U.S. patent application number 13/923468 was filed with the patent office on 2014-12-25 for secured in place gasket for sealing plastic pipelines, method of manufacture and method of installation.
This patent application is currently assigned to S & B Technical Products, Inc.. The applicant listed for this patent is S & B Technical Products, Inc.. Invention is credited to Guillermo Monteil.
Application Number | 20140374994 13/923468 |
Document ID | / |
Family ID | 52105472 |
Filed Date | 2014-12-25 |
United States Patent
Application |
20140374994 |
Kind Code |
A1 |
Monteil; Guillermo |
December 25, 2014 |
Secured in Place Gasket for Sealing Plastic Pipelines, Method of
Manufacture and Method of Installation
Abstract
A pipe sealing gasket is shown which is designed to be received
within a raceway provided within a socket end of a female bell
plastic pipe end which is assembled with a mating male pipe end to
form a plastic pipe joint. The raceway in the female bell plastic
pipe end is preformed during manufacture and the gasket is
installed thereafter. The gasket has a rubber body portion which is
reinforced by a hard plastic band formed as a series of integral,
spaced wedges which are interconnected by a flexible ribbon. The
hard plastic band acts to prevent extrusion of the gasket during a
variety of pressure conditions as well as preventing displacement
during field assembly.
Inventors: |
Monteil; Guillermo; (San
Jose, CR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
S & B Technical Products, Inc. |
Fort Worth |
TX |
US |
|
|
Assignee: |
S & B Technical Products,
Inc.
Fort Worth
TX
|
Family ID: |
52105472 |
Appl. No.: |
13/923468 |
Filed: |
June 21, 2013 |
Current U.S.
Class: |
277/314 ;
264/279; 277/626 |
Current CPC
Class: |
F16L 17/035 20130101;
F16L 37/091 20130101; B29C 45/14631 20130101; F16L 21/03 20130101;
B29K 2071/00 20130101; B29K 2701/12 20130101; B29L 2031/265
20130101; F16L 17/025 20130101; F16J 15/022 20130101; F16L 47/08
20130101; B29K 2021/00 20130101; B29C 45/1459 20130101; F16L
37/0845 20130101 |
Class at
Publication: |
277/314 ;
277/626; 264/279 |
International
Class: |
F16J 15/02 20060101
F16J015/02; F16L 17/025 20060101 F16L017/025; B29C 45/14 20060101
B29C045/14 |
Claims
1. A pipe sealing gasket designed for receipt within a raceway
provided within a female bell socket end of a thermoplastic pipe,
the female bell socket end being designed to receive a mating male
thermoplastic pipe end to form a pipe joint, the gasket comprising:
a ring shaped elastomeric body having a main body portion formed of
rubber which, when viewed in cross section, includes a leading nose
region, a lower compression region and a trailing tail region, the
leading nose region facing generally towards the female socket end
of the pipe once the gasket is inserted within the pipe; wherein
the leading nose region of the main body portion of the gasket is
reinforced by a hard plastic band formed as a series of integral,
spaced wedges interconnected by a flexible ribbon, the hard plastic
band being embedded within the leading nose region of the main body
portion of the gasket during gasket manufacture; and wherein the
wedges on the hard plastic band act to prevent extrusion of the
gasket from the groove provided in the female bell socket end of
the thermoplastic pipe once a spigot end of a mating male pipe is
installed to form a pipe joint.
2. The sealing gasket of claim 1, wherein the main body portion of
the gasket is formed of a natural or synthetic rubber.
3. The sealing gasket of claim 2, wherein the main body portion of
the gasket is formed of a rubber selected from the group consisting
of styrene butadiene rubber, ethylene propylene diene monomer
rubber and nitrile rubber.
4. The sealing gasket of claim 1, wherein the hard plastic band is
formed of a synthetic plastic material having a durometer which is
greater than the durometer of the main body portion of the gasket
while being flexible enough to allow the gasket to accept inverse
curvature during installation into the groove provided in the
female, socket end of the thermoplastic pipe.
5. The sealing gasket of claim 4, wherein the synthetic plastic
material is a modified polyphenylene ether.
