A fusion welding method for heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing

Abstract

The present invention discloses a fusion welding method for heat exchange tubes and tube sheets under ultra-narrow hole bridge spacing, belonging to the field of aluminum coiled tube heat exchangers. The method uses a power supply that provides AC and DC mixed waves as a welding power supply, cleans the weld surface in AC mode, and achieves narrow arc and high penetration in DC mode; divides a number of tube holes on the tube sheet into 1 group for every 3 columns, and each tube hole is divided into two semicircles on the left and right; welds one side semicircle of each column of tube holes from bottom to top, and then welds the other side semicircle of the remaining columns of tube holes to avoid excessive local temperature affecting the quality of the weld; the welding process uses a heat dissipation copper rod as an auxiliary forming tooling for the wire adding welding process, and the wire adding welding process uses non-continuous inching wire feeding, and a single layer is welded and formed. The weld surface and interior of the weld obtained by the fusion welding method are defect-free, and can achieve welding of heat exchange tubes and tube sheets under narrower hole bridge spacing, reduce the overall volume and equipment deadweight of the heat exchanger, and improve the heat exchange efficiency per unit volume.

Description

Technical Field

[0001] The invention belongs to the field of aluminum coiled tube heat exchangers, and in particular relates to a fusion welding method for heat exchange tubes and tube sheets under ultra-narrow hole bridge spacing. Background Art

[0002] Aluminum coil heat exchanger is a new type of high-efficiency and energy-saving aluminum heat exchange equipment. This heat exchanger has many advantages: light weight, compact structure, small temperature difference stress, large heat transfer area per unit volume, and can transfer heat of multiple media at the same time. It is suitable for occasions with small temperature difference, large heat transfer and high operating pressure of the medium in the tube, such as application in low-temperature oxygen production process. However, its design process involves many variable factors, such as material density, thermal conductivity, hole bridge spacing, welding process, etc., which requires design and manufacturing personnel to have certain technical literacy in material performance understanding, spatial arrangement of heat exchange tubes, and quality control of tube sheet welds. Only by comprehensively considering various factors can the final design route be determined.

[0003] Aluminum coiled heat exchangers usually use 3003 aluminum alloy heat exchange tubes, which have good rust resistance, formability and high corrosion resistance. The tube sheet uses 5083-H112 aluminum alloy plate, which has high strength, excellent low temperature performance and strong corrosion resistance. Although both are aluminum alloys, they belong to different series, so there will be certain fusion difficulties during welding. In addition, due to the large difference between the wall thickness of the heat exchange tube and the thickness of the tube sheet, and the limited welding space, these unfavorable factors increase the difficulty of the welding process.

[0004] The hole bridge spacing refers to the difference between the center distance of the heat exchange tube and the hole diameter of the tube sheet in the aluminum coiled tube heat exchanger. When designing the hole bridge spacing, a smaller hole bridge spacing can improve the overall heat exchange efficiency, but the smaller the hole bridge spacing, the denser the arrangement of the heat exchange tubes in a small area. Currently, the commonly used TIG welding AC welding mode is Tungsten Inert Gas Welding, which is a method of welding using infusible tungsten as an electrode and generating an arc under the protection of an inert gas. The AC welding mode usually refers to the welding mode using an AC power supply. In TIG welding, the AC mode is used, and the alternating current can break the oxide film by alternating between the positive and negative poles and achieve a cleaning effect. In the existing TIG welding AC welding mode, the current is usually not less than 300A to ensure the fusion between the tube sheet and the heat exchange tube. However, such parameters may lead to excessive heat input when welding a single tube mouth, and overlap of heat-affected zones generated when welding adjacent heat exchange tube holes, causing multiple thermal cycles of the weld and surrounding parent material, resulting in material performance loss. In addition, the internal force concentration at the weld and the serious deformation of the tube mouth after welding may lead to defects such as cracks, incomplete penetration and pores. These quality problems will affect the long-term working performance of the heat exchange tube. If the tube sheet weld leaks, it will not only reduce the heat exchange efficiency, but also lead to a long repair cycle and difficult operation of the leak point in the case of a complex structure of the coiled tube heat exchanger.

