BACKGROUND OF THE INVENTION Numerous industries use tubing and fittings of flurorplastics, e. g., polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), and other synthetic resins, for the transfer of various fluids in extreme temperatures and conditions. These fluoroplastic fittings offer extraordinary corrosion resistance and high purity which make the materials ideal for the semiconductor processing industry. However, such plastic fittings and tubings, in that they are made of plastic rather than traditional materials such as stainless steel, bronze and copper, do not have the rigidity and strength of conventional fittings. Thus particular connection configurations that may work very well with metal fittings and metal tubing, do not work adequately when made from fluoropolymer materials. To maintain a clean and non-hazardous process it is essential that the fittings provided for coupling sections of tubing are not easily disconnected and that the integrity of tubing/fitting interface is maintained.

Various types of fluoropolymer fittings have been provided for these purposes.

One standard type of fitting known as FLARETEK fitting, available from the assignee of this application, and illustrated in prior art Fig. 1, provides for a fitting body, having a nose with a rounded tip and cylindrical section, and a threaded portion at the base of the nose. A fitting nut is typically placed on the tubing before the tubing end is flared. The end portion of tubing with the flared end is placed over the nose section and the fitting nut is slid over and secured to the fitting body axially compressing the flared end on the nose by the collar of the nut creating a seal between the inside surface of the tubing and nose. When assembled the nut extends completely over the flared section. The seal is created around the substantially cylindrical nose but is principally at the tip of the nose. In these fittings, the inside diameter of the flared section is slightly greater that the outside diameter of the non- flared portion of the tubing. The tubing flare forms an exaggerated s-shape with the flared section axially extending and having a constant diameter. The flare is formed by heating the end of the tubing and expanding same on an appropriately shaped form.

Referring to prior art Figures 2 and 3, alternative tubing connectors are illustrated that utilize either a groove cut into the exterior of the tubing to be joined or additional gripping collets. The flared fitting has proven most satisfactory compared to the other known fluoropolymer fittings in sealing performance and overall ease of use.

Such flared fitting bodies have the nose portion including the portions which seal exposed when they are unassembled subjecting the fitting bodies to potential damage.

Similarly, the exterior threads are also exposed subjecting them to possible damage.

However in certain applications it would be desireable to have a flared fitting that offers further advantages such as additional secondary sealing, a fitting in which the sealing surfaces of fitting body are not exposed when the fitting is unassembled, and moreover that provides more protection to the sealing components when assembled.

SUMMARY OF THE INVENTION A plastic fitting couples a section of tubing with a flared end to a fitting body. In a preferred embodiment, the flared end wall has an expanded's-shape in the cross-section and the plastic fitting generally comprises a fitting body and a fitting nut. The fitting body includes an internal nose section having a curvilinear sidewall that has been pre-formed to substantially match in shape the flare of the tubing. The fitting nut may be threadably coupled to the fitting body and includes a flare-engaging collar. Additional securement of the end edge portion of the tubing is provided by an axially inset annular recess defining a seat proximate the tapered nose section for receiving the end edge portion. In a preferred embodiment, the nut has external threads that engage internal threads on the fitting body.

During assembly, the flared end of the tubing with the fitting nut thereon is placed over the nose section of the fitting body. The fitting nut is rotated and drawn towards the fitting body by virtue of interfacing threads. As the fitting nut is drawn closer to the fitting body, the flare-engaging collar operates to axially compress the flared end of the tubing on the nose as well as axially seat the edge portion of the flared end into the axially inset converging annular seat.

Both the fitting body and fitting nut are designed for easy grasping and, thus, assembly of the plastic fitting. The fitting body is preferably provided with one or more planar surfaces for easier grasping while the fitting nut is preferably provided with a number of winged extensions for easier grasping. The fitting body may be integral or part of a component or device, such as a valve, or may have connection means such as external threads, another flared end fitting, or a flange.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of a prior art fluoropolymer plastic fitting.

Fig. 2 is a cross-sectional view of a prior art fluoropolymer plastic fitting.

Fig. 3 is a cross-sectional view of a prior art fluoropolymer plastic fitting.

Fig. 4 is a perspective view of a plastic fitting for flared tubing of the present invention.

Fig. 5 is a front plan view of the plastic fitting of Fig. 4.

Fig. 6 is a cross-sectional view of the plastic fitting of Fig. 4 taken along line 6-6 of Fig. 5.

Fig. 7 is a detailed cross-section view of the plastic fitting of Fig. 4 as indicated by detail section on Fig. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plastic fitting 10 for flared tubing of the present invention is depicted in Figs. 4-7.

