Method of manufacturing a flat tube
By designing a raised shape and a rounded transition on the longitudinal wall of the flat tube, the problem of poor contact between the flat tube and the turbulent insert during brazing is solved, thereby improving strength and heat transfer, making it suitable for heat exchangers in motor vehicles.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MAHLE INT GMBH
- Filing Date
- 2022-11-22
- Publication Date
- 2026-07-14
AI Technical Summary
The existing flat tubes are difficult to braze to achieve ideal brazing contact between the flat tube and the turbulent insert during the brazing process, resulting in insufficient strength and poor heat transfer, especially poor resistance under thermal cycling conditions.
By designing a raised shape on the longitudinal wall of the flat tube, the turbulent insert can be effectively pressed against the wall during brazing, and stress peaks are avoided through a circular transition design. The welding process ensures good contact and connection.
It achieves good brazing contact between the flat tube and the turbulent insert, improves strength and heat transfer efficiency, enhances resistance to thermal cycling, and is suitable for heat exchangers in motor vehicles.
Smart Images
Figure CN116197528B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing a flat tube for a heat exchanger, particularly for a motor vehicle, and a brazed heat exchanger having at least one flat tube. Background Technology
[0002] For example, a general manufacturing method for flat tubes is known from DE 10 2005 050 366 A1, wherein the flat tube is open on one side to accommodate a turbulent insert, but has a straight wall that forms the longitudinal side of the flat tube in the finished tube. Summary of the Invention
[0003] The method for manufacturing a flat tube according to the invention has advantages over other methods, namely, due to the raised shape of the longitudinal wall of the flat tube, when the flat tube is closed, the turbulent insert is advantageously pressed against the wall by the raised wall, thus achieving ideal brazing contact between the flat tube and the turbulent insert during the subsequent brazing process, when the heat exchanger has been fully brazed. This not only ensures strength, especially resistance to thermal cycling, but also ensures heat transfer between the flat tube and the turbulent insert.
[0004] The flat tube for a heat exchanger according to the invention has a first wall and a second wall opposite to the first wall. These two walls form the long sides of the flat tube in cross-section. Two short sides are formed by a third wall and a fourth wall, thus forming corresponding flat tubes. The transitions between the walls are advantageously rounded to avoid creating excessively sharp edges that would generate stress peaks in the material and weaken the tube at these corners. It is also conceivable that the entire third and fourth walls are designed to be arc-shaped, continuously merging into the first and second walls in each case. These walls enclose the inner cavity of the flat tube, in which the medium typically flows in the fully assembled heat exchanger. The medium can be a coolant, oil, or a gaseous fluid, such as exhaust gas or air. A turbulent insert is introduced into the inner cavity. This turbulent insert is typically made of a very thin sheet of metal folded and / or rolled, and is designed such that it is deflected and redirected in a specific manner as the medium flows through the inner cavity, thereby generating turbulence. This significantly increases heat transfer from the flowing medium to the tube. Turbulent inserts must also be designed to generate the lowest possible pressure loss while still achieving good heat transfer. The turbulent insert also absorbs heat and dissipates it to the pipe wall. Turbulent inserts can be simply inserted into a flat pipe, or they can be brazed to the wall at each contact point.
[0005] Good surface contact between the turbulent insert and the flat tube wall is essential for good brazing or, in the case of a non-brazed turbulent insert, good heat transfer. For brazing, a suitable solder-plated sheet or a solder foil separately introduced between the turbulent insert and the flat tube is required. In addition to good heat transfer, brazed turbulent inserts also have the advantage of the very high strength increase of the flat tube, especially increased resistance to thermal cycling.
[0006] Depending on the application and the medium to be cooled, flat tubes can be made of stainless steel or aluminum. Turbulence inserts can also be made of aluminum and / or stainless steel, respectively. Stainless steel is particularly suitable for applications involving exhaust or other corrosive media. However, this does not affect the manufacture of flat tubes.