[0005] Therefore, it is urgent to develop a fusion welding method that can obtain stable tube sheet weld quality under ultra-narrow hole bridge spacing conditions. Summary of the invention

[0006] The purpose of the present invention is to solve the deficiencies in the prior art and provide a method for fusion welding a heat exchange tube and a tube sheet under ultra-narrow hole bridge spacing.

[0007] The specific technical solutions adopted by the present invention are as follows:

[0008] The present invention provides a method for fusion welding a heat exchange tube and a tube sheet under ultra-narrow hole bridge spacing, and the specific steps are as follows:

[0009] S1: A number of tube holes for welding heat exchange tubes are opened on the welding surface of the tube sheet, and a chamfer groove is set in each tube hole;

[0010] S2: The processed tube sheet and heat exchange tube are washed with NaOH solution, water, HNO3 solution and water in turn to thoroughly remove surface impurities and dried for later use;

[0011] S3: Assemble the tube sheet and the heat exchange tube so that the heat exchange tube extends out of the welding surface of the tube sheet;

[0012] S4: using a heat dissipation copper rod as an auxiliary forming tooling in the wire welding process; the heat dissipation copper rod comprises an end head for positioning and a copper rod inserted into the heat exchange tube for heat conduction, and the diameter of the end head is larger than the copper rod;

[0013] S5: A power source that provides a mixed AC and DC wave is used as the welding power source, in which the DC mode accounts for 10% to 80% in one cycle; the weld surface is cleaned in the AC mode, and a narrow arc and high penetration are achieved in the DC mode;

[0014] Divide the tube holes on the tube sheet into a group of 3 columns, and divide each tube hole into two semicircles on the left and right; weld one semicircle of each column of tube holes from bottom to top, and then weld the other semicircles of the remaining columns of tube holes to avoid excessive local temperature affecting the quality of the weld;

[0015] When welding each tube hole, start the arc from the outside of the tube hole and gradually transition to the inside of the tube hole; first, add wire from the bottom to the top of one semicircle in a counterclockwise manner, the weld is led out from the chamfer groove, and the arc is extinguished on the outside of the tube hole; when welding the other semicircle, the arc stops at the overlapping part of the semicircular welds on both sides of the tube hole, so that the overlapping part of the weld is opened and remelted, and then add wire clockwise from the bottom to the top, the weld is also led out from the chamfer groove, and the arc is extinguished on the outside of the tube hole; the wire adding welding process adopts non-continuous inching wire feeding, and a single layer of welding is formed; repeat the above steps until the welding of all tube holes is completed.

[0016] Preferably, the tube sheet is made of 5083-H112 aluminum alloy plate with a thickness of 30 to 80 mm; the heat exchange tube is made of 3003 aluminum alloy with a diameter of 12 mm; the diameter of the tube hole opened on the tube sheet welding surface is 12 to 12.1 mm; the hole bridge spacing is the difference between the center distance of the heat exchange tube and the hole diameter of the tube sheet, and the value is 3.4 to 3.8 mm.

[0017] Preferably, the angle of the chamfered groove is 30° to 45°, and the chamfering depth is 1.65 to 2 mm, forming a funnel-shaped groove.

[0018] Preferably, in step S2, the concentration of the NaOH solution is 25% to 30%, and the cleaning is carried out at 45°C for 10 minutes; the concentration of the HNO3 solution is 3.5 to 4%, and the cleaning is carried out at room temperature for 3 minutes.

[0019] Preferably, in step S3, the heat exchange tube extends out of the tube sheet welding surface by 1.0 to 2.0 mm.

[0020] Preferably, in the heat dissipation copper rod, the end diameter is 10.0 mm and the length is 20 mm; the copper rod diameter is 7.6 mm and the length is 120 mm.

[0021] Preferably, the welding power supply in step S5 adopts a digital pulse TIG welding machine, model weld tecpower AC / DC 502; the AC / DC mixed wave frequency is 135-165 Hz, the welding current is 115-125 A, the DC mode accounts for 30% in one cycle, the tungsten electrode diameter is 3.0 mm, the shielding gas is 99.99% Ar, and the gas flow rate is 10-15 L / min.

[0022] Preferably, in the wire adding welding process in step S5, ER5183 aluminum welding wire is used, the wire diameter is 1.6 mm, and the length of each section is 25 cm; the welding position is horizontal welding; if the ambient temperature is lower than 5°C, the tube sheet needs to be preheated to 60°C for welding.

