Two piece composite inlet

A plastic pressure vessel having an access fitting is disclosed. The pressure vessel has a liner defining a container with an access opening. The fitting comprises a body portion defined by a hollow cylindrical neck portion having an upper annular rim and a radially flaring flanged portion. The fitting further comprises a plastic covering portion surrounding the neck portion and covering and conforming to an upper surface of the flanged portion and conforming to the upper annular rim. The body portion is formed from a plastic material having a higher tensile modulous and higher deflection temperature than the plastic covering portion which forms a fusion bond with the liner.

BACKGROUND OF THE INVENTION 
This invention relates to hollow plastic articles having a blow-molded or 
rotationally cast portion fused to a second prefabricated portion. More 
particularly this invention relates to a plastic pressure vessel having an 
access fitting fused to a blow-molded or rotationally cast liner which may 
be filament wound to provide a pressure vessel. There are two basic 
techniques for fusing a flanged access fitting within a wall portion of a 
hollow thermoplastic pressure vessel liner. One such technique is set 
forth in U.S. Pat. No. 4,994,132. In that patent a thermoplastic pressure 
vessel is manufactured by a rotational casting technique which distributes 
molten or softened thermoplastic molding material evenly over the inner 
wall of the mold. A preformed access opening fitting is positioned within 
the mold cavity in a location which is initially spaced from the mold wall 
and the thermoplastic material covering the mold wall during the 
rotational casting operation. The fitting is then retracted into the 
softened or molten thermoplastic material so that a portion of the fitting 
is fused to the molding material. When the casting is cooled to ambient 
temperature a fusion bond results between the fitting and the wall of the 
molded article. 
Another technique for bonding an access fitting to a pressure vessel or 
tank liner is set forth in U.S. Pat. No. 4,589,563. According to the 
technique set forth in that patent a pressure vessel or tank liner is 
formed by a blow molding operation wherein a parison is extruded from an 
extrusion head and the open mouth of the parison is grasped, expanded, and 
guided over a preformed access fitting positioned in axial alignment with 
the parison extrusion head. A portion of a surrounding hollow mold is 
advanced to define the shape of the blow-molded article and to form the 
parison around the access fitting. 
In practicing both these techniques the side wall of the pressure vessel or 
liner is molded from a polyethylene resin and the access fitting is 
preformed from the same or a closely similar resin which may be reinforced 
with chopped fibers so that the fitting is capable of a fusion bond with 
the vessel or liner side wall. A disadvantage in this procedure is that 
the pressure vessel wall or liner is molded from a material with a low 
deflection temperature and low tensile modulous. Since it is necessary to 
employ an identical or similar plastic for the access fitting for proper 
fusion of the fitting to the liner or wall, it is apparent that the 
fitting will likewise have a low deflection temperature and low tensile 
modulous. Even with the addition of chopped fibers to strengthen the 
preformed access fitting, temperature and pressure limitations are 
apparent. 
BRIEF SUMMARY OF THE INVENTION 
This invention provides a technique for employing fusion bonding between a 
pressure vessel wall or liner manufactured from a low deflection 
temperature and low modulous material such as polyethylene and an access 
fitting manufactured from a high deflection temperature and high tensile 
modulous material such as polypropylene or a nylon polypropylene blend 
which is normally difficult to fusion bond to polyethylene. 
According to this invention an access fitting is preformed from a material 
having a relatively high deflection temperature and high tensile modulous, 
such as polypropylene or a blend of polypropylene and nylon. The access 
fitting has a flanged base portion which is intended to be joined to the 
interior surface of a blow-molded or rotationally cast tank liner and has 
an axial extending hollow cylindrical portion which provides access to the 
interior of the liner. At least an upper surface of the flanged base 
portion, the outer surface of the cylindrical neck portion, and an upper 
annular rim portion of the cylindrical neck are coated or covered with a 
plastic which is fusible to the tank liner. The coating or covering may be 
preformed and joined to the fitting by an adhesive or by a mechanical 
locking device. Alternately the coating may be applied by an injection 
molding technique wherein the fitting forms part of the mold. 
Since the coating material is fusible with the liner, the fitting and its 
coating may be fused into a tank liner according to the molding technique 
set forth in U.S. Pat. Nos. 4,589,563 and 4,994,132, the subject matter of 
which is incorporated herein by reference.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIGS. 1-4 there is illustrated an access fitting 10 for a 
pressure vessel. The access fitting 10 comprises a body portion 12 defined 
by a hollow cylindrical neck portion 14 having an upper annular rim 16 and 
a radially flaring flanged portion 18. The fitting 10 further comprises a 
covering portion 20 which is adapted to surround the neck portion 14 and 
conform to the upper surface of the flanged portion 18. The covering 
portion 20 includes a radially inwardly extending lip 22. The covering 20 
has an inner surface 24 which conforms to the outer surface of the body 
portion 12. In FIG. 1 the inner surface 24 is provided with a plurality of 
projecting tangs 26 which are received in recesses 28 in the cylindrical 
side wall 14 so that the covering portion and the body portion may be 
locked together. 
