METHOD OF MAKING HEAT EXCHANGER AND HOLLOW SHAPE FOR SUCH

Abstract: Method of making a motor vehicle radiator in which extruded hollow shapes (1) of oval cross-section provided inwardly with at least one longitudinally extending web (2) lying transversely of the larger major axis of the oval cross-section, are reshaped, e.g. rolled under pressure to a cross-sec­ tional form of a flat profile tube having two parallel sides, soldered to cooling fins and fitted into a radiator housing. The extruded hollow shape (1) of light metal with a substantial oval cross-section for use in this method comprising inwardly at least one web (2) which extends in the lon­ gitudinal direction of the shape (1) and transversely to the large major axis of the oval cross-section of the shape.

Description: The invention relates to a method of forming a heat exchanger in particular a motor vehicle radiator and to a hollow section of tubing for use in such a method, as defined in the pre-characterising portion of Claims 1 and 6,7 respectively. From the US-A-3 662 582 a method of forming a heat exchanger is already known comprising forming hollow sections of tubing each having at least one longitudinally inwardly extending web reshaping each of said sections of tubing into respective flattened hollow tubes with two parallel sides and assembling said hollow tubes. With this known method it is started from hollow sections of tubing having a round cross-section formed for example by brazing. The pre-characterising portion of Claim 1 is based on the disclosure of the document US-A-3662582 Furthermore, from the EP-A-188314 or from the EP-A-186130 metallic hollow sections of tubings having an oval cross-section are known to be used for forming a heat exchanger. The pre-characterising portion of Claims 6 and 7 is based on the disclosure of the document EP-A-188 314 Hitherto, radiators, in particular water radiators for internal-combustion engines of motor vehicles, have been made in Europe to about 20% from conventional brass and copper tubes and to about 80% from aluminium tubes. Aluminium radiators, which due to their higher efficiency and their lower weight are preferred to the radiators of brass and copper tubes, are made in the form of plug-type radiators with plugged aluminium tubes or using welded aluminium tubes. The proportion of plug-type radiators of aluminium is about 50%, while the proportion of radiators of welded aluminium tubes is about 30%. Radiators with welded aluminium tubes are in particular used in internal-combustion engines in which a high cooling power is required, as is the case in particular in engines for small trucks and high-performance engines for automobiles. The welded tubes for such radiators are made in that metal sheets are rounded from strip metal and welded by pressure welding in the longitudinal direction at one side. These tubes have a flat profile, in contrast to the tubes for plug-type radiators which have a circular profile, and are coated on the outside with AlSi alloys. This silicon coating is applied during the rolling of the sheet metal itself prior to the round forming and serves to enable the welded tubes to be subsequently soldered to the water tank and the cooling fins. This soldering of the welded flat tubes, which consist of e.g. an Al Mg Si 0.5 or an Al Mn alloy, to the water tank and the cooling fins of the same or similar material is made by brazing or hard soldering at a temperature above 450°C, in particular at 607 to 636°C, with the aid of flux or under vacuum without flux. Both these possibilities of soldering the welded tubes to the fins and the water tank involve serious problems. When soldering with a flux the environmental problems are serious because detrimental substances are liberated by the flux and being very aggressive to aluminium and iron sheet and must therefore be washed off the soldered radiator to prevent the latter corroding. Furthermore, the arisen fumes must also be removed from the air to prevent sheet metal possibly pressed in the vicinity for the vehicle bodyworks from being attacked. For this purpose air cleaning is necessary, which involves high costs. When soldering without flux said problems, due to detrimental substances, admittedly do not occur, but because this soldering must take place under vacuum and requires extremely accurate temperature control high costs are also involved. Due to the high temperature of the soldering under vacuum in addition only a short holding time in the soldering furnace is possible so that at the soldering joint a spot tends to be formed rather than an area contact, and this impairs the thermal conductivity at this point. In radiators hitherto having such welded flat tubes usually two tubes are arranged parallel to each other, each having a width of for example 22 mm. This width means the outer dimension of the tubes in the direction of the larger major axis of the flat profile. It has, however, been found that the cooling efficiency increases with increasing outer diameter so that preferably only one flat tube with correspondingly larger width should be provided. In the manufacture of the radiators, however, the flat tubes are laterally screwed and pressed to the fins before the soldering to obtain a continuous exactly defined area contact between the two components, and thereafter soldered in the furnace. Due to the pressure on the flat tube in the pressing and the temperature obtaining in the furnace during soldering, however, a deformation (collapse) of the side faces of the flat profile occurs in the furnace because the aluminium becomes soft and sinks in due to the pressure applied. This effect occurs in particular due to the fact that the aluminium tubes have a very small wall thickness of for example only 0.4 