Process for preparing backward extrusion tube blank of hydrogen cylinder liner

Abstract

The invention discloses a hydrogen cylinder liner backward extrusion tube blank preparation process which comprises the following steps: sequentially smelting, primary refining, heat preserving furnace refining and casting according to a designed ratio of alloy raw materials, and then homogenizing to obtain a round cast ingot blank with a corresponding specification; the blank is heated after being cut off and sawn, the heated blank is added into a split type die to be forged, an annular induction heating device is arranged on a lower die of the split type die, the blank is heated in a gradient mode, reverse extrusion is carried out through a reverse extrusion forming process with the connected skin thickness-extrusion speed linkage after forging, and the blank is obtained. And machining according to technical requirements to obtain a pipe blank with a corresponding specification. A lower die heat preservation device is designed and manufactured, and continuity of the forging process and uniform and stable structure performance of a pipe blank are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and particularly relates to a preparation process for an inner liner of a hydrogen cylinder by backward extrusion of a tube blank. Background Art

[0002] Due to a series of advantages such as low specific gravity, high specific strength, high specific stiffness, and corrosion resistance, aluminum alloys have been widely used in various industrial sectors. High-performance seamless aluminum alloy tubes have become essential materials in various industries. With the progress of science and technology and the development of the national economy, higher requirements have been put forward for the demand of aluminum alloy tubes. Especially in the past decade, hydrogen energy vehicles, as the main application scenario of hydrogen energy, have received attention and emphasis from society and enterprises and have developed rapidly.

[0003] Type III composite-wound hydrogen storage cylinders with an aluminum alloy inner liner are the main hydrogen container carriers. The inner liner of the Type III cylinder generally uses 6061 aluminum alloy material to ensure its good compatibility with hydrogen and corrosion resistance, and to ensure that the active and light hydrogen is blocked and does not leak. There are problems such as uneven organization, unstable performance, large discreteness of fatigue performance, unqualified pressure test, and high cost in the batch production and application of 6061 tubes for hydrogen storage cylinders. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent.

[0005] To this end, the first object of the present invention is to provide a preparation process for an inner liner of a hydrogen cylinder by backward extrusion of a tube blank, including the following steps:

[0006] The alloy raw materials in the designed ratio are successively smelted, subjected to primary refining, refining in a holding furnace, and casting, and then homogenized to obtain round ingot blanks of corresponding specifications;

[0007] The blank is cut off by sawing in the middle and then heated. The heated blank is added to a split die for forging. The lower die of the split die is provided with a ring-shaped induction heating device to cooperate with the gradient heating of the blank, and the starting forging temperature of the blank is controlled at 420 - 460 °C, and the final forging temperature is ≥ 380 °C;

[0008] After forging, a backward extrusion forming process with a linkage of the thickness of the continuous skin and the extrusion speed is used for backward extrusion, and machining is carried out according to technical requirements to obtain tube blanks of corresponding specifications.

[0009] According to the embodiments of the present invention, the components of the alloy raw materials are recorded by mass percentage as follows: Si 0.6 - 0.8%, Fe 0.2 - 0.23%, Cu 0.3 - 0.4%, Mn 0.09 - 0.15%, Mg 0.9 - 1.15%, Cr 0.18 - 0.3%, Ti 0.01 - 0.025%, and the balance is Al and other inevitable impurities.

[0010] According to an embodiment of the present invention, during the smelting process, the alloying temperature is controlled at 730 - 760 °C, electromagnetic stirring is turned on, intermediate alloys of Si, Fe, Cu, Mn, and Cr are added first, and finally, a magnesium ingot is added using a magnesium ingot cage. The aluminum-titanium alloy should be added to the holding furnace when tilting the furnace.

[0011] According to an embodiment of the present invention, the primary refining temperature is 730 - 760 °C, the refining gas pressure is not less than 0.4 MPa, and the refining time is 40 - 50 minutes; and / or

[0012] The refining temperature of the holding furnace is 720 - 750 °C, the refining time is 50 minutes, and the refining gas pressure is not less than 0.4 MPa.

[0013] According to an embodiment of the present invention, the homogenization process uses furnace homogenization, the holding temperature is 560 ± 5 °C, and the holding time is 12 hours.

[0014] According to an embodiment of the present invention, the temperature for heating the billet after interrupted sawing is 460 ± 10 °C, and the holding time is ≥ 6 h.

[0015] According to an embodiment of the present invention, the upper die of the split die is decomposed into a die base and a working belt split structure.

