0036] The method for conducting an ultra-low temperature liquid nitrogen immersion test using the above device comprises the following steps:

[0037] S1) Carry out nondestructive testing and dimensional inspection on the welded or machined workpieces to be tested, and record the important dimensions of the workpieces after they pass the test;

[0038] S2) Use a robot arm or crane to open the box cover, place the workpiece to be immersed in liquid nitrogen on the test bench, then close the box cover to make the test box sealed, and open the exhaust pipe cap;

[0039] S3) turning on the PLC industrial control cabinet, starting the liquid nitrogen input program, and allowing the liquid nitrogen to be input into the liquid nitrogen tank through the liquid inlet main pipe;

[0040] S4) The electronic liquid level gauge monitors the liquid level. When the liquid nitrogen reaches 90% of the depth of the liquid nitrogen tank, the PLC industrial control cabinet shuts off the liquid nitrogen input pump;

[0041] S5) Turn on the vaporization delivery pump, let the liquid nitrogen in the liquid nitrogen tank enter the vaporizer through the vaporization inlet pipe to form low-temperature nitrogen, and the vaporization outlet pipe delivers the ultra-low temperature nitrogen to the test box. The thermometer monitors the temperature in the test box. The PLC industrial control cabinet controls the cooling speed inside the test box by controlling the flow of the vaporization delivery pump;

[0042] S6) After the temperature in the test chamber reaches -100°C, turn off the vaporization delivery pump, restart the liquid nitrogen input program, input liquid nitrogen into the liquid nitrogen tank, let the liquid nitrogen overflow from the liquid nitrogen tank, and fill the test chamber with liquid nitrogen until the workpiece to be immersed in the test is submerged. When the workpiece is completely immersed below the liquid nitrogen level and the temperature reaches -196°C±0.5°C, tighten the exhaust pipe cap to carry out the insulation immersion treatment;

[0043] S7) turning on the liquid nitrogen recovery pump to recover the liquid nitrogen to an external liquid nitrogen tank through the recovery pipe;

[0044] S8) simultaneously starting the vaporization delivery pump to vaporize the liquid nitrogen in the liquid nitrogen tank, and controlling the flow rates of the liquid nitrogen recovery pump and the vaporization delivery pump to slowly raise the temperature inside the test chamber;

[0045] S9) When the temperature in the test chamber rises to above -50℃, open the cover and use a blower to purge the liquid nitrogen tank through the liquid inlet main pipe to allow the natural temperature to convect with the low temperature in the test chamber. After the workpiece returns to room temperature, continue the next cycle test or complete the single test. After the test is completed, lift the test workpiece out of the test chamber;

[0046] S10) After the test, re-check the corresponding dimensions of the workpiece to see if there is any dimensional change, and observe whether there is brittle cracking in the weld.

[0047] Embodiment 1

[0048] Cryogenic treatment of Invar steel welded parts:

[0049] Invar steel is the steel with the smallest expansion coefficient among existing metal materials. It is suitable for use in ultra-low temperature environments, but it is extremely difficult to weld. In order to test the reliability of the welded joints of Invar steel parts in ultra-low temperature environments, deep cryogenic treatment is performed on them. The requirements are as follows:

[0050] a. Cryogenic treatment should be carried out in a temperature-controlled manner. The lowest test temperature is liquid nitrogen temperature (77K). The cooling rate of the workpiece should not be too fast to prevent uneven heating of the workpiece or rapid cooling and rapid drop, which may cause cracks in the component under temperature difference stress. Therefore, the maximum cooling rate should not exceed 5K / min;

[0051] b. The workpiece is cooled by slowly draining liquid nitrogen, and the cooling rate is no more than 10K / min;

[0052] c. The workpiece is gradually cooled from room temperature to the liquid nitrogen temperature zone and then heated up to room temperature for one cryogenic treatment cycle. The number of cycles is 3. After the workpiece is cooled to the liquid nitrogen temperature zone and completely cooled, the single immersion time is not less than 30 minutes. After the workpiece is completely warmed up, a time interval of not less than 3 hours is required before the next cryogenic cycle treatment can be carried out.

