Soldering frame, method for manufacturing a heat exchanger and heat exchanger

Abstract

The present invention relates to a soldering frame (1) for pre-tensioning a heat exchanger stack (2) comprising tubes (3) and heat exchanger elements (4) during a soldering process. The essential feature of the invention is that at least one additional spring element (5) is provided, designed separately from the soldering frame (1), by means of which the heat exchanger stack (2) can be additionally pre-tensioned. This makes it particularly effective to avoid shrinkage cracks.

Description

[0001] The present invention relates to a brazing frame for pre-tensioning a heat exchanger stack comprising tubes and heat exchanger elements during a brazing process, according to the preamble of claim 1. The invention further relates to a method for manufacturing a heat exchanger and to a heat exchanger manufactured according to this method.

[0002] When brazing heat exchangers, which typically consist of a stack of alternating stacked tubes and heat exchanger elements, the application of so-called CAB (Controlled Atmosphere Brazing) technology repeatedly results in the heat exchanger elements, such as corrugated fins, not being brazed precisely to the tubes. Even with extremely tight dimensional tolerances, stacking the individual tubes and heat exchanger elements—averaging 50–60 tubes and 50–60 heat exchanger elements—leads to a comparatively large variation in dimensional tolerance across the entire heat exchanger stack.A soldering frame used for soldering is set to a predefined dimension and is often unable to reliably compensate for all dimensional tolerances occurring in the heat exchanger stack clamped in the soldering frame, so that, especially when the soldered heat exchanger stack cools down, the heat exchanger elements can tear off from the associated tubes at certain points, resulting in increased rejects.

[0003] The present invention therefore addresses the problem of providing an improved or at least an alternative embodiment for a soldering frame of the generic type, by means of which, in particular, the disadvantages known from the prior art can be overcome.

[0004] This problem is solved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject matter of the dependent claims.

[0005] The present invention is based on the general concept of using not only a soldering frame, as previously known, in which the heat exchanger stack to be soldered is clamped / pre-tensioned, but also providing at least one additional spring element, designed separately from the soldering frame, by means of which the heat exchanger stack can be further pre-tensioned. By adding or inserting at least one additional spring element, the elastic pressure on the heat exchanger stack to be soldered can be increased during the soldering process and, in particular, also during cooling after the actual soldering process, for example, in a cooler downstream of the soldering furnace, thereby significantly reducing the risk of shrinkage cracks.By means of at least one spring element (and of course, several such spring elements can be used), an individual and therefore extremely flexible additional and, in particular, local preload can be achieved on the heat exchanger stack to be brazed, without requiring any complex modifications to the brazing frame itself. The at least one additional spring element can thus be stored, for example, in a container next to the brazing frame and used as needed. With at least one additional spring element, the reject rate can be significantly reduced, and at the same time, a cost-effective and highly flexible solution is created that can be used as needed and does not require significant financial investment. Furthermore, such additional spring elements can be mounted quickly and easily on the respective brazing frame.The additional spring elements also allow for relatively easy disassembly for cleaning after flux deposits, compared to spring elements permanently attached to the soldering frame. Furthermore, cycle time is not increased when the soldering frame is placed on the heat exchanger stack to be soldered, which is advantageous for production throughput times.

[0006] In an advantageous embodiment of the soldering frame according to the invention, at least one spring element is a torsion spring or is designed as such. Torsion springs, also called helical springs, are subjected to a torque about their spring body axis, whereby a spring wire is subjected to bending stress. Such torsion springs can be manufactured relatively easily and cost-effectively in a wide variety of embodiments, including with different arms and spring stiffnesses. The improved preload of the heat exchanger stack to be soldered in the soldering frame according to the invention can therefore be achieved with cost-effective, easy-to-manufacture, and easy-to-assemble torsion springs.

[0007] In a particularly preferred embodiment of the soldering frame according to the invention, the torsion spring is supported by a first arm directly or indirectly via a clamping strip on the heat exchanger stack and by a second arm on the soldering frame. The clamping strip, in turn, is supported on the heat exchanger stack to be pre-tensioned, and the clamping strip can, for example, be mounted on a rotatable arm. The torsion spring can be pre-tensioned by compressing its two arms and attached to the soldering frame in such a pre-tensioned state. By releasing the tension on the two arms, the torsion spring is thus clamped between the soldering frame and the clamping strip, thereby pre-tensioning the latter against the heat exchanger stack to be pre-tensioned. Such torsion springs can be manually, i.e.,They can be mounted without any additional tools, although it is of course conceivable that, for higher spring stiffnesses, appropriate positioning tools, such as pliers, could be used. These torsion springs are usually made of stainless steel and are therefore both corrosion-resistant and easy to clean of flux deposits, which are used during the soldering process to ensure the reliable flow of the solder.

