PROCESS FOR MAKING A FLUID-TIGHT CONNECTION BETWEEEN A TUBE AND A PLATE-SHAPED PART

Abstract: Process for making a fluid-tight connection between a tube and a plate-shaped part, comprising providing a hole (4) in the plate-shaped member substantially corresponding to the cross section of the tube, inserting one end of the tube into the hole (4), so that the tube end is partly extending beyond the surface of the plate-shaped part, inserting a mandrel (10) into said tube end, said mandrel (10) comprising a first portion (11) having a cross section substantially corresponding to the inner cross section of the tube, a second portion (13) having an increased cross section and a transition portion (12) between these two portions, maintaining the tube in its inserted position while pressing the mandrel into the inserted end of the tube, and heating the mandrel to a temperature at least sufficient to soften the tube material and maintaining this situation during a time sufficient to deform the tube end on the plate-shaped parts.

Description: Process for making a fluid-tight connection between a tube and a plate -shaped part The invention relates to a process for making a fluid-tight connection between a tube and a plate-shaped part, comprising providing a hole in the plate-shaped part substantially corresponding to the cross-section of the tube, inserting one end of the tube into the hole, so that the tube end is partly extending beyond the surface of the plate-shaped part. Such a process is described in EP-A-0 379 701. There is a permanent need to secure leak proof and strong connections between tubes and plate-shaped part such as e.g. used in heat exchangers. By plate-shaped part is meant any object having at least one portion which consisting of relatively thin wall with a substantially flat surface. Examples are tubes with at least one substantially flat surface, such as headers in heat exchangers, box-like structures to be used as containers, such as gasoline tanks etc. It is known to use mechanical expansion of the tube end into the plate-shaped part in order to anchor the tube ends in the header plates. This is especially used in heaters and radiators where resilient gaskets may be used as well in order to obtain the required fluid tight connection. However such arrangements are not sufficiently secure for containment of the heat exchanging fluid such as used in air conditioning arrangements in which higher pressures/smaller molecules are used than in water-based domestic heaters and radiators. Furthermore, where the said heat exchanger tube is present in a hart temper, it becomes increasingly difficult to obtain a good seal by mechanical expansion alone due to the "spring-back" effect. There is also an increasing risk of splitting the tube if a too high expansion force is applied to such a hard tube. It is therefor an object of the invention to provide a process for making a fluid tight connection between a tube and a plate-shaped member which has improved characteristics compared to the known processes. This and other objects are achieved in a process according to the introductory part of the description in that a mandrel is inserted into said tube end, said mandrel comprising a first portion having a cross-section substantially corresponding to the inner cross-section of the tube, a second portion having an increased cross-section and a transition portion between these two portions, in that the tube is maintained in its inserted position while pressing the mandrel into the inserted end of the tube and heating, the mandrel maintaining heated to a temperature at least sufficient to soften the tube material, and this situation is maintained during a time sufficient to deform the tube end on the plate-shaped part. By using a mandrel according to the invention and applying heat to the mandrel, it became possible to provide a connection between the plate-shaped part and the tube which is partly obtained by deformation of the tube over the edge of the hole in the plate-shaped part. This can be achieved easily due to the local annealing of the tube end with minimal risk of splitting the tube and without waste energy by heating only the places where the heat is needed. In this way a fluid-tight and mechanically reliable connection is obtained between the tube and the plate-shaped part. Preferably the tube and / or the plate-shaped part are made out of aluminium or an aluminium -alloy. This type of material is especially effective in heat transfer applications and can be easily deformed at lower temperatures. Due to the spring-back effects from the mechanical deformation, it might be necessary to seal the tube to the plate shaped member by a more secure method, such as by using a brazing connection. Present brazing techniques for aluminium utilize AI:Si alloys for achieving a brazed joint, usually by use of clad sheet. This is a fairly high temperature operation, well above the temperature at which aluminium alloys become annaeled and softened. Therefor, heating of the whole of the assembly plate-shaped part and tube to effect a braze would soften the tube and the part so that deformation of the assembly is likely to occur under normal service conditions where high internal pressures can be encountered. Localized heating such as used when flame brazing is not feasible or is difficult to realize due to geometrical