Bearing controlled atmosphere heat treatment furnace with external circulation cooling and dynamic heat preservation cover

Abstract

The invention discloses a bearing controlled atmosphere heat treatment furnace with an external circulation cooling and dynamic heat preservation cover, and relates to the technical field of metal heat treatment process equipment. The muffle tank is arranged in the shell, the muffle tank is provided with a telescopic ring and an internal circulation fan, a material frame is arranged in the muffle tank during working, and through the combination of controllable atmosphere protection and special thermal cycle treatment, the microscopic structure of a bearing workpiece is effectively refined, and the form and distribution of carbide are improved. The impact toughness and the fatigue strength of the finally-treated workpiece are remarkably improved while the high hardness is kept, the deformation amount of heat treatment is small, the size stability is high, the structure uniformity is good, the retained austenite content is effectively restrained, and the overall comprehensive mechanical property is superior to that of a conventional heat treatment method; and meanwhile, the device has the advantages of energy conservation and consumption reduction and is suitable for automatic production.

Description

Technical Field

[0001] This invention relates to the field of metal heat treatment process equipment technology, specifically to a bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover. Background Technology

[0002] A controlled atmosphere heat treatment furnace for bearings is an industrial furnace used for heat treatment of bearing parts, such as carburizing and quenching. Its core is a sealed container (such as a muffle furnace) through which a controlled inert or reactive atmosphere is introduced to replace air, thereby preventing oxidation and decarburization of the workpiece at high temperatures and precisely controlling the surface chemical composition to ultimately obtain a microstructure with high hardness, high wear resistance, and good fatigue strength.

[0003] Currently, a technical problem still exists in the application of this type of equipment: after the workpiece has finished heating, during the brief process of removing it from the furnace to the quenching tank, the workpiece is exposed to the air and dissipates heat rapidly, resulting in a large temperature difference between its surface and core. This temperature difference not only causes uneven cooling during subsequent quenching, affecting the hardness and consistency of the microstructure, but is also the main source of workpiece deformation and large residual stress.

[0004] This invention solves the problem of temperature uniformity control of workpieces during furnace transfer and the initial stage of quenching. By integrating dynamic heat preservation and external circulation directional cooling technology, it effectively reduces the core-surface temperature difference of the workpiece during this critical stage, thereby improving the overall consistency of quenching quality. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a bearing controllable atmosphere heat treatment furnace with external circulating cooling and a dynamic heat insulation cover, which solves the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a bearing-controlled atmosphere heat treatment furnace with external circulation cooling and a dynamic insulation cover, comprising: a shell, the interior of which is provided with a refractory fiber layer and an electric heating tape; a muffle tank, disposed inside the shell, the muffle tank being provided with a telescopic ring and an internal circulation fan, the air inlet of the internal circulation fan being connected to the interior of the muffle tank, the air outlet being connected to an internal circulation pipe, the internal circulation pipe being connected to an air inlet and an air extraction pipe, a catalyst being installed at the bottom of the muffle tank, a cooling water ring being provided at the top of the muffle tank, and a material frame being provided inside the muffle tank during operation; a furnace cover mechanism, which is provided with a fan, multiple hydraulic cylinder locking buckles, a locking ring, a furnace cover insulation cover, an explosion-proof vent, and an atmosphere recovery pipe; the furnace cover mechanism is driven by the locking buckles, locking rings, and hydraulic cylinders to form a sealing and locking structure with the top of the muffle tank; external circulation... The cooling device includes an air inlet, an external circulation cooling mechanism, a dust filter, an atmosphere recovery interface, an air inlet pipe connected to a vacuum pump, and an air outlet pipe connected to a vacuum pump. The explosion-proof port is located on the furnace cover mechanism and is connected to the air inlet and exhaust pipes. The atmosphere recovery pipe is connected to the external circulation cooling mechanism via the atmosphere recovery interface. The external circulation cooling mechanism is connected to the dust filter. The dust filter is connected to the air inlet pipe 25 connected to the vacuum pump. The air outlet pipe connected to the vacuum pump is connected to both the air inlet and exhaust pipes, thus forming a closed gas circulation path. When the vacuum pump is operating, it extracts gas from the atmosphere recovery pipe, which flows sequentially through the external circulation cooling mechanism 22 for cooling, the dust filter for fine filtration, and finally returns to the air inlet and exhaust pipes via the vacuum pump exhaust pipe 26, achieving circulating cooling and purification of the atmosphere inside the furnace.

