Metal surface heat treatment device and method

Abstract

The invention discloses a metal surface heat treatment device and method. The device comprises a heat treatment equipment shell, and an electric heating guide wire, an air suspension rotary supporting system, a telescopic rotary driving system and a cooling and air source pretreatment system which are arranged in the heat treatment equipment shell. Wherein the air suspension rotary supporting system is used for supporting a metal pipe in a non-contact manner by utilizing low-temperature high-pressure gas precooled by a heat exchange coil through a hollow suspension shaft with a suspension gas nozzle; the telescopic rotation driving system drives the suspended metal pipe to rotate through magnetic coupling; and the cooling system cools the introduced gas through cooling water in the heat exchange frame. The treatment method comprises the following steps: charging, starting air floatation and heating, driving to rotate, implementing hot-cold circulation and cooling and discharging. According to the invention, non-contact and uniform heat treatment of the metal tube at high temperature is realized, the problem of magnetic suspension high-temperature field loss is solved, and the surface performance of the metal tube is remarkably improved by actively controlling'heat-cold circulation '.

Description

Technical Field

[0001] This invention relates to the field of metal surface heat treatment, specifically to a metal surface heat treatment apparatus and method. Background Art

[0002] Metal surface heat treatment is a key process that involves heating, holding, and cooling the surface layer of a workpiece to alter its surface microstructure without changing its composition, thereby obtaining desired surface properties (such as high hardness and wear resistance) while maintaining core toughness. For critical components such as pipes and shafts, surface hardening and other treatments can significantly improve their wear resistance, fatigue strength, and service life, and are widely used in machinery manufacturing, automotive, aerospace, and other fields.

[0003] Traditional heat treatment of tubular and shaft parts typically employs induction heating, flame heating, or box furnace heating followed by quenching. In these methods, workpiece clamping and securing are the primary steps. However, mechanical clamping inevitably introduces a series of problems: First, the heat transfer conditions at the clamping area (usually the chuck or fixture contact point) differ from other areas, leading to uneven heating and potentially causing soft spots or insufficient hardness, affecting performance consistency. Second, for precision workpieces with surface coatings (such as protective coatings or pre-coated catalytic layers), mechanical clamping forces can easily cause coating damage, scratches, or even peeling, rendering the workpiece unusable. Third, at high temperatures, the fixture itself may undergo thermal deformation, further affecting clamping accuracy and heat treatment effectiveness.

[0004] To avoid the problems caused by clamping, existing technologies have proposed some improvement solutions. For example, patent CN113621781B provides a device for intermittent feeding of metal tubes in a non-clamping manner, utilizing the frictional heat generated by heating blocks and damping blocks as an auxiliary heat source. However, this solution has obvious limitations: physical gaps exist between multiple independent heating blocks, resulting in uneven heating of the metal tube and difficulty in obtaining uniform microstructure; its reliance on frictional heat generation is inefficient and has poor heat control; more seriously, the friction process itself can cause wear and damage to the workpiece surface, especially precision coatings, violating the original intention of non-contact processing.

[0005] Another approach attempts to employ non-contact support. For example, patent CN118006881A proposes the concept of levitizing a metal tube using magnetic force. While this avoids physical contact, it introduces a more fatal flaw: permanent magnets demagnetize at high temperatures (Curie effect). When the temperature exceeds their Curie temperature, the magnetism weakens rapidly or even disappears completely. Surface heat treatment processes such as normalizing and quenching typically require austenitizing temperatures of 700°C to 900°C or even higher, far exceeding the Curie point of most high-performance permanent magnet materials (such as NdFeB, typically between 310-400°C). Therefore, this approach will inevitably fail to levitate due to magnet demagnetization during high-temperature processing, causing the workpiece to fall, posing serious safety risks and quality hazards, and significantly reducing its practicality.

