Process for preparing niobium-titanium alloy capillary tube based on multi-stage drawing and intermediate vacuum annealing

Abstract

The present application relates to the technical field of capillary preparation, and particularly relates to a preparation process of a niobium-titanium alloy capillary based on multistage drawing and intermediate vacuum annealing, which comprises the following steps: dividing the drawing process into multistage stages according to the section shrinkage characteristics, and corresponding to the annealing nodes; judging the drawing state based on the actual drawing force and the temperature rise rate in the single drawing cycle; when the state is abnormal, increasing the lubricant flow or stopping the drawing and forcibly annealing according to the change pattern of the acoustic emission signal energy rate and the high-frequency harmonic component amplitude; and judging the drawing stability according to the drawing force fluctuation amplitude and the temperature distribution uniformity after adjustment, and further adjusting the process parameters when the drawing stability is not up to the standard. The present application solves the technical problems of the increase of the drawing force caused by hardening, the increase of the friction force and the sharp change of the temperature rise rate, and the high-frequency oscillation of the adhesion-slippage and the micro-crack initiation caused thereby.

Description

Technical Field

[0001] This invention relates to the field of capillary fabrication technology, and in particular to a process for fabricating niobium-titanium alloy capillaries based on multi-stage drawing and intermediate vacuum annealing. Background Technology

[0002] Niobium-titanium alloy capillary tubes are widely used in cooling channels for superconducting magnets and precision medical devices. Their preparation usually employs a multi-pass drawing process. The drawing machine and its supporting lubrication supply system, infrared thermal imager, acoustic emission sensor, and other equipment involved in the drawing process are all commonly used existing equipment in this field. In existing technologies, the control of the drawing process mainly relies on operational experience or offline detection, which has the following technical defects: First, work hardening leads to an increase in drawing force, and frictional heat causes an abnormal rate of temperature rise on the tube blank surface. However, existing online monitoring only focuses on whether the drawing force exceeds the limit and cannot distinguish between normal frictional temperature rise and abnormal temperature rise induced by hardening, resulting in missed detection in the early stages of hardening. Second, when hardening develops to a certain extent, it will trigger high-frequency oscillations of adhesion-slip and the initiation of microcracks. Existing technologies lack online detection methods for specific phenomena such as acoustic emission signals and high-frequency harmonics of drawing force, and abnormalities are often only detected after surface damage or tube breakage. Furthermore, even if abnormalities are detected, existing adjustment strategies of simply slowing down or stopping annealing lack graded responses to different degrees of severity, and there is no effect verification or adaptive adjustment mechanism after adjustment, making it easy for the same problem to recur.

[0003] Therefore, there is an urgent need for a niobium-titanium alloy capillary drawing process that can perform online diagnosis across the entire chain, from the abnormal temperature rise rate in the early stage of hardening, to the high-frequency oscillation of adhesion-slip in the middle stage, and then to the microcrack initiation in the later stage, and adjust and verify the process according to the severity of the problem.

[0004] Chinese Patent Publication No. CN119703646A discloses a method for preparing niobium and niobium alloy capillary tubes. The method includes: 1. Filling the inner hole of a seamless tube with high-purity argon gas and sealing both ends with argon arc welding; 2. Oxidizing the surface of the tube using an electromagnetic induction constant-temperature oxidation device to obtain a tube to be cold-drawn; 3. Cold-drawing to obtain a capillary tube; 4. Cleaning the outer surface of the capillary tube, cutting off the sealing head, performing finished product heat treatment, and straightening to obtain a finished tube. This invention, by filling the inner hole of the tube with argon gas and welding the two ends to seal, changes the existing surface oxidation technology. It only oxidizes the outer surface of the drawn tube, avoiding oxidation of the inner hole during surface oxidation; it also avoids the trouble caused by oil contamination of the inner hole during cold drawing, thus preventing problems with later cleaning; using an electromagnetic induction constant-temperature oxidation device results in a very uniform oxide layer thickness, and the yield can reach 100% during the later cold drawing process, improving the overall yield.

[0005] However, the aforementioned method for preparing niobium and niobium alloy capillaries has the following problems: This scheme only ensures the yield rate through billet pretreatment and finished product heat treatment, but lacks real-time monitoring of the work hardening state during the drawing process. It cannot distinguish between normal frictional temperature rise and abnormal temperature rise induced by hardening online, resulting in missed reports in the early stage of hardening. When hardening causes adhesion-slip high-frequency oscillation and microcrack initiation, no online detection methods such as acoustic emission and high-frequency harmonics are set up, and inspection is only carried out after drawing. Even if abnormalities occur during drawing, no graded control is carried out, and there is no verification of the effect after adjustment, which makes it easy for the same problem to recur at the same size node in subsequent batches. Summary of the Invention

[0006] To address this, the present invention provides a niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing, in order to overcome the problems in the prior art where the increased drawing force caused by hardening leads to increased friction and drastic changes in the temperature rise rate, thereby causing high-frequency oscillations of adhesion-slip and the initiation of microcracks.

[0007] To achieve the above objectives, this invention provides a process for preparing niobium-titanium alloy capillaries based on multi-stage drawing and intermediate vacuum annealing. This includes: Preparation of niobium-titanium alloy tube blanks to be drawn; Based on the initial size characteristics of the niobium-titanium alloy tube blank to be drawn and the target size characteristics of the niobium-titanium alloy capillary, the cross-sectional shrinkage characteristics of the niobium-titanium alloy tube blank to be drawn are determined. According to the cross-sectional shrinkage characteristics, the entire drawing process is automatically divided into multi-stage drawing stages, and each drawing stage corresponds to a set of intermediate vacuum annealing nodes. The drawing process is performed using standard drawing techniques. The actual drawing force and the actual temperature rise rate of the billet surface in the drawing deformation zone are collected in real time during the current drawing process. The drawing status of the current drawing is determined based on the changing trends of the actual drawing force and the actual temperature rise rate within a single drawing cycle. Based on the current draw force signal and the acoustic emission signal of the billet surface in the draw deformation zone, determine whether to increase the standard spray flow rate of the lubricant or stop the draw and force the intermediate vacuum annealing according to the actual change of the acoustic emission signal energy rate and the amplitude of the high-frequency harmonic component of the draw force signal within a single draw cycle. The second actual drawing force and the temperature distribution on the surface of the tube blank in the drawing deformation zone are obtained during the actual drawing process. Based on the fluctuation range of the second actual drawing force within the preset stable period and the uniformity of the temperature distribution, it is determined whether the drawing stability of the current pass meets the standard. If it does not meet the standard, the standard drawing process is adjusted, or intermediate vacuum annealing is inserted.