[0008] It is of course clear that the leg spring can also have more than one first and one second arm, for example also an additional middle arm, so that it is supported via the middle arm on the soldering frame and via the first and second arms on the heat exchanger stack, for example directly or indirectly via the clamping strip.

[0009] Furthermore, retaining contours can be arranged on at least the first and / or second arm, for example by means of a corresponding development of the first / or second arm, which enable, for example, the first arm to be hooked onto the clamping strip or the second arm onto the soldering frame, and thereby ensure reliable fixation of the leg spring on the soldering frame.

[0010] In an advantageous embodiment of the soldering frame according to the invention, several spring elements are attached at different locations. Experience in soldering heat exchanger stacks has shown that the preload applied by the soldering frame is often insufficient to reliably prevent shrinkage cracks during cooling after soldering. Since such shrinkage cracks, in which, for example, a heat exchanger element detaches from its associated tube, particularly a flat tube, can lead to the rejection of the entire heat exchanger stack, such shrinkage cracks must be avoided at all costs. By means of at least one additional spring element, preventing such shrinkage cracks is easily achievable, so that the rejection rate can be significantly reduced, preferably even eliminated, requiring only the use of inexpensive and easy-to-install additional spring elements.The spring elements are arranged particularly at those points of the heat exchanger stack to be pre-tensioned that are especially prone to cracking during cooling after the actual soldering process.

[0011] The present invention is further based on the general concept of providing a method for manufacturing a heat exchanger, for example a cooler, in which tubes and heat exchanger elements arranged between them are first stacked to form a heat exchanger stack, and this stack is clamped in a corresponding brazing frame according to one of the preceding paragraphs. Subsequently, at least one additional spring element is inserted or clamped between the brazing frame and the heat exchanger stack to be pre-tensioned, by means of which the heat exchanger stack can be additionally tensioned / pre-tensioned. The heat exchanger stack thus pre-tensioned is then placed in a brazing furnace and heated therein, whereby a brazing alloy applied to the tubes or the heat exchanger elements melts and creates a metallurgical bond between the heat exchanger elements and the tubes.The brazed heat exchanger stack is then removed from the brazing furnace and cooled, for example in a cooling section. Finally, the at least one spring element is removed and the brazed heat exchanger stack is taken out of the brazing frame. After removal, the brazed heat exchanger stack can, of course, be inspected for cracks, whereby shrinkage cracks, which previously occurred, can be reliably avoided due to the additional spring elements. With the method according to the invention, a heat exchanger or a heat exchanger stack can thus be manufactured reliably with significantly reduced reject rates and therefore with significantly reduced unit costs.

[0012] In an advantageous embodiment of the method according to the invention, a torsion spring is used as the spring element. Such torsion springs can be manufactured not only cost-effectively but also in virtually any embodiment, particularly with a wide variety of spring stiffnesses. This allows, for example, a worker to be offered a variety of torsion springs when clamping a heat exchanger stack to be brazed into a brazing frame, in order to exert additional elastic pressure on the heat exchanger stack. The worker compresses the torsion spring with both arms, thereby exerting a bending moment on a spring wire of the torsion spring. The torsion spring is then positioned so that it is supported by a first arm, either directly or indirectly via a clamping bar on the heat exchanger stack, and by a second arm on the brazing frame.This allows the additional preload of the heat exchanger stack to be brazed to be achieved in an extremely flexible, cost-effective and yet highly effective manner.

[0013] If the heat exchanger stack to be brazed has areas where there is an increased risk of shrinkage cracks, for example in areas with significantly different masses and a correspondingly significantly different cooling behavior, the heat exchanger stack can be additionally prestressed elastically in these areas with, for example, two or more additional spring elements in order to reliably prevent such shrinkage cracks.