[0007] Preferably, the external circulation cooling mechanism is a shell-and-tube or plate heat exchanger, and its cooling medium is circulating water or ethylene glycol solution.

[0008] Preferably, the cooling rate of the external circulation cooling mechanism is adjustable, with a control range of 30~60℃ / min.

[0009] Preferably, the temperature inside the muffle furnace is heated by an electric heating tape, and an atmosphere is driven to flow through the catalyst by an internal circulation fan, so that the oxygen content inside the furnace is reduced to below 10 ppm.

[0010] Preferably, the furnace cover mechanism is opened, closed and rotated by a hydraulic cylinder, and is sealed to the muffle tank by a locking ring.

[0011] Preferably, the process includes the following steps: S1: Load the bearing workpiece into the material frame and send it into the muffle furnace. Introduce a protective atmosphere, start the internal circulation fan, and heat to 820~930℃. Hold for 10~30 minutes to fully dissolve the carbides and obtain a uniform austenitic structure; S2: Start the external circulation cooling device and cool the workpiece to 600~700℃ at a cooling rate of 30~60℃ / min. Hold for 10~30 minutes to transform the supercooled austenite into fine sorbite or precipitate fine carbides; S3: Reheat to 820~860℃ and hold for 10~30 minutes for final austenitization to obtain fine, uniform austenitic grains and undissolved carbides; S4: Open the furnace cover mechanism and transfer the material frame to the nitrate quenching tank for isothermal quenching to obtain a martensitic / lower bainitic multiphase structure; S5: Temper the quenched workpiece to relieve stress and stabilize the structure.

[0012] Preferably, the cooling rate in step S2 is adjusted according to the size of the bearing workpiece to ensure uniformity of microstructure transformation.

[0013] Preferably, the residual austenite content in the final obtained bearing workpiece microstructure is less than 3%, and the average carbide size is less than 0.5 μm.

[0014] Preferably, the heat treatment method improves the impact toughness of the bearing workpiece by more than 20%, increases the fatigue life by more than 30%, and reduces the deformation by more than 40% after heat treatment.

[0015] Beneficial effects This invention provides a controlled atmosphere heat treatment furnace for bearings with external circulating cooling and a dynamic heat insulation cover. By combining controlled atmosphere protection with special thermal circulation treatment, this invention effectively refines the microstructure of bearing workpieces and improves the morphology and distribution of carbides. The final treated workpiece maintains high hardness while significantly improving impact toughness and fatigue strength. Furthermore, the heat treatment results in minimal deformation, high dimensional stability, good microstructure uniformity, and effective suppression of retained austenite content. Overall, the comprehensive mechanical properties are superior to conventional heat treatment methods, while also offering advantages such as energy saving, reduced consumption, and suitability for automated production. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of a bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover as described in this invention.

[0017] Figure 2 This is a partial isometric structural schematic diagram of a bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover as described in this invention.

[0018] Figure 3This is a schematic diagram of the overall isometric structure of a bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover as described in this invention.

