Method of forming a rocket thrust chamber

Abstract: Molten metal is sprayed onto the outer shell 32 of a cooling tube bundle 10, and the ends of tubes 18, 20 are covered with predetermined thicknesses of the metal 52, 54. Circumferentially extending manifold channels 60, 64 that intersect each of the tube ends 18, 20 are then machined into the predetermined thicknesses of metal, and mating assemblies 74, 76 are attached to enclose the manifold channels 60, 64.

Description: This invention is related to rocket engines, and particularly to a process for forming manifolds for rocket engine thrust chambers. Rocket engines, such as those used to launch satellites, are costly to design and manufacture. At the same time the demand for rocket engines capable of carrying payloads to space or near-Earth orbits continues to grow. Consequently, manufacturers of such rocket engines are constantly seeking new ways to reduce the design and manufacturing costs of producing rocket engine components. One such component is the rocket thrust chamber within which the propellants of the rocket engine are combusted and accelerated. Because of the extremely high temperatures of the propellants moving through the thrust chamber, the walls of the thrust chamber must be cooled in those applications that require sustained engine firings. Such cooling is typically accomplished by flowing a coolant through tubes that form the inner wall of the thrust chamber. European Patent Application EP 0 780 563 A2 discloses a method of making rocket thrust chamber comprising a number of tubes forming a tube bundle according to the preamble of claim 1. Since the manufacture of such thrust chambers is costly, novel ways of manufacturing such thrust chambers have been developed. One example of the manufacture of such a thrust chamber is shown in U.S. Pat. No. 5,375,325 to Bales et al., which discloses a rocket chamber produced by positioning sleeved cooling tubes within a structural jacket to form a tube bundle, and positioning a liner within the tube bundle thereby sandwiching the tubes between the jacket and the liner. The tubes are then subjected to high internal pressure and inflated at high temperature while the liner is simultaneously subjected to the same high pressure, thereby forcing the sleeved tubes into intimate contact with adjacent sleeved tubes, the liner and the jacket. The temperature is maintained until bonding has occurred between the liner, sleeved tubes and jacket. While the aforementioned patent represents an improvement over the prior art, the manufacture of the structural jacket which is used in the manufacture requires a great deal of machining, and each end of each of the tubes must be individually welded into manifold channels in the jacket. The time and effort associated with this machining and welding represents a significant portion of the manufacturing cost of the thrust chamber. What is needed is a method of making a rocket thrust chamber requires less machining to form a structural jacket, and eliminates the need for each end of each of the tubes to be individually welded into manifold channels in the jacket. It is therefore an object of the present invention to provide a method for forming a rocket thrust chamber that reduces the amount of machining required to form a structural jacket, as compared to the prior art. Another object of the present invention to provide a method for forming a rocket thrust chamber which eliminates the need for each end of each of the tubes to be individually welded into manifold channels in the jacket. According to the method of the present invention as defined in claim 1, a method of making a rocket thrust chamber is disclosed in which molten metal is sprayed onto the outer shell of a cooling tube bundle, and the ends of tubes are covered with predetermined thicknesses of the metal. Circumferentially extending manifold channels that intersect each of the tube ends are then machined into the predetermined thicknesses in of metal, and mating assemblies are attached to enclose the manifold channels. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a cross-sectional view of a quarter section of the tube bundle used in a method of making the rocket thrust chamber of the present invention. Fig. 2 is a cross-sectional view of the assembly of Fig. 1 taken along line 2-2 of Fig. 1. Fig. 3 shows the assembly of Fig. 1 with the tubes ends crimped to form the sealed tips. Fig. 4 shows the assembly of Fig. 3 after the various thicknesses of metal have been sprayed onto the assembly. Fig. 5 shows the assembly of Fig. 4 after the lids have been removed and the sprayed metal has been machined to form the structural jacket. Fig. 6 shows the assembly of Fig. 5 after the sealed tips of the tubes have been machined away and the manifold channels have been machined into the jacket. Fig. 7 shows the assembly of Fig. 6 of with the mating assembly is welded to the manifold