[0006] In summary, existing technologies face a dilemma when performing surface heat treatment on tubular and shaft-type parts: mechanical clamping can lead to uneven heating, coating damage, and deformation; while non-contact magnetic levitation solutions cannot operate stably in high-temperature environments. Furthermore, most existing technologies focus on the heating method itself, lacking effective means to dynamically and uniformly heat the workpiece and precisely control the process during heat treatment, and failing to utilize the cooling medium as an active process control factor to further improve the final performance.

[0007] Therefore, there is an urgent need in this field to develop a novel surface heat treatment apparatus and method that must be able to: 1) achieve stable, non-contact support of the workpiece at high temperatures, completely avoiding the risks of clamping damage and demagnetization; 2) ensure uniform heating of the workpiece during heat treatment, eliminating soft spots and uneven microstructure; and 3) actively and precisely control the heat treatment process, especially the cooling stage, to obtain superior material properties. Such technology will greatly improve the manufacturing level of high-end metal parts. Summary of the Invention

[0008] The purpose of this invention is to overcome the three major technical bottlenecks in the existing surface heat treatment technology for metal tubes / shafts: 1) uneven heating, coating damage and workpiece deformation caused by mechanical clamping; 2) reliability problems of non-contact magnetic levitation schemes failing due to magnet demagnetization in high-temperature environments; 3) limited means of heat treatment process control, making it impossible to optimize material structure and properties by actively intervening in the cooling process.

[0009] Based on this, the present invention proposes a novel technical solution, the specific objectives of which include: A non-contact support system based on the principle of air flotation is provided to ensure that the workpiece remains in a stable suspended state throughout the high-temperature heat treatment process, thereby fundamentally avoiding any form of mechanical contact damage.

[0010] An integrated rotary drive mechanism enables the workpiece in a suspended state to rotate at a uniform speed, thereby achieving uniform heating in both the circumferential and axial directions, eliminating soft spots in heat treatment, and improving the consistency of microstructure properties.

[0011] Design an active and controllable cooling airflow system to upgrade the introduction of cooling medium from a simple protective function to an active process control method. Through precise regulation, achieve "heat-cold cycle" treatment, thereby refining grains and improving the overall mechanical properties of the workpiece.

[0012] Ultimately, this provides a complete solution for efficient, reliable, and suitable surface heat treatment of precision workpieces in an atmospheric environment.

[0013] To achieve the above objectives, the present invention provides the following technical solution: a metal surface heat treatment apparatus, comprising a heat treatment equipment shell, wherein an electric heating wire is installed on the inner wall of the shell; and further comprising: Air suspension rotation support system: includes a vertical shaft fixed to the inner left side wall of the heat treatment equipment shell, a rotating sleeve rotatably fitted on the vertical shaft, and a hollow suspension shaft whose left end is fixedly connected to the rotating sleeve and communicates with it internally; the top and front and rear side surfaces of the suspension shaft are evenly provided with a number of horizontal suspension air nozzles along the axial direction; the right end of the suspension shaft is open, and its right end can be placed on an arc-shaped limiting plate fixed to the inner right side wall of the heat treatment equipment shell; Telescopic rotary drive system: includes a telescopic rod that can be telescopically mounted on the right side wall of the heat treatment equipment housing, a magnetic head fixed to the left end of the telescopic rod and extending into the opening at the right end of the suspension shaft, a driven bevel gear splined to the right end of the telescopic rod, a motor mounted on the right side wall of the heat treatment equipment housing, and a driving bevel gear fixed to the output end of the motor and meshing with the driven bevel gear; the magnetic head consists of a magnetic block and heat insulation blocks encapsulated at both ends of it; Cooling and gas source pretreatment system: includes a heat exchange frame installed on the left side wall of the heat treatment equipment shell, and a heat exchange coil coiled inside the heat exchange frame; one end of the heat exchange coil is connected to the left end of the rotating sleeve through a rotary joint, and the other end is connected to a high-pressure nitrogen source; the heat exchange frame is provided with a cooling water inlet and an outlet; The suspended air nozzle, the inner cavity of the suspended shaft, the inner cavity of the rotating sleeve, and the heat exchange coil are connected in sequence to form an airflow passage.

