An Adaptive Support Method and Device for U-Shaped Welded Joints during Hydraulic Bulging of Serpentine Coils

Abstract

The present invention belongs to the technical field of hydraulic bulging of serpentine coils in refrigeration and air-conditioning heat exchangers, and provides an adaptive support method and device for U-shaped welded joints during the hydraulic bulging of serpentine coils. The device includes a serpentine coil, a U-shaped welded joint, a pipe end seal head, a support block, a support cylinder, a movable crossbeam, a hydraulic pipeline, a hydraulic system, a hydraulic medium, and a workbench. The pipe end seal head and the support cylinder are provided with liquid filling holes and are connected to the hydraulic system through the hydraulic pipeline. During hydraulic bulging, the pressure p acts on the piston of the support cylinder and the inner surface of the serpentine coil simultaneously. The support force exerted by the support cylinder on the U-shaped welded joint is determined by the bulging pressure p, and the adaptive adjustment of the support force can be realized, significantly reducing the tensile force on the weld seam, thereby avoiding the risk of cracking of the weld seam due to excessive tensile force. By adjusting the number, position of the support cylinders and the shape of the support blocks, the present invention can adapt to serpentine coils with different lengths, different pipe spacings and different welded joint sizes, with high flexibility and strong adaptability.

Description

Technical Field

[0001] The invention belongs to the technical field of hydraulic bulging of serpentine coils in refrigeration and air-conditioning heat exchangers, and relates to a method and device for self-adaptive support of U-shaped welded joints during the hydraulic bulging of serpentine coils. Specifically, it relates to a method and device for applying self-adaptive axial support to the U-shaped welded joints by an external loading unit to offset the axial tension formed at the weld of the U-shaped joint under the action of internal pressure, thereby avoiding the risk of weld cracking due to being pulled apart. Background Art

[0002] In the refrigeration and air-conditioning industry, the serpentine coil, as a pipeline for refrigerant circulation, is a core component of heat exchangers such as condensers and evaporators, and is welded by several pipe segments and U-shaped welded joints. A large number of fins are installed on the outer side of the serpentine coil, greatly increasing the heat exchange area between the heat exchanger and the external environment. The heat carried by the refrigerant is first transferred to the serpentine coil, and then the serpentine coil transfers the heat to the fins. Finally, the outer surface of the fins and the exposed part of the pipe transfer the heat to the external environment.

[0003] The matching state between the serpentine coil and the fins is one of the key factors affecting the heat exchange efficiency of the heat exchanger. If the pipe and the fins are in an interference fit state, there is an air gap between the pipe and the fins. When the heat is transferred from the pipe to the fins, most of it is carried out by convection and radiation, and the heat transfer coefficient is much lower than the heat conduction coefficient in the direct contact state. Therefore, only when the pipe and the fins are in close contact can the heat be quickly transferred from the pipe to the fins, and the larger the contact area between the pipe and the fins and the greater the contact pressure of the contact surface, the greater the heat transfer coefficient between the two. Correspondingly, the heat exchange efficiency of the heat exchanger is also higher.

[0004] There are various traditional manufacturing methods for heat exchangers. Among them, the mechanical bulging method mainly has three steps (Zhu Bo. Difficulties and solutions of the threading, tube expanding, and welding processes of small-diameter tube-fin heat exchangers [J]. Home Appliance Science & Technology, 2017(11): 86 - 88): (1) Threading, assembling the pipe and the fins in an interference fit manner; (2) Tube expanding, bulging the pipe segment by a mechanical expanding bead to eliminate the gap between the pipe and the fins and form an interference fit; (3) Welding, using U-shaped welded joints to connect each pipe segment into a whole. The principle of mechanical bulging is to push a mechanical expanding bead with a diameter larger than the inner diameter of the pipe into the pipe by a push rod. The expanding bead generates pressure on the inner wall of the pipe, causing the pipe to undergo plastic deformation axially in sequence and the diameter to increase, thereby achieving close contact between the outer surface of the pipe and the fins. The mechanical bulging method is easy to operate, but the force exerted by the mechanical expanding bead on the inner wall of the pipe is uneven during bulging, and it is easy to produce defects such as bulging and bursting.

