1. Field of the Invention
The present invention relates generally to sealing systems for thermoplastic pipes and, more specifically, to an improved pipe gasket and 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.
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 sealing 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.
In the Rieber process, the gasket is installed in a circumferential groove provided upon the working surface of a mandrel and abuts a backup collar which helps to position and retain the gasket during the subsequent belling operation. It is critical that the gasket be properly positioned on the forming mandrel and that the gasket not ride over the backup collar during the belling process.
With prior art gaskets used with the Rieber belling process, it was sometimes possible to reverse or otherwise mis-install the gasket in the circumferential groove provided on the outer working surface of the mandrel. When the heated thermoplastic pipe end was forced over the mandrel, the gasket would fail to be seated properly in the subsequently formed pipe groove within the female, belled pipe end. It was then generally necessary to discard the defective pipe section.
A need exists for an improved sealing gasket for use in a Rieber type manufacturing process, which sealing gasket would be easier and more reliable to seat on the working surface of the forming mandrel.
A need also exists for such a sealing gasket which would be simple in design and simple to manufacture and which could also be used with existing belling technologies.
A need also exists for such a sealing gasket which would simplify handling, which would help to insure correct position on the exterior surface of the working mandrel and which would thereby improve quality control in the pipe belling process.
A need also exists for such a sealing gasket which would effect a more stable bell shape in the subsequently formed female, belled pipe end.
A need also exists for such a gasket which would incorporate a wiping lip feature to wipe the male, spigot pipe end of dirt or other contamination upon subsequent assembly of a pipe joint.