[0008] Furthermore, the process of automatically dividing the entire drawing process into multi-stage drawing stages includes: The total reduction of area is determined based on the target cross-sectional area of ​​the target capillary and the initial cross-sectional area of ​​the niobium-titanium alloy tube blank to be drawn. The maximum cumulative cross-sectional reduction rate is determined based on the maximum allowable cross-sectional reduction ratio between two adjacent annealing stages; The cumulative section shrinkage rate at the start of the current drawing stage of the billet is determined based on the cross-sectional area at the start and the cross-sectional area at the end of the current drawing stage. The number of stages is determined based on the ratio of the total section shrinkage rate to the maximum cumulative section shrinkage rate, and the entire drawing process is automatically divided into multi-stage drawing processes according to the number of stages.

[0009] Furthermore, the process of determining the changing trend of the actual drawing force within a single drawing cycle includes: The drawing process is performed using standard drawing techniques, and the actual drawing force of the current pass is collected in real time during the actual drawing process. According to the multi-stage drawing process, the drawing time period from the starting size of the current stage to the ending size of the current stage is taken as a single drawing cycle. The single drawing cycle is divided into several consecutive and equally long time periods, and the average drawing force in each time period is determined. Based on the fact that the increase in average pulling force between each time period shows an increasing trend along the single pulling cycle, the trend of pulling force change is determined to be a continuous increase. Based on the fact that the increase in average pulling force between each time period shows a decreasing trend or tends to be consistent along the single pulling cycle, the trend of pulling force change is determined to be a stable trend.

[0010] Furthermore, the process of determining the trend of the actual temperature rise rate includes: The drawing process is performed using standard drawing techniques, and the actual temperature rise rate of the tube blank surface in the drawing deformation zone during the current drawing pass is collected in real time. The single drawing cycle is divided into several consecutive and equally long time periods, and the average temperature rise rate in each time period is determined. Based on the fact that the increase in the average temperature rise rate between each time period shows an increasing trend along the single drawing cycle, it is determined that the temperature rise rate changes continuously. Based on the fact that the increase in the average temperature rise rate between the aforementioned time periods shows a decreasing trend or tends to be consistent along the single drawing cycle, the trend of temperature rise rate change is determined to be a stable trend.

[0011] Furthermore, the process of determining the pull-out status of the current track includes: Based on the fact that the trends of the pulling force and the temperature rise rate are both stable within a single pulling cycle, it is determined that the pulling status of the current pass is normal. Based on the fact that the trend of the pulling force or the trend of the temperature rise rate continuously increases within a single pulling cycle, it is determined that the pulling state of the current pass is abnormal.

[0012] Furthermore, the process of determining the standard spray flow rate for increasing the lubricant includes: Acquire the drawing force signal of abnormal passes and the acoustic emission signal of the billet surface in the drawing deformation zone; The amplitude of the high-frequency harmonic component of the pull-out force under abnormal pull-out conditions is determined based on the pull-out force signal. The acoustic emission signal energy rate of the tube blank surface in the drawing deformation zone during abnormal passes is determined based on the acoustic emission signal. Based on the fact that the amplitude of the high-frequency harmonic components and the energy rate of the acoustic emission signal are both gradually changing within a single drawing cycle, the standard spraying flow rate of the lubricant is increased.

[0013] Furthermore, the process of stopping the drawing and forcibly inserting intermediate vacuum annealing includes: Based on the fact that the amplitude of the high-frequency harmonic component or the energy rate of the acoustic emission signal changes abruptly within a single drawing cycle, the current drawing is stopped, and intermediate vacuum annealing is forcibly inserted using an intermediate vacuum annealing process. After annealing, the drawing process restarts.

[0014] Furthermore, the process of determining whether the pull-out stability of the current pass meets the standard includes: The second actual drawing force during the actual drawing process within the preset stabilization period was re-acquired, and the temperature distribution data of the tube blank surface in the drawing deformation zone was obtained. The preset stabilization period is divided into several equal-length time periods, and the fluctuation range of the second actual pull-out force and the standard deviation of the temperature distribution data are determined between each time period. Determine the trends of the fluctuation amplitude and the standard deviation within the preset stabilization period: Based on the fact that the fluctuation amplitude shows an increasing trend along the preset stabilization period, or that the standard deviation shows an increasing trend along the preset stabilization period, it is determined that the pull-out stability of the current pass does not meet the standard.

[0015] Furthermore, adjusting the standard drawing process, or inserting an intermediate vacuum annealing process, includes: Based on the fact that the fluctuation range of the second actual pulling force is continuously increasing and the temperature distribution uniformity is trending towards stabilization, the speed of the drive motor is reduced to decrease the pulling speed. Based on the fact that the fluctuation range of the second actual pulling force tends to stabilize and the temperature distribution uniformity tends to deteriorate, the opening of the proportional valve is increased to improve the lubricant spraying flow rate. Based on the fact that the fluctuation range of the second actual drawing force is continuously increasing and the temperature distribution uniformity is continuously deteriorating, drawing is stopped, and intermediate vacuum annealing is performed again using an intermediate vacuum annealing process.

[0016] Furthermore, the intermediate vacuum annealing process includes, The annealing temperature is 500℃~800℃; The heat preservation time is 2 to 3 hours; The heating rate is 5℃ / min to 12℃ / min; The vacuum level inside the furnace is less than or equal to 5 × 10⁻⁶. -3 Pa; The cooling method is to cool it in the furnace to below 150°C before removing it from the furnace.

