Ball joint apparatus and method of fabrication

A ball joint apparatus for a pressurized fluid line includes a bellows and a pair of opposed tube portions to accommodate limited flexure between the tube portions. The apparatus also includes an annular ball element positioned over one of the tube portions and an annular housing member mounted on the other tube portion and overlapping the ball member. As initially formed, the overlapping end of the housing member is open and of a diameter exceeding the maximum diameter of the ball member to permit ease of assembly. After the component parts are in position and welded as desired, the apparatus is placed in a hydraulic press and the open end of the housing member is necked down by a swaging process to establish bearing contact with the ball member. Alternative arrangements of the apparatus are provided for use with stainless steel tubing and with titanium tubing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to pressurized fluid lines and, more particularly, to a ball joint apparatus for permitting relative flexure in such lines.

2. Description of the Related Art

Ball joint apparatus for pressurized fluid lines in the past has incorporated a somewhat flexible bellows between two end tubes encompassed within a protective assembly in the form of a ball joint. Such apparatus as are known include a ball which is welded to one end tube and a housing which is welded to the other end tube. The housing and the ball together establish a ball joint which holds the end tubes and bellows in relative position. Since both ends of the housing are smaller in diameter than the ball member, it has been the practice to fabricate the housing in two pieces and assemble them from both ends of the apparatus so as to enclose the ball member. Thereafter, the two pieces of the housing are welded together by fusion welding. This is a relatively difficult and costly step and introduces a further opportunity for failure in the joint.

SUMMARY OF THE INVENTION

Ball joints are used in fluid lines to impart limited flexibility for the purpose of accommodating tolerances, thermal expansion and vehicular motion. They can be used in almost any type of fluid line. However, the particular joint under consideration is adapted for use in jet aircraft engine bleed air ducting.

It should be kept in mind that the term “ball joint”, as used herein and as such terms are understood in the related industry dealing with pressurized fluid lines, is not a precisely defined descriptive term. That is, applying the term to a pivotable hollow structure does not mean that the core member is a ball or sphere; neither is the encasing structure (housing) necessarily of a spherical shape, as these terms are used in the mathematical sense. Only when true mathematically defined spherical shape is described in mathematical terms, as in U.S. Pat. No. 5,611,577 (“tri-axial symmetry”), is it intended that terms such as “ball” and “sphere” or “spherical” are to be defining in the precise mathematical sense. A better understanding of the meaning of such terminology as used herein will be gained from a review of disclosed structure in the patent drawings with interpretation of shape in accordance with the related description thereof.

In brief, particular arrangements in accordance with the present invention comprise a bellows and two end tubes for coupling into a fluid line. An inner ball and outer housing surround the bellows to maintain integrity of the assembly. It is a feature of the present invention that the outer housing is fabricated in one piece, thereby eliminating the need for the fusion welding step of previously known ball joint assemblies. There is no fusion welding in particular embodiments of the present invention and only two roll-resistant seam welds are required for assembly.

In accordance with particular aspects of the present invention, the outer housing is formed in one piece having an open end of sufficient diameter to be assembled over the ball member without interference. Thereafter, the housing is further formed by means of a unique coining or swaging operation. The unit, after the bellows is seam welded, is put in a hydraulic press and the outer surface on the end of the housing is formed into a sphere. This sphere conforms to the surface of the inner ball. A reinforcing lip is also formed in the housing, during the swaging process, for additional strength.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The ball joint assembly10ofFIG. 1can best be understood by reference toFIG. 2, which is a schematic diagram showing structural details of the ball joint assembly10.FIG. 2shows the assembly10as comprising left and right tubes12,14which are joined at a central portion by a bellows16. The bellows16serves to permit relative flexure within a limited angular range between the tubes12and14. Assembly10has a ball20of annular shape increasing in diameter from a collar portion22to an enlarged ring portion24. The collar portion22is welded to the right-hand tube14at26. The collar and ring portions22,24, are shaped to be generally parallel to the tube14, and the transition portion28between them has a generally arcuate shape adapted to provide a bearing surface for the engagement portion of the other half of the ball joint assembly.

A housing30extends from a collar portion32having an inner diameter matching the outer diameter of the tube12to which it is welded at34. From the collar32, the housing30increases in diameter to a midportion36. As initially fabricated, the diameter of the midportion36of the housing30is continued, as shown by the broken outline37, to the right-hand end38. After the housing30and ball20are welded in place on the tubes12,14, the assembly is placed in a hydraulic press for a swaging step which closes down the right-hand end38to assume the general arcuate shape shown for the portion40. The shape terminates in a lip41for additional strength. The necked-down end40in cooperation with the ball member20serves to retain the entire assembly of the bellows and tubes against undue expansion while permitting a limited flexure of the joint as needed in operation. Adjacent bearing surfaces42, along the inside of the necked-down housing portion40, and44, along the outer surface of the ball portion28, are suitably lubricated to permit flexure of the joint without undue friction or binding.

In the test fixture assembly shown inFIG. 1, the tube portions12and14are welded to tube extensions47and49at weld points46and48, respectively. The tubes47and49extend to mounting flanges50and52which affix the ball joint assembly in the recycling fixture for extended testing. A pressurizing tube54extends to the back of tube49and a recording device56is shown connected to a pressure sensor59via electrical conduit58. A jackscrew60is provided at the top of the test stand for adjusting the axial loading on the ball joint assembly10during testing.

