Dissimilar Pipe Joining With Heat-Shrink Sealing for Cryogenic Airtightness
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Solution Overview
Problem
Existing methods for joining dissimilar material pipes, such as stainless steel and aluminum, face issues like increased weight and size due to thickness requirements, poor quality due to cracks and galvanic corrosion, and difficulty in securing airtightness, especially in high-pressure and low-temperature applications like liquefied hydrogen systems.
Innovation Solution
A method involving a heat shrink tube made of PTFE, PCTFE, UHMW PE, or PolyMide is used to insert and heat-treat a first pipe, which is then press-inserted into a second pipe, followed by plastic deformation using a rotary swaging device with tapered jigs to form a non-contact joint, ensuring airtightness and preventing galvanic corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rotational friction welding is used to join dissimilar material pipes, then the joining strength is improved, but the pipe thickness must be increased which leads to increased weight and size
Solution Approach 1:
The patent uses a multi-layer nested structure where an inner pipe is inserted into an outer pipe, and a heat shrink tube is inserted into the inner pipe. This nesting allows dissimilar materials to be joined through plastic deformation of the heat shrink tube without requiring increased pipe thickness, thereby maintaining lightweight design while achieving strong joints.
Solution Approach 2:
The patent changes the physical state of the heat shrink tube through temperature control. The heat shrink tube is heated to a specific temperature range to become pliable, then cooled to harden and form a strong joint. This parameter change allows the thin-walled tube to achieve joining strength without increasing thickness.
2Strength
If dissimilar materials are joined by welding, then the joining strength is improved, but the probability of poor quality and airtightness issues increases
Solution Approach 1:
The patent replaces traditional welding (thermal-chemical process) with a mechanical joining process using plastic deformation. The heat shrink tube is mechanically deformed through press insertion and rotary swaging to form a metal-to-metal interlocked joint, eliminating welding-related quality issues while maintaining joining strength.
Solution Approach 2:
The heat shrink tube acts as an intermediary component between the inner pipe and outer pipe. It mediates the joining process by being plastic deformed to form interlocked joints with both pipes, ensuring reliable connection and airtightness without direct welding between dissimilar materials.
3Ease of manufacture
If dissimilar materials are joined by fitting with a joint portion, then the ease of manufacture is improved, but the application to hard materials like steel becomes difficult and fastening members remain intact
Solution Approach 1:
The patent uses temperature as a control parameter to change the properties of the heat shrink tube. By heating to a specific temperature range, the tube becomes pliable for easy insertion, then cooling hardens it to form a strong mechanical joint with hard materials like steel, achieving both ease of manufacture and versatility.
Solution Approach 2:
The patent employs a rotary swaging device with tapered jigs that apply radial compressive forces in a curved rotational motion. This curved deformation path enables the heat shrink tube to be plastic deformed and joined to hard materials without requiring complex fastening members.
4Productivity
If dissimilar materials are joined by welding with electromagnetic pulses, then the joining speed is improved, but the probability of poor quality and difficulty in securing airtightness increases
Solution Approach 1:
The patent replaces electromagnetic pulse welding with a mechanical plastic deformation process using a rotary swaging device. The rapid rotational pressing achieves fast joining speeds through mechanical interlocking, ensuring high quality and airtightness without the defects associated with electromagnetic welding.
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 method achieves a durable, airtight joint between dissimilar materials that operates at high pressure and low temperature without direct contact, preventing corrosion and quality defects, suitable for connecting liquefied hydrogen system components.
Implementation Method 1
performing heat treatment on the first pipe joined to the heat shrink tube to shrink the heat shrink tube
Implementation Method 2
plastic deforming and joining a plastic deformation portion where the first pipe, the second pipe, and the heat shrink tube overlap
Data Source
AI summary
A method of joining dissimilar material pipes includes inserting an end portion of a first pipe into a heat shrink tube, performing heat treatment on the first pipe joined to the heat shrink tube to shrink the heat shrink tube, press-inserting the end portion of the first pipe to which the heat shrink tube is joined into a second pipe, and plastic deforming and joining a plastic deformation portion where the first pipe, the second pipe, and the heat shrink tube overlap. The joined dissimilar material pipes have improved airtightness and can operate at a high pressure and an extremely low temperature.