[0017] Compared with the prior art, the beneficial effects of this invention are as follows: This invention automatically divides the drawing process into multiple stages using the total reduction of area and the maximum cumulative reduction of area, ensuring that the cumulative deformation in each stage does not exceed the safety limit. This avoids hardening cracking directly caused by excessive deformation in a single stage, and also prevents efficiency loss caused by excessively frequent annealing. After stage division, the changing trends of drawing force and temperature rise rate within a single drawing cycle are used as the criteria for determining whether the drawing state is abnormal. If an abnormality is determined, the hardening development trend is further distinguished by the changing patterns of acoustic emission signal energy rate and high-frequency harmonic component amplitude of drawing force within the drawing cycle, and the lubricant spray is adjusted according to the development trend. By adjusting the flow rate of the lubricant and reducing the friction coefficient through enhanced interfacial lubrication, adhesion-slip oscillations can be suppressed, avoiding unnecessary downtime and annealing. Discrete variations correspond to abrupt changes in microcrack initiation or adhesion tearing. In this case, forced insertion of intermediate vacuum annealing and redrawing eliminates dislocation accumulation and heals microcracks through recrystallization, while avoiding grain coarsening and strength reduction caused by excessive annealing. After adjustment, the stability of the adjusted drawing is verified by the trend of changes in the amplitude of drawing force fluctuation and the uniformity of temperature distribution. Under unstable conditions, the drawing speed is reduced, the lubricant spray flow rate is increased, or enhanced annealing is carried out until the stability meets the standard, which significantly improves the yield and batch consistency of niobium-titanium alloy capillary preparation.

[0018] Furthermore, the present invention, through the tube blank preparation process, can obtain niobium-titanium alloy tube blanks with uniform microstructure and smooth surface, providing high-quality blanks for subsequent drawing. Based on the cross-sectional shrinkage characteristics, the invention automatically divides the drawing stages into multiple stages, ensuring that intermediate vacuum annealing is inserted in time after each stage, avoiding hardening cracks caused by excessive deformation, and preventing excessively frequent annealing from reducing production efficiency. This allows the material to maintain a fine equiaxed crystal structure at each stage, significantly improving the plasticity and dimensional stability of subsequent precision drawing.

[0019] Furthermore, this invention monitors the acoustic emission signal energy rate and high-frequency harmonic component amplitude of the drawing force on the tube blank surface in the drawing deformation zone during the drawing process. Based on the gradual change morphology within a single drawing cycle, discrete changes correspond to abrupt changes in the morphology of adhesion tearing or microcrack initiation after the hardening reaches the critical point. This distinguishes different development stages of hardening. When both are gradual changes, the hardening is in a gradual development stage. Only the lubricant spraying flow rate needs to be increased to reduce the friction coefficient and suppress adhesion-slip oscillation by strengthening interface lubrication, thus avoiding unnecessary downtime or annealing and ensuring production continuity. When either parameter shows discrete changes, the hardening has entered the abrupt stage, and microcrack initiation or adhesion tearing has appeared on the tube blank surface. Drawing is immediately stopped and forced into intermediate vacuum annealing. Recrystallization eliminates dislocation accumulation and heals microcracks. Simultaneously, after annealing, the tube blank is redrawn according to the original process. This prevents hardening residue caused by insufficient annealing and avoids grain coarsening and strength reduction caused by excessive annealing, effectively reducing the tube breakage rate and significantly improving the continuity and stability of single-batch drawing.

[0020] Furthermore, this invention determines the drawing stability after adjusting the standard drawing process by observing the changing trends of the drawing force fluctuation amplitude and temperature distribution uniformity within a preset stable period. The drawing force fluctuation amplitude reflects the mechanical stability of the drawing process; its continuous decrease or stabilization indicates that the relative motion between the tube blank and the die is becoming more uniform. The temperature distribution uniformity reflects the consistency of the friction state on the tube blank surface; its continuous improvement or stabilization indicates that the lubricating film has been effectively covered and the frictional heat distribution is uniform. When both tend to stabilize, the drawing process has recovered from an abnormal state to a stable state. When the drawing force fluctuation amplitude continues to rise, the mechanical stability has not yet recovered; the fluctuation can be suppressed by reducing the drawing speed and deformation rate. When the temperature distribution uniformity continues to deteriorate, the lubrication state is uneven; the lubrication coverage can be improved by increasing the lubricant spray flow rate. When both continue to deteriorate, the hardening has not been eliminated; a second intermediate vacuum annealing is performed before drawing, avoiding blind adjustment and excessive intervention, effectively ensuring the consistency of the drawing process between multiple batches, and significantly improving the yield and production efficiency of niobium-titanium alloy capillary preparation. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing, as described in an embodiment of the present invention. Figure 2 This is a flowchart illustrating the process of determining the pull-out state of the current pass in an embodiment of the present invention; Figure 3 A flowchart for determining the adjustment of the standard drawing process in an embodiment of the present invention; Figure 4 This is a flowchart illustrating how to determine the drawing stability of the current pass and adjust the standard drawing process in accordance with an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0023] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0024] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0025] Please see Figure 1 The diagram shown is a process flow chart of the niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to an embodiment of the present invention. The niobium-titanium alloy capillary preparation process of this embodiment includes: Step S1: Prepare the niobium-titanium alloy tube blank to be drawn; Step S2: Based on the initial size characteristics of the niobium-titanium alloy tube blank to be drawn and the target size characteristics of the niobium-titanium alloy capillary, determine the cross-sectional shrinkage characteristics of the niobium-titanium alloy tube blank to be drawn, and determine the number of stages required for multi-stage drawing, so as to automatically divide the entire drawing process into multi-stage drawing stages, with each drawing stage corresponding to a set of intermediate vacuum annealing nodes. Step S3: Perform drawing using the standard drawing process, and collect the actual drawing force and the actual temperature rise rate of the billet surface in the drawing deformation zone during the current pass in real time. Determine the drawing state of the current pass based on the changing trends of the actual drawing force and the actual temperature rise rate within a single drawing cycle. Step S4: Under the condition of abnormal drawing state in the current pass, the drawing force signal and the acoustic emission signal of the billet surface in the drawing deformation zone of the current pass are collected. Based on the actual change pattern of the acoustic emission signal energy rate and the amplitude of the high frequency harmonic component of the drawing force signal within the drawing cycle, the standard drawing process is adjusted. The actual change pattern includes gradual change pattern and abrupt change pattern. Step S5: After implementing the adjustment strategy, the second actual drawing force during the actual drawing process is re-acquired, and the temperature distribution on the surface of the billet in the drawing deformation zone is obtained. Based on the fluctuation range of the second actual drawing force within the preset stable period and the uniformity of the temperature distribution, it is determined whether the drawing stability of the current pass meets the standard. If it does not meet the standard, the standard drawing process is adjusted.