restrictions and the possibility of heat application outside the desired region. According to the invention, use is made of the plate-shaped or extruded part which is at least partly coated with a brazing and / or flux material. In this way it becomes possible to heat the assembled tube and plate-shaped part through the heated mandrel in order to obtain a brazed connection between the two parts to be joined. If needed only the area around the hole of the plate-shaped or extruded part which needs to be connected to the tube may be provided with such a coating. An advantageous coating material is zinc, allowing to reduce the temperature of the joining process substantially as zinc will melt and diffuse into the aluminium and form a reliable brazing material at low temperatures. The invention also relates to a process for making a fluid-tight connection between a header and a number of aluminium tubes coated with brazing and / or flux material, for making a heat exchanger, wherein the header at least comprises a plate-shaped member. Heat exchanger of this tube requires a substantial number of connections to be made between a header and a number of tube ends in order to provide the flow channels. Obtaining a reliable fluid-tight connection between the header and the tube ends is still a cumbersome operation, and most failures in this type of heat exchanger occur at the connection between the tube ends and the header. This is partly due to the fact that connection place between the header and the tubes is difficult to reach as a result of the number of tubes and the fins already arranged around the tubes. This can result in unsound brazed joints. It is therefor also an object of this invention to provide process whereby the making of the connection between the header and the tubes is substantially improved and facilitated. This object is obtained in that the connection between each tube and the plate-shaped member of the header is made in accordance with the invention and the plate-shaped member is subsequently modified into a header. In this way it becomes possible to make a number of connections between tubes and the plate-shaped member of the header in one operation by using the required number of mandrels, and without overheating the already partly assembled heat exchanger, thereby avoiding unwanted deformation of the assembled unit. The transformation of the plate-shaped member into a header can be easily done either by deformation of the plate-shaped member so that a closed tube-like header is obtained which can easily and reliable be made fluid-tight by brazing, as the joint can be made at an easily accessible place. Otherwise it is possible to make the header by adding another unit to the plate-shaped member and sealing the connection edges between the member and the added unit, thereby providing a tube-like header. Other characteristics and advantages of the invention will become clear from the following description reference being made to the annexed drawings. In the drawings Figure 1 is a schematic view of a tube and plate-shaped member before assembly, and Figure 2 is a corresponding view during the assembling of the two parts. In Fig. 1 there is shown the end portion 2 of a tube 1 which should be connected in a fluid-tight manner to a plate-shaped part 3. The plate-shaped part 3 may be any wall-like portion of a unit to be used as fluid container or fluid transport conduct. The only requirement for the application of the invention is that both sides of the plate-shaped part are accessible for handling purposes as will be elucidated below. In order to connect the tube end 2 in a fluid-tight manner with the plate-shaped part a hole 4 has been made in the plate-shaped part, which hole can be made in any conventional way. According to the invention it is however preferred to making the hole by punching whereby a surrounding edge 5 is formed around the hole 4 thereby providing a bigger contact surface between the tube end 2 and the edge 5 of the hole 4. the dimensions of the tube end 2 and the hole 4 are selected in such a way that as seen in cross-section the shape of the hole 4 substantially corresponds to the shape of the tube end 2, while allowing some clearance between the tube end 2 and the hole 4 often the tube end 2 has been inserted in the hole 4. After having prepared the hole 4 in that way, the tube end 2 is inserted into the hole 4 up to a defined depth and is temporarily fixed in this position by any suitable clamping means. While maintained in that position a mandrel 10 may be moved into the open end of tube 3. In case the tube isused in a heat echanger wherein the tube is surrounded by fins, the expansion of the tube in order to give it a close contact with the fins can be performed simultaneously with the above cited expansion of the tube end. The mandrel 10 is fixed to any suitable moving means (not shown) suitable for inserting the mandrel 10 into the tube end 2 will sufficient force to generate the deformation to be obtained as explained below. The mandrel itself consists in fact of three parts, a first part or guiding part 11 , a second of transition part 12 and a third or bay part 13. The guiding part 11 has a cross-section which is substantially equal to the internal cross-section of the tube end, in such a way that the free end portion (leading part) has dimensions which gradually