A vacuum high-pressure gas quenching method for thin-walled cylindrical parts with end caps

Abstract

A method for vacuum high-pressure gas quenching of thin-walled cylindrical parts with heads, wherein an air-gathering ring is installed at the heads before vacuum high-pressure gas quenching of the thin-walled cylindrical parts, so as to achieve maximum synchronous cooling of the heads and the cylinder walls of the thin-walled cylindrical parts, and reduce deformation of the cylinder walls while ensuring full hardening of the heads. The present invention uses an air-gathering ring to converge the upwardly ejected airflow at the heads in a vacuum gas quenching furnace with circumferential blowing and bottom blowing, greatly increasing the gas flow rate near the surface of the heads, so that the heat at the heads is quickly taken away by the gas, increasing the cooling rate of the heads, and ensuring the hardenability. At the same time, the gas is converged only at the heads, and the flow rate at other parts of the thin-walled cylindrical parts is relatively small, so as to reduce the quenching stress on the cylinder walls away from the heads while ensuring the quenching effect, thereby ensuring the hardenability of the heads and the overall straightness and roundness of the thin-walled cylindrical parts.

Description

Technical Field

[0001] The invention relates to the field of metal heat treatment processing, and in particular to a vacuum high-pressure gas quenching method for a thin-walled cylindrical part with a head. Background Art

[0002] Vacuum high-pressure gas quenching technology is a clean and environmentally friendly heat treatment technology that heats in a vacuum and partial pressure protective atmosphere and uses high-pressure inert gas as a cooling medium to achieve quenching. Due to its advantages of no oxidation and pollution on the workpiece surface and brightening treatment, it has been increasingly used in the heat treatment industry and is also the focus of research in the field of heat treatment at home and abroad.

[0003] The synchronous control of hardenability and deformation of thin-walled cylindrical parts with heads during vacuum high-pressure gas quenching has always been a difficult problem that has plagued the aviation, aerospace and other manufacturing industries. Thin-walled cylindrical parts are generally formed by spinning, which has a large residual pressure and is easy to deform during quenching. Especially for thin-walled cylindrical parts with heads, the thickness at the head is relatively large, 20mm to 40mm, and a higher gas quenching pressure is required to quench the core of the head. However, when a high cooling rate is achieved by adjusting the quenching pressure, the wall of the thin-walled cylindrical part will be subjected to greater quenching stress, resulting in greater deformation of the wall. Summary of the invention

[0004] In order to solve the problem that thin-walled cylindrical parts with sealed heads are difficult to be quenched during vacuum high-pressure gas quenching and adjusting the gas quenching pressure easily causes deformation of the cylinder wall, the present invention proposes a vacuum high-pressure gas quenching method for thin-walled cylindrical parts with sealed heads.

[0005] The specific process of the present invention is:

[0006] Step 1: Determine the structural dimensions of the air gathering ring:

[0007] The air gathering ring is a conical ring-shaped thin-walled shell with openings at both ends.

[0008] The inner diameter of the small opening end of the air gathering ring is determined to be D3, the inner diameter of the large opening end of the air gathering ring is determined to be D4, and the height of the end face of the small opening end of the air gathering ring from the maximum outer diameter of the head is h1. The total height of the air gathering ring is h2; the difference between the inner diameter of the air gathering ring and the maximum outer diameter of the thin-walled cylindrical head is δ, δ = D3-D2; the thickness of the air gathering ring shell is 1-10mm.

[0009] When determining the structural dimensions of the fixed air-gathering ring, the influence of the air-gathering ring on the cooling rate of the thin-walled long cylindrical part with a head is calculated by flow field simulation COMSOL, and the results are: D1 = D4, D3 = 1.1-1.4D 2， Then h2=L1-L2-L3-h1.

