High-precision small-diameter thermocouple probe and manufacturing method thereof

Abstract

The invention relates to the technical field of thermocouples, in particular to a high-precision small-diameter thermocouple probe and a manufacturing method thereof. The manufacturing method comprises the following steps: firstly, performing at least two times of rotary swaging processing on a thermocouple metal sleeve, so that the outer diameter of the end part of a probe is gradually reduced to a final target size of 2.0 mm or below from an initial size; after at least one time of rotary swaging processing, annealing the end part of the rotary swaged probe in a protective atmosphere; wherein the deformation quantity and the internal stress of the end part of the probe are controlled through a process of alternately performing rotary swaging and annealing, so that the position precision of the internal temperature sensing element is kept while the diameter reduction is realized. According to the method, the processing stress accumulated by rotary swaging is actively and periodically eliminated and the microstructure of the material is stabilized through the process of alternately performing rotary swaging and annealing, so that the technical problems that the position of an internal temperature sensing element is deviated and the temperature measurement precision is degraded due to continuous plastic deformation when the diameter of the probe is processed to be less than or equal to 2.0 mm in the prior art are fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of thermocouple technology, specifically to a high-precision, small-diameter thermocouple probe and its manufacturing method. Background Technology

[0002] In the field of high-temperature combustion gas temperature measurement in engines, thermocouples are key sensing elements. In existing technologies, armored thermocouple structures are often used to improve the mechanical strength and service life of thermocouples. For example, Chinese invention patent CN116147794A discloses a "semi-flexible, semi-armored high-performance thermocouple assembly," which solves the assembly stress and easy breakage problems caused by rigid connections in fully armored thermocouples by designing the probe end of the thermocouple as an armored, sealed, spin-forged necked structure and changing the compensation extension section to a flexible structure.

[0003] Specifically, the probe end of the prior art (such as CN116147794A) is formed by a multi-segment variable diameter rotary forging process to achieve a balance between the structural strength of the rear end and the fast response time of the front end.

[0004] The core of its process lies in compacting the internal magnesium oxide powder through multi-stage drawing and radial high-speed hammering (rotary forging), thereby ensuring insulation performance and structural density.

[0005] However, after in-depth analysis and practice, the applicant found that the existing technical solution still has obvious limitations: its rotary forging process mainly focuses on reducing the probe size from a relatively large outer diameter in multiple segments to a conventional size (e.g., 2.5mm level) to optimize the macroscopic structural strength and assembly stress. But when it is necessary to further refine the probe tip size to a smaller scale (e.g., 2.0mm or less) to pursue the ultimate temperature response speed, directly using the existing rotary forging process will cause the internal temperature sensing element (thermal wire) to shift position or even be damaged due to severe plastic deformation.

[0006] The probe's internal structure is complex, making the precise positioning of the temperature-sensing element crucial. Current technologies employing single-pass or continuous multi-stage rotary forging processes struggle to guarantee the stability of the temperature-sensing element at the microscale when excessive deformation accumulates. Consequently, while the probe's external dimensions may meet requirements, the product may exhibit issues such as abnormal temperature sensing position, significantly reduced temperature detection accuracy, and prolonged response time. This has become a key bottleneck restricting the development of high-performance, small-size thermocouple probe technology.

[0007] Therefore, there is an urgent need for a new manufacturing method that can effectively protect the structural integrity and positional accuracy of the internal temperature sensing element while achieving extremely small probe dimensions, thereby truly achieving a balance between high precision and rapid response. Summary of the Invention

[0008] This invention provides a high-precision, small-diameter thermocouple probe and its manufacturing method, to solve the technical problem that the existing rotary forging process cannot simultaneously achieve temperature measurement accuracy and response speed when realizing ultra-small diameter probes (≤2.0mm) due to the positional offset of the internal temperature sensing element.

