FERRULE WITH RELIEF TO REDUCE GALLING
High localized loading, galling, and high torque forces have been generally eliminated or greatly reduced in a two ferrule tube fitting assembly through suitable modification of the rear ferrule so as to redirect the reaction forces acting between the front ferrule and the drive nut. The rear ferrule has a cylindrical interior wall that closely surrounds the tube end and is provided on the interior cylindrical wall with a circumferentially continuous radial recess that is located between the nose and rear wall of the rear ferrule. The rear ferrule also has a radially external wall that is substantially conical and additionally shaped to extend radially outward toward the enlarged diameter portion or flange of the rear ferrule. The rear ferrule further includes a contoured face on the rear driven surface of the ferrule that engages the drive surface of the drive nut.
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This application is a continuation of U.S. patent application Ser. No. 10/374,026 filed on Feb. 25, 2003, which is a continuation of U.S. application Ser. No. 09/469,549 filed Dec. 22, 1999, which is continuation-in-part of U.S. patent application Ser. No. 09/054,186 filed on Apr. 2, 1998, now U.S. Pat. No. 6,131,963, which is a continuation-in-part of U.S. patent application Ser. No. 08/834,255 filed on Apr. 15, 1997, now U.S. Pat. No. 5,882,050, the entire disclosures of which are fully incorporated herein by reference.BACKGROUND OF INVENTION
The subject invention is directed to the art of ferrule type tube fittings. More particularly, the invention concerns a two ferrule fitting wherein the rear ferrule is designed to reduce the torque required to rotate the associated nut and to also reduce galling between the rear ferrule and the interior surface of the drive nut. The invention may also be applied in a single ferrule fitting.
A commercially available and highly successful two ferrule fitting used for tubing is illustrated in
Associated with the front ferrule 16 and located axially outward therefrom is a rear ferrule 22 configured as shown with a tapered nose portion 24 and a rear flange 26 having an inclined end surface 28. The inclined end surface of the rear ferrule 22 provides a radial component as well as an axial component of the pull-up forces acting on the end surface as will be apparent to those skilled in the art. The tapered nose 24 enters a tapered camming surface in the rear surface of the front ferrule.
The ferrules 16, 22 are enclosed by a drive nut member 30 threaded to the body 10. During tightening and make-up of the fitting, the inner end face, flange, or shoulder 32 of the nut acts against the inclined end surface 28 of the rear ferrule to drive the ferrules forwardly into the fully engaged position shown in
The small diameter portion or nose of the rear ferrule is dimensioned so that it plastically deforms during make-up of the fitting. This action is desirable since it results in tight gripping engagement of the outer wall of the tubing. The thickness of the nose portion cannot be reduced to an extent that the rear ferrule deforms too much and only the rear ferrule adequately grips the outer wall of the tubing. That is, the two ferrule assembly requires desired deformation of both the front and rear ferrules for the gripping and sealing capabilities that have made this two ferrule assembly a commercially successful product. On the other hand, the thickness of the nose of the rear ferrule cannot be enlarged to such an extent that it results in a structural arrangement that is too stiff and does not permit the desired rear ferrule deformation.
A more complete description and understanding of the conventional two ferrule phase controlled sequential gripping action resulting from the inclined rear surface and the interaction of the front and rear ferrules is set forth in U.S. Pat. No. 3,103,373 issued to Lennon, et al., the entire disclosure of which is fully incorporated herein by reference.
Accordingly, it will be recognized by those skilled in the art that a predetermined wall thickness of the nose of the rear ferrule is desired that achieves the desired gripping of the tube and cooperates with the front ferrule in such a manner that it achieves its desired goals of gripping and sealing the tube.
It is also recognized that operators of fluid systems test the system prior to a production run by pressurizing the system to an appropriate factor times the rated system pressure. In this manner, the operator can easily detect whether the fluid system is sealed, i.e. that there are no leaks. With this knowledge, the manufacturer can provide a fitting in which the nose of the rear ferrule will not have any additional plastic deformation at the elevated test pressure. Accordingly, the elevated test pressure is used to determine the desired wall thickness of the nose portion of the rear ferrule to achieve the desired amount of deformation of the nose and permit the front and rear ferrules to properly grip and seal with the outer wall of the tube.
