Method for heat treating a compressor main shaft

Abstract

The embodiment of the application relates to the technical field of heat treatment methods, in particular to a compressor main shaft heat treatment method. The compressor main shaft heat treatment method comprises the following steps: performing surface light treatment on a main shaft forge piece, and then performing annealing treatment; performing rough machining on the main shaft after the annealing treatment; vertically hoisting the main shaft after the rough machining, and then performing quenching and tempering treatment; vertically hoisting the main shaft after the quenching and tempering treatment, and then performing stabilization treatment, wherein the stabilization treatment comprises the following steps: heating and heat-preserving the main shaft after the quenching and tempering treatment in a segmented heating mode comprising at least two heating stages, then heat-preserving after cooling, and then cooling to room temperature in a segmented variable-speed cooling mode comprising at least two cooling stages; and performing finish machining on the main shaft after the stabilization treatment. Through the above process, the residual stress of the 30Cr2Ni4MoV steel main shaft can be stably controlled within -50 MPa (i.e. the absolute value is less than or equal to 50 MPa), and all are beneficial compressive stresses, so that the risk of bending deformation in the running process is significantly reduced.

Description

Technical Field

[0001] This application relates to the technical field of heat treatment methods, specifically to a heat treatment method for a compressor spindle. Background Technology

[0002] The compressor spindle is the core rotating component of a centrifugal compressor. During operation, it endures complex high temperatures, high pressures, and alternating loads. This is especially true for medium- and high-temperature energy storage compressors, where the unit requires frequent daily start-ups and shutdowns, causing the spindle to undergo repeated heating and cooling cycles over a wide temperature range. Under these harsh conditions, if the residual stress inside the spindle is not effectively controlled, the following problems will occur: First, the superposition of residual stress and service loads significantly reduces the actual fatigue strength of the spindle, accelerating crack initiation and propagation. Second, the relaxation and redistribution of residual stress during long-term service leads to a decrease in the dimensional stability of the spindle, resulting in rotor dynamic balance failure. Third, excessively high residual tensile stress may induce stress corrosion cracking or brittle fracture during low-temperature start-ups and shutdowns. The mainstream material for medium- and high-temperature energy storage compressors is 30Cr2Ni4MoV steel, which has a high alloy content and contains vanadium, leading to a significant increase in internal stress during heat treatment.

[0003] Taking the most widely used 40NiCrMo7 steel as an example, the traditional heat treatment manufacturing process for centrifugal compressor spindles typically involves: forging arrival at the factory → rough machining → normalizing + quenching and tempering → mechanical property testing → semi-finishing → non-destructive testing → stabilization treatment. The holding time during the stabilization stage is calculated based on the design drawing dimensions / 25 + 1 hour. This method is simple to operate and has been used for many years in the manufacturing of conventional centrifugal compressor spindles.

[0004] However, the residual internal stress level of the compressor spindle manufactured using the above heat treatment method is still relatively high. The measured internal stress in some step areas can reach 400 MPa, which is about 54% of the material's yield strength. Even with the optimization of the stabilization process by extending the heat treatment time, the residual stress is still maintained at around 200 MPa, which is about 27% of the yield strength. This seriously affects the dimensional stability and safe operating life of the compressor spindle under frequent start-stop conditions. Summary of the Invention

[0005] The summary section introduces a series of simplified concepts, which will be further explained in detail in the detailed description section. This part of the invention is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0007] Therefore, the present invention provides a method for heat treatment of a compressor spindle, the heat treatment method comprising: The spindle forgings are surface-lit and then annealed to eliminate the original residual stress. The annealed spindle is then rough-machined. After rough machining, the spindle is vertically hoisted and then subjected to heat treatment. After the heat-treated spindle is vertically hoisted, it is stabilized. The stabilization process includes heating and holding the heat-treated spindle in a segmented heating method with at least two heating stages, then cooling and holding it, and finally cooling it to room temperature in a segmented variable speed cooling method with at least two cooling stages. The spindle, after stabilization, is then precision machined.