[0014] The present invention is further based on the general idea of ​​manufacturing a heat exchanger according to the method described in the preceding paragraphs and thus transferring the advantages described with respect to the inventive method to the inventive heat exchanger. Specifically, these advantages lie in a significantly reduced reject rate, since shrinkage cracks, which often occur during cooling after brazing, can now be reliably, cost-effectively, and with extreme ease of manufacturing.

[0015] In an advantageous embodiment of the heat exchanger according to the invention, the tubes of the heat exchanger stack are designed as flat tubes and the heat exchanger elements as corrugated fins. By means of flat tubes and the corrugated fins arranged between them, a particularly large surface area available for heat transfer can be created, thereby increasing the performance of such a heat exchanger. To ensure high performance of the heat exchanger, a reliable, material-bonded connection between the flat tubes and the corrugated fins is essential.

[0016] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0017] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention. The components of a higher-level unit, such as a device, apparatus, or arrangement, mentioned above and those to be mentioned below, which are designated separately, can form separate parts or components of this unit or be integral areas or sections of this unit, even if this is depicted differently in the drawings.

[0018] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0019] Each of these shows, schematically, Fig. 1 a view of a soldering frame according to the invention in the area of ​​an additional spring element, Fig. 2 a top view of another embodiment of a soldering frame according to the invention, Fig. 3 a detailed representation of the soldering frame according to the invention made of Fig. 2. Viewed from the back.

[0020] According to the Fig. Figures 1-3 describe a soldering frame 1 according to the invention for pre-tensioning a heat exchanger stack 2 consisting of tubes 3 and heat exchanger elements 4 during a soldering process. The spring element 5 is designed separately from the soldering frame 1 and allows the heat exchanger stack 2 to be additionally pre-tensioned by means of this spring element 5. "Separate from the soldering frame 1" means that the additional spring element 5 does not form a permanent part of the soldering frame 1, but is manufactured and stored separately and is only used as needed.

[0021] When soldering a heat exchanger stack 2 consisting of alternating stacks of tubes 3 and heat exchanger elements 4 arranged between them, shrinkage cracks can occur, particularly during cooling after the actual soldering process. These cracks can lead to rejection or at least defects. To reduce or prevent such shrinkage cracks, the soldering frame 1 typically has the capability to pre-tension the heat exchanger stack 2 arranged within it.

[0022] Even with small dimensional tolerances of individual tubes 3 or heat exchanger elements 4, this leads to comparatively large variations in the dimensional tolerance in the entire heat exchanger stack 2 with, for example, 100-120 elements, i.e., for example, 50-60 tubes 3 and 50-60 heat exchanger elements 4, which cannot be compensated for with a rigid soldering frame 1, since the soldering frame 1 is usually set to a predefined dimension.

[0023] By adding at least one additional spring element 5, designed separately from the soldering frame 1 according to the invention, an additional pressure can be exerted on the heat exchanger stack 2 after its arrangement in the soldering frame 1, which at least minimizes, and preferably even prevents, the problem of cracking, especially during cooling after the actual soldering process.

[0024] If one considers the spring elements 5 according to the Fig. Figures 1-3 show that at least one of the spring elements 5 depicted in each figure is designed as a torsion spring 6. Such a torsion spring 6 typically has a first arm 7 and a second arm 8. Its first arm 7 is supported on the heat exchanger stack 2 either directly or indirectly via a clamping strip 9, and its second arm 8 is supported on the brazing frame 1. Because they are designed as torsion springs, these torsion springs 6 offer the advantage of being able to store a large amount of elastic energy and release it as needed. Furthermore, their spiral design allows for space-saving arrangement, and they are extremely durable and precise with regard to the forces they deliver. In addition, such torsion springs 6 can be manufactured cost-effectively and with virtually any desired spring stiffness.

[0025] The corresponding to the Fig. The torsion spring 6 shown in Figure 1 is to be understood as purely exemplary, so that other torsion springs 6 are also to be included in the invention, in particular if they have, for example, an additional central arm besides a first arm 7 and a second arm 8. In this case, it would be conceivable, for example, that such a torsion spring 6 is supported with the central arm on the soldering frame 1 and with the first and second arms 7, 8 directly or indirectly on the heat exchanger stack 2.

[0026] If one considers the first arm 7, which corresponds to the Fig. As shown in Figure 1, the torsion spring 6 can be seen to have a retaining contour 10 in the form of a bent area, which allows the torsion spring 6 to be reliably fixed.