mm. Furthermore, after the soldering of the tubes and the fins the core of the radiator formed in this manner is fitted into the radiator housing or into a radiator bottom, and this operation must not cause any stress in the assembled radiator. However, due to the deformation of the components during soldering the necessary exact fit is difficult to achieve. The problems regarding the collapse of the tubes and the lack of an exact fit become even more serious when for increasing the efficiency wider flat profile tubes are to be used. Due to the aforementioned deformation of the tubes during soldering the waste in production then increases, and because of the silicon coating of the tubes this leads to a further problem because these reject radiators cannot simply be scrapped. It is therefore an object of the present invention to avoid the above problems and to provide a method of making heat exchangers, in particular a motor vehicle radiator and a hollow shape for use in such a method, by which high-performance radiators of aluminium with high efficiency can be made. For this purpose the method according to the present invention comprises the steps mentioned in the characterizing part of the patent claim 1. Preferred embodiments of the method according to the present invention are subject-matter of the patent claims 2 to 5. The extruded metallic hollow section of tubing to be used in the method according to the present invention is constructed as it is stated in the claims 6 or 7. Preferred embodiments of the hollow section of tubing are subject-matter of the patent claims 8 and 9. Thus, in the method according to the invention none of the welded tubes are used, but extruded hollow shapes provided by a conventional extrusion press or Conform machine, said shapes being provided with at least one web situated in the shape cavity having a triple function: Firstly, the web ensures during a subsequent rolling of the shape that flat profiled tubes are formed, where the wide sides of the flat profile lie exactly parallel to another. Secondly, said web effects a rigidity of the shapes giving a better stability during the rolling or drawing operation and obtaining a higher dimensional stability with wide flat shapes. At last it also represents a turbulator which, when used for example as water cooler, ensures a turbulent flow of the water circulating in the tubes, thus resulting in a lower flow rate of the water and a higher cooling efficiency. Due to the webs provided in the hollow shapes tubes of greater outer diameter of up to 40 mm can thus be used for making a heat exchanger, in particular a motor vehicle radiator, with high efficiency. In a particular embodiment of the shapes according to the invention the shapes made of aluminium or Al-alloy are provided with a zinc coating or a coating with an alloy on a zinc basis. The resulting tubes may then be soft-soldered to the cooling fins at a temperature below 450°C, and this contributes to the dimensional stability of the tubes compared to hard-soldering of the welded tubes because at these temperatures by nature a reduced deformation of the aluminium material is to be expected. Hereinafter the invention will be described in more details and by examples of preferred embodiments with the aid of the attached drawings, Figs. 1-3, wherein: Fig 1 is a first example of embodiment of the hollow shape according to the invention in the extruded state in Fig. 1A and in the rolled state as a finished tube in Fig. 1B. Fig. 2 is a second example of embodiment of the hollow shape according to the invention in the extruded state in Fig. 2A and in the rolled state in Fig. 2B, and Fig. 3 is a third example of embodiment of the hollow shape according to the invention in the extruded state in Fig. 3A and in the rolled sate in Fig. 3B. An example of embodiment of the hollow shape according to the invention used for making a motor vehicle radiator by the method according to the invention is shown in Fig. 1 of the attached drawings. The shape 1 shown in Fig. 1A having an oval cross-section and made of aluminium alloy, e.g. of Al Mg Si 0.5 or Al Mn, has an oval cross-section with an outer diameter in the direction of the smaller major axis of for example 4 to 6 mm and an outer radius at the two outer sides of 1.2 mm. In the cavity of the shape two webs are formed which extend continuously from one inner face to the other transversely of the direction of the large major axis of the oval cross-section and in the longitudinal direction of the shape. These transverse webs 2 have a thickness substantially equal to the wall thickness of the shape 1. The transverse webs are provided with a preformed curvature in the transverse direction. As illustrated in Fig. 1B this curvature serves to cause the webs 2 to buckle in on rolling of the shape 1 illustrated in Fig. 1A so that the resulting half-circular webs 5 illustrated in Fig. 1B reinforce the flat arisen tube 3 as well as serving as turbulator for the water to be cooled flowing through. The flat tube illustrated in Fig. 1B may have an outer dimension in the direction of the shorter major axis of 2 mm, the outer radius at the two sides remaining unchanged 1.2 mm. The example of embodiment of the hollow shape according to the invention shown in Fig. 1A may have a width, i.e. outer dimension in the direction of the larger major axis, such that the flat tube illustrated in Fig. 1B has corresponding outer dimensions of for example 32 mm to 40 mm without the dimensional accuracy and exact fit being impaired by the following soldering operation. In Fig. 2A a further example of embodiment of the hollow shape 1 according to the invention is shown, which comprises a single web protrusion 2 in the cavity which is integrally formed on an inner side of the