[0009] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides a method for manufacturing a high-precision, small-diameter thermocouple probe, characterized by comprising the following steps: The thermocouple metal sheath is subjected to at least two rotary forging processes to gradually reduce the outer diameter of its probe tip from the initial size to the final target size of 2.0 mm or less; After at least one rotary forging process, the tip of the rotary forged probe is annealed in a protective atmosphere. The process of alternating forging and annealing controls the deformation and internal stress at the probe tip, thereby achieving a smaller diameter while maintaining the positional accuracy of the internal temperature sensing element.

[0010] This invention, by forcibly inserting annealing after at least one rotary forging process, can actively and promptly interrupt and release the internal stress accumulated during rotary forging, and restore the uniformity of the material's microstructure. This "interruption-recovery" mechanism fundamentally changes the internal state evolution path of the probe during ultra-fine diameter machining, transforming it from continuous, uncontrollable plastic flow to a staged, controllable "deformation-stabilization" cycle. This effectively overcomes the technical problems inherent in existing technologies that inevitably lead to uneven densification of the internal insulation layer and displacement of the temperature sensing element when continuous or single large deformation rotary forging is performed to achieve dimensions of 2.0 mm and below. Thus, while achieving the ultimate size target, it ensures the reliable maintenance of the positional accuracy of the temperature sensing element, the cornerstone of temperature measurement accuracy.

[0011] As a preferred embodiment of the present invention, the rotary forging process is performed in two steps, successively reducing the outer diameter of the probe tip from a first dimension to an intermediate dimension, and then reducing it from the intermediate dimension to the final target size of 2.0 mm.

[0012] As a preferred embodiment of the present invention, the first dimension is 5.0±0.05mm, and the intermediate dimension is 2.5±0.1mm.

[0013] By decomposing the total deformation (e.g., from 5.0 mm to 2.0 mm) into two differentiated stages, the plastic deformation process was controlled and optimized. (1) The first rotary forging (rough necking) is responsible for completing most of the deformation, quickly reducing the probe tip to a critical intermediate size. This size (e.g., 2.5 mm) ensures that the deformation can effectively approach the final target while keeping the single deformation within a reasonable range that the material can withstand and that work hardening can be completely eliminated by subsequent annealing. This avoids macroscopic defects (such as wrinkling and cracking) and severe disturbances to the internal structure that may result from a single extreme deformation.

[0014] (2) Intermediate annealing is performed immediately after the first rotary forging. At this time, the material is in a high stress and high hardening state due to the large deformation. Annealing plays a pivotal role here: it completely eliminates the residual stress of the first rotary forging, restores the plasticity of the material, and provides a valuable "thermal relaxation" opportunity for the internal insulating medium and temperature sensing element, so that their position and state can be stabilized and optimized at high temperature.

[0015] (3) The second rotary forging (precision necking) is carried out on the intermediate-sized matrix that has been annealed, softened and reset. Due to the uniform material state and low stress level, this rotary forging can complete the precision micro-deformation towards the final 2.0mm target with less deformation force, higher dimensional accuracy and shape consistency, thereby minimizing secondary interference to the internally stabilized structure.

[0016] As a preferred embodiment of the present invention, the annealing process is carried out in a mixed protective atmosphere of hydrogen and nitrogen, and the annealing temperature is 1000℃-1100℃.

[0017] Setting the annealing temperature in the high-temperature range of 1000℃-1100℃ is the preferred option for commonly used sleeve materials such as nickel-based alloys. At this temperature, the material can undergo sufficient recrystallization, completely eliminating work hardening, and its atomic diffusion ability is enhanced, which is beneficial for the repair of internal micro-defects and deep relaxation of residual stress. This high-temperature protective atmosphere annealing is not a simple heat treatment, but a specific technical means that must be adopted in deep collaboration with the rotary forging process to achieve the "stabilization and reset" of the internal structure.

[0018] As a preferred embodiment of the present invention, the volume percentage of hydrogen in the mixed protective atmosphere is 70%-80%, and the volume percentage of nitrogen is 20%-30%.

