Manufacturing method of a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure

Abstract

The present invention discloses a manufacturing method of a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure, comprising the following steps: a. obtaining an intermediate product of a high-precision heat transfer tube light tube; b. performing a first cold working on the intermediate product to form the internal tooth structure of the whole tube, but the tooth shape size is slightly higher and narrower than the final tooth shape, obtaining an intermediate product with teeth; c. performing a second cold working on one end of the intermediate product with teeth to reduce the diameter and wall thickness, the wall thickness reduction being S1, and at this time the internal die tooth shape structure is the final tooth shape size, obtaining a small-diameter section; d. performing a third cold working on the other end of the intermediate product with teeth starting from the cold working stop position of the small-diameter section to reduce the diameter and wall thickness, the wall thickness reduction being S2, S2 < S1, and at this time the internal die tooth shape structure is the final tooth shape size, obtaining a large-diameter section. The seamless heat transfer tube prepared by the present invention has the characteristics of high dimensional accuracy, a special internal surface structure, variable outer diameter and smooth transition, and excellent straightness of the tube body, and can simultaneously realize the functions of heat transfer and providing a medium flow channel.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat transfer tubes for high-end equipment and new energy systems, and particularly relates to a manufacturing method for a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure. Background Art

[0002] With the development of the high-end equipment industry and the new nuclear energy system industry, the miniaturization, modularization, and high efficiency of equipment are inevitable development trends. Especially for new nuclear energy systems, it is required to have a high power generation capacity, consider a small volume, and improve safety and reliability at the same time. Therefore, optimizing the reactor structure design, improving the heat transfer efficiency, and reducing the risk weak links of material use are the keys to enhancing the competitiveness of this technology.

[0003] The heat transfer tube is a core component material in the reactor, and its function is to conduct the heat generated in the core of the nuclear reactor to the outside of the core for secondary circuit power generation. The inner surface of the heat transfer tube for the new nuclear energy system needs to be designed with a medium flow channel; the outer surface is mainly divided into two parts: the outer surface at one end of the core is a smooth tube, and the outer surface at the end outside the core is designed with a finned structure to enhance heat dissipation by increasing the outer surface area of the tube.

[0004] In order to improve the overall performance consistency of the tube and reduce welding and internal weak links, it is necessary to form the above complex structure integrally as much as possible, so new requirements are put forward for the manufacturing process.

[0005] Generally, the heat transfer tube is a conventional structure steel tube. In order to enhance heat dissipation, a certain number of fins are processed in a certain area on the outer surface of the steel tube. The inner wall of the tube is generally a smooth tube structure, and then a medium flow channel is constructed by adding other materials such as mesh and sleeves into the tube. However, there are several problems in such conventional products and manufacturing technologies:

[0006] (1) Most steel tubes are welded steel tubes, and the weld area is a weak link and potential high-risk area of the material. During long-term operation, it is easy to fail in this area, affecting the system operation.

[0007] (2) After the fins are processed and formed, the remaining wall thickness of the tube body in the fin area is inconsistent with the wall thickness of the tube body without fins. The fin area is thinner, and during long-term operation, the thin-wall area is more likely to have a failure risk. Moreover, the wall thickness of the tube body without fins is too thick, which is not conducive to heat transfer of the tube body and has low efficiency.

[0008] (3) The medium flow channel constructed by adding other materials such as mesh and sleeves in the tube is unstable, and it is easy to have situations such as blockage and interface fitting. And due to the additional materials, the overall structure is uneven, and the heat transfer efficiency between different tubes is inconsistent. Summary of the Invention

[0009] The object of the present invention is to provide a manufacturing method for a high-precision seamless heat transfer tube with an internal tooth structure and variable diameter, which integrally realizes the manufacturing of the internal tooth groove structure and the outer diameter variable diameter structure on a single pipe, and the obtained heat transfer tube has the functions of heat transfer and providing a medium flow channel at the same time.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A manufacturing method for a high-precision seamless heat transfer tube with an internal tooth structure and variable diameter, the inner wall of the seamless heat transfer tube has longitudinal tooth-shaped grooves, and the outer diameter includes a small-diameter section and a large-diameter section integrally connected; it is characterized by including the following steps:

[0012] a. Process the tube blank to obtain an intermediate product of a high-precision heat transfer tube light tube.