[0014] Furthermore, the outer diameter of the suspension shaft is smaller than the inner diameter of the metal tube to be processed, and there is a concentric annular gap between the two.

[0015] Furthermore, the radius of curvature of the groove of the arc-shaped limiting plate matches the outer diameter of the right end of the suspension shaft, which is used for radial limiting and auxiliary support.

[0016] Furthermore, the heat insulation block in the magnetic head is made of high-temperature resistant heat insulation material, such as ceramic fiber or aerogel.

[0017] Furthermore, the device also includes a control system for controlling the start and stop of the motor and its speed, the extension and retraction of the telescopic rod, the heating power of the heating wire, and the on / off state and flow rate of the nitrogen source and cooling water.

[0018] A method for heat treating a metal surface using the above-described apparatus, characterized by comprising the following steps: S1. Loading: Unscrew the suspension shaft out of the heat treatment equipment housing, put the metal tube over the suspension shaft, and then screw the assembly back into the heat treatment equipment housing so that the right end of the suspension shaft falls onto the arc-shaped limiting plate. S2. Start air flotation and heating: Turn on the nitrogen source and cooling water. Low-temperature and high-pressure nitrogen enters the suspension shaft after being cooled by the heat exchange coil and is sprayed out from the suspension air nozzle to lift and suspend the metal tube. At the same time, turn on the electric heating wire to heat the metal tube. S3. Drive rotation: Push the telescopic rod to the left so that the magnetic head extends into the right end of the suspension shaft and approaches the metal tube; start the motor to drive the magnetic head to rotate, and drive the metal tube to rotate synchronously through magnetic coupling; S4. Implement a hot-cold cycle: During the heating and rotation process, low-temperature nitrogen gas is continuously introduced, causing the inner wall of the metal tube to be instantly cooled under the action of the low-temperature gas flow, while its outer wall is continuously heated by the electric heating wire. By adjusting the process parameters, multiple rapid austenitic-martensite phase transformation cycles are induced in the thickness direction of the metal tube wall. S5. Cooling and unloading: After the process is completed, stop heating, continue to purge nitrogen to cool to a safe temperature, then stop all power, remove the magnetic head, and unscrew and remove the metal tube.

[0019] Further, in step S2, the temperature of the cryogenic nitrogen gas... The temperature is controlled below 50°C by a heat exchange system.

[0020] Furthermore, in step S2, the minimum air buoyancy pressure required to suspend the metal tube is determined. The weight of the metal tube must be overcome, and it must satisfy the following:

[0021] Where m is the mass of the metal tube, and g is the acceleration due to gravity. The effective bearing area of ​​the air-supported membrane, and the actual operating pressure. To ensure stability, it is 1.5 to 3 times that of the standard.

[0022] Furthermore, in step S3, the rotational speed ω of the metal tube is selected according to the size of the metal tube and the requirements of the heat treatment process, and is usually between 5 and 50 RPM.

[0023] Furthermore, step S4 is the key to improving the performance of this invention, and its core lies in controlling the nitrogen temperature. ,flow Heating power A controllable cyclic phase transition is achieved in the near-surface region of the metal tube. The cooling rate for each cooling process... It is a key parameter, which approximately satisfies:

[0024] in, and These are the density and specific heat capacity at constant pressure of nitrogen, respectively. It is the temperature of the inner wall of the metal tube. To ensure the effective quality of heat exchange. This is achieved through control. Phase transformation can be achieved by cooling a rate higher than the critical cooling rate for the martensitic transformation of the material.

[0025] Compared with the prior art, the present invention provides a metal surface heat treatment apparatus and method, which have the following beneficial effects: 1. The metal tube is supported by air suspension technology, which completely avoids the damage, deformation and coating caused by mechanical clamping, and is especially suitable for the processing of precision workpieces.