lands. The method of the present invention is practised by applying a spray of molten metal onto a tube bundle 10 such as the one shown in the sectional view of Fig. 1. This metal spraying process is commonly referred to as Vacuum Plasma Spray ("VPS") by those skilled in the art It is to be understood that Fig. 1 shows only ¼ of the tube bundle 10, and that the entire tube bundle 10 is symmetric about a longitudinally extending reference axis 12.The tube bundle 10 includes a plurality of cooling tubes 14 that are circumferentially located about a longitudinally extending reference axis 12. The longitudinal axis 12 defines the axis of symmetry for the tube bundle 10, and, as shown in Fig. 1, each of the tubes extends along the longitudinal axis 12 in spaced relation thereto. Each of the tubes 14 is bonded to two of the tubes 14 immediately adjacent thereto along the entire length 16 which the tubes 14 extend along the longitudinal axis 12. This bonding, which is preferably accomplished by brazing, fills the interstices between adjacent tubes 14, thereby preventing the spray of molten metal from infiltrating into the interior of the tube bundle 10 during the metal spraying process described below. Each of the tubes 14 has a first tube end 18 and a second tube end 20, and each of the first tube ends is in spaced relation to each of the other first tube ends, as shown in Fig. 2. Likewise, each of the second tube ends 20 is in spaced relation to each of the other second tube ends 20 (not shown). As shown in Fig. 1, each of the first tube ends 18 is located radially outward of a first segment 22 of the longitudinal axis 12, and each of the second tube ends 20 is located radially outward of a second segment 24 of the longitudinal axis 12. As shown in Fig. 1, the outer surface 26 of each of the tubes 14 comprises a radially inward portion 28 and a radially outward portion 30. The radially inward portion 28 of each tube 14 faces the longitudinal axis 12 and the radially outward portion 30 of each tube 14 faces away from the longitudinal axis 12. Collectively, the radially outward portions 30 define the tube bundle outer shell 32. A first structural ring 34 is secured to the first tube ends 18, and a second structural ring 36 is secured to the second tube ends 20 such that tube bundle 10 is sandwiched between the first and second structural rings 34, 36, as shown in Fig. 1. The structural rings 34, 36 are made of the same metal that is used in the spraying process described below, and each of the structural rings 34, 36 is preferably secured to the immediately adjacent tube ends 18, 20 by brazing. A lid 38, 40 is secured to each of the structural rings 34, 36, thereby isolating the inner cavity 42 of the tube bundle 10 from the ambient environment 44, as shown in Fig. 2. Each of the first and second tube ends 18, 20 is then sealed, preferably by crimping each tube end 18, 20 and folding it back onto its respective tube 14, thereby defining a sealed tip 46, 48 at each of the first and second tube ends 18, 20, as shown in Fig. 3. The tube bundle 10, with the attached rings 34, 36 and lids 38, 40, is then placed into a VPS chamber of the type known in the art, and molten metal, preferably steel or a steel alloy, is sprayed onto the tube bundle outer shell 32 and the first and second tube ends 18, 20, until a first predetermined thickness 50 of the metal covers the tube bundle outer shell 32, as shown in Fig. 4. Additional amounts of molten metal are then sprayed onto the first tube ends 18 until a second predetermined thickness 52 of metal covers the first tube ends 18, and additional amounts of molten metal are sprayed onto the second tube ends 20 until a third predetermined thickness 54 of metal covers the second tube ends 20. Once the sprayed metal has reached the desired thicknesses 50, 52, 54, additional processing (e.g. heat treatment) is performed to produce the desired material characteristics in the sprayed metal. After the additional processing has been completed, the lids 38, 40 are removed and excess sprayed metal is machined away yielding the desired structural jacket 56 encasing the tube bundle 10, as shown in Fig. 5. The inlet manifold 58, as shown in Fig. 6, is formed by machining a first circumferential channel 60 in the second predetermined thickness 52 of metal by machining away some of the second predetermined thickness 52 of metal and the sealed tip 46 of each of the first tube ends 18, and the outlet manifold 62 is formed by machining a second circumferential channel 64 in the third predetermined thickness 54 of metal by machining away some of the third predetermined thickness 54 of metal and the sealed tip 48 of each of the second tube ends 20. The resulting structural jacket 56, as shown in Fig. 6, includes circumferentially extending inlet and outlet manifold channels 60, 64. After the machining operation is complete, additional processing (e.g. Hot Isostatic