[0008] In one feasible implementation, after the spindle forging undergoes surface brightening treatment, the process further includes: The corners and sharp edges of the spindle after exposure to light are rounded, and the radius of the rounded corner is ≥5mm.

[0009] In one feasible implementation, the annealing process includes: The spindle, after being exposed to light, is loaded into the furnace at a temperature of ≤350℃. After loading, the temperature is increased to 690℃~720℃ at a rate of ≤70℃ / h and held for t1. Then, the temperature is increased to 810℃~850℃ at a rate of ≤100℃ / h and held for t2. After that, the temperature is cooled to 350℃~400℃ at a rate of ≤50℃ / h and finally removed from the furnace and air-cooled. Where: t1 = 1h ~ 5h; t2=D max / (30~50) h, D max The maximum step diameter of the spindle forging is in mm.

[0010] In one feasible implementation, the roughing process includes: The outer diameter of the smallest step on both sides of the spindle after annealing is machined to the finishing diameter + 8a / 3, the outer diameter of the remaining steps of the spindle is machined to the finishing diameter + 2a, the length of the largest step of the spindle is machined to the finishing length + 2a, and the length of the remaining steps is machined to the finishing length. Where a is the single-sided allowance, a = 5mm ~ 20mm.

[0011] In one feasible implementation, the roughing process further includes: After annealing, the root of each step of the spindle is rounded, and the radius of the rounded arc is ≥5mm and ≤ the difference in radius between two adjacent steps. One end of the annealed spindle is set as a heat treatment chuck with a diameter of 160mm to 330mm, and the heat treatment chuck has an inner hole with a diameter of 100mm to 160mm at its center.

[0012] In one feasible implementation, the conditioning process includes: The rough-machined spindle is vertically hoisted into the furnace, with a furnace loading temperature ≤500℃; After loading the furnace, the main shaft is heated to 640℃~680℃ at a rate of ≤100℃ / h and held for 1h~5h. Then, it is heated to 860℃~890℃ at a rate of ≤90℃ / h and held for 6h~10h. Then it is taken out of the furnace and cooled in oil. Continue to vertically hoist the main shaft into the furnace. The furnace temperature is ≤350℃. The temperature is increased to 570℃~640℃ at a rate of ≤70℃ / h, and then held for 9h~15h before air cooling.

[0013] In one feasible implementation, it further includes: Before stabilization after heat treatment, the spindle is semi-finished, with the semi-finished dimension having a 1mm to 3mm allowance on one side for the finishing dimension.

[0014] In one feasible implementation, the segmented heating method in the stabilization process includes: After the treated spindle is vertically hoisted into the furnace, the temperature is increased to 200℃~240℃ at a rate of ≤70℃ / h and held for t3. Then the temperature is increased to 380℃~420℃ at a rate of ≤50℃ / h and held for t4. Finally, the temperature is increased to 540℃~560℃ at a rate of ≤50℃ / h and held for t5. Where t3 = 1h ~ 3h; t 4= 2h~4h; t5=D max / (25~35) + 4h, D max The maximum step diameter of the spindle forging is in mm.

[0015] In one feasible implementation, the stabilization process further includes: After the heating is completed, the spindle is cooled to 530℃~550℃ and then kept at that temperature for t6. Where t6=D max / (20~30) + 4h, D max The maximum step diameter of the spindle forging is in mm.