[0026] 2. The supporting force of air suspension comes from the gas dynamics effect, and its performance does not decrease with the increase of ambient temperature. It fundamentally solves the global problem of magnetic levitation losing magnetism at high temperature and has extremely high reliability.

[0027] 3. By driving the suspended metal tube to rotate at a uniform speed, combined with the heating of the surrounding electric heating wire, the heating temperature of the metal tube is highly uniform in both the circumferential and axial directions, effectively eliminating heat treatment soft spots and uneven structure.

[0028] 4. Innovatively combining cooling airflow with heat treatment process, and achieving "hot-cold cycle" through precise control, it can actively induce multiple fine grain strengthening and phase transformation strengthening of material structure, significantly improving the hardness, strength and wear resistance of metal tube surface, breaking through the limitation of traditional heat treatment that can only rely on the material's own properties.

[0029] 5. The continuously introduced low-temperature nitrogen gas not only serves as a process gas, but also provides forced cooling for internal components such as the magnetic head and rotating sleeve, ensuring the long-term reliable operation of the drive system in high-temperature environments and extending the equipment's lifespan.

[0030] 6. This device and method are suitable for high-quality surface heat treatment of various tubular and shaft-type metal parts in an atmospheric environment. The process is flexible and easy to integrate into automated production lines. Attached Figure Description

[0031] Figure 1This is a three-dimensional structural diagram of the suspension shaft rotating out of the outer shell of the heat treatment equipment in this invention; Figure 2 This is a three-dimensional structural diagram of the suspension shaft of the present invention when it is screwed into the outer shell of the heat treatment equipment. Figure 3 This is a schematic diagram of the installation structure of the telescopic component of the present invention on the side wall of the heat treatment equipment housing; Figure 4 This is a schematic diagram of the installation structure of the heat exchange frame of the present invention on the side wall of the outer shell of the heat treatment equipment; Figure 5 This is a three-dimensional structural diagram of the suspension shaft mounting of the present invention; Figure 6 This is a three-dimensional structural diagram of the telescopic assembly of the present invention; Figure 7 This is a schematic diagram of the magnetic head structure of the present invention; Figure 8 This is a schematic diagram of the heat exchange coil structure of the present invention.

[0032] In the diagram: 1. Telescopic assembly; 2. Heating wire; 3. Heat treatment equipment shell; 4. Metal tube suspension assembly; 5. Metal tube; 6. Suspension shaft; 7. Rotating sleeve; 8. Magnetic block; 9. Vertical shaft; 10. Heat insulation block; 11. Water inlet; 12. Heat exchange frame; 13. Heat exchange coil; 14. Water outlet; 15. Suspension air nozzle; 16. Arc-shaped limiting plate; 17. Magnetic head; 18. Telescopic rod; 19. Motor; 20. Driven bevel gear; 21. Driving bevel gear. DETAILED DESCRIPTION

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] Example 1: Please see Figures 1 to 8 This embodiment provides a metal surface heat treatment apparatus and method. The core design concept of this apparatus is to solve three major pain points in the traditional surface heat treatment of tubular and shaft parts: first, uneven heating, coating damage, and deformation caused by mechanical clamping; second, uneven static heating of the workpiece during heat treatment, affecting the consistency of microstructure transformation; and third, the failure of existing non-contact suspension solutions at high temperatures due to demagnetization of magnetic materials. This invention cleverly integrates air suspension, rotational drive, and active cooling technologies to achieve stable, non-contact, and uniform treatment of workpieces in high-temperature environments, and can improve the final performance through a unique "hot-cold cycle" process.

[0035] The main body of the device is a heat treatment equipment shell 3, and an electric heating wire 2 for heating is installed on its inner wall. The heat treatment equipment shell 3 forms a closed or semi-closed heat treatment chamber, providing a high-temperature environment for heat treatment and reducing heat loss.

