A brazing method for assembling a finned tube heat exchanger

Abstract

The finned tube heat exchanger assembly brazing method, during the fin layer installation process, the spacer ring is inserted between the layers to limit the layer distance; the symmetric process holes are made on the edge of each layer of fins, the spacer stud is inserted into the process hole during the assembly process, after each layer of fins is installed to the required position, the spacer nut is screwed on the stud until it contacts the fin, the fin flatness is adjusted by adjusting the position of the nut; after all the fins are installed, the argon arc welding is used to weld the fin and the heat exchange tube end girth weld; before brazing, the special tool is used to press the upper and lower fins of the heat exchanger, the tool is brazed with the product; by pre-plating the nickel layer, the No. 2 alloy filler metal is used for gas protection brazing. The fin layer spacing of the heat exchanger can be controlled and adjusted during the assembly process, the fin layer spacing after the assembly is uniform and consistent; during the brazing process, the deformation of the fin is effectively limited, so that the fin layer spacing of the heat exchanger after welding is uniform and consistent.

Description

Technical Field

[0001] This invention belongs to the field of civilian application of aerospace engine manufacturing technology, and specifically relates to a brazing method for assembling finned tube heat exchangers. Background Technology

[0002] Currently, when brazing stainless steel finned tube heat exchangers with thin fins (fin thickness less than 1mm) and narrow spacing (layer spacing less than 3mm) in China, the only method used is to add a limiting ring to control the fin layer spacing. During the assembly process, the flatness of the fins cannot be guaranteed, nor can the uniformity of the fin layer spacing be controlled. After brazing, the fins deform greatly, resulting in poor product quality stability and consistency. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide an effective method for controlling the deformation of heat exchanger fins after brazing. This method involves inserting a limiting ring between the fin layers while using limiting screws and limiting nuts to adjust the height position of the fin edges, thereby adjusting the flatness of the fins and the interlayer spacing. The limiting nuts restrict the amount of deformation of the fins during the brazing process and, in conjunction with the limiting rings, ensure a uniform interlayer gap after brazing.

[0004] The technical solution of this invention is: a brazing method for assembling a finned tube heat exchanger, comprising the following steps:

[0005] Step 1: Based on the shape of the heat exchanger fins and the distribution of the heat exchange tubes, symmetrical process holes are made near the edge of the fins.

[0006] Step 2: Pickle and degrease the fins and heat exchange tubes. After degreasing, electroplate nickel onto the surface of the fins and heat exchange tubes. Clean all the limiting rings and brazing rings with alcohol.

[0007] Step 3: Fix the heat exchange tube and the limiting screw on the special assembly fixture according to the hole positions on the fins, and install the heat exchange tube and the screw through each hole of the fins;

[0008] Step 4: After installing one layer of fins, fit a limiting ring of equal thickness onto each heat exchange tube, fit a brazing filler ring between the limiting ring and the heat exchange tube, and install a limiting nut on the screw to adjust the flatness of the fins.

[0009] Step 5: Install the fins layer by layer, and install the limiting ring, brazing ring and limiting nut between each layer as in Step 3 and Step 4;

[0010] Step 6: After the last layer of fins is installed, remove the heat exchanger from the assembly fixture, use argon arc welding to weld the heat exchange tube ends to the upper and lower fin circumferential welds, and clean the heat exchanger with alcohol.

[0011] Step 7: Install the heat exchanger in a special brazing fixture, and then put the heat exchanger and the brazing fixture into the furnace together for gas-protected brazing.

[0012] Step 8: After brazing is completed, remove the heat exchanger along with the tooling and air cool it to room temperature before disassembling the tooling.

[0013] The holes made in step 1 are φ4 in size, and there are 16 holes in total;

[0014] The nickel plating thickness of the nickel-plated fins and heat exchange tubes obtained in step 2 is 8 μm;

[0015] The screw used in step 6 is M3.

[0016] Step 7: The height of the limiting ring is 2mm, and the gap between the limiting ring and the heat exchange tube is 0.5mm;

[0017] In step 8, the limiting nut is M3 with a height of 1.6mm;

[0018] In step 10, the number of layers installed is 100.

[0019] In step 12, the temperature of the assembly is raised to 1150-1200℃ at a heating rate of 20-25℃ / min, and the holding time is 40-50min.