[0026] Specifically, this invention automatically divides the drawing process into multiple stages using the total reduction of area and the maximum cumulative reduction of area, ensuring that the cumulative deformation in each stage does not exceed the safety limit. This avoids hardening cracking caused by excessive deformation in a single stage and prevents efficiency loss due to excessively frequent annealing. After stage division, the changing trends of drawing force and temperature rise rate within a single drawing cycle are used as the criteria for determining whether the drawing state is abnormal. If an abnormality is determined, the hardening development trend is further distinguished by the changing patterns of acoustic emission signal energy rate and high-frequency harmonic component amplitude of drawing force within the drawing cycle. The lubricant spraying flow rate is adjusted according to the development trend, through strong... By reducing the friction coefficient through interfacial lubrication, adhesion-slip oscillations can be suppressed, avoiding unnecessary downtime and annealing. Discrete changes correspond to abrupt changes in microcrack initiation or adhesion tearing. In this case, forced insertion of intermediate vacuum annealing and redrawing eliminates dislocation accumulation and heals microcracks through recrystallization, while avoiding grain coarsening and strength reduction caused by over-annealing. After adjustment, the stability of the adjusted drawing is verified by the trend of changes in the amplitude of drawing force fluctuation and temperature distribution uniformity. Under unstable conditions, the drawing speed is reduced, the lubricant spraying flow rate is increased, or annealing is strengthened until the stability meets the standard, which significantly improves the yield and batch consistency of niobium-titanium alloy capillary preparation.

[0027] In this embodiment, the standard drawing process includes: standard drawing speed, standard single-pass section reduction rate, standard lubricant supply parameters, and standard drawing die geometry parameters.

[0028] Specifically, taking the drawing of niobium-titanium alloy capillary tubes as an example, the standard drawing speed is 1.0 m / min; the standard single-pass section reduction rate is 15% for rough drawing with an outer diameter greater than 6 mm and 10% for fine drawing with an outer diameter less than or equal to 3 mm; the lubricant is a composite lubricant containing molybdenum disulfide and graphite, and the standard spraying flow rate is 100 ml / min, which is uniformly applied through an annular nozzle; the standard drawing die has an outer die half-cone angle of 12°, a sizing band length of 1.5 mm, and a floating mandrel half-cone angle of 9°, with the difference between the two being between 2° and 5°. The die parameters are fixed before drawing and are not adjusted with real-time monitoring.

[0029] It is understandable that the specific process parameters of the standard drawing process can be adjusted according to the actual working conditions, and no specific limitations are made here.

[0030] In this embodiment, the process of preparing the niobium-titanium alloy tube blank to be drawn includes: Niobium-titanium alloy ingots are prepared by vacuum arc melting, the niobium-titanium alloy ingots are forged into round ingots, and the round ingots are extruded to form niobium-titanium alloy tube blanks to be drawn. Specifically, high-purity niobium and high-purity titanium raw materials are prepared in a ratio of 45-55 at% niobium content and 45-55 at% titanium content. The prepared raw materials are pressed into consumable electrodes and remelted 2-3 times in a vacuum consumable arc furnace to obtain niobium-titanium alloy ingots with a diameter of 150-200 mm and a length of 500-800 mm; wherein the melting vacuum degree is less than or equal to 1×10⁻⁶. -3 The melting current is 3–5 kA, and the voltage is 25–35 V. The ingot is heated to 900–1100℃ and held for 1–2 hours. Then, it is forged in multiple directions on a forging machine to form a round ingot. During the forging process, the final forging temperature is controlled to be no less than 750℃. The deformation amount of each forging pass is 20%–30%, and a total of 3–5 forging passes are performed to obtain a round ingot with a diameter of 60–70 mm and a length of 300–500 mm. After forging, the ingot is air-cooled to room temperature and then heated to 800–950℃. After being kept at a constant temperature for 0.5 to 1 hour, the material is extruded into a tube blank on a horizontal extrusion press. The extrusion ratio is controlled between 5 and 15, the extrusion speed is 20 to 50 mm / s, the mandrel diameter of the extrusion die is 12 to 14 mm, and the outer die aperture is 25 to 27 mm. After extrusion, a tube blank with an outer diameter of 25 mm and a wall thickness of 6 to 7 mm is obtained. The extruded tube blank is cooled to room temperature in a protective atmosphere, such as argon, and then the surface is cleaned to remove the surface oxide scale and residual lubricant, thus obtaining the niobium-titanium alloy tube blank to be drawn.

[0031] In this embodiment, the process of automatically dividing the entire drawing process into multi-stage drawing stages includes, The total reduction of area is determined based on the ratio of the target cross-sectional area of ​​the target capillary to the initial cross-sectional area of ​​the niobium-titanium alloy tube blank to be drawn. This ratio is used to determine the total deformation required from the initial tube blank to the target capillary. The entire drawing process is automatically divided into the required number of stages, with each drawing stage corresponding to a set of intermediate vacuum annealing nodes. Without causing fracture or surface damage due to work hardening, the maximum cumulative section shrinkage rate is determined based on the maximum allowable section reduction ratio between two adjacent intermediate vacuum annealings. This is used to determine the upper limit of safe deformation between two intermediate vacuum annealings, avoiding tube blank fracture or surface microcracks due to excessive work hardening.