[0019] Using a mixed atmosphere of hydrogen and nitrogen (especially an atmosphere with a high proportion of hydrogen) can effectively reduce trace oxides that may form on the metal surface at high temperatures and prevent the new surface from being oxidized, ensuring the purity of the material surface and internal quality after annealing. This is crucial for subsequent welding and long-term performance stability at high temperatures.

[0020] As a preferred embodiment of the present invention, the method further includes: after the outer diameter of the probe tip reaches the final target size and undergoes annealing, drilling a hole in the probe tip to form a cavity for accommodating the thermocouple leads. The formed probe tip size (≤2.0mm) is stable; using this as a reference for drilling ensures the concentricity of the cavity and the probe shape, avoiding hole deformation or misalignment caused by drilling before forging. Furthermore, the material after final annealing exhibits excellent plasticity and toughness, which is more conducive to high-quality drilling and reduces the generation of burrs and microcracks.

[0021] As a preferred embodiment of the present invention, after drilling the head, the method further includes: adjusting and fixing the top positions of the thermocouple leads in the cavity so that they are in contact with each other; and performing laser welding on the tops of the contacting thermocouple leads to form a thermal junction.

[0022] Precise adjustment and fixation of the lead wire position within a pre-formed, stable cavity allows full utilization of the high-precision structural foundation created by the aforementioned processes. Laser welding, with its concentrated energy and small heat-affected zone, is ideal for precision operations within micro-cavities, enabling robust and reliable micro-welding with minimal impact on surrounding filled or soon-to-be-filled insulating materials.

[0023] As a preferred embodiment of the present invention, the method further includes: backfilling the cavity with insulating material and sealing the tip of the probe by welding.

[0024] Specifically, magnesium oxide powder is backfilled into the cavity and then dried and extruded; the tip of the necked section is sealed using argon arc welding; finally, the probe after sealing welding undergoes a third annealing treatment.

[0025] Backfilling with insulating material (such as MgO) ensures electrical insulation and mechanical support between the sensing element and the metal sleeve. Backfilling after precision forming and welding of the probe ensures that the insulating material fully fills the defined space. The final tip sealing weld (such as argon arc welding) provides long-term, reliable moisture-proof and contamination-proof encapsulation, ensuring stable operation of the probe in harsh environments such as high-temperature engine exhaust.

[0026] On the other hand, the present invention also provides a high-precision, small-diameter thermocouple probe, which is manufactured by the above-described manufacturing method, and the outer diameter of the probe tip is ≤2.0mm.

[0027] The beneficial effects are: 1. By employing an alternating process of "multi-stage rotary forging + intermediate annealing" (e.g., from 5.0mm → 2.5mm → 2.0mm), the internal stress distribution of the metal sleeve during deformation is effectively controlled, avoiding micro-cracks in the material or uneven MgO filling caused by a single large deformation. The intermediate annealing step releases the internal stress generated by work hardening, preventing the internal temperature sensing element (thermocouple wire) from shifting due to material embrittlement or uneven deformation. This achieves an ultra-fine structure with an outer diameter of ≤2.0mm at the probe tip while ensuring that the thermal contact is precisely located at the probe axis, guaranteeing the authenticity and repeatability of the temperature measurement signal. Consequently, the temperature measurement accuracy at 950℃ is improved from ±8℃ of the traditional process to within ±6℃.

[0028] 2. This invention proposes a process paradigm of "alternating rotary forging and intermittent annealing," breaking away from the conventional thinking of "forming first and then processing" or "continuous forming." By actively inserting annealing under specific conditions during rotary forging, it achieves the phased and proactive elimination of work-hardened internal stress and the periodic stabilization of the microstructure. This ensures that as the probe evolves towards ultra-fine dimensions, its internal structure (temperature sensing element and insulating layer) remains in a controllable state of "deformation → stabilization → re-deformation → re-stabilization," rather than an uncontrolled cumulative distortion process. This fundamental process innovation is not revealed or obvious in existing technologies; it fundamentally guarantees that while achieving an ultra-fine diameter of 2.0 mm, the absolute positional accuracy of the internal temperature sensing element is perfectly maintained.

