METHOD OF MANUFACTURING A THERMOPRAM.

Abstract

A method of manufacturing a heat exchanger includes sealing the tubes to the header slots and brazing the tubes to the header slots. The method further includes attaching a cover to the header to cover the liquid-side surface of the header and the ends of the tubes, and applying flux to the air-side surface of the header and the tubes. Attaching the cover to the header is done after sealing the tubes to the header slots and before applying flux to the air-side surface of the header and the tubes. Applying flux is done before brazing each tube to the header slot, and sealing each tube to the header slot includes sealing the perimeter of each tube to the header slot.

Description

The present invention relates to thermocouples and to a method of manufacturing thermocouples. BACKGROUND OF THE INVENTION Thermoexchangers include components such as tubes, heads, and fins that are joined together in a brazing process. Flux is commonly applied to the thermoexchanger components before brazing to ensure high-quality welded joints. The fluxing process typically involves immersing an assembled thermoexchanger in a flux composition or spraying the flux composition around the assembled thermoexchanger. The fluxing process can be complex, and it is undesirable for a significant amount of flux to remain on the thermoexchanger. Therefore, the thermoexchanger assembly is often cleaned at or near the end of thermoexchanger production to at least partially remove the flux. SUMMARY OF THE INVENTION The present invention provides, in one aspect, a method for manufacturing a heat exchanger. The method comprises arranging a plurality of tubes in a formation, coupling the plurality of tubes to a header, including sealing each of the tubes of the plurality of tubes to a header groove of a plurality of header grooves in the header and welding each of the tubes of the plurality of tubes to said header groove of the plurality of header grooves, coupling a cover to the header to cover the liquid-side surface of the header and to cover the ends of the tubes, and applying flux to an air-side surface of the header and to the plurality of tubes, wherein the coupling of the cover to the header is performed after sealing each of the tubes of the plurality of tubes to said header groove of the plurality of header grooves.wherein the cover is coupled to the head before applying flux to the air-side surface of the head and to the plurality of tubes, wherein the flux application is performed before welding each of the tubes of the plurality of tubes to said head slot of the plurality of head slots, and wherein sealing each of the tubes of the plurality of tubes to said head slot includes sealing the perimeter of each of the tubes to said head slot. In some models, the tank is attached to the head by crimping. In some embodiments, the step of coupling the ends of each of the plurality of tubes to a liquid-side surface of the head includes welding each of the plurality of tubes to the liquid-side surface of the head. In some embodiments, the method also includes a step of placing a header on the plurality of tubes after arranging the plurality of tubes in a formation. In some embodiments, the stage of attaching the cover to the head to cover the liquid-side surface and the ends of the tubes is performed before the stage of applying flux to the plurality of tubes adjacent to the air-side surface of the head and to the head. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view of a thermocouple. Figure 2 is a flow diagram illustrating the installation of the thermochanger in Figure 1. Figure 3 is a partial exploded perspective view of the thermocouple in Figure 1. Figure 4 is a perspective view of the tubes being welded to a thermochanger head of Figure 1. Figure 5 is a partial exploded view of the thermocouple from Figure 1. Figure 6 is an enlarged cross-sectional view of the thermocouple in Figure 1. Before any embodiment of the invention is explained in detail, it should be understood that the invention is not limited in its application to the construction details and arrangement of components set forth in the following description or illustrated in the following drawings. The invention is susceptible to other embodiments and may be practiced or carried out in various ways. Furthermore, it should be understood that the phraseology and terminology used herein are for descriptive purposes and should not be considered limiting. DETAILED DESCRIPTION OF THE INVENTION Figure 1 illustrates a thermocouple 10 comprising a first collection tank 14 and a second collection tank 18. The first collection tank 14 includes a header 22 and a collection tank 26 with an inlet 30. The second collection tank 18 includes a header 34 and a collection tank 38 with an outlet 42. In some embodiments, each of the headers 22 and 34 is made of aluminum with a brazed coating on one or both sides. In some embodiments, the collection tanks 26 and 38 are made of plastic, and in such embodiments, sealing gaskets are arranged between the