In the test fixture ofFIG. 1with a particular ball joint assembly10, fabricated for 2.0 inch diameter stainless steel tubing, various tests were conducted. The test unit was pressurized at room temperature with helium at 605 pounds per square inch gauge (psig) underwater for two minutes. No leakage was observed. At 810° F., th unit was pressurized at 375 psig for two minutes. Again no leakage or deformation was observed.

The tested ball joint apparatus was angulated from 0 to +3, 5 and 7 degrees for more than 60,000 cycles at 60, 120, 175 and 250 psig at 600° F. in one particular test procedure. During the course of cycling, the unit was observed to operate smoothly and showed no scratches or significant wear in the drive lubricant material which was applied to the bearing surfaces during fabrication. In fact, cycle testing tended to burnish the lubricant and stainless steel surfaces as cycling progressed. There was no evidence of damage to the unit during this testing. The test unit was subjected to internal pressure with water up to 1200 psig. In this pressure test, no out-of-tolerance deformation or leakage was observed.

The ball joint assembly10ofFIGS. 1 and 2is fabricated of stainless steel for use in a stainless steel pressurized line The alternative embodiment ofFIGS. 3 and 4is constructed for welding into titanium ducting.

The ball joint apparatus100ofFIGS. 3 and 4is similar in construction to the ball joint assembly10ofFIGS. 1 and 2except for the addition of particular structural elements and an assembly configuration which are adapted for use with titanium tubing and provide added structural support in the joint. The assembly100ofFIG. 3includes a bellows116which is formed as an extension of the right-hand tube114. (FIG. 4shows the assembly100in an inverse orientation toFIG. 3.) The ball element120is not welded to the tube114but is supported in position by an annular restraint collar80which is flared at its right-hand end82to provide support for the ball element120. The restraint element80is welded at84to the tube114.

On the left-hand side of the bellows116within the housing member130, a corresponding flared restraint member90is positioned to provide restraint for the bellows116and support for the housing member130. This is welded in place between the reduced diameter end92of the housing130and the extension94of the bellows116. The welded assembly also includes a necked-down collar portion96of the left-hand tube112, all four elements being welded together in a sort of sandwich configuration.

As with the embodiment ofFIGS. 1 and 2, following installation of the housing130, the entire assembly100is mounted in a press and rotated to swage the open end comprising portions137and138into the reduced diameter curved portion140. This operation results in a collar142at the open end for added strength. The ball and housing members120,130are supported in position by the respective restraint elements84and90. Operation of the device ofFIGS. 3 and 4is as described above for the device ofFIGS. 1 and 2.

The method of fabricating the ball joint ofFIGS. 1 and 2is represented schematically in the block diagram ofFIG. 5as comprising the steps of:assembling a bellows between a pair of tube portions for attachment in a pressurized fluid line;forming an annular ball member having an outer end of reduced diameter to match the diameter of a first one of the tube portions and an inner end of enlarged diameter suitable for overlapping the bellows;sliding the ball member into position overlapping the bellows;forming an annular housing member having a first end of reduced diameter matching the diameter of the second tube portion and a second end having a diameter exceeding the outer diameter of the ball member;sliding the housing member along the second tube portion to a position where the second end overlaps the arcuate portion of the ball member between the inner and outer ends;welding the first end of the housing member and the outer end of the ball member to the respective adjacent tube portions; andplacing the thus-assembled combination in a hydraulic press and rotating the combination to swage the second end of the housing member radially inward to make contact with the outer surface of the ball member in the region of the generally arcuate portion thereof.

The method of fabrication of the ball joint assembly ofFIGS. 3 and 4is schematically represented in the block diagram ofFIG. 6as comprising the steps of:assembling a bellows between a pair of tube portions for attachment in a pressurized fluid line;forming an annular ball member having an outer end of reduced diameter to match the diameter of a first one of the tube portions and an inner end of enlarged diameter suitable for overlapping the bellows;forming a first annular restraint member configured to maintain the position of the bellows and support the ball member;sliding the first annular restraint onto the first tube portion to a position adjacent the bellows;welding the first restraint member to the first tube portion to retain it in position adjacent the bellows;sliding the ball member onto the first tube portion to a position overlapping the first restraint and the bellows;forming an annular housing member having a first end of reduced diameter matching the diameter of the second tube portion and a second end having a diameter exceeding the outer diameter of the ball member;forming a second annular restraint member configured to provide support for a selected portion of the housing;sliding the second restraint member onto the tubular extension adjacent the bellows on the side remote from the first annular restraint;sliding the housing member along the second tube portion to a position adjacent the second annular restraint such that the second end overlaps the arcuate portion of the ball member between the inner and outer ends;forming a necked-down collar of the second tube member and inserting the collar into the bellows extension;welding the collar portion, the bellows extension, the second restraint member and the first end of the housing member together;placing the thus-assembled combination in a hydraulic press and rotating the combination to swage the second end of the housing member radially inward to make contact with the outer surface of the ball member and the first restraint in the region of the generally arcuate portion thereof.

Although there have been described hereinabove various specific arrangements of a BALL JOINT APPARATUS AND METHOD OF FABRICATION in accordance with the invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention as defined in the claims.