[0029] 3. The total deformation is reasonably allocated, and 2.5mm is set as the critical annealing node, so that the deformation of each rotary forging is within the optimal range, which not only ensures processing efficiency, but also minimizes the impact of a single deformation on the internal structure. Attached Figure Description

[0030] Figure 1 The graph shows the dynamic response time test results of a conventional probe (2.5 mm in diameter). Figure 2 The graph shows the test results of the dynamic response time of the probe (2mm in diameter) of this invention. The horizontal axis represents different products, and each product is tested 10 times. Figure 3 The image shows the temperature accuracy test results of a traditional probe (2.5 mm in diameter). Figure 4 The figure shows the temperature accuracy test results of the probe (2mm in diameter) of this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0032] The principles and essence of the present invention will be explained in detail below with reference to several representative embodiments.

[0033] In existing technologies, to meet the demands for rapid response and high spatial resolution of temperature sensors under high-dynamic and high-temperature conditions such as those in engines, reducing the diameter of thermocouple probe tips to 2.0 mm or less has become a key technological direction. Currently, the industry commonly uses a single, continuous rotary forging process to achieve radial compression and forming of the probes. However, this method is suitable for probe tip diameters ≥ 2.5 mm. When attempting to directly reduce the probe tip from a conventional size (e.g., 5.0 mm) to the extreme size of 2.0 mm using this rotary forging process, technological bottlenecks become apparent.

[0034] During this process, the metal sleeve (usually austenitic stainless steel or nickel-based superalloy) undergoes severe cold plastic deformation, forcibly elongating and twisting its grains, accumulating extremely high residual stress at the microscopic level. Simultaneously, due to the periodic hammering of the rotary forging hammer and the uneven flow of the material, macroscopically, this easily leads to uneven wall thickness and axial bending, among other uneven deformations. More critically, the temperature-sensing element (thermocouple wire) encapsulated inside the sleeve and the surrounding magnesium oxide (MgO) insulating powder are entrained and disturbed in this intense and uncontrollable plastic flow, causing irreversible shifts in their relative positions. This microscopic instability of the internal structure directly causes a deviation between the actual temperature-sensing position of the hot junction and the theoretical design point, ultimately manifesting as a significant decrease in product temperature detection accuracy, prolonged response time, and reduced long-term reliability under high vibration and thermal cycling conditions. Furthermore, excessive residual stress may induce stress corrosion or fatigue cracks in the probe during subsequent processing or use, further threatening product lifespan.

[0035] Based on the aforementioned profound technical challenges and industry pain points, and to resolve the inherent contradiction between "dimensional forming" and "internal conformation preservation" in the machining of extreme small diameters using a single rotary forging process, this application provides a method for manufacturing a high-precision small-diameter thermocouple probe, which includes the following steps: S101: Raw material pretreatment Nickel-based alloy metal wire (with two built-in thermocouple leads) is provided as the raw material for the probe sleeve. The metal wire is cold-drawn using a wire drawing machine, with the drawing speed and die size controlled to precisely stretch its diameter to 5.0 ± 0.05 mm. After passing multi-point measurement with a micrometer, it proceeds to the next process.

[0036] S102: Fixed-length cutting and straightening Using a high-precision CNC cutting machine, the aforementioned 5.0mm diameter cable is cut into a certain length (e.g., 120±1mm). After cutting, the cable segment is placed on a precision straightening platform, and its straightness is checked using a dial indicator to ensure that the straightness error is controlled within ±0.1mm along the entire length, in order to meet the alignment requirements of subsequent precision machining.

[0037] S103: First rotary forging (rough necking) The straightened line segment is placed into the fixture of the CNC rotary forging machine. The rotary forging process parameters are set as follows: forging frequency 18Hz, clamping torque 15N·m. The machine is started, and the first rotary forging is performed on the approximately 30mm section at the front end of the line segment. During the rotary forging process, multiple hammers strike the workpiece at high speed and synchronously in the radial direction, causing radial compression deformation. After processing, the diameter of the necked section is checked using an outside micrometer, controlling it to reach 2.5±0.1mm. The main goal of this stage is to achieve a significant diameter reduction and to leave allowance for subsequent finishing.