[0016] In one feasible implementation, the segmented variable-speed cooling method in the stabilization process includes: After the heat preservation is completed, the main shaft is cooled to 380℃~420℃ at a rate of ≤30℃ / h, then cooled to 200℃~300℃ at a rate of ≤50℃ / h, and finally removed from the furnace and air-cooled to room temperature.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: This invention discloses a heat treatment method for compressor spindles. It employs an optimized process route of incoming material finishing → annealing → rough machining → quenching and tempering. Instead of air-cooled normalizing, it uses furnace-cooled slow annealing, significantly reducing the original residual tensile stress introduced by casting and forging. Simultaneously, rough machining is moved to after annealing to avoid deformation and dimensional drift caused by disrupting stress balance. Furthermore, it utilizes a stable treatment process of stepped heating + high-to-low segmented holding + segmented variable-speed cooling. Stepped heating controls thermal stress generation, high-to-low segmented holding creates a micro-alternating stress field to eliminate stubborn microscopic residual stress, and segmented variable-speed cooling... Rapid cooling avoids stress recombination, and vertical hoisting is used during tempering and stabilization to ensure uniform distribution of internal stress along the circumferential direction. Through the above process, the residual stress of the 30Cr2Ni4MoV steel spindle can be stably controlled within -50MPa (i.e., absolute value ≤ 50MPa), and all of them are beneficial compressive stresses. In summary, the heat treatment method of this invention effectively avoids the risk of poor dimensional stability and micro-area plastic deformation caused by excessive residual stress, significantly improves the dimensional stability and fatigue strength of the spindle, and meets the stringent service requirements of frequent daily start-stop of medium and high temperature energy storage compressors.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A simplified schematic diagram of the compressor spindle structure provided in the various embodiments of this application. Detailed Implementation

[0020] The following description provides numerous specific details to offer a more thorough understanding of the technical solutions provided by this invention. However, it will be apparent to those skilled in the art that the technical solutions provided by this invention can be implemented without one or more of these details.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or combinations thereof.

[0022] Exemplary embodiments according to the present invention will now be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of the invention is thorough and complete, and that the concept of these exemplary embodiments is fully conveyed to those skilled in the art.

[0023] To better understand the above technical solutions, the technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0024] Example 1 This embodiment provides a heat treatment method for a compressor spindle. The spindle material is 30Cr2Ni4MoV, and its maximum step diameter D is... max 410mm (finishing drawing as shown) Figure 1 As shown), the specific steps include: S1: Surface treatment and annealing The spindle forging is surface-polished to remove the oxide scale and decarburized layer, revealing the metallic luster. The corners and sharp edges of the spindle after polishing are then rounded with a radius of R=8mm. After light treatment, the spindle was placed in a furnace at 300℃, heated to 700℃ at a rate of 60℃ / h, and held for 3 hours; then heated to 830℃ at a rate of 80℃ / h and held for 10 hours; then cooled to 380℃ at a rate of 40℃ / h, and then removed from the furnace and air-cooled; after annealing, the spindle sample was tested, and the material grain size was improved to grade 6.8, and the residual austenite content was reduced to 0.9%, effectively cutting off the hereditary structure; S2: Rough machining The outer diameter of the steps at both ends of the annealed spindle is machined to 223 + (8 × 10 / 3) ≈ 250 mm; The outer diameter of each step of the spindle is machined according to the finishing diameter + 2a (a=10mm). The roughing diameters of each section from left to right are as follows: outer diameter of the second step 300 mm, outer diameter of the third step 340 mm, outer diameter of the fourth step 380 mm, outer diameter of the fifth step 350 mm, and outer diameter of the sixth step 300 mm. The step with diameter of 380 mm is the largest step diameter of the spindle. The maximum step, i.e. the fourth step, is machined to a length of 1555 + 2a = 1575 mm (a = 10 mm). Since this shaft section is the maximum diameter, the length needs to be extended according to the heat treatment allowance. The lengths of the remaining steps are all machined to the finishing length. The base of each step is machined with rounded corners of different specifications such as R10, R5, and R10 according to the drawings to ensure that there are no sharp corners or edges. A heat treatment chuck is installed on the left side of the spindle, and the center of the chuck has an inner hole with a diameter of 130mm; After the above rough machining, the surface roughness of the spindle reaches Ra≤12.5μm, which meets the requirements for vertical hoisting and furnace loading of subsequent quenching and tempering treatment; S3: Conditioning The rough-machined spindle is vertically hoisted into the furnace using heat treatment fixtures. The furnace temperature is 150℃, and the temperature is increased to 660℃ at a rate of 80℃ / h, and held for 2 hours. Then, the temperature is increased to 880℃ at a rate of 70℃ / h, held for 8 hours, and then removed from the furnace and cooled in oil. After quenching, the spindle is vertically hoisted into the furnace at a furnace temperature of 100℃. The temperature is increased to 570℃ at a rate of 40℃ / h, and held at that temperature for 12 hours before being removed from the furnace and air-cooled. S4: Semi-finishing The heat-treated spindle is semi-finished using a lathe, with a 2mm allowance on each side based on the finished dimensions of the spindle. S5: Stabilization Processing The semi-finished spindle is vertically hoisted into the furnace for stabilization treatment. During segmented heating, the temperature is increased to 220℃ at 60℃ / h and held for 2 hours, then increased to 400℃ at 40℃ / h and held for 3 hours, and then increased to 550℃ at 40℃ / h and held for 17 hours. After the heating is completed, the spindle is first cooled to 540℃ and held for 20 hours. Then it is cooled to 400℃ at 25℃ / h, then to 250℃ at 40℃ / h, and finally removed from the furnace and air-cooled to room temperature.

