Heat Exchanger Brazing Screen for Fluxless Mg Vapor Control
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Solution Overview
Problem
Existing brazing methods for heat exchangers using aluminum alloy cladded materials face challenges such as the need for flux, complex equipment, and low mass-productivity, particularly in CAB and VB methods, with issues like flux residue and high vacuum furnace costs.
Innovation Solution
A screen formed from a metal sheet is used to enclose a stacked body of core plates, maintaining a specific gap with the taper portions, capturing vaporized Mg to prevent dispersion and oxygen/moisture interference, allowing brazing without flux or vacuum furnaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CAB method is used with flux coating, then brazing can be performed under atmospheric pressure with short cycle time, but flux residue cleaning is required and equipment cost increases
Solution Approach 1:
The invention extracts and removes the flux from the brazing process entirely. By using a metal cover to create a localized reducing atmosphere, the process eliminates the need for flux coating and subsequent cleaning operations, while still enabling successful brazing under atmospheric pressure conditions.
Solution Approach 2:
The metal cover creates a localized inert or reducing atmosphere environment around the workpiece during brazing. This confined atmosphere prevents oxidation and enables fluxless brazing, combining the advantages of both CAB and VB methods without their respective drawbacks.
2Ease of manufacture
If VB method is used with vacuum furnace, then flux is not required, but mass-productivity is low and equipment cost is very high
Solution Approach 1:
The invention segments the furnace atmosphere into two zones: a general atmospheric pressure environment for most of the furnace volume, and a localized covered zone around the workpiece where fluxless brazing occurs. This allows high-speed atmospheric brazing while maintaining the fluxless advantage locally.
Solution Approach 2:
The metal cover acts as an intermediary element that creates a protective atmosphere environment around the workpiece without requiring the entire furnace to be under vacuum. This mediator enables fluxless brazing while maintaining atmospheric pressure conditions for high productivity.
3Ease of manufacture
If box-shaped cover is used over support stand, then fluxless brazing is enabled, but gap management becomes difficult and operation process is troublesome
Solution Approach 1:
Instead of placing the cover over the workpiece on a support stand (complex approach), the invention inverts the approach by integrating the cover directly with the workpiece structure itself, making the workpiece self-contained and eliminating separate cover attachment operations.
Solution Approach 2:
The invention merges the cover and workpiece into a single integrated structure. By forming the cover as an integral part of the workpiece rather than a separate component, the design eliminates gap management issues and simplifies the operation process while maintaining fluxless brazing capabilities.
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
Enables efficient brazing of heat exchangers with improved brazing properties and reduced complexity and cost by preventing Mg dispersion, thus eliminating the need for flux and vacuum furnaces.
Implementation Method 1
the evaporated Mg captures traces of oxygen and moisture which are brazing inhibitory substances
Implementation Method 2
the evaporated Mg captures traces of oxygen and moisture which are brazing inhibitory substances which exist near the surface
Implementation Method 3
Heating the Mg in the furnace breaks down the oxide film on the surface of the brazing material layer of the brazing sheet
Implementation Method 4
a melted brazing material spreads into an interstice between members due to surface tension and a bond between the members is formed
Implementation Method 5
the radiant heat of the furnace has no effect on the workpiece
Data Source
AI summary
A screen for brazing a heat exchanger including a plurality of core plates and a base plate. The plurality of core plates may be formed from an aluminum alloy brazing sheet containing magnesium and may have a shape having a taper portion at a periphery. The base plate may be larger and thicker than a core plate of the plurality of core plates. The plurality of core plates and the base plate may be heated and brazed under an inert gas atmosphere. The screen may include a metal tube enclosing a stacked body of the plurality of core plates. The tube may follow the outer border of the plurality of core plates such that a specific minute gap is defined between an inner wall face of the tube and a tip edge of the taper portion.