Preparation process of stretchable fixed-length metal corrugated gas hose

Abstract

The invention relates to the technical field of corrugated pipes, and discloses a stretchable fixed-length metal corrugated gas hose preparation process which comprises the following steps: S1, corrugated pipe manufacturing: putting a metal pipe into a mold, injecting hydraulic oil into the mold through a high-pressure pump, and then starting a hydraulic forming machine to form the metal pipe, the pressure is released after the pressure is continuously maintained, and the formed corrugated pipe is taken out; S2, the corrugated pipe is pretreated; S3, welding and assembling are conducted; S4, a protective layer is installed; the metal pipe is formed into the corrugated pipe with the corrugated surface through the hydraulic forming machine, axial, transverse and angular displacement caused by temperature change, equipment vibration, foundation settlement and the like can be compensated in a pipeline system, fatigue damage in a pipeline is effectively reduced, the service life of the pipeline and equipment is prolonged, and the service life of the pipeline is prolonged. Therefore, the effects of reducing damage caused by overlarge stress and being beneficial to improving the reliability of a pipeline system are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of corrugated pipes, and in particular to a process for preparing a stretchable fixed-length metal corrugated gas hose. Background Art

[0002] As an efficient and clean energy source, gas has been widely used in modern life and industrial production. Whether it is home cooking, heating, or heating and combustion in the industrial field, gas plays a vital role. With the acceleration of urbanization and the improvement of people's living standards, the scope of gas use continues to expand, and higher requirements are placed on the safety and reliability of gas transportation. Therefore, gas hoses are needed for transportation, which are usually made of rubber or plastic to ensure a stable supply of gas.

[0003] However, with current technology, gas hoses are unable to withstand high pressures and are prone to dangerous situations such as rupture and leakage. They are also unable to absorb external force shocks, affecting the reliability of the pipeline system. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a process for preparing a stretchable fixed-length metal corrugated gas hose, which solves the problem that the hose is unable to withstand higher pressures and affects the reliability of the pipeline system.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A process for preparing a stretchable fixed-length metal corrugated gas hose comprises the following steps: S1: Bellows production, put the metal pipe into the mold, inject hydraulic oil into the mold through the high-pressure pump, and then start the hydraulic forming machine to form the metal pipe to form the corrugated shape of the bellows. Then, the pressure is maintained and then released. The formed bellows is taken out and its size is determined by the cutting device; S2: Pretreatment of the bellows: completely immerse the bellows in the pickling liquid in the acid-resistant container for pickling treatment, then rinse it through the spray device, then put it into the passivation liquid for passivation treatment, and finally rinse it with clean water, dry it and bake it; S3: Welding assembly, positioning the welding core and the threaded welding core on both sides of the bellows, cleaning the oil, rust and other impurities on the welding part for the second time to ensure that the welding surface is clean, and then using argon arc welding technology to start the arc at high frequency to generate an arc at the welding part, aligning the tungsten electrode with the welding part, controlling the welding speed and arc length, so that the molten pool is evenly filled in the welding joint, and gradually reducing the welding current at the end of welding; S4: Installation of protective layer. The surface of the metal bellows is roughened by controlling the sandblasting distance and angle through sandblasting technology. Then glue is evenly applied to the surface of the metal bellows, and the rubber material is pasted on it. The metal bellows with the rubber sleeve pasted is initially pressed by hand, and then the metal bellows with the rubber sleeve pasted is placed in the mold, and the rubber sleeve is heated and pressed using hot pressing equipment. S5: Quality inspection, fix one end of the metal corrugated gas hose on the lower fixture of the tensile testing machine, and connect the other end of the hose to the upper fixture, also ensuring that the connection is firm, then adjust the position and angle of the fixture, turn on the tensile testing machine, and observe the display screen of the testing machine and the status of the sample; S6: Packaging and storage. Before packaging, use a detergent to clean the dust, oil and impurities on the surface of the metal corrugated gas hose. Then add plastic protective caps or plugs to both ends of the hose, place it in the groove of the sponge pad, and then place it in a dry and light-proof environment.