6. The sealing gasket of claim 1, wherein the lower compression
region of the gasket includes a series of circumferential
engagement grooves for engaging the mating male spigot pipe
end.
7. The sealing gasket of claim 6, wherein the main gasket body has
an outer bulbous region which is also provided with a series of
circumferential engagement grooves for engaging the female socket
end of the pipe.
8. A pipe sealing gasket designed for receipt within a raceway
provided within a socket end of a female bell pipe member, whereby
fitting the gasket within the raceway allows a mating male pipe
having a spigot pipe end to be inserted therein to form a
continuous pipe joint, the gasket comprising: a ring shaped
elastomeric body having a main body portion formed of rubber which,
when viewed in cross section, includes a leading nose region, a
lower compression region and a trailing tail region, the leading
nose region facing generally towards the female socket end of the
pipe once the gasket is inserted within the pipe; wherein the
leading nose region of the main body portion of the gasket is
reinforced by a hard plastic band formed as a series of integral,
spaced wedges interconnected by a flexible ribbon, the hard plastic
band being embedded within the leading nose region of the main body
portion of the gasket during gasket manufacture, the wedges each
having a front edge, a rear edge and opposing side edges, as viewed
in cross section, and wherein the opposing side edges slope evenly
in the direction of the leading nose region of the gasket; and
wherein hydraulic pressure due to fluid in the pipe acts upon the
wedges on the hard plastic band to push the wedges into tighter
engagement with the mating male and female pipe members to prevent
extrusion of the gasket from the raceway provided in the female
bell socket end of the thermoplastic pipe once a spigot end of a
mating male pipe is installed to form a pipe joint and the pipe is
conveying fluid.
9. A method of manufacturing a sealing pipe gasket designed for
receipt within a raceway provided within a socket end of a female
bell pipe member, whereby fitting the gasket within the raceway
allows a mating male pipe having a spigot pipe end to be inserted
therein to form a continuous pipe joint, the method comprising the
steps of: providing a mold having a first mold face with a
circumferential recess; placing a hard plastic band formed as a
series of integral, spaced wedges teeth interconnected by a
flexible ribbon within the circumferential recess in the first mold
face, the wedges each having a front edge, a rear edge and opposing
side edges, as viewed in cross section, and wherein the opposing
side edges slope evenly from the rear edges to the front edges
thereof; providing a second mating mold face; uniting the first and
second mold faces and injecting a rubber compound into the mold
recess; applying heat and pressure to the mold to form a ring
shaped elastomeric body having a main body portion formed of rubber
which, when viewed in cross section, includes a leading nose
region, a lower compression region and a trailing tail region, the
leading nose region facing generally towards the female socket end
of the pipe once the gasket is inserted within the pipe; curing the
main body portion with the hard plastic band contained therein,
whereby the leading nose region of the main body portion of the
gasket is reinforced by the hard plastic band, whereby hydraulic
pressure due to fluid in the pipe acts upon the wedges on the hard
plastic band to push the wedges into tighter engagement with the
mating male and female pipe members to prevent extrusion of the
gasket from the groove provided in the female socket end of the
thermoplastic pipe once a spigot end of a mating male pipe is
installed to form a pipe joint and the pipe is conveying fluid.
10. The method of claim 9, wherein the main body portion of the
gasket is formed of a natural or synthetic rubber.
11. The method of claim 10, wherein the main body portion of the
gasket is formed of a rubber selected from the group consisting of
styrene butadiene rubber, ethylene propylene diene monomer rubber
and nitrile rubber.
12. The method of claim 11, wherein the hard plastic band is formed
of a synthetic plastic material having a durometer which is greater
than the durometer of the main body portion of the gasket, while
being flexible enough to allow the gasket to accept inverse
curvature during installation into the groove provided in the
female, socket end of the thermoplastic pipe.
13. The method of claim 12, wherein the synthetic plastic material
is a modified polyphenylene ether.
