Manufacturing method for front shell of large austenitic stainless steel shrinkage section

Abstract

The present application provides a method for manufacturing a large-scale austenitic stainless steel contraction section front shell, comprising: dividing the outer shell on the front shell into shells and dividing each shell layer into multiple shell petals; leaving margins for the shell petals, cutting and pressing them, and assembling them vertically from the entrance, assembling the first shell layer, the second shell layer, the third shell layer, and the outlet shell layer in sequence; welding the splicing welds and spot welding the girth weld between the third shell layer and the outlet shell layer; assembling and welding reinforcement rings, and then assembling and welding flanges; installing four sets of closing blocks at the long axis and short axis of the girth weld between the third shell layer and the outlet shell layer; disconnecting the outlet and inlet of the front shell layer, machining flanges, and then closing the outlet and inlet to complete the welding of the girth weld at the closing position; installing a bottom plate; inspecting the inner surface of the contraction section front shell and polishing unqualified parts. This method reduces the difficulty of press forming and improves the surface accuracy of the shell.

Description

Technical Field

[0001] The present application relates to the field of wind tunnels, and in particular to a method for manufacturing a large austenitic stainless steel contraction section front shell. Background Art

[0002] The main function of the contraction section is to accelerate the airflow to the required velocity, improve its uniformity, and appropriately reduce its turbulence intensity. Its inlet is connected to the stable section, and its outlet is connected to the test section. The manufacturing quality of the contraction section outlet directly affects the flow field quality of the test section. The surface coordinate deviation is usually required to be less than 0.25mm. This can only be manufactured through outsourcing. This is called the rear shell. The surface coordinate deviation of the contraction section inlet is usually required to be less than 0.05%D (cross-sectional diameter). It is generally assembled and welded on-site. This is called the front shell. The front and rear shells are connected by flanges.

[0003] The front shell of a conventional carbon steel wind tunnel's contraction section consists of a pressure shell (a "round sky, square earth" structure), longitudinal annular ribs, an inner thin-walled plate, and flanges. The longitudinal annular ribs are welded to the interior of the pressure shell, and the inner thin-walled plate is intermittently welded to the longitudinal annular ribs to form the inner profile. The precision of the longitudinal annular ribs determines the quality of the flow field. Under cryogenic conditions, wind tunnels operate at extremely low temperatures, approaching -196°C. The front shell of the contraction section is made of austenitic stainless steel and designed as a single-layer shell structure. The inner shell wall serves as the inner profile and is installed within the pressure shell.

[0004] The inlet of the front shell of the large austenitic stainless steel contraction section is on the order of 11 meters, the outlet is on the order of 7 meters, and the axial length is more than 7 meters. It consists of a shell, a reinforcement ring, a flange, and a mounting base plate. However, there are three difficulties in its production: First, the front shell is large in size, and when the flange needs to be machined after welding, there are problems of limited transportation and equipment; second, the left and right side walls of the front shell are quintic curves, and the upper and lower walls are bicubic curves. If the shell is not properly divided, it will increase the difficulty of press forming and deteriorate the surface accuracy after welding; third, the shell is a complex hyperbolic surface, and flame correction cannot be used during the assembly process, resulting in greater difficulty in assembly and low assembly efficiency. Summary of the Invention

[0005] The present application provides a method for manufacturing a large austenitic stainless steel contraction section front shell, aiming to solve the problem of difficulty in manufacturing the contraction section front shell in existing wind tunnels.

[0006] The technical solution of this application is:

[0007] A method for manufacturing a large austenitic stainless steel contraction section front shell comprises the following steps:

[0008] S1. Determine a shell petal division scheme. According to the distribution position and size of the reinforcement ring on the front shell of the contraction section and the processing width of the CNC bending machine, divide the outer shell on the front shell into a first shell layer, a second shell layer, a third shell layer and an outlet shell layer in the axial direction and gradually approaching the outlet of the front shell. Then, each of the first shell layer, the second shell layer, the third shell layer and the outlet shell layer is divided into multiple shell petals. The principle of dividing the shell petals is as follows: the ruled surface shell on each shell layer is not further divided, and the hyperbolic shell petal does not include part of the ruled surface shell, the ruled surface shell petal does not include part of the hyperbolic shell, and the projection line of the edge of each shell petal on the plane where the first end face of the first shell layer away from the outlet is located does not coincide with the bicubic curve or quintic curve obtained by the projection of the front shell on the plane where the first end face is located.