[0016] According to an embodiment of the present invention, during the forging process, the final forging temperature is continuously monitored by an infrared thermometer ≥ 380 °C. When the temperature approaches the lower limit, the die is returned to the furnace and heated at 460 °C for 2 h to stabilize the grain size at 15 - 20 μm.

[0017] According to an embodiment of the present invention, during reverse extrusion, the thickness of the web is controlled within 25 - 30 mm, and the extrusion load is set to 65 MN.

[0018] According to an embodiment of the present invention, during reverse extrusion, a downward pressure speed-temperature coupling control technology is adopted. The servo press accurately executes a downward pressure speed of 8 mm / s with a fluctuation of ±0.5 mm / s. Combined with spraying a lubricant on the surface of the billet, the surface roughness Ra of the tube billet is ≤ 6.3 μm.

[0019] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of the embodiments in conjunction with the drawings, wherein:

[0021] Figure 1 is a flow chart of a preparation process for a reverse extrusion tube blank of a hydrogen cylinder inner liner according to the present invention. Specific Embodiments

[0022] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] According to one aspect of the present invention, referring to Figure 1 , the present invention provides a preparation process for the inner liner of a hydrogen cylinder by reverse extrusion of a tube blank, including the following steps:

[0024] S100: Melting and casting to prepare a blank.

[0025] The alloy raw materials in the designed ratio are successively smelted, subjected to primary refining, refined in a holding furnace, cast, and then homogenized to obtain a round ingot blank of corresponding specifications.

[0026] In some embodiments, the components of the alloy raw materials are recorded by mass percentage as follows: Si 0.6 - 0.8%, Fe 0.2 - 0.23%, Cu 0.3 - 0.4%, Mn 0.09 - 0.15%, Mg 0.9 - 1.15%, Cr 0.18 - 0.3%, Ti 0.01 - 0.025%, and the balance is Al and other inevitable impurities. It can be understood that in the design of chemical composition, in addition to the main components, the content of impurity elements and trace elements is precisely controlled, ensuring the fatigue performance of the final gas cylinder. By suppressing hydrogen diffusion through the co-precipitation of Cr / Mn, the lower limit of the Cr content is increased to 0.17%. By the dispersed distribution of Cr / Mn-rich nano-precipitates, the hydrogen diffusion path is blocked, reducing the hydrogen permeability.

[0027] In the embodiments of the present invention, the alloy material is smelted, specifically including processes such as cold charging, taking an initial sample, alloying, primary refining, primary slag skimming, secondary sampling, guiding the furnace, refining in a holding furnace, slag skimming in the holding furnace, and standing. In the cold charging of the present invention, the amount of scrap added per furnace: only pressed scrap, self-produced scrap or aluminum ingots are allowed to be added, and the amount of scrap added each time is 28 - 34 tons. During the process of adding scrap to the furnace, attention should be paid to detecting slag inclusions to ensure the cleanliness of the scrap. Initial sample sampling is also required, with the sampling temperature being 710 - 750 °C, the stirring time before sampling not less than 20 minutes, and stirring evenly to ensure the authenticity of the initial sample. The sampling spoon is inserted about 1 meter into the furnace door and 1 / 2 position (about 40 cm) into the molten aluminum, and initial samples are taken at three different positions of left, middle, and right in the furnace. According to the test analysis results and the customer's composition requirements, the addition amounts of various alloys are calculated.

[0028] In some embodiments, the alloying temperature is controlled at 730-760°C during the smelting process, electromagnetic stirring is turned on, Si, Fe, Cu, Mn, and Cr intermediate alloys are added first, and finally magnesium ingots are added using a magnesium ingot cage. The aluminum-titanium alloy should be added to the holding furnace when the furnace is poured.

[0029] In some embodiments, the primary refining temperature is 730-760°C, the refining gas pressure is not less than 0.4MPa, and the refining time is 40-50 minutes; the refining temperature of the insulation furnace is 720-750°C, the refining time is 50 minutes, and the refining gas pressure is not less than 0.4MPa.

[0030] Specifically, the refining temperature of the primary refining is 730-760℃, the furnace door opening height is less than 20cm, the refining tube moves in an "N" shape in the furnace, the bending of the refining tube must penetrate 2 / 3 of the aluminum liquid, the aluminum liquid tumbling height does not exceed 20cm, argon refining is used, the gas pressure is not less than 0.4MPa, the Perrick refining agent is 50Kg, and the refining time is 40-50 minutes.

[0031] During the first slag removal, the electromagnetic stirring is turned off, the melt temperature is 710-740℃ during slag removal, and the surface is clean without slag after slag removal.