14. A method of installing a gasket with an embedded reinforcing
hard plastic band within a gasket receiving raceway provided within
the belled end of a female pipe member, the belled end having a
mouth opening which is engageable with a spigot end of a mating
male plastic pipe section to form a pipe joint, the method
comprising the steps of: providing a plastic pipe section having a
preformed female belled end opening with a gasket receiving
raceway; installing a sealing gasket within the gasket receiving
raceway by bending the gasket to temporarily transformed the gasket
from a generally cylindrical shape to a generally elliptical shape,
placing the gasket within the gasket receiving groove and releasing
the gasket, whereby the gasket returns to the generally cylindrical
shape; wherein the gasket is formed as a ring shaped elastomeric
body having a main body portion formed of rubber which, when viewed
in cross section, includes a leading nose region, a lower
compression region and a trailing tail region, the leading nose
region facing generally towards the female socket end of the pipe
once the gasket is inserted within the pipe; wherein the leading
nose region of the main body portion of the gasket is reinforced by
a hard plastic band formed as a series of integral, spaced wedges
interconnected by a flexible ribbon, the hard plastic band being
embedded within the leading nose region of the main body portion of
the gasket during gasket manufacture, the wedges each having a
front edge, a rear edge and opposing side edges, as viewed in cross
section, and wherein the opposing side edges slope evenly in the
direction of the leading nose region of the gasket; and wherein
hydraulic pressure due to fluid in the pipe acts upon the wedges on
the hard plastic band to push the wedges into tighter engagement
with the mating male and female pipe members to prevent extrusion
of the gasket from the raceway provided in the female socket end of
the thermoplastic pipe once a spigot end of a mating male pipe is
installed to form a pipe joint and the pipe is conveying fluid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to sealing gaskets
and sealing systems used for pipe joints in plastic pipelines in
which a male spigot pipe section is installed within a mating
female socket pipe section to form a pipe joint and, more
specifically, to an improved gasket, simplified method of
manufacture, as well as an installation method for installing a
locked-in gasket within a preformed gasket groove in a section of
pipe used to form a pipe joint.
[0003] 2. Description of the Prior Art
[0004] Fluid sealing systems for plastic, fluid conveying pipes are
used in a variety of industries. The pipes used in such systems are
typically formed from thermoplastic materials including polyolefins
and PVC. In forming a joint between sections of pipe, the spigot or
male pipe end is inserted within the female or socket pipe end. An
annular, elastomeric ring or gasket is typically seated within a
groove formed in the socket end of the thermoplastic pipe. As the
spigot is inserted within the socket, the gasket provides the major
seal capacity for the joint. Various types of sealing technologies
have been employed to assure the sealing integrity of the pipe
joint. It is important that the sealing gasket not be dislodged
during the joint make up and that the gasket not become twisted or
otherwise compromised in field applications. It is also important
that the gasket not extrude out of the pipe groove under various
pressure conditions.
[0005] Earlier gasketed sealing systems are known in which a
homogeneous rubber gasket was generally deformable, allowing it to
be flexed or bent by hand, accepting inverse curvature, and
inserted within a mating internal raceway formed in the female,
belled pipe end. The raceway in the female pipe bell end was
pre-formed using a collapsible mandrel belling tool at the pipe
manufacturing facility. A prior art attempt to insure the integrity
of such pipe joints involved the use of a pipe gasket having a
first distinct body region formed of an elastically yieldable
sealing material, such as rubber, bonded to a second distinct body
region formed of a more rigid material, such as a rigid plastic.
The intent was that the rigid body region of the gasket would
assist in holding the gasket in place within the pipe groove. Other
approaches to the problem included the use of a homogeneous rubber
ring with a stiffening band which was inserted into a mating groove
provided on the internal diameter of the rubber ring. In the other
prior art systems, a homogeneous rubber gasket body was bonded with
an internal or external metal, or plastic, reinforcing band or an
internal metal band or ring. Each of these solutions had critical
limitations. For example, the prior art plastic/rubber composites
sometimes allowed the infiltration of dirt and debris between the
bell raceway and the outer diameter of the gasket. The plastic
region in some cases, reduced the rubber surface contact area,
sometimes leading to problems in providing the needed sealing in
all conditions, including high pressure, low pressure and cyclic
surges. Compatible materials were necessary when bonding the
homogeneous rubber gasket body with the plastic reinforcing band.