[0020] The beneficial effects of this invention compared to the prior art are:

[0021] In this invention, in addition to inserting a limiting ring between every two fin layers to restrict the installation position of each fin layer, a limiting nut is also installed at the edge position between every two fin layers by inserting a stud to adjust the assembly position of each fin layer during the assembly process, thereby improving the assembly accuracy. At the same time, the limiting nut located at the edge of the fin limits the amount of deformation of the fin during the brazing process, resulting in uniform fin layer spacing after welding, which improves the stability and consistency of product quality. Attached Figure Description

[0022] Figure 1 This is a process flow diagram for implementing the method of the present invention;

[0023] Figure 2 A schematic diagram showing the machining locations of the process holes for the fins;

[0024] Figure 3 This is a schematic diagram showing the installation of the limiting ring, brazing ring, limiting stud, and limiting nut in the method of the present invention. Detailed Implementation

[0025] like Figure 1 As shown, this invention proposes a brazing method for assembling a finned tube heat exchanger, comprising the following steps:

[0026] (1) Based on the shape of the heat exchanger fins and the distribution of the heat exchange tubes, process holes are symmetrically made near the edge of the fins. The process holes are symmetrically distributed along the center line of the fins near the edge of the fins, with a number of 12 to 36. The diameter of the process holes is φ4 to 8 mm.

[0027] (2) Pickling and degreasing the fins and heat exchange tubes, and electroplating nickel on the surface of the fins and heat exchange tubes after degreasing. The plating thickness is 5-20 μm. All limiting rings and brazing rings are cleaned with alcohol. After cleaning, the limiting rings and brazing rings are soaked in clean alcohol for use.

[0028] (3) Fix the heat exchange tube and the limiting screw to the special assembly fixture according to the hole positions on the fins. The fixture is fixed horizontally on the platform. The special fixture has slots to achieve rigid fixation of the heat exchange tube and screw ends. After the heat exchange tube and the limiting screw are fixed, start installing the fins. Insert the heat exchange tube and the limiting screw through the holes on the fins and install them to the bottom. The limiting screw specifications are M3 to M6.

[0029] (4) After installing one layer of fins, fit equal-thickness limiting rings onto each heat exchange tube, and fit a brazing ring between the limiting ring and the heat exchange tube. Install limiting nuts on the screw to adjust the flatness of the fins. Select limiting rings with a height of 1-3mm, a gap of 0.2-1mm between the limiting ring and the heat exchange tube, brazing ring material of No. 2 alloy, and limiting nuts of M3-M6 specifications, selected to match the screw. The height of the limiting nut should not be greater than that of the limiting ring, and the height difference should not be greater than 0.5mm. Install the limiting rings on time, ensuring that the lower end face of the limiting ring is tightly fitted with the fins, and then fit the brazing ring between the limiting ring and the heat exchange tube. After the limiting rings are installed, screw the limiting thread into the limiting screw. Adjust the height of the fin edge position by adjusting the position of the limiting nut, thereby controlling the overall flatness of the fins. Adjust the height difference of the fin edge to within 0.1mm.

[0030] (5) Install the fins layer by layer. For each layer, install the limiting ring, brazing ring, and limiting nut according to steps 3 and 4. During installation, ensure that the limiting ring is tightly fitted to the fin. Use the limiting nut to adjust the flatness of each layer of fins to within 0.1mm. The number of fin layers that can be installed is 10 to 200.

[0031] (6) After the last layer of fins is installed, the heat exchanger is removed from the assembly fixture. The heat exchange tube ends are welded to the upper and lower fin circumferential welds using argon arc welding. The heat exchanger is then cleaned with alcohol.

[0032] (7) Install the heat exchanger in a special brazing fixture, and put the heat exchanger and the brazing fixture into the furnace together for gas-protected brazing. The temperature of the assembly is raised to 1150-1200℃ at a heating rate of 20-25℃ / min, and the holding time is 40-50min.

[0033] (8) After brazing, remove the heat exchanger along with the tooling and air cool it to room temperature before disassembling the tooling.

[0034] Example 1

[0035] This invention provides a brazing method for assembling a finned tube heat exchanger, comprising the following steps:

[0036] (1) Create 16 φ4 process holes near the edge of the fin, with the machining positions as follows: Figure 2 As shown, they are symmetrically distributed along the center of the fins;

[0037] (2) Pickling and degreasing the fins and heat exchange tubes and electroplating them with a nickel plating thickness of 8μm. All limiting rings and brazing rings are cleaned with alcohol and soaked in clean alcohol for use.

[0038] (3) Fix the heat exchange tube and the limiting screw on the special assembly fixture according to the hole positions on the fins. The limiting screw is M3. Install the heat exchange tube and the screw through the holes of the fins.