It has also been found that galling of the drive nut sometimes occurs in the drive face area of engagement between the inner end face of the drive nut and the rear wall of the rear ferrule. After analysis, it is believed that the axial thrust or pull-up force between the front and rear ferrule is essentially parallel to the axis of the fitting. This axial thrust causes the rear corner region of the rear ferrule to selectively concentrate pull-up stress at the inside drive surface of the nut particularly in a localized area to produce the galling. This also noticeably increases the nut torque forces experienced during make-up even if galling is absent. Accordingly, it would be highly desirable to provide a design wherein the thrust forces do not produce the high localized loading with the resultant galling and high torque forces.SUMMARY OF INVENTION
In accordance with one embodiment of the invention, a tube fitting includes a fitting body having a cylindrical bore for receiving a tube end and including a tapered mouth at one end of the bore; a drive member having a threaded engagement with the body and having a ferrule drive surface; a first ferrule having a tapered first end that extends into the tapered mouth of the fitting body and having a second end with a tapered recess that axially extends toward the first end; and a second ferrule having a cylindrical interior wall, a tapered first end that extends into the tapered recess of the first ferrule, and having a contoured face on a second end thereof that engages the drive member ferrule drive surface; the second ferrule interior wall having a circumferential recess located between the first and second ends of the second ferrule; the recess and the contoured face reducing stress concentrations on the drive member drive surface when the fitting is made up.
Another aspect of the invention includes forming the rear ferrule with a cylindrical interior wall that has a first diameter at the forward or nose end of the ferrule and a second diameter at the rear end of the ferrule wherein the second diameter is greater than the first diameter so that, for example, a single tool can be use to form the circumferential recess and the cylindrical wall. Still a further aspect of the invention includes forming a notch on the outside diameter of the ferrule body that joins the second ferrule first and second ends. In another aspect of the invention, a contoured drive surface is provided on the drive member rather than on the rear ferrule second end. The present invention may also be practiced with ferrules that are made of harder base metal than prior ferrules. The invention may also be practiced with ferrules that have been case hardened either entirely or selectively on the ferrule surface. In general, the present invention may be used in single ferrule fittings as well.
These and other aspects and advantages of the present invention will be apparent to those skilled in the art from the following description of the preferred embodiments in view of the accompanying drawings.
The invention may take physical form in certain parts and arrangements of parts, preferred embodiments and a method of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof, and wherein:
Referring now to the drawings wherein the showings are for the purposes of illustrating preferred embodiments of the invention only and not for purposes of limiting same,
While the invention is described herein with particular reference to a two ferrule system, such explanation is exemplary in nature and should not be construed in a limiting sense. Various aspects of the present invention may also find application in a single ferrule fitting.
In one embodiment of the invention, a redirection of the reaction forces is achieved by providing a circumferential recess 40 throughout the inner surface of rear ferrule 22′. Note that circumferential recess 40 is located generally midway between the opposite ends of rear ferrule 22′ and this results in the inner surface of the rear ferrule being reduced to two relatively axially narrow substantially cylindrical and continuous contact areas 42 and 44. By so modifying the rear ferrule, the forces which are conducted from the front ferrule through the rear ferrule to the nut shoulder 32″ tend to be directed more radially outward such as diagrammatically illustrated by the force line B of
In this embodiment, the generally flat contact areas 42 and 44 have substantially the same diameter; however in an alternative embodiment, these two regions may have different diameters, for example it may be desirable in some applications to have the diameter of the rear flat contact area 42 slightly greater than the diameter of the forward flat contact area 44, for example, by a few thousandths, more preferably one to three thousandths of an inch. In yet a further alternative embodiment, the rear flat contact area 42 may be eliminated as a contact area by providing a counterbore in this area. Particularly for larger ferrule sizes, the single flat in the nose section of the rear ferrule may be sufficient to maintain proper ferrule alignment on the tubing during installation. These alternatives will be more fully described hereinafter.
Another important feature of the invention is best exemplified by comparing the rear ferrule 22 of
The wall thickness “t” and the geometry and configuration of the rear ferrule 22′ are selected for a particular application in order to balance and properly align rear ferrule 22′ on the tubing and to assure that the rear ferrule 22′ cooperates with the front ferrule 16′ to achieve the desired phase controlled sequential gripping operation during pull-up to assure a proper seal on the tubing. During fitting pull-up, the rear ferrule 22′ applies a vector force against the outer surface of the tube end 13 that has both axial and radial components. The radial component force enables an axial friction force on the tube surface to achieve excellent gripping and sealing action. This axial friction force balances against an axial tube grip reaction force from the tube end 13.
