GB2110964A - A method of manufacturing hollow flow sections - Google Patents

Abstract

In order to simplify the manufacture of flow sections, e.g. for use in the matrix of a heat exchanger or as vanes or blades in turbomachines the following steps are performed during manufacture: a) thickenings (2', 3) are formed at preselected points over the circumference of a tube (1) having a substantially circular, square or polygonal cross-section; b) the tube is deformed so that the thickenings (3) are situated adjacent leading and trailing edges of the flow section (8) and other thickenings (2') form opposed separating webs; c) the opposed webs are then joined, e.g. by welding or brazing, to form at least two separate air ducts (9, 10) in the flow section. <IMAGE>

Description

SPECIFICATION A method of manufacturing hollow flow sections This invention relates to a method of manufacturing hollow flow sections of aerodynamically optimum shape.

Hollow flow sections are known in which the outer skin is wetted in operation by a first working medium (hot gas), while ducts arranged in the interior of the flow sections are simultaneously internally wetted by a second working medium (compressed air).

Such hollow flow sections are used, e.g., in heat exchangers of the type disclosed by German patent Specification DE-OS 29 07 810. These previously disclosed heat exchangers are provided with a manifold having two separate compressed air ducts.

The one compressed air duct directs the incoming compressed air into spear-shaped flow ducts, where it is heated by the hot gases to be directed in the preheated condition into the other compressed air duct, through which the preheated air is then ducted to a consumer, e.g. to the combustion chamber of a gas turbine engine. With the said heat exchangers the heat exchanger matrix formed by the spear-shaped flow sections project laterally from the manifold in U-shape configuration.

Such flow sections can also be used as, e.g., stator or rotor blades of a turbomachine, e.g. of a gas turbine engine, where in a turbine application, e.g., the respective blades are wetted by hot gas externally, and where on the other hand they are cooled by means of high pressure air bled from the compressor and directed through ducts in the interior of the blade.

It has always been rather difficult to provide a method that would be suitable for manufacturing flow sections such that they will be highly temperature resistant on the one hand and possess, on the other, the requisite strength properties, especially of static strength, to sustain high fatigue loads. Another requirement for the flow sections is a smooth outer wall to minimize turbulence.

Experimentally, such flow sections have been drawn from semisections, where the respective semisections are then joined together back-to-back and secured by means of a longitudinal welded or brazed joint. The difficulties involved in processes like these are considerable: - the respective semi-spear-shape sections are asymmetrical and accordingly very difficult to produce by drawing, - the back-to-back connection ofthe semi-spear-shape sections is difficult in that gaps or offset edges occur in the respective outer contour which may cause considerable turbulence, - the longitudinal welded or brazed joint resulting from the experimental manufacture of said sections is exposed to the continuous action of hot gas corrosion.

Another consideration is that in the case of such experimentally manufactured flow sections it is impossible to shape the ends of the resultant double section into a circular connection, should one be required, to join the section, e.g. in said heat exchanger, to the central manifold.

An object of the present invention is to provide aerodynamically favourably configured flow sections or hollow sections in a relatively simple manner and which are optimally suited to sustain both high and possibly alternating compressive and thermal stresses.

The invention provides a method of manufacturing a hollow flow section as claimed in claim 1.

An essential benefit is that the requirements imposed on the flow sections especially regarding aerodynamics, strength and resistance to temperature, are met early at the starting point of the process. The finished product generally requires no additional processing, except when the resultant flow section is intended for use as a turbine nozzle vane or rotor blade, where the requisite precision forming of the blade, as perhaps incorporation of blade twist, can still be achieved subsequently, as can additional duct connections, such as at the ends of the sections, required when use is made of the previously described heat exchanger.

A further essential advantage afforded by the present invention is that the pipe is formed as a generally finished product (hollow section) also regarding its internal structure, owing to the distribution and conformation of the thickening achieved at the starting point of the process and ultimately to the further deforming process, and that it possesses suitably separated duct for containing the flow of compressed air to be heated in the heat exchanging process (heat exchanger) or the flow of cooling air (nozzle vane or rotor blade) in the envisioned application.