[0025] S6: Finishing After stabilization treatment, the outer diameter and length of each step of the spindle are machined to the final precision dimensions, and the heat-treated chuck is removed.

[0026] Example 2 This embodiment provides a heat treatment method for a compressor spindle. The spindle material is 30Cr2Ni4MoV, and its maximum step diameter D is... max 410mm (finishing drawing as shown) Figure 1 As shown), the specific steps include: S1: Surface treatment and annealing The spindle forging is surface-polished to remove the oxide scale and decarburized layer, revealing the metallic luster. The corners and sharp edges of the spindle after polishing are rounded. The spindle, after light treatment, was placed in a furnace at 300℃, heated to 720℃ at a rate of 70℃ / h, and held for 1 hour; then heated to 850℃ at a rate of 100℃ / h and held for 10 hours; then cooled to 400℃ at a rate of 50℃ / h, and then removed from the furnace and air-cooled; after annealing, the spindle sample was tested, and the material grain size was improved to grade 6, and the residual austenite content was reduced to 0.8%, effectively cutting off the hereditary structure; S2: Rough machining The outer diameter of the steps at both ends of the annealed spindle is machined to 223 + (8 × 20 / 3) ≈ 276 mm; The outer diameter of each step of the spindle is machined according to the finishing diameter + 2a (a=20mm). The roughing diameters of each section from left to right are as follows: outer diameter of the second step 320 mm, outer diameter of the third step 360 mm, outer diameter of the fourth step 400 mm, outer diameter of the fifth step 370 mm, and outer diameter of the sixth step 320 mm. The step with a diameter of 400 mm is the largest step diameter of the spindle. The maximum step, i.e. the fourth step, is machined to a length of 1555 + 2a = 1595 mm (a = 20 mm). Since this shaft section is the maximum diameter, the length needs to be extended according to the heat treatment allowance. The lengths of the remaining steps are all machined to the finishing length. The base of each step is machined with rounded corners of different specifications such as R10, R5, and R10 according to the drawings to ensure that there are no sharp corners or edges. A heat treatment chuck is installed on the left side of the spindle, and the center of the chuck has an inner hole with a diameter of 130mm; After the above rough machining, the surface roughness of the spindle reaches Ra≤12.5μm, which meets the requirements for vertical hoisting and furnace loading of subsequent quenching and tempering treatment; S3: Conditioning The rough-machined spindle is vertically hoisted into the furnace using heat treatment fixtures. The furnace temperature is 200℃, and the temperature is increased to 680℃ at a rate of 100℃ / h and held for 1 hour. Then, the temperature is increased to 870℃ at a rate of 90℃ / h and held for 7 hours before being removed from the furnace and cooled in oil. After quenching, the spindle is vertically hoisted into the furnace at a furnace temperature of 200℃. The temperature is increased to 640℃ at a rate of 70℃ / h, and held at that temperature for 11 hours before being removed from the furnace and air-cooled. S4: Semi-finishing The heat-treated spindle is semi-finished using a lathe, with a 3mm allowance on each side based on the finished dimensions of the spindle. S5: Stabilization Processing The semi-finished spindle is vertically hoisted into the furnace for stabilization treatment. During segmented heating, the temperature is increased to 240℃ at 70℃ / h and held for 1 hour, then increased to 420℃ at 50℃ / h and held for 2 hours, and then increased to 560℃ at 50℃ / h and held for 17 hours. After the heating is completed, the spindle is first cooled to 550℃ and held for 20 hours. Then it is cooled to 420℃ at 25℃ / h, then to 300℃ at 50℃ / h, and finally removed from the furnace and air-cooled to room temperature. S6: Finishing After stabilization treatment, the outer diameter and length of each step of the spindle are machined to the final precision dimensions, and the heat-treated chuck is removed.

