Composite gasket and fitting including same

A composite gasket for forming a seal between a pipe bell 52 and a spigot 58 comprises a major portion 12 of non-elastomeric plastic material and a minor portion 14 of elastomeric material. The minor portion is axially encased by the major portion. The minor portion includes a sealing lip 16 extending radially inwardly from the major portion. The composite gasket can be manually inserted within a preformed grooved bell or the grooved bell can be formed over the gasket while the gasket is mounted on a mandrel.

FIELD OF THE INVENTION 
The present invention relates to a composite gasket comprising a major 
portion of non-elastomeric material and a relatively minor elastomeric 
portion forming a sealing lip. Additionally, the present invention relates 
to an improved pipe fitting including the composite gasket, and a method 
of forming a pipe bell with the composite gasket. 
BACKGROUND OF THE INVENTION 
In plastic pipe systems, connections between the various components must be 
sealed to prevent escape of fluids from the connections. The connections 
typically comprise an enlarged bell which receives a spigot. The spigot 
and bell can be formed as segments of pipe lengths or connecting members, 
such as elbows, T's, etc. In this application, the terms "fitting" and 
"pipe" are intended to include both pipe lengths and connecting members. 
The seal between the bell and spigot is conventionally provided by a gasket 
mounted in one of the components of a connection and sealingly and 
resiliently engaging the other component. Most often, the seal is mounted 
in the bell and has at least one radially inwardly projecting sealing lip 
which is engaged and deformed by the spigot such that a tight interference 
fit is formed between the spigot and sealing lip to prevent the escape of 
fluid. 
Gaskets formed exclusively of elastomeric material, such as natural rubber, 
are disadvantageous since they can be displaced from their intended 
position so as not to provide an adequate seal. For example, such gaskets 
may blow out of their mounting when pressurized or may be pushed from 
their intended position during insertion of the spigot within the bell. 
Gaskets reinforced with metal bands can be deformed and the metal can 
corrode rendering the gaskets useless. Moreover, when such gaskets are 
made an integral segment of the pipe spigot, deformation or corrosion of 
the metal band renders the entire pipe section useless. 
More recently, gaskets reinforced with plastic locking rings have been 
increasingly used. Such gaskets are described in U.S. Pat. No. 4,343,480 
to E. D. Vassallo. However, the cost of elastomeric materials, such as 
rubber, has significantly increased in recent years, thus forming a 
significant factor in the cost of fittings. Although the gaskets utilizing 
plastic locking rings contain less rubber than those made entirely of 
rubber, the rubber still forms a major portion of the gasket and thus 
greatly affects its cost. 
SUMMARY OF THE INVENTION 
It has now been discovered that the disadvantages associated with the use 
of conventional seals for plastic pipe systems are eliminated by employing 
a composite gasket comprising a major portion of non-elastomeric plastic 
material and a minor portion of elastomeric material encased within the 
major portion and provided with an elastomeric sealing lip extending 
radially from the major portion. The major portion axially encases the 
minor portion and a sealing lip extends from the major portion in a radial 
direction. 
By forming the gasket in this manner, material costs for forming the gasket 
can be significantly reduced since the amount of the relatively expensive, 
elastomeric material is reduced substantially. The material forming the 
major portion is significantly less expensive, thus reducing the cost of 
the entire gasket. The more rigid, non-elastomeric material reinforces the 
gasket and retains it in its proper position such that it is not blown out 
when subjected to pressure or pushed from its desired mounting upon 
joining of the bell and spigot. The plastic reinforcement will not corrode 
and its inherent resiliency will prevent permanent damage by deformation. 
Additionally, if the present gasket becomes defective, it can readily be 
removed from the fitting and replaced without the need to replace the 
entire fitting. 
Manufacture of the composite gasket can be facilitated by forming the major 
portion in first and second segments which entrap the minor, elastomeric 
portion between them. The connection between these segments is preferably 
provided by a latch member on one segment and a recess in the other member 
which mate to positively interlock the two segments. The segments can also 
be bonded by welding or by an adhesive. The non-elastomeric material for 
forming the major portion can be a polyolefin, such as polyethylene or 
polypropylene; poly(vinylchloride), and the like materials which are 
usually synthetic, thermoplastic polymers and capable of being processed 
by extrusion, moulding, etc., but which are not capable of rapidly 
returning to their original length after being significantly stretched. 