[0027] Depending on the desired additional elastic preload of the heat exchanger stack 2, several such spring elements 5, for example leg springs 6, can of course be arranged to additionally preload the heat exchanger stack 2.

[0028] In a method according to the invention for manufacturing a heat exchanger or the heat exchanger stack 2, tubes 3 and heat exchanger elements 4 are first stacked alternately to form a heat exchanger stack 2, which is then clamped or arranged in a soldering frame 1 in accordance with the preceding paragraphs. In order to further increase the elastic preload of the heat exchanger stack 2 manufactured in this way and thus, in particular, to prevent shrinkage cracks, at least one additional spring element 5, for example a torsion spring 6, is used, by means of which the heat exchanger stack 2 is additionally preloaded.

[0029] The pre-stressed heat exchanger stack 2 is then placed in a brazing furnace, brazed, and subsequently removed and cooled. Finally, at least one spring element 5 can be removed, and the brazed heat exchanger stack 2 can be taken out of the brazing frame 1. This allows for the production of a heat exchanger stack 2, and thus ultimately a heat exchanger, with a significantly lower reject rate and therefore significantly lower unit costs. The tubes 3 can, for example, be designed as flat tubes, while the heat exchanger elements 4 can be designed as corrugated fins. This allows for a comparatively large, yet weight-optimized surface area for heat transfer.

[0030] All in all, the inventive method and the inventive heat exchanger stack 2 or heat exchanger can achieve a significant reduction in the reject rate, with the additional spring elements 5 used for this purpose being cost-effective and available in virtually any embodiment. For example, it is conceivable that a worker loading the soldering frame 1 with the heat exchanger stack 2 to be soldered could be provided with a kit of different spring elements 5, from which he could select and additionally pre-tension the heat exchanger stack 2 to be soldered at individual, local, and required points.

[0031] Furthermore, by designing the spring elements 5 in particular as a torsion spring 6, quick and easy assembly can be achieved, as well as easy disassembly for cleaning the spring elements 5 after, for example, flux deposits. Reference symbol list 1 soldering frame 2 heat exchanger stacks 3 pipes 4 heat exchanger elements 5 spring element 6 leg springs 7 first arm 8 second arm 9 tension strip 10 Holding contour

Claims

[1] Soldering frame (1) for pre-tensioning a heat exchanger stack (2) comprising tubes (3) and heat exchanger elements (4) during a soldering process, characterized by , that at least one additional spring element (5) designed separately from the soldering frame (1) is provided, via which the heat exchanger stack (2) can be additionally pre-tensioned. [2] Soldering frame (1) according to claim 1, characterized by , that at least one spring element (5) is designed as a torsion spring (6). [3] Soldering frame (2) according to claim 2, characterized by , that the leg spring (6) is supported by means of a first arm (7) directly or indirectly via a clamping strip (9) on the heat exchanger stack (2) and by means of a second arm (8) on the soldering frame (1). [4] Soldering frame (1) according to one of the preceding claims, characterized by , that several spring elements (5) are attached at different locations. [5] Method for manufacturing a heat exchanger wherein - Tubes (3) and heat exchanger elements (4) are stacked alternately to form a heat exchanger stack (2) and this stack is clamped in a soldering frame (1) according to one of the preceding claims, - the heat exchanger stack (2) is additionally pre-tensioned by at least one additional spring element (5) designed separately from the soldering frame (1), - the heat exchanger stack (2) is placed in a soldering furnace and soldered there, - the heat exchanger stack (2) is removed from the soldering furnace and cools down, - that at least one spring element (5) is removed and the heat exchanger stack (2) is taken out of the soldering frame (1). [6] Method according to claim 5, characterized by , that a torsion spring (6) is used as the spring element (5). [7] Method according to claim 6, characterized by, that the leg spring (6) is supported by means of a first arm (7) directly or indirectly via a clamping strip (9) on the heat exchanger stack (2) and by means of a second arm (8) on the soldering frame (1). [8] Method according to any one of claims 5 to 7, characterized by , that several spring elements (5) are attached at different locations. [9] Heat exchanger with a heat exchanger stack (2) manufactured according to the method of any one of claims 5 to 8. [10] Heat exchanger stack (2) according to claim 9, characterized by , that the tubes (3) are designed as flat tubes and the heat exchanger elements (4) as corrugated fins.

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