Specifically, referring to Figs. 4 and 5, plastic fitting 10 generally comprises a fitting body (or first coupling means) 12 and a fitting nut (or second coupling means) 14, which is shown fastened to fitting body 12. Those exterior portions of fitting nut 14 and fitting body 12 not concealed by virtue of the fastening of fitting nut 14 to fitting body 12 may be appreciated herewith. Specifically, the non-concealed portion of the exterior of fitting body 12 is generally cylindrical in shape and preferably incorporates one or more planar surfaces 16 for easier grasping of fitting body 12 during assembly. The fitting has a first end 17 for receiving the flared tubing and nut and second end 19 which is illustrated as a threaded nipple 19.1 with the dashed lined representing the threads 19.2. As best shown in Fig. 6, the flared tubing end exterior surface has a concave region 28.1 which transitions to a convex region 28. 2. Similarly the interior surface of the flared portion has a convex region 28.3 and a concave region 28.4.

The non-concealed portion of the exterior of fitting nut 14 is also generally cylindrical in shape but is provided with rotation means configured as a plurality of winged extensions 18, which provide for easier grasping and torquing of fitting nut 14 during assembly of fitting 10. Each winged extension 18 generally comprises an elongate, substantially planar top face 20 and a pair of elongate, substantially parallel and planar side faces 22 that extend substantially perpendicularly from planar top face 20. Further defining the exterior of fitting nut 14 are a plurality of elongate separator faces 24 that are positioned between opposite side faces 22 of adjacent winged extensions 18 and a pair of substantially parallel end faces 25,26. Other rotation means may be utilized such as tool interfaces, flats, knurled or textured surfaces. A section of smaller diameter tubing having a pre-fonned flared end 29 (shown in Figs. 6 and 7) is shown extending from fitting nut 14.

Referring to Fig. 6, a cross-sectional view of fitting 10 is provided illustrating the interior configuration of fitting body 12 and fitting nut 14. As shown, fitting body 12 is preferably of a unitary configuration having a central bore 40 extending therethrough and an inner body portion 42. Inner body portion 42 comprises a tapered nose section 44 that is defined by a curvilinear side wall 45 surrounding central bore 40. Inner body portion 42 further comprises a spacer wall 46 that is substantially perpendicular to the linear portion of side wall 45 and that connects side wall 45 with an angular wall 48. Angular wall 48, which also defines inner body portion 42, is preferably provided at an acute angle, e. g., 30 degrees, to spacer wall 46. Spacer wall 46, separating side wall 45 and angular wall 48, defines a an axially extending and converging annular recess 47 with a tubing seat 49 appropriately sized for the thickness of tubing 28 that is placed over tapered nose section 44. In a preferred embodiment the annular space dimension converges to a dimension d less than the thickness T of the tubing wall. Angular wall 48 is connected via a substantially cylindrical section 50 to a threaded side portion 52 of inner body portion 42. Threaded side portion 52 extends to the exterior of fitting body 12 and connects with the fitting end 54.

Fitting nut 14, like fitting body 12, is also preferably of a unitary configuration, and incorporates a proximal portion 60. Proximal portion 60 is preferably defined by a annular collar 62. Collar 62 includes a concave corner section 64 defining an annular recess having an upper leg 66 and a lower leg 68, a convex corner portion 69, a substantially radial face 70, and an angular face 72 defining a taper, a second convex corner portion 69.1. Proximate collar 62, and further defining outer fitting portion 60, is a threaded side portion 74.

Threaded exterior portion 74 is designed to interface with threaded interior portion 62 of fitting body 12. Outer fitting portion 60 further includes a recessed, annular void 76 that is intermediate threaded side portion 74 and winged extensions 18. Fitting nut 14 further comprises a central bore 78 that extends from collar 62 to the exterior of the fitting at end face 26.

In securing plastic fitting 10 to tubing 28, flared end 29 of tubing 28 is preferably manually placed over tapered nose section 44 of fitting body 12 while the non-flared end of tubing 28 is preferably inserted through central bore 78 of fitting nut 14. Where the non- flared end of the tubing section is not readily accessible or is part of a component or will not receive the nut, said nut would be put on the tubing section. Fitting nut 14 is then pushed towards fitting body 12 until threaded side portion 74 of fitting nut 14 contacts threaded side portion 52 of fitting body 12. Fitting nut 14 is preferably then rotated by the rotating means such that the threads of fitting body 12 and fitting nut 14 act to draw fitting nut 14 towards fitting body 12.

As fitting nut 14 is drawn closer into fitting body 12, collar 62 of fitting nut 14 is pressed against flared end 29 of tubing 28 operating to pinch and secure flared end 29 of tubing 28 between collar 62 and curvilinear side wall 45 thereby effecting a seal between tubing 28 and plastic fitting 10. The collar provides axial compressive force on the flared end of the tubing, the tapered nose interface 80 which is at approximately 45° translates the axial compression into a radial component. Flared end 29 is additionally secured by virtue of the seating of the tip 51 of flared end 29 within annular space 47.

The present invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.