Starting with a pipe of circular or rectangular section, then, the method of the present invention employs suitable deforming techniques (drawing, circular swaging or rolling) at preselected points to produce especially web-like accumulations of material. If the proper materials are used for the purpose, the contoured sections can be formed also by extruding. The webs can, depending upon the requirements of preceding or succeeding process operations, be formed externally, internally or on both sides of the pipe matrial. The actual deforming process to produce the flow section can then be drawing or rolling, with several processing steps used in between as required.The webs formed for said intents and purposes accordingly provide the accumulations of material or thickenings needed at the various points, e.g. at the leading and trailing edges and at the intermediate webs of the hollow section. Finish forming can likewise be achieved in several operations and using an internal tool as required. Final forming of the respective section is by compressing and welding the respective internal webs under, e.g., the rollers of a roller seam welding machine. The resultant sections, moreover, can be manufactured in any desired length. The webs, which in the interior of the section partially provide the ducts or separate them one from the other, can serve static functions, for relief of the forces resulting from the pressure of the medium flowing inside, as well as functions for improving the heat transfer.

In order to improve the heat transfer, metal strips of turbulence-inducing contours may be inserted, if necessary, through the length of the interior of the section before the webs are welded and brazed together, and can then be secured in place between the webs as part of the structure by welding or brazing process.

In order to manufacture twisted flow sections, as for turbine vanes or rotor blades, the various aerofoils are first cut to length and then forged into the respective final shape.

With regard to the "several process operations" cited above, it may be noted that these become necessary if the amount of deformation must be limited to allow for the properties of the specific material (cold working) and if, e.g., intermediate heat treatments are required. A property to consider in this respect, e.g., would be limited ductility of the material in deformation, so that the final shape must be approached via several intermediate shapes.

With finished shapes heavily departing from the circular shape, e.g., it may additionally be necessary to limit local hoop stresses (e.g. at small contour radii and edges) and achieve the final shape via various intermediate shapes to keep tool wear in reasonable limits.

In order to connect the flow sections to other structural components, e.g., heat exchanger tubes to the respective bottoms of the manifold and distributor pipes, it may be desirable to give ends of the flow sections a circular shape. Under the present process, said circular connecting ends can be formed using an intermediate operation, as follows: Before the intermediate webs are welded together, the end portions of the contour tube - when the tube is in an intermediate condition - are given a circular shape by swaging or other process. In the process the outer shell of the resultantcirculartube section can be provided with toroidal or helical grooves to improve the flexibility, if necessary, of said connecting portions.In lieu of said circular connections, or in addition to them, the outer shells of the connecting ends can be given circumferential shape patterns especially adapted to suit the specific application, using suitable forming processes. Such shape patterns may be, e.g., square, rectangular, trapezoidal, also hexagonal or octagonal.

Following the operation giving the end sections their shapes, the webs of the sections can be welded or brazed together, in this case, however, only partially in the area of the length of section not affected by the forming process.

Embodiments of the invention will now be described with reference to the accompanying draw ings, wherein: Figs. 1,2 and 3 illustrate respectively a square and two essentially circular pipe sections; Figs. 4 and 5 illustrate essentially circular pipe sections, in which the thickenings have a web-like shape; Fig. 6 illustrates the essentially square pipe section of Fig. 1 and related thereto, a hollow section shape manufactured therefrom; Figs. 7 and 9 illustrate flow sections derived and manufactured from the basic pipe section of Fig. 5, but again in an intermediate phase in which the forming process has been interrupted; Figs. 8 and 10 illustrate respectively the final configuration of the flow sections of Figs. 7 and 9 related thereto, the processing tools required for heir final forming;; Figs. 9 and 10 illustrate the installation of additional turbulence baffles; Figs. 11 and 13 illustrate the same flow profile in different positions and related thereto, the longitudinal contour; Figs. 12 and 14 illustrate respective sectional views taken along line A-A of Fig. 11 and line B-B of Fig. 13; Fig. 15 is a perspective view of the finished flow section of Figs. 12 and 14; Fig. 16 is a perspective view of a heat exchanger for application of flow sections manufactured in accordance with the present invention; and Figs. 17, 18, 19 and 20 shown a turbine nozzle vane section during its final forming, and having twist in the final form of Fig. 20.

The method of the present invention is now described more fully as follows: The starting material is e.g. a substantially square-section pipe in Fig. 1 or a substantially circular-section pipe 2 of Fig. 2. The pipe 1 of Fig. 1 is provided with accumulations of material or thickenings preferably in the corners 2', 3, whereas in Fig. 2 the pipe has an internally-cylindrical section having external accumulations of material or thickenings 4, 5. The thickenings are circumferentially, approximately-equally, spaced such that the pipe 2 is nearly square on its outer circumference, and has diametrically-opposed radiused corners.

In the embodiment of Fig. 3, a pipe 3 has an outer cylindrical surface, whereas the inner circumference of pipe 3 has a mixed square and circular inner wall structure with diametrically-opposed accumulations of material orthickenings 6 and diametrically-opposed oppositely arranged accumulations of material or thickenings 7.