[0013] b. Use a tooth-shaped internal mold to perform the first cold processing on the intermediate product to form the internal tooth structure of the entire pipe; the tooth shape size is slightly higher and narrower than the final tooth shape, and an intermediate product with teeth is obtained.

[0014] c. Perform the second cold processing on one end of the intermediate product with teeth to reduce the diameter and wall thickness; the wall thickness reduction is S1, and at this time, the tooth shape structure of the internal mold is the final tooth shape size, and a small-diameter section is obtained.

[0015] d. Perform the third cold processing on the other end of the intermediate product with teeth starting from the stop point of the cold processing of the small-diameter section to reduce the diameter and wall thickness, and the wall thickness reduction is S2, S2 < S1, and at this time, the tooth shape structure of the internal mold is the final tooth shape size, and a large-diameter section is obtained.

[0016] Since the inner wall of the seamless heat transfer tube in the present invention has longitudinal tooth-shaped grooves and the outer part has a variable diameter structure at the same time, the structure is complex. During the processing, it not only involves diameter reduction and wall thickness reduction, but also the forming process of the special-shaped inner wall. If the inner wall forming and diameter reduction and wall thickness reduction are simply carried out at the same time, the wall thickness reduction per single pass of the pipe is too large, and the precision rolling of this specification of pipe cannot be guaranteed. Therefore, considering the requirements of both inner tooth forming and variable diameter forming, three passes of cold processing are determined. In addition, the tooth shape size of the intermediate product is slightly higher and narrower than the final tooth shape, which can ensure that the inner teeth of the intermediate product are aligned with the internal mold during the second and third cold processing, ensuring dimensional accuracy. If the minimum distance between the tooth vertices on the inner surface of the intermediate product is too large, it may cause the internal mold teeth and the intermediate product teeth not to be aligned in the subsequent passes, and the inner teeth will be flattened during the subsequent processing of the variable diameter pipe, and it is impossible to achieve both having inner teeth and being able to process variable diameter.

[0017] It is further characterized in that: the final tooth height h of the inner wall of the seamless heat transfer tube, the width of the top of the final tooth is c1, and the width of the bottom is c2; in step b, the height of each inner tooth of the toothed intermediate product after the first cold working is controlled at 1.2 - 1.5h, and each tooth forms a nearly trapezoidal shape with a rounded chamfer. The width of the top of the tooth is controlled at 0.5 - 0.8c1, and the width of the bottom is 0.5 - 0.8c2. The parameter setting of the toothed intermediate product after the first cold working can ensure that the inner die can be smoothly inserted into the inside of the pipe during the second and third cold workings for subsequent processing.

[0018] Furthermore: the wall thickness of the small-diameter section is 0.4 - 0.95 times that of the large-diameter section.

[0019] Preferably: in step c, the second cold working and in step d, the third cold working are carried out with the same inner die.

[0020] A combination method of cold working: when the deformation amount during the third cold working exceeds 30%, or when the wall thickness reduction amount during the third cold working exceeds 0.5 mm, all three cold working processes are cold rolling.

[0021] Another combination method of cold working: when the deformation amount during the third cold working does not exceed 30% and the wall thickness reduction amount during the third cold working does not exceed 0.5 mm, the first and second cold working processes are both cold rolling, and the third cold working process is cold drawing.

[0022] Preferably: a spiral fin structure can be processed on the outer surface of the large-diameter section of the pipe by roll pressing or cutting to prepare a finned tube with an inner tooth structure.

[0023] The present invention has the following beneficial effects:

[0024] For the variable-diameter seamless heat transfer tube with an inner tooth structure prepared by the method of the present invention, the internal tooth groove structure and the outer diameter variable-diameter structure are integrally manufactured on one pipe. The product has high dimensional accuracy, a special inner surface structure, a smooth outer diameter variable-diameter and transition, and excellent straightness of the pipe body, and can simultaneously realize the functions of heat transfer and providing a medium flow channel. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of a high-precision variable-diameter seamless heat transfer tube with an inner tooth structure.