[0019] In the diagram: 1. Refractory fiber layer; 2. Electric heating tape; 3. Muffle tank; 4. Expansion ring; 5. Internal circulation fan; 6. Internal circulation pipe; 7. Inlet and exhaust pipes; 8. Catalyst; 9. Cooling water ring; 10. Material frame; 11. Furnace cover mechanism; 12. Fan; 13. Second hydraulic cylinder; 14. First hydraulic cylinder; 15. Locking buckle; 16. Hydraulic cylinder; 17. Locking ring; 18. Furnace cover insulation cover; 19. Explosion-proof port; 20. Atmosphere recovery pipe; 21. Air inlet; 22. External circulation cooling mechanism; 23. Dust filter; 24. Atmosphere recovery interface; 25. Vacuum pump inlet pipe; 26. Vacuum pump outlet pipe. Detailed Implementation

[0020] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1-3This invention provides a technical solution: a bearing-controlled atmosphere heat treatment furnace with external circulation cooling and dynamic insulation cover, comprising: a shell, the interior of which is provided with a refractory fiber layer 1 and an electric heating tape 2; a muffle tank 3, disposed inside the shell, the muffle tank 3 being provided with a telescopic ring 4 and an internal circulation fan 5, the air inlet of the internal circulation fan 5 being connected to the interior of the muffle tank 3, the air outlet being connected to an internal circulation pipe 6, the internal circulation pipe 6 being connected to an air inlet and an air extraction pipe 7, a catalyst 8 being installed at the bottom of the muffle tank 3, a cooling water ring 9 being provided at the top of the muffle tank 3, and a material frame 10 being provided inside the muffle tank 3 during operation; a furnace cover mechanism 11, on which a fan 12 and multiple hydraulic cylinders 13, 14 are provided. 16. Locking buckle 15, locking ring 17, furnace cover insulation cover 18, explosion-proof port 19, and atmosphere recovery pipe 20; the furnace cover mechanism 11 is driven by the locking buckle 15, locking ring 17, and hydraulic cylinder to form a sealed locking structure with the top of the muffle tank 3; the external circulation cooling device includes an air inlet 21, an external circulation cooling mechanism 22, a dust filter 23, an atmosphere recovery interface 24, an air inlet pipe 25 connected to a vacuum pump, and an air outlet pipe 26 connected to a vacuum pump; wherein, the explosion-proof port 19 is provided on the furnace cover mechanism 11 and is connected to the air inlet and exhaust pipes 7; the atmosphere recovery pipe 20 is connected to the atmosphere recovery... Interface 24 is connected to the external circulation cooling mechanism 22; the external circulation cooling mechanism 22 is connected to the dust filter 23; the dust filter 23 is connected to the vacuum pump inlet pipe 25; the vacuum pump outlet pipe 26 is connected to the inlet and exhaust pipes 7, thus forming a closed gas circulation path; when the vacuum pump is working, it draws gas from the atmosphere recovery pipe 20, flows through the external circulation cooling mechanism 22 for cooling, the dust filter 23 for fine filtration, and finally returns to the inlet and exhaust pipes 7 through the vacuum pump outlet pipe 26, realizing the circulation cooling and purification of the atmosphere inside the furnace.

[0022] In this embodiment, the external circulation cooling mechanism 22 is further configured as a shell-and-tube or plate heat exchanger, and its cooling medium is circulating water or ethylene glycol solution.

[0023] In this embodiment, the cooling rate of the external circulation cooling mechanism 22 is adjustable, with a control range of 30~60℃ / min.

[0024] In this embodiment, the temperature inside the muffle tank 3 is heated by the electric heating tape 2, and the atmosphere is driven to flow through the catalyst 8 by the internal circulation fan 5, so that the oxygen content in the furnace is reduced to below 10 ppm.

[0025] In this embodiment, the furnace cover mechanism 11 is further configured to open, close and rotate via hydraulic cylinders 13, 14 and 16, and is sealed to the muffle tank 3 via a locking ring 17.

[0026] This embodiment is further configured to include the following steps: S1: Load the bearing workpiece into the material frame 10 and send it into the muffle tank 3, introduce a protective atmosphere, start the internal circulation fan 5 and heat to 820~930℃, hold for 10~30min to fully dissolve the carbides and obtain a uniform austenitic structure; S2: Start the external circulation cooling device to cool the workpiece to 600~700℃ at a cooling rate of 30~60℃ / min, hold for 10~30min, so that... S3: The supercooled austenite is partially transformed into fine sorbite or fine carbides are precipitated; S4: Reheat to 820~860℃ and hold for 10~30min to perform final austenitization, obtaining fine and uniform austenite grains and undissolved carbides; S5: Open the furnace cover mechanism 11 and transfer the material frame 10 to the nitrate quenching tank for isothermal quenching to obtain a martensitic / lower bainite multiphase structure; S6: Temper the quenched workpiece to relieve stress and stabilize the structure.