[0036] The core motion and support mechanism of the device includes: Vertical shaft 9: Fixedly installed on the inner left side wall of the heat treatment equipment shell 3, serving as the static support foundation for the entire rotating mechanism.

[0037] Rotating sleeve 7: It is mounted on the vertical shaft 9 via a rotating mechanism such as bearings, and can rotate freely around the vertical shaft 9. Its right end is open, used to connect the external air source with the internal suspension air supply system.

[0038] Metal tube suspension assembly 4: Its core is a hollow suspension shaft 6, the left end of which is fixedly connected to and communicates with the rotating sleeve 7. Several suspension air nozzles 15 are evenly distributed axially at the center of the top, front, and rear surfaces of the suspension shaft 6. The direction of these nozzles is precisely designed, all spraying horizontally outwards. The right end of the suspension shaft 6 is open. During operation, the metal tube 5 to be processed is fitted onto the outside of the suspension shaft 6.

[0039] A telescopic assembly 1 is installed on the right side of the device, which functions to drive the metal tube 5 to rotate and protect the driving magnet. It includes: Telescopic rod 18: Its left end extends into the housing 3 of the heat treatment equipment, and its right end extends out of the housing 3 of the heat treatment equipment. A magnetic head 17 is fixedly connected to its left end.

[0040] The magnetic head 17 is a key component that drives the metal tube 5 to rotate. It consists of a central magnetic block 8, preferably a permanent magnet with high magnetic energy product and high Curie temperature such as neodymium iron boron, and heat insulation blocks 10 encapsulated at both ends of the magnetic head 8. The heat insulation blocks 10 can be made of high-performance heat insulation materials such as ceramics or aerogel. The function of the heat insulation blocks 10 is to prevent the transmission of high temperature to the magnetic block 8.

[0041] Drive mechanism: Composed of motor 19, driving bevel gear 21, and driven bevel gear 20. Driven bevel gear 20 is connected to telescopic rod 18 via spline, enabling it to transmit torque while allowing axial movement of telescopic rod 18. Motor 19 drives driving bevel gear 21, thereby causing driven bevel gear 20 and telescopic rod 18 to rotate.

[0042] The device also includes a sophisticated cooling and air pretreatment system: Arc-shaped limiting plate 16: Fixed to the inner right side wall of the heat treatment equipment shell 3. When the suspension shaft 6 is screwed into the working position, its right end rests in this arc-shaped groove to achieve precise positioning and auxiliary support.

[0043] Heat exchange frame 12: Installed on the left side wall of the heat treatment equipment shell 3. It is provided with a water inlet 11 and a water outlet 14 for circulating cooling water.

[0044] Heat exchange coil 13: Coiled inside the heat exchange frame 12. One end is connected to the left end of the rotating sleeve 7 via a rotary joint (not shown in the figure, but a common technique in the art), and the other end is connected to a high-pressure nitrogen source. Its function is to use flowing cooling water to forcibly cool the high-pressure nitrogen gas that is about to be introduced into the suspension shaft 6.

[0045] The working principle and processing procedure of this invention are as follows: Step 1: Loading In the initial state, the telescopic component 1 is retracted, and the magnetic head 17 is located outside the heat treatment equipment housing 3.

[0046] Operators or robotic arms use rotating sleeves 7 to rotate the entire suspension shaft 6 out of the heat treatment equipment housing 3.

[0047] Carefully place the metal tube 5 to be processed onto the outside of the suspension shaft 6.

[0048] The suspension shaft 6, fitted with the metal tube 5, is rotated back into the outer shell 3 of the heat treatment equipment until the right end of the suspension shaft 6 rests steadily on the arc-shaped limiting plate 16, thus completing the precise positioning.

[0049] Step 2: Start air suspension and heating Start the external high-pressure nitrogen source and cooling water circulation system.