After a square pipe 1 as shown in Fig. 1 has been provided with the thickening 2', 3, the pipe 1 is deformed to the shape shown in Fig. 6 by drawing and rolling such that the thickenings 3 form the upstream and downstream thickened walls adjacent the leading and trailing edges of the flow section 8, while the other thickenings 2' form separating webs between the ducts 8,9 of the flow section to be completed at a later stage. As it has been mentioned earlier the arrangement and configuration of the separating webs is of significance primarily for the stress design and for optimization of heat transfer. It will become apparentfrom Fig. 6that the flow section 8 is basically finished in its shape, but that a gap still remains between the adjacent ends of the separating webs 2; this gap is bridged completely by lightly compressing the flow section in a further operation and then welding the web ends together.

Figs. 4 and 5 show pipes having substantially cylindrical profiles 11 and 12 with respective thickenings 13 and 14, which already have the approximate shape of webs. The web-like thickenings 13 of Fig. 4 not only project beyond the inner circumference of the pipes section 11, but also beyond the outer circumference of the wall. The embodiment of Fig. 5 differs from that of Fig. 4 in that web-like thickenings 14 and 15, project only beyond the inner wall circumference of the pipe section 12. Such thickenings, and also the pipe sections on which they are formed, be produced by drawing, circular swaging, rolling or extruding.

The embodiments shown in Figs. 4 and 5 can each be used as a separate starting point in the further manufacture of a hollow body or flow section.

Figs. 4 and 5, however, can be taken also as representing two successive process phases, where the relatively large amount of material needed to produce the intended inner separating webs at a latertime,e.g. is providedbyfirstsuitablyforming the thickenings 13 projecting beyond the inner and outer walls of the pipe section 11 (Fig. 4). In a subsequent processing operation these thickenings 13 are then fashioned into contour 15 (pile section 11 - Fig. 5), after which the further or finishing contour forming operation is performed.

The embodiments shown in Figs. 7 to 10 each start with the pipe section 12 of Fig. 5, which has thickenings 14 and 15 projecting beyond the circumference of the inner wall only. In accordance with Fig. 7 the flow section 16 is almost ready, with the adjacent web ends ofthethickenings 15 not yet touching. It is here assumed, e.g. that the process of forming the pipe contour 12 has been interrupted between the configurations of Figs. 5 and 7 to insert a tool corresponding to the desired inner contour 17, 18 (Fig.7) of the duct, after which the further forming process to produce the contour 16 (Fig. 7) is performed.The tool having first been removed, the contour 16 is formed transversely by means of open dies 19,20 in accordance with Fig. 8 to produce the final contour 16', in which where the web ends are welded or brazed together shortly before they touch.

FIG. 9 illustrates a flow section 16 again derived from FIG. 5 in an intermediate forming stage of FIG.

7 whereturbulence baffles21 are inserted, before thefinishingpressing operation of FIG. 10, into the respective ducts between the ends of the webs formed bythethickenings IS. The baffles 21 also form an internal structural component under the final forming operation as shown in FIG. 10 to produce the flow section 16' and are then welded or brazed into place on either side of the webs to form part of the flow section.

In a method (not shown) the finishing forming operation on the flow section may be performed by simultaneously compressing and wedling together the inner webs under the rollers of a roller seam welding machine.

FIGS 11, 12, as well as 13 and 14, illustrate another example of a flow section 16 produced by drawing from the basic pipe body 12 of FIG. 5. As it will become apparent from FIGS 11 and 13 the central web ends are still spaced apart a certain distance: accordingly, the section 16 still requires a little forming, as do the sections of FIGS 7 and 9. Prior to final forming and welding or brazing along the web ends, the flow sections of FIGS 11 to 14 are still provided with a circular connecting portion 21 produced by circular swaging so that the flow section can be connected to a heat exchanger base.

The connecting portion 21 may of course be produced by using other suitable methods (drawing, pressing or rolling) and can be made polygonal, where the term "POLYGONAL" also embraces square, rectangular, trapezoidal, hexagonal and octagonal sections.

The connecting portion 21 can also be provided, as shown in FIG. 5, with grooves 22 formed either before or after welding or brazing the web ends together. In accordance with FIG. 15 the grooves 22 can be successively equally spaced in the outer circumferential wall of the connecting portion 21, or they may be coiled helically in a circumferential direction into the connecting portion.