[0027] In this embodiment, the cooling rate in step S2 is further adjusted according to the size of the bearing workpiece to ensure the uniformity of the microstructure transformation.

[0028] In this embodiment, the residual austenite content in the final obtained bearing workpiece microstructure is less than 3%, and the average carbide size is less than 0.5 μm.

[0029] In this embodiment, the heat treatment method is further configured to increase the impact toughness of the bearing workpiece by more than 20%, increase the fatigue life by more than 30%, and reduce the deformation by more than 40% after heat treatment.

[0030] Its detailed connection method is a well-known technology in this field. The following mainly introduces the working principle and process, and the specific work is as follows.

[0031] Example 1: Detailed Configuration and Connection Relationships of Equipment Structure The heat treatment furnace is a precision system that integrates controllable atmosphere heating, online rapid cooling, atmosphere purification, and dynamic heat preservation functions.

[0032] 1. Furnace body and heating system: Shell: Welded from Q235B steel plate, providing structural support.

[0033] Refractory fiber layer (1): 1260 type zirconium-containing aluminum silicate fiber modules are used and laid in layers with staggered joints on the inner wall of the shell. The total thickness is 280mm, which ensures that the furnace wall temperature rise does not exceed 45℃ (when the ambient temperature is 25℃), greatly reducing heat loss.

[0034] Electric heating tape (2): It is made of 0Cr27Al7Mo2 iron-chromium-aluminum alloy strip, which is wound into a spiral and evenly distributed in the upper, middle and lower zones. The total power is 160kW, the maximum working temperature is 950℃, and the furnace temperature can be precisely controlled by PID adjustment. The temperature difference within the zone is ≤±5℃.

[0035] The muffle tank (3) is made of 310S heat-resistant stainless steel and is a straight cylindrical structure with an effective working size of Φ800×1200mm, forming a sealed processing space that can be protected by atmosphere. Its top is flexibly connected to the furnace cover mechanism (11) through a telescopic ring (4) (made of heat-resistant stainless steel corrugated pipe), which effectively absorbs the stress generated by the thermal expansion and contraction of the muffle tank itself, and prevents structural deformation and sealing failure.

[0036] 2. Atmosphere recirculation and purification system: Internal circulation fan (5): Installed at the top inside the muffle tank (3), its main shaft is water-cooled, and the impeller is made of HK40 heat-resistant alloy precision casting with a rated speed of 1450 rpm. During operation, its air inlet draws in atmosphere from the top of the muffle tank, and the air outlet is connected to the air inlet and exhaust pipes (7) at the bottom of the tank through the internal circulation pipe (6) (Φ150mm stainless steel pipe). This design forces the atmosphere inside the furnace to form a strong convection from top to bottom.

[0037] Catalyst (8): It is placed in the tray at the bottom of the muffle tank (3) and located in the gas flow path. The model is CN-32 rare earth catalyst. The internal circulating gas flow continuously through the catalyst bed, which can efficiently crack trace amounts of oxygen molecules and residual hydrocarbons in the atmosphere, and keep the oxygen content in the furnace stable below 10ppm for a long time.

[0038] Cooling water ring (9): It is a ring-shaped water pipe made of brass, integrated into the top opening flange of the muffle tank (3), and is filled with circulating cooling water to cool the high-temperature area and protect the flexible graphite seal below it to prevent it from aging and failing at high temperature.

[0039] 3. Furnace lid and locking sealing system: Furnace lid mechanism (11): It is a water-cooled sandwich structure with water channels welded inside. It integrates the following: Blower (12): Used for air cooling of the outside of the furnace cover.

[0040] Hydraulic cylinders (13, 14, 16): respectively control the vertical lifting and lowering of the furnace cover, the horizontal rotation, and the locking and unlocking of the locking ring (17).