[0009] S2, blanking all the shell petals of each layer, and leaving a press-forming margin on the outer edges of all the shell petals; using a CNC bending machine to press-form all the blanked shell petals;

[0010] S3, assemble the shell petals vertically in sequence starting from the direction toward the inlet of the front shell, first assemble the shell petals on the first shell layer, and then gradually assemble the shell petals on the second shell layer, the shell petals on the third shell layer, and the shell petals on the outlet shell; when assembling the first shell layer, first assemble the four shell petals located at the two end points of the first long axis of the first shell layer and the four shell petals located at the two end points of the first short axis of the first shell layer, and then assemble the other shell petals close to the two end points of the first long axis and the first short axis of the first shell layer in sequence; when assembling the second shell layer, first assemble the four shell petals located at the two end points of the first long axis and the first short axis of the second shell layer the two shell petals at the two end points of the second major axis and the two shell petals at the two end points of the second minor axis of the second shell layer, and then assemble the four shell petals at the two end points of the second minor axis of the second shell layer in sequence, and finally assemble the other shell petals in sequence; when assembling the third shell layer, first assemble the hyperbolic shell petal corresponding to the quintic curve on the third shell layer, and then assemble the other hyperbolic shell petals in sequence, and finally assemble the other shell petals in sequence; when assembling the outlet shell, first assemble the hyperbolic shell petal corresponding to the quintic curve on the outlet shell layer, and then assemble the other hyperbolic shell petals in sequence, and finally assemble the other shell petals in sequence;

[0011] S4, welding the spliced welds on the front shell, and spot welding the girth welds between the third shell and the outlet shell;

[0012] S5, assembling and welding the reinforcement ring on the outside of the front shell, and then assembling and welding the flange on the front shell;

[0013] S6, installing a set of closing blocks at both end points of the long axis and the short axis of the girth weld between the third shell and the outlet shell, and then grinding and removing the spot weld between the third shell and the outlet shell;

[0014] S7, disconnecting the front housing outlet from the front housing inlet, and processing a flange at the front housing outlet;

[0015] S8, closing the outlet and the inlet of the processed front shell, and welding the girth weld at the closing position;

[0016] S9, installing and welding the base plate based on the machined surface of the flange;

[0017] S10, flip the front shell of the contraction section 180 degrees, adjust the elevation of the machining surface of the flange to be consistent, and use a template to detect the coordinate deviation of the inner surface of the front shell of the contraction section with the machining surface of the flange as a reference. Use a grinding wheel to grind the inner surface of the front shell of the contraction section for unqualified parts until it is qualified.

[0018] As a technical solution of the present application, in step S1, the CNC bending machine with model SKWB-2500 is used to perform shell flap forming, and the shell widths of the first layer shell, the second layer shell, the third layer shell and the outlet shell are all less than 2500 mm, and the welds between the first layer shell, the second layer shell, the third layer shell and the outlet shell are circumferential welds, and the vertical distance between the circumferential weld and the reinforcement ring is greater than 200 mm.

[0019] As a technical solution of the present application, in step S1, the projection surface of the front shell on the plane where the first end surface of the first layer shell away from the outlet is located is symmetrical about the first long axis and the first short axis respectively; the outer shell on the front shell corresponding to the area enclosed by multiple bicubic curves is a first ruled surface shell, and the outer shell corresponding to the area enclosed by multiple quintic curves is a second ruled surface shell; the shell on the front shell corresponding to the area enclosed by bicubic curves and quintic curves is a hyperbolic surface shell.

[0020] As a technical solution of the present application, in step S2, the principle of reserving pressing molding allowances for the shell petals whose ruled surface area accounts for more than 50% is as follows: reserving a pressing molding allowance of 2 to 4 mm along the transverse outer edge of the shell petals, and reserving a pressing molding allowance of 4 to 6 mm along the longitudinal outer edge; the principle of reserving pressing molding allowances for the shell petals whose hyperbolic surface area accounts for more than 50% is as follows: reserving a pressing molding allowance of 4 to 6 mm along the outer edges of the shell petals on the first layer of shell and the shell petals on the second layer of shell, reserving a pressing molding allowance of 8 to 10 mm along the transverse outer edge of the shell petals on the third layer of shell and the shell petals on the outlet shell, and reserving a pressing molding allowance of 4 to 6 mm along the longitudinal outer edge.

