TUBE COUPLING

Abstract: A coupling for swaged attachment to thin wall tubing. The coupling is a cylindrical body (10) with a longitudinal axis and an inner peripheral wall (12). At least one groove (14) is located in the inner peripheral wall. In one embodiment, the groove is substantially rectangular in cross section. The rectangular groove has a base and two side walls. The side walls meet the base to form corners. The corners have a radius of curvature of at least the depth of the groove. Alternatively, the cross section of the groove can be ramped in shape. The ramped shape groove has a base and two side walls. One of the two side walls meets the base at about 90°, and the second side wall meets the base at an angle substantially greater than 90°. In a third embodiment of the invention, the groove is ramped with one side wall meeting the inner peripheral wall of the coupling sleeve at about 90°, and a second side wall meeting the inner peripherai sleeve of the inner peripheral wall of the coupling sleeve at substantially less than 90°. The preferred material for the coupling sleeve for aerospace use is titanium.

Description: The present invention relates to a coupling for sealing attachment to metallic tubing. In particular the invention relates to a rigid coupling having an interior configuration such that it can be secured on such tubing in a pressure tight relationship by swaging the tubing while satisfying all mechanical and performance requirements for such swaged joints. In hydraulic systems as used in aircraft and aerospace applications, end fittings for tubing in such systems are flareless fittings with swaged on couplings or sleeves. Such sleeves have been characterized by internal annular grooves and were developed for use with light weight, thin wall, hydraulic tubing to eliminate the leakage and inadequate tensile joint strength problems encountered with bite type sleeves. US-A-3474519 describes a coupling having a deformable sleeve with internal annular grooves each of which is generally rectangular in shape. More specifically each groove has a base and two side walls, one side wall meeting the base at about 90° to form a corner having a small radius of curvature, and the other side wall meeting the base at an unspecified greater angle to form a ramped profile, there being narrow lands between the grooves. The coupling is secured by deforming the sleeve to force the grooved portion into engagement with the tube periphery by means of external taper locking rings. US-A-3730567 describes an arrangement in which a coupling sleeve has a plurality of non-uniform grooves having small radius rounded corners, said sleeve being attached by internal swaging of the tube walls to expand them radially outwardly. Currently used couplings with rectangular grooves are less than optimal for a number of reasons. Because of the small radius of curvature at the corners of the grooves where the sidewalls meet the base, tubing being swaged into the rectangular grooves tends to develop cracks. This is especially a problem with titanium tubing. Titanium does not like to flow into rectangular grooves. In fact, when swaged into rectangular grooves, the tubing deforms into a trapezoidal shape, leaving areas of highly stressed and unsupported material in shear. The swaged tubing therefore tends to develop cracks and leaks. Theoretically, ramped grooves can be preferable to rectangular grooves for use in swaged contact with tubing. This is because the ramped groove allows the tubing material to flow smoothly into the grooves resulting in continuous grain flow. This continuous grain flow reduces shear stresses in the tube material. In addition, the ramp causes a more gradual transition from swaged to unswaged material than a rectangular groove, thus reducing the number of stress points and stress risers in the swaged tubing. The theoretical advantages of the ramped groove, such as those in the coupling sleeve of U.S.-A- 4,026,006 are limited by the fact that many currently used coupling sleeves are swaged only by force from outside the sleeve. External swaging fails to take advantage of the highly desirable compressive stresses which can be exerted on the outside of the tubing when swaging is internal. Therefore, currently used coupling sleeves with ramped grooves tend to induce an unacceptable amount of cracking in tubing to which they are swaged. Currently used couplings with ramped grooves also tend to vibrate loose in aerospace use, causing premature failures. There exists therefore the need for improved couplings for attachment to thin wall, flareless tubing which have improved metal fatigue characteristics, which do not tend to vibrate loose from the tubing and which are attached by internally swaging the tubing within the coupling. According to the invention, there is provided a coupling for attachment to thin wall tubing as distinguished by the characterising part of the appended Claim 1. The body of the coupling is adapted to remain unchanged when the tube is swaged outwardly into the grooves. Preferably, for aerospace use, the coupling is made of titanium or stainless steel, particularly 15-5 PH (precipitation hardened). The coupling is readily formed to be interchangeable with existing couplings. DESCRIPTION OF THE DRAWINGS The details of the invention will be further understood by reference to the drawings, wherein: Fig.1 is a side elevation view of a coupling shown partly in section wherein a coupling sleeve and a coupling union are swaged to thin wall flareless tubing. Fig.2 is an enlarged fragmentary sectional view of a portion of Fig.1, illustrating in greater detail the coupling union. Fig. 3 is an enlarged section of a portion of Fig. 1 showing in greater detail the coupling sleeve, and Fig.4 is an enlarged cross section of a groove of the coupling sleeve of Fig. 1. DESCRIPTION Figure 1 shows, in half section, an embodiment of a coupling installation wherein a coupling union 10 