[0041] Locking buckle (15) and locking ring (17): adopts a wedge-type mechanical locking design, driven by a hydraulic cylinder (16), which can generate huge locking force to ensure that the furnace cover and the top flange of the muffle tank achieve absolute sealing through the flexible graphite sealing strip.

[0042] Furnace cover insulation cover (18): Attached to the bottom of the furnace cover, the inside is filled with 1260 type aluminum silicate fiber cotton to reduce heat loss at the furnace opening.

[0043] Explosion-proof port (19): Installed on the furnace cover, filled with metal explosion-proof plates, and connected to the air inlet and exhaust pipes (7) through pipes. It automatically releases pressure when the pressure inside the furnace rises abnormally, ensuring equipment safety.

[0044] Atmosphere recovery pipe (20): Its inlet is funnel-shaped and extends deep into the muffle tank. It is used to draw in high-temperature atmosphere when starting the external circulation.

[0045] 4. External Circulation Cooling and Purification System (Core Innovation): This system is a closed-loop atmosphere circulation system achieved through pipelines and a vacuum pump. Its connection relationship and working process are as follows: The atmosphere recovery pipe (20) is connected to the inlet of the external circulation cooling mechanism (22) through the atmosphere recovery interface (24).

[0046] External circulation cooling mechanism (22): This embodiment uses a BR0.5 type detachable plate heat exchanger with a heat exchange area of ​​5m². 2 The primary side is circulated with an ethylene glycol solution at 5℃±1℃ provided by the refrigeration unit as the refrigerant; the secondary side is circulated with a high-temperature atmosphere extracted from the furnace.

[0047] The heat exchanger outlet is connected to a dust filter (23), which uses multiple sets of sintered metal ceramic filter elements with a filtration accuracy of 0.1μm to capture trace amounts of smoke and tar particles that may be released during the cooling process.

[0048] The filtered, pure, low-temperature atmosphere enters a 2BV series water ring vacuum pump (as the power source of the system) through the vacuum pump inlet pipe (25).

[0049] Finally, the atmosphere discharged by the vacuum pump returns to the intake and extraction pipes (7) through the vacuum pump outlet pipe (26), thus completing a complete closed-loop cycle.

[0050] By adjusting the operating frequency (i.e., pumping speed) of the vacuum pump and the flow rate and temperature of the ethylene glycol solution, the cooling rate of the workpiece can be precisely controlled and continuously adjusted within the range of 30~60℃ / min.

[0051] Innovative heat treatment method process examples Process objective: Through an innovative thermal cycle of "high-temperature dissolution → rapid cooling to induce transformation → secondary heating to refine grains", the microstructure of bearing steel is refined to the extreme, thereby obtaining ultra-high comprehensive mechanical properties.

[0052] S1: First heating (carbide dissolution and homogenization of austenite) The bearing rings are loaded into the material frame (10) and fed into the muffle furnace (3) by the automated system. The furnace cover mechanism (11) is closed and hydraulically locked. High-purity nitrogen (99.999%) is introduced into the furnace through the air intake and exhaust pipes (7), and the internal circulation fan (5) is started to clean the furnace. When the oxygen content drops to <10ppm, the electric heating tape (2) is started, and the temperature is raised to 880℃ at a rate of 12℃ / min and held for 25 minutes. The purpose of this stage is to fully dissolve the carbides (Fe3C) in the original microstructure of the workpiece into the austenite to obtain a single-phase austenite microstructure with uniform composition and fine grains.

[0053] S2: After the intermediate temperature transformation (rapid cooling and preparation for sorbite / carbide precipitation) is completed, the external circulation cooling system is immediately started. The vacuum pump operates to extract the high-temperature atmosphere of 880°C from the furnace, which is then rapidly cooled to near room temperature in the external circulation cooling mechanism (22). This low-temperature atmosphere is then continuously and in large quantities returned to the muffle furnace for intense convective heat exchange with the workpiece. The system rapidly reduces the core temperature of the workpiece to 650°C at a rate of 55±3°C / min and holds it at this temperature for 20 minutes. This temperature range is near the "C-curve nose" of the transformation from supercooled austenite to sorbite in GCr15 steel. The purpose of this process is: The induced transformation of partially supercooled austenite into an extremely fine sorbite structure.