The combined geometry of the tapered outer wall 50 along with the recess 40 cause a “hinge” effect of forward nose portion 52. The selected geometry and configurations will depend on such factors including but not necessarily limited to the materials used for the fitting components, the tube material and wall thickness, the operating pressure for the fitting, whether the rear ferrule is to be case hardened or not, and so forth. In order to maintain proper sequential gripping operation during make-up, it is important that the rear ferrule 22′ forward nose portion 52 does not collapse too soon otherwise the front ferrule 16′ may not have sufficient gripping force on the tube wall or an inadequate seal force between the front ferrule 16′ and the tapered camming mouth 14′. If the rear ferrule 22′ collapses too late relative to the front ferrule, then the rear ferrule 22′ may not have adequate gripping force on tube end 13.
The rear ferrule 22′ hinge effect directs the rear ferrule applied force at the forward nose portion 52 against the tube wall at a significant radial vector angle from the tube surface. This ferrule applied force vector B thus has a significant radial component while enabling the significant axial friction force. Thus, a smaller axial component force applied via the drive nut member 30′ sufficiently opposes the axial tube gripping reaction force in contrast to when the applied force is substantially axial as in the prior art of
In addition, during fitting pull-up, this hinge characteristic directs the tube reaction force through the rear ferrule 22′ generally toward the central region of the rear ferrule driven surface 28′ that contacts the drive surface of the nut shoulder 32′. This results in the reaction forces being more evenly distributed across the rear ferrule driven surface 28′ to avoid or reduce high concentrations of stress, thus reducing or eliminating galling and reducing pull-up torque without loss of tube gripping force. In many cases it may be preferred that the reaction forces be directed in a direction generally normal to rear ferrule driven surface 28′. The increased tube gripping force resulting from the applied radial force also imparts greater penetration or swaging of the rear ferrule 22′ nose portion 52′ onto tube end 13. This provides an excellent tube grip and seal with lower applied torque, and also provides greater resistance to vibration fatigue by providing a swaged region of high gripping pressure behind (i.e. axially rearward) of the tube stress riser created at the forward end of the nose of the rear ferrule 22′.
Another benefit resulting from the reduced galling and lower pull-up torque of the present invention is that re-make of the fitting is facilitated. By “re-make” is simply meant that, in some applications, the user desires to separate a tube fitting after installation, possibly to replace a valve, tubing or to perform other routine maintenance and repair, and then to re-install the same fitting without replacing the ferrules and/or nut or body. If the rear ferrule and drive nut have become galled, then the torque required for re-make of the fitting may be prohibitive or impossible, or the fitting may not adequately re-seal. With the use of the present invention to significantly reduce or eliminate galling and reduce pull-up torque, re-make is facilitated.
Although the present invention is useful with many different materials, it has particular advantages when used with stainless steel fittings and tubing, including but not limited to 316 and 316L stainless tubing, but includes in addition to other alloys, Hastalloy, Inconel, Monel alloys 400 and 500, 254SMO and steel, and duplex stainless steel such as, for example, SAF 2507. The present invention can be used with or without case hardening on all or part of the surfaces of the ferrules as required.
With respect to case hardened ferrules or ferrules made of materials substantially harder than 316L stainless steel, the present invention allows the fitting 10 to be properly pulled up with the desired phase controlled sequential gripping of the tube wall. If a conventional ferrule, particularly the rear ferrule, was case hardened or made of a very hard material, the ferrule would be too stiff to achieve proper seal and grip of the tube wall. The present invention however facilitates the use of ferrules of hard materials or that have been case hardened over part or all of their surface. Case hardening herein refers to the treatment of the ferrules in such a manner as to provide a carbon or nitrogen rich surface that substantially hardens the ferrule body as compared to the underlying base metal, as is known to those skilled in the art.
The embodiment of
As is apparent with the various embodiments described above, the recess and the tapered outer wall do not require a particular conformation to achieve the stress distribution and reduced torque for make-up of the fitting. In fact, a number of proposed alternative embodiments are illustrated in table form in
With reference to
In accordance with this further aspect of the invention a two ferrule fitting is shown having a rear ferrule which is modified so as to reduce further the pull up stress concentrations by substantially distributing the stress concentration along the rear surface that engages nut shoulder 32 of the drive nut member 30′. As is shown in
With specific reference to
Associated with the front ferrule 116 and located axially adjacent (i.e., in a rearward direction concentrically aligned with the longitudinal axis of the fitting) is a rear ferrule 122 configured with a tapered nose portion 124 having a rearward tapered surface 127, The rear ferrule 122 also includes a radially extending rear flange 126 having a contoured end face 128. The contoured face 128 includes a rearward-facing driven surface 129 which is engaged by a respective driving surface 132 of the drive nut member 130.
