Fluxless Brazing Sheet Material Oxygen Partial Pressure Control
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Solution Overview
Problem
The existing brazing methods for sheet materials, particularly in heat exchangers, face challenges with oxide layer formation on brazing filler alloys, which reduces fluidity and brazability, and the use of flux can lead to residue issues and incomplete fillet formation.
Innovation Solution
A method that reduces the oxygen partial pressure in an inert gas atmosphere using an oxygen pump with a solid electrolyte to minimize oxide layer formation, allowing the brazing filler alloy to maintain high fluidity and form stable fillets without flux, by controlling the composition of the core and brazing filler alloys with specific ranges of Al, Mg, Si, and Mn.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux is used to remove oxide layer from brazing filler alloy, then fluidity of brazing filler alloy is improved, but flux residue causes clogging of heat exchanger passages
Solution Approach 1:
The harmful flux substance is completely removed from the brazing process. Instead of using flux to remove oxides, the patent employs an oxygen partial pressure control mechanism that prevents oxide formation on the brazing filler alloy surface during brazing, eliminating the need for flux and thus eliminating flux residue clogging issues.
Solution Approach 2:
The patent creates a controlled inert atmosphere by reducing oxygen partial pressure to 1×10^-10 Pa or less using an oxygen pump with solid electrolyte. This ultra-low oxygen environment prevents oxide layer formation on the brazing filler alloy, allowing fluxless brazing with maintained fluidity.
2Ease of manufacture
If Mg is added to destroy oxide layer without flux, then brazing can be performed without flux residue, but oxide layer reforms due to insufficient oxygen removal, reducing fluidity
Solution Approach 1:
The patent fundamentally changes the oxygen partial pressure parameter to 1×10^-10 Pa or less, which is significantly lower than conventional inert gas atmospheres. This extreme parameter change ensures that oxide layers do not reform during brazing, maintaining fluidity without requiring high Mg content or flux.
Solution Approach 2:
The patent replaces the chemical mechanism (Mg reacting with oxides) with a physical control mechanism (oxygen partial pressure control using solid electrolyte oxygen pump). This substitution provides more reliable and controllable prevention of oxide formation.
3Reliability
If oxygen partial pressure is reduced to prevent oxide formation, then fluidity is maintained, but complex oxygen pump equipment with solid electrolyte is required
Solution Approach 1:
The solid electrolyte oxygen pump serves multiple functions: it acts as both a vacuum pump to reduce oxygen partial pressure and as an oxygen sensor to monitor the atmosphere. This multi-functionality reduces the need for separate components and simplifies the overall system.
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 enhances the brazability of sheet materials by maintaining high fluidity and ensuring complete fillet formation, improving the quality of heat exchangers without the need for flux, as demonstrated by experiments showing high brazability scores across various compositions.
Implementation Method 1
an oxygen pump provided with a solid electrolyte having an oxygen ion conductivity
Implementation Method 2
a voltage is applied to the solid electrolyte to reduce the partial pressure of oxygen
Implementation Method 3
Mg has a property of destroying the oxide layer of the brazing filler alloy
Implementation Method 4
a method for brazing a sheet material without use of flux
Data Source
AI summary
In a method for brazing a sheet material without use of flux, an inert gas is firstly introduced into an oxygen pump to reduce an oxygen partial pressure in the inert gas to 1×10−10 Pa or less, and the sheet material is heated in a brazing furnace in an atmosphere of the inert gas discharged from the oxygen pump. A core alloy of the sheet material or a brazing filler alloy cladded to a surface of the core alloy contains Mg. Both the core alloy and the brazing filler alloy may contain Mg. Accordingly, brazability of the sheet material is sufficiently improved.