[0006] Preferably, the metal tube in S1 is made of stainless steel, with an outer diameter of 10-16 mm and a wall thickness of 0.2 mm. The upper mold of the molding machine performs compression molding on the metal tube in the lower mold. The molding pressure is 100 MPa, and the pressure is maintained for 1-5 minutes. The outer diameter of the corrugated tube after molding is 12-20 mm, the corrugation height is 1-3 mm, and the corrugation spacing is 5-15 mm.

[0007] Preferably, the pickling solution in S2 is a mixture of hydrochloric acid and nitric acid in a volume ratio of 3:1, the concentration of the pickling solution is 10%-20%, the pickling time is 10-30 minutes, and the subsequent spraying and rinsing time is 5-10 minutes. The passivation solution is nitric acid with a concentration of 5%-10%, and the passivation time is 15-30 minutes. Spraying is performed here, the rinsing time is 5-10 minutes, and then drying is performed at a temperature of 50-80°C for 30-60 minutes.

[0008] Preferably, the welding current of the argon arc welding machine in S3 can be set to 80-120A, and the argon gas flow rate is between 8-12L / min.

[0009] Preferably, the sandblasting pressure in S4 is controlled at 0.5-0.8MPa, and the distance between the nozzle and the surface of the metal bellows is 100-200 mm, the angle between the nozzle and the surface of the metal bellows is generally 45°-90°, the sandblasting time is 5-10 minutes, the coating thickness of the glue is 0.2-0.5 mm, and then the hot pressing temperature of the hot pressing equipment is 120-180°C, and the pressure is 5-10MPa, and the hot pressing time is 5-15 minutes.

[0010] Preferably, the stretching speed of the tensile testing machine in S5 is 50-100 mm / min, and the maximum tensile force value can be set to 300-500N.

[0011] Preferably, the groove width of the sponge pad in S6 is 12-18 mm, the depth is 6-9 mm, the sponge density is 20-40 kg / m³, the relative humidity of the air in the packaging place and storage is 30%-50%, and the storage temperature is 10-30°C.

[0012] The present invention provides a process for preparing a stretchable fixed-length metal corrugated gas hose, which has the following beneficial effects: 1. The present invention forms a corrugated tube with a corrugated surface on a metal tube by a hydraulic forming machine, which can compensate for the axial, lateral and angular displacements caused by temperature changes, equipment vibrations, foundation settlement and the like in the pipeline system, effectively reduce fatigue damage in the pipeline, and extend the service life of the pipeline and equipment, thereby reducing damage caused by excessive stress and helping to improve the reliability of the pipeline system.

[0013] 2. The present invention can effectively remove oxides, rust, oil stains and other impurities on the surface of the bellows through pickling technology, activate the metal surface, and then passivate the surface of the bellows to produce a protective film, which can effectively block the erosion of external corrosive media, extend the service life of the bellows, and achieve the effect of improving the corrosion resistance and safety of the metal bellows.