[0026] Figure 2 It is a sectional view of the tooth groove structure.

[0027] Figure 3 It is a schematic diagram of the forming principle of Embodiment 1.

[0028] Figure 4 It is a schematic structural diagram of a finned tube with an inner tooth structure.

[0029] In the figure, 1 - tooth-shaped groove, 2 - small-diameter section, 3 - transition section, 4 - large-diameter section, 40 - fin heat dissipation structure, 41 - plain tube section, 42 - heat dissipation section, 43 - tube-end plain tube section. Specific embodiments

[0030] The following further elaborates in detail in combination with the embodiments and drawings of the present invention. Embodiment 1

[0031] As Figure 1 shown, a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure includes longitudinally evenly distributed tooth-shaped grooves 1 on the inner surface, and the outer surface is divided into a small-diameter section 2, a transition section 3, and a large-diameter section 4 according to the outer diameter size; the small-diameter section 2 and the large-diameter section 4 are connected through the transition section 3; the specific dimensions are as follows:

[0032] (1) The total length of the tube body is 5150 mm;

[0033] (2) There are 20 tooth-shaped grooves 1 on the inner surface of the whole tube, each tooth height is 0.5 mm, the width at the top of the tooth is about 0.3 mm, the width at the bottom is 0.6 mm, and a single tooth forms a nearly trapezoidal shape with a rounded chamfer. The cross-sectional view of the tooth groove structure is as Figure 2 shown;

[0034] (3) The outer diameter of the tube body in the small-diameter section 2 is Φ20 mm, the outer diameter deviation is ±0.05 mm, the wall thickness is 1 mm, and the length is 2500 mm;

[0035] (4) The outer diameter of the tube body in the large-diameter section 4 is Φ22 mm, the wall thickness is 2 mm, and the length is 2500 mm;

[0036] (5) The difference in wall thickness between the tube body in the large-diameter section 4 and the tube body in the small-diameter section 2 is 1 mm;

[0037] (6) The tube body of the transition section 3 has a length of 150 mm, and the inside is a tooth-groove structure consistent with that of the small-diameter section and the large-diameter section, and the outside is an inclined surface structure.

[0038] As Figure 3 shown, a manufacturing method of a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure includes the following steps:

[0039] a. Select a suitable round steel with a specification of Φ130 mm for piercing, and then obtain an intermediate product of a high-precision heat transfer tube plain tube with a specification of Φ38 mm × 3 mm through multi-pass cold rolling deformation and heat treatment.

[0040] b. Perform the first cold working on the intermediate product. After cold rolling, the outer diameter is Φ24 mm and the nominal wall thickness is 2.5 mm. At the same time, the internal tooth structure of the whole pipe is formed. Each internal tooth has a tooth height of 0.6 mm. A single tooth forms a nearly trapezoidal shape with a rounded chamfer. The width at the top of the tooth is about 0.2 mm, and the width at the bottom is 0.4 mm. The tooth shape size is slightly higher and narrower than the final tooth shape, obtaining an intermediate product with teeth.

[0041] c. Perform the second cold working on one end of the intermediate product with teeth, reducing the diameter and wall thickness. The diameter reduction is 24 - 20 = 4 mm, and the wall thickness reduction is 2.5 - 1 = 1.5 mm. At this time, the internal die tooth shape structure is the final tooth shape size with a tooth height of 0.5 mm, a width at the top of the tooth of about 0.3 mm, and a width at the bottom of 0.6 mm. At the same time, a small-diameter section with an outer diameter of Φ20 mm and a nominal wall thickness of 1 mm is obtained. The second cold rolling stops at 2500 mm, leaving a cone as a transition section.

[0042] d. Perform the third cold working on the other end of the intermediate product with teeth starting from the stop point of the cold working of the small-diameter section, reducing the diameter and wall thickness. The diameter reduction is 24 - 22 = 2 mm, and the wall thickness reduction is 2.5 - 2 = 0.5 mm. At this time, the internal die is the same size as the internal die in the second cold working, and the tooth shape structure is the final tooth shape size, obtaining a large-diameter section with an outer diameter of Φ22 mm and a nominal wall thickness of 2 mm. The third cold rolling can be rolled more than 2500 mm. While ensuring that the pipe length meets the final size requirements, a length margin for subsequent processing can be left at the end.

