Friction Welding Tube Sheet Connections
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Solution Overview
Problem
Existing methods for connecting tube sheets and tubes in heat exchangers, such as rolling and flanging, laser welding, and MIG welding, face issues like loosening due to temperature and vibration, outgassing, stress cracks, and incompatibility with high-melting oxide skins, leading to integrity and reliability problems.
Innovation Solution
A friction welding method using a rotating friction tool with a cylindrical friction pin and collars of varying diameters, where the friction tool is inserted into the tube end and rotated to generate heat, plasticizing the tube end and surrounding tube sheet area to form a strong connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rolling and flanging are used to fix tubes in tube sheets, then the connection is sufficient at the start of operation, but the connections partially dissolve under temperature and vibration loads over time
Solution Approach 1:
The invention changes the fundamental parameter of the joining process from mechanical deformation (rolling/flanging) to friction-based plasticization. The friction tool rotates at high speed against the tube end, generating intense localized heat that plasticizes the material, creating a metallurgical bond that resists dissolution under thermal and vibrational loads.
Solution Approach 2:
The invention replaces the purely mechanical rolling and flanging process with a friction-based thermal-mechanical process. The rotating friction tool substitutes for traditional mechanical fastening methods, using frictional heat to create a plasticized connection zone that provides superior long-term reliability under operating conditions.
2Manufacturing precision
If YAG laser welding is used to weld tubes into tube sheets, then complex process control is required, but outgassing occurs resulting in pore formation
Solution Approach 1:
The invention replaces laser welding with a friction-based mechanical-thermal process. Instead of using laser energy to melt and fuse materials, a rotating friction tool generates heat through mechanical friction, plasticizing the materials without the outgassing problems inherent in laser welding of aluminum and its alloys.
Solution Approach 2:
The invention converts the harmful effect of friction (heat generation that could cause distortion) into a beneficial plasticization process. The frictional heat, which could be considered a harmful byproduct of mechanical contact, is instead utilized to create the plasticized connection zone that forms the basis of the reliable joint.
3Productivity
If YAG laser welding is used, then welding speed is high, but welding depth of 0.8 times pipe thickness cannot be achieved in all configurations
Solution Approach 1:
The invention changes the heat generation mechanism from laser energy to frictional heating, allowing for deeper penetration. The rotating friction tool can be pressed with sufficient force to generate intense localized heat that achieves the required 0.8 times pipe thickness welding depth, a level of penetration that cannot be consistently achieved with YAG laser welding in all geometric configurations.
4Shape
If MIG welding is used to achieve visually good appearance, then stress cracks reaching just below the surface repeatedly occur
Solution Approach 1:
The invention replaces MIG welding with friction-based plasticization. This substitution eliminates the complex heat conduction patterns of arc welding that cause stress cracks, while still achieving a sound structural connection. The friction process creates a more uniform thermal field that avoids the localized overheating and subsequent cracking problems of MIG welding.
5Strength
If fusion welding is used on aluminum with oxide skins, then high energies are required to melt the oxides, but this negatively impacts the lower-melting alloy components
Solution Approach 1:
The invention converts the presence of oxide skins, which are normally a barrier to welding, into part of the connection process. The friction tool plasticizes both the aluminum base material and the oxide layer, incorporating them into the connection zone. This approach uses the friction heat to break down and integrate the oxides rather than requiring their complete melting, thereby protecting the sensitive alloy components from excessive thermal damage.
Solution Approach 2:
The invention changes the thermal process from high-temperature fusion welding to lower-temperature friction plasticization. By using mechanical friction to generate heat locally and plasticize the materials, the process avoids the need to melt the high-melting-point oxide layer, thereby protecting the lower-melting aluminum alloy components from thermal damage while still achieving strong connections.
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 reliable and efficient connection that withstands temperature and vibration loads without outgassing or stress cracks, ensuring the integrity and durability of the heat exchanger connections.
Implementation Method 1
a rotating friction tool with a cylindrical friction pin and collars of varying diameters, where the friction tool is inserted into the tube end and rotated to generate heat
Implementation Method 2
pressed against the end face of the tube in such a way that the tube end and the area of the tube sheet surrounding the tube end can be plasticized and form a welded connection
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for joining a tube sheet (10) and tubes (11) in a tube bundle heat exchanger using a rotating friction tool. The friction tool is moved in a rotating direction into the open end of a tube (11) surrounded by the tube sheet (10) and pressed against the end face of the tube (11) in such a way that the tube end (12) and the area of the tube sheet (10) surrounding the tube end are plasticized and form a welded joint.