[0007] The method for manufacturing a flat tube according to the invention comprises the following process steps. In a first step, a sheet material for forming the flat tube is provided. The sheet material may be a single sheet or a metal sheet, or a long strip of thin metal unwound from a large coil or otherwise provided. In a manufacturing apparatus, the provided sheet material is formed into an intermediate tube. This can be carried out in one or more consecutive manufacturing steps. In this case, either the forming tools are changed continuously and the sheet material is formed in directly consecutive forming steps, or the sheet material can be continuously formed in forming tools arranged in a directly consecutive manner. In particular, particularly long sheets unwound from large coils can therefore be formed into intermediate tubes.
[0008] The intermediate tube is shaped such that the sheet metal bulges in at least two sections, and these sections at least partially form a first wall and a second wall, thereby forming the long side of the flat tube. The bulging sections are shaped such that the walls curve inward toward the center of the finished tube. The entire wall may be bulging. In a particularly advantageous embodiment, a portion of the first and second walls may first be made straight, and then the bulging sections may transition continuously onto them. Starting from a third or fourth wall, the first sections of the first and second walls are shaped to be straight and parallel to each other. Sections bulging inward toward the center of the finished tube are respectively adjacent to them. At least a portion of the third or fourth wall, forming the still-open separation point of the flat tube, follows the bulging sections.
[0009] Based on the total width b, i.e., the length of the long side of the flat tube formed by the first and second walls, the length of the straight section is 5% to 40% of the total width b, and in a particularly advantageous embodiment, between 10% and 20% of the total width b. The introduced turbulent insert is held in its final position by the straight section, which largely corresponds to the profile of the finished flat tube in this region. In particular, these straight sections ensure particularly good contact of the turbulent insert with the first and second walls of the flat tube when the tube is subsequently closed.
[0010] The flat tube remains open in the region of the third or fourth wall, thus forming an opening there. This opening is used to insert a turbulence insert into the inner cavity of the flat tube. For this purpose, a turbulence insert is provided accordingly and introduced into the inner cavity of the flat tube. After the turbulence insert is introduced, the flat tube is closed using a welding process.
[0011] In order to advantageously introduce the turbulent insert, the height h2 of the formed opening is at least 80% to 120% of the inner cavity height h of the flat tube. Therefore, by only slightly opening the opening, or particularly advantageously without any further measures, the turbulent insert can be directly introduced into the inner cavity of the flat tube through the opening.
[0012] The opening formed in the intermediate tube is primarily formed by the at least partially raised first and second walls of the flat tube. After the insertion of the turbulent insert, the flat tube is no longer shaped using forming tools, but rather the opening is kept closed simply by applying force before welding. The butt joints of the formed plates are particularly advantageously butt-jointed with each other bluntly. Thus, particularly good welds can be achieved. For example, welding methods that do not introduce additional welding equipment (such as welding wire) can also be used. Laser welding or electrode beam welding can be mentioned here as examples of suitable welding processes, both of which cause the material surface to melt, resulting in a strong weld of the flat tubes at the joint.
[0013] If the flat tube is closed without a turbulent insert, the first and second walls will be recessed inward due to their raised shape. Therefore, a flat tube manufactured in this way is advantageously used only with a turbulent insert inserted into the flat tube. The recessed walls support the inserted turbulent insert, allowing the walls to press well against it. This results in a particularly good brazing connection between the flat tube and the turbulent insert during the subsequent brazing process.
[0014] In another advantageous embodiment of the manufacturing method according to the invention, the sheet metal is provided with protrusions before or after it is provided for forming. On the one hand, these protrusions can advantageously facilitate flow in the flat tubes, but they can also serve as spacers for subsequent installation in the heat exchanger. For this purpose, two flat tubes are positioned adjacent to or stacked on top of each other such that the protrusions contact each of the flat tubes. Thus, the fixed composite of the flat tubes can be manufactured by applying appropriate solder or coating to the sheet metal, particularly in the contact areas.