shape. The web 2 has a height which corresponds to the height of the interior of the flat tube in Fig. 2B after rolling. It is ensured in this manner that the two outer sides of the flat tube in Fig. 2B extend exactly parallel due to the support by the web 2. The tube illustrated in Fig. 2A can for example have an outer dimension in the direction of the shorter major axis of 4 to 6 mm, a height of the web 2 of 1.6 mm and a wall thickness of 0.4 mm. This gives after the rolling a flat tube 3 which is illustrated in Fig. 2B and has an outer dimension in the direction of the shorter major axis of 2.4 mm, a height of the interior of 1.6 mm and a width, i.e. an outer dimension in the direction of the larger major axis, of 32 mm. The outer radius at the two sides is once again 1.2 mm. Finally, Fig. 3 shows a third example of embodiment of the hollow shape 1 according to the invention which comprises two webs 2 which are integrally formed at an inner side of the shape 1 at a predetermined angle at the same distance apart and from the sides of the hollow shape 1. This angle is chosen so that the webs 2 in the rolled flat tube 3, which is shown in Fig. 3B, are perpendicular to the inner faces. The webs 2 again have a height corresponding to the height of the interior of the flat tube 3 in Fig. 3B. The remaining dimensions correspond to the dimensions of the example of embodiment illustrated in Fig. 2. Since in the example of embodiment illustrated in Fig. 3 two webs 2 are provided, a still greater stability of the tube results along with a more pronounced swirl formation, i.e. turbulence, of the medium to be cooled flowing in the interior when the profile is used in a radiator so that still wider tube profiles can be used in a radiator so that still wider tube profiles can be employed and thus motor vehicle radiators made having extremely high efficiency, as required for example for the engines of commercial vehicles. Although several preferred embodiments of the invention have been described it is apparent that modifications may be made therein by people skilled in the art. Such modifications may be made without departing from the scope of the invention as set forth in the appended claims, e.g. the hollow shapes can be made of other metals than the disclosed Al-alloy and with other configurations of the cross-section than the illustrated oval one.

Claims: A method of forming a heat exchanger comprising forming hollow sections of tubing each having at least one longitudinally inwardly extending web, reshaping each of said sections of tubing into respective flattened hollow tubes with two parallel sides and assembling said hollow tubes characterized in that the hollow sections of tubing are formed by extruding and each have an oval cross-section with predetermined radii of curvature at the outer sides in the direction of the larger major axis, the web extending in a direction transverse to the larger major axis, said hollow sections of tubing are reshaped such that the web forms an internal partition that establishes a predetermined transverse width of the hollow tubes and the hollow tubes are assembled to external cooling fins thereby forming a heat exchanger core. A method according to claim 1, characterized in that the hollow sections of tubing are reshaped while said predetermined radii of curvature are maintained whereby the radii of curvature of the flattened hollow tubes remain the same as those formed in the step of extrusion. A method according to claim 1, characterized in that hollow sections of tubing of aluminium or aluminium alloy are extruded. A method according to claim 3, characterized in that the hollow tubes are coated with zinc or an alloy on a zinc basis and thereafter soldered to the coolling fins, and the assembly of tubes and cooling fins is fitted into a radiator housing. A method according to claim 4, characterized in that the tubes coated with zinc are soft-soldered to the cooling fins at a temperature below 450°C. Extruded metallic hollow section (1) of tubing having an oval cross-section for use in the method according to claim 1, characterized in that the cavity of the section of tubing is provided with at least one web (2) integrally formed and inwardly extending in the longitudinal direction of the hollow section (1) and situated transversely to the larger major axis of the oval cross-section of the section of tubing, the web (2) being made integrally extending from one inner face to the other inner face of the hollow section (1) and being provided with a curvature in the transverse direction of the section (1). Extruded metallic hollow section (1) of tubing having an oval cross-section for use in the method according to claim 1, characterized in that the cavity of the section of tubing is provided with at least one web (2) integrally formed and inwardly extending in the longitudinal direction of the hollow section (1) and situated transversely to the large major axis of the oval cross-section of the section of tubing, the web (2) being formed integrally on one inner face of the hollow section of tubing (1) and having a height which is equal to the desired height of the interior space which the tube is to have after the reshaping into a flat tube (3). A section of tubing according to claim 7, characterized in that the web (2) is provided protruding in the center of the section (1) in the direction of the larger major axis. A section of tubing according to claim 7, characterized in that two webs (2) are provided situated at the same distance from each other and from the section ends in the direction of the larger major axis.

Inventors: KNOLL, RICHARD, JR.
Applicants: NORSK HYDRO A.S.
Application year: 1988
Main classification: B23P15
IPC codes: B21C23, B23P15, F28F1, F28F13, B21D53, B23K1