[0038] Of course, in other embodiments, the forging frequency can also be any value in the range of 15-21Hz, such as 16Hz or 20Hz, and the clamping torque can be 14N·m or 16N·m.

[0039] S104: First intermediate annealing (stress relief and microstructure stabilization) The workpiece, after its first rotary forging, is transferred to a through-type atmosphere-protected annealing furnace. A protective gas mixture consisting of 75% hydrogen (H2) and 25% nitrogen (N2) is introduced into the furnace to prevent oxidation of the nickel-based alloy surface at high temperatures. The annealing temperature is set to 1050°C, and the holding time is 15 minutes. At this high temperature, the metal grains recrystallize, the work hardening caused by the first rotary forging is completely eliminated, the internal micro-stress is fully released, and the material's plasticity and toughness are restored. This step is crucial to preventing displacement of the internal structure (temperature sensing element) during subsequent finishing.

[0040] Of course, in other embodiments, the annealing temperature can also be any value in the range of 1000-1100°C, such as 1040°C or 1060°C.

[0041] S105: Second rotary forging (finish necking) The annealed and cooled workpiece is then loaded back into the rotary forging mill. Using the same process parameters as the first rotary forging (frequency 18Hz, torque 15N·m), the already formed 2.5mm necked section is subjected to a second rotary forging. The goal of this forging is to achieve precise micro-deformation, further reducing the diameter to a final 2.0±0.05mm. Due to the annealing in step S104, the material is in a uniform and soft "reset" state, allowing for more stable and precise forming during this forging process. This significantly reduces the risk of uneven compaction of the internal MgO insulation layer or disturbance of the thermocouple wire position caused by uneven deformation.

[0042] S106: Second intermediate annealing (final shaping) The necked workpiece is then placed back into the same protective annealing furnace for a second annealing at 1050°C under a 75% H2 + 25% N2 atmosphere, and held for 10 minutes. This step aims to eliminate any minor stresses that may have been introduced by the second rotary forging, ensuring complete stabilization of the metal grain structure and dimensional stability in the 2.0mm diameter segment, thus providing a dimensionally stable matrix for subsequent welding and encapsulation processes.

[0043] S107: Probe segmentation, head drilling The probe is cut into two sections using a cutting machine. A precision micro-drill is then used to drill a hole at the center of the necked section (2.0 mm section) of the probe. A 1.1 mm diameter carbide drill bit is used to drill to a depth of approximately 8 mm, thus creating a cylindrical cavity at the probe tip to accommodate the thermocouple wire.

[0044] S108: Cavity interior cleaning After drilling, burrs or excess magnesium oxide (MgO) powder may adhere to the inner wall of the cavity. Using a micro blasting machine, white corundum abrasive with a particle size of 50μm is sprayed into the cavity at a pressure of 0.5MPa for 4 seconds to ensure that the lead wire is exposed; at the same time, the blasting treatment can effectively clean the inner wall and form a micro-rough surface, which is beneficial to the subsequent adhesion and filling of MgO powder.

[0045] S109: Precision positioning and in-situ visual verification of temperature sensing elements After cleaning, the clean ends (i.e., leads) of the two N-type thermocouple wires inside the cavity were exposed. The probe was fixed to the fixture, and under real-time monitoring with a high-magnification optical microscope, the positions of the two leads inside the probe were finely adjusted until the metal end faces of the two leads achieved tight contact without gaps over the entire area. Then, the clamping mechanism of the fixture was activated to lock and fix the two leads simultaneously behind the contact point, ensuring that the tips of the leads were in contact together to eliminate any micro-displacement that might be caused by subsequent operations.