[0015] The dimensions of the flat tubes are manufactured to model specifications based on the heat exchanger. Heat exchangers typically consist of a large number of flat tubes supplied in bundles. The ends of the flat tubes are housed in tube sheets, each tube sheet having an opening for each flat tube. These sheets partially enclose a condensation space, which is closed using a cap. This condensation space then has suitable interfaces for supplying or discharging the medium flowing through the flat tubes. The flat tubes themselves may also have ribs between the individual flat tubes, which are additionally introduced into the bundle and thus enable particularly good heat transfer from the flat tubes to the medium flowing around them. The space with the flat tubes can also be enclosed by a housing, creating additional space for flow. However, the flat tubes can also be freely circulated and therefore ideally circulated by ambient air, supplied as an oncoming wind by a fan or by the movement of a vehicle.
[0016] The tube bundles, consisting of arranged thin plates and optionally caps, are typically brazed in a brazing furnace to form a robust composite, which is also sealed relative to the connection between the flat tubes and the thin plates. In this working step, a turbulent insert introduced into the flat tubes is subsequently brazed to the flat tubes as well. The robustly brazed composite, and particularly the dimensional stability of the flat tubes (advantageously achieved through the exceptionally good brazing of the turbulent inserts to the flat tubes), improves the heat exchanger's tolerance to thermal cycling. Thermal cycling refers to more frequent and larger temperature changes in a heat exchanger, such as when a cooler in a cooling circuit suddenly opens as needed, due to temporary high cooling requirements, for example, when a truck is driving uphill, or when a fuel cell or internal combustion engine causes a large amount of heat to be introduced into the cooling system.
[0017] Due to these temperature fluctuations, the heat exchanger will be subjected to enormous mechanical stress due to the temperature-dependent expansion of the components. Over time, this can lead to critical point failure of the components, where stress peaks occur.
[0018] Depending on the intended use of the heat exchanger, the medium to be cooled can thus be guided through a flat tube, through which a cooling medium such as coolant or air flows. Exhaust heat exchangers can be designed in this way, where exhaust gas, possibly from an internal combustion engine but also from a fuel cell, is guided through the flat tube and coolant is directed into the space surrounding the flat tube. However, flat tubes manufactured in this way can also be used in other types of heat exchangers, such as coolant heat exchangers, booster air heat exchangers, or condensers. Attached Figure Description
[0019] Further advantageous embodiments of the invention are described in conjunction with the following drawings. In the drawings:
[0020] Figure 1 A flat tube formed into an intermediate tube according to the present invention is shown.
[0021] Figure 2 A flat tube according to the present invention is shown as a finished tube.
[0022] Figure 3 A schematic diagram of the various process steps used to manufacture flat tubes is shown. Detailed Implementation
[0023] Figure 1 A flat tube 1, formed into an intermediate tube 2 according to the present invention, is shown. The intermediate tube 2 is formed such that the sheet 5 protrudes in at least two sections B1 and B2 and the sections B1 and B2 at least partially form a first wall W1 and a second wall W2, thereby forming the long side of the flat tube 1.
[0024] The raised sections B1 and B2 are shaped such that the walls W1 and W2 curve inward toward the center of the finished tube. Only portions of the first wall W1 and the second wall W2 in sections B1 and B2 are raised. The first portions of the walls W1 and W2 are made straight in sections A1 and A2 and then continuously incorporated into the raised sections B1 and B2. However, it is also conceivable that the entire walls W1 and W2 are raised. The straight sections A1 and A2 are then advantageously used to securely house the turbulent insert 4 arranged in the flat tube 1 in the correct position until the flat tube 1 is welded closed, since the flat tube 1 already largely corresponds to the subsequent profile of the finished flat tube 1 in this region. The lengths of the straight sections A1 and A2 are respectively 5% to 40% of the total width b of the flat tube 1. In a particularly advantageous manner, the lengths are between 10% and 20%.
[0025] Therefore, starting from the third and fourth walls W3, W4, the first sections A1, A2 of the first and second walls W1, W2 are formed as straight sections parallel to each other. Sections B1, B2, which bulge inward toward the center of the finished tube, are adjacent to them. A portion of the third and fourth walls W3, W4, forming the opening 6 of the intermediate tube 2, is at least partially following the bulging sections B1, B2. In the region of the opening 6, the free ends of the sheet metal 5 form butt joints 9, 9', which are subsequently welded together in the finished flat tube.