Poor bonding resulted in separation of the two elements. The
reinforcing band was subject to being misplaced and breakage in the
two part system. Thus, in some cases, the prior art solutions
failed to provide the needed joint integrity, often contributing to
the complexity and expense of the manufacturing operation and field
installation. In the early 1970's, a new technology was developed
by Rieber & Son of Bergen, Norway, referred to in the industry
as the "Rieber Joint." The Rieber system employed a combined mould
element and sealing ring for sealing a joint between the socket end
and spigot end of two cooperating pipes formed from thermoplastic
materials. In the Rieber process, an elastomeric gasket was
installed within an internal groove in the socket end of the female
pipe as the female or belled end was simultaneously being formed.
Rather than utilizing a preformed groove, the Rieber process
provided a prestressed and anchored elastomeric gasket during the
belling operation. Because the gasket was installed simultaneously
with the formation of the belled pipe end, a rigid, embedded
reinforcing ring could be supplied as a part of the gasket. Because
the pipe groove was, in a sense, formed around the gasket with its
embedded reinforcing ring, the gasket was securely retained in
position and did not tend to twist or flip or otherwise allow
impurities to enter the sealing zones of the joint, thus increasing
the reliability of the joint and decreasing the risk of leaks or
possible failure due to abrasion. The Rieber process is described
in the following issued United States patents, among others: U.S.
Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958;
3,887,992; 3,884,612; and 3,776,682.
[0006] Despite the advances offered by the Rieber process, the
belling operation was somewhat complicated and costly. Also,
certain situations exist in which it would be desirable to manually
remove one gasket and reinstall another within a preformed raceway
in the selected pipe end, rather than utilizing an integrally
installed gasket in which the groove in the pipe is formed around
the gasket. For example, municipal and consulting engineers will
specify specialty elastomers based on the pipelines end-use and
soil conditions. While SBR is the most common rubber used in North
America, engineers will specify EPDM based on water treatment
technique, and nitrile rubber when there is hydrocarbon soil
contamination due to gasoline or oil pollution. Distributors and
contractors cannot exchange Rieber process gaskets in their pipe
inventory.
[0007] It would therefore be advantageous to be able to install a
gasket of the type having a reinforcing element within a previously
belled pipe end, as opposed to those systems like the Rieber
systems, where the female pipe end is formed about the sealing
gasket during the manufacture of the female pipe end. However,
prior art gaskets with reinforcing elements are subject to breakage
and are not easily bent or flexed by hand, thus generally
precluding hand assembly in the field. The size and position of the
reinforcing element, which is bonded to the gasket body, generally
was greater than the diameter of the mouth opening of the belled
pipe end, presenting a further complication for assembly.
[0008] U.S. Pat. No. 6, 044, 539, issued Apr. 4, 2000, to Guzowski,
and commonly owned by the present applicant describes a machine for
inserting a "snap-fit" gasket, unable to accept inverse curvature,
having an embedded reinforcing ring into a preformed gasket
receiving groove in a belled pipe end. However, such a machine was
fairly costly to construct and presented difficulties in being hand
carried by a worker in the field.
[0009] The present invention has, as one object, to provide an
improved pipe gasket for use in pipe joints which offers the
advantage of a Rieber type seal, while allowing the gasket to
accept inverse curvature, to be installed in a preformed groove by
hand, either at the manufacturing plant or in a field
operation.
[0010] Another object of the invention is to provide an improved
gasket which is securely retained within a preformed pipe groove
without the necessity of a separate retaining band.
[0011] Another object of the invention is to provide an improved
sealing gasket of the plastic/rubber variety which optimizes the
rubber sealing surface contact of the gasket with the pipe bell
raceway.
[0012] Another object of the invention is to provide a reinforcing
element that is not required to be bonded to the rubber element,
hence creating the possibility of being made from a multitude of
materials.