[0021] As a technical solution of the present application, in step S3, when assembling the first layer of the shell: before assembling the four shell petals at the two end points of the first long axis and the four shell petals at the two end points of the first short axis, the press-molded residues at the contact points of the outer edges of adjacent shell petals and the lower side of the shell petals are removed; before assembling other shell petals, the press-molded residues at the opposite sides and lower side of the outer edges of the shell petals are first removed, and then pre-assembly is performed, and finally the opposite sides and lower side of the outer edges of the shell petals are repaired for the second time.

[0022] As a technical solution of the present application, in step S3, when assembling the second layer of the shell: before assembling the two shell petals located at the two end points of the second long axis and the two shell petals at the two end points of the second short axis, first remove the press-molded excess at the opposite sides and lower side of the outer edge of the shell petals; before assembling the four shell petals close to the second short axis, first remove the press-molded excess at the outer edge of the shell petals close to the second short axis and lower side; before assembling the other shell petals, first remove the press-molded excess at the opposite sides and lower side of the outer edge of the shell petals, then perform pre-assembly, and finally perform a second trimming on the opposite sides and lower side of the outer edge of the shell petals.

[0023] As a technical solution of the present application, in step S3, when assembling the third shell layer: before assembling the hyperbolic shell petal close to the second ruled curved shell, the press-molding allowance on the lower side of the outer edge of the hyperbolic shell petal is removed; before assembling the other hyperbolic shell petals, the press-molding allowance on the outer edge of the other hyperbolic shell petals close to the third short axis and the lower side is removed; before assembling the remaining shell petals, the press-molding allowance on the opposite sides and the lower side of the outer edge of the shell petal is removed, and then pre-assembly is performed, and finally the opposite sides and the lower side of the outer edge of the shell petal are repaired for the second time.

[0024] As a technical solution of the present application, in step S3, when assembling the outlet shell: before assembling the hyperbolic shell petal close to the second ruled curved shell, the press-molding allowance on the lower side of the outer edge of the hyperbolic shell petal is removed; before assembling the other hyperbolic shell petals, the press-molding allowance on the outer edge of the other hyperbolic shell petals close to the outlet short axis and the lower side is removed; before assembling the remaining shell petals, the press-molding allowance on the opposite sides and lower side of the outer edge of the shell petal is removed, and then pre-assembly is performed, and finally the opposite sides and lower side of the outer edge of the shell petal are repaired for the second time.

[0025] As a technical solution of the present application, in step S3, when the remaining shell petals are assembled on the second-layer shell, the third-layer shell, and the outlet shell respectively, the horizontal projection lines of the longitudinal center lines of the shell petals of each layer on the plane where the first end face of the first-layer shell away from the outlet is located coincide with their corresponding long axes or short axes.

[0026] As a technical solution of the present application, in step S4, when spot welding is performed on the circumferential weld between the third shell and the outlet shell, the length of each spot weld is greater than 200 mm, and the spacing between adjacent spot welds is less than 100 mm.

[0027] As a technical solution of the present application, in step S6, each group of closing blocks includes matching convex blocks and concave blocks, and the convex blocks and the concave blocks are connected by mortise and tenon joints.

[0028] Beneficial effects of this application:

[0029] This application provides a method for fabricating a large austenitic stainless steel contraction section front shell. By developing a rational shell splitting scheme, the method allows for separation of ruled and hyperbolic shell surfaces, significantly reducing the difficulty of press-forming the contraction section front shell. Furthermore, the projections of the longitudinal outer edges of the shell petals onto the plane of the front shell inlet do not overlap with bicubic or quintic curves, significantly improving the surface accuracy of the shell where curvature changes dramatically after welding. Furthermore, the method reserves different press-forming allowances for the curved surface characteristics of different shell petals and utilizes different assembly processes, improving assembly efficiency while ensuring assembly accuracy and reducing assembly difficulty. Furthermore, the method employs a process where the contraction section front shell is assembled as a whole and then divided into two parts for flange machining, addressing the challenges of limited transportation and equipment during machining of large contraction section front shells. The method also utilizes closing blocks to ensure final assembly accuracy. Furthermore, the method ensures the positional accuracy of the base plate by installing and welding the base plate after flange machining. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate the following technical solutions of the present application.