[0023] Preferably, in step S5, the weld is extinguished 3 mm outside the tube hole; the size of the overlapping part of the semicircular welds on both sides of the tube hole is 3×3 mm, and the arc stays at the overlapping part of the welds for 1.5 to 2.0 seconds to open the overlapping part of the welds for remelting.

[0024] Preferably, when welding each tube hole in step S5, arcing is started from 3 to 5 mm outside the tube hole.

[0025] Preferably, in step S5, the wire feeding is continued for 0.5 to 1.0 s and then stopped for 1.0 s, and the welding speed is controlled to be 6.4 to 8.0 cm / min.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In the fusion welding method provided by the present invention, an AC / DC mixed wave power source is selected to solve the shortcomings of large heat affected zone and poor forming quality when welding in alternating current (AC) mode alone; in the present invention, the weld surface is cleaned in AC mode, and a narrow arc and high penetration depth are achieved in DC mode, which can achieve welding of heat exchange tubes and tube sheets at a narrower hole bridge spacing, reduce the overall volume of the heat exchanger and the weight of the equipment, and improve the heat exchange efficiency per unit volume.

[0028] (2) In the fusion welding method provided by the present invention, the tube holes on the tube plate are welded in different areas to avoid excessive local temperature. A single tube hole is also welded in left and right semicircles respectively, which can avoid the problem of weld collapse caused by top-down welding of the left weld of a single hole. Discontinuous inching wire feeding is used in the welding process to avoid excessive aluminum liquid on the tube hole, which may cause weld collapse and weld nodules, thereby affecting the weld quality.

[0029] (3) The present invention uses a heat dissipation copper rod as an auxiliary forming tool, which effectively reduces the problem of serious temperature rise of the heat exchange tube during batch welding and avoids the generation of cracks. The welding process of this fusion welding method has a small heat input, low production cost, and a tube sheet weld with stable quality can be obtained after welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the fusion welding of the tube sheet and the heat exchange tube provided in this embodiment;

[0031] Figure 2 A cross-sectional view of the fusion welding of the tube sheet and the heat exchange tube provided for this embodiment;

[0032] Figure 3 The AC / DC mixed waveform diagram of the welding power supply provided in this embodiment;

[0033] Figure 4 A schematic diagram of a heat dissipation copper rod provided in this embodiment;

[0034] Figure 5 This is a schematic diagram of the tube hole welding grouping in this embodiment;

[0035] Figure 6 This is a schematic diagram of a welding path for a single tube hole in this embodiment;

[0036] Figure 7 This is the result diagram after PT testing of the tube sheet weld in this embodiment;

[0037] Figure 8 This is a cross-sectional view of the tube sheet weld in this embodiment;

[0038] In the figure: tube sheet 1, heat exchange tube 2, chamfer groove 3, heat dissipation copper rod 4, end 401, copper rod 402. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0040] In a preferred embodiment of the present invention, a method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing is provided, and the specific steps are as follows.

[0041] (1) Workpiece preparation

[0042] like Figure 1 and Figure 2 As shown, a plurality of tube holes for welding heat exchange tubes 2 are provided on the welding surface of the tube sheet 1, and a chamfered groove 3 is provided in each tube hole.

[0043] In this embodiment, the tube sheet 1 is made of 5083-H112 aluminum alloy plate with a thickness of 54mm; the heat exchange tube 2 is made of 3003 aluminum alloy with a diameter of 12mm. The diameter of the tube hole opened on the welding surface of the tube sheet 1 is slightly larger than the diameter of the heat exchange tube 2. In this embodiment, the diameter of the tube hole is 12.1mm. The angle of the chamfer groove 3 in all tube holes is 45°, and the chamfer depth is 1.65mm, forming a funnel-shaped groove.

[0044] It should be noted that the hole bridge spacing is the difference between the center distance of the heat exchange tube and the hole diameter of the tube sheet. Reducing the hole bridge spacing can reduce the overall volume of the heat exchanger, reduce the weight of the equipment, and improve the heat exchange efficiency per unit volume of the heat exchanger. In this embodiment, the center distance of the heat exchange tube 2 is set to 15.5mm, so the hole bridge spacing is 3.4mm. Those skilled in the art can set the hole bridge spacing within the range of 3.4 to 3.8mm according to actual construction needs.

