Heat Exchanger Brazing Screen for Flux-Free