[0031] Certain embodiments of the application should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 A schematic diagram of the front shell structure of the contraction section provided in an embodiment of the present application;

[0033] Figure 2 A schematic diagram of the front shell structure of the contraction section provided by an embodiment of the present application from a first angle;

[0034] Figure 3 A schematic diagram of the petal division of the housing provided in an embodiment of the present application;

[0035] Figure 4 A schematic diagram showing the first angle of division of the shell into petals provided in an embodiment of the present application;

[0036] Figure 5 A schematic diagram of the first process of assembling the housing provided in an embodiment of the present application;

[0037] Figure 6 A schematic diagram of the second process of assembling the housing provided in an embodiment of the present application;

[0038] Figure 7 A schematic diagram of the third process of assembling the housing provided in an embodiment of the present application;

[0039] Figure 8 A schematic diagram of the fourth process of assembling the housing provided in an embodiment of the present application;

[0040] Figure 9 A schematic diagram of the fifth process of assembling the housing provided in an embodiment of the present application;

[0041] Figure 10 A schematic diagram of the sixth process of assembling the housing provided in an embodiment of the present application;

[0042] Figure 11 A schematic diagram of the seventh process of assembling the housing provided in an embodiment of the present application;

[0043] Figure 12 A schematic diagram of the eighth process of assembling the housing provided in an embodiment of the present application;

[0044] Figure 13 A schematic diagram of the first process of manufacturing the front housing of the contraction section provided in an embodiment of the present application;

[0045] Figure 14 A schematic diagram of the second process of manufacturing the front housing of the contraction section provided in an embodiment of the present application;

[0046] Figure 15 A schematic diagram of the third process of manufacturing the front housing of the contraction section provided in an embodiment of the present application;

[0047] Figure 16 A schematic diagram of the fourth process of manufacturing the front housing of the contraction section provided in an embodiment of the present application;

[0048] Figure 17 A schematic diagram of the closing block structure provided in an embodiment of the present application.

[0049] Icons: 1-front shell of contraction section; 2-outer shell; 3-reinforcement ring; 4-base plate; 5-flange; 6-first short axis; 7-quintic curve; 8-bicubic curve; 9-first shell layer; 10-second shell layer; 11-third shell layer; 12-outlet shell; 13-shell petals; 14-first long axis; 15-closing block; 16-outlet; 17-inlet. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0051] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without making any creative efforts shall fall within the scope of protection of the present application.

[0052] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0053] In the description of this application, it should be noted that the terms "upper" and "lower" etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the invented product is usually placed when in use. These are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on this application.

[0054] In addition, in this application, unless otherwise expressly specified or limited, the phrase "a first feature is above or below a second feature" may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, the phrases "above, above, and above the second feature" may include the first feature being directly above and obliquely above the second feature, or simply indicate that the first feature is higher in level than the second feature. The phrases "below, below, and below the second feature" may include the first feature being directly below and obliquely below the second feature, or simply indicate that the first feature is lower in level than the second feature.

[0055] Furthermore, terms such as "horizontal" and "vertical" do not necessarily mean that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0056] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0057] Example:

[0058] Please refer to Figure 1 , with reference Figures 2 to 17 The subject of the solution of this embodiment is as follows Figure 1 As shown, it is a large austenitic stainless steel contraction section front shell, with an inlet 17 of φ11000mm and an outlet 16 of 7050mm. The contraction section front shell 1 consists of an outer shell 2, a reinforcement ring 3, a bottom plate 4, and a flange 5. The outer shell 2 is 20mm thick and made of S30403. The outer shell 2 of the contraction section front shell 1 is divided into a first shell 9, a second shell 10, a third shell 11, and an outlet shell 12 in sequence along the axial direction. The first shell 9, the second shell 10, the third shell 11, and the outlet shell 12 gradually approach the outlet 16. At the same time, the first shell 9 has an annular first end face and a second end face, the first end face is far away from the outlet 16, and the second end face is close to the outlet 16. The projection surface of the entire contraction section front shell 1 on the plane where the first end face is located is symmetrical about the first major axis 14 and the first minor axis 6 of the first shell 9. The outer shell 2 corresponding to the area enclosed by the multiple bicubic curves 8 on the contraction section front shell 1 is a first ruled surface shell. The outer shell 2 corresponding to the area enclosed by the multiple quintic curves 7 on the contraction section front shell 1 is a second ruled surface shell. In addition, the outer shell 2 corresponding to the area enclosed by the bicubic curves 8 and the quintic curves 7 on the contraction section front shell 1 is a hyperbolic surface shell.