[0050] High-pressure, ambient-temperature nitrogen gas is introduced into heat exchange coil 13, while low-temperature cooling water is pumped into heat exchange frame 12 from inlet 11 and flows out from outlet 14. Inside the heat exchange coil, the refrigerant and heat medium exchange heat in a counter-current manner through the coil wall. After heat exchange, the nitrogen gas temperature drops significantly, becoming low-temperature nitrogen gas.

[0051] This stream of low-temperature, high-pressure nitrogen flows through the rotating sleeve 7, enters the hollow cavity of the suspension shaft 6, and finally exits at high speed from the evenly distributed suspension gas nozzles 15.

[0052] According to fluid mechanics principles, the high-speed ejected gas forms a stable gas film in the narrow gap between the suspension shaft 6 and the inner wall of the metal tube 5, generating sufficient pressure to completely lift the metal tube 5, achieving contactless air suspension. The minimum required air buoyancy pressure... The force of gravity 5 on the metal tube needs to be overcome; the calculation formula can be simplified to:

[0053] Where m is the mass of metal tube 5, and g is the acceleration due to gravity. The effective bearing area of ​​the air film is related to the number, layout, and spacing of the nozzles. Actual operating pressure. The demand is much greater than To ensure stability.

[0054] At the same time, the heating wire 2 is energized to generate heat, which radiates heat to the suspended metal tube 5, causing its surface temperature to rise rapidly to the predetermined austenitizing temperature.

[0055] Step 3: Driving rotation and homogenization processing After the surface temperature of the metal tube 5 reaches the set value and is maintained for a certain period of time, activate the telescopic assembly 1. Push the telescopic rod 18 to the left so that the magnetic head 17 at its end extends into the right end opening of the suspension shaft 6 and is as close as possible to the right end of the metal tube 5.

[0056] Start the motor 19. The motor 19 transmits power to the telescopic rod 18 through the meshing of the driving bevel gear 21 and the driven bevel gear 20, thereby driving the magnetic head 17 to rotate at high speed.

[0057] The rotating magnetic head 17, through strong magnetic coupling, penetrates the air gap and any possible tiny spaces, causing the suspended metal tube 5 to rotate together around the axis of the suspension shaft 6.

[0058] The uniform rotation of the metal tube 5, combined with the surrounding heating wire 2, ensures extremely uniform heat treatment temperature in both the circumferential and axial directions, laying a solid foundation for subsequent microstructural transformation. The rotation speed ω (rad / s) should be selected to avoid drastic fluctuations in the airflow field; its upper limit can be estimated from the critical Reynolds number.

[0059] Step 4: Implement the hot-cold cycle process This is the key to the improved performance of this invention. Pre-cooled, low-temperature nitrogen gas is continuously introduced during heating and rotation.

[0060] Instantaneous cooling effect: The low-temperature nitrogen gas ejected from the suspension nozzle 15 lifts the metal tube 5 and instantly carries away the heat from the inner wall of the metal tube 5 in contact with it. For a metal tube 5 that has been heated to 800°C, its inner wall will undergo rapid localized cooling.

[0061] Continuous heating effect: At the same time, the external electric heating wire 2 continuously radiates heat to the outer wall of the metal tube 5, and the heat is conducted from the outside to the inside.

[0062] Dynamic equilibrium and cyclic phase transition: This creates an interesting "tug-of-war": the outer wall is heated, and the inner wall is cooled. A dynamic temperature field is formed along the wall thickness of metal tube 5. This is achieved through precise control of the nitrogen temperature (…). ),flow( ), heating power ( ) and process time ( This can induce multiple rapid austenite-martensite phase transformation cycles inside the metal tube 5, especially in the near-surface region.

[0063] Cooling rate per cycle The heat exchange efficiency of nitrogen can be estimated:

[0064] in, and These are the density and specific heat capacity of nitrogen. It is the temperature of the inner wall of metal tube 5. It is the effective mass that participates in heat exchange.