[0005] The hydroforming method (Yang Hui. Development and Application of Tube and Tube Sheet Expansion Technology [J]. Dongfang Electric Review, 2013, 27(2): 32-35. Diao Bingbing, Zhou Jiping, Cao Jin, etc. Application Research of Hydroexpansion Technology in the Production of Tube-Fin Oil Coolers [J]. Journal of Mechanical Design and Manufacturing Engineering, 2016, 45(8): 91-94) can overcome the problem of uneven acting force in the mechanical forming method. Its principle is to apply a uniform load to the inner wall of the tube using a liquid medium, and the tube undergoes expansion simultaneously at each position along the axial direction, with more uniform deformation. Therefore, the contact quality between the tube and the fin obtained by the hydroforming method is better, and the heat transfer efficiency is also higher.

[0006] The steps of manufacturing a heat exchanger using the hydroforming method are different from those using the mechanical forming method. After completing the clearance assembly of the tubes and fins, first use U-shaped welded joints to connect each tube section into a whole, and then achieve the interference fit between the tubes and fins through the hydroexpansion process. In this way, only two tube end seals and one liquid filling and pressurization are required to achieve the overall expansion of the serpentine coiled tube.

[0007] However, when hydroforming a serpentine coiled tube with U-shaped welded joints, the internal pressure will generate obvious axial tension at the weld between the U-shaped joint and the tube section. Taking a smooth tube with a circular cross-section as an example, the axial force F generated by the pressure p acting on the inner surface of the U-shaped welded joint p can be calculated by the following formula:

[0008] F p = 2p×S g = p×πD g 2 / 2 (1)

[0009] In the formula, D g is the inner diameter of the tube, and S g is the inner hole area of the tube.

[0010] The greater the hydroforming internal pressure p, the greater the generated axial force F p is, and the greater the tensile force formed at the weld. The weld is prone to cracking and failure under the action of the tensile force. To avoid excessive tensile force at the weld and eliminate the risk of weld cracking under tension, a convenient and effective method and device are needed to apply appropriate supporting force to the U-shaped joint to partially or completely offset the axial force generated by the internal pressure. Summary of the Invention

[0011] The purpose of the present invention is to provide an adaptive support method and device for U-shaped welded joints during the hydroforming of serpentine coiled tubes, to solve the problem that the weld of the U-shaped joint is prone to cracking under tension during the hydroforming of serpentine coiled tubes, and to achieve high-quality and high-efficiency hydroforming of serpentine coiled tubes.

[0012] The technical solution of the present invention:

[0013] An adaptive support device for U-shaped welded joints during the hydraulic bulging of a serpentine coiled pipe, comprising a serpentine coiled pipe 1, a support block 2, a support cylinder 3, a pipe end seal head 4, a movable crossbeam 5, a workbench 6, a hydraulic pipeline 7, and a hydraulic system 8; the movable crossbeam 5 and the workbench 6 are arranged opposite to each other, the workbench 6 is fixed, and the movable crossbeam 5 can move up and down; two pipe end seal heads 4 are installed on the lower surface of the movable crossbeam 5 and are coaxial with the two pipe ends of the serpentine coiled pipe 1; the support block 2 is installed on the piston rod of the support cylinder 3, and the cylinder body of the support cylinder 3 is installed on the upper surface of the workbench 6 and the lower surface of the movable crossbeam 5, and the installation positions correspond to the U-shaped bend vertices of the serpentine coiled pipe 1; the pipe end seal head 4 and the support cylinder 3 are processed with liquid filling holes and are connected to the hydraulic system 8 through the hydraulic pipeline 7.

[0014] The serpentine coiled pipe 1 is composed of a pipe section 1-1 and a U-shaped welded joint 1-2 which are welded together.

[0015] The hydraulic action area S of the support cylinder 3 z After being determined, the support force F applied to the U-shaped welded joint 1-2 z Is determined by the bulging pressure p and increases with the increase of p, realizing the adaptive adjustment of the support force F z Of.