[0013] Another object of the invention is to provide such a sealing
gasket with special reinforcing attributes which allow it to seal
under a variety of pressure conditions without being twisted or
extruded, or displaced during field assembly, and yet which can be
installed by hand in the bell raceway.
SUMMARY OF THE INVENTION
[0014] The sealing gasket of the invention is a rubber/plastic
secured-in design which is especially useful in sealing PVC pipes
having bell ends made using collapsible mandrel tools. The gasket
is reinforced with a reinforcing element, or band, comprised of a
series of wedges which are interconnected by a flexible ribbon. The
band is preferably imbedded within the rubber body portion of the
gasket, avoiding the use of bonding elements. The rubber element of
the gasket provides the primary sealing capacity while the plastic
element improves resistance to extrusion due to water pressure and
displacement during field assembly.
[0015] The gasket accepts inverse curvature to allow easy
installation in a pre-formed pipe bell raceway by hand. Once the
gasket is installed, it works as a combined compression and lip
seal. It is preferaby installed by the PVC pipe manufacturer and,
once installed, is a secured part of the pipe. The rubber portion
of the gasket can be, for example, SBR, EPDM, NR, etc., combined
with a hard plastic band.
[0016] In its preferred form, a pipe sealing gasket is shown which
is designed for receipt within a groove provided within a female
socket end of a thermoplastic pipe, the female socket end being
designed to receive a mating male thermoplastic pipe end to form a
pipe joint. The gasket comprises a ring shaped elastomeric body
having a main body portion formed of rubber which, when viewed in
cross section, includes a leading nose region, a lower compression
region and a trailing tail region. The leading nose region faces
generally towards the female socket end of the pipe once the gasket
is inserted within the pipe.
[0017] The leading nose region of the main body portion of the
gasket is reinforced by a hard plastic band comprised of a series
of wedges interconnected by a flexible ribbon, the hard plastic
band being embedded within the leading nose region of the main body
portion of the gasket during gasket manufacture. In use, the wedges
spaced along the ribbon act to prevent extrusion and displacement
of the gasket from the raceway provided in the female socket end of
the thermoplastic pipe. The main body portion of the gasket can
conveniently be formed of a natural or synthetic rubber, for
example, styrene butadiene rubber, ethylene propylene diene monomer
rubber and nitrile rubber. The hard plastic ribbon is formed of a
synthetic plastic material having a durometer which is greater than
the durometer of the main body portion of the gasket. The material
is selected based upon its having sufficient rigidity to prevent
extrusion and displacement in use, while being flexible enough to
allow the gasket to accept inverse curvature during installation.
The material chosen must also not be so rigid as to break while
being flexed or bent.
[0018] The lower compression region of the gasket can be provided
with a series of circumferential engagement ribs for engaging the
mating male spigot pipe end. The main gasket body has an outer
bulbous region which can similarly be provided with a series of
circumferential engagement ribs for engaging the female socket end
of the pipe. Preferably, the main gasket body has a lower, primary
sealing surface which forms a combination lip and compression seal
region for the gasket. The "lip" region is separated from the
convex sealing surface and trailing tail portion of the gasket body
by a V-shaped recess. The V-shaped recess allows the lip region of
the gasket body to bend inwardly as the mating male, spigot end of
a mating pipe section encounters the primary sealing surface of the
gasket.
[0019] A method is also shown for manufacturing a sealing pipe
gasket designed for receipt within a bell pipe groove provided
within a socket end of a female pipe member, whereby fitting the
gasket within the groove allows a mating male pipe having a spigot
pipe end to be inserted therein to form a continuous pipe joint.
The method includes providing a mold having a first mold face with
a circumferential recess. A hard plastic reinforcing element, the
band, is placed within the circumferential recess in the first mold
face, the hard plastic band being formed as a series of wedges
interconnected by a flexible ribbon. The wedges each have a front
edge, a rear edge and opposing side edges, as viewed in cross
section, and wherein the opposing side edges slope evenly from the
rear edges to the front edges thereof.