[0026] Ideally, the opening 6 has a minimum width h2 that is greater than or almost equal to the height h of the inner cavity 3. Therefore, the turbulent insert 4 to be arranged in the inner cavity 3 can be easily inserted. Alternatively, to insert the turbulent insert 4, the tube must be slightly compressed in the elastic region to prevent further deformation of the wall.
[0027] The flat tube 1 may have protrusions 8 on its long side surface, which is formed by a first wall W1 and a second wall W2. The protrusions may serve as contact points between the flat tubes 1 arranged adjacent to each other to optimize the turbulence of the fluid circulating in the flat tube or for brazing in the tube complex later in the heat exchanger.
[0028] Figure 2 A flat tube 1 in its finished state according to the invention is shown. Walls W1 and W2, and walls W3 and W4, are each parallel to each other and form the outer boundary of the flat tube 1, wherein walls W3 and W4 form the short side of the flat tube 1, and walls W1 and W2 form the long side of the flat tube. Radius is provided at the transition of the walls, which is advantageous for any stress peaks, thereby increasing the load-bearing capacity of the tube. It is also conceivable that walls W3 and W4 are formed as continuous arcs. The total width b of the flat tube 1 is several times the internal height of the flat tube. The wall thickness of the flat tube 1, and therefore the thickness of the sheet metal 5 used, is typically in the range of 0.1 mm to 1.5 mm. Depending on the application, the flat tube 1 is suitably made of aluminum or stainless steel, wherein stainless steel tubes are suitable for, for example, gas heat exchangers, such as exhaust coolers or coolers for fuel cell applications, and aluminum tubes are suitable for use with coolants or oils. The decisive factor here is whether the medium to be cooled contains corrosive substances that corrode materials, as is the case with exhaust coolers. The exhaust contains combustion residues that can condense together with water in the exhaust and thus, as an acidic or alkaline fluid, rapidly damage the aluminum flat tube 1.
[0029] Turbulent insert 4 is arranged within the inner cavity 3 of the flat tube 1. Walls W1 and W2 are pressed against the turbulent insert 4 and thus shaped to be parallel to each other. Without the turbulent insert 4, they would bulge inwards. The flat tube 3 is then inserted, with its ends inserted into the tube sheet as an assembly, and then brazed to form a heat exchanger. For a tight brazed connection between the tube sheet and the flat tube 3, the opening of the tube sheet and the contour of the flat tube 1 must be identical, resulting in only a very small gap. Therefore, the flat tube 3 must have very high shape accuracy after welding.
[0030] In steps a) to e), Figure 3Various process steps for manufacturing the flat tube 3 according to the invention are shown. In the first step, a sheet material 5 is provided. The intermediate tube 2 is formed in the first forming step b) and the immediately following forming step c). Depending on the design of the forming apparatus, the forming processes shown in steps b) and c) may also be carried out in one or more steps. The exemplary representation of the forming process here is only one possible embodiment and does not show the required steps in detail. In the next step d), the turbulent insert 4 is at least partially wrapped with solder foil 7 and then introduced into the inner cavity 3 through the opening 6 in the intermediate tube 2 and positioned there. Instead of solder foil 7, the sheet material 5 or the turbulent insert 4 itself may also be solder-plated. This means that the auxiliary materials required for the brazing process have been applied to the corresponding materials before assembly.
[0031] In the final step e), the intermediate tube 2 is pressed together by the device using forces F1 and F2, so that the butt joints 9 and 9' remain stacked on top of each other. The closed tubes are then welded by a welding method, particularly advantageously by beam welding, especially by laser welding 10. The flat tube 1 is thus completed and can be further used for installation in a heat exchanger. The final brazing connection of the flat tube 1 to the turbulent insert 4 arranged in the inner cavity 3 is advantageously performed during the final brazing process, in which the entire heat exchanger is brazed.