[0032] During the secondary sampling, the sampling temperature is 730-750℃, and the sampling method is the same as the initial sampling. Except for titanium, all other alloys in the smelting furnace are required to meet the ingredient range.

[0033] When inducting the furnace, the pouring furnace chute is preheated for more than 30 minutes in advance, the pouring furnace temperature is 730-760℃, various tools are ready, the aluminum outlet of the smelting furnace and the aluminum inlet of the holding furnace are guaranteed to be unobstructed and free of debris, and a dedicated person monitors the aluminum inlet of the holding furnace to ensure that the aluminum liquid enters normally. The alloy required for inducting the furnace is added from the holding furnace or the chute.

[0034] When refining in a holding furnace, the refining temperature is 720-750℃, the Perrick refining agent is 70 kg, the manual refining takes 30 minutes, and the refining car refining takes 50 minutes. Turn on the electromagnetic stirring before refining, and confirm that the electromagnetic stirring is operating normally before starting refining. Set the rotor speed of the refining car to 220 rpm, and the refining gas pressure is not less than 0.4MPa. After refining, turn off the electromagnetic stirring, place the slag basin and start slag removal. The slag removal should be stable, and the melt fluctuation should be minimized. After slag removal, the aluminum liquid surface should be clean like a mirror. After slag removal, start to stand for ≥40 minutes. Take samples according to the standard operating procedures for sampling in the furnace. If the composition is unqualified, add alloy and re-refine according to the refining steps of the holding furnace.

[0035] In addition, casting is also required during the processing of the present invention. During the casting process, the pre-inspection temperature of the furnace is 710 - 730°C, the temperature of the cylinder is 710 - 730°C, the temperature of the plate filter box is 700 - 720°C, the temperature of the tube filter inlet is 700 - 720°C, and the temperature of the casting platform is 685 - 710°C. The refining agent used is MQP titanium wire, added in a double-wire manner at a speed of 180 mm / min. After the maintenance of the launder platform, ensure that the launder is dry. Bake it for more than 40 minutes before casting, and there should be no pits, aluminum inclusions, large refractory materials and other sundries. Apply a thin layer of boron nitride on the surface, and add 5 m of titanium wire to the launder before casting. Before casting, it is necessary to clean the launder and the platform workshop after the filter box. Degassing and filtration are also required. Skim the slag before casting, with the rotor speed of 250 revolutions, using argon gas with a flow rate of 6 Nm3 / min and a gas pressure of 2 bar. Add 4 m of titanium wire into the degassing cylinder before casting, and the filter box uses an imported 60-mesh filter plate + RC-class tube group.

[0036] In the present invention, sawing is required after casting, for the head and tail of the material. After homogenization, saw it according to the required length of the order. The sawing length at the starting end is ≥ 450 mm, and the sawing length at the ending end is ≥ 250 mm. Marking is also required. Use a steel stamp to mark on the end face of the dummy bar from top to bottom: alloy grade, casting number, homogenization furnace number, and mold number. Sampling is also required. Randomly select one bar per heat for the macro sample, take one sample from each of the head and tail; randomly select one bar for the composition sample, take one sample from each of the head and tail; randomly take one sample per homogenization heat for the micro sample.

[0037] In some embodiments, the homogenization process uses furnace homogenization, with the holding temperature of 560 ± 5°C and the holding time of 12 hours. It can be understood that homogenization is required during the processing. Process requirements: use furnace homogenization, monitor two material temperature points, with the holding temperature of 560 ± 5°C and the holding time of 12 hours, and adopt air cooling + water cooling for (2 + 1) hours. Requirements for sample bars: randomly select two sample bars per homogenization heat, take the composition from one and the micro from the other.

[0038] For the quality of the bar stock processed by the present invention, there should be no center cracks in the whole bar during surface flaw detection. After casting, the casting operator in charge is responsible for checking the edge cracks of each round bar. There should be no oil stains, rust, pits or mechanical damage not exceeding 5 mm on the surface of the round bar, and the camber ≤ 6 mm / m.

[0039] S200: Dynamic extrusion control technology with the cooperation of split die and temperature field, through the innovation of die structure and real-time linkage processing with the temperature field.

[0040] The blank is heated after being interrupted and sawn, and the heated blank is forged in a split die. The lower die of the split die is provided with a ring-shaped induction heating device to cooperate with the gradient heating of the blank, and the starting forging temperature of the blank is controlled at 420-460 °C, and the final forging temperature is ≥380 °C. It can be understood that the lower die is provided with a ring-shaped induction heating device (460±10 °C) to cooperate with the gradient heating of the blank (the temperature difference between the core and the surface ≤15 °C), so as to reduce the standard deviation of the metal flow speed during the extrusion process. The present invention ensures the continuity of the forging process and the uniform and stable structure and properties of the tube blank by designing and manufacturing a lower die heat preservation device.