[0053] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for ultra-low temperature liquid nitrogen immersion test, characterized in that: The test is carried out using an ultra-low temperature liquid nitrogen immersion test device, the test device includes a test box, a liquid nitrogen tank, a test bench, a liquid nitrogen circulation pipe system, a temperature adjustment mechanism and a control system, the test box includes a box body and a box cover, the liquid nitrogen tank and the test bench are both arranged inside the box body, the liquid nitrogen circulation pipe system includes a liquid inlet main pipe and a recovery branch pipe, the two ends of the liquid inlet main pipe are respectively connected to the liquid nitrogen tank and the liquid nitrogen tank, the recovery branch pipe is connected to the liquid inlet main pipe, the temperature adjustment mechanism includes a thermometer and a vaporization component, the thermometer is arranged on the upper part of the box body and is connected to the control system, the vaporization component includes a vaporizer, a vaporization inlet pipe and a vaporization outlet pipe, the two ends of the vaporization inlet pipe are respectively connected to the inlet of the vaporizer and the liquid inlet main pipe, the two ends of the vaporization outlet pipe are respectively connected to the outlet of the vaporizer and the test box, the control system is a PLC industrial control cabinet, which controls the liquid nitrogen to enter or discharge the test box, and adjusts the temperature in the test box; The test method using the above test device specifically includes the following steps: S1) Carry out nondestructive testing and dimensional inspection on the welded or machined workpieces to be tested, and record the important dimensions of the workpieces after they pass the test; S2) Use a robot arm or crane to open the box cover, place the workpiece to be immersed in liquid nitrogen on the test bench, then close the box cover to make the test box sealed, and open the exhaust pipe cap; S3) Turn on the PLC industrial control cabinet and start the liquid nitrogen input program, so that the liquid nitrogen is input into the liquid nitrogen tank through the liquid inlet main pipe; S4) The electronic liquid level gauge monitors the liquid level. When the liquid nitrogen reaches 90% of the depth of the liquid nitrogen tank, the PLC industrial control cabinet shuts off the liquid nitrogen input pump; S5) Turn on the vaporization delivery pump to allow the liquid nitrogen in the liquid nitrogen tank to enter the vaporizer through the vaporization inlet pipe to form low-temperature nitrogen. The vaporization outlet pipe delivers the ultra-low temperature nitrogen to the test chamber. The thermometer monitors the temperature in the test chamber. The PLC industrial control cabinet controls the cooling speed inside the test chamber by controlling the flow of the vaporization delivery pump. S6) After the temperature in the test chamber reaches -100℃, turn off the vaporization delivery pump, restart the liquid nitrogen input program, input liquid nitrogen into the liquid nitrogen tank, let the liquid nitrogen overflow the liquid nitrogen tank, and fill the test chamber with liquid nitrogen until the workpiece to be immersed in the test is submerged. When the workpiece is completely immersed below the liquid nitrogen level and the temperature reaches -196℃±0.5℃, tighten the exhaust pipe cap to carry out the insulation immersion treatment; S7) Turn on the liquid nitrogen recovery pump to recover the liquid nitrogen to an external liquid nitrogen tank through the recovery pipe; S8) At the same time, the vaporization delivery pump is turned on to vaporize the liquid nitrogen in the liquid nitrogen tank, and the flow rates of the liquid nitrogen recovery pump and the vaporization delivery pump are controlled to slowly raise the temperature inside the test chamber; S9) When the temperature in the test chamber rises to above -50℃, open the cover and use a blower to purge the liquid nitrogen tank through the liquid inlet main pipe to allow the natural temperature to convect with the low temperature in the test chamber. After the workpiece returns to room temperature, continue the next cycle test or complete the single test. After the test is completed, lift the test workpiece out of the test chamber; S10) After the test, re-check the corresponding dimensions of the workpiece to see if there is any dimensional change, and observe whether there is brittle cracking in the weld.

2. The ultra-low temperature liquid nitrogen immersion test method according to claim 1, characterized in that: The test box includes a test inner shell and a thermal insulation outer shell which are arranged inside and outside. The thermal insulation outer shell includes a thermal insulation inner shell and a thermal insulation outer shell which are arranged inside and outside to form a thermal insulation cavity. The thermal insulation cavity is filled with thermal insulation cotton. A vacuum cavity is provided between the test inner shell and the thermal insulation inner shell. The vacuum cavity is connected to a vacuum tube arranged on the thermal insulation outer shell. A vacuum tube cap is provided at the pipe mouth of the vacuum tube. The vacuum degree of the vacuum cavity is ≥0.005pa.

3. The ultra-low temperature liquid nitrogen immersion test method according to claim 2, characterized in that: The liquid inlet main pipe, the recovery branch pipe and the vaporization inlet pipe are respectively provided with a liquid nitrogen input pump, a liquid nitrogen recovery pump and a vaporization delivery pump, and are all connected to the PLC industrial control cabinet.

4. The ultra-low temperature liquid nitrogen immersion test method according to claim 3, characterized in that: A liquid level meter is arranged in the test box and is connected to the PLC industrial control cabinet.

5. The ultra-low temperature liquid nitrogen immersion test method according to claim 1 or 4, characterized in that: A polytetrafluoroethylene pad is laid between the liquid nitrogen tank and the bottom plate of the test box.

6. The ultra-low temperature liquid nitrogen immersion test method according to claim 1 or 4, characterized in that: An exhaust pipe is arranged on the box cover, and an exhaust pipe cap is arranged at the pipe opening of the exhaust pipe.

7. The ultra-low temperature liquid nitrogen immersion test method according to claim 2, characterized in that: Support ribs are arranged between the heat-insulating inner shell and the test inner shell.

8. The ultra-low temperature liquid nitrogen immersion test method according to claim 2, characterized in that: 30% to 60% of the test inner shell volume.

9. The ultra-low temperature liquid nitrogen immersion test method according to claim 1, characterized in that: The test bench is composed of legs and a platform, wherein the platform is higher than the top of the liquid nitrogen tank, and the legs are located in the gap between the liquid nitrogen tank and the inner wall of the test box.

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