[0043] In the above manufacturing method, the tooth shape of the intermediate product is specially designed so that the minimum distance between the tooth vertices on the inner surface of the intermediate product is 17.8 mm, which is exactly less than the maximum diameter value of the internal die, 18 mm, during the second and third cold workings (design the inner diameter and tooth height values of the intermediate product so that the minimum distance between the tooth vertices on the inner surface of the intermediate product is 10% - 15% less than the maximum diameter value of the internal die during the second and third cold workings), ensuring that the internal teeth of the intermediate product can be aligned with the internal die during the second and third cold workings and ensuring dimensional accuracy. At the same time, the widths at the top and bottom of the intermediate product teeth are slightly narrower (designed to be 0.5 - 0.8 times the final size), and the nominal inner diameter is 19 mm, which is greater than the maximum diameter value of the internal die, 18 mm (ensuring that the clearance between the feeding inner diameter and the internal die in the subsequent pass is more than 0.5 mm). Therefore, it can be ensured that the internal die during the second and third cold workings can be smoothly inserted into the pipe for subsequent processing.

[0044] After the second cold working is completed, since the reduction in diameter and wall thickness of the small-diameter section is large, the outer diameter of the pipe is smaller than the inner diameter of the outer die in the third cold working, and it can be smoothly fed for further processing.

[0045] During the second and third cold working processes, either continuous operation or two-stage operation can be adopted, and the inner die dimensions remain consistent, so that the tooth-shaped structure on the inner surface of the finally processed pipe can be ensured to be consistent throughout the whole pipe. For the above-mentioned third cold working process, either cold rolling forming or cold drawing forming can be selected. When cold drawing forming is selected, the inner die dimensions of cold drawing are consistent with the structure of the inner die of cold rolling.

[0046] During the above-mentioned second and third cold working processes, the diameter and wall thickness reduction can be carried out once or in multiple times, and the amount of diameter and wall thickness reduction each time can be adjusted until the diameter and wall thickness reduction meet the design requirements, which is easy to understand for those skilled in the art. Example Two

[0047] The variable-diameter seamless heat transfer pipe prepared in Example One is further processed to make a finned pipe with an inner tooth structure.

[0048] As Figure 4 shown, a finned pipe with an inner tooth structure includes longitudinally evenly distributed tooth-shaped grooves 1 on the inner surface, a small-diameter section 2, a transition section 3, and a large-diameter section 4 on the outer surface divided according to the outer diameter size. The small-diameter section 2 is connected to the large-diameter section 4 through the transition section 3; the large-diameter section 4 includes a smooth pipe section 41 connected to the transition section 3, a heat dissipation section 42 provided with a fin heat dissipation structure 40, and a pipe-end smooth pipe section 43.

[0049] The fin heat dissipation structure 40 is a spiral structure on the outer surface of the heat dissipation section 42 and is an integral spiral structure with the heat dissipation section 42, with a pitch of 1 mm and a fin thickness of 0.3 times the pitch.

[0050] The specific dimensions of a finned pipe with an inner tooth structure are as follows:

[0051] (1) The total length of the pipe body is 5150 mm;

[0052] (2) There are 20 longitudinal groove teeth evenly distributed on the inner surface of the whole pipe for the tooth-shaped grooves 1, each tooth height is 0.5 mm, the width at the top of the tooth is about 0.3 mm, the width at the bottom is 0.6 mm, and a single tooth forms a nearly trapezoidal shape with a round chamfer. The cross-sectional view of the tooth groove structure is as Figure 2 shown;

[0053] (3) The outer diameter of the pipe body in the small-diameter section 2 is Φ20 mm, the outer diameter deviation is ±0.05 mm, the wall thickness is 1 mm, and the length is 2500 mm;