[0020] A second mating mold face is provided which is then united
with the first mold face, with a rubber compound being injected
into the mold recess. Heat and pressure are applied to the mold to
form a ring shaped elastomeric body having a main body portion
formed of rubber which, when viewed in cross section, includes a
leading nose region, a lower compression region and a trailing tail
region. The main body portion of the gasket is then cured with the
hard plastic ribbon contained therein, whereby the leading nose
region of the main body portion of the gasket is reinforced by the
hard plastic ribbon.
[0021] The gasket of the invention, while being reinforced by the
hard plastic ribbon, is nevertheless flexible enough to allow the
ribbon to be bent at an oblique angle for insertion within the
mating bell groove provided in the female socket pipe end. The
gasket then returns to a generally cylindrical shape and is
secured-in within the bell socket groove by the action of the hard
plastic ribbon.
[0022] Additional objects, features and advantages will be apparent
in the written description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is an end view of a section of plastic pipe, partly
broken away, and showing the bell end and raceway, with a gasket of
the invention in place in the raceway, the male pipe section being
position for insertion into the bell.
[0024] FIG. 2 is a perspective view of the sealing gasket of the
invention, showing the hard plastic band with its wedges and
associated flexible ribbon in dotted lines.
[0025] FIGS. 3-6 are simplified views of the steps of installing
the hard plastic band within an associated mold, the mold
thereafter being injected with rubber and heated and cured to make
the completed gasket of the invention.
[0026] FIG. 7 is a side, partial cross sectional view of the gasket
of the invention in place in the internal groove provided in the
female bell socket pipe end, the direction of travel of the mating
male pipe member being shown in dotted lines.
[0027] FIG. 8 is a broken away view of the hard plastic band used
in the manufacture of the gasket of the invention, and illustrating
the wedges which are interconnected by the flexible ribbon.
[0028] FIG. 9 is a top view of a portion of the gasket of the
invention, showing the placement of the hard plastic band, the
rubber portion of the gasket body being shown in phantom lines.
[0029] FIG. 10 shows the beginning step of the make up of a pipe
joint with the male pipe end just beginning to make contact with
the sealing gasket of the invention
[0030] FIG. 11 is a view similar to FIG. 10, showing a completed
pipe joint, with an external pressure force acting on the sealing
gasket.
[0031] FIG. 12 is another view of the completed pipe joint, this
time with the sealing gasket having an internal pressure force
acting on the gasket.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Turning now to the attached illustrations, FIG. 1 shows the
gasket 11 of the invention in place prior to the assembly of a pipe
joint. The gasket 11 is installed within a raceway 13 provided
within the belled end 15 of a female pipe section of thermoplastic
pipe 17. The female pipe section 17 can be formed of any of a
variety of commercially available thermoplastic materials, such as
the polyolefin family including polyethylene and polypropylene as
well as polyvinyl chloride and similar materials. Thermoplastic
pipes of this general type are used in a variety of industrial
settings including water, sewage and chemical industries. The
belied end 15 of the thermoplastic pipe section has a mouth opening
19 which is engageable with a spigot end 23 of a mating male pipe
section 25 to form a pipe joint. The gasket receiving raceway 13
has been pre-formed in the pipe mouth opening 19 at the pipe
manufacturing facility, as by using a collapsible mandrel belling
tool.
[0033] A particularly preferred form of the gasket 11 which can be
used in the method of the invention is shown in profile in FIG. 2
and in cross-section in FIG. 7. Preferably, the gasket 13 is an
annular, ring-shaped member having a main gasket body 28 formed of
a flexible elastomeric material, such as a suitable natural or
synthetic rubber. The elastomeric material used to form the body 28
of the gasket will vary in composition depending upon the end
application but may encompass a number of different natural and
synthetic rubbers including, for example, styrene butadiene rubber
(SBR), ethylene propylene diene rubber (EPDM),
acrylonitrile-butadiene rubber (NBR), nitrile rubber, etc.