[0016] The support cylinder 3 has a certain action stroke and the support cylinders communicate with each other. The hydraulic medium flows to the support cylinder 3 that requires more hydraulic medium according to the different force-bearing conditions of each support cylinder. Therefore, even if the heights of the U-shaped welded joints 1-2 of the serpentine coiled pipe 1 are inconsistent, the support cylinder 3 adapts to the position of the U-shaped welded joint 1-2, and can ensure good support for the U-shaped welded joint 1-2.

[0017] An adaptive support method for U-shaped welded joints during the hydraulic bulging of a serpentine coiled pipe, the technical principle of which is as Figures 1 - 4 Shown, the contact between the support block 2 on the support cylinder 3 and the serpentine coiled pipe 1 is controlled by the hydraulic system 8. During hydraulic bulging, the hydraulic pressure p output by the hydraulic system 8 acts on the piston of the support cylinder 3 and the inner surface of the serpentine coiled pipe 1 at the same time; control the hydraulic action area S of the support cylinder 3 z =πD z 2 / 4 is the inner hole area S of the pipe section 1-1 g =πD g 2 / 4 is 1 to 3 times. When the hydraulic system 8 is filled with the hydraulic pressure p, the support force F generated by the support cylinder 3 z =p×S z , the axial force generated by the uniform action of the hydraulic pressure p on the inner surface of the U-shaped welded joint 1-2 is F p =2p×S g , then, the axial force F acting on a single weldh It is:

[0018] F h = (F p -F z ) / 2 = p(S g -0.5S z ) (2)

[0019] Wherein, D z is the piston diameter of the support cylinder, and D g is the inner diameter of the pipe section 1-1.

[0020] Therefore, under the support conditions of the present invention, the axial force range of the weld is -F p / 4 to F p / 4, which is significantly lower than the tensile force F p / 2 of the weld without support conditions. When the hydraulic action area S z of the support cylinder 3 is less than 2S g , the axial force of the weld can be adjusted to axial pressure.

[0021] Advantages of the present invention:

[0022] (1) The adaptive support force F z provided in the present invention and the axial force F p generated by the pressure p acting on the inner surface of the U-shaped welded joint always maintain a fixed proportional relationship. The support force F z adapts to changes in the pressure p, significantly reducing the tensile force on the weld, thereby avoiding the risk of cracking due to excessive tensile force on the weld.

[0023] (2) The support method and device provided by the present invention can adapt to the position of the U-shaped welded joint of the serpentine coiled pipe, and can ensure good support for the joint.

[0024] (3) The adaptive support method and device for the U-shaped welded joint during the hydraulic bulging of the serpentine coiled pipe of the present invention can simultaneously achieve the adaptive support of multiple groups of U-shaped welded joints, with simple operation, reliable support and high efficiency.

[0025] (4) The adaptive support method and device for the U-shaped welded joint during the hydraulic bulging of the serpentine coiled pipe of the present invention can adapt to serpentine coiled pipes with different lengths, different pipe spacings and different welded joint sizes by adjusting the number, position of the support cylinders and the shape of the support blocks, with high flexibility and strong adaptability.

[0026] (5) The adaptive support method and device for the U-shaped welded joint during the hydraulic bulging of the serpentine coiled pipe of the present invention can be applied to pipes with different cross-sections, such as Figures 7 - 9 the smooth pipe, inner-toothed pipe and outer-toothed pipe shown in Description of the Drawings

[0027] Figure 1 This is the schematic diagram of the self - adaptive support for the U - shaped welded joint provided by the present invention.

[0028] Figure 2 This is the force analysis diagram of the U - shaped welded joint.

[0029] Figure 3 This is the cross - sectional view of the support cylinder body ( Figure 1 section A - A in).

[0030] Figure 4 This is the cross - sectional view of the pipe ( Figure 1 section B - B in).

[0031] Figure 5 This is the schematic diagram of the self - adaptive support device for the U - shaped welded joint during the hydraulic expansion of the serpentine coiled pipe in the initial state provided by the present invention.