[0027] Example 3 This embodiment provides a heat treatment method for a compressor spindle. The spindle material is 30Cr2Ni4MoV, and its maximum step diameter D is... max 410mm (finishing drawing as shown) Figure 1 As shown), the specific steps include: S1: Surface treatment and annealing The spindle forging is surface-polished to remove the oxide scale and decarburized layer, revealing the metallic luster. The corners and sharp edges of the spindle after polishing are rounded. The spindle, after light treatment, was placed in a furnace at 300℃, heated to 690℃ at a rate of 60℃ / h, and held for 5 hours; then heated to 810℃ at a rate of 80℃ / h and held for 10 hours; then cooled to 350℃ at a rate of 40℃ / h, and then air-cooled after being removed from the furnace. After annealing, the spindle sample was tested. The material grain size was improved to grade 7.2, and the residual austenite content was reduced to 0.4%, effectively cutting off the hereditary structure. S2: Rough machining The outer diameter of the steps at both ends of the annealed spindle is machined to 223 + (8 × 10 / 3) ≈ 250 mm; The outer diameter of each step of the spindle is machined according to the finishing diameter + 2a (a=10mm). The roughing diameters of each section from left to right are as follows: outer diameter of the second step 300 mm, outer diameter of the third step 340 mm, outer diameter of the fourth step 380 mm, outer diameter of the fifth step 350 mm, and outer diameter of the sixth step 300 mm. The step with diameter 380 mm is the largest step diameter of the spindle. The maximum step, i.e. the fourth step, is machined to a length of 1555 + 2a = 1575 mm (a = 10 mm). Since this shaft section is the maximum diameter, the length needs to be extended according to the heat treatment allowance. The lengths of the remaining steps are all machined to the finishing length. The base of each step is machined with rounded corners of different specifications such as R10, R5, and R10 according to the drawings to ensure that there are no sharp corners or edges. A heat treatment chuck is installed on the left side of the spindle, and the center of the chuck has an inner hole with a diameter of 130mm; After the above rough machining, the surface roughness of the spindle reaches Ra≤12.5μm, which meets the requirements for vertical hoisting and furnace loading of subsequent quenching and tempering treatment; S3: Conditioning The rough-machined spindle is vertically hoisted into the furnace using heat treatment fixtures. The furnace temperature is 150℃, and the temperature is increased to 640℃ at a rate of 80℃ / h, and held for 5 hours. Then, the temperature is increased to 860℃ at a rate of 70℃ / h, held for 10 hours, and then removed from the furnace and cooled in oil. After quenching, the spindle is vertically hoisted into the furnace at a furnace temperature of 100℃. The temperature is increased to 570℃ at a rate of 40℃ / h, and the spindle is held at this temperature for 15 hours before being removed from the furnace and air-cooled. S4: Semi-finishing The heat-treated spindle is semi-finished using a lathe, with a 1mm allowance on each side based on the finished dimensions of the spindle. S5: Stabilization Processing The semi-finished spindle is vertically hoisted into the furnace for stabilization treatment. During segmented heating, the temperature is increased to 200℃ at 60℃ / h and held for 3 hours, then increased to 380℃ at 40℃ / h and held for 4 hours, and then increased to 540℃ at 40℃ / h and held for 15 hours. After the heating is completed, the spindle is first cooled to 530℃ and held for 16 hours. Then it is cooled to 380℃ at 25℃ / h, then to 200℃ at 40℃ / h, and finally removed from the furnace and air-cooled to room temperature.