The elastomeric portion is formed from those materials commonly termed 
"elastomeric", such as the various rubbers, for example, styrene-butadiene 
copolymer, neoprene, butyl rubber, nitrile rubber, silicone rubber and the 
like. Since the minor portion forms a sealing lip, it must be more 
resilient than the major portion. However, both the major and minor 
portions of the gasket can be resilient for insertion of the gasket into a 
preformed bell groove. When the bell groove is formed about the gasket, 
the major portion should be relatively rigid. 
A second sealing lip can be mounted in and can extend from the major 
portion in a radial direction, opposite to the first sealing lip. 
The minor portion of the composite gasket can have a generally T-shaped 
transverse cross-sectional configuration. The sealing lip is formed by the 
vertical leg of the T-shape and may have a generally triangular 
configuration, while the cross member of the T-shape forms an enlarged 
head facilitating retention of the minor portion within the major portion. 
The connection between the pipe bell and the gasket can be enhanced by 
bonding the gasket directly to the bell by adhesive or welding. This 
connection can be enhanced by forming the bell and the composite gasket 
major portion of the same material. 
The composite gasket can be mounted within a pipe bell formed with a 
radially inwardly opening circumferential groove by deforming the gasket 
into a "heart" shape, and then releasing the gasket to fit within the 
preformed groove. Alternatively, the composite gasket can be mounted on a 
mandrel, and then a portion of the fitting is softened by heating and 
passed over the mandrel and gasket. In this alternative method, the gasket 
serves to form the groove and is firmly retained within the formed groove 
after cooling of the bell around the gasket. 
Other advantages and salient features of the present invention will become 
apparent from the following detailed description, which, taken in 
conjunction with the annexed drawings, discloses preferred embodiments of 
the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring initially to FIG. 1, the composite gasket of the present 
invention comprises a major portion 12 of non-elastomeric, plastic 
material and a minor portion 14 of elastomeric material. The major portion 
encases the minor portion in both axial directions and in a radially 
outward direction. The minor portion has a non-encased radially inwardly 
extending sealing lip 16 in which the non-encased portion has a greater 
radial length than the encased portion of said minor portion. 
Major portion 12 includes a front axial segment 18 and a rear axial segment 
20. The segments are generally annular in shape and are coupled or 
interlocked to each other. In transverse cross section, each segment has a 
generally triangular peripheral configuration. Segments 18 and 20 are 
preferably formed of a polyolefin, such as polyethylene or polypropylene, 
with polyethylene being especially preferred. 
Front axial segment 18 has a generally cylindrical inner surface 22, with a 
tapered portion 24 adjacent its free, front end 26 and with a radially 
extending shoulder 27 spaced axially from tapered portion 24. Its outer 
surface 28 extends upwardly and radially outwardly. The radially 
extending, rear axial face of front segment 18 has an axially and 
rearwardly extending latch member 30 with an enlarged free end 32. 
Radially inwardly of latch member 30, a circumferential recess 34 is 
formed within the rear face of front segment 18 for receiving a section of 
minor portion 14. 
Rear axial segment 20 has an inner surface 36 and an outer surface 38 
terminating at a rear edge 40. The cylindrical surface 41, forming the 
portion of inner surface 36 adjacent minor portion 14, has a greater 
diameter than cylindrical inner surface 22 to provide an annular space in 
the major portion for sealing lip 16 upon insertion of a spigot. The front 
face of rear segment 20 has an axially extending circumferential recess 
42. Recess 42 has an enlarged inner or rear end for receiving enlarged end 
32 of latch member 30. The radially inward portion of recess 42 is 
configured similarly and somewhat smaller than recess 34 in front segment 
18. The upper front end 44 has an undercut 46 and is spaced in an axial 
direction from the adjacent portion of front axial segment 18. This space 
and undercut 46 house a second seal lip 48 which is circumferential and 
which is generally L-shape in transverse cross section. Alternatively, 
second seal lip 48 can be an O-ring. The second seal extends in a radial 
direction from major portion 12 opposite to that of first sealing lip 16. 
Minor portion 14 is circumferential and has a substantially T-shaped 
transverse, cross-sectional configuration. The vertical leg of the T forms 
first sealing lip 16 which is generally triangular in transverse cross 
section and tapers in a radially inward direction. Cross member 50 extends 
in an axial direction, and forms an enlarged head for the minor portion 
with its axial ends received and retained in recesses 34 and 42. The 
radially outwardly directed cylindrical surface of cross member 50 
underlies latch member 30. In this manner, the minor portion is encased in 
both axial directions and in a radially outward direction by the major 
portion. 