[0032] The cumulative section shrinkage rate is determined based on the cross-sectional area at the beginning and end of the current drawing stage of the billet. This is used to determine the actual deformation that occurs within the current drawing stage, ensuring that the cumulative section shrinkage rate within each stage does not exceed the maximum cumulative section shrinkage rate.

[0033] The number of stages is determined based on the ratio of the total section reduction rate to the maximum cumulative section reduction rate. This is used to determine the number of drawing stages that need to be divided in the entire drawing process and the intermediate dimension nodes between each stage. An intermediate vacuum annealing process is then inserted after each node.

[0034] In this embodiment, the intermediate vacuum annealing process includes annealing temperature, holding time, heating rate, furnace vacuum degree, and cooling method. Specifically, taking the drawing of niobium-titanium alloy capillary tubes as an example, the annealing temperature is 500℃~800℃, specifically selected according to the cumulative deformation amount at each stage; the holding time is 2 hours; the heating rate is 5℃ / min~12℃ / min, rising from room temperature to the holding temperature; and the furnace vacuum degree is less than or equal to 5×10⁻⁶. -3 Pa, the cooling method is to cool it in the furnace to below 150°C before taking it out of the furnace.

[0035] Specifically, this invention can obtain niobium-titanium alloy tube blanks with uniform microstructure and smooth surface through a tube blank preparation process, providing high-quality blanks for subsequent drawing. Based on the cross-sectional shrinkage characteristics, it automatically divides the drawing stages into multiple stages, ensuring that intermediate vacuum annealing is inserted in time after each stage, avoiding hardening cracks caused by excessive deformation, and preventing excessively frequent annealing from reducing production efficiency. This allows the material to maintain a fine equiaxed crystal structure at each stage, significantly improving the plasticity and dimensional stability of subsequent precision drawing.

[0036] Please see Figure 2 As shown, this is a flowchart illustrating the process of determining the pull-out state of the current test track according to an embodiment of the present invention. In this embodiment, the process of determining the pull-out state of the current test track includes: The drawing process is performed using standard drawing technology, and the actual drawing force and the actual temperature rise rate of the tube blank surface in the drawing deformation zone are collected in real time during the current pass. According to the multi-stage drawing process, the drawing time period from the starting size of the current stage to the ending size of the current stage is taken as a single drawing cycle. Based on the actual pulling force variation data within a single pulling cycle, the trend of pulling force variation during the actual pulling process is determined; Based on the actual temperature rise rate variation data within a single drawing cycle, the trend of temperature rise rate variation on the tube blank surface in the drawing deformation zone is determined. The drawing status of the current pass is determined based on the trends of drawing force and temperature rise rate within a single drawing cycle.

[0037] In this embodiment, the current drawing state is determined to be normal based on the fact that the trend of the drawing force and the trend of the temperature rise rate are both stable within a single drawing cycle; the current drawing state is determined to be abnormal based on the fact that the trend of the drawing force or the trend of the temperature rise rate are continuously increasing within a single drawing cycle.

[0038] In this embodiment, a single pulling cycle is divided into three consecutive and equal-length periods: the pre-term period, the middle-term period, and the post-term period. The arithmetic mean of all representative pulling force values ​​in each period is calculated to determine the average pulling force for each period.

[0039] If the average increase in pulling force between different time periods shows an increasing trend along the single pulling cycle, then the trend of pulling force change is determined to be a continuous increase; if the average increase in pulling force between different time periods shows a decreasing trend or tends to be consistent along the single pulling cycle, then the trend of pulling force change is determined to be a stable trend.

[0040] In this embodiment, a single drawing cycle is divided into three equal-length time periods in the same way as the trend of the drawing force change. The arithmetic mean of all temperature rise rate values ​​in each time period is calculated to determine the average temperature rise rate of each time period.

[0041] If the average temperature rise rate between different time periods shows an increasing trend along the single drawing cycle, then the temperature rise rate change trend is determined to be a continuous increasing trend; if the average temperature rise rate between different time periods shows a decreasing trend or tends to be consistent along the single drawing cycle, then the temperature rise rate change trend is determined to be a stable trend.

[0042] It is understandable that the number of time periods in a single pull-out cycle is not limited to three; four or more time periods can also be used, and no specific limitation is made here.

[0043] In this embodiment, the actual drawing force is collected in real time by a strain gauge tension / compression sensor installed on the drawing machine, and the maximum value within 0.5 seconds is taken as the representative value of the drawing force at that moment; the actual temperature rise rate is obtained by continuously collecting the temperature of the tube blank surface by a non-contact infrared thermal imager installed 5mm to 10mm from the exit side of the drawing die, performing differential calculations on the collected temperature data to obtain the instantaneous temperature rise rate, and using a sliding window averaging to eliminate noise, with a window width of 10 sampling points.

[0044] Please see Figure 3 As shown, this is a flowchart illustrating the process of determining and adjusting the standard drawing process according to an embodiment of the present invention. In this embodiment, the process of determining and adjusting the standard drawing process includes: Under the condition of abnormal drawing, the drawing force signal of the abnormal pass and the acoustic emission signal of the tube blank surface in the drawing deformation zone are obtained. The amplitude of the high-frequency harmonic component of the drawing force under abnormal drawing conditions is determined based on the drawing force signal. The larger the amplitude of the high-frequency harmonic component, the more intense the high-frequency oscillation of adhesion-slippage between the tube blank and the die caused by work hardening during the drawing process. The acoustic emission signal energy rate of the tube blank surface in the drawing deformation zone during abnormal passes is determined based on the acoustic emission signal. The higher the acoustic emission signal energy rate, the more severe the microcrack initiation or adhesion tearing caused by hardening on the tube blank surface in the drawing deformation zone. The standard drawing process is determined based on the actual changes in the amplitude of high-frequency harmonic components and the energy rate of acoustic emission signals within a single drawing cycle.

