METHOD OF MANUFACTURE OF MANIFOLDS AND MANIFOLD PROVIDED BY SUCH METHOD

Abstract: A new method of manufacturing of integrated manifolds for heat exchangers is disclosed. A hollow shape (2) with a plurality of individual risers (23) having a substantially solid cross-section is provided and subsequently the risers (23) are reshaped by means of a reverse impact extrusion process into hollow risers (3). Finally, by perforating the hollow shape's (2) wall under the hollow risers (3), apertures are pro­ vided constituting inlets connecting the cavity of the hollow shape (2) with the individual hollow risers (3).

Description: The present invention concerns a method for manufacturing of integrated manifolds, particularly for heat exchangers, comprising a hollow body having a plurality of hollow risers for connection to heat exchanger tubes, and furthermore a manifold provided by such method. Background of the invention Connections between manifold/header plate and tubes in heat exchangers applied as e.g. condensers or radiators in a vehicle, are in principle provided by two methods - soldering/brazing or mechanical expansion of the tubes after their insertion into the manifold or a header plate. All methods are at the present time characterized by several problems connected to the providing of a reliable, leakage-proof connection having satisfying mechanical strength. GB 1 492 555 describes a heat exchanger for vehicles based upon a mere expansion connection between the tubes and the manifold without use of supplementary rubber packing. The construction is characterized by a precisely specified interaction between a number of parameters like wall thickness, tube diameter, material strength, length of support and others expressed in empirical formulas. This construction requires high tolerance from the components, and furthermore it has obvious limitations with regard to free choice of materials, wall thickness, tube diameter, etc. A further disadvantage of the disclosed construction is represented by the process applied for making fastening apertures in the tube wall. The wall is "knocked down" and pressed and drawn further inwards to constitute a collar or flange which ensures the necessary support or backing area for fastening of the heat exchanger tubes. The height of the collar is related to the wall thickness of the manifold, which gives poor possibilities of achieving an adequate collar height on thin-walled manifolds due to the limited material mass which can be transferred in the deformation zone. Limited material flow is also the disadvantage of the so-called T-drill or Flow-drill processes, as disclosed e.g. in FR-A-1 534 065, where by means of special tools the manifold tube is perforated and a low collar is formed. Depending on the type of tool applied, this collar is formed on the outside or both on the innerside and on the outside of the manifold. In those cases where the collar protrudes inwards in the manifold the available, free cross-section of the manifold is reduced and an increased pressure drop in the heat exchanger arises due to turbulent currents in the manifold. Additionally to the above mentioned disadvantages also several other problems arise by brazing of the heat exchanger tubes to such manifolds. Because of the short collar a penetration of brazing material and flux along the tubes into the manifold occurs quite frequently, which further contributes to the reduction of the available, free cross-section. Flux residues being entrapped in this way are difficult to remove and they have a corrosion promoting effect on the components. Furthermore, it is difficult to achieve a tight and rigid connection because of too short available brazing length. In the case of inwards protruding brazing hollow risers it is difficult to control the amount of heat since the joining zone is concealed in the manifold. Differences in wall thickness between the joined components represents another obstacle for achieving a proper control over heat balance in the joining process. Overheating of the tubes and mechanical weakening of the connection as a result of this, therefore represents an imminent danger of a high reject rate by manufacture of heat exchangers according to this principle. A co-pending EP-A-181548, not published at the date of filing of the present application discloses still another manifold construction and method of its manufacture. The construction is characterized by provision of a shaped tube with an outwardly, longitudinally running protrusion part which constitutes an integrated portion of fastening flanges for the heat exchanging tubes. The resulting manifolds overcome the above mentioned disadvantages, ensuring leakage-proof and rigid connection to the heat exchanger tubes. However, the disclosed manufacturing method and resulting manifold design does not offer a flexible solution with regard to current, alternative methods of joining manifolds to heat exchanger tubes. This manifold design, for example, allows only for insertion of tubes into the fastening flanges so that not all presently installed industrial assembling lines can be used for the subsequent brazing process. EP 0 122 392 discloses a variant of the above prosess. In order to ensure possibility of positioning the branch tubing outside of the hollow risers the excess (bridging) material between the adjacent risers is removed. The hollow risers provided by perforation (drilling) of the co-extruded neck part have a height identical with the height of the neck part which represents, apart from poor economics because of an excessive removal of the material, also a limitation with regard to an optimal design of the manifold and size (height) of the risers. There is still another known process of manifold manufacture where the hollow risers are provided by a stepwise deep drawing operation on the aluminium sheet. The reworking steps in this process are bending of the sheet and welding of butted sheet ends in order to form a tube. A weakness of this construction is a longitudinally running welded seam which does not provide a reliable and tight rigid joint under high pressure in heat exchangers. Thickness of the applied sheet limits also in this case the achieved maximum length of the risers. Furthermore, GB patent No. 518 403 relates to pipe fittings formed of integral metal wrought to final form by a cold operation where a tubular blank of copper is inserted in a die having a longitudinal bore intersected by a branch recess. A cold upward flow of metal into such a branch recess and simultaneously a lateral flow of metal axially to the tubular blank is caused by a plunger device resulting in formation of a desired outer shape of the fitting which is then in successive steps subjected to boring and piercing finishing