Thermoplastic Socket Coupling Using Shape Memory Heating Element
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Solution Overview
Problem
Existing electrofusion systems fail to achieve a tight connection when assembling parts made of amorphous or weakly crystalline polymers like PVC, CPVC, or ABS, due to high viscosity and low thermal stability, which prevents the elastic heating member from returning to its natural state and degrades the material, leading to poor weld quality.
Innovation Solution
A coupling element with a prestressed heating element embedded in a thermoplastic socket, where the heating element transitions from a prestressed state to a pasty viscous state, allowing it to straddle the tube and socket, ensuring interpenetration and mechanical anchoring, and is heated by induction to achieve a stable connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an elastic heating member is used in electrofusion welding, then the material can be melted and the parts can be joined, but the elastic member cannot move easily in amorphous or weakly crystalline polymers due to high viscosity, preventing it from returning to its natural state and positioning itself at the interface
Solution Approach 1:
The patent changes the physical parameters of the heating element by using a shape memory alloy instead of a traditional elastic member. This material can be deformed at low temperature and then recover its original shape when heated above its transformation temperature, enabling it to move through the high-viscosity amorphous polymer material and position itself at the interface between the fitting and tube.
Solution Approach 2:
The shape memory alloy heating element utilizes phase transition between martensite (low temperature, deformable) and austenite (high temperature, recoverable) states. During welding, the element transitions from deformed state to recovered state when heated, allowing it to push through the viscous polymer material and achieve proper positioning for creating the weld bead at the interface.
2Reliability
If the elastic member is heated to melt the material, then the material viscosity decreases and the member can move, but amorphous or weakly crystalline polymers have low thermal stability and degrade before the member can return to its natural state
Solution Approach 1:
The shape memory alloy is selected with a specific transformation temperature range that is lower than the degradation temperature of amorphous or weakly crystalline polymers. This parameter change enables the heating element to become mobile and position itself at the interface before the polymer material degrades, allowing successful welding of thermally unstable materials.
Solution Approach 2:
The patent replaces the traditional mechanical elastic member with a shape memory alloy element that uses thermomechanical coupling. The alloy's ability to recover its shape through phase transition provides the necessary mechanical action to move through and position at the interface, substituting a purely mechanical system with one that utilizes thermal-structural phase changes.
3Strength
If crystalline polymers are heated, they expand strongly and develop pressure that promotes intimate contact and molecular interpenetration, but amorphous or weakly crystalline polymers do not exhibit this expansion phenomenon, resulting in poor weld quality
Solution Approach 1:
The shape memory alloy heating element acts as an intermediary that compensates for the lack of thermal expansion in amorphous or weakly crystalline polymers. As the alloy recovers its shape, it mechanically pushes the polymer materials together to create intimate contact and promote molecular interpenetration, substituting the expansion pressure normally provided by crystalline polymer thermal expansion.
Solution Approach 2:
The shape memory alloy heating element performs multiple functions: it heats the polymer material to reduce viscosity, positions itself at the interface through shape recovery, and simultaneously applies mechanical pressure to ensure intimate contact between the fitting and tube. This self-service capability compensates for the absence of thermal expansion pressure in amorphous polymers.
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
The solution enables a tight mechanical and sealing connection in amorphous or weakly crystalline polymers by allowing the heating element to move and soften the material, creating local interpenetrations and ensuring mechanical stability, despite the lack of thermal expansion pressure, resulting in a durable and leak-proof assembly.
Implementation Method 1
the at least one prestressed element is capable of assuming a second prestressed state when its temperature exceeds a local transition temperature from a solid state to a pasty viscous state of the thermoplastic material
Implementation Method 2
the at least one prestressed element, in a stable unstressed state, has an outside diameter smaller than the inside diameter of the socket... when its temperature exceeds a local transition temperature from a solid state to a pasty viscous state
Data Source
Figure 1~6
Figure 7~8c
AI summary
The present invention provides a connecting element, a fitting comprising such a connecting element, and a method for manufacturing such a connecting element. The connecting element (10) comprises a socket (15) made of thermoplastic material for inserting a tube element, the socket being able to be welded to the tube element along a junction surface, the socket (15) having an internal diameter (D1) of the socket, at least one heated prestressed element (30) embedded in the socket (15), in a first expanding prestressed state in an initial position in which an internal diameter of the at least one prestressed element is equal to or greater than the internal diameter of the socket and around the periphery of the junction surface, in which the at least one prestressed element is capable of assuming a second prestressed state when its temperature exceeds a local melting temperature of the thermoplastic material.At least one prestressed element, in a stable unstressed state, has an outside diameter smaller than the inside diameter of the socket.