[0054] (4) The outer diameter of the pipe body in the large-diameter section 4 is Φ22 mm, the wall thickness is 2 mm, and the length is 2500 mm;

[0055] (4) The difference in wall thickness between the pipe body in the large-diameter section 4 and the pipe body in the small-diameter section 2 is 1 mm;

[0056] (6) The tube body of the transition section 3 has a length of 150 mm. Inside, it has a toothed groove structure consistent with that of the small-diameter section and the large-diameter section, and its outside has an inclined surface structure;

[0057] (7) The smooth tube section 41 connected to the transition section 3 has an outer diameter of Φ22 mm and a length of 200 mm;

[0058] (8) The heat dissipation section 42 has a length of 2000 mm;

[0059] (9) The other smooth tube section 43 has an outer diameter of Φ22 mm and a length of 300 mm;

[0060] (10) After processing, the height of the fin 40 is ≥1.0 mm, and the remaining thickness is ≥1.0 mm.

[0061] The preparation method of the finned tube with the internal tooth structure is as follows:

[0062] S1. Use the product prepared in Example 1;

[0063] S2. Adopt a rolling or cutting processing method to process a spiral structure on the outer surface of the large-diameter heat dissipation section tube body. The pitch is 1 mm, and the fin thickness is 0.3 times the pitch. At both ends of the outer surface of the large-diameter section tube body where the spiral structure is not processed, that is, the smooth tube 41 connected to the transition section 3 and the other smooth tube section 43, retain the smooth tube structure with an outer diameter of Φ22 mm.

[0064] S3. Heat-treat the tube body. The heat treatment temperature is 1020 °C, and keep it warm for 10 min; after the heat preservation ends, cool the tube body to below 100 °C, and the cooling rate is ≥150 °C / min; thus obtain the product.

Claims

1. A method for manufacturing a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure, wherein the inner wall of the seamless heat transfer tube has a longitudinal toothed groove, and the outer diameter includes a small diameter section and a large diameter section connected in one piece; characterized in that The following steps are involved: a. Process the tube blank to obtain a high-precision heat transfer tube intermediate product; b. Use the toothed inner die to perform the first cold working on the intermediate product, reduce the diameter and wall, and form the internal tooth structure of the entire pipe; the tooth shape is slightly higher and narrower than the final tooth shape, and the intermediate product with teeth is obtained; c. Perform a second cold working on one end of the toothed intermediate product to reduce the diameter and wall; the wall reduction amount is S1, at which point the inner die tooth profile structure is the final tooth profile size, and a small diameter section is obtained; d. The other end of the toothed intermediate product is subjected to a third cold working from the point where the cold working of the small diameter section stops, so as to reduce the diameter and wall. The wall reduction amount is S2, S2<S1. At this time, the inner die tooth profile structure is the final tooth profile size, and the large diameter section is obtained; The final tooth profile height of the inner wall of the seamless heat transfer tube is h, the final tooth top width is c1, and the bottom width is c2; the tooth height of each inner tooth of the toothed intermediate product subjected to the first cold working in step b is controlled to be 1.2-1.5h, and a single tooth is formed into a nearly trapezoidal shape with rounded chamfers, the tooth top width is controlled to be 0.5-0.8c1, and the bottom width is 0.5-0.8c2; The wall thickness of the small diameter section is 0.4 to 0.95 times the wall thickness of the large diameter section.

2. The method for manufacturing a high-precision seamless heat transfer tube with internal teeth structure as claimed in claim 1, characterized in that: The second cold working in step c and the third cold working in step d adopt the same inner mold.

3. The method for manufacturing a high-precision seamless heat transfer tube with internal teeth structure as claimed in claim 1, characterized in that: The three cold working processes are all cold rolling.

4. The method for manufacturing a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure according to claim 1, characterized in that: The first and second cold working processes are cold rolling, and the third cold working process is cold drawing.

5. The method for manufacturing a high-precision variable-diameter seamless heat transfer tube with an internal tooth structure according to claim 1, characterized in that: The spirally structured fins are processed on the outer surface of the large-diameter tube body by rolling or cutting to prepare a fin tube with an internal tooth structure.

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