[0045] Since the amplitude of high-frequency harmonic components and the energy rate of acoustic emission signals are both gradually changing within a single drawing cycle, the lubricant spraying flow rate is increased to suppress adhesion-slip oscillations. The increase is based on whether the acoustic emission signal energy rate stops rising after adjustment. If the acoustic emission signal energy rate begins to decrease or tends to stabilize, the current flow rate is maintained and drawing continues. If the acoustic emission signal energy rate continues to rise, the spraying flow rate is increased until the acoustic emission signal energy rate shows a decreasing trend or reaches the maximum allowable flow rate of the equipment. If the flow rate has increased to the maximum allowable flow rate of the equipment, the current drawing pass is stopped and intermediate vacuum annealing is forcibly inserted.

[0046] Based on the fact that the amplitude of the high-frequency harmonic components or the energy rate of the acoustic emission signal changes abruptly within a single drawing cycle, it is determined to stop the current drawing pass and force the intermediate vacuum annealing process to be inserted. After annealing, the drawing process is restarted.

[0047] In this embodiment, the single pull-out cycle is divided into three consecutive and equal-length time periods. The arithmetic mean of the amplitudes of all high-frequency harmonic components and the arithmetic mean of the energy rates of all acoustic emission signals are calculated for each time period to determine the average amplitude of the high-frequency harmonic components and the average energy rate of the acoustic emission signal for each time period. If the increase in the average high-frequency harmonic component amplitude between different time periods shows a continuous change along the single pulling cycle, the change pattern of the high-frequency harmonic component amplitude is determined to be a gradual change pattern; if the increase in the average high-frequency harmonic component amplitude between different time periods shows a discrete change along the single pulling cycle, the change pattern of the high-frequency harmonic component amplitude is determined to be an abrupt change pattern.

[0048] If the increase in the average acoustic emission signal energy rate between different time periods is continuous along the single pull-out cycle, the change pattern of the acoustic emission signal energy rate is determined to be a gradual change pattern; if the increase in the average acoustic emission signal energy rate between different time periods is discrete along the single pull-out cycle, the change pattern of the acoustic emission signal energy rate is determined to be a sudden change pattern.

[0049] In this embodiment, continuous change means that the increase in each time period shows a gradual and continuous trend along the time axis, without any sudden increase or decrease during the change process, and the increase rate remains relatively consistent. The overall change trend can be approximated by a smooth curve. Discrete change means that the increase in a certain time period is abruptly increased relative to the previous adjacent time period. The overall change trend cannot be approximated by a smooth curve. The abrupt increase is a non-continuous jump on the increase change curve.

[0050] In this embodiment, the acoustic emission signal is acquired by an acoustic emission sensor installed at 5mm to 15mm on the exit side of the drawing die. The acquired acoustic emission signal is subjected to envelope detection and root mean square calculation to obtain the acoustic emission signal energy rate. The amplitude of the high-frequency harmonic components is determined by extracting the acquired drawing force signal after bandpass filtering.

[0051] Specifically, this invention monitors the acoustic emission signal energy rate and high-frequency harmonic component amplitude of the drawing force on the tube blank surface in the drawing deformation zone during the drawing process. Based on the gradual change morphology within a single drawing cycle, discrete changes correspond to abrupt changes in the hardening process after reaching the critical point, such as sudden adhesion tearing or microcrack initiation. This distinguishes different stages of hardening development. When both are gradual changes, the hardening is in a gradual development stage, requiring only an increase in lubricant spray flow rate. By strengthening interfacial lubrication and reducing the friction coefficient, adhesion-slip oscillations are suppressed, avoiding unnecessary downtime or annealing and ensuring production continuity. When either parameter exhibits discrete changes, the hardening has entered the abrupt stage, and microcrack initiation or adhesion tearing has appeared on the tube blank surface. Drawing is immediately stopped, and intermediate vacuum annealing is forced in. Recrystallization eliminates dislocation accumulation and heals microcracks. Simultaneously, after annealing, the tube blank is redrawn according to the original process. This prevents hardening residue caused by insufficient annealing and avoids grain coarsening and strength reduction caused by excessive annealing, effectively reducing the tube breakage rate and significantly improving the continuity and stability of single-batch drawing.

[0052] Please see Figure 4 As shown, this is a flowchart illustrating how to determine the drawing stability of the current pass and adjust the standard drawing process according to an embodiment of the present invention. In this embodiment, the process of determining the drawing stability of the current pass and adjusting the standard drawing process includes: The second actual drawing force during the actual drawing process within the preset stabilization period was re-acquired, and the temperature distribution data of the tube blank surface in the drawing deformation zone was obtained. Based on the fluctuation trend of the second actual drawing force within the preset stable period, and the variation trend of the uniformity of temperature distribution within the preset stable period, it is determined whether the drawing stability of the current pass meets the standard. Based on the fact that the fluctuation range of the second actual pulling force shows a continuous downward trend or tends to stabilize along the preset stabilization cycle, and the uniformity of temperature distribution shows a continuous improvement trend or tends to stabilize along the preset stabilization cycle, it is determined that the pulling stability of the current pass meets the standard, and subsequent pulling continues. If the fluctuation range of the second actual drawing force shows a continuous upward trend along the preset stabilization period, or the uniformity of the temperature distribution shows a continuous deterioration trend along the preset stabilization period, it is determined that the drawing stability of the current pass does not meet the standard, and the standard drawing process is adjusted.

[0053] In this embodiment, the preset stabilization period is divided into three consecutive and equal-length periods: the pre-period period, the middle period, and the post-period period. The arithmetic mean of all second actual pull-out forces in each period is calculated to determine the average pull-out force of each period. Then, based on the ratio of the difference between the maximum and minimum pull-out forces in that period to the average value, the fluctuation range of each pull-out force value in each period relative to the average pull-out force in that period is determined.