[0014] 3. The present invention roughens the surface of the metal bellows through sandblasting technology, increases the surface roughness and surface area, can ensure the pressing quality of glue and rubber materials, and effectively prevent the rubber sleeve from falling off during use. At the same time, hot pressing further improves the firmness of the bond, ensuring that the product can maintain stable performance in various harsh environments, thereby achieving the effect of improving the protection and stability of the corrugated gas hose. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a process flow chart for preparing the metal corrugated gas hose. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Please refer to the attached Figure 1 The embodiment of the present invention provides a process for preparing a stretchable fixed-length metal corrugated gas hose, comprising the following steps: S1: Bellows production, put the metal pipe into the mold, inject hydraulic oil into the mold through the high-pressure pump, and then start the hydraulic forming machine to form the metal pipe to form the corrugated shape of the bellows. Then, the pressure is maintained and then released. The formed bellows is taken out and its size is determined by the cutting device; S2: Pretreatment of the bellows: completely immerse the bellows in the pickling liquid in the acid-resistant container for pickling treatment, then rinse it through the spray device, then put it into the passivation liquid for passivation treatment, and finally rinse it with clean water, dry it and bake it; S3: Welding assembly, positioning the welding core and the threaded welding core on both sides of the bellows, cleaning the oil, rust and other impurities on the welding part for the second time to ensure that the welding surface is clean, and then using argon arc welding technology to start the arc at high frequency to generate an arc at the welding part, aligning the tungsten electrode with the welding part, controlling the welding speed and arc length, so that the molten pool is evenly filled in the welding joint, and gradually reducing the welding current at the end of welding; S4: Installation of protective layer. The surface of the metal bellows is roughened by controlling the sandblasting distance and angle through sandblasting technology. Then glue is evenly applied to the surface of the metal bellows, and the rubber material is pasted on it. The metal bellows with the rubber sleeve pasted is initially pressed by hand, and then the metal bellows with the rubber sleeve pasted is placed in the mold, and the rubber sleeve is heated and pressed using hot pressing equipment. S5: Quality inspection, fix one end of the metal corrugated gas hose on the lower fixture of the tensile testing machine, and connect the other end of the hose to the upper fixture, also ensuring that the connection is firm, then adjust the position and angle of the fixture, turn on the tensile testing machine, and observe the display screen of the testing machine and the status of the sample; S6: Packaging and storage. Before packaging, use a detergent to clean the dust, oil and impurities on the surface of the metal corrugated gas hose. Then add plastic protective caps or plugs to both ends of the hose, place it in the groove of the sponge pad, and then place it in a dry and light-proof environment.

[0018] The material of the metal tube in S1 is stainless steel, with an outer diameter of 10-16 mm and a wall thickness of 0.2 mm. The upper mold of the molding machine performs compression molding on the metal tube in the lower mold. The molding pressure is 100 MPa, and the pressure is maintained for 1-5 minutes. The outer diameter of the formed corrugated tube is 12-20 mm, the corrugation height is 1-3 mm, and the corrugation spacing is 5-15 mm.

[0019] Specifically, stainless steel has good toughness and can bend and deform to a certain extent without breaking, and the hydraulic forming process can make the surface of the bellows smoother and flatter, reduce the surface defects and scratches of the metal bellows, improve the appearance quality of the bellows, and reduce the corrosion and wear caused by surface defects, thereby extending the service life of the bellows.

[0020] The pickling solution in S2 is a mixture of hydrochloric acid and nitric acid in a volume ratio of 3:1. The concentration of the pickling solution is 10%-20%. The pickling time is 10-30 minutes, and the subsequent spraying and rinsing time is 5-10 minutes. The passivation solution is nitric acid with a concentration of 5%-10%. The passivation time is 15-30 minutes. Spraying is performed here, the rinsing time is 5-10 minutes, and then drying is performed at a temperature of 50-80°C for 30-60 minutes.

[0021] Specifically, the pickling process can activate the surface of the metal bellows, increase its surface reactivity, and react chemically with the metal oxides on the surface of the bellows to dissolve and remove them, thereby improving the surface quality. At the same time, removing surface oil and impurities can improve the welding performance, coating adhesion and other processing properties of the bellows. The nitric acid in the passivation solution reacts with the surface of the bellows to form a dense oxide protective film on the metal surface, which can effectively block corrosive substances in the external environment, thereby improving the corrosion resistance of the bellows and the oxidation resistance of the metal corrugated gas hose. At the same time, spraying can effectively remove various impurities, pickling solution residues and passivation solution residues on the surface of the bellows, making the surface clean and ensuring product quality.

[0022] The welding current of the argon arc welding machine in S3 can be set to 80-120A, and the argon gas flow rate is between 8-12L / min.

[0023] Specifically, secondary cleaning before welding can ensure welding quality: remove impurities such as oil and rust to avoid affecting the strength, sealing and appearance quality of the weld. Argon arc welding can produce a very stable arc. For the welding of metal bellows and related components, the transition between the weld and the base material can be natural, improving the overall appearance of the product. At the same time, the protective effect of argon gas can effectively prevent the pollution of the molten pool by oxygen, nitrogen and other gases in the air, reduce the occurrence of welding defects, and thus improve the strength of the weld.

