Etched Aluminium Brazing Sheet for Flux-Free CAB Stability
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Solution Overview
Problem
Current brazing processes for aluminum heat exchangers face challenges such as clogging due to flux residues, health and environmental concerns, and difficulty in applying flux to complex structures, necessitating a flux-free but flux-tolerant solution for controlled atmosphere brazing (CAB) that stabilizes brazing performance.
Innovation Solution
A pre-treated aluminum multilayer brazing sheet with a core layer of 3xxx alloy containing 0.1 to 0.25 wt.% Mg, clad with a 4xxx alloy layer on both sides, optionally including an interlayer, surface-treated with an alkaline or acidic etchant, for use in flux-free CAB, allowing for stable brazing performance and tolerance to flux residues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If flux is used in controlled atmosphere brazing to facilitate the process and prevent oxidation, then brazing ease is improved, but flux residues cause clogging of cooling liquid circulation and increase in viscosity
Solution Approach 1:
The invention extracts and eliminates the flux substance from the brazing process entirely. By using a pre-treated brazing sheet with modified surface properties, the process achieves fluxless brazing, removing the source of harmful flux residues that cause clogging and viscosity increase in cooling liquid circulation systems.
Solution Approach 2:
The invention uses a disposable pre-treated brazing sheet where the surface treatment layer is consumed during brazing to create the necessary metallurgical bond. This single-use treatment eliminates the need for flux application and removal, preventing residue formation while maintaining brazing effectiveness.
2Manufacturing precision
If flux is applied to complex shaped structures to enable brazing, then brazing coverage is improved, but flux application difficulty and quantity of flux residues increase
Solution Approach 1:
The invention applies the necessary surface treatment to the brazing sheet during manufacturing, before the actual brazing process. This preliminary action ensures that the entire surface, including complex geometries, is pre-conditioned for brazing without requiring difficult post-manufacturing flux application steps.
Solution Approach 2:
The pre-treated brazing sheet provides universal brazing capability across all surface geometries. The surface treatment creates a consistent reactive layer that enables reliable brazing on flat, curved, and complex shaped surfaces without requiring different application methods or increased flux quantities.
3Reliability
If magnesium is added to aluminium alloys for vacuum brazing to disrupt oxide film, then brazing quality is improved, but excess magnesium condenses on cold spots and requires frequent removal
Solution Approach 1:
The invention extracts the magnesium element from the brazing alloy composition and replaces it with alternative surface treatment methods. This eliminates the magnesium evaporation and condensation cycle that disrupts furnace operation, allowing continuous production without frequent interruptions for cold spot cleaning.
Solution Approach 2:
The invention changes the chemical composition parameters of the brazing alloy by reducing or eliminating magnesium content. Instead of relying on magnesium's oxide-disrupting properties, the invention uses controlled surface treatment and alternative alloying elements to achieve reliable brazing without the adverse effects of excess magnesium condensation.
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 provides stable and reproducible brazing quality, reducing clogging issues and environmental concerns, while being compatible with existing equipment, and is particularly advantageous for producing heat exchangers with high cleanliness requirements.
Implementation Method 1
The etching of the Al—Si filler layer includes an alkaline or acidic etchant
Data Source
AI summary
The present invention relates to a process for the production of an aluminium multilayer brazing sheet which comprises a core layer made of a 3xxx alloy comprising 0.1 to 0.25 wt. % Mg, a brazing layer made of a 4xxx alloy on one or both sides of the core layer, and optionally an interlayer between the core layer and the brazing layer on one or both sides of the core layer, the process comprising the successive steps of:providing the layers to be assembled or simultaneous casting of the layers to obtain a sandwich;rolling of the resulting sandwich to obtain a sheet; andtreating the surface of the sheet with an alkaline or acidic etchant.