[0034] Turning now to FIG. 7, the main gasket body 28 includes an
outer convex sealing surface 27 which, in this case, is provided
with a series of ribs or serrations 29. The main gasket body also
includes a lower, primary sealing surface 31. In the preferred
embodiment shown, the primary sealing surface 31 is an evenly
sloping face of the gasket body which forms a combination lip and
compression seal region for the gasket. The lip region is separated
from the outer convex sealing surface 27 and trailing tail portion
30 by a V-shaped recess (shown generally as 33 in FIG. 7). The
V-shaped recess allows the lip region of the gasket body to bend
inwardly as the mating male, spigot end of a mating pipe section
encounters the primary sealing surface 31 of the gasket (see FIGS.
10-12).
[0035] Returning to FIG. 7, the main gasket body 28 also has a
leading nose region, designated generally as 35 in FIG. 7 which is
initially contacted by the mating male spigot pipe end during the
assembly of the pipe joint. The leading nose region 35 faces
generally towards the female socket end of the pipe once the gasket
is inserted within the pipe.
[0036] With reference now to FIG. 8, it will be appreciated that
the leading nose region of the gasket is reinforced by a hard
plastic band 37 formed as a series of integral, spaced wedges (such
as wedges 39, 41, 43) interconnected by a flexible ribbon 45. As
will be apparent from FIGS. 4 and 8, the wedges 39 each have a
front edge 53, a rear edge 55 and opposing side edges 57, 59. The
opposing side edges (such as side edge 59 in FIG. 10) slope evenly
from the rear edges 55 to the front edges 53 thereof, as viewed in
this cross section. FIG. 2 shows the reinforcing hard plastic band
with its associated wedges in phantom lines (see, e.g., wedges 39,
41, 43). The gasket body can thus be thought of as having a rubber
element and as having a hard plastic element, the hard plastic
element serving as the reinforcing element for the gasket body.
[0037] During the manufacture of the gasket, the hard plastic band
37 is embedded within the leading nose region of the gasket during
the gasket manufacturing operation. As will be explained in greater
detail, the wedges 39 on the hard plastic band 37 act to prevent
extrusion of the gasket from the raceway (13 in FIG. 1) provided in
the female socket end of the thermoplastic pipe once a spigot end
of a mating male pipe is installed to form a pipe joint.
[0038] As was previously mentioned, the main body portion of the
gasket is formed of a natural or synthetic rubber, such as a
styrene butadiene rubber, ethylene propylene diene monomer rubber
or nitrile rubber. The durometer of the rubber used for the main
gasket body may vary depending on the end application but will
typically be in the range from about 40-70 Shore A hardness,
preferably about 40-60 Shore A. The hard plastic band 37, on the
other hand, is formed of a synthetic plastic material having a
durometer which is greater than the durometer of the main body
portion of the gasket. The synthetic plastic material used for the
band is preferably a material which shows an appropriate stiffness
for the application at hand while allowing flexing (accepts inverse
curvature) during installation. The band can have a higher
durometer than the remaining main body portion of the gasket since
it does not participate in the sealing function of the gasket to
the same extent as the primary sealing region of the gasket.
[0039] Various hard plastic type materials may be suitable
candidates for use as the hard plastic band. These materials
include such materials as polypropylene, polyvinylchloride and
various "engineered plastics." For example, one such material is
those hard plastics which fall into the family group of modified
polyphenylene ethers (PPE). These commercially available materials
have high heat resistance, making them suitable for injection or
compression molding and are generally suitable for plastic/rubber
composites. One commercially available family is the VESTORAN.RTM.
family of materials. VESTORAN.RTM. is the registered trademark of
Evonik Degussa GmbH for molding compounds containing
poly-2,6-dimethyl-1,4-phenylene ether as polymeric constituent
(polyphenylene ether, PPE, also referred to as PPO).