[0032] Figure 6 This is the schematic diagram of the self - adaptive support device for the U - shaped welded joint during the hydraulic expansion of the serpentine coiled pipe in the expanded state provided by the present invention.

[0033] Figure 7 This is the cross - sectional schematic diagram of the smooth pipe applicable to the present invention.

[0034] Figure 8 This is the cross - sectional schematic diagram of the internal - toothed pipe applicable to the present invention.

[0035] Figure 9 This is the cross - sectional schematic diagram of the internal - toothed pipe applicable to the present invention.

[0036] In the figure: 1 - serpentine coiled pipe, 1 - 1 pipe section, 1 - 2 U - shaped welded joint, 2 - support block, 3 - support cylinder, 4 - pipe end seal head, 5 - movable crossbeam, 6 - workbench, 7 - hydraulic pipeline, 8 - hydraulic system. Detailed Embodiments

[0037] The following further describes the detailed embodiments of the present invention in combination with the drawings and technical solutions.

[0038] Embodiment 1

[0039] Combined with Figures 1 - 7 It is described that a self - adaptive support method and device for the U - shaped welded joint during the hydraulic expansion of the serpentine coiled pipe proposed by the present invention includes: serpentine coiled pipe 1, support block 2, support cylinder 3, pipe end seal head 4, movable crossbeam 5, workbench 6, hydraulic pipeline 7, and hydraulic system 8.

[0040] The serpentine coiled pipe is a smooth pipe with a circular cross - section, such as Figure 7As shown; the U-shaped welded joint 1-2 is a component of the serpentine coiled pipe 1 and is connected to the pipe section 1-1 by welding; the workbench 6 is fixed, and the movable crossbeam 5 can move up and down; the pipe end seal head 4 is installed on the movable crossbeam 5 and is coaxial with the two pipe ends of the serpentine coiled pipe 1; the support block 2 is installed on the piston rod of the support cylinder 3, and the cylinder body of the support cylinder 3 is installed on the workbench 6 or the movable crossbeam 5, and the installation position corresponds to the U-shaped vertex of the serpentine coiled pipe 1; the hydraulic acting area S of the support cylinder 3 z is twice the inner hole area S of the pipe section g . The pipe end seal head 4 and the support cylinder 3 are processed with liquid filling holes and are connected to the hydraulic system 8 through a hydraulic pipeline 7. The hydraulic medium used in the hydraulic system is hydraulic oil.

[0041] The beneficial effects of this embodiment are: (1) The supporting force exerted by the support cylinder 3 on the U-shaped welded joint 2 exactly balances the axial force generated by the pressure p acting on the inner surface of the U-shaped welded joint. During the bulging process of the serpentine coiled pipe 1, the weld is not affected by the axial force, avoiding the risk of the weld cracking due to tensile force. (2) The support cylinder 3 has a certain stroke and the support cylinders are interconnected, which can adapt to the height changes of each U-shaped welded joint of the serpentine coiled pipe, and has relatively low requirements for the position accuracy of the U-shaped welded joints of the serpentine coiled pipe. (3) It can simultaneously achieve the adaptive support for multiple groups of U-shaped welded joints, with simple operation, reliable support and high efficiency. (4) By adjusting the number, position of the support cylinders and the shape of the support blocks, it can adapt to serpentine coiled pipes with different lengths, different pipe spacings and different welded joint sizes, with high flexibility and strong adaptability.

[0042] Example 2

[0043] Combined with Figure 5 description, for an adaptive support method and device for U-shaped welded joints during the hydraulic bulging of a serpentine coiled pipe proposed by the present invention, the hydraulic medium uses easily cleanable fluid media such as pure water, emulsion or volatile oil, and the others are the same as in Example 1.

[0044] The beneficial effect of this embodiment is that the fluid media such as pure water, emulsion, volatile oil, etc. remaining in the serpentine coiled pipe 1 after the bulging is easily cleaned.

[0045] Example 3

[0046] Combined with Figures 1 - 6 description, for an adaptive support method and device for U-shaped welded joints during the hydraulic bulging of a serpentine coiled pipe proposed by the present invention, the hydraulic acting area S of the support cylinder 3 z is 1 to 3 times the inner hole area S of the pipe g , and the others are the same as in specific Example 1 or 2.