[0028] S6: Finishing After stabilization treatment, the outer diameter and length of each step of the spindle are machined to the final precision dimensions, and the heat-treated chuck is removed.

[0029] Comparative Example 1 This comparative embodiment provides a heat treatment method for a compressor spindle. The spindle material is 30Cr2Ni4MoV, and its maximum step diameter Dmax is 410mm (see finishing drawing). Figure 1 As shown), the specific steps include: S1: Rough machining The outer diameter of each step of the spindle is machined according to the finishing diameter + 2a (a=10mm). The roughing diameters of each section from left to right are as follows: outer diameter of the first step 243mm, outer diameter of the second step 300mm, outer diameter of the third step 340mm, outer diameter of the fourth step 380mm, outer diameter of the fifth step 350mm, outer diameter of the sixth step 300mm, and outer diameter of the seventh step 243mm. The step with diameter of 380mm is the largest step diameter of the spindle. The maximum step, i.e. the fourth step, is machined to a length of 1555 + 2a = 1575 mm (a = 10 mm). Since this shaft section is the maximum diameter, the length needs to be extended according to the heat treatment allowance. The lengths of the remaining steps are all machined to the finishing length. The base of each step is machined with rounded corners of different specifications such as R20, R15, and R10 according to the drawings to ensure that there are no sharp corners or edges. A heat treatment chuck is installed on the left side of the spindle, and the center of the chuck has an inner hole with a diameter of 130mm; S2: Conditioning Normalizing treatment: The furnace temperature is 130℃, and the temperature is increased to 650℃ at 80℃ / h and held for 1 hour; then the temperature is increased to 880℃ at 70℃ / h and held for 7.5 hours, and then the furnace is removed and air-cooled. Quenching treatment: The normalized spindle is placed in the furnace at a temperature of 160℃, heated to 660℃ at a rate of 70℃ / h, and held for 1 hour; then heated to 870℃ at a rate of 80℃ / h, held for 7.5 hours, and then oil-cooled after being taken out of the furnace. After quenching, the spindle is placed back into the furnace at a temperature of 200℃, and then heated to 580℃ at a rate of 40℃ / h. After holding at this temperature for 11.5h, it is removed from the furnace and air-cooled. S4: Semi-finishing The heat-treated spindle is semi-finished using a lathe, with a 1.5mm allowance on each side based on the finished dimensions of the spindle. S5: Stabilization Processing The semi-finished spindle is stabilized by heating it to 550℃ at 50℃ / h and holding it at that temperature for 12.5h. Then it is cooled to 250℃ at 40℃ / h and finally removed from the furnace and air-cooled to room temperature.

[0030] S6: Finishing After stabilization treatment, the outer diameter and length of each step of the spindle are machined to the final precision dimensions, and the heat-treated chuck is removed.