has a longitudinal axis 11, an inner peripheral surface 12 and an externally threaded surface 19. As shown in detail in Figs. 2 and 3, a titanium alloy tube 4 is rigidly affixed to the coupling union 10 by a swaging operation which is performed prior to the joining of the coupling assembly. There are grooves 14 in the inner peripheral surface 12 of union 10, spaced axially along the longitudinal axis 11. Portions 6 of the tubing wall are deformed in an annular pattern outwardly such that the portions of the tubing wall extend into and substantially fill the annular cavities defined by the grooves 14 of the union 10, and the tubing is in compression. This deformation is accomplished by application of pressure at the tube inner wall which forces the tube material to expand outwardly into the grooves 14 of the union 10. Such internal swaging results in less metal fatigue both to the tubing being swaged and to the coupling sleeve than does external swaging. As shown in Figs. 2 and 3, the width 53 of each of the grooves 14 in the inner peripheral surface 12 of union 10 is about equal, and the depth 56 of the grooves is also about equal for all the grooves. The depth and width of grooves 14 is also specified according to the requirements of the present invention, as set out in detail hereinbelow. As shown in Fig.4, the grooves 14 comprise in cross-section a base 52 and at two side walls 54 which meet the base to form internal corners 58. The grooves 14 have a depth 56 which is the distance between the inner peripheral surface 12 of the union 10 and the base 52 of the grooves 14. They also have a width 53 defined as the maximum distance between the side walls 54. The depth 56 and width 53 of each groove 14 can vary dependent upon the outer diameter of the tubing to be swaged as shown in Table I. Example of Suitable Groove Width and Depth All Dimensions are in Inches, with centimetres in brackets. Tube O.D. Groove Width Groove Depth 1/4 (.635) .060 (.152) .003 (.0076) 5/16 .063 .004 3/8 .065 .0045 1/2 .073 .005 5/8 .081 .005 3/4 .070 .0055 1" .070 .0055 1/4 .070 .006 1 1/2 (3.81) .070 (.178) .0065 (.0165) The corners 58 are each rounded so that the radius of curvature of each corner 58 is about equal to the depth of the groove to ensure high tensile strength of the tube in swaged connection to the coupling union 10. Alternatively, the radius of curvature of corners 58 is greater than the depth of the groove. The side walls 54 meet the internal peripheral surface 12 of union 10 to form edges 59. The edges 59 are sharp, smooth and free of nicks and burrs. Located intermediate the grooves 14 are annular lands 15. The annular lands have the same diametrical dimension as the inner diametrical measurement of the sleeve. A lip 16 is located on the exterior side of the last groove 14 and defines the tube end of the union. The lip 16 has the same diameter as lands 15. The right circular cylinder angularity of the surfaces defining the lands 15 and grooves 14 provides the means whereby the lands, particularly, engage the walls of the tubing in the regions of deflection to provide sound, reliable, and pressure tight seals upon application of proper swaging forces from inside the tubing. The tube 4 is coupled to a tube 8 by the coupling union 10, a sleeve member 13, and a nut member 40, with an internally threaded surface 44. The tube 8 is rigidly affixed to the sleeve member 13 by a swaging operation which is performed prior to the joining of the coupling assembly. Sleeve member 13 has an inner peripheral surface 30. The tube 8 is swaged at points 36 into grooves 38 in the inner peripheral surface of the sleeve member 13. The nut 40 with the internally threaded surface 44 is torqued onto the externally threaded surface 19 of the outer peripheral surface of union 10. The nut 40 is interfaced with the sleeve member 13 at 27. Upon torquing the nut onto the union 10, a force is exerted to hold the union 10 in contact with union member 13 whereby an inwardly tapered edge outer peripheral surface 18 on sleeve member 13 contacts an outwardly tapered inner peripheral surface 17 on union 10, forming metal to metal between mating union 10 and sleeve member 13. On the exterior peripheral surface of the union 10 there is a raised central section 20 located intermediate portions 22 and 24. End portions 22 and 24 are each of a diameter less than the diameter of central section 20 and are integrally formed therewith to define at the respective points of juncture a first and second shoulder 26 and 28 facing in opposite directions from central section 20. The raised central section 20 gives the union added thickness at the point of the grooves whereby the sleeve is not deformed when tubing is swaged outwardly into the grooves, and additionally provides an hexagonal region 121 for receiving a wrench or other suitable tool. In Figure 3, the central portion 122 serves as a similar reinforcement against deformation. The coupling sleeve is preferably made of titanium or steel alloy for aerospace use up to 8000 psi (55.16 MPa). Aluminum can be used if the coupling sleeve is used in commercial applications at much lower pressures. From the foregoing description it is seen that the present invention provides an improved coupling sleeve with internal grooves for attachment onto thin wall tubing by swaging the latter. Made of titanium or steel alloy as described the coupling is suitable for aerospace use, typically to withstand pressures up to 8000 psi (55.16 MPa). The coupling could, for example, be made of a lighter material such as aluminum for commercial, non-aerospace use. It is therefore clear that the invention may have uses which are not specifically pointed out. There may be more of the uniform grooves than in the specific embodiment described. Another form of coupling for thin wall tubing is described and claimed in our co-pending European patent application divided from this present application and of even date herewith.