[0024] In S4, the sandblasting pressure is controlled at 0.5-0.8MPa, and the distance between the nozzle and the surface of the metal bellows is 100-200mm, the angle between the nozzle and the surface of the metal bellows is generally 45°-90°, the sandblasting time is 5-10 minutes, and the thickness of the glue is 0.2-0.5mm. After that, the hot pressing temperature of the hot pressing equipment is 120-180℃, and the pressure is 5-10MPa, and the hot pressing time is 5-15 minutes.

[0025] Specifically, the surface of the metal bellows is roughened by sandblasting technology to increase the surface roughness and surface area, which helps to improve the adhesion of the subsequent glue, better combine the rubber material with the metal bellows, improve the connection strength between the rubber sleeve and the metal bellows, and reduce the risk of the rubber sleeve falling off during use. The glue plays the role of bonding the rubber material and the metal bellows, providing reliable bonding force to ensure a firm connection between the rubber sleeve and the metal bellows. The rubber material has good elasticity, corrosion resistance and wear resistance, which can protect the metal bellows from the influence of the external environment, provide additional protection and stretchability, and the initial pressing can make the rubber material better contact with the glue, eliminate bubbles and gaps, and ensure the tightness of the bonding. After that, the glue can be fully cured through hot pressing of hydraulic equipment to form a strong bond, while making the contact between the rubber material and the metal bellows closer, reducing the risk of leakage.

[0026] The tensile speed of the S5 tensile testing machine is 50-100 mm / min, and the maximum tensile force can be set to 300-500N.

[0027] Specifically, fixing both ends of the hose can ensure that the hose will not slip or loosen during the tensile test, ensuring the accuracy and repeatability of the test. By monitoring the changes in tensile force and displacement, the strength, stiffness, ductility and other performance indicators of the hose can be understood to ensure the stability and consistency of product quality.

[0028] The groove width of the sponge pad in S6 is 12-18 mm, the depth is 6-9 mm, and the sponge density is 20-40 kg / m³. The relative humidity of the air in the packaging place and storage is 30%-50%, and the storage temperature is 10-30℃.

[0029] Specifically, cleaning with a detergent can help remove dust and impurities to reduce the possibility of damage to the hose due to friction during storage and transportation. Adding plastic protective caps or plugs at both ends of the hose can protect the hose port from damage and prevent dust, moisture, etc. from entering the interior of the hose, ensuring safe and stable gas transportation. The groove of the sponge pad can provide buffering and support for the hose, preventing the hose from being deformed or damaged by external forces such as squeezing and collision during storage and transportation, preventing the hose from being deformed by external forces, and ensuring that the performance of the hose is not affected. At the same time, a dry and light-proof environment can reduce the risk of rusting of the metal bellows and reduce the aging rate of the hose material, thereby ensuring the strength and quality stability of the hose.

[0030] The following is an introduction in conjunction with specific embodiments: Embodiment 1 The material in S1 is a stainless steel metal tube with an outer diameter of 10 mm and a wall thickness of 0.2 mm. The shaping pressure of the hydraulic forming machine is 100 MPa and the pressure lasts for 1 minute. The target outer diameter of the formed metal bellows is 12 mm, the corrugation height is 1 mm, and the corrugation spacing is 5 mm.

[0031] In S2, the volume ratio of hydrochloric acid to nitric acid in the pickling solution is 3:1, the overall concentration is 10%, the pickling time is 10 minutes, the two spray rinse times are 5 minutes each, the concentration of the nitric acid passivation solution is 5%, the passivation time is 15 minutes, the temperature of the drying environment is 50°C, and the drying time is 30 minutes.

[0032] In S3, the welding current of the argon arc welding machine is 80A and the argon gas flow rate is 8L / min.

[0033] In S4, the sandblasting pressure is controlled to 0.5MPa, and the distance between the nozzle and the surface of the metal bellows is 100mm, the angle is controlled to 45°, the sandblasting time is 5 minutes, and the thickness of the glue coating is 0.2mm. The hot pressing temperature of the hot pressing equipment is 120℃, the pressure is 5MPa, and the hot pressing time is 5 minutes.

[0034] In S5, the tensile speed of the tensile testing machine was 50 mm / min, and the maximum tensile force was set to 300N.