[0059] like Figure 3 and Figure 4 As shown, the outer shell 2 is sequentially divided into a first shell 9, a second shell 10, a third shell 11, and an outlet shell 12, ensuring that the vertical distance between the girth welds between adjacent first shells 9, second shells 10, third shells 11, and outlet shells 12 is greater than 200 mm and the reinforcement ring 3. The first shell 9, second shell 10, third shell 11, and outlet shell 12 are then divided into a plurality of shell petals 13, ensuring that the maximum width of each shell petal 13 does not exceed 2500 mm. The principles for dividing the shell petals 13 are as follows: the first and second ruled curved shells of each layer are minimized from further division, the hyperbolic shell petals contain as little as possible of the first or second ruled curved shells, and the first or second ruled curved shells contain as little as possible of the hyperbolic shells, and the edges of each shell petal 13 are minimized from overlapping with the outer shell 2 corresponding to the area enclosed by the bicubic curve 8 and the quintic curve 7. Furthermore, the first shell 9 , the second shell 10 , and the third shell 11 are each divided into 12 shell petals 13 , and the outlet shell 12 is divided into 8 shell petals 13 .

[0060] The shell petals 13 are cut and a pressing allowance is reserved on the outer edge of the shell petals 13. The principle of reserving a pressing allowance for the shell petals 13 with a straight curved surface area accounting for more than 50% is as follows: the shell petals 13 have a pressing allowance of 2mm along the horizontal outer edge and a pressing allowance of 5mm along the longitudinal outer edge. The principle of reserving a pressing allowance for the shell petals 13 with a hyperbolic curved surface area accounting for more than 50% is as follows: the shell petals 13 on the first shell 9 and the second shell 10 have a pressing allowance of 5mm along the outer edge; the shell petals 13 on the third shell 11 and the outlet shell 12 have a pressing allowance of 10mm along the horizontal outer edge and a pressing allowance of 5mm along the longitudinal outer edge.

[0061] The blanked shell petals 13 are press-formed by a CNC plate bending machine of model SKWB-2500.

[0062] like Figures 5 to 12 As shown, the shell petals 13 are assembled, starting from the inlet 17 of the front shell 1 of the contraction section, vertically assembling the first shell 9 first, and then gradually assembling the second shell 10, the third shell 11, and the outlet shell 12.

[0063] Furthermore, when assembling the first shell 9, first assemble the eight shell petals 13 at the two end points of the first major axis 14 and the first minor axis 6 in sequence, and finally assemble the remaining four shell petals 13 in sequence; when assembling the second shell 10, first assemble the four shell petals 13 located on the second major axis and the second minor axis of the second shell 10 in sequence, then assemble the four shell petals 13 close to the second minor axis in sequence, and finally assemble the remaining four shell petals 13 in sequence; when assembling the third shell 11, first assemble the four hyperbolic shell petals on the third shell 11 close to the area corresponding to the quintic curve 7 in sequence, then assemble the remaining hyperbolic shell petals in sequence, and finally assemble the remaining four shell petals 13; when assembling the outlet shell 12, first assemble the four hyperbolic shell petals on the area corresponding to the quintic curve 7 close to the outlet shell 12, and finally assemble the remaining four shell petals 13. When assembling the remaining shell segments 13 from the second shell layer 10, third shell layer 11, and outlet shell layer 12, ensure that the horizontal projection of the longitudinal centerline of each shell segment 13 coincides with the major or minor axis of each layer. Furthermore, after the assembly and spot welding of each shell segment is complete, remove any excess material from the upper side of each segment.

