Patent Application
20130174935
This disclosure relates to a method of manufacturing a thin walled duct with a bend. This disclosure also relates to an engine having one or more thin walled ducts with bends.
Thin walled ducts or tubes are used in a wide variety of applications. Typically, a duct having a uniform wall thickness is bent to the desired shape. The wall thickness of the duct is selected based upon the most highly stressed area of the duct. Such an approach to duct design results in ducts having a thicker than necessary wall thickness along much of the length of the duct.
In aerospace applications, for example, ducts are used frequently. Precise alignment is required between the ends of the ducts and the adjoining components to which the ends are attached. Thus, flow lined pressure compensating bellows, which are heavy and costly, are often used to join the duct ends to their adjoining components. The use of compensating bellows may be avoided by increasing the wall thickness of the duct, along its entire length, which enables the ends to be welded to attaching flanges that then can be secured to the adjoining components, however, this approach increases the overall stiffness of the duct. Most aerospace architecture applications are, in part, centered around compactness which yield benefits in the form of reduced vehicle weight and improved aerodynamics. More compact duct arrangements help reduce vehicle engine envelope and thereby reduce overall vehicle gross weight. Variable wall thickness ducts increase ability to compact engine systems within smaller envelopes.
Chemical milling has been used to thin the wall thickness of bent ducts in aerospace applications. Typically, a uniform thickness duct is bent to the desired shape. The duct is masked around the desirably thick areas, and then chemicals are applied to the unmasked areas to chemically remove some of the wall thickness.
The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to
A duct 10 is shown in
The duct 10 is mechanically worked, as illustrated in
Example mechanical working processes include flow forming, turning and grinding in which material is plastically deformed and/or removed from the exterior surface of the duct 10. Flow forming produces a smooth, wavy surface, which may in some cases have subtle surface ripples or waves. It also should be understood that the interior surface may be deformed to provide the variable wall thickness described above.
In the example, the end portions 28 are generally uniformly cylindrical. However, it should be understood than the end portions 28 may become ovalized from the bending operation, but if this occurs the ends will typically undergo a rounding operation. A transition 36 adjoins the end portion 28 and the portion 32 such that an abrupt step is avoided, which may be a byproduct of a given mechanical working process. Transition 36 is structurally beneficial as it mitigates the occurrence of undesirable stress concentrations from developing in the duct during engine operation.
A bending process is employed to produce a bend in the area of the portion 32. A spacer 39 is provided about the portion 32 prior to bending the duct 10 to the desired shape, as shown in
Referring to
The thicker first wall thickness 30 provides strength in desired circumferential areas, while the thinner second wall thickness 34 provides a smaller cross section to reduce stiffness and/or eliminate unneeded weight. For example, the end portion 28 provides sufficient structure to accommodate the heat produced when securing to a flange 52 to the duct 10 by a weld bead 54. The end portion 28 has an end portion width 44 that is approximately four times the first wall thickness 30, for example, which sufficiently accommodates the heat when applying the weld bead 54. The transition 36 extends a transition width 46 that is three times the first wall thickness 30 in one example. The contour of the transition 36 is based upon the forming process and profile of the tool 26, for example.
The intrados (inner radius) 48 may be slightly thicker and the extrados (outer radius) 50 slightly thinner than the second wall thickness 34 from the bending process. The inner diameter 18 has a circular cross-section and is uniform in its dimensions and without wrinkles. It is desirable to provide the distance 56 adjoining the transition 36 and any bends for at least the reasons described above.
A rocket engine 58 is illustrated in
A fuel turbopump discharge duct 60 fluidly connects a fuel turbopump 62 to a main fuel valve 64. An oxidizer turbopump discharge duct 66 fluidly connects an oxidizer turbopump 68 to a main oxidizer valve 70. A nozzle coolant discharge duct 72 fluidly connects a nozzle 74 to an injector mixer 76. The thinner portions of the duct are less stiff than the thicker portions to which the flanges are secured. This reduced stiffness desirably reduces the loads and stresses imparted to the components to which the ducts are secured.
Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.
This invention was made with government support from the National Aeronautics and Space Administration under Contract No.: NNM06AB13C. The government may have certain rights to this invention pursuant to Contract No. NNM06AB13C awarded by the National Aeronautics and Space Administration.
