Such a process is generally known and is used for producing different types of tubing such as wrapped tubes, folded tubes or so-called welded tubes.

For a number of such shaped products it is required to interconnect different portions of the shaped product in order to obtain a sealed construction, such as e. g. required for tubing, or to obtain the required strength such as e. g. required in folded tubes. This is commonly done by brazing. If such connection is required it becomes necessary to at least provide the surface of one portion to be brazed with a flux coating.

All known flux coatings, however, have the disadvantage that they have to be applied after the reshaping of the intermediate object into the shaped product. These known flux coatings are generally brittle and/or lack the adherence to the aluminium surface to withstand the deformation forces while reshaping the intermediate object. Therefor the common flux coating will partly spring off from the aluminium surface while reshaping, and this especially in these areas where deformation occurs.

It is therefore an object of the invention to provide a process which makes it possible to apply the flux coating before deformation/bending of the intermediate object takes place. This object is obtained by means of a process as described in claim 1.

In this way it becomes possible to apply the flux coating by means of a simple coating process, which is technically simple compared with the known application techniques, and which can easily be adapted to such an extend as that the coating is only applied to the positions needed for the brazing.

The type of brazing flux is not a limiting factor in this process, as any type of flux coating as described in the claims 3-12 can be used.

The invention is also not restricted to one type of product, but different types of products can be made, such as described in the claims 13-16.

Further characteristics and advantages of the invention will become clear from the following description, references being made to the annexed drawings in which: Fig. 1 is a schematic cross-sectional view of a tube made in accordance with the invention, Fig. 2 is a schematic cross-sectional view of a modified embodiment of a tube made in accordance with the invention, Fig. 3 is a schematic cross-sectional view of a third embodiment of a tube made in accor- dance with the invention, Fig. 4 is a schematic cross-sectional view of a so-called folded tube with multiple ports, made in accordance with the invention, Fig. 5 is a schematic cross-sectional view of a modified embodiment of a folded tube, Fig. 6 is a schematic cross-sectional view of a third embodiment of a folded tube, Fig. 7 is a schematic cross-sectional view of a so-called welded tube produced in accor- dance with the invention.

In fig. 1 there is shown a so-called wrapped tube 10. This wrapped tube 10 has been obtained by producing a flat shaped object by e. g. rolling, and subsequently bending this flat object so as to obtain a substantially cylindrical shape with overlapping side portions 11. According to the invention at least one part of the overlapping side portions 11 has been coated with a brazing flux containing coating while the object is in its flat shape, so that the coating can be applied in a very simple way by means of conventional coating systems, such as e. g. described in PCT/EP99/09162. In case the wrapped tube is intended to be used as a header tube or manifold in a heat exchanger it is possible to provide the side portions of the flat shaped object with recesses or cut-outs, which after shaping into a wrapped tube form holes for the end portions of heat exchanging tubes 12. Also for this purpose the outer wall portion of the zone 11 may be coated before bending with a brazing flux retaining coating. When subsequently the obtained tube 10 and if present the inserted heat exchanging tubes 12 are placed in a brazing oven, or the like, no additional flux application is required and a brazed connection between the overlapping side portions 11 and between the tubes 10 and 12 is directly obtained because of the presence of the braze flux containing coating.

In fig. 2 there is also shown a wrapped tube 20 corresponding substantially to the wrapped tube 10 shown in fig. 1 and having overlapping side portions 21, which can be provided with a brazing flux retaining coating, so as to make brazing possible. In the embodiment shown in fig. 2 the central part of the flat sheet forming the intermediate object is provided with a number of holes or piercings, which holes can accommodate end portions of heat exchanging tubes 22 after shaping the final product in this case a header tube 20 or manifold. At least the central portion of the flat sheet is also provided before deformation with a brazing flux retaining coating so that after shaping the manifold 20 and inserting the tubes 22, the brazing connection between the manifold 20 and the tubes can be made directly by heating without any further process step.

In fig. 3 there is shown a third embodiment of a wrapped tube obtainable by means of the process according to the invention. This type of tube may be especially useful in high pressure applications such as brake lines or hydraulic applications. The intermediate object is a flat sheet which at least at one side is provided with a braze flux retaining coating. Subsequently the flat sheet is wrapped to a cylindrical tube whereby a number of layers are formed so that the wall of the tube is thicker than the thickness of the flat sheet. Preferably two or more layers are formed, dependent upon the application of the final product. In a last step the wrapped tube is heated to a temperature above the required braze temperature, which is dependent upon the flux used whereby as a result of the presence of the flux retaining coating between the layers of the wrapped tube a firm connection between the successive layers can be obtained.

In the figs. 4,5 and 6 there are shown different embodiments of so-called folded multiple part flat tubes. The intermediate objects for each of these tubes 40,50 or 60 is a flat sheet of rectan- gular shape. After coating at least one side of the sheet with a brazing flux retaining coating the sheet is folded into the desired shape and subsequently heated in order to obtain the required brazed connections.

In fig. 4 there must be provided at least a coating on the outer side of the tube 40, so as to enable end portions 41 and 42 to be connected and sealed by the brazing process. The embodiment of fig. 5 requires a brazing flux retaining coating on both sides of the tube, but it may be limited to these portions where actual brazing is required. In this case this is the portion with the gusset fold 51 and the two end portions 52 and 53. In this way a sealing connection can be obtained between the gusset fold portion 51 and the end portions 52 and 53, so as to obtain two separate channels 54 and 55. Moreover, the strength of the tube can be improved by having the two halves of the gusset fold 51 brazed together.

In fig. 6 there is shown how in the same way starting from a flat sheet coated with a brazing flux retaining coating according to the invention a multiple port flat tube can be obtained by using gusset folds and brazing together of the relevant positions. In this way a tube 60 with five channels can be obtained, but it will be obvious that any other configuration can be obtained.

In fig. 7 there is shown a so-called welded tube 70 i. e. a tube which has been obtained by shaping two half-tubes, e. g. by extrusion, which on one end portion may be connected to each other. After reshaping a flat tube is obtained by welding together the two halves along a seam 71. The intermediate object may be the half-tube flat outer side wall of which may be provided with a brazing flux retaining coating, or the final welded tubes which on both flat sides may be provided with a brazing flux retaining coating. The end result is the same and the coating makes it possible to make a brazed connection between the tubes 70 and e. g. finstock. The process according to the invention even makes it possible to shape the tube in a serpentine way before the brazing but after the coating and to have the finstock then brazed to the tube.

It is obvious that the invention is not restricted to the above described embodiment but that numerous modifications can be applied without departing from the scope of the annexed claims.