[0045] (2) Cleaning the workpiece

[0046] Wash the processed tube sheet 1 and heat exchange tube 2 in a 30% NaOH cleaning pool for 10 minutes at a cleaning temperature of 45°C. Then rinse with clean water for 2 minutes, place in a 3.5% HNO3 cleaning pool at room temperature for 3 minutes, and then rinse with distilled water for 2 minutes to thoroughly wash away the oxide scale, oil stains and other impurities on the surface of the tube sheet 1 and heat exchange tube 2 to avoid affecting the welding quality. Finally, dry and set aside;

[0047] (3) Assembly materials

[0048] Assemble the tube sheet 1 and the heat exchange tube 2 so that the heat exchange tube 2 extends 1.5 mm beyond the welding surface of the tube sheet 1.

[0049] The heat dissipation copper rod 4 is used as an auxiliary forming tool for the wire welding process. Figure 4 As shown, the heat dissipation copper rod 4 includes a thicker end 401 and a thinner copper rod 402 , and the diameter of the end 401 is larger than that of the copper rod 402 .

[0050] In this embodiment, the total length of the heat dissipation copper rod 4 is 140 mm, and the end 401 part is convenient for positioning and removal, with a diameter of 10.0 mm and a length of 20 mm; the copper rod 402 part has a diameter of 7.6 mm and a length of 120 mm. Before welding, the heat dissipation copper rod 4 is inserted into the heat exchange tube 2. This arrangement can guide the heat inside the heat exchange tube during welding, thereby quickly reducing the temperature between the tube hole weld layers. This helps to ensure uniform heat distribution during welding, prevent aluminum liquid from flowing into the heat exchange tube, avoid thermal cracks in the tube hole weld, and control the deformation of the tube mouth size.

[0051] (4) Welding process

[0052] A digital pulse TIG welder is used as the welding power source, and the model of the welder is weld tec power AC / DC 502. This power source can provide AC / DC mixed waves. The characteristics of AC / DC mixed waves are that they can combine the excellent protection ability of TIG welding alternating current (AC) mode with the strong penetration ability of TIG welding direct current (DC) mode, and integrate them in one cycle. The weld surface is cleaned in AC mode, and a narrow arc and high penetration depth are achieved in DC mode.

[0053] It should be noted that narrow arc refers to the relatively small width or diameter of the arc during welding. Narrow arcs can concentrate heat and are usually used to weld narrow seams, thin plates, or areas that require more delicate welding. High penetration means that the arc can penetrate the surface of the workpiece during welding to achieve a deeper weld. In aluminum coiled heat exchangers, high penetration usually means that the weld can better penetrate the interior of the tube and plate, ensuring a stronger connection.

[0054] Under the same current, the DC mode has a much higher waveform than the AC mode, which can obtain a deeper molten pool and reduce the current required for welding thick aluminum plates. The arc capacity is concentrated in a small area, and the concentrated heat acts on the center of the weld, making the heat-affected zone around the weld very small and the welding deformation very small. By adjusting the proportion of AC mode and DC mode in a cycle, the welding process can be controlled, the welding pool can be opened quickly and the welding speed can be increased. The proportion of DC mode in a cycle can be set to 10% to 80%. Those skilled in the art can make adjustments according to specific working conditions.

[0055] Figure 3 The AC / DC mixed waveform of the welding power supply provided in this embodiment. In this embodiment, the AC / DC mixed wave frequency in the welding power supply is 150 Hz, the welding current is 115-125 A, the DC mode accounts for 30% in one cycle, the tungsten electrode diameter is 3.0 mm, the shielding gas is 99.99% Ar, and the gas flow rate is 10-15 L / min.

[0056] like Figure 5 As shown, the plurality of tube holes on the tube sheet 1 are divided into a group of 3 columns, each group including three columns A, B and C. The welding order of each group is to weld the columns A and B on both sides first, and finally the middle column C. The tube holes in each column are welded in order from bottom to top, and the column is changed when 4 to 5 tube holes are welded.

[0057] This arrangement can take advantage of the fast heat transfer characteristics of aluminum alloy to utilize the residual heat of the previous weld and achieve a relative balance with the welding current, thereby avoiding unnecessary work pauses caused by excessive temperature rise of the tube sheet and heat exchange tubes during continuous welding, and also avoiding excessive heat input of a single weld when the distance between the previous and next welds is far, causing burning of alloy elements.