[0054] This step creates favorable conditions for the precipitation of carbides in the untransformed supercooled austenite. The fine sorbite and precipitated carbide particles produced in this step will provide abundant, dispersed nucleation sites for subsequent reaustitization. S3: After the second heating (final austenitization) and holding at medium temperature, stop the external circulation system. Restart the heating tape (2) to reheat the workpiece to 840°C at a rate of 15°C / min and hold for 30 minutes. Since the previous step yielded a pretreated microstructure containing a large number of fine, dispersed carbide particles, these carbide particles can effectively pin the austenite grain boundaries during this heating process, strongly inhibiting grain growth. As a result, the final austenite grain size is more than 2 grades smaller than that of the traditional single-heating process, and there are more, finer, and more uniformly distributed undissolved carbides.

[0055] S4: After the final austenitization of the furnace after quenching and tempering, the hydraulic cylinders (13, 14, 16) are activated, the locking mechanism is released, and the furnace cover is lifted and rotated to open. The automated system quickly removes the material frame (10) and immediately immerses it in a 170°C nitrate quenching tank for isothermal quenching, holding the temperature for 60 minutes before air cooling. Finally, a multiphase structure mainly composed of fine lamellar martensite and lower bainite is obtained. Then, a low-temperature tempering at 180°C for 3 hours is performed to completely eliminate stress and stabilize the structure.

[0056] Beneficial effects verification The GCr15 bearing rings processed by the equipment and method of this embodiment were inspected by a third-party testing agency, and the results are as follows: Microstructure: Approximately 15% lower bainite and a large amount of fine, uniform granular carbides are distributed on a cryptocrystalline martensite matrix. The average grain size reaches grade 10.5. The retained austenite content is only 1.8%.

[0057] Mechanical properties: Surface hardness: HRC 63.2 ± 0.3 (excellent uniformity).

[0058] Impact toughness (AKU): 35 J, a 25% improvement over conventional processes (~28 J).

[0059] Contact fatigue life (L10): Bench tests showed a 38% improvement in life compared to products manufactured using conventional processes.

[0060] Deformation control: After heat treatment, the ovality deformation of the bearing ring is controlled on average to 0.035 mm, the roundness error is ≤0.02 mm, the deformation is reduced by more than 45%, and the dimensional requirements of P4 and P2 grade ultra-precision bearings can be met without straightening.

[0061] Energy saving and automation: Full atmosphere protection, no oxidation and decarburization; dynamic sealing and insulation design reduces furnace opening heat loss by 80%; fully automated operation, stable production cycle, and extremely high product consistency.

[0062] The above description is a specific, detailed, and feasible preferred embodiment of the present invention, fully demonstrating the technical solution claimed in the claims and the significant technical progress it brings. Any equivalent substitutions or modifications based on the principles and spirit of the present invention should be considered to fall within the protection scope of the present invention.

[0063] It should be noted that in this paper, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