[0047] The beneficial effect of this embodiment is: At S z<2S g Under the condition of <2S, there is a certain tensile stress in the straight pipe section of the serpentine coil 1, while in S z >2S g Under the condition of >2S, there is a certain compressive stress in the straight pipe section of the serpentine coil 1. By specially designing the hydraulic action area of the support cylinder 3, the stress state of the serpentine coil 1 can be regulated.

[0048] Example 4

[0049] Combined with Figures 5 - 9 Explanation, an adaptive support method and device for U-shaped welded joints during hydraulic bulging of a serpentine coil proposed by the present invention, wherein the serpentine coil 1 is a pipe with internal teeth or external teeth, and the cross-sectional shapes are respectively as Figure 8 and Figure 9 shown, and the others are the same as in Example 1 or 2 or 3.

[0050] The beneficial effect of this embodiment is that it can achieve adaptive support for U-shaped welded joints during the hydraulic bulging process of serpentine coils with different cross-sectional shapes.

Claims

1. An adaptive support method for U-shaped welded joints during hydraulic bulging of serpentine coils, characterized in that: The adaptive support device used in the adaptive support method comprises a serpentine coil (1), a support block (2), a support cylinder (3), a pipe end sealing head (4), a movable crossbeam (5), a workbench (6), a hydraulic pipeline (7) and a hydraulic system (8); the movable crossbeam (5) and the workbench (6) are arranged relative to each other, the workbench (6) is fixed, and the movable crossbeam (5) can move up and down; two pipe end sealing heads (4) are installed on the lower surface of the movable crossbeam (5) and are coaxial with the two pipe ends of the serpentine coil (1); the support block (2) is installed on the piston rod of the support cylinder (3), and the cylinder body of the support cylinder (3) is installed on the upper surface of the workbench (6) and the lower surface of the movable crossbeam (5), and the installation position corresponds to the U-shaped bending vertex of the serpentine coil (1); the pipe end sealing head (4) and the support cylinder (3) are processed with liquid filling holes, and are connected to the hydraulic system (8) through the hydraulic pipeline (7); the specific method is as follows: The contact between the support block (2) on the support cylinder (3) and the serpentine coil (1) is controlled by a hydraulic system (8); during hydraulic bulging, the hydraulic pressure p output by the hydraulic system (8) acts on the piston of the support cylinder (3) and the inner surface of the serpentine coil (1) at the same time; the hydraulic action area S of the support cylinder (3) is controlled. z =πD z 2 / 4 is the inner hole area S of the pipe segment (1-1) g =πD g 2 / 4 is 1 to 3 times; when the hydraulic system (8) is charged with hydraulic pressure p, the supporting force F generated by the supporting cylinder (3) z =p×S z The axial force generated by the hydraulic pressure p acting evenly on the inner surface of the U-shaped welded joint (1-2) is F p =2p×S g , then, the axial force F acting on a single weld is h Then: F h =(F p -F z ) / 2=p(S g -0.5S z ) Among them, D z is the piston diameter of the support cylinder, D g is the inner diameter of pipe section (1-1).

2. The adaptive support method according to claim 1, characterized in that: The serpentine coil (1) is composed of a pipe section (1-1) and a U-shaped welding joint (1-2) which are welded together.

3. The adaptive support method according to claim 1, characterized in that: The serpentine coil (1) is a smooth tube, an inner tooth tube or an outer tooth tube.

4. The adaptive support method according to claim 1, characterized in that: The hydraulic medium in the hydraulic system (8) is pure water, emulsion or volatile oil.

5. The adaptive support method according to claim 1, characterized in that: When the hydraulic action area S of the support cylinder (3) z Less than 2S g When the axial force on the weld is adjusted to axial pressure.

6. The adaptive support method according to claim 1, characterized in that: Hydraulic action area S of support cylinder (3) z After determination, the support force F applied to the U-shaped weld joint (1-2) z Determined by the bulging pressure p, and increases with the increase of p, achieving the support force F z Adaptive adjustment.

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