[0035] In S6, the groove width of the sponge pad is 12 mm, the depth is 6 mm, the density is 20 kg / m³, the relative humidity of the air in the packaging place and storage is controlled at 30%, and the storage temperature is 10°C.

[0036] Embodiment 2 The material in S1 is a stainless steel metal tube with an outer diameter of 10 mm and a wall thickness of 0.2 mm. The shaping pressure of the hydraulic forming machine is 100 MPa and the pressure lasts for 3 minutes. The target outer diameter of the formed metal bellows is 12 mm, the corrugation height is 1 mm, and the corrugation spacing is 15 mm.

[0037] In S2, the volume ratio of hydrochloric acid to nitric acid in the pickling solution is 3:1, the overall concentration is 10%, the pickling time is 10 minutes, the two spray rinse times are 5 minutes each, the concentration of the nitric acid passivation solution is 5%, the passivation time is 15 minutes, the temperature of the drying environment is 50°C, and the drying time is 30 minutes.

[0038] In S3, the welding current of the argon arc welding machine is 80A and the argon gas flow rate is 8L / min.

[0039] In S4, the sandblasting pressure is controlled to 0.5MPa, and the distance between the nozzle and the surface of the metal bellows is 100mm, the angle is controlled to 45°, the sandblasting time is 5 minutes, and the thickness of the glue coating is 0.2mm. The hot pressing temperature of the hot pressing equipment is 120℃, the pressure is 5MPa, and the hot pressing time is 5 minutes.

[0040] In S5, the tensile speed of the tensile testing machine was 75 mm / min, and the maximum tensile force was set to 300N.

[0041] In S6, the groove width of the sponge pad is 12 mm, the depth is 6 mm, the density is 20 kg / m³, the relative humidity of the air in the packaging place and storage is controlled at 30%, and the storage temperature is 10°C.

[0042] Embodiment 3 The material in S1 is a stainless steel metal tube with an outer diameter of 16 mm and a wall thickness of 0.2 mm. The shaping pressure of the hydraulic forming machine is 100 MPa and the pressure lasts for 5 minutes. The target outer diameter of the formed metal bellows is 20 mm, the corrugation height is 3 mm, and the corrugation spacing is 15 mm.

[0043] In S2, the volume ratio of hydrochloric acid to nitric acid in the pickling solution is 3:1, the overall concentration is 20%, the pickling time is 30 minutes, the two spray rinse times are 10 minutes each, the concentration of the nitric acid passivation solution is 10%, the passivation time is 30 minutes, the temperature of the drying environment is 80°C, and the drying time is 60 minutes.

[0044] In S3, the welding current of the argon arc welding machine is 120A, and the argon gas flow rate is 12L / min.

[0045] In S4, the sandblasting pressure is controlled to 0.8MPa, and the distance between the nozzle and the surface of the metal bellows is 200mm, the angle is controlled to 90°, the sandblasting time is 10 minutes, and the thickness of the glue coating is 0.5mm. The hot pressing temperature of the hot pressing equipment is 180℃, the pressure is 10MPa, and the hot pressing time is 15 minutes.

[0046] In S5, the tensile speed of the tensile testing machine was 50 mm / min, and the maximum tensile force was set to 500N.

[0047] In S6, the groove width of the sponge pad is 18 mm, the depth is 9 mm, the density is 40 kg / m³, the relative humidity of the air in the packaging place and storage is controlled at 50%, and the storage temperature is 30°C.

[0048] Table 1 shows the tensile effect of metal corrugated gas hose Test items Embodiment 1 Embodiment 2 Embodiment 3 Tensile Strength 200Mpa 220Mpa 250Mpa The tensile strength is the maximum tensile force that the hose can withstand during the stretching process.