[0010] The inner diameter of the large opening end of the air gathering ring is D4=D1=550mm, and the inner diameter of the small opening end of the air gathering ring is D3=1.227D2=270mm. According to the maximum outer diameter of the head of the thin-walled cylindrical part D2=220mm, δ=D3-D2=50mm, the height of the end face of the small opening end of the air gathering ring from the maximum outer diameter of the head is h1=100mm, and the height of the air gathering ring is h2=L1-L2-L3-h1=200mm.

[0011] Step 2: Make and install the air gathering ring:

[0012] Make an air gathering ring according to the structural dimensions determined in step 1.

[0013] The manufactured air gathering ring is welded to the tooling bottom plate, and the central axis of the air gathering ring is made to coincide with the central axis of the air outlet at the bottom of the furnace body.

[0014] When installing the air gathering ring, the large opening end is welded to the tooling bottom plate near the air outlet at the bottom of the furnace body.

[0015] Step 3: Hoisting thin-walled cylindrical parts:

[0016] When hanging thin-walled cylindrical parts, the air collecting ring should be placed at the bottom of the head, and the head should be located below the furnace body when the workpiece is hung vertically. The height of the bottom end of the process hanging ring from the bottom of the tooling upper plate is L3 = 600mm.

[0017] The center line of the tooling, the center line of the air focusing ring, the center line of the thin-walled cylindrical part and the center line of the air outlet at the bottom of the furnace body coincide with each other.

[0018] Step 4, gas quenching:

[0019] The equipment for installing the air focusing ring and hanging the thin-walled cylindrical parts is placed in a vacuum high-pressure gas quenching furnace for gas quenching.

[0020] Preheating treatment: The temperature of preheating treatment is 600±10℃ and the time is 80±10min.

[0021] After the preheating is completed, the temperature is raised to the quenching temperature in 60±10min; the quenching temperature is 900±10℃, and the holding time is 120±10min, and the hanging thin-walled cylindrical part is quenched. After the quenching and holding is completed, nitrogen gas with a pressure of 8 bar is introduced into the furnace for cooling.

[0022] At this point, the vacuum high-pressure gas quenching of the thin-walled long cylindrical part with a head is completed.

[0023] The technical core point of the present invention is to add an air gathering ring at the head of the thin-walled cylindrical part before vacuum high-pressure gas quenching to achieve maximum synchronous cooling of the head and the cylinder wall of the thin-walled cylindrical part, while ensuring the thorough quenching of the head and reducing the deformation of the cylinder wall.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention adds a gathering ring at the head, which can converge the upwardly ejected airflow at the head in a vacuum gas quenching furnace with circumferential blowing and bottom blowing, greatly increase the gas flow rate near the head surface, so that the heat at the head is quickly taken away by the gas, increase the cooling rate of the head, and ensure its hardenability. At the same time, the gas is only converged at the head, and the flow rate at other parts of the thin-walled cylindrical part is relatively small, which can reduce the quenching stress of the cylinder wall away from the head while ensuring the quenching effect. The gas pressure during quenching is generally 10 bar in the prior art, but the addition of the gathering ring in the present invention greatly increases the gas flow rate at the head of the thin-walled cylindrical part, which can ensure the hardenability of the head. Therefore, the gas quenching pressure is reduced to 8 bar through a series of experimental results in the present invention, which can further reduce the deformation of the thin-walled cylindrical part on the premise of ensuring the hardenability of the head of the thin-walled cylindrical part, and ensure the overall straightness and roundness of the thin-walled cylindrical part. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the wind gathering ring in the present invention.

[0027] Figure 2 It is a schematic diagram of the installation of the hanging tooling, the thin-walled cylindrical part and the air gathering ring in the present invention.

[0028] Figure 3 Schematic diagram of the structure of a thin-walled cylindrical member according to an embodiment of the present invention.

[0029] Figure 4 It is a schematic diagram of the hanging tool and the hanging method of the thin-walled cylindrical part used in the embodiment of the present invention.

[0030] Figure 5 It is a schematic diagram of the structure of the wind focusing ring in an embodiment of the present invention.

[0031] Figure 6 It is a schematic diagram of the installation of the wind gathering ring in the embodiment of the present invention.