[0031] Table 1 below shows the residual stress test results for Example 1 and Comparative Example 1. Table 1

[0032] In summary, this invention effectively reduces the residual stress generated in the 30Cr2Ni4MoV steel spindle at each processing stage by optimizing the heat treatment process and stabilizing the treatment process. Experimental data shows (see Table 1): the residual stresses of Examples 1-3 using the method of this invention are -28.34MPa, -24.56MPa, and -38.68MPa, respectively, all stably controlled within -50MPa (i.e., absolute value ≤ 50MPa), and all are beneficial compressive stresses; while the residual stress of the same specification spindle in Comparative Example 1 treated with the traditional process is as high as -115MPa, significantly higher than that of the embodiments of this invention. Therefore, the heat treatment method of this invention effectively avoids the risk of poor dimensional stability and micro-area plastic deformation caused by excessive residual stress, significantly improves the dimensional stability and fatigue strength of the spindle, and fully meets the stringent service requirements of frequent daily start-stop of medium- and high-temperature energy storage compressors, demonstrating significant social benefits and promising industrial application prospects.

[0033] To achieve the above objectives, the heat treatment method disclosed in this invention is improved in accordance with the following three core directions: I. Optimize the heat treatment process route The process route adopts a method of smoothing incoming materials → annealing → rough machining → quenching and tempering, replacing the traditional normalizing process with annealing and moving the annealing step before rough machining. During annealing, atoms diffuse fully, lattice distortion is completely relaxed, and the temperature gradient is minimal throughout the slow furnace cooling process. The cooling process generates almost no new residual stress, significantly reducing the original residual tensile stress introduced by casting and forging. Rough machining only generates a thin, uniform layer of machining stress on the cutting surface. The subsequent high-temperature tempering process completely removes the internal stress generated by quenching and machining, ultimately achieving an extremely low level of residual stress.

[0034] II. Improved Stabilization Process The stabilization process employs a stepped heating + high-to-low segmented heat preservation + segmented variable-speed cooling, specifically including: Stepped heating stage: By slowing down the heating rate and keeping the temperature in between, the heat is gradually conducted to the core, ensuring that the surface of the spindle and the core expand synchronously. At the same time, the residual stresses of different depths and magnitudes are gradually relaxed at the corresponding temperatures, thus avoiding the generation of new thermal stresses from the source. High-low segmented heat preservation stage: First, heat preservation is carried out at 540℃~560℃, so that the residual tensile stress exceeding the yield strength undergoes plastic relaxation through atomic diffusion and dislocation slip; then, it is cooled to 530℃~550℃ and heat preservation is carried out. During the cooling process, a micro-alternating stress field of alternating tension and compression is formed, which eliminates the micro-residual stress that cannot be removed by ordinary constant temperature process. Segmented speed-controlled cooling stage: By controlling the cooling rate at different stages, the spindle surface and core are cooled synchronously, completely avoiding stress regeneration during the cooling process and forming a uniform low-stress distribution.

[0035] III. Introduction of Vertical Heat Treatment Method During the quenching and stabilization processes, the spindle is vertically hoisted into the furnace. This makes the internal stress of the spindle tend to be consistent along the circumferential direction, ensuring that the microstructure and mechanical properties of the spindle are relatively balanced in the circumferential direction, and effectively reducing the amount of deformation during heat treatment.

[0036] In this invention, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can mean a fixed connection, a detachable connection, or an integral connection; "link" can mean a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0038] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for heat treatment of a compressor spindle, characterized in that, include: The spindle forgings are surface-lit and then annealed to eliminate the original residual stress. The annealed spindle is then rough-machined. After rough machining, the spindle is vertically hoisted and then subjected to heat treatment. After the heat-treated spindle is vertically hoisted, it is stabilized. The stabilization process includes heating and holding the heat-treated spindle in a segmented heating method with at least two heating stages, then cooling and holding it, and finally cooling it to room temperature in a segmented variable speed cooling method with at least two cooling stages. The spindle, after stabilization, is then precision machined.