FIG 16 illustrates part of a heat exchanger incorporating a flow section of the present invention and having a cross countercurrent matrix 23. The hollow sections, e.g. 16 of FIGS 8 and 10, forming the matrix are connected on the one hand to a first stationary pipe duct 24 to feed compressed air D into the matrix, and are connected on the other hand to a second stationary pipe duct 25 from which the compressed air D', having been heated via the matrix by hot gas H, is routed to a suitable consumer, such as the combustion chamber of a gas turbine engine. In accordance with FIG. 16 the two separate pipe ducts 24 and 25 are integrated into a common manifold 26, with the heat exchanger matrix 23 projecting laterally from the manifold 26 in U-fashion. The route of the compressed air through the matrix 23 is indicated by the arrow D.The place of a common manifold for the two pipe ducts 24 and 25 can conceivably be taken by a heat exchanger configuration which exhibits two separately arranged, essentially parallel pipes, one pipe carrying the compressed air into the matrix and the other pipe leading the compressed air away from the matrix and to a suitable consumer.

FIG. 17 illustrates a basic flow section 27 manufactured from a polygonal pipe having separate internal ducts 28, 29 and 30. If e.g. the basic flow section of FIG. 17 is intended for turbine nozzle vane or rotor blade applications, the procedure in accordance with the present invention would be to cut the basic section 27 of FIG. 17to a suitable length and then give it the intended optimum shape to suit aerodynamic and thermodynamic requirements. In accord ante with FIG. the section 27' is essentially curved and, in accordance with the contour 27" of FIG. 19, is drawn in predominantly the longitudinal direction for final shape, after which in accordance with FIG 20 and contour 27 the blade is given the intended amount of twist, e.g. by way of a forging process in which the aerofoil of FIG. 19 is hammered into final shape over suitably formed dies as shown in FIG. 20.

For application of the flow sections manufactured in accordance with the present invention to known heat exchangers, it will not inevitably be necessary to form circular connecting portions on the flow sections; instead, the spear-shaped flow sections may be made to open directly into the base portions of the heat exchanger and be attached there.

Claims (13)

1. Amethod of manufacturing a hollow flow section of aerodynamically optimum shape to suit the respective application, the respective outer skin of which is wetted in operation by a first working medium (hot gas), while ducts arranged in the interior of the flow sections are simultaneously internally wetted by a second working medium (compressed air), characterized by the following features: comprising: a) forming thickenings at preselected points over the circumference of a tube having a substantially circular square, or polygonal cross-section; b) deforming the tube so that thickenings are situated adjacent leading and trailing edged of the flow section and other thickenings form opposed separating webs, and joining the opposed webs to form at least two separate air ducts in the flow section.

2. A method as claimed in claim 1, wherein at least two pairs of diametrically-opposed web-like thickenings are formed on the circumference of the tube before the tube is deformed and the thickenings extend inwardly and/or outwardly of the tube.

3. A method as claimed in claim 1 or 2, wherein the thickenings are produced by drawing, circular swaging, rolling, hot pressing or extruding.

4. A method as claimed in claim 1,2 or 3, wherein an internal tool is used inside the flow section during deformation of the tube.

5. A method as claimed in claim 1,2 or 3, wherein turbulence-inducing metal plates or strips are inserted between adjacent web ends of the finish formed flow section and are welded or brazed together with the web ends and as an internal structural component of the flow section.

6. A method as claimed in any one of claims 1 to 5, wherein final finish forming is achieved by pressing the inner webs together and welding them together under the rollers of a roller seam welding machine.

7. A method as claimed in any one of claims 1 to 6, wherein the flow section is cut to size, subjected to a forging operation and twisted to a desired geometry, the flow-section being shaped or hammered over suitably shaped dies to achieve its final form.

8. A method as claimed in any one of claims 1 to 6, wherein, before the webs of the flow section are joined together, at least one end portion of the flow section is deformed into a circular or polygonal connecting piece as hereindefined.

9. A method as claimed in claim 8, wherein the connecting piece is provided with coaxially or helically extending grooves formed into its inner and/or outer wall.

10. A method as claimed in any one of claims 1 to 9, wherein, web-like thickenings extending inwardly of the inner wall of the tube are formed from the said thickenings.

11. A method of manufacturing a hollowflow section substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.

12. Aflowsection manufactured by the method as claimed in any one of the preceding claims.

13. Flow sections manufactured bythe method as claimed in claim 8 or 9 and incorporated in a cross counterflow matrix of a heat exchanger, wherein the hollow sections are connected to a first stationary pipe duct for directing compressed air into the matrix, and to a second stationary pipe duct for directing compressed air heated in its passage through the matrix to a consumer, the two separate pipe ducts being either integrated into a common manifold or are formed by essentially mutually parallel individual pipes, the heat exchanger matrix formed by the hollow sections projecting laterally relative to the manifold orto the individual pipes substantially in the shape of a letter U.