Unitary Assembly of Tubing and a Pressed On, Interference Fit, Terminating Fitting

This invention relates to tubing connectors and, more particularly, to such connectors wherein the terminating fitting is brazed, welded, staked, or extruded onto the associated tube.

Tubing connectors for threadless pipe, tubing, conduit and like are known and have been widely used in the art. The tubes are mechanically connected by means of a threaded fitting which fits over an expansion on the tube end and are screwed together to clamp the expansion to the mating part. These known tubing connectors are exemplified by U.S. Pat. Nos. 2,522,194 and 3,494,643. These known tubing connectors have the disadvantage of being susceptible to leaking because gaps, inherent to the design, of significant size occur between the expansion, or flare, and fitting to allow the expansion to deform during assembly. The resultant deformation allows vibration and the like to loosen the fitting assembly and unseat the sealing surfaces, and repeated reassembly and sealing to other identical mating components is rendered impossible.

Tubes that are brazed to fittings via salt, flame, induction, or furnace braze processes or welded via magnesium insert gas, tungsten insert gas, or resistance welding processes are also known. These known processes are exemplified by U.S. Pat. No. 4,887,853. These known processes have the disadvantage of using large amounts of energy to heat and cool components, polluting the environment and requiring pre- and post-treatments and fluxes, all of which are hazardous, and produce a braze or weld joint that forever represents a leak path.

Fittings that are impact extruded onto tubes are known. These known processes have the disadvantage that great expense causes these processes to currently be commercially inviable.

Briefly, a unitary assembly of tubing with a threaded terminating fastener is provided. The threaded fitting includes a tubular opening therein extending through the fitting along the longitudinal axis thereof. A conical constriction is provided at the thread/hex interface. A non-expanded end of an expanded tube is received within the larger opening of the fitting. Insertion continues until expansion and fitting interference has been overcome and the expansion is completely seated in the fitting. The internal characteristics are machined coaxially using a special five step tool.

The present invention provides a low cost, leak free tube and fitting assembly. This development provides a tube and fitting connection without a potential leak path, such as is present in a braze or weld joint. The present invention also provides better dimensional and strength characteristics than a step bead, that may distort in the area of the O-ring gland and leak. The present invention can be made using a pollution free, low tech process that is also less costly than brazing, welding or impact extrusion. The leak free characteristics eliminate the loss of fluid and increases the reliability of products that use tube and fitting connections. Present technology uses welding, brazing, end forming, or impact extrusion. The first two have inherent leak potential, the third is structurally and dimensionally inferior and is prone to distortion, and the fourth is expensive.

Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.

The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:

FIGS. 1 and 2 are sectional and end views respectively of a first hit impaction of a tube, during an end forming operation according to the present invention;

FIGS. 3 and 4 are sectional and end views respectively of a second hit expansion and the third hit sizing of a tube, during the end forming operation according to the present invention;

FIGS. 5 and 6 are sectional and end views respectively of a fitting, prior to an assembling operation according to the present invention;

FIGS. 7 and 8 are sectional and end views respectively of the fitting pressed onto the formed end of the tube after the assembling operation according to the present invention; and

FIGS. 9 and 10 are sectional and end views respectively of the finished tube and fitting assembly according to the present invention.

Referring now to FIGS. 9 and 10, there are shown generally sectional and end views respectively of a finished tube and fitting assembly 10 in accordance with the present invention. The tube 12 and fitting 14 are connected along parting line 40. The terminating fitting 14 includes a hexagonal head portion 16 and a threaded connecting portion 18 which is joined with and coaxially extends away from the head portion 16. The material of the end fitting 14 and tube 12 may comprise any desired metallic material, such as aluminum, copper, steel or the like.

Referring now to FIGS. 1 and 2, there are shown sectional and end views respectively of a first hit impaction, which maintains the original outside diameter of the tube 12, and coaxially constricts the inside diameter and thickens the wall 20 three fold.

Referring now to FIGS. 3 and 4, there are shown sectional and end views respectively of a second hit expansion, which coaxially expands the impacted material to an interference fit outside diameter expansion surface 22 relative to the larger of the two inside diameters of the fitting 14 and roughly sizes the inside diameter to a machineable condition relative to the dimension of the female pilot land 24 of the finished assembly 10. There is also shown in FIGS. 3 and 4 sectional and end views respectively of a third hit sizing, which sizes the length of the end form relative to the transition of the outside diameters and the non-end formed tube end to provide an exact mating surface 40a to an inside diameter surface 40b and length capability from the hex shoulder to the opposite end. The mating surface 40a of the formed end of the tube 12 and the inside diameter surface 40b of the fitting forms a pressed on, interference fit along parting line 40 as illustrated in FIG. 9.

Referring to FIGS. 5 and 6, there are shown sectional and end views respectively of the fitting 14 including the conical transition 26 from the major and minor inside diameters 28 and 30 respectively, coaxial to the threaded and hexagonal portions 18 and 16 respectively.

Referring to FIGS. 7 and 8, there are shown sectional and end views respectively of the tube and fitting assembly which shows the expansion surface 22 extending beyond the thread lead 32 on the fitting 14 so both may be machined simultaneously. The interference fit parting line 40 eliminates any chance that a gap between tube 12 and fitting 14 will allow the tube 12 to deform into the fitting 14.

Referring to FIGS. 9 and 10, there are shown sectional and end views respectively of the finished tube and fitting assembly 10 which shows the constricted portion 34 of the tube 12 is open to the inside diameter along the entire length of the tube 12, the portion 36 of the tube 12 inside the hex 16 swaged into the hex 16, the female pilot land area 24, the O-ring gland 38 and precise mating seam or parting line 40 between tube 12 and fitting 14.

A method for forming a unitary assembly of tubing with a threaded terminating fastener is therefore disclosed. The method includes the steps of providing a threaded fitting 14 having a tubular opening therein extending through the fitting 14 along the longitudinal axis thereof, providing a conical transition 26 at the thread/hex interface in the fitting 14, providing a tube 12 with a coaxial impacted, expanded, and sized end to an interference dimension relative to the inside diameter of the fitting 14, inserting the non-expanded end of the tube 12 through the major inside diameter of the fitting 14 until interference is encountered, pressing the tube 12 into the fitting 14 in coaxial alignment until the fitting 14 is completely seated and finishing the inside diameter of the tube 12 coaxially with the fitting 14 so that the tube inside diameter is consistent over its entire length, wherein the tube 12 is swaged into the inside of the hex, the female pilot land and the O-ring gland are machined, and the overall length of the fitting 14 is machined concurrently with the tube 12 at the thread lead. It is believed that the tube and fitting assembly 10 as described above is superior in form, fit, function and cost competitiveness.

What has been taught, then, is a method and apparatus for providing a unitary assembly of tubing and a terminating fitting facilitating, notably, a pressed-on fitting and which overcomes the disadvantages of the prior art. It will be appreciated by those skilled in the art, that the present invention provides consistency and reliability of the completed connection heretofore deemed unattainable at a marketable cost. The form of the invention illustrated and described herein is but a preferred embodiment of the teachings. It is shown as an illustration of the inventive concepts, however, rather than by way of limitation, and it is pointed out that various modifications and alterations may be indulged in within the scope of the appended claims.