[0064] Specifically, when assembling the first layer of the shell 9: before assembling the eight shell petals 13 close to the first long axis 14 and the first short axis 6 of the first layer of the shell 9, the contact positions of the outer edges of adjacent shell petals 13 and the press-molded margins on the lower side are removed; before assembling the remaining four shell petals 13, the press-molded margins on the left, right and lower sides of the outer edges of the shell petals 13 are removed, and then pre-assembly is performed, and finally the left, right and lower sides of the outer edges of the remaining four shell petals 13 are subjected to secondary repair.

[0065] When assembling the second shell 10: before assembling the four shell petals 13 located on the second long axis and the second short axis of the second shell 10, remove the press-molded excess on the left, right and lower sides of the outer edges of the shell petals 13; before assembling the four shell petals 13 close to the second short axis, remove the press-molded excess on the outer edges of the shell petals 13 close to the second short axis and the lower side; before assembling the remaining four shell petals 13, remove the press-molded excess on the left, right and lower sides of the outer edges of the shell petals 13, then perform pre-assembly, and finally perform secondary repairs on the left, right and lower sides of the outer edges of the remaining four shell petals 13.

[0066] When assembling the third shell 11: before assembling the four hyperbolic shell petals close to the second ruled curved shell, remove the press-molding allowance on the lower side of the outer edge of the hyperbolic shell petal; before assembling the remaining hyperbolic shell petals, remove the press-molding allowance on the outer edge of the hyperbolic shell petal close to the third short axis and the lower side of the third shell 11; before assembling the remaining four shell petals 13, remove the press-molding allowance on the left side, right side and lower side of the outer edge of the shell petal 13, then perform pre-assembly, and finally perform secondary repair on the left side, right side and lower side of the outer edge of the remaining four shell petals 13.

[0067] When assembling the outlet shell 12: before assembling the four hyperbolic shell petals close to the second ruled curved shell, remove the press-molded excess on the lower side of the outer edge of the hyperbolic shell petal; before assembling the remaining four shell petals 13, remove the press-molded excess on the opposite sides and lower side of the outer edge of the shell petal 13, then perform pre-assembly, and finally perform a second repair on the opposite sides and lower side of the outer edge of the shell petal 13.

[0068] like Figures 13 to 16 As shown, the splicing welds of the outer shell 2 are welded, and the circumferential welds between the third shell 11 and the outlet shell 12 are only spot welded. The length of each spot weld is more than 200 mm and the spacing is less than 100 mm. All welding is completed on the remaining splicing welds.

[0069] like Figures 13 to 17As shown, the reinforcement ring 3 on the exterior of the outer shell 2 is assembled and welded, followed by the flange 5. Four sets of closing blocks 15 are installed at positions corresponding to the major and minor axes of the girth weld between the third shell 11 and the outlet shell 12. Each set of closing blocks 15 consists of two trapezoidal blocks, one convex and the other concave, connected by a mortise and tenon joint. Finally, the spot weld between the third shell 11 and the outlet shell 12 is ground away.

[0070] like Figures 13 to 16 As shown, the outlet 16 of the front housing is disconnected from the inlet 17 of the front housing, and the flange 5 is machined on the outlet 16 of the front housing.

[0071] Close the machined outlet 16 and inlet 17, completing the girth weld at the joint. Using the machined surface of flange 5 as a reference, install and weld base plate 4. Turn the contraction section front housing 1 180° and align the machined surface elevations of flange 5. Using the machined surface of flange 5 as a reference, use a template to check for coordinate deviations in the internal profile of the contraction section front housing 1. Polish any unqualified sections with a grinding wheel until they meet the requirements.