The rearward tapered surface 127 of the rear ferrule 122 engages and may have, but not necessarily, substantially the same angle as a tapered cam surface 125 in the rear area of the front ferrule 116. The nose portion 124 is joined with the rear flange 126 by a preferably tapered outer wall 131. In the illustrated embodiment the outer wall 131 tapers with an increasing radial dimension in the axially rearward direction. The outer wall 131 could also be cylindrical, although it is preferred to be tapered to further facilitate reduction of stress concentrations on the driven surface 129.
The ferrules 116 and 122 are enclosed by a threaded drive nut member 130 which includes a drive surface 132 that engages the driven surface 129 of the rear ferrule 122. The drive nut member 130 threadably engages a threaded portion of the body 110. During tightening and make-up of the fitting, the drive surface 132 of the drive nut member 130 applies pull up forces against the driven surface 129 of the rear ferrule 122 to drive both ferrules axially forward (to the right as viewed in
In the embodiments illustrated in
Although the use of a radius or other curvilinear surface for the contoured end surface 128 is desirable, there is a practical limit as to how small that radius can be made. If the radius of curvature is made too small then there will possibly be undesired stress concentrations develop in the center region of the contoured end face 128.
A distinct advantage of the contoured rear ferrule 122 is that pull up stresses between the nut drive surface 132 and the contoured end face 128 of the rear ferrule 122 are more uniformly distributed across the contoured end face 128 of the rear ferrule, thus reducing and substantially eliminating stress concentrations. This further reduction of stress concentrations on the drive nut member 130 reduces pull up torque and reduces galling, thus facilitating re-make of the fitting.
It is important to note that although the illustrated embodiments show an initial contact between the rear ferrule 122 and the drive nut member 130 as generally in the middle of the contoured end face 128, this is not required in every application. The initial point of contact will be a function of the overall fitting design, including the geometry of the tapered outer wall 131, the recess 140, the rearward tapered surface 127, the front ferrule 116 configuration and so forth. But in keeping with a general aspect of the invention, the contoured end face 128 will be convex or axially variant in the region between the radial inner and outer portions of the rear flange 126 so as to distribute more uniformly the pull up forces acting on the drive nut surface 132 to reduce galling and pull up torque as compared to a conventional rear ferrule design that has a substantially flat non-contoured driven surface.
With reference to
With reference to
With reference to
The ferrule illustrated in
The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
31. A ferrule for a metal tube fitting, comprising:
- a generally annular one-piece metal body that remains one piece when used in a tube fitting, said body comprising a central and circumferentially continuous cylindrical interior wall that extends through the ferrule from a front end to a back end of said body, a single recess formed in said cylindrical interior wall between said front end and said back end, said cylindrical interior wall having a first portion that is axially forward of said recess and adjoining said front end and a second portion that is axially rearward of said recess and adjoining said back end,
- a nose portion with a rearward tapered surface that extends from said front end,
- a radially extending flange at said back end of said body, said flange having an end face that provides a ferrule driven surface, and
- an outer wall, said outer wall comprising a radially tapered outer wall portion extending from said nose portion to said radially extending flange, said tapered outer wall portion being tapered with a continuously increasing radial dimension in a rearward direction.
32. The ferrule of claim 31 wherein said radially tapered outer wall portion is joined to said nose portion with a cylindrical portion of said outer wall.
33. The ferrule of claim 31 wherein said single recess is rearward and generally within an axial dimension of said radially extending flange.
34. The ferrule of claim 31 wherein said end face is contoured.
35. The ferrule of claim 34 wherein said end face is convex.
36. The ferrule of claim 31 wherein said body is case hardened over its entire surface.
37. The ferrule of claim 31 wherein a portion of said radially tapered outer wall and a portion of said recess define a wall section having a constant thickness t.
38. The ferrule of claim 31 wherein said cylindrical interior wall first portion and said cylindrical interior wall second portion have different diameters.
39. The ferrule of claim 38 wherein said cylindrical interior wall second portion has a larger diameter than said cylindrical interior wall first portion.
40. The ferrule of claim 31 wherein said metal body comprises stainless steel.
International Classification: F16L 19/10 (20060101);