[0039] (4) After installing one layer of fins, fit a matching thickness limiting ring onto each heat exchange tube. Insert a brazing filler ring between the limiting ring and the heat exchange tube. Install a limiting nut on the screw to adjust the fin flatness. The installation position is as follows: Figure 3 As shown. The height of the limiting ring is 2mm, the gap between the limiting ring and the heat exchange tube is 0.5mm, the brazing ring material is alloy No. 2, and the limiting nut specification is M3.

[0040] (5) The fins are installed layer by layer. Between each layer, the limiting ring, brazing ring and limiting nut are installed according to steps 3 and 4. The number of fin installation layers is 100.

[0041] (6) After the last layer of fins is installed, the heat exchanger is removed from the assembly fixture. The heat exchange tube ends are welded to the upper and lower fin circumferential welds using argon arc welding. The heat exchanger is then cleaned with alcohol.

[0042] (7) Install the heat exchanger in a special brazing fixture, and put the heat exchanger and the brazing fixture into the furnace together for gas-protected brazing. The temperature of the assembly is raised to 1150-1200℃ at a heating rate of 20-25℃ / min, and the holding time is 40-50min.

[0043] (8) After brazing, remove the heat exchanger along with the tooling and air cool it to room temperature before disassembling the tooling.

Claims

1. A brazing method for assembling a finned tube heat exchanger, characterized in that, include: Step 1: Based on the shape of the heat exchanger fins and the distribution of the heat exchange tubes, symmetrical process holes are made near the edge of the fins. Step 2: Pickle and degrease the fins and heat exchange tubes. After degreasing, electroplate nickel onto the surface of the fins and heat exchange tubes. Clean all the limit rings and brazing rings to be used. Step 3: Fix the heat exchange tube and the limiting screw on the assembly fixture according to the hole positions on the fins, and install the heat exchange tube and the screw through each hole of the fins; Step 4: After installing one layer of fins, fit a limit ring of equal thickness onto each heat exchange tube, and fit a brazing filler ring between the limit ring and the heat exchange tube. Install a limit nut on the screw to adjust the flatness of the fins; the upper and lower end faces of the limit ring should fit tightly against the fins. Step 5: Install the fins layer by layer, and install the limiting ring, brazing ring and limiting nut between each layer as in Step 3 and Step 4; Step 6: After the last layer of fins is installed, remove the heat exchanger from the assembly fixture, use argon arc welding to weld the heat exchange tube ends to the circumferential welds of the upper and lower fins, and clean the heat exchanger. Step 7: Install the heat exchanger in the brazing fixture, and then put the heat exchanger and the brazing fixture into the furnace together for gas-protected brazing. Step 8: After brazing is completed, remove the heat exchanger along with the brazing fixture and air cool it to room temperature before disassembling the fixture.

2. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 1, the fins and heat exchange tubes are made of stainless steel.

3. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 1, the process holes are symmetrically distributed along the center line of the fin near the edge of the fin, with a number of 12 to 36, and the diameter of the process holes is φ4 to 8 mm.

4. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 2, the nickel plating thickness of the fins and heat exchange tubes is 5~20μm.

5. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 3, the assembly fixture has a slot to achieve rigid fixation of the heat exchange tube and the screw end.

6. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 4, the height of the limiting ring is 1~3mm, the gap between the limiting ring and the heat exchange tube is 0.2~1mm, and the brazing ring material is alloy No.

2.

7. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 4, the limiting nut and the screw are selected to match. The height of the limiting nut is not greater than that of the limiting ring, and the height difference is not greater than 0.5mm.

8. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 4, after installing one layer of fins, a limiting ring of equal thickness is fitted onto each heat exchange tube, and a brazing ring is fitted between the limiting ring and the heat exchange tube. A limiting nut is installed on the screw to adjust the flatness of the fins. The limiting rings are installed to ensure that the lower end face of the limiting rings is in close contact with the fins. Then, a brazing ring is fitted between the limiting rings and the heat exchange tubes. After the limiting rings are installed, the limiting nut is screwed into the limiting screw. The height of the fin edge position is adjusted by adjusting the position of the limiting nut, thereby controlling the overall flatness of the fins. The height difference of the fin edge is adjusted to within 0.1mm.

9. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 5, the number of fin layers that can be installed is 10 to 200.

10. The brazing method for assembling a finned tube heat exchanger according to claim 1, characterized in that: In step 7, the temperature of the assembly is raised to 1150~1200℃ at a heating rate of 20-25℃ / min, and the holding time is 40~50min.

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