[0072] In summary, this method, by developing a rational shell petal splitting scheme, minimizes the separation between the first and second ruled curved shells and the hyperbolic shell, significantly reducing the difficulty of press-forming. Furthermore, it minimizes overlap between the longitudinal outer edges of the shell petals 13 and the regions corresponding to the bicubic and quintic curves 8 and 7, significantly improving the surface accuracy of the shell where curvature changes dramatically after welding. Furthermore, this method reserves different press-forming allowances for the curved surface characteristics of different shell petals 13 and employs different assembly processes, improving assembly efficiency while ensuring assembly accuracy and reducing assembly difficulty. Secondly, by assembling the entire contraction section front shell 1 and then dividing it into two parts for machining the flange 5, this method addresses the challenges of limited transportation and equipment during machining of large contraction section front shells 1. The use of closing blocks 15 ensures final assembly accuracy. Furthermore, this method ensures the positional accuracy of the base plate 4 by installing and welding it after machining the flange 5. At the same time, it has developed a complex hyperbolic shell petal forming technology, which solves the problem that the shell around the bicubic curve 8 and the quintic curve 7 is difficult to press and form due to the drastic change in curvature, and the surface accuracy after welding is poor; in addition, it adopts a method of reserving different pressing and forming allowances and formulating different assembly orders according to the surface characteristics of different shell petals of the complex hyperbolic surface, which solves the problem of the inability to take into account both the shell assembly efficiency and assembly accuracy, and greatly reduces the difficulty of shell assembly.

[0073] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for manufacturing a large austenitic stainless steel contraction section front shell, characterized in that: The following steps are involved: S1. Determine a shell segmentation scheme. Based on the distribution position and size of the reinforcement ring on the front shell of the contraction section and the processing width of the CNC plate bending machine, axially and gradually approaching the outlet, the outer shell on the front shell is divided into a first shell layer, a second shell layer, a third shell layer, and an outlet shell layer. Then, each of the first shell layer, the second shell layer, the third shell layer, and the outlet shell layer is divided into multiple shell segments. S2, blanking all the shell petals of each layer, and leaving a press-forming margin on the outer edges of all the shell petals; using a CNC bending machine to press-form all the blanked shell petals; S3, assemble the shell petals vertically in sequence starting from the direction toward the inlet of the front shell, first assemble the shell petals on the first shell layer, and then gradually assemble the shell petals on the second shell layer, the shell petals on the third shell layer, and the shell petals on the outlet shell; when assembling the first shell layer, first assemble the four shell petals located at the two end points of the first long axis of the first shell layer and the four shell petals located at the two end points of the first short axis of the first shell layer, and then assemble the other shell petals close to the two end points of the first long axis and the first short axis of the first shell layer in sequence; when assembling the second shell layer, first assemble the four shell petals located at the two end points of the first long axis and the first short axis of the second shell layer the two shell petals at the two end points of the second major axis and the two shell petals at the two end points of the second minor axis of the second shell layer, and then assemble the four shell petals at the two end points of the second minor axis of the second shell layer in sequence, and finally assemble the other shell petals in sequence; when assembling the third shell layer, first assemble the hyperbolic shell petal corresponding to the quintic curve on the third shell layer, and then assemble the other hyperbolic shell petals in sequence, and finally assemble the other shell petals in sequence; when assembling the outlet shell, first assemble the hyperbolic shell petal corresponding to the quintic curve on the outlet shell layer, and then assemble the other hyperbolic shell petals in sequence, and finally assemble the other shell petals in sequence; S4, welding the joint welds on the outer shell, and spot welding the girth welds between the third shell and the outlet shell; S5, assembling and welding the reinforcement ring on the outside of the front shell, and then assembling and welding the flange on the front shell; S6, installing a set of closing blocks at both end points of the long axis and the short axis of the girth weld between the third shell and the outlet shell, and then grinding and removing the spot weld between the third shell and the outlet shell; S7, disconnecting the front housing outlet from the front housing inlet, and processing a flange at the front housing outlet; S8, closing the outlet and the inlet of the processed front shell, and welding the girth weld at the closing position; S9, installing and welding the base plate based on the machined surface of the flange; S10, flip the front shell of the contraction section 180 degrees, adjust the elevation of the machining surface of the flange to be consistent, and use a template to detect the coordinate deviation of the inner surface of the front shell of the contraction section with the machining surface of the flange as a reference. Use a grinding wheel to grind the inner surface of the front shell of the contraction section for unqualified parts until it is qualified.

2. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 1, characterized in that: In step S1, the shell widths of the first shell layer, the second shell layer, the third shell layer, and the outlet shell layer are all less than 2500 mm, and the welds between the first shell layer, the second shell layer, the third shell layer, and the outlet shell layer are girth welds, and the vertical distance between the girth welds and the reinforcement ring is greater than 200 mm.

3. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 1, characterized in that: In step S1, the projection surface of the front shell on the plane where the first end surface of the first layer shell away from the outlet is located is symmetrical about the first major axis and the first minor axis respectively; the outer shell on the front shell corresponding to the area enclosed by multiple bicubic curves is a first ruled surface shell, and the outer shell corresponding to the area enclosed by multiple quintic curves is a second ruled surface shell; the shell on the front shell corresponding to the area enclosed by the bicubic curves and the quintic curves is a hyperbolic surface shell.

4. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 3, characterized in that: In step S2, the principle of reserving press-molding allowances for the shell petals whose ruled surface area accounts for more than 50% is as follows: a press-molding allowance of 2 to 4 mm is reserved along the transverse outer edge of the shell petals, and a press-molding allowance of 4 to 6 mm is reserved along the longitudinal outer edge; the principle of reserving press-molding allowances for the shell petals whose hyperbolic surface area accounts for more than 50% is as follows: a press-molding allowance of 4 to 6 mm is reserved along the outer edges of the shell petals on the first layer of shell and the shell petals on the second layer of shell, and a press-molding allowance of 8 to 10 mm is reserved along the transverse outer edge of the shell petals on the third layer of shell and the shell petals on the outlet shell, and a press-molding allowance of 4 to 6 mm is reserved along the longitudinal outer edge.

5. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 1, characterized in that: In step S3, when assembling the first layer of the shell: before assembling the four shell petals at the two end points of the first long axis and the four shell petals at the two end points of the first short axis, the pressing and forming margins at the contact points of the outer edges of adjacent shell petals and the lower side of the shell petals are removed; before assembling other shell petals, the pressing and forming margins at the opposite sides and lower side of the outer edges of the shell petals are first removed, and then pre-assembly is performed, and finally the opposite sides and lower side of the outer edges of the shell petals are repaired for the second time.

6. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 1, characterized in that: In step S3, when assembling the second layer of the shell: before assembling the two shell petals located at the two end points of the second long axis and the two shell petals at the two end points of the second short axis, first remove the press-molded excess at the opposite sides and lower side of the outer edge of the shell petals; before assembling the four shell petals close to the second short axis, first remove the press-molded excess at the outer edge of the shell petals close to the second short axis and lower side; before assembling the other shell petals, first remove the press-molded excess at the opposite sides and lower side of the outer edge of the shell petals, then perform pre-assembly, and finally perform a second repair on the opposite sides and lower side of the outer edge of the shell petals.

7. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 3, characterized in that: In step S3, when assembling the third layer of the shell: before assembling the hyperbolic shell petal close to the second ruled curved shell, the press-molding allowance on the lower side of the outer edge of the hyperbolic shell petal is removed; before assembling the other hyperbolic shell petals, the press-molding allowance on the outer edges of the other hyperbolic shell petals close to the third short axis and the lower side is removed; before assembling the remaining shell petals, the press-molding allowance on the opposite sides and the lower side of the outer edge of the shell petal is removed, and then pre-assembly is performed, and finally the opposite sides and the lower side of the outer edge of the shell petal are repaired for the second time.

8. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 3, characterized in that: In step S3, when assembling the outlet shell: before assembling the hyperbolic shell petal close to the second ruled curved shell, the press-molding allowance on the lower side of the outer edge of the hyperbolic shell petal is removed; before assembling the other hyperbolic shell petals, the press-molding allowance on the outer edge of the other hyperbolic shell petals close to the short axis and the lower side of the outlet of the front shell is removed; before assembling the remaining shell petals, the press-molding allowance on the opposite sides and the lower side of the outer edge of the shell petal is removed, and then pre-assembly is performed, and finally the opposite sides and the lower side of the outer edge of the shell petal are repaired for the second time.

9. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 1, characterized in that: In step S4, when spot welding is performed on the girth weld between the third shell and the outlet shell, the length of each spot weld is greater than 200 mm, and the spacing between adjacent spot welds is less than 100 mm.

10. The method for manufacturing a large austenitic stainless steel contraction section front shell according to claim 1, characterized in that: In step S6, each group of closing blocks includes a convex block and a concave block that match each other, and the convex block and the concave block are connected by mortise and tenon joints.

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