Claims: A coupling for attachment to deformable thin wall tubing (4) comprising substantially non-deformable hollow cylindrical body (10) having an inner wall (12) on a longitudinal axis (11) through the body in which an end portion of the tubing is received in use, and right circular lands (15) located in the inner wall of the body separating annular grooves (14) spaced from each other along the longitudinal axis and located in the inner wall, each said groove having a cross-section defined by a base (52) and side walls (54) meeting the base to form corners (58); characterised in that there are at least three grooves and that both of the corners between the base and the side walls of each groove are rounded on a radius of curvature at least equal to the depth (56) of the groove, said curvature starting at the junction of the inner wall and side wall and ending at the base, and all the grooves have the same cross-section, whereby said tubing may be internally swaged into positive sealing engagement to withstand high pressure, and the tubing material includes a titanium alloy. A coupling as in Claim 1 characterised in that the corners (58) of each groove (14) are both rounded on a radius greater than the depth of the groove. A coupling as in Claim 1 characterised in that the corners (58) of each groove (14) are both rounded on a radius equal to the depth of the groove. A coupling as in Claim 1,2 or 3 characterised in that tubing (4) is about 1/4 inch (.635 cm) in diameter, the depth of each groove (14) is about 0.003 inches (.0076 cm), and the radius of curvature of the corners (58) is about 0.007 inches (.0178 cm). A coupling as in Claim 1,2 or 3 characterised in that the tubing (4) has an outer diameter of about 1-1/2 inches (3.81 cm), the depth of each groove (14) is about 0.0065 inches (.165 cm), and the radius of curvature of the corners (58) is about 0.007 inches (.0178 cm). A coupling as in Claim 1,2 or 3 characterised in that the tubing (4) has an outer diameter between 1/4 inch (.635 cm) and 1-1/2 inches (3.81 cm), each groove (14) has a depth of from about 0.003 inches (.0076) to about 0.0065 inches (.0165 cm), and the radius of curvature of the corners (58) is about 0.007 inches (.0178 cm). A coupling as in Claim 1,2 or 3 characterised in that the tubing (4) has an outer diameter of about 1/4 inch (.635 cm), each groove (14) has a width of about 0.060 inches (.152 cm), and the radius of curvature of the corners (58) is about 0.007 inches (.0178 cm). A coupling as in Claim 1,2 or 3 characterised in that the tubing (4) has an outer diameter of about 1-1/2 inches (3.81 cm), each groove (14) has a width of about 0.070 inches (.178 cm), and the radius of curvature of the corners (58) is about 0.007 inches (.0178 cm). A coupling as in Claim 1,2 or 3 characterised in that the tubing (4) has an outer diameter of from about 1/4 inch (.635 cm) to about 1-1/2 inches (3.81 cm), each groove (14) has a width from about 0.060 inch (.152 cm) to about 0. 070 inch (.178 cm), and the radius of curvature of the corners (58) is about 0.007 inches (.0178 cm). A coupling as in any one of Claims 1 to 9 characterised in that there are only three said annular grooves (14).

Inventors: BEILEY, MARK J., CALLANAN, PATRICK J., MIKHAIL, MAKRAM T.
Applicants: SIERRACIN CORPORATION
Application year: 1988
Main classification: F16L13
IPC codes: F16L19, F16L13