Tube coupling

Abstract: Coupling for thin wall tubing comprises a sleeve (70) provided with a series of internal grooves (78), each said groove, in cross section, having a base (82), a first side wall (86) meeting the base at an angle of about 90 deg. and a second side wall (90) meeting the base at a substantially greater angle, typically between 135 and 165 deg; the tubing (94) being swaged radially outwardly into sealing engagement with the grooved inner wall. The coupling will withstand pressures of several thousand p.s.i. used with titanium alloy tubing.

Description: This invention relates to couplings for thin walled tubing and is divided from our co-pending European patent application 88308223.2 publication number 0357849 of even date herewith. 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 characterised 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-3 74519 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. Said one side wall is located forwardly of said other side wall and relatively closer to the fore end of the sleeve. 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 improve 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 swaged attachment to thin wall titanium tubing as defined by appended claim 1 or claim 5. 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. An example of the invention is now more particularly described with reference to accompanying drawings, wherein: Figure 1 is a side elevation of an assembled coupling shown in partial section, and Figure 2 is an enlargement of part of Figure 1 illustrating in greater detail grooves in an inner peripheral wall of a sleeve of the coupling. Figure 1 illustrates a coupling sleeve 70 and other components, partially in section. The sleeve 70 has an inner peripheral surface 74 (Figure 2) with ramped annular grooves 78 and a rectangular end groove 80 spaced axially along the longitudinal axis of the sleeve. The drawings show the ramped grooves 78 and rectangular groove 80 of sleeve 70 swaged to a section of thin wall titanium tubing 94. Sections 81 of the tubing are outwardly swaged to flow into ramped grooves 78 and rectangular groove 80 of sleeve 70. Each groove 78 comprises a base 82, and two side walls. A first side wall 86 of each ramped groove 78 meets the base 82 at about 90° to form corners 88. The radius of curvature of corners 88 is no greater than about .005 inches (.0127 cm). A second side wall 90 meets the base at an angle of about 135° to form corners 92. The radius of curvature of corners 92 is about 0.035 inches (.889 cm). Side walls 86 of the ramped grooves 78 meet the inner peripheral surface 74 of the sleeve at 90° at edges 87. Edges 87 are sharp and free from burrs. The sharp edges 87 maintain leak tight integrity of the joint between the coupling sleeve and the tubing swaged therein. Side walls 90 of the grooves 78 meet the inner peripheral surface 74 of the sleeve at an angle of less than about 15° the angle being defined between theoretical extensions to the surfaces 74 and 90. The second side wall thus meets the base at a complementary angle of greater than about 165°. The overall length of the groove and depth of the groove dictates the ramp angle which is preferably less than the said 15°. In the embodiment illustrated with the four ramped grooves the angle is about 9° and said compllementary angle is therefore about 171°. This angle ensures that the ramp surface places a compression load or force on the swaged tubing. As shown in Fig.2, the end groove 80, namely a relief groove, is rectangular in shape with two side walls 89 meeting the base 82 at about 90° to form corners 93. The radius of curvature of corners 93 is about .005 inches (.0127 cm). When the tubing 94 is swaged outwardly into the grooves 78 and groove 80, a permanent seal is formed which does not tend to loosen when exposed to vibration. The internally swaged tubing fills or partially fills grooves 78, possibly leaving a small space 75. As a result of the swaging of the tubing into the ramped grooves 78 material from the tubing end flows into rectangular groove 80 so that no burrs are left on the swaged tubing. Sidewall 89 extends into the fitting to a diameter less than the diameter at 74 and in fact less than the applicable outside diameter 94. Side wall 89 is therefore referred to as a stop, which limits tube insertion into the fitting to a required depth. The base 82 of each groove is about 0.030 inches (.0762 cm) long. The depth 72 of the ramped grooves varies from 0.005 inches (.0127 cm) at the tapered end of the sleeve 70 to a maximum of 0.009 inches (.0229 cm) at the non-tapered end. The gradation in groove depth provides a smooth transition from swaged to unswaged tubing so that a minimum stress and disruption of grain flow is exerted on the tubing 94 swaged into the grooves 78 and 80. The sleeve 70 illustrated is suitable for size 4 through 12 tubing. For use with larger tubing, the groove depth can vary from .005 inches (.0127 cm) at the non-tapered end to .014 inches (.0356 cm) at the blunt end. The outer peripheral surface 76 is tapered so that the coupling sleeve 70 is interchangeable with existing coupling sleeves. The outer peripheral surface 76 of sleeve 70 has a shoulder 84. The outward peripheral surface 76 also has a raised section 85 contiguous with shoulder 84. The shoulder 84 fits a retaining wire 110 located in the inner peripheral surface of a nut 120, and the raised section 85 abuts the retaining wire 110 and holds the sleeve in place. The nut 120 has an internally threaded surface 130. A coupling union 160 has an externally threaded surface 140. The nut 120 is torqued onto union 160 to force sealing lip 112 of the coupling sleeve 70 against the sealing surface 113 of male union 160. Internally directed lip 114 effectively locates the retaining wire 110 in position thereby sealing the swaged sleeve 70 to union 160. The coupling sleeve is preferably made of titanium or steel alloy for aerospace use up to 8000 psi (55.158 MPa). Aluminium 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 titanium 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 (55.158 MPa). There may be more or less of the ramped grooves 78 than in the above embodiment.