[0032] Figure 7 These are the roundness measurement results of different cross sections of the thin-walled cylindrical part before and after heat treatment in the embodiment of the present invention.

[0033] Figure 8 It is the straightness measurement result of the thin-walled cylindrical part before and after heat treatment in the embodiment of the present invention.

[0034] Fig. 9 It is the hardness test result of the core of the thin-walled cylindrical part head after heat treatment in the embodiment of the present invention.

[0035] In the figure: 1. Tooling; 2. Thin-walled cylindrical part with head; 3. Air focusing ring; 4. Straightness before gas quenching; 5. Straightness after gas quenching; 6. Roundness before gas quenching; 5. Roundness after gas quenching. DETAILED DESCRIPTION

[0036] The present invention is a vacuum high-pressure gas quenching method for thin-walled cylindrical parts with heads. The diameter of the bottom air outlet of the vacuum high-pressure gas quenching furnace used is D1, the effective height of the hanging tool is L1, the length of the thin-walled cylindrical part with a head is L2, the height of the bottom end of the process hanging ring from the bottom of the tool upper plate is L3, the maximum outer diameter of the head of the thin-walled cylindrical part is D2, the inner diameter of the small opening end of the air gathering ring is D3, the inner diameter of the large opening end of the air gathering ring is D4, the difference between the inner diameter of the air gathering ring and the maximum outer diameter of the head of the thin-walled cylindrical part is δ, δ=D3-D2, the height of the end face of the small opening end of the air gathering ring from the maximum outer diameter of the head is h1, and the height of the air gathering ring is h2. The effective height is the height of the tool column.

[0037] In this embodiment, when vacuum high-pressure gas quenching is performed on thin-walled long cylindrical parts with front heads, a wind-gathering ring is installed at the bottom of the front head to achieve maximum synchronous cooling of the cylinder wall and the front head, while reducing the gas pressure during gas quenching, thereby achieving synchronous control of its hardenability and deformation. In this embodiment, the air outlet mode of the vacuum high-pressure gas quenching furnace is circumferential blowing plus bottom blowing, the bottom air outlet diameter of the vacuum high-pressure gas quenching furnace D1 = 550mm, the effective height of the tooling L1 = 2500mm, the length of the thin-walled cylindrical part with a head L2 = 1600mm, the height of the bottom end of the process lifting ring from the bottom of the tooling upper plate L3 = 600mm, the maximum outer diameter of the head of the thin-walled cylindrical part D2 = 220mm, the maximum thickness of the front head is 27.5mm, and the number of thin-walled long cylindrical parts to be heat treated is 1, such as Figure 3 As shown, the material is D406A steel; the tooling and workpiece hanging method used for heat treatment are as follows Figure 4 shown.

[0038] The specific process of this embodiment is as follows:

[0039] Step 1: Determine the structural dimensions of the air gathering ring:

[0040] The air gathering ring is made of stainless steel and is a conical ring-shaped thin-wall shell with openings at both ends.

[0041] The inner diameter of the small opening end of the air gathering ring is determined to be D3, the inner diameter of the large opening end of the air gathering ring is determined to be D4, and the height of the end face of the small opening end of the air gathering ring from the maximum outer diameter of the head is h1. The total height of the air gathering ring is h2; the difference between the inner diameter of the air gathering ring and the maximum outer diameter of the thin-walled cylindrical head is δ, δ=D3-D2; the thickness of the air gathering ring shell is 1 to 10 mm.

[0042] When determining the structural dimensions of the fixed air-gathering ring, the influence of the air-gathering ring on the cooling rate of the thin-walled long cylindrical part with a head is calculated by flow field simulation COMSOL, and the results are: D1 = D4, D3 = 1.1-1.4D 2， Then h2=L1-L2-L3-h1.