collection tanks 26 and 38 and their respective headers 22 and 34. In some embodiments, the collection tanks 26 and 38 are made of aluminum and brazed to the headers 22 and 34.A plurality of tubes 46 seamlessly connect the first and second collection tank assemblies 14, 18 and are coupled to the headers 22, 34 of the first and second collection tank assemblies 14, 18. In some embodiments, the tubes 46 are formed of aluminum with a brazing coating on one or both sides. In some embodiments, the tubes 46 are brazed, but in other embodiments, they may be folded. In some embodiments, the tubes 46 have a coating on both sides. Fins 47 are arranged between the tubes 46 and are formed of uncoated aluminum. Side plates 56, as shown in Figure 3, are located at the ends of the heat exchanger 10. The side plates 56 are formed of aluminum with a coating on one or both sides. Each side plate 56 is attached to one of the fins 47. In the operation of the thermoexchanger 10, a liquid (e.g., water and / or coolant) flows into the inlet 30 of the collection tank 26 at a relatively high temperature, then flows through the tubes 46 into the collection tank 38, before flowing out to the outlet 42. As it flows through the tubes 46, the liquid cools, as heat escapes from the liquid through the tubes 46, which are normally cooled by airflow. In some embodiments, the thermoexchanger is used as a coolant for fuel cell cooling, and in such cases, the coolant must have fewer impurities, such as flux residue. Figure 2 illustrates a method 50 for fabricating the thermoexchanger 10, or at least the first collection tank installation 14 and / or the second collection tank installation 18 of the thermoexchanger 10. For simplicity, the following explanation will only cover the fabrication of the first collection tank installation 14. First, as shown in step 54, the tubes 46 are arranged in a matrix, stack, or formation in which they will be coupled to the header 22. During step 54, the side plate 56 is located at the bottom of the stack, and an opposite side plate 56 is located at the top of the stack. One of the fins 47 is located adjacent to each of the side plates 56. The stack is completed by alternating fins and tubes 46. In step 58, as shown in Figure 3, the header 22 is placed over the tubes 46 by inserting the tubes 46 through the slots 60 in the header 22. In step 62, the ends 66 of the tubes 46 are welded to the header 22 at a liquid-side surface 70 (Figure 3), thus preventing flow from penetrating the header 22 to make contact with the liquid-side surface 70 or the ends 66 of the tubes 46. Figure 4 illustrates an exemplary process of welding the tubes 46 to the header 22, using a multi-torch welder 74. No brazing filler or post-brazing is applied between the tubes 46 and the respective headers 22, 34, as the mating surfaces are coated with brazing material that eventually melts to join the tubes 46 to the respective headers 22, 34. The slots 60 have collars that extend into the head 22.These collars have a thinner wall than the nominal thickness of the 22 head, tapering as they are formed. In some embodiments, the collars are formed in such a way that they are thinner than the nominal thickness of the material forming the 22 head. Ideally, the thickness of the collar material would be equal to the thickness of the tube material. The collar extends in one direction into the 22 head. During stage 62, the production line includes a welder on one side, which could be a torch welder as shown in Figure 4, or it could be another type of conventional welder. The production line may include welders on both sides. As the die 22 and the tubes 46 stop at the welder's location, the welder welds the tubes 46 to die 22. For a production line with a welder on only one side, die 22 must be rotated to weld the tubes 46 to die 22 on the opposite side. For a production line with welders on both sides, the tubes 46 can be welded to dies 22 on both sides of die 22 simultaneously. The geometry of groove 60 in die 22 helps create the weld between the tube 46 and die 22.The insertion distance of the tubes 46 into the head 22 is such that the ends of the tubes 46 extend through the head 22 and beyond the edges of the collars. The welding process melts the ends of the tubes 46 and part of the collars to create a weld bead completely around the tube groove 60, sealing the tubes 46 to the tube grooves 60. In some models, the welder includes a torch head, which can move in a predetermined pattern, and the torch head includes a plurality of torches. The pattern is programmed so that at least one torch moves around the perimeter of each tube 46 or collar during the welding of the tube 46 to the collar. The torch can also follow a pattern that crosses an area of ​​the tip (the narrow end of the tube) of tube 46 at least once in each area of ​​the tip of tube 46 and, ideally, several times. The welding pattern in the tip areas may appear as an X. The purpose of the welding in stage 62 is to completely seal the tube 46 to the head 22 around the groove 60 of the tube. The weld