[0041] In some embodiments, the temperature for heating the blank after being interrupted and sawn is 460±10 °C, and the heat preservation time is ≧6h.

[0042] In some embodiments, the upper die of the split die is decomposed into a die base and a working belt split structure. It can be understood that through the design of the split and replaceable working belt, the traditional integral upper die is decomposed into a die base (service life ≥5000 pieces) and a working belt (service life ≥300 pieces) split structure. The unique die design, first, changes the traditional integral upper die design to a split design. When replacing the die, only the working belt needs to be replaced, which not only saves a large amount of die costs, but also improves the die applicability and production efficiency.

[0043] In some embodiments, during the forging process, the final forging temperature ≥380 °C is monitored in real time by an infrared thermometer. When the temperature approaches the lower limit, the die is triggered to return to the furnace and heated at 460 °C for 2h to make the grain size stable at 15-20μm.

[0044] S300: Process by using a backward extrusion forming process with the linkage of the thickness of the web and the extrusion speed.

[0045] After forging, a backward extrusion is carried out by using a backward extrusion forming process with the linkage of the thickness of the web and the extrusion speed, and machining is carried out according to technical requirements to obtain a tube blank of corresponding specifications. By using a backward extrusion forming process with the linkage of the thickness of the web and the extrusion speed, the matching relationship between the thickness of the web and the extrusion speed is optimized based on metal flow simulation, breaking through the traditional empirical trial-and-error mode.

[0046] In some embodiments, the thickness of the web during backward extrusion is controlled within 25-30 mm, and the extrusion load is set at 65 MN.

[0047] In some embodiments, during backward extrusion, a coupling control technology of the downward pressing speed and the temperature is adopted, and the servo press accurately executes a downward pressing speed of 8 mm / s with a fluctuation of ±0.5 mm / s. Combined with the spraying of lubricant on the surface of the blank, the surface roughness Ra of the tube blank is ≤6.3μm.

[0048] Specifically, during forging and backward extrusion, when installing the die, the center deviation after installing the upper and lower dies should be ≤ 3 mm; the first three billets should be inspected one by one; then, the die fixing bolts should be inspected and tightened every time 5 billets are produced, and the working belt and the top plate should be checked for normality. When controlling the forging temperature, the starting forging temperature of the billet is 420 - 460 °C, and the final forging temperature is ≥ 380 °C. The starting and final forging temperatures of the first piece should be measured, and then measured again every time 5 pieces are produced, and recorded truthfully. When the final forging temperature is close to 380 °C, production should be stopped, the die should be returned to the furnace and heated to 460 °C and kept warm for more than 2 h before continuing production. When loading, place the end face with identification marks facing up; ensure that the billet is placed in the positioning groove of the lower die, and the upper plane of the billet remains horizontal. In addition, it is also necessary to upset the billet in the die with the working belt on a 100 MN press, and the height controlled by the press stroke is: 280 ± 5 mm. Lubricate the bottom of the lower die before upsetting, and the lubrication should be uniform without over-lubrication. During the backward extrusion process, after the billet is upset, lubricate the lower die, the surface of the billet and the working belt. When performing backward extrusion, the thickness of the web is controlled within 25 - 30 mm. Multiple lubrications can be carried out during backward extrusion production to prevent sticking to the upper die and bending. The downward pressing speed is 8 mm / s, and the length after extrusion is 1125 ± 15 mm. The wall thickness difference of the billet is controlled within 3 mm, and the straightness is controlled within 3 mm / m. When discharging, the root section number of each billet should be checked, and a corresponding table of the billet sequence number and the root section number should be made. Mark the batch and sequence number on each piece one by one, and observe and detect the surface quality, straightness, eccentricity and length of the billet.