[0043] In this embodiment, the diameter of the air outlet at the bottom of the furnace body is D1=550mm, D3=1.227D2, The inner diameter of the large opening end of the air gathering ring is D4=D1=550mm, the inner diameter of the small opening end of the air gathering ring is D3=1.227D2=270mm, and according to the maximum outer diameter of the head of the thin-walled cylindrical part D2=220mm, it is calculated that: δ=D3-D2=50mm, so the height of the end face of the small opening end of the air gathering ring from the maximum outer diameter of the head is h1=100mm, and the height of the air gathering ring is h2=L1-L2-L3-h1=200mm.

[0044] Step 2: Make and install the air gathering ring:

[0045] According to the structural dimensions determined in step 1, the wind gathering ring is manufactured using conventional processing methods.

[0046] In this embodiment, the thickness of the air gathering ring is 10mm, the inner diameter of the large opening end of the air gathering ring D4 = 550mm, the inner diameter of the small opening end of the air gathering ring D3 = 270mm, and the height of the air gathering ring h2 = 200mm. The air gathering ring is made in this way, and the material of the air gathering ring is heat-resistant stainless steel. The structural diagram of the air gathering ring is shown in the attached figure. Figure 5 As shown, Figure 5 This is a cross-sectional view of the air gathering ring, in which D4=550mm, D3=270mm, and h2=200mm.

[0047] After the production is completed, the air gathering ring is welded to the tooling bottom plate, and the central axis of the air gathering ring is made to coincide with the central axis of the air outlet at the bottom of the furnace body.

[0048] When installing the air focusing ring, the large opening end should be welded to the tooling bottom plate close to the air outlet at the bottom of the furnace body.

[0049] Step 3: Hoisting thin-walled cylindrical parts:

[0050] After the installation of the air gathering ring is completed, the thin-walled cylindrical parts are hung. When hanging the thin-walled cylindrical parts, the air gathering ring should be placed at the bottom of the head, and when the workpiece is hung vertically, the head should be located below the furnace body to achieve a better air gathering effect.

[0051] The center line of the tooling, the center line of the air gathering ring, the center line of the thin-walled cylindrical part and the center line of the air outlet at the bottom of the furnace body coincide. The height of the bottom end of the process lifting ring from the bottom of the tooling upper plate is L3 = 600mm, and the height of the end face of the small opening of the air gathering ring from the maximum outer diameter of the head is h1 = 100mm.

[0052] Step 4, gas quenching:

[0053] The equipment for installing the air focusing ring and hanging the thin-walled cylindrical parts is placed in the vacuum high-pressure gas quenching furnace.

[0054] Preheating treatment: The preheating temperature is 600±10℃ and the time is 80±10min. After the preheating is completed, the temperature is raised to the quenching temperature in 60±10min; the quenching temperature is 900±10℃ and the holding time is 120±10min. The hanging thin-walled cylindrical parts are quenched for a long distance.

[0055] After quenching and heat preservation, nitrogen with a pressure of 8 bar is introduced into the furnace for cooling to ensure that the deformation of the thin-walled cylindrical part is further reduced under the premise of the hardenability of the thin-walled cylindrical part head.

[0056] At this point, the vacuum high-pressure gas quenching of the thin-walled long cylindrical part with a head is completed.

[0057] In order to verify the effect of the present invention, the roundness and straightness of the thin-walled long cylindrical parts after heat treatment were measured as a whole. The roundness measurement results are as follows: Figure 7 As shown, Figure 7 The horizontal axis is the 8 measurement sections of the thin-walled long cylindrical part, and the vertical axis is the roundness measurement value of the 8 measurement sections of the thin-walled long cylindrical part before and after gas quenching. The average roundness change of these 8 sections before and after gas quenching is 0.28mm. Figure 8 As shown, Figure 8 The horizontal axis is the four measuring quadrants of the thin-walled long cylindrical parts, and the vertical axis is the straightness measurement value of the four measuring quadrants of the thin-walled long cylindrical parts before and after gas quenching. The average straightness change of these four quadrants before and after gas quenching is 0.37mm / m; the hardness of the core of the head of the thin-walled long cylindrical parts after heat treatment is tested, and the hardness is required to be ≥HRC47. The test results are as follows Fig. 9 shown. Fig. 9 The horizontal axis is the four test points at the core of the head, and the vertical axis is the hardness value of the four test points. The average hardness value of the four test points is HRC48.45. After the above tests, the roundness of the eight sections, the straightness of the four quadrants and the hardness test results of the core of the head of the thin-walled long cylindrical part after heat treatment in the embodiment all meet the index requirements.