[0058] like Figure 6As shown, each tube hole is divided into two semicircles at 12 o'clock and 6 o'clock. First weld the right semicircle, and weld counterclockwise along the semicircle arc from bottom to top (i.e. 6 o'clock → 3 o'clock → 12 o'clock). When welding, start the arc from 5mm outside the tube hole and gradually transition to the inside of the tube hole. When reaching the 12 o'clock position, the weld is drawn out and the arc is extinguished at 3mm outside the tube hole. Then weld the semicircles of the remaining tube holes to avoid excessive local temperature affecting the quality of the weld. When welding the left semicircle, weld clockwise along the semicircle arc from bottom to top (i.e. 6 o'clock → 9 o'clock → 12 o'clock). The arc extinguishing position of the left semicircle is not in the chamfer groove of the tube hole. The weld is also drawn out and the arc is extinguished at 3mm outside the tube hole. The overlapped welds of the left and right semicircles are at 6 and 12 o'clock, and the size of the overlapped welds is 3×3 mm. The arc stays at the overlapped welds for 1.5 to 2.0 seconds to open and remelt the overlapped welds. Repeat the above steps until all the pipe holes are welded.

[0059] In this embodiment, the wire-adding welding process adopts non-continuous inching wire feeding, and a single layer is welded and formed. The wire-adding welding process uses ER5183 aluminum welding wire, the wire diameter is 1.6mm, and the length of each section is 25cm; the welding position is horizontal welding. If the ambient temperature is lower than 5°C, the tube sheet 1 needs to be preheated to 60°C for welding. If the ambient temperature is 20-28°C, there is no need to preheat the tube sheet 1.

[0060] It should be noted that this embodiment adopts manual wire welding, and the employee wears clean welding gloves before welding to avoid contamination of welding materials, tube sheets and heat exchange tubes. In other embodiments, a mechanical non-continuous inching wire feeding method can also be used. After the inching wire feeding lasts for 0.5 to 1.0 seconds, the wire feeding is stopped for 1.0 seconds, and the welding speed is controlled to be 6.4 to 8.0 cm / min to avoid too much aluminum liquid metal on the tube hole, forming weld collapse and weld nodules, which affect the weld quality.

[0061] Welding walking path Figure 6 As shown, a→b→c→d→e→f→g→h. In the conventional tube-sheet welding process, the tube hole is generally welded counterclockwise from the 5 o'clock direction. The welding path planning in this embodiment avoids local overheating and effectively avoids the weld collapse and aluminum liquid downflow caused by the welding process of the left half circle of the tube hole (from 12 o'clock→9 o'clock→6 o'clock half circle) in the conventional tube-sheet welding process.

[0062] (5) Weld inspection

[0063] After welding, use a wire brush to remove a little black smoke on the surface of the weld. After cooling, use the penetrant testing (PT) method to detect whether there are defects on the weld surface: first spray the colorant evenly on the weld surface, and the colorant will penetrate into the weld surface along the tiny gaps. After waiting for a while, clean the weld surface with a cleaning agent, and then apply a developer. The results are as follows: Figure 7 As shown, no developer appears on the weld surface, thus proving that the weld surface obtained by welding of the present invention has no defects.

[0064] According to the measurement, the inner diameter of the tube hole weld obtained by the fusion welding method provided by the present invention is ≥7mm, and the effective weld thickness obtained is >2mm, which can ensure the heat exchange efficiency. Figure 8 As shown, it can be seen that there are no obvious defects in the weld cross section, which can avoid gap corrosion and ensure that the heat exchange tube rarely or never leaks during use. The weld sealing of the aluminum coiled tube heat exchanger is guaranteed.