Pressing) is performed to produce the final desired material characteristics in the sprayed metal. The inlet manifold channel 60 is bounded by inlet manifold lands 66, 68, and the outlet manifold channel 64 is bounded by outlet manifold lands 70, 72, as shown in Fig. 6. As shown in Fig. 7, a first mating assembly 74, which has been machined to fit the inlet manifold lands 66, 68 is sealingly attached to the inlet manifold lands 66, 68 of the second predetermined thickness 52 of metal, and a second mating assembly 76, which has been machined to fit the outlet manifold lands 70, 72, is sealingly attached to the third predetermined thickness 54 of metal. The mating assemblies 74, 76, which are made of the same metal as the jacket 56, preferably are sealingly attached to the jacket 56 by welding the mating assemblies 74, 76 to the manifold lands 60, 68, 70, 72 immediately adjacent thereto. Once the circumferential channels 60, 64 have been enclosed by the mating assemblies 74, 76, fluid, such as coolant, can only enter or exit the cooling tubes 14 through orifices (not shown) in the manifolds. As those skilled in the art will readily appreciate, the method of the present invention requires less machining than the prior art to form a structural jacket,, since only the outer surface of the structural jacket needs to be machined. Furthermore, the need to individually weld each of the cooling tubes into the manifold channels in the jacket is eliminated, since the molten metal sprayed onto the tube ends during the jacket formation seals each of the tube ends to the structural jacket. Accordingly, the time and effort, and the attendant cost, necessary to manufacture the thrust chamber is reduced as compared to the prior art. Although this invention has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the scope of the claimed invention.

Claims: A method of making a rocket thrust chamber, said method comprising: providing a tube bundle (10) including a plurality of tubes (14), said tube bundle (10) having a longitudinal axis (12) defined therethrough, each of said tubes (14) extending along said longitudinal axis in spaced relation thereto, each of said tubes (14) being bonded to two of said tubes (14) immediately adjacent thereto along a first length that the tubes (14) extend along said axis (12), each of said tubes (14) having a first tube end (18) and a second tube end (20), each of said first tube ends (18) being in spaced relation to each of said other first tube ends and located radially outward of a first segment (22) of said reference axis (12), and each of said second tube ends (20) being in spaced relation to each of said other second tube ends (20) and located radially outward of a second segment (24) of said reference axis (12), the outer surface (26) of each of said tubes (14) comprises a radially inward portion (28) and a radially outward portion (30), the radially inward portion (28) of each tube (14) facing said axis (12) and the radially outward portion (30) of each tube (14) facing away from said axis (12), said radially outward portions collectively defining an tube bundle outer shell (32), spraying molten metal onto said tube bundle outer shell (32) and said first and second tube ends (18, 20) until a first predetermined thickness (50) of said metal covers said tube bundle outer shell (32), characterised in that before spraying molten metal onto said tube bundle said first and second tube ends are sealed (18, 20), thereby defining a sealed tip (46, 48) at each of said first and second tube ends (18, 20), further characterised in that after spraying molten metal onto said tube bundle, the following steps are carried art : spraying additional amounts of molten metal onto said first tube ends (18) until a second predetermined thickness (52) of metal covers said first tube ends (18), spraying additional amounts of molten metal onto said second tube ends (20) until a third predetermined thickness (54) covers said second tube ends (20), forming a first circumferential channel (60) in said second predetermined thickness (52) of metal by machining away some of said second predetermined thickness of metal and the sealed tip (46) of each of said first tube ends (18), and forming a second circumferential channel (62) in said third predetermined thickness (54) of metal by machining away some of said third predetermined thickness of metal and the sealed tip (48) of each of said second tube ends (20); enclosing said first circumferential channel (60) by sealingly attaching a first mating assembly (74) to said second predetermined thickness of metal (52), and enclosing said second circumferential channel (64) by sealingly attaching a second mating assembly (76) to said third predetermined thickness of metal.

Inventors: WRIGHT ROBERT J, WRIGHT, ROBERT J.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1999
Main classification: B23P15
IPC codes: B64G1, F02K9, B23P15