PVC-O Pipe Socket Heat-Shrink Joining for Pressure Sealing
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Solution Overview
Problem
Current methods for joining molecularly oriented PVC-O pipes face challenges in providing a securely sealed and restrained joint due to the unique geometry of the 'Anger Raceway', which is difficult to hold gasket raceway dimensions, leading to limited pressure range and reliance on indentation of hard and brittle PVC-O pipe, resulting in high costs and joint failure.
Innovation Solution
A heat-shrink method is employed where the PVC-O pipe is heated to a rubbery state, allowing the socket end to conform tightly to the spigot end, followed by cooling to create an interference fit, and enhanced with techniques like gasket placement, adhesive application, or mechanical gripping elements to increase friction and sealing capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional gasket sealing systems with Anger Raceway are used for PVC-O pipe joints, then the joint can be formed with the unique geometry required for molecularly oriented pipe, but the joint fails to provide secure sealing and restraint under pressure due to difficulty in holding gasket raceway dimensions
Solution Approach 1:
The patent changes the fundamental joining parameter from mechanical gasket retention to thermal interference fit. By heating the socket above the glass transition temperature of PVC-O and then cooling it, the material parameters change to enable shrinkage and create a tight interference fit that provides reliable sealing and restraint without relying on precise gasket raceway dimensions
Solution Approach 2:
The patent replaces the mechanical gasket-based sealing system with a thermal processing system. Instead of relying on mechanical retention of gaskets in the Anger Raceway, the invention uses controlled heating and cooling to create a interference fit that provides both sealing and restraint functions
2Strength
If indentation methods are used to join PVC-O pipe sections, then the hard and brittle pipe material can be connected, but the joint reliability is limited due to the brittle nature of the material
Solution Approach 1:
The patent changes the temperature parameter to above the glass transition temperature during the joining process, transforming the brittle PVC-O material into a more ductile state that can be formed and fitted without indentation. After cooling, the material returns to its brittle state but maintains the interference fit, avoiding the reliability issues of indentation-based joining
Solution Approach 2:
The patent performs preliminary heating of the socket before insertion of the spigot section. This preliminary thermal action prepares the material to accommodate the interference fit without damage, and the subsequent cooling locks in the connection, preventing the joint failures associated with indentation methods
3Ease of manufacture
If conventional heating and shaping methods are used to form socket ends, then the pipe ends can be prepared for joining, but the molecular orientation and strength properties are compromised
Solution Approach 1:
The patent applies local quality by heating only the socket end region above the glass transition temperature while leaving the rest of the pipe unaffected. This localized thermal processing allows the socket to be prepared for interference fit without compromising the molecular orientation and strength properties of the main pipe body
Solution Approach 2:
The patent uses controlled parameter changes in temperature to enable socket preparation. By temporarily raising the temperature above the glass transition point only in the socket region, the material becomes formable, and upon cooling, the molecular orientation is restored, maintaining strength properties
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides a cost-effective, securely sealed, and restrained joint for PVC-O pipes without relying on indentation, utilizing the inherent shrinking capabilities of the material to ensure a strong and reliable connection under various pressures.
Implementation Method 1
the socket end is heated so that the internal diameter of the socket end comes into contact with the external diameter of the spigot end. The molecularly oriented pipe at this point is in a rubbery state and exhibits a low elastic modulus due to the heating
Implementation Method 2
The socket end is then cooled sufficiently to cause the socket end to undergo thermal contraction to produce an interference fit with the spigot end
Data Source
AI summary
A pipe joining system and pipe joint are shown m which two sections of molecularly oriented pipe are joined using heat shrinking techniques. A first section of pipe is provided having a straight, pre-formed socket with an internal diameter and with an end opening having enough clearance to allow a mating spigot section having a given external diameter to be inserted into the socket end opening. After the spigot end is inserted to a given depth, the socket is heated sufficiently so that the internal diameter of the socket end comes into contact with the external diameter of the spigot end, the molecularly oriented pipe being in a rubbery state and exhibiting a low elastic modulus which allows the socket end to conform tightly to the spigot end external diameter without deforming the spigot end.