Claims

1. A bearing controlled atmosphere heat treatment furnace with external circulating cooling and dynamic heat insulation cover, characterized in that, include: The shell has a fire-resistant fiber layer (1) and an electric heating tape (2) inside. A muffle tank (3) is located inside the shell. The muffle tank (3) is equipped with a telescopic ring (4) and an internal circulation fan (5). The air inlet of the internal circulation fan (5) is connected to the inside of the muffle tank (3), and the air outlet is connected to the internal circulation pipe (6). The internal circulation pipe (6) is connected to the air inlet and air extraction pipes (7). The catalyst (8) is installed at the bottom of the muffle tank (3). A cooling water ring (9) is provided at the top of the muffle tank (3). During operation, a material frame (10) is provided inside the muffle tank (3). The furnace cover mechanism (11) is equipped with a fan (12), multiple hydraulic cylinders (13, 14, 16), a locking buckle (15), a locking ring (17), a furnace cover insulation cover (18), an explosion-proof port (19), and an atmosphere recovery pipe (20); the furnace cover mechanism (11) is driven by the locking buckle (15), the locking ring (17), and the hydraulic cylinders to form a sealed locking structure with the top of the muffle tank (3); The external circulation cooling device includes an air inlet (21), an external circulation cooling mechanism (22), a dust filter (23), an atmosphere recovery interface (24), an air inlet pipe (25) connected to a vacuum pump, and an air outlet pipe (26) connected to a vacuum pump. The explosion-proof port (19) is located on the furnace cover mechanism (11) and is connected to the air inlet and exhaust pipes (7); the atmosphere recovery pipe (20) is connected to the external circulation cooling mechanism (22) through the atmosphere recovery interface (24); the external circulation cooling mechanism (22) is connected to the dust filter (23); the dust filter (23) is connected to the vacuum pump inlet pipe (25); the vacuum pump outlet pipe (26) is connected to the air inlet and exhaust pipes (7), thereby forming a closed gas circulation path; When the vacuum pump is working, it draws the gas out from the atmosphere recovery pipe (20), and flows through the external circulation cooling mechanism (22) for cooling and the dust filter (23) for fine filtration. Finally, it returns to the air inlet and exhaust pipe (7) through the vacuum pump outlet pipe (26), thereby realizing the circulation cooling and purification of the atmosphere in the furnace.

2. The bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover according to claim 1, characterized in that, The external circulation cooling mechanism (22) is a shell-and-tube or plate heat exchanger, and its cooling medium is circulating water or ethylene glycol solution.

3. A bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover according to claim 1, characterized in that, The cooling rate of the external circulation cooling mechanism (22) is adjustable, and the control range is 30~60℃ / min.

4. A bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover according to claim 1, characterized in that, The temperature inside the muffle tank (3) is heated by the electric heating tape (2), and the atmosphere is driven to flow through the catalyst (8) by the internal circulation fan (5), so that the oxygen content in the furnace is reduced to below 10 ppm.

5. A bearing controllable atmosphere heat treatment furnace with external circulating cooling and dynamic heat preservation cover according to claim 1, characterized in that, The furnace cover mechanism (11) is opened, closed and rotated by hydraulic cylinders (13, 14, 16) and is sealed to the muffle tank (3) by locking ring (17).

6. A bearing heat treatment method using the heat treatment furnace according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Load the bearing workpiece into the material frame (10) and send it into the muffle tank (3), introduce a protective atmosphere, start the internal circulation fan (5) and heat it to 820~930℃, keep it warm for 10~30min, so that the carbides are fully dissolved and a uniform austenitic structure is obtained. S2: Start the external circulation cooling device to cool the workpiece to 600-700℃ at a cooling rate of 30-60℃ / min, and hold it for 10-30 minutes to transform the supercooled austenite into fine sorbite or precipitate fine carbides. S3: Reheat to 820~860℃, hold for 10~30min, and perform final austenitization to obtain fine and uniform austenite grains and undissolved carbides; S4: Open the furnace cover mechanism (11) and transfer the material frame (10) to the nitrate quenching tank for isothermal quenching to obtain a martensite / lower bainite multiphase structure; S5: Tempering is performed on the quenched workpiece to relieve stress and stabilize the microstructure.

7. The heat treatment method according to claim 6, characterized in that, The cooling rate in step S2 is adjusted according to the size of the bearing workpiece to ensure uniform microstructure transformation.

8. The heat treatment method according to claim 6, characterized in that, The final bearing workpiece microstructure has a residual austenite content of less than 3% and an average carbide size of less than 0.5 μm.

9. The heat treatment method according to claim 6, characterized in that, The heat treatment method improves the impact toughness of the bearing workpiece by more than 20%, increases the fatigue life by more than 30%, and reduces the deformation by more than 40% after heat treatment.

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