Claims: A coupling for swaged attachment to deformable thin wall titanium tubing (94) comprising a hollow cylindrical body (70) formed of a material which is relatively non-deformable under swaging action and having an inner wall; a plurality of non-right circular grooves (78) located in the inner wall (74) and spaced axially along the longitudinal axis of the body, the cross-section of each said groove having a base (82) and first and second side walls (86,90), the first side wall (86) meeting the base at an angle of about 90 deg. and the second side wall (90) meeting the base at an angle substantially greater than 90 deg.; with the first side wall located forwardly of the second side wall and relatively closer to a leading free end of the cylindrical body; characterised in that said inner wall also has an annular substantially rectangular end groove (80) spaced axially rearwardly from the non-right circular grooves to accommodate tubing material on deformation of the tubing; whereby, when the tubing (94) is swaged radially outwardly into engagement with the grooved inner wall, a secure sealing engagement to withstand several thousand p.s.i. is achieved solely by the body (70) and the tubing (94). The coupling of Claim 1 wherein the angle at which the second side wall meets the base is more than 165 deg. The coupling of Claim 2 wherein said angle is about 171 deg. The coupling of any one of Claims 1 to 3 in which the base of the groove is 0.030 inches (.0762 cm) long and the depth of the groove is between 0.005 inches (.0127 cm) deep and 0.009 inches (.0229 cm) deep. A coupling for swaged attachment to deformable thin wall titanium tubing (94) comprising a hollow cylindrical body (70) formed of a material which is relatively non-deformable under swaging action and having an inner wall; a plurality of non-right circular grooves (78) located in the inner wall (74) and spaced axially along the longitudinal axis of the body, the cross-section of each said groove having a base (82) and first and second side walls (86,90) the first side wall (86) meeting the base at an angle of about 90 deg. and the second side wall (90) meeting a theoretical extension across the groove of ungrooved parts of said inner wall of the body at an angle substantially less than 90 deg. with the first side wall located forwardly of the second side wall and relatively closer to a leading free end of the cylindrical body; characterised in that said inner wall also has an annular substantially rectangular end groove (80) spaced axially rearwardly from the non-right circular grooves to accommodate tubing material on deformation of the tubing; whereby when the tubing (94) is swaged radially outwardly into engagement with the grooved inner wall, a secure sealing engagement to withstand several thousand p.s.i. is achieved solely by the body (70) and the tubing (94). The coupling of Claim 5 wherein the second side wall meets said theoretical extension at less than 15 deg. The coupling of either Claim 5 or 6 in which the base of the groove is 0.030 inches (.0762 cm) long and the depth of the groove is between 0.005 inches (.0127 cm) deep and 0.014 inches (.0356 cm) deep. The coupling of any one of Claims 1 to 7 further comprising right circular lands located in the inner wall of the body separating the annular grooves. The coupling of any one of Claims 1 to 9 wherein there are at least three said non-right circular grooves. The coupling of any preceding claim wherein the base of each said groove extends substantially parallel to the longitudinal axis of the body.

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