[0065] This process is similar to multiple ultra-short-time surface hardening processes, which can significantly refine grains and increase dislocation density, thereby greatly improving surface hardness, strength, and wear resistance without excessively sacrificing toughness. It achieves superior microstructure and properties through multiple controllable phase transformations.

[0066] Step 5: Cooling and Unloading After the heat treatment process is completed, the heating of the electric heating wire 2 is stopped first.

[0067] Continue to introduce low-temperature nitrogen gas to perform final overall cooling of metal tube 5 until it reaches a safe temperature.

[0068] Stop motor 19, and stop the supply of nitrogen and cooling water.

[0069] The telescopic assembly 1 retracts, retracting the magnetic head 17.

[0070] Unscrew the suspension shaft 6 and the processed metal tube 5 together, and remove the metal tube 5.

[0071] The device's self-protection mechanism: Throughout the process, the introduced low-temperature nitrogen gas also plays a crucial role in cooling: Cooling the magnet: Low-temperature nitrogen flowing through the interior of the suspension shaft 6 continuously removes heat from around the magnetic head 17, providing forced air cooling to the heat insulation block 10 and the magnetic block 8, ensuring that their temperature is always far below the Curie temperature of the magnet, thereby avoiding the risk of high-temperature demagnetization.

[0072] Cooling mechanism: The low-temperature airflow also ensures that the internal mechanisms such as the rotating sleeve 7 and the suspension shaft 6 will not be damaged by overheating due to radiant heat, thus improving the reliability and service life of the equipment.

[0073] Experimental Example To verify the superiority of this device and treatment method, we conducted a comparative experiment using a No. 45 steel pipe as an example.

[0074] Experimental conditions: Metal pipe 5: φ50mm×500mm No.45 steel pipe with a wall thickness of 5mm.

[0075] Control group: Oil quenching after heating in a traditional box-type resistance furnace.

[0076] Experimental group: Processed using this apparatus. Heated to 840°C and held for 5 minutes. Nitrogen gas with a pressure of 1.0 MPa and a cooled temperature of 25°C was introduced at a flow rate of 50 L / min, and the metal tube 5 was rotated at a speed of 20 RPM. Three cycles of "heating-cooling" were performed, with a total processing time of 15 minutes.

[0077] Testing: After processing, four points were evenly distributed on the same circumference in the middle of the metal tube 5 to measure the hardness (HRC), and metallographic samples were cut to observe the microstructure.

[0078] The experimental results are shown in Table 1 below: Table 1

[0079] Experimental conclusion: Performance Improvement: The surface hardness of metal tube 5 in the experimental group is significantly higher than that of the traditional method, which is due to the fine grain strengthening and dislocation strengthening generated by the cyclic phase transformation.

[0080] Excellent uniformity: The experimental group showed excellent uniformity in both hardness data and microstructure, proving the superiority of air suspension rotation heating and completely eliminating clamping cold spots and unevenness in static heating.

[0081] No damage: Throughout the entire process, the metal tube 5 remains in a non-contact state, the surface pretreatment coating is intact, and there is no clamping deformation.

[0082] High reliability: Throughout the experiment, the magnetic levitation drive system worked normally without any signs of demagnetization, proving the effectiveness of the integrated cooling system.

[0083] In summary, the metal surface heat treatment apparatus and method provided by this invention successfully integrate non-contact support, uniform rotation heating, active cooling protection, and innovative thermal cycling process, effectively solving many drawbacks of traditional heat treatment, significantly improving the treatment quality and overall performance of the metal tube 5, and possessing extremely high industrial application value.