[0040] The method of manufacturing the sealing pipe gasket of the
invention will now be described. The gasket is designed for receipt
within a bell pipe raceway provided within a socket end of a female
bell pipe member, whereby fitting the gasket within the raceway
allows a mating male pipe having a spigot pipe end to be inserted
therein to form a continuous pipe joint. The manufacturing method
will be described primarily with respect to FIGS. 3-6. FIG. 3 shows
one half of an injection molding die 47 of the type that will be
familiar to those skilled in the relevant arts. As can be seen in
FIG. 3, the first mold half has a first mold face 49 with a
circumferential recess 51. As shown in FIG. 4, in the first step of
the manufacturing process, the hard plastic band 37 with its series
of integral, spaced wedges interconnected by the flexible ribbon 45
is placed within the circumferential recess 51. It will be
appreciated that placing the wedges into the mold as discrete and
individual elements would be very time consuming. However, because
the teeth are interconnected by the flexible ribbon, they can
easily be placed in the mold integrally, in a single step. This
also assures the proper spacing of the individual teeth about the
circumference of the gasket.
[0041] Next, there is provided a second mating mold face which is
essentially a mirror image of the first mold face. FIG. 5 shows the
hard plastic band partially installed in the circumferential groove
of the first mold face, while FIG. 6 shows the band fully
installed. The first and second mold faces are then united and the
moldable rubber compound is injected into the circumferential
recess. In the known manner, heat and pressure are then applied to
the mold to form a ring shaped elastomeric body. The heat and
pressure in the mold cures the main body portion with the hard
plastic band embedded therein, whereby the main body portion of the
gasket is reinforced by the hard plastic band, whereby hydraulic
pressure due to fluid in the pipe acts upon the wedges on the hard
plastic band to push the teeth into tighter engagement with the
mating male and female pipe members to prevent extrusion of the
gasket from the raceway provided in the female bell socket end of
the thermoplastic pipe once a spigot end of a mating male pipe is
installed to form a pipe joint and the pipe is conveying fluid.
[0042] While the gasket body is reinforced to prevent extrusion
under various fluid pressure conditions, as well as from being
displaced during field assembly, it remains flexible enough to
allow the gasket to be bent by hand and installed within a gasket
receiving raceway provided within the belled end of a female pipe
member. The sealing gasket can be installed within the gasket
receiving raceway by bending the gasket to temporarily transforms
the gasket from a generally cylindrical shape to a generally
elliptical shape, followed by placing the gasket within the gasket
receiving groove and releasing the gasket, whereby the gasket
returns to the generally cylindrical shape. Hydraulic pressure due
to fluid in the pipe acts upon the wedges on the hard plastic band
to push the wedges into tighter engagement with the mating male and
female pipe members to prevent extrusion of the gasket from the
raceway provided in the female bell socket end of the thermoplastic
pipe once a spigot end of a mating male pipe is installed to form a
pipe joint and the pipe is conveying fluid. FIG. 11 shows a cross
section of the gasket of the invention 11 installed in a pipe joint
with external pressure acting upon the gasket. FIG. 12 is a view
similar to FIG. 11 but shows the cross sectional shape of the
gasket where an internal fluid pressure is acting upon the gasket
body.
[0043] An invention has been provided with several advantages. The
method for installing a gasket of the invention allows a pipe
gasket to be installed within a preexisting and preformed groove in
a thermoplastic pipe. Once the gasket has been secured in position
in snap-fit fashion, it is securely retained within the pipe
raceway and resists axial forces tending to displace the gasket
from the raceway. Because a gasket is inserted within a preformed
pipe groove or raceway, the manufacturing and installation
processes are simplified and made less costly. The design of the
gasket also makes it possible to remove one gasket and reinstall
another within a preformed raceway in the selected pipe end. The
gasket which is utilized in the process is simple in design and
relatively economical to manufacture. There is no need for an
external retaining band or an internal metal ring to assist in
securing the gasket within the pipe groove. Because the metal
retaining band or ring are not necessary, it is also possible to
eliminate the pins necessary to hold the band or ring in place
inside the mold during manufacture, as in the previous Reiber
gasket art. The hard plastic band with its integral, spaced wedges
acts to prevent extrusion of the gasket from the female pipe groove
under a variety of fluid pressure situations, or from being
displaced during field assembly. Providing the wedges as an
integral part of a continuous ribbon simplifies the manufacturing
process and saves time.
[0044] While the invention has been shown in only one of its forms,
it is not thus limited but is susceptible to various changes and
modifications without departing from the spirit thereof.
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