2. The compressor spindle heat treatment method according to claim 1, characterized in that, After surface finishing of the spindle forging, the process further includes: The corners and sharp edges of the spindle after exposure to light are rounded, and the radius of the rounded corner is ≥5 mm.

3. The compressor spindle heat treatment method according to claim 1, characterized in that, The annealing process includes: The spindle, after being exposed to light, is loaded into the furnace at a temperature of ≤350℃. After loading, the temperature is increased to 690℃~720℃ at a rate of ≤70℃ / h and held for t1. Then, the temperature is increased to 810℃~850℃ at a rate of ≤100℃ / h and held for t2. After that, the temperature is cooled to 350℃~400℃ at a rate of ≤50℃ / h and finally removed from the furnace and air-cooled. Where: t1 = 1h ~ 5h; t2=D max / (30~50) h, D max The maximum step diameter of the spindle forging is in mm.

4. The compressor spindle heat treatment method according to claim 1, characterized in that, The roughing process includes: The outer diameter of the smallest step on both sides of the spindle after annealing is machined to the finishing diameter + 8a / 3, the outer diameter of the remaining steps of the spindle is machined to the finishing diameter + 2a, the length of the largest step of the spindle is machined to the finishing length + 2a, and the length of the remaining steps is machined to the finishing length. Where a is the single-sided allowance, a = 5mm ~ 20mm.

5. The compressor spindle heat treatment method according to claim 4, characterized in that, The roughing process also includes: After annealing, the root of each step of the spindle is rounded, and the radius of the rounded arc is ≥5mm and ≤ the difference in radius between two adjacent steps. One end of the annealed spindle is set as a heat treatment chuck with a diameter of 160mm to 330mm, and the heat treatment chuck has an inner hole with a diameter of 100mm to 160mm at its center.

6. The compressor spindle heat treatment method according to claim 1, characterized in that, The conditioning process includes: The rough-machined spindle is vertically hoisted into the furnace, with a furnace loading temperature ≤500℃; After loading the furnace, the main shaft is heated to 640℃~680℃ at a rate of ≤100℃ / h and held for 1h~5h. Then, it is heated to 860℃~890℃ at a rate of ≤90℃ / h and held for 6h~10h. Then it is taken out of the furnace and cooled in oil. Continue to vertically hoist the main shaft into the furnace. The furnace temperature is ≤350℃. The temperature is increased to 570℃~640℃ at a rate of ≤70℃ / h, and then held for 9h~15h before air cooling.

7. The compressor spindle heat treatment method according to claim 1, characterized in that, Also includes: Before stabilization after heat treatment, the spindle is semi-finished, with the semi-finished dimension having a 1mm to 3mm allowance on one side for the finishing dimension.

8. The compressor spindle heat treatment method according to claim 1, characterized in that, The segmented heating method in the stabilization process includes: After the treated spindle is vertically hoisted into the furnace, the temperature is increased to 200℃~240℃ at a rate of ≤70℃ / h and held for t3. Then the temperature is increased to 380℃~420℃ at a rate of ≤50℃ / h and held for t4. Finally, the temperature is increased to 540℃~560℃ at a rate of ≤50℃ / h and held for t5. Where t3 = 1h ~ 3h; t 4= 2h~4h; t5=D max / (25~35) + 4h, D max The maximum step diameter of the spindle forging is in mm.

9. The compressor spindle heat treatment method according to claim 8, characterized in that, The stabilization process also includes: After the heating is completed, the spindle is cooled to 530℃~550℃ and then kept at that temperature for t6. Where t6=D max / (20~30) + 4h, D max The maximum step diameter of the spindle forging is in mm.

10. The compressor spindle heat treatment method according to claim 9, characterized in that, The segmented variable-speed cooling method in the stabilization process includes: After the heat preservation is completed, the main shaft is cooled to 380℃~420℃ at a rate of ≤30℃ / h, then cooled to 200℃~300℃ at a rate of ≤50℃ / h, and finally removed from the furnace and air-cooled to room temperature.

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