[0065] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing, characterized in that: The specific steps are as follows: S1: a plurality of tube holes for welding heat exchange tubes (2) are provided on the welding surface of the tube sheet (1), and a chamfer groove (3) is provided in each tube hole; S2: The processed tube sheet (1) and heat exchange tube (2) are washed with NaOH solution, water, HNO3 solution and water in sequence to thoroughly remove surface impurities, and then dried for later use; S3: Assembling the tube sheet (1) and the heat exchange tube (2) so that the heat exchange tube (2) protrudes from the welding surface of the tube sheet (1); S4: using a heat dissipation copper rod (4) as an auxiliary forming tool for the wire welding process; the heat dissipation copper rod (4) comprises an end head (401) for positioning and a copper rod (402) inserted into the heat exchange tube (2) for heat conduction, and the diameter of the end head (401) is larger than that of the copper rod (402); S5: A power source that provides a mixed AC and DC wave is used as the welding power source, in which the DC mode accounts for 10% to 80% in a cycle; the weld surface is cleaned in the AC mode, and a narrow arc and high penetration are achieved in the DC mode; The plurality of tube holes on the tube sheet (1) are divided into a group of three rows, and each tube hole is divided into two left and right semicircles; one side semicircle of each row of tube holes is welded from bottom to top, and then the other side semicircles of the remaining rows of tube holes are welded to avoid excessive local temperature affecting the quality of the weld; When welding each tube hole, the arc is started from the outside of the tube hole and gradually transitions to the inside of the tube hole; first, the wire is added counterclockwise from bottom to top on one side of the semicircle, the weld is led out from the chamfer groove (3), and the arc is extinguished on the outside of the tube hole; when welding the other side of the semicircle, the arc is stopped at the overlapping part of the semicircle welds on both sides of the tube hole, so that the overlapping part of the weld is opened and remelted, and then the wire is added clockwise from bottom to top, the weld is also led out from the chamfer groove (3), and the arc is extinguished on the outside of the tube hole; the wire addition welding process adopts non-continuous inching wire feeding, and a single layer of welding is formed; the above steps are repeated until the welding of all the tube holes is completed; The tube sheet (1) is made of 5083-H112 aluminum alloy plate with a thickness of 30 to 80 mm; the heat exchange tube (2) is made of 3003 aluminum alloy with a diameter of 12 mm; the diameter of the tube hole provided on the welding surface of the tube sheet (1) is 12 to 12.1 mm; the hole bridge spacing is the difference between the center distance of the heat exchange tube and the hole diameter of the tube sheet, and is 3.4 to 3.8 mm.

2. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1 is characterized in that: The angle of the chamfered groove (3) is 30° to 45°, and the chamfering depth is 1.65 to 2 mm, forming a funnel-shaped groove.

3. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1 is characterized in that: In step S2, the concentration of the NaOH solution is 25%-30%, and the cleaning is performed at 45°C for 10 minutes; the concentration of the HNO3 solution is 3.5-4%, and the cleaning is performed at room temperature for 3 minutes.

4. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1 is characterized in that: In step S3, the heat exchange tube (2) extends out of the welding surface of the tube sheet (1) by 1.0 to 2.0 mm.

5. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1 is characterized in that: In the heat dissipation copper rod (4), the end (401) has a diameter of 10.0 mm and a length of 20 mm; the copper rod (402) has a diameter of 7.6 mm and a length of 120 mm.

6. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1, characterized in that: The welding power source described in step S5 adopts a digital pulse TIG welding machine, model weld tec power AC / DC 502; the AC / DC mixed wave frequency is 135~165Hz, the welding current is 115~125A, the DC mode accounts for 30% in one cycle, the tungsten electrode diameter is 3.0mm, the shielding gas is 99.99%Ar, and the gas flow rate is 10~15L / min.

7. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1 is characterized in that: In the wire welding process described in step S5, ER5183 aluminum welding wire is used, the diameter of the welding wire is 1.6 mm, and the length of each section is 25 cm; the welding position is horizontal welding; if the ambient temperature is lower than 5° C., it is necessary to preheat the tube sheet (1) to 60° C. for welding.

8. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1 is characterized in that: In step S5, the weld is extinguished at 3 mm outside the tube hole; the size of the weld overlapped part of the semicircle on both sides of the tube hole is 3×3 mm, and the arc stays at the weld overlapped part for 1.5 to 2.0 seconds to open the weld overlapped part for remelting.

9. The method for fusion welding of heat exchange tubes and tube sheets with ultra-narrow hole bridge spacing according to claim 1 is characterized in that: When welding each tube hole in step S5, the arc is started from 3 to 5 mm outside the tube hole; the wire feeding is continued for 0.5 to 1.0 s and then stopped for 1.0 s, and the welding speed is controlled to be 6.4 to 8.0 cm / min.

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