increase toward its trailing part i.e. the part which is connected to the conical part 12. In the conical part 12 the dimensions of the cross-section gradually increase to dimensions such that the cross-section is larger than the cross-section of the tube end 2. The mandrel 10 can be made of material such as stud, and it may be completely solid, such as shown in Fig. 1 , or it may be partly hollow, so that heating means can be incorporate inside the mandrel 10. Preferably the tube and the plate-shaped part are made out of aluminium or an aluminium alloy. The operation of the system according to the invention is clearly shown in Fig. 2 While maintaining the tube in a fixed position the mandrel 10 is inserted with sufficient force into the tube end. By this force the tube end is deformed initially by expansion, as a result of the shape of this guiding part 11 of the mandrel 10, and at the end of the insertion by deformation of the edge around the edge 5 of the hole 4. As a result of these deformations a reliable mechanical connection has been obtained. In order to reduce the forces to be used and to reduce the risk for damage during deformation the mandrel 10 may be heated, either directly by some suitable heating means provide inside the mandrel itself or its supporting means, or indirectly, i.e. the mandrel is preheated and its heat content is used during the insertion.- The use of a heated mandrel, offers more over the possibility to generate a brazed connection between the tube end 2 and the edge 5 of the hole 4, especially in case aluminium parts are used. For that purpose, some brazing material must be present on the surface of at least one of the parts, i.e. either on the tube end 2, or on the hole edge 4 or on both. For that reason there might be applied a filler to the aluminium surface of one or both parts, such as a zinc clad. The application of a flux may be superfluous as due to the mechanical deformation the oxyde - layer on the aluminium surface are cracked sufficiently to allow brazing . Otherwise it is also possible to apply a flux to one or both surfaces to be joined, in order to improve the joint. By combining the mechanical deformation and a brazing effect improved joint will be obtained providing a better guarantee against fluid leakage, especially in high pressure application such as heat exchangers.

Claims: Claims 1. Process for making a fluid-tight connection between a tube and a plate-shaped part, comprising providing a hole in the plate-shaped member substantially corresponding to the cross-section of the tube, inserting one end of the tube into the hole, so that the tube end is partly extending beyond the surface of the plate-shaped part, inserting a mandrel into said tube end, said mandrel comprising a first portion having a cross-section substantially corresponding to the inner cross-section of the tube, a second portion having an increased cross-section and a transition portion between these two portions, maintaining the tube in its inserted position while pressing the mandrel into the inserted end of the tube, and heating the mandrel to a temperature at least sufficient to soften the tube material and maintaining this situation during a time sufficient to deform the tube end on the plate-shaped parts. 2. Process according to claim 1 , characterized in that the tube end / or the plate-shaped part are made out of aluminium or an aluminium alloy. 3. Process according to any one of the preceding claims, characterized in that at least the area around the hole and / or the tube is coated with a brazing and / or flux material. 4. process according to any one of the preceding claims, characterized in that the hole in the plate-shaped member is formed in such a way that an edge is formed around the hole. 5. Process according to claim 4, characterized in that the edge is oriented to the side of the plate-shaped member where the tube end is located. 6. Process according to any one of the preceding claims, characterized in that before pressing the mandrel into the tube end, the tube is mechanically expanded in the hole. 7. Process for making a fluid-tight connection between a header and a number of aluminium tubes coated with brazing and / or flux material, for making a heat exchanger, wherein the header at least comprises member having a plate-shaped part, characterized in that the connection between each tube and the plate-shaped member is made in accordance to the process according to any one of the preceding claims, and that the member is subsequently modified into a header. 8. Process according to claim 7 characterized in that the header is made out of at least two parts, a first part having a U-shaped cross-section and constituting the member, and a second part having a cross-section fitting over or in the first part, and in that after connecting the tubes to the first part the first part is closed in longitudinal direction by combining it to the second part and making a fluid-tight connection between these two parts.

Inventors: MORLEY EDWARD, PASCOLINI MAURO, VESTERGAARD BJORN, MORLEY, EDWARD, PASCOLINI, MAURO, VESTERGAARD, BJORN
Applicants: IND SCAMBIATORI CALORE S P A, MORLEY EDWARD, PASCOLINI MAURO, VESTERGAARD BJORN, INDUSTRIA SCAMBIATORI CALORE S.P.A., MORLEY, EDWARD, PASCOLINI, MAURO, VESTERGAARD, BJORN
Application year: 1998
Main classification: B21D39
IPC codes: B21D39