[0032] List of reference numerals
[0033] 1. Flat tube
[0034] 2. Intermediate pipe
[0035] 3. Inner cavity
[0036] 4 Turbulent Insert
[0037] 5. Board material
[0038] 6 Openings
[0039] 7 Solder foil
[0040] 8. Protrusion
[0041] 9. 9' connector
[0042] 10 laser beams
[0043] A1, A2: First straight segment and second straight segment
[0044] B1, B2: the first raised section and the second raised section
[0045] W1 First Wall
[0046] W2 Second Wall
[0047] W3 Third Wall
[0048] W4 Fourth Wall
[0049] F1, F2 force
[0050] b. Total width of the flat tube
[0051] h is the height of the inner cavity of the flat tube.
[0052] h2 Width of the opening in the intermediate tube
Claims
1. A method for manufacturing a flat tube (1) for a heat exchanger in a motor vehicle, the flat tube having a first wall (W1), a second wall (W2) opposite to the first wall (W1), a third wall (W3) connecting the first wall and the second wall (W1, W2), a fourth wall (W4) connecting the second wall and the first wall (W2, W1), and an inner cavity (3) through which a medium flows, wherein the first wall and the second wall are longer than the third wall and the fourth wall, wherein a turbulent insertion member (4) is disposed in the inner cavity (3), wherein the method comprises at least the following process steps: - Provide sheet materials (5) - The sheet material (5) is shaped into an intermediate tube (2) such that the sheet material (5) is raised in at least two raised sections and the raised sections at least partially form the first wall and the second wall (W1, W2) of the flat tube (1) and the intermediate tube (2) forms an opening (6) in a region of either the third wall or the fourth wall (W3, W4). - Provide a turbulent insert (4) and insert it into the cavity (3). - The opening (6) is closed by welding.
2. The method for manufacturing a flat tube (1) according to claim 1, wherein in the intermediate tube (2) manufactured during the forming process, the opposing first wall and second wall (W1, W2) are oriented parallel to each other with a first straight segment (A1) or a second straight segment (A2) adjacent to the third wall (W3) or the fourth wall (W4), and a first raised segment (B1) of the raised segments is adjacent to the first straight segment (A1) and a second raised segment (B2) of the raised segments is adjacent to the second straight segment (A2).
3. The method for manufacturing a flat tube (1) according to claim 2, wherein the lengths of the first straight section (A1) and the second straight section (A2) are 5% to 40% of the total width b of the flat tube (1).
4. The method of manufacturing a flat tube (1) according to claim 3, wherein the raised section is oriented such that the height h2 of the opening (6) in the intermediate tube (2) is at least 80% to 120% of the height h of the inner cavity (3) of the flat tube (1).
5. The method of manufacturing a flat tube (1) according to any one of claims 1 to 4, wherein the turbulent insert (4) is at least partially wrapped with solder foil (7) before being inserted into the inner cavity (3).
6. The method of manufacturing a flat tube (1) according to any one of claims 1 to 4, wherein the turbulent insert (4) is introduced into the inner cavity (3) through the opening (6).
7. The method of manufacturing a flat tube (1) according to any one of claims 1 to 4, wherein the sheet (5) is provided with protrusions (8) before or after it is provided.
8. The method of manufacturing a flat tube (1) according to any one of claims 1 to 4, wherein the intermediate tube (2) is closed by applying forces (F1, F2) to the first wall and the second wall (W1, W2) before closure, thereby closing the opening (6).
9. The method for manufacturing a flat tube (1) according to any one of claims 1 to 4, wherein the intermediate tube (2) is closed by laser welding (10).
10. The method for manufacturing a flat tube (1) according to claim 3, wherein the lengths of the first straight section (A1) and the second straight section (A2) are 10% to 20% of the total width b of the flat tube (1).
11. The method of manufacturing a flat tube (1) according to claim 8, wherein the intermediate tube (2) is brought together before closure by applying forces (F1, F2) to the first wall and the second wall (W1, W2), such that the butt joints (9, 9') of the formed sheet (5) are butted together in a blunt manner.
12. A heat exchanger for a motor vehicle having at least one flat tube (1) manufactured according to any one of the preceding claims, wherein the heat exchanger is brazed and the flat tube is formed of aluminum or stainless steel.