Segments 18 and 20 are separately formed and are then joined, trapping 
minor portion 14 and second seal lip 48 therebetween. The segments can be 
held together solely by the positive interlocking engagement of latch 
member 30 and recess 42. The resilient and flexible nature of elastomeric 
cross member 50 provides a biasing force against latch member 30 to retain 
it in a locking position with recess 42 by pushing it radially outwardly, 
while permitting it to move radially inwardly for connecting the two 
segments. After attachment of the two segments with the minor portion and 
second seal lip entrapped therebetween, segments 18 and 20 can be bonded 
by an adhesive or by welding, e.g., ultrasonic or spin welding to prevent 
disengagement. 
Composite gasket 10, as illustrated in FIG. 2 is located within a 
cylindrical fitting 52. The fitting has a radially extending, inwardly 
opening circumferential groove 54 which receives composite gasket 10. 
When a spigot 58 is inserted within fitting 52, first sealing lip 16 is 
deformed to provide a fluid tight seal between fitting 52 and spigot 58. 
Second sealing lip 48 is pressed against the fitting surface defining 
groove 54 and enhances the fluid tight seal by preventing fluid from 
travelling between major portion 12 and fitting 52, along groove 54. 
The relative rigid nature of non-elastomeric major portion 12 positively 
retains the composite gasket properly within groove 54. Thus, blowout 
during pressurization of the conduits, and fishmouthing during insertion 
of the spigot is prevented. The connection between the composite gasket 
and the fitting can be enhanced by bonding axial segments 18 and 20 to 
body 52. This bonding can be accomplished by an adhesive or by welding, 
such as ultrasonics or spin welding. The welding can be enhanced by 
forming major portion 12 and fitting 52 of substantially identical 
materials. 
FIG. 4 illustrates one method of installing composite gasket 10 within a 
fitting bell having a preformed groove 54. The gasket is manually bent in 
the form of a "heart", and is then introduced by hand within the bell. The 
gasket is slowly released inside groove 54 to properly seat the gasket 
within the groove. If desired, major portion 12 of gasket 10 can be bonded 
to fitting 52 by adhesive or welding. For this installation method, major 
portion 12 should be relatively flexible and resilient. 
FIGS. 5-7 illustrate a method of assembling the fitting bell and the 
composite gasket in which groove 54 is formed by the composite gasket 
during the belling operation. In this method, the gasket is suitably 
retained on a belling mandrel 64. 
Shoulder 27 of gasket 10 cooperates with annular projection 65 on mandrel 
64 to aid in preventing movement of gasket 10 during formation of the 
fitting. However, shoulder 27 is optional since adequate frictional 
engagement is normally provided by deformation of sealing lip 16 against 
mandrel 64. In such event, tapered portion 24 extends to cylindrical 
surface 22 and projection 65 on the mandrel is eliminated. 
Mandrel 64 can be provided with a recess 66 for receiving sealing lip 16 to 
prevent possible excessive pressure upon sealing lip 16 and, thus, gasket 
10. Alternatively, recess 66 can be eliminated resulting in a cylindrical 
mandrel. 
One end of a fitting 67 is heated and passed over mandrel 64, as 
illustrated in FIGS. 5 and 6, to form the bell. The fitting is pushed 
along the mandrel and over the gasket, as illustrated in FIGS. 6 and 7, to 
form the groove. According to this embodiment of the invention, major 
portion 12 may be formed of a non-resilient rigid polymer to provide a 
good molding surface for forming the groove. Upon subsequent cooling, the 
fitting with the gasket retained therein can be removed from the mandrel. 
In FIGS. 5-7, the gasket is depicted having enlarged end 32 on latch member 
30 for locking parts 18 and 20. However, the provision of enlarged end 32 
is optional and may be eliminated when adequate frictional engagement 
between parts 18 and 20 is present without enlarged end 32. 
The composite gasket of the present invention can be reversed such that the 
gasket is mounted within the spigot and forms a seal with the bell. In 
such arrangement, the sealing lip on the minor portion would extend in a 
radially outward direction and the minor portion would be encased axially 
and in a radially inward direction. 
Although the invention has been described in considerable detail with 
particular reference to certain preferred embodiments thereof, variations 
and modifications can be effected within the spirit and scope of the 
invention as defined in the appended claims.