operations. The disclosed method does not obviously provide a possibility of forming two or more risers distributed longitudinally along the extruded hollow shape. Object of the invention The object of the present invention is to provide a new and improved manufacturing method providing integrated manifolds having a plurality of individual hollow risers for connection to heat exchanger tubes and where the tubes can be positioned both inside and outside of the hollow risers. Another object of the invention is to provide low cost manifolds made out of an extruded shape having no longitudinally running welds. The object is achieved by the method according to claims 1 to 3. Brief description of the drawings The above and other objectives and advantages of the present manufacturing method will become apparent from the following description taken in connection with the accompanying drawings 1-6, wherein Fig. 1 is a fragmentary view partially in cross-section of the manifold and the attached heat exchanger tubes (hairpins). Figs. 2-6 illustrate schematically the individula steps in the manufacturing process. Description of the preferred embodiments Fig. 1 shows in a vertical cross-section a variant of the manifold manufactured according to the present invention. The manifold (1) is shown as two co-extruded, hollow shapes (2,2') constituting respectively an inlet and an outlet tube for circulation of cooling medium in a heat exchanger, e.g. a condenser. Individual hollow risers (3,3') protruding from the surface of the hollow shapes (2,2') constitute resting surfaces for the caps (6) formed on the ends of the so-called hairpin tubing (8), connecting the hollow shapes together and forming a circulation path in the heat exchanger. The tapered shape of the caps (6) facilitates insertion and positioning of the hairpin tubing (8) and provides an accomodation for brazing material (7). Fig. 2 illustrates schematically the first step in the manufacturing process. An extruded or possibly drawn hollow shape, shown as a single tube (2) provided with an integral, longitudinally running neck part (21) and having an inserted cylinder (9) complementary shaped and dimensioned to fit the tube's void, is fixed in a fixture device (5). The neck part (21) is then subjected to a cold forming process by means of a press tool (10). The press tool (10), shown schematically and partly in a vertical cross-section as an extrusion member (12) comprising a plurality of cylindrical voids (11), is forced against the neck part (21) of the fixed tube (2). Exposed to such pressure the neck part is subjected to a deformation process resulting in a material flow into the voids (11) in the extrusion member (12) under formation of individual, cylindrical solid risers. Fig. 3 shows the intermediate product (2) from the first step of the manufacturing process positioned in a new fixture arrangement (5) ready for a subsequent working step. The height of the neck part (21) is now substantially reduced and the achieved cylindrical solid risers (23) are subjected to a reverse impact extrusion by means of a new set of extrusion tools comprising a housing mandrel (14). The impact extrusion may be conducted as a sequential operation done by one tool only, as shown for illustration purpose in the figure, or by one operation on all risers (23) using a set of tools. As it appears from the Figure, showing in a cross-section a final stage of the impact extrusion operation on one of the shown risers (23), the riser is converted into a thin-walled hollow riser (3) by penetration of the mandrel (14) into the riser and the resulting material flow between the mandrel and the walls of cylindrical voids (51) provided in the upper part of the fixture (5) for each riser (23). By an appropriate dimensioning of the original neck part (21) and the intermediate solid risers (23), height and form of the final hollow risers (3) is determined and achieved by this single operation. Fig. 4 shows a segment of the manifold tube (2) with three integral, individual hollow risers (3) prior to a final step in the manufacturing process illustrated schematically in Fig. 5. In Fig. 5 a cutting or perforating tool (15) is applied in order to form apertures under the hollow risers (3) by removing parts (16) of the manifold tube's (2) wall. Free inlets are thus formed, ensuring distribution of medium from the manifold tube to all individual hollow risers. Fig. 6 illustrates an alternative step to the one shown in Fig. 2. Instead of applying an extrusion operation in order to provide individual solid risers (23) from the co-extruded, protruding neck part (21), a specially designed cutting tool (17) is used to remove excess material and form a plurality of discrete risers (23). This operation will of course give a slight increase in the use of material. From the foregoing it will be apparent that various modifications of the presently illustrated and described manufacturing process and the achieved manifolds may be made by those skilled in the art without departing from the spirit of the invention as expressed in the accompanying claims. E.g. the hollow shapes (2) can also be provided as multicavity shapes, or the manifold as an intermediate product can be cut down to pieces providing smaller units, e.g. T-formed fittings. Therefore all matter shown and described is to be interpreted as illustrative and not in a limiting sense.

Claims: Method of manufacturing integrated manifolds, particularly for heat exchangers, provided with a plurality of lateral connecting pieces from an extruded hollow shape, having one or more longitudinally running protruding neck parts (21) comprising the steps of forming risers (23) of solid cross-section by removing or relocating portions of the neck part (21), extruding the risers (23) of solid cross-section by reverse impact, forming hollow risers (3), each having a cavity limited by part of the hollow shape's wall; perforating these parts of the hollow shape's wall ensuring formation of inlets, each inlet connecting the individual cavity of the hollow risers (3) with the cavity of the hollow shape (2). Method as claimed in claim 1, characterized in that the formation of the individual risers (23) from the solid integrated neck part (21) is made by a cold forming process, where the height of the intermediate formed risers is higher than the original neck part (21). Method as claimed in claim 1, characterized in that the formation of the individual risers (23) from the solid integrated neck part (21) is made by removal of excess bridging material in between the required necks.

Inventors: CLAUSEN, EDVIN LIST
Applicants: NORSK HYDRO A.S.
Application year: 1987
Main classification: B21C37
IPC codes: B21D53, F28D1, F16L41, B23K20, B21C23, B21C37, B21D39, B21K1, F28F9