[0049] In some embodiments of the invention, after forging and backward extrusion, it is necessary to cut the head and tail, and then perform machining. Use a horizontal sawing machine to cut the head and tail of the billet. First, cut the tail end, and the cutting length is 30 mm (just ensure that the web is cut), and then cut the head end. The length of the billet after cutting is 1040 ± 3 mm, and the cutting slope is ≤ 3 mm. After sawing, transfer the marks at the head end of the billet, including batch, sequence number, etc. For machining, select appropriate tooling and tools and process according to the requirements of the drawings attached to this process. The machining is divided into three processes: rough turning the outer circle, finish turning the inner circle and finish turning the outer circle. The surface roughness of the final workpiece (≤ 4.8), and no tool joint is allowed on the inner and outer surfaces. Before machining, it should be checked and confirmed whether the billet is abnormal (whether the identification is complete, whether the billet has defects), and then machining can be carried out after no abnormality. Before getting on the lathe, confirm the head and tail ends of the billet, and try to machine more at the head end. After each process of machining, the marks must be marked on the head end part of the billet. When rough turning the outer circle, it is required to reserve a finishing allowance of ≥ 3 mm for the outer circle. The first piece of machining needs to be inspected and qualified before continuing machining. The inspection is jointly confirmed by the quality inspector and the machining operator. After machining is completed, transfer the marks one by one according to the requirements, and the mark content: batch, sequence number.

[0050] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0051] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "below" and "beneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0052] In the description of this specification, descriptions with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0053] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A preparation process for the reverse extrusion tube blank of the inner liner of a hydrogen cylinder, characterized in that, The steps include: The alloy raw materials according to the designed proportion are sequentially smelted, refined once, refined in a holding furnace, cast, and then homogenized to obtain round ingots; The billet is cut and then heated, and the heated billet is added into a split die for forging, and a ring-shaped induction heating device is arranged on the lower die of the split die to coordinate with the billet gradient heating, and the billet start forging temperature is controlled to be 420-460°C, and the final forging temperature is ≥380°C; After forging, reverse extrusion is performed by a reverse extrusion forming process in which skin thickness and extrusion speed are linked, and then machining is performed to obtain a tube blank.

2. The preparation process of the reverse extrusion tube blank for the inner liner of a hydrogen cylinder according to claim 1, characterized in that, The components of the alloy raw material are recorded in mass percentage as follows: Si 0.6-0.8%, Fe 0.2-0.23%, Cu 0.3-0.4%, Mn 0.09-0.15%, Mg 0.9-1.15%, Cr 0.18-0.3%, Ti 0.01-0.025%, and the balance is Al and other inevitable impurities.

3. The preparation process of the reverse extrusion tube blank for the inner liner of a hydrogen cylinder according to claim 1, characterized in that, During the smelting process, the alloying temperature is controlled at 730-760° C., electromagnetic stirring is turned on, Si, Fe, Cu, Mn, and Cr intermediate alloys are added first, and finally a magnesium ingot is added using a magnesium ingot cage. The aluminum-titanium alloy should be added to the holding furnace when the furnace is poured.

4. The preparation process of the reverse extrusion tube blank for the inner liner of a hydrogen cylinder according to claim 1, characterized in that, The primary refining temperature is 730-760°C, the refining gas pressure is not less than 0.4MPa, and the refining time is 40-50 minutes; and / or The refining temperature of the insulation furnace is 720-750° C., the refining time is 50 minutes, and the refining gas pressure is not less than 0.4 MPa.

5. The preparation process of the inner liner reverse extrusion tube blank of the hydrogen cylinder according to claim 1, characterized in that, The homogenization process uses a furnace homogenizer with a holding temperature of 560±5° C. and a holding time of 12 hours.

6. The manufacturing process of the inner liner of a hydrogen cylinder by reverse extrusion of a tube blank, characterized in that, The temperature of heating the blank after interruption of sawing is 460±10° C., and the heat preservation time is ≧6h.

7. The preparation process of the inner liner of the hydrogen cylinder by reverse extrusion of the tube blank according to claim 1, characterized in that, The upper mold of the split mold is decomposed into a mold base and a working belt split structure.

8. The preparation process of the reverse extrusion tube blank for the inner liner of a hydrogen cylinder according to claim 1, characterized in that, During the forging process, the final forging temperature is monitored in real time by an infrared thermometer to be ≥380°C. When the temperature approaches the lower limit, the mold is triggered to return to the furnace and heat at 460°C for 2 hours to stabilize the grain size at 15-20 μm.

9. The preparation process of the inner liner reverse extrusion tube blank of the hydrogen cylinder according to claim 1, characterized in that, During the reverse extrusion, the skin thickness is controlled within 25 to 30 mm, and the extrusion load is set to 65 MN.

10. The preparation process of the reverse extrusion tube blank for the inner liner of a hydrogen cylinder according to claim 1, characterized in that, The reverse extrusion adopts the pressing speed-temperature coupling control technology, and the servo press accurately executes the pressing speed of 8mm / s with a fluctuation of ±0.5mm / s. Combined with the lubricant spraying on the billet surface, the surface roughness of the tube billet Ra is made ≤6.3μm.

Images