Alternately the covering portion 20 and the body portion 14 may be cemented 
together to form the access fitting 10 as is illustrated in FIG. 3. 
The body portion 12 is preformed such as by injection molding from a 
polypropylene-nylon blend such as Akuloy produced by DSM Engineering 
Plastics of Evansville, Ind. This compound does not readily fuse with 
conventional tank liner materials such as polyethylene but exhibits 
desirable tensile and high temperature characteristics which are desirable 
for access fittings. The covering portion 20 is preformed from 
polyethylene which will readily fuse from the liner and the covering may 
be mechanically locked to the body portion or cemented thereto as was 
previously discussed. Also the covering may be injection molded onto the 
body portion. 
The access fitting 10 is fused to a polyethylene tank liner 30 according to 
the technique set forth in U.S. Pat. No. 4,589,563, or in accordance with 
the rotational casting operation set forth in U.S. Pat. No. 4,994,132. 
In accordance with the preferred procedure set forth in U.S. Pat. No. 
4,589,563 and as is illustrated in FIGS. 5 through 9, a pressure vessel 
100 (FIG. 10) may be produced by an apparatus which includes a 
conventional parison extrusion head 50, a segmented hollow mold 52 which 
includes a pair of mold halves 54 and 56 having an inside surface which 
defines the outside surface of the pressure vessel 100 to be molded, and a 
parison stretching assembly 60. 
The assembly 60 comprises a base 62 which supports a plurality of curved 
plates 64. The plates are arranged on a first platform 66 mounted on rod 
and piston assemblies 68. A rod 70 is axially disposed through an 
appropriate hole in the platform 66 and supports a second platform 72 
which is provided to hold the fitting 10 as shown. The rod and piston 
assemblies 68 are provided to move the platform 66 and the plates 64 from 
a lower position below the platform 72 to an upper position above the 
platform 72 as shown in FIGS. 5, 6 and 7. (In FIG. 6 one of the plates 42 
has been cut away for the sake of clarity). The plates are pivotally 
secured to the platform 66 by pins 74 which permits the plates to turn 
radially inwards so that in the upper position they can form a protective 
dome over the fitting 10, as shown in FIG. 7. Pneumatically-operated 
control rods are used to pivot the plates 64 about its pin 74. These rods 
have been omitted for the sake of clarity. 
At the beginning to the molding process the first platform 66 is raised and 
the plates are closed around the platform 72 and the fitting 10 disposed 
thereon. 
A tube or parison 78 is next extruded downwardly by the extrusion head 50 
and is in a flowable plastic state in the condition illustration in FIGS. 
7 and 8. The extrusion rate is inversely proportional to the extruded wall 
thickness of the parison so that a fast extrusion rate produces a 
relatively thin wall and a slow rate produces a relatively thick wall. 
When the parison reaches the position illustrated in, FIG. 7 of the 
drawings, it has just encircled the plurality of inwardly directed plates 
64. As previously mentioned, in this position the plates form a protected 
dome over the portion 14. Next the plates separate as they move downwardly 
to pull down the parison to envelope the fitting 10 as is shown in FIG. 8. 
When the parison has completed its travel to envelope the fitting 10, the 
mold segments 54 and 56 are moved radially inwardly to the position 
illustrated in FIG. 9. The mold surface 58 surrounds a major portion of 
the parison and pinches off the top and bottom of the parison as indicated 
at the location 80 and 82. Since the parison is in a hot moldable 
condition the covering portion 20 of the fitting 10 is fused to the liner 
wall formed by the parison. 
As may be seen in FIG. 10 the pressure vessel 100 may be provided with a 
plumbing connection 102 which is threaded into the fitting 10. The 
connection 102 is provided with an O-ring 104 which provides a seal 
between the plumbing connection 102 and an upper annular rim 106 of the 
fitting 10. Thus, any leakage of fluids through the thread connection 
between the plumbing connection 102 and the fitting 10 and/or the 
interface between the portions 14 and 20 is blocked by the O-ring 104. 
The polyethylene liner 30 may be, and typically is, wrapped with a 
helically wound resin-impregnated filament to form a winding layer 108. 
The winding layer 108 is applied with conventional filament winding 
techniques. 
Although the preferred embodiment of this invention has been shown and 
described, it should be understood that various modifications and 
rearrangements of the parts may be restored to without departing from the 
scope of the invention as disclosed and claimed herein.