Claims

1. A metal surface heat treatment apparatus, comprising a heat treatment equipment shell (3) and an electric heating wire (2) installed on its inner sidewall, characterized in that: It also includes, The air suspension rotation support system includes a vertical shaft (9) fixedly installed on the inner left side wall of the heat treatment equipment shell (3), a rotating sleeve (7) rotatably fitted on the vertical shaft (9), and a hollow suspension shaft (6) fixedly connected to the rotating sleeve (7). The outer surface of the suspension shaft (6) has several horizontally arranged suspension air nozzles (15) evenly distributed along the axial direction. The right end of the suspension shaft (6) is an opening. The telescopic rotation drive system includes a telescopic rod (18) that can be telescopically mounted on the right side wall of the heat treatment equipment housing (3), a magnetic head (17) fixed to the left end of the telescopic rod (18) and extending into the right end opening of the suspension shaft (6), a driven bevel gear (20) mounted on the telescopic rod (18) via a spline, a motor (19) mounted on the right side wall of the heat treatment equipment housing (3), and an active bevel gear (21) fixed to the output end of the motor (19) and meshing with the driven bevel gear (20). The cooling and air source pretreatment system includes a heat exchange frame (12) installed on the left side wall of the heat treatment equipment shell (3) and a heat exchange coil (13) coiled inside the heat exchange frame (12). One end of the heat exchange coil (13) is connected to the rotating sleeve (7), and the other end is used to connect to an external high-pressure air source. The heat exchange frame (12) is provided with a cooling water inlet (11) and an outlet (14).

2. The metal surface heat treatment apparatus according to claim 1, characterized in that: The suspension air nozzle (15) is provided at the top and the center of the front and rear sides of the suspension shaft (6).

3. The metal surface heat treatment apparatus according to claim 1, characterized in that: An arc-shaped limiting plate (16) is fixedly installed on the inner right side wall of the heat treatment equipment shell (3), and the right end of the suspension shaft (6) can be placed on the arc-shaped limiting plate (16).

4. The metal surface heat treatment apparatus according to claim 1, characterized in that: The magnetic head (17) is composed of a magnetic block (8) and heat insulation blocks (10) fixedly encapsulated at both ends.

5. The metal surface heat treatment apparatus according to claim 4, characterized in that: The heat insulation block (10) is made of ceramic or aerogel material.

6. The metal surface heat treatment apparatus according to claim 1, characterized in that: The suspended air nozzle (15), the inner cavity of the suspended shaft (6), the inner cavity of the rotating sleeve (7), and the heat exchange coil (13) are connected in sequence to form an airflow passage.

7. The metal surface heat treatment apparatus according to any one of claims 1 to 6, characterized in that: It also includes a control system, which is electrically connected to the motor (19) and the heating wire (2), and is used to control the on / off state and flow rate of the air source connected to the heat exchange coil (13) and the cooling water source connected to the water inlet (11).

8. A method for heat treatment of metal surfaces, used in the metal surface heat treatment apparatus according to any one of claims 1-7, characterized in that, The following steps are involved: S1. Unscrew the suspension shaft (6) out of the heat treatment equipment housing (3), put the metal tube (5) over the suspension shaft (6), and then screw the assembly back so that the right end of the suspension shaft (6) falls onto the arc-shaped limiting plate (16); S2. High-pressure gas is introduced into the heat exchange coil (13) and cooling water is introduced into the heat exchange frame (12). The cooled gas enters the suspension shaft (6) through the rotating sleeve (7) and is ejected from the suspension gas nozzle (15) to suspend the metal tube (5). At the same time, the electric heating wire (2) is turned on to heat the metal tube (5). S3. Push the telescopic rod (18) to the left so that the magnetic head (17) extends into the right end of the suspension shaft (6); start the motor (19) to drive the magnetic head (17) to rotate, and drive the metal tube (5) to rotate through magnetic coupling; S4. During the heating and rotation process, the cooled gas is continuously introduced so that the inner wall of the metal tube (5) is cooled while the outer wall is continuously heated. By controlling the process parameters, multiple austenitic-martensite phase transformation cycles are induced in the wall thickness direction of the metal tube (5). S5. Stop heating, continue to introduce cooling gas to cool the metal tube (5) to a safe temperature, then stop all power, remove the magnetic head (17), and unscrew and remove the metal tube (5).

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