[0054] If the fluctuation amplitude between different time periods shows a decreasing trend or tends to be consistent along the preset stable period, the trend of the pull-out force fluctuation amplitude is determined to be stable; if the fluctuation amplitude between different time periods shows an increasing trend along the preset stable period, the trend of the pull-out force fluctuation amplitude is determined to be continuously rising.

[0055] In this embodiment, the preset stabilization period is divided into three equal-length periods—before, during, and after—in the same manner as the fluctuation amplitude of the drawing force. Temperature distribution data of the tube blank surface in the drawing deformation zone is obtained by a non-contact infrared thermal imager, and the standard deviation of the temperature distribution data in each period is calculated to determine the uniformity of temperature distribution in each period.

[0056] Specifically, temperature distribution data is obtained through thermal images captured by an infrared thermal imager. The temperature values ​​of all pixels in the thermal image are used as samples to calculate the standard deviation. If the standard deviation between different time periods shows a decreasing trend or tends to be consistent along a preset stable period, the trend of temperature distribution uniformity is determined to be stable. If the standard deviation between different time periods shows an increasing trend along a preset stable period, the trend of temperature distribution uniformity is determined to be continuously deteriorating.

[0057] In this embodiment, based on the fact that the fluctuation amplitude of the second pulling force is continuously increasing and the temperature distribution uniformity is trending towards stabilization, the speed of the drive motor is reduced to decrease the pulling speed. The reduction is based on whether the fluctuation amplitude of the pulling force shows a downward trend after adjustment. Specifically, if the fluctuation amplitude begins to decrease, the current speed is maintained and observation continues; if the fluctuation amplitude continues to increase, the pulling speed is gradually reduced until the fluctuation amplitude shows a downward trend or reaches the minimum allowable speed of the equipment; if the speed has been reduced to the minimum allowable speed of the equipment and the fluctuation amplitude continues to increase, intermediate vacuum annealing is inserted.

[0058] Based on the trend of the pull-out force fluctuation amplitude tending to stabilize and the trend of the temperature distribution uniformity continuously deteriorating, the opening of the proportional valve is increased to increase the lubricant spraying flow rate. The increase is based on whether the standard deviation of the temperature distribution after adjustment shows a downward trend. Specifically, if the standard deviation begins to decrease, the current flow rate is maintained and observation continues; if the standard deviation continues to increase, the flow rate is gradually increased until the standard deviation shows a downward trend or reaches the maximum allowable flow rate of the equipment; if the flow rate has increased to the maximum allowable flow rate of the equipment and the standard deviation continues to increase, intermediate vacuum annealing is inserted.

[0059] Based on the fact that the trend of the fluctuation of the drawing force is continuously increasing and the trend of the temperature distribution uniformity is continuously deteriorating, the drawing is stopped, and intermediate vacuum annealing is performed again. After annealing, the drawing is restarted.

[0060] In this embodiment, the preset stabilization period is a period of continuous pulling for 3 to 8 minutes; the number of time periods of the preset stabilization period is not limited to three, but can also be four or more time periods, and no specific limitation is made here.

[0061] In this embodiment, the minimum allowable speed of the equipment is determined based on the minimum stable operating speed of the drawing machine drive motor; the maximum allowable flow rate of the equipment is determined based on the maximum opening of the proportional valve; the adjustment step size for successively decreasing and increasing is manually determined based on the equipment accuracy and current state, and is not specifically limited here.

[0062] Specifically, this invention determines the drawing stability after adjusting the standard drawing process by observing the changing trends of the drawing force fluctuation amplitude and temperature distribution uniformity within a preset stable period. The drawing force fluctuation amplitude reflects the mechanical stability of the drawing process; its continuous decrease or stabilization indicates that the relative motion between the tube blank and the die is becoming more uniform. The temperature distribution uniformity reflects the consistency of the friction state on the tube blank surface; its continuous improvement or stabilization indicates that the lubricating film has been effectively covered and the frictional heat distribution is uniform. When both tend to stabilize, the drawing process has recovered from an abnormal state to a stable state. When the drawing force fluctuation amplitude continues to rise, the mechanical stability has not yet recovered; the fluctuation can be suppressed by reducing the drawing speed and deformation rate. When the temperature distribution uniformity continues to deteriorate, the lubrication state is uneven; the lubrication coverage can be improved by increasing the lubricant spray flow rate. When both continue to deteriorate, the hardening has not been eliminated; a second intermediate vacuum annealing is performed before drawing, avoiding blind adjustment and excessive intervention, effectively ensuring the consistency of the drawing process between multiple batches, and significantly improving the yield and production efficiency of niobium-titanium alloy capillary preparation.

[0063] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A process for preparing niobium-titanium alloy capillaries based on multi-stage drawing and intermediate vacuum annealing, characterized in that, include, Preparation of niobium-titanium alloy tube blanks to be drawn; Based on the initial size characteristics of the niobium-titanium alloy tube blank to be drawn and the target size characteristics of the niobium-titanium alloy capillary, the cross-sectional shrinkage characteristics of the niobium-titanium alloy tube blank to be drawn are determined. According to the cross-sectional shrinkage characteristics, the entire drawing process is automatically divided into multi-stage drawing stages, and each drawing stage corresponds to a set of intermediate vacuum annealing nodes. The drawing process is performed using standard drawing techniques. The actual drawing force and the actual temperature rise rate of the billet surface in the drawing deformation zone are collected in real time during the current drawing process. The drawing status of the current drawing is determined based on the changing trends of the actual drawing force and the actual temperature rise rate within a single drawing cycle. Based on the current draw force signal and the acoustic emission signal of the billet surface in the draw deformation zone, determine whether to increase the standard spray flow rate of the lubricant or stop the draw and force the intermediate vacuum annealing according to the actual change of the acoustic emission signal energy rate and the amplitude of the high-frequency harmonic component of the draw force signal within a single draw cycle. The second actual drawing force and the temperature distribution on the surface of the tube blank in the drawing deformation zone are obtained during the actual drawing process. Based on the fluctuation range of the second actual drawing force within the preset stable period and the uniformity of the temperature distribution, it is determined whether the drawing stability of the current pass meets the standard. If it does not meet the standard, the standard drawing process is adjusted, or intermediate vacuum annealing is inserted.

2. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 1, characterized in that, The process of automatically dividing the entire drawing process into multi-stage drawing phases includes: The total reduction of area is determined based on the target cross-sectional area of ​​the target capillary and the initial cross-sectional area of ​​the niobium-titanium alloy tube blank to be drawn. The maximum cumulative cross-sectional reduction rate is determined based on the maximum allowable cross-sectional reduction ratio between two adjacent annealing stages; The cumulative section shrinkage rate at the start of the current drawing stage of the billet is determined based on the cross-sectional area at the start and the cross-sectional area at the end of the current drawing stage. The number of stages is determined based on the ratio of the total section shrinkage rate to the maximum cumulative section shrinkage rate, and the entire drawing process is automatically divided into multi-stage drawing processes according to the number of stages.

3. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 2, characterized in that, The process of determining the trend of actual drawing force changes within a single drawing cycle includes: The drawing process is performed using standard drawing techniques, and the actual drawing force of the current pass is collected in real time during the actual drawing process. According to the multi-stage drawing process, the drawing time period from the starting size of the current stage to the ending size of the current stage is taken as a single drawing cycle. The single drawing cycle is divided into several consecutive and equally long time periods, and the average drawing force in each time period is determined. Based on the fact that the increase in average pulling force between each time period shows an increasing trend along the single pulling cycle, the trend of pulling force change is determined to be a continuous increase. Based on the fact that the increase in average pulling force between each time period shows a decreasing trend or tends to be consistent along the single pulling cycle, the trend of pulling force change is determined to be a stable trend.

4. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 3, characterized in that, The process of determining the trend of the actual temperature rise rate includes: The drawing process is performed using standard drawing techniques, and the actual temperature rise rate of the tube blank surface in the drawing deformation zone during the current drawing pass is collected in real time. The single drawing cycle is divided into several consecutive and equally long time periods, and the average temperature rise rate in each time period is determined. Based on the fact that the increase in the average temperature rise rate between each time period shows an increasing trend along the single drawing cycle, it is determined that the temperature rise rate changes continuously. Based on the fact that the increase in the average temperature rise rate between the aforementioned time periods shows a decreasing trend or tends to be consistent along the single drawing cycle, the trend of temperature rise rate change is determined to be a stable trend.

5. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 4, characterized in that, The process of determining the pull-out status of the current track includes: Based on the fact that the trends of the pulling force and the temperature rise rate are both stable within a single pulling cycle, it is determined that the pulling status of the current pass is normal. Based on the fact that the trend of the pulling force or the trend of the temperature rise rate continuously increases within a single pulling cycle, it is determined that the pulling state of the current pass is abnormal.

6. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 5, characterized in that, The process of determining the standard spray flow rate for increasing the lubricant includes: Acquire the drawing force signal of abnormal passes and the acoustic emission signal of the billet surface in the drawing deformation zone; The amplitude of the high-frequency harmonic component of the pull-out force under abnormal pull-out conditions is determined based on the pull-out force signal. The acoustic emission signal energy rate of the tube blank surface in the drawing deformation zone during abnormal passes is determined based on the acoustic emission signal. Based on the fact that the amplitude of the high-frequency harmonic components and the energy rate of the acoustic emission signal are both gradually changing within a single drawing cycle, the standard spraying flow rate of the lubricant is increased.

7. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 6, characterized in that, The process of stopping the pulling and forcibly inserting the intermediate vacuum annealing includes: Based on the fact that the amplitude of the high-frequency harmonic component or the energy rate of the acoustic emission signal changes abruptly within a single drawing cycle, the current drawing is stopped, and intermediate vacuum annealing is forcibly inserted using an intermediate vacuum annealing process. After annealing, the drawing process restarts.

8. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 7, characterized in that, The process of determining whether the pull-out stability of the current pass meets the standard includes: The second actual drawing force during the actual drawing process within the preset stabilization period was re-acquired, and the temperature distribution data of the tube blank surface in the drawing deformation zone was obtained. The preset stabilization period is divided into several equal-length time periods, and the fluctuation range of the second actual pull-out force and the standard deviation of the temperature distribution data are determined between each time period. Determine the trends of the fluctuation amplitude and the standard deviation within the preset stabilization period: Based on the fact that the fluctuation amplitude shows an increasing trend along the preset stabilization period, or that the standard deviation shows an increasing trend along the preset stabilization period, it is determined that the pull-out stability of the current pass does not meet the standard.

9. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 8, characterized in that, Adjusting the standard drawing process, or inserting an intermediate vacuum annealing process, includes: Based on the fact that the fluctuation range of the second actual pulling force is continuously increasing and the temperature distribution uniformity is trending towards stabilization, the speed of the drive motor is reduced to decrease the pulling speed. Based on the fact that the fluctuation range of the second actual pulling force tends to stabilize and the temperature distribution uniformity tends to deteriorate, the opening of the proportional valve is increased to improve the lubricant spraying flow rate. Based on the fact that the fluctuation range of the second actual drawing force is continuously increasing and the temperature distribution uniformity is continuously deteriorating, drawing is stopped, and intermediate vacuum annealing is performed again using an intermediate vacuum annealing process.

10. The niobium-titanium alloy capillary preparation process based on multi-stage drawing and intermediate vacuum annealing according to claim 9, characterized in that, The intermediate vacuum annealing process includes, The annealing temperature is 500℃~800℃; The heat preservation time is 2 to 3 hours; The heating rate is 5℃ / min to 12℃ / min; The vacuum level inside the furnace is less than or equal to 5 × 10⁻⁶. -3 Pa; The cooling method is to cool it in the furnace to below 150°C before removing it from the furnace.

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