Dual-Layer Brazing Coating for Heat Exchanger Micro-Interstices
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Solution Overview
Problem
The challenge in manufacturing small heat exchangers is the difficulty in brazing closing bars onto accordion-folded sheet metal parts with micro-interstices, which requires precise control of filler alloys and multiple brazing steps, and there is a need to reduce the bulk and mass of thermal circuits while minimizing fluid usage.
Innovation Solution
A brazing method involving a coating with a first layer of metal or metal alloy powder and a second layer of nickel-based alloy powders, where the first layer is non-fusible at the heating temperature and the second layer partially melts to form a solidified residue that seals the interstices, reducing the need for multiple brazing steps and allowing for the production of small exchangers with reduced material usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple brazing steps are used to seal micro-interstices in small heat exchangers, then sealing reliability is improved, but manufacturing complexity and production time increase
Solution Approach 1:
The coating is divided into two distinct layers with different functions: the first layer (non-fusible metal powder) provides structural support and prevents excessive filler penetration, while the second layer (brazing alloy powder) melts to seal the interstices. This segmentation allows each layer to be optimized for its specific function, achieving reliable sealing in a single brazing step.
Solution Approach 2:
The invention changes the temperature parameter by heating to a specific range (Ts3 < T ≤ Ts2) that selectively melts the second layer while keeping the first layer solid. This parameter control enables the dual-layer coating to function as intended, with the non-fusible layer providing structure and the fusible layer providing sealing, thereby achieving reliable seals without multiple brazing steps.
2Manufacturing precision
If multiple brazing steps with machining operations are performed, then sealing quality is improved, but production time and manufacturing cost increase
Solution Approach 1:
The invention merges the sealing function and the structural support function into a single dual-layer coating applied in one step. The first layer provides structural integrity while the second layer provides sealing, both achieving their purposes simultaneously during a single brazing operation, thereby eliminating the need for multiple separate brazing and machining steps.
Solution Approach 2:
The dual-layer coating is applied in advance before the brazing process, with the first layer already in position to prevent excessive filler penetration. This preliminary preparation ensures that when heating occurs, the sealing process proceeds correctly without requiring subsequent corrective machining operations, thus reducing production time.
3Loss of substance
If the exchanger size is reduced to minimize bulk and fluid usage, then environmental impact is reduced, but brazing difficulty increases due to micro-interstices
Solution Approach 1:
The invention applies different properties to different parts of the coating: the first layer has non-fusible properties to provide local structural support at the interstices, while the second layer has fusible properties to provide local sealing. This local differentiation of material properties allows the coating to address the specific challenges of micro-interstices in compact exchangers, enabling successful brazing despite the reduced size and micro-scale features.
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 effectively seals interstices in small heat exchangers with a solidified residue, minimizing material usage and reducing the number of brazing steps, thereby enabling the cost-effective production of compact heat exchangers with improved thermal efficiency.
Implementation Method 1
heating with at least partial melting of the coating
Implementation Method 2
the second layer comprising a mixture of a second powder and a third powder... one and/or the other of these alloys for example being a nickel alloy, the second powder having a solidus temperature TSB, and the third powder having a solidus temperature TSC strictly lower than the solidus temperature TSB
Data Source
AI summary
Method for brazing or refilling comprising the following steps:providing at least one part (51) containing a metal or metal alloy, for example stainless steel, the part (51) having at least one face (59) defining a plurality of interstices (61) comprising at least two opposite edges separated on the face (59) by a maximum distance of not more than 250 micrometres;obtaining a coating (R) in contact with said face and comprising at least a first layer (85), located at least partially in the interstices, and a second layer (87) adjacent to the first layer, the first layer (85) comprising a first powder (A) containing a metal or metal alloy, the second layer comprising a mixture of a second powder (B) and a third powder (C), the second powder and the third powder being, respectively, different alloys suitable for brazing or refilling the part, and the solidus temperature TSC of the third powder being lower than the solidus temperature TSB of the second powder;heating the part and the coating at a heating temperature strictly lower than the solidus temperature TSA of the first powder, lower than the solidus temperature TSB, and strictly higher than the solidus temperature TSC, and at least partially melting the coating; andcooling the part and the coating to obtain a solidified residue attached to the part.