Claims

1. A vacuum high-pressure gas quenching method for thin-walled cylindrical parts with end caps, characterized in that: The specific process is: Step 1: Determine the structural dimensions of the air gathering ring: The air gathering ring is a conical ring-shaped thin-walled shell with openings at both ends; The inner diameter of the small opening end of the air gathering ring is determined to be D3, the inner diameter of the large opening end of the air gathering ring is determined to be D4, and the height of the end face of the small opening end of the air gathering ring from the maximum outer diameter of the head is h1; the total height of the air gathering ring is h2; the difference between the inner diameter of the air gathering ring and the maximum outer diameter of the thin-walled cylindrical head is δ, δ=D3-D2; the thickness of the shell of the air gathering ring is 1-10 mm; Step 2: Make and install the air gathering ring: Make an air gathering ring according to the structural dimensions determined in step 1; Weld the manufactured air gathering ring to the tooling bottom plate, and make the central axis of the air gathering ring coincide with the central axis of the air outlet at the bottom of the furnace body; During installation, the large opening end of the air gathering ring is welded to the tooling bottom plate near the air outlet at the bottom of the furnace body; Step 3: Hoisting thin-walled cylindrical parts: When hanging thin-walled cylindrical parts, the air collecting ring should be placed at the bottom of the head, and the head should be located below the furnace body when the workpiece is hung vertically; the height between the bottom of the process hanging ring and the bottom of the tooling upper plate is L3 = 600mm; Step 4, gas quenching: The equipment for installing the air focusing ring and hanging the thin-walled cylindrical parts is placed in a vacuum high-pressure gas quenching furnace for gas quenching; Preheating treatment; after the preheating is completed, the temperature is raised to the quenching temperature in 60±10min; the quenching temperature is 900±10℃, the holding time is 120±10min, and the hanging thin-walled cylindrical part is quenched; After quenching and heat preservation, nitrogen with a pressure of 8 bar is introduced into the furnace for cooling; At this point, the vacuum high-pressure gas quenching of the thin-walled long cylindrical part with a head is completed.

2. The vacuum high-pressure gas quenching method for thin-walled cylindrical parts with end caps according to claim 1, characterized in that: When determining the structural dimensions of the fixed air-gathering ring, the influence of the air-gathering ring on the cooling rate of the thin-walled long cylindrical part with a head is calculated by flow field simulation COMSOL, and the results are: D1 = D4, D3 = 1.1-1.4D 2， but h2=L1-L2-L3-h1.

3. The vacuum high-pressure gas quenching method for thin-walled cylindrical parts with end caps according to claim 1, characterized in that: The inner diameter of the large opening end of the air gathering ring is D4=D1=550mm, and the inner diameter of the small opening end of the air gathering ring is D3=1.227D2=270mm. According to the maximum outer diameter of the head of the thin-walled cylindrical part D2=220mm, δ=D3-D2=50mm, the height of the end face of the small opening end of the air gathering ring from the maximum outer diameter of the head is h1=100mm, and the height of the air gathering ring is h2=L1-L2-L3-h1=200mm.

4. The vacuum high-pressure gas quenching method for thin-walled cylindrical parts with end caps according to claim 1, characterized in that: The center line of the tooling, the center line of the air focusing ring, the center line of the thin-walled cylindrical part and the center line of the air outlet at the bottom of the furnace body coincide with each other.

5. The vacuum high-pressure gas quenching method for thin-walled cylindrical parts with end caps according to claim 1, characterized in that: The temperature of the preheating treatment in step 4 is 600±10°C and the time is 80±10min.

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