[0049] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a stretchable fixed-length metal corrugated gas hose, characterized in that: The following steps are involved: S1: Bellows production, put the metal pipe into the mold, inject hydraulic oil into the mold through the high-pressure pump, and then start the hydraulic forming machine to form the metal pipe to form the corrugated shape of the bellows. Then, the pressure is maintained and then released. The formed bellows is taken out and its size is determined by the cutting device; S2: Pretreatment of the bellows: completely immerse the bellows in the pickling liquid in the acid-resistant container for pickling treatment, then rinse it through the spray device, then put it into the passivation liquid for passivation treatment, and finally rinse it with clean water, dry it and bake it; S3: Welding assembly, positioning the welding core and the threaded welding core on both sides of the bellows, cleaning the oil, rust and other impurities on the welding part for the second time to ensure that the welding surface is clean, and then using argon arc welding technology to start the arc at high frequency to generate an arc at the welding part, aligning the tungsten electrode with the welding part, controlling the welding speed and arc length, so that the molten pool is evenly filled in the welding joint, and gradually reducing the welding current at the end of welding; S4: Installation of protective layer. The surface of the metal bellows is roughened by controlling the sandblasting distance and angle through sandblasting technology. Then glue is evenly applied to the surface of the metal bellows, and the rubber material is pasted on it. The metal bellows with the rubber sleeve pasted is initially pressed by hand, and then the metal bellows with the rubber sleeve pasted is placed in the mold, and the rubber sleeve is heated and pressed using hot pressing equipment. S5: Quality inspection, fix one end of the metal corrugated gas hose on the lower fixture of the tensile testing machine, and connect the other end of the hose to the upper fixture, also ensuring that the connection is firm, then adjust the position and angle of the fixture, turn on the tensile testing machine, and observe the display screen of the testing machine and the status of the sample; S6: Packaging and storage. Before packaging, use a detergent to clean the dust, oil and impurities on the surface of the metal corrugated gas hose. Then add plastic protective caps or plugs to both ends of the hose, place it in the groove of the sponge pad, and then place it in a dry and light-proof environment.

2. The process for preparing a stretchable fixed-length metal corrugated gas hose according to claim 1, characterized in that: The material of the metal tube described in S1 is stainless steel, with an outer diameter of 10-16 mm and a wall thickness of 0.2 mm. The upper mold of the molding machine performs compression molding on the metal tube in the lower mold. The molding pressure is 100 MPa, and the pressure is maintained for 1-5 minutes. The outer diameter of the formed corrugated tube is 12-20 mm, the corrugation height is 1-3 mm, and the corrugation spacing is 5-15 mm.

3. The process for preparing a stretchable fixed-length metal corrugated gas hose according to claim 1, characterized in that: The pickling solution in S2 is a mixture of hydrochloric acid and nitric acid in a volume ratio of 3:

1. The concentration of the pickling solution is 10%-20%, the pickling time is 10-30 minutes, and the subsequent spraying and rinsing time is 5-10 minutes. The passivation solution is nitric acid with a concentration of 5%-10%, and the passivation time is 15-30 minutes. Spraying is performed here, the rinsing time is 5-10 minutes, and then drying is performed at a temperature of 50-80°C for 30-60 minutes.

4. The process for preparing a stretchable fixed-length metal corrugated gas hose according to claim 1, characterized in that: The welding current of the argon arc welding machine described in S3 can be set to 80-120A, and the argon gas flow rate is between 8-12L / min.

5. The process for preparing a stretchable fixed-length metal corrugated gas hose according to claim 1, characterized in that: The sandblasting pressure in S4 is controlled at 0.5-0.8MPa, and the distance between the nozzle and the surface of the metal bellows is 100-200 mm, the angle between the nozzle and the surface of the metal bellows is generally 45°-90°, the sandblasting time is 5-10 minutes, the coating thickness of the glue is 0.2-0.5 mm, and then the hot pressing temperature of the hot pressing equipment is 120-180°C, and the pressure is 5-10MPa, and the hot pressing time is 5-15 minutes.

6. The process for preparing a stretchable fixed-length metal corrugated gas hose according to claim 1, characterized in that: The tensile speed of the S5 tensile testing machine is 50-100 mm / min, and the maximum tensile force can be set to 300-500N.

7. The process for preparing a stretchable fixed-length metal corrugated gas hose according to claim 1, characterized in that: The groove width of the sponge pad described in S6 is 12-18 mm, the depth is 6-9 mm, and the sponge density is 20-40 kg / m³. The relative humidity of the air in the packaging place and storage is 30%-50%, and the storage temperature is 10-30°C.

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