[0046] After locking and before welding, a critical process quality verification is performed: the fixed lead end position is photographed using a coaxial vision system (such as an automatic camera) integrated into the tooling. The system compares the captured image with a pre-stored "ideal contact position template" in real time, and analyzes parameters such as contact area contour and alignment through algorithms. Only when the system determines that the lead alignment accuracy fully meets the stringent position tolerance requirements of laser welding will it output a "positioning confirmation qualified" signal and automatically unlock subsequent welding processes. This step replaces subjective human eye judgment with objective machine vision judgment, ensuring that each product achieves consistent ultra-high positioning accuracy before welding, fundamentally eliminating performance defects in hot contacts caused by poor alignment.

[0047] S110: Laser welding of hot contacts After confirming the lead wire positions were correct, a pulsed laser welding machine was used to weld the tips of the contacting coupler wires. The laser power was set to 170W and the pulse width to 35ms. The laser beam was focused on the contact point, instantly and locally melting the metal to form a strong weld joint. Immediately after welding, a coaxial vision system (automatic camera) was used to photograph the weld joint morphology. Image processing algorithms were used to analyze the fullness, symmetry, and presence of any incomplete welds to ensure the welding quality met standards.

[0048] S111: Backfilling and compaction of insulation materials High-purity magnesium oxide (MgO) insulating powder is carefully backfilled into the cavity at the tip of the probe using a micro-vibration feeding device until it is full. The probe is then placed in an oven at 140°C for 30 minutes to remove any moisture that may have been absorbed by the powder. Immediately after drying, a special fixture is used to gently compress the probe head radially, causing the metal sleeve to slightly shrink inward through plastic deformation. This compacts and fixes the internal MgO powder, forming a dense insulating layer.

[0049] S112: Tip-mounted argon arc welding seal A micro TIG welder was used to seal the metal sleeve tip of the probe. The probe was used as the negative electrode, and the tungsten electrode as the positive electrode, under pure argon gas protection. The welding current was set to 35A, and the arc duration was 6 seconds. The arc melted the tip metal, forming a smooth, dense, sealed weld cap that completely encapsulated and protected the internal temperature sensing element and MgO powder, isolating it from the external environment.

[0050] S113: Final annealing (to relieve welding stress) The overall probe after hermetic welding is placed again in an atmosphere-protected annealing furnace and annealed for the third time under the conditions of 75% H2 + 25% N2 and 1050 °C for 5 minutes of heat preservation. This step aims to eliminate the local thermal stress generated by the hermetic welding in step S112, ensure the dimensional stability of the overall probe and the uniformity of material properties, and avoid performance drift during long-term use due to residual stress.

[0051] S114: Final Polishing and Detection After annealing and cooling, a polishing machine equipped with a fine wool wheel is used to gently polish the TIG welding sealed end of the probe to remove the trace oxidation color and burrs on the surface and make its surface smooth. Finally, a micro-focus X-ray real-time imaging system is used to perform non-destructive testing on the finished probe. The X-ray image can clearly show the wall thickness uniformity of the probe, the density of the internal MgO filling, and the precise position of the thermocouple wire (especially the hot junction). Only products that meet the preset standards for all inspection items are judged to be qualified.

[0052] In addition, this embodiment also provides a high-precision fine-diameter thermocouple probe, which is made by the manufacturing method of the above embodiment, and the outer diameter of the probe end is ≤ 2.0 mm.

[0053] The probe includes a metal sleeve, thermocouple leads encapsulated inside it, a hot junction, cavity insulation material, and a tip seal weld; the metal sleeve is processed by the alternating process of swaging and annealing defined in the above embodiment, and the outer diameter of the probe end is finally controlled within 2.0 mm or less, with a tolerance of ±0.05 mm; this size range is, for example, 1.8 mm, 1.9 mm, 2.0 mm, and the embodiments of this application do not make special limitations on this.

