Patent Application
20100052318
This invention generally relates to a system and method of joining a tube to a header, more particularly, an assembly of a fluid transporting tube and a header joined using a ferrule.
Much development has been made in the area of joints formed between ends of fluid transporting tubes and a header plate receiving those tubes. For example, various methods of joining fluid tubes, such as coolant tubes, to a header has been developed to extend duration and durability of heat exchangers.
One of the well known methods of joining a tube to a header involves a ferrule. Often, a ferrule is designed to gradually transfer stress from the tube to the ferrule, thereby increasing allowable loading and life span of the joint. Without the ferrule, a header-tube joint is subjected to a maximum stress of the system, and thus, often becomes a point of failure. In some applications, the ferrule is integrally formed with the header, wherein the tube is received and seated. Such a joining method using an integral ferrule-header is commonly practiced in manufacturing of afterburner spray bars for some jet engines.
There are several limitations with the integral ferrule-header designs. First, the integral ferrule-header systems can be relatively costly to manufacture. This is because manufacturing of the integral ferrule-header can involve complex engineering and equipment, which can be a lengthy and expensive process. Second, a design of the integral ferrule-header is limited by current manufacturing capabilities, which often does not allow for production of a desired geometry of a ferrule-header. Further, in such a ferrule-header system a stress concentration can be induced in the tube proximate a ferrule.
In view of these limitations, there is a need in the art for improved system and method of joining fluid transporting tubes with a header. The present invention pertains to such improvements to the state of the art of a tube-header assembly using an internal ferrule.
In view of the above, embodiments of the present invention provide a new and improved system and method of joining tubes to a header that overcomes one or more of the limitations existing in the art. More particularly, embodiments of the present invention provide a new and improved tube-header assembly incorporating an internal ferrule. Such embodiments significantly improve the performance of the tube-header assembly by more evenly distributing external stress. Such embodiments are relatively simple to engineer and easy to manufacture, and thus reduce overall cost of the tube-header assembly.
In one aspect, the invention provides a tube-header joint for a fluid transport system including a tube, an internal ferrule and a header, wherein the internal ferrule is attached within the tube. Further, the header includes an aperture, wherein the tube is fixed.
In another aspect, the invention provides a method of assembling a tube-header joint for a fluid transport system including forming a tube, forming a flared end in at least one end of the tube, making an internal ferrule, fitting the internal ferrule in the flared end of the tube, forming a header including an aperture, and attaching the flared end of the tube in the aperture
In yet another aspect, the invention provides a method of reducing an external stress concentration on a tube-header joint for a fluid transport system including forming a tube-header joint comprising a tube, a header and a ferrule, wherein the ferrule is positioned inside of the tube. The method of reducing an external stress concentration on a tube-header joint also excludes an external ferrule from the tube-header joint.
Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.
The tube 12 of this embodiment is adapted to transport fluid, for example, fuel in an afterburner system in some jet engines, through a flow path 30 defined within the tube 12. The cylindrical tube 12 has a circular cross section having an inner diameter 32, which gradually increases from point 34 to point 36, thereby forming the flared end 18. The flared end 18 has a sloped portion 20, defined by a portion of the tube 12 between the point 34 and the point 36, and a tube insert 40 having a constant inner diameter 38.
The aperture 22 of the header 14 has a circular cross section to fit the tube insert 40. Thus, an inner diameter 42 of the aperture 22 is almost equal to an outer diameter 44 of the tube insert 40 with just enough clearance to tightly fit them together. In other embodiments, the tube insert 40 may be sloped, either flaring or constricting, as such the aperture 22 of such embodiments is configured accordingly to fit such shapes.
Now that each component of the tube-header joint 10 is described, a method of assembling the tube-header joint 10 according to the present invention will be explained.
In one embodiment, the tube 12 is swaged at one end in a swaging machine using swaging dies designed to form the flared end 18. For example, the tube 12 can be fed into a swaging die opening, wherein the swaging die rotates to widen an end of the tube 12 into a desired shape by centrifugal force. Once the tube 12 is swaged to form the flared end 18 the internal ferrule 16 is inserted, with the tip 56 first, into the flared end 18 through the tube insert 40. In other embodiments, the tube 12 may be preformed to include a flared end 18.
In the tube 12, the internal ferrule 16 is joined with the flared end 18 of the tube 12 by a suitable manufacturing process such as brazing, welding, press-fit, shrink-fit, hold-down spring, etc. For example, in a brazing process, an inner surface 24 of the flared end 18 and/or an outer surface 52 of the internal ferrule 16 maybe applied with a filler material, such as silver, tin, zinc, copper, etc., and heated to the melting temperature of the filler material such that the filler material melts and metallurgically bonds the tube 12 and the internal ferrule 16 together. In such an embodiment, the tube 12 and the internal ferrule 16 are formed of a metallic material having a higher melting temperature than the brazing filler material. The tube 12 and the internal ferrule 16 may be formed of a same or different metallic materials. The tube 12 joined with the internal ferrule 16 is fitted into the aperture 22 of the header 14, wherein the tube insert 40 is joined with the header 14 by a suitable manufacturing process similar to the process used for joining the internal ferrule 16 and the flared end 18 of the tube 12.
In a different embodiment, the tube 12 may be first joined with the header 14 by attaching an outer surface of tube insert 40 with an inner surface of the header aperture 22 by a suitable manufacturing process. The internal ferrule 16 may then be inserted into the flared end 18 of the tube 12 such that the outlet end 48 of the internal ferrule 16 is flushed with an end of the tube insert 40. The internal ferrule 16 may be attached with the flared end 18 via suitable process. For example, the internal ferrule 16 can be press-fit into the flared end 18.
The internal ferrule 16 is advantageous over a conventional system, wherein a ferrule is integrally formed with a header plate. An example of the conventional tube-header joint is illustrated in
Further, the placement of a ferrule inside of a tube also improves stress distribution on a tube-header joint.
Test results confirmed reduced von Mises stress at an intersection of the ferrule and tube for the tube-header joint 10 of the present invention when compared with the conventional tube-header joint 60. The test results showed that the tube-header joint 10 had von Mises (Max) stress of 164.3 Ksi at a tube-ferrule intersection 26. (
A tube-header joint comprising an internal ferrule according to the present invention provides many benefits. The internal ferrule substantially decreases manufacturing costs, because it is a separate piece from a header, and has a relatively simple structure. As such, the internal ferrule allows for a decrease in complexity of engineering and manufacturing the header and the ferrule, resulting in savings in manufacturing costs. Further, the internal ferrule improves overall performance of the tube-header joint, by eliminating a stress concentration point.
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