bead will be flush with the inside of the head 22, 2–3 mm from the inner wall of the head 22. In step 86, a temporary cover 90 is fitted over the header 22, thereby covering the liquid-side surface 70 and the ends 66 of the tubes 46 welded to the header 22. During step 86, the temporary cover 90 extends completely over the header 22, around its perimeter, and overlaps the header's side walls on the outside. In some embodiments, the temporary cover 90 fits inside the header 22, completely covering the inside of the header and the ends 66 of the tubes 46, and overlaps the header's side walls on the inside. In another embodiment, instead of the temporary cover 90, the collection tank 26 is welded to the header 22 during the brazing operation. The temporary cover 90 can be made of plastic or metal.The temporary cover 90 can be attached to the printhead by means of a squeeze fit, a press fit, clamps, straps, or a mechanical fitting having a geometry that fits both the printhead 22 and the temporary cover 90. In step 94, flux is applied to the tubes 46, fins 47, side plates 56, and the header surfaces 22 that face the tubes 46. The flux removes oxidation from these surfaces during a subsequent brazing process, thereby preventing corrosion and promoting the free flow of brazing material from the brazing lining. Because the temporary cover 90 covers the liquid-side surface 70 and the ends 66 of the hubs 46 are brazed to the header 22 before the flux is applied in step 94, tube contamination, which can sometimes occur during flux application, is inhibited. Therefore, subsequent contamination of the liquid, such as the fuel cell coolant, as it passes through the tubes 46 is inhibited.In some embodiments, the temporary cover 90 is removed from the head 22 after the flux and before brazing, particularly when the temporary cover 90 is formed from a plastic material. In step 98, the head 22 undergoes a brazing process while the temporary cover 90 remains on the head 22. During step 98, the brazing material of the brazing liner melts to join the tubes 46 to the head 22 on the air-side surface 82, thus forming a brazing fillet 102 (Figure 6) on the air-side surface 82, which further strengthens the bonds between the tubes 46 and the head 22. In some embodiments, the thermocouple 10 is moved into the brazing furnace, which is for a Controlled Atmosphere Brazing (CAB) process. In the brazing process, the liner materials are melted by the heat of the furnace, while the base materials of the components do not melt. The liner materials flow into the bonding areas between the components.The bonding areas are where the tubes 46 meet the header 22 on the air-side surface of the header 22, where the tubes 46 meet the fins 47, and where the fins 47 meet the side plates 56. As the heat exchanger assembly 10 is removed from the furnace, the coated material cools and forms bonds in these areas. In some embodiments, the collection tank 26 is brazed to the header 22 to form heat exchanger tanks. In some embodiments, unwanted residues will be brazed to the inner coating of the tube 46 (for double-sided coated tubes 46, the inner coating is used to remove residues) during the brazing process to provide cleaner tube volumes. In step 106, the temporary cover 90 is removed from the head 22. In step 110, to replace the temporary cover 90, the collection tank 26 is attached to the head 22 by, e.g., crimping. In some embodiments, the collection tank 26 is made of stainless steel and is press-fitted onto the head 22. When the collection tank 26 is attached to the head 22, a sealing gasket is placed between the collection tank 26 and the head 22. In an alternative embodiment, the collection tank 26 is attached to the header 22 in step 86, instead of the temporary cover 90. In this alternative embodiment, the collection tank 26 remains closed during step 94, thus preventing contamination of the tubes 46. Also in this alternative embodiment, the collection tank 26 is removed before step 98, so that the collection tank 26 (which may be made of plastic) does not melt during the brazing process. After the brazing process in step 98, the collection tank 26 would be reattached to the header 22. In some embodiments, the thermocouple 10 is part of a fuel cell, and the liquid is the fuel cell coolant. In some embodiments, instead of brazing the ends 66 of the tubes 46 to the liquid-side surface 70 of the header 22, the grooves 60 in the header 22 are filled with a sealant, preventing the flux from entering the header 22 and making contact with the liquid-side surface 70. The sealant is then dissolved during the brazing process. In some embodiments, the collection tanks 26, 38 are made of aluminum with a coating on one or both sides, and the collection tanks 26, 38 are brazed to the headers 22, 34 during the brazing stage 98 of method 50. Although the invention has been described in detail with reference to certain preferred embodiments, there are variations and modifications within the scope and spirit of one or more independent aspects of the invention as described.