[0054] Through the above technical solutions, this application has achieved: due to the strict control of the outer diameter of the probe end within 2.0 mm or less, and the suppression of deformation and stress accumulation through the alternating process of swaging - annealing, the spatial positioning accuracy of the temperature-sensing element is maintained; and because the hot junction is reliably fixed by laser welding, and the cavity is backfilled with MgO and hermetically welded by TIG to form a low thermal capacity - high thermal conductivity composite structure, jointly reducing the thermal inertia and interfacial thermal resistance; thus, under the disturbance of the high-speed flow field, the probe can quickly track temperature changes with a response time of less than 4 seconds, while maintaining a detection accuracy of ±2 °C, meeting the dual requirements of the dynamic performance and static accuracy of the thermocouple for harsh working conditions such as engine exhaust temperature monitoring and combustion chamber transient temperature measurement.

[0055] Verification of the Embodiment Effect: To verify the performance of the thermocouple probe obtained in this embodiment, it is compared and tested with a 2.5 mm tip diameter probe manufactured by the traditional single swaging process. The test is carried out in a wind tunnel test bench simulating the engine exhaust flow field.

[0056] Temperature accuracy test: The two probes were compared and measured in a constant temperature field. At 950℃, the temperature measurement error of the traditional probe was within ±8℃. Figure 3 The temperature measurement error of the 2.0mm probe manufactured in this embodiment is reduced to within ±6℃. Figure 4 The improved accuracy is directly attributable to the precise maintenance of the position of the internal temperature sensing element.

[0057] Dynamic response time test: The probe is suddenly placed in a high-speed (flow rate > 90 m / s) hot gas stream, and the time (time constant) required for its output to reach a stable value of 63.2% is recorded. Figure 1 As shown in the comparison of dynamic response curves, the response time of the traditional probe is approximately 6 seconds, while the response time of the probe in this embodiment is shortened to less than 4 seconds (e.g., Figure 2 As shown in the comparison of the dynamic response curves, the improved response speed is due to the smaller probe diameter (2.0 mm) and the better heat conduction path brought about by the integrity of the internal structure.

Claims

1. A method for manufacturing a high-precision, small-diameter thermocouple probe, characterized in that, Includes the following steps: The thermocouple metal sheath is subjected to at least two rotary forging processes to gradually reduce the outer diameter of its probe tip from the initial size to the final target size of 2.0 mm or less; After at least one rotary forging process, the tip of the rotary forged probe is annealed in a protective atmosphere. The process of alternating forging and annealing controls the deformation and internal stress at the probe tip, thereby achieving a smaller diameter while maintaining the positional accuracy of the internal temperature sensing element.

2. The manufacturing method according to claim 1, characterized in that, The rotary forging process is performed in two steps, successively reducing the outer diameter of the probe tip from a first size to an intermediate size, and then from the intermediate size to the final target size of 2.0 mm.

3. The manufacturing method according to claim 2, characterized in that, The first dimension is 5.0±0.05mm, and the intermediate dimension is 2.5±0.1mm.

4. The manufacturing method according to claim 1, characterized in that, The annealing process is carried out in a protective atmosphere of mixed hydrogen and nitrogen, at a temperature of 1000℃-1100℃.

5. The manufacturing method according to claim 4, characterized in that, The volume percentage of hydrogen in the mixed protective atmosphere is 70%-80%, and the volume percentage of nitrogen is 20%-30%.

6. The manufacturing method according to any one of claims 1-5, characterized in that, Also includes: After the outer diameter of the probe tip reaches the final target size and is annealed, a head hole is drilled in the probe tip to form a cavity for accommodating the thermocouple leads.

7. The manufacturing method according to claim 6, characterized in that, After drilling the head, the process also includes: adjusting and fixing the top positions of the thermocouple leads inside the cavity so that they are in contact with each other.

8. The manufacturing method according to claim 7, characterized in that, Also includes: Laser welding is performed on the tips of the thermocouple leads that have already come into contact with each other to form a thermal junction.

9. The manufacturing method according to claim 8, characterized in that, Also includes: Insulating material is backfilled into the cavity, and the tip of the probe is sealed by welding.

10. A high-precision, small-diameter thermocouple probe, characterized in that, The probe is manufactured by the manufacturing method of any one of claims 1-5 and 7-9, and the outer diameter of the probe tip is ≤2.0 mm.

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