Seal for a joint or juncture – Process of static sealing – Pipe – conduit – or cable
Reexamination Certificate
1999-11-24
2001-12-11
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Process of static sealing
Pipe, conduit, or cable
C277S627000, C277S652000, C425S393000, C425SDIG002, C264S516000, C264S275000
Reexamination Certificate
active
06328309
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to sealing systems for thermoplastic pipes and, specifically, to an improved belling process for installing a gasket in a socket end of a thermoplastic pipe.
2. Description of the Prior Art
Pipes formed from thermoplastic materials including polyethylene and PVC are used in a variety of industries. 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. It is critical, during the installation process, that the gasket not be able to twist or flip since a displaced or dislocated gasket will adversely affect the ultimate sealing capacity of the joint.
One early attempt to ensure the integrity of such pipe joints was to provide local reinforcement of the groove portion of the socket end by means of a heavier wall thickness in this region of the pipe. In some cases, reinforcing sleeves were also utilized. Each of these solutions was less than ideal, in some cases failing to provide the needed joint integrity and often contributing to the complexity and expense of the manufacturing or field assembly operations.
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, the elastomeric gasket was inserted within an internal groove in the socket end of the female pipe as the female or belling end was simultaneously being formed. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint with a scaling gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint. These features increased the reliability of the joint and decreased the risk of leaks or possible failure due to abrasion or other factors. The Rieber process is described in the following issued 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.
Despite the advances offered by the Rieber process, certain problems could occur both in the manufacture of the joint and integral gasket and in certain field applications. In the manufacturing plant, frictional resistance between the gasket and mandrel or pipe could hamper the forming operation. In some field operations, particularly involving larger diameter pipe, the insertion force needed to install the male spigot end within the mating socket end could, on some occasions, cause the gasket to be distorted or displaced.
One attempted solution, both in the manufacturing plant and in the field, was to utilize a lubricant to reduce frictional forces. The lubricant could be applied during formation of the pipe joint and at the point of assembly of the pipe joint in the field, as by brushing, spraying or dipping the gasket in a suitable liquid or viscous lubricant compound. This approach was messy and inconsistent and often proved to be unsatisfactory. The lubricating effect was not permanent or even semi-permanent.
Accordingly, it is an object of the present invention to provide an improved pipe belling process of the type described which is more efficient and which produces more consistent results without the use of a liquid lubricant.
It is also an object of the present invention to provide a pipe gasket with a novel spray-on anti-friction coating on selected surfaces thereof which facilities the manufacturing operation and which also provides a lower insertion force for the male, spigot end when entering the female, spigot end to facilitate assembly of the pipe joint in the field.
SUMMARY OF THE INVENTION
A method is shown for installing a gasket in a socket end of a thermoplastic pipe which is used to form a pipe coupling. A mandrel is provided with an inner end and an outer end and having a generally cylindrical outer working surface. A gasket is installed at a first circumferential position on the outer working surface. The gasket has at least selected surfaces coated with a spray-on anti-friction coating. A retention member is provided at a second circumferential location on the mandrel nearer the inner end of the mandrel with the retention member abutting the gasket in a normally extended position. A socket end of a thermoplastic pipe is then heated and forced over the working surface of the mandrel and over the gasket, whereby the heated socket end of the thermoplastic pipe flows over the gasket to form a retention groove for retaining the gasket and again contacts the working surface of the mandrel. The heated socket end of the thermoplastic pipe is then cooled and retracted from the mandrel leaving the gasket within the retention groove of the pipe end.
Preferably, the spray-on anti-friction coating is applied by spraying on a dry powder followed by heating the powder to cause it to be fixed. The preferred dry powder is a fluoropolymer powder, most preferably polytetrafluoroethylene.
In the preferred embodiment, the gasket is an elastomeric, ring shaped member having a circumferential contact area and an exterior surface, the anti-friction coating being applied to at least selected portions of the circumferential contact area.
Additional objects, features and advantages will be apparent in the written description which follows.
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patent: 4410185 (1983-10-01), Sporre
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Bracewell & Patterson LLP
Knight Anthony
Pickard Alison K.
LandOfFree
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