Claims

1. A method of manufacturing a heat exchanger, the method comprising: arranging a plurality of tubes in a formation; attaching the plurality of tubes to a header, including sealing each of the tubes of the plurality of tubes to a header groove of a plurality of header grooves in the header and welding each of the tubes of the plurality of tubes to said header groove of the plurality of header grooves; attaching a cover to the header to cover the liquid-side surface of the header and to cover the ends of the tubes;and applying flux to a surface on the air side of the head and to the plurality of tubes, wherein the coupling of the cover to the head is performed after sealing each of the tubes of the plurality of tubes to said head slot of the plurality of head slots, wherein the coupling of the cover to the head is performed before applying the flux to the surface on the air side of the head and to the plurality of tubes, wherein the application of flux is performed before welding each of the tubes of the plurality of tubes to said head slot of the plurality of head slots, and wherein sealing each of the tubes of the plurality of tubes to said head slot includes sealing the perimeter of each of the tubes to said head slot.

2. The method of claim 1, wherein sealing each of the tubes of the plurality of tubes to said header groove includes welding the perimeter of each of the tubes to said header groove of the plurality of header grooves on the liquid-side surface of the header.

3. The method of claim 1, wherein sealing each of the tubes of the plurality of tubes to said head slot includes filling a sealant around the perimeter of each of the tubes and between each of the tubes and said head slot of the plurality of head slots.

4. The method of claim 1, further comprising forming head grooves in the head by forming a flange around each of the head grooves, wherein the flange extends from the liquid-side surface of the head.

5. The method of claim 4, further comprising forming a rim edge to have a rim thickness, wherein the rim thickness is less than the head thickness and greater than or equal to the tube thickness.

6. The method of claim 5, wherein the edge thickness is formed to be equal to the tube thickness.

7. The method of claim 4, wherein the tubes are inserted into the header slots such that the ends of the tubes extend beyond the edges of the flanges.

8. The method of claim 4, wherein the tubes are inserted into the header slots such that the ends of the tubes are parallel to the edges of the flanges.

9. The method of claim 2, wherein the welding step includes melting the ends of the tubes and melting the flanges of the header grooves to form a weld bead around the perimeter of each of the tubes.

10. The method of claim 1, further comprising wherein the cover is removed after the stage of welding each of the tubes of the plurality of tubes to said head slot of the plurality of head slots.

11. The method of claim 1, further comprising wherein the cover is removed after the step of applying flux to the air-side surface of the head and the plurality of tubes.

12. The method of claim 11, wherein the cover is removed before the stage of welding each of the tubes of the plurality of tubes to said head slot of the plurality of head slots.

13. The method of claim 10, further comprising wherein a tank is assembled to the head after removing the cover.

14. The method of claim 11, further comprising wherein a tank is assembled to the head after removing the cover.

15. The method of claim 1 further comprising overlapping the cover over at least a portion of the perimeter of the head.

16. The method of claim 15 further comprising removably attaching the cover to the print head.

17. The method of claim 15 further comprising removably attaching the cover to at least one of the side plates.

18. The method of claim 1 further including welding the cover to the head.

19. The method of claim 13 further comprising assembling a sealing gasket on the liquid side of the head before assembling the tank in the head.

20. The method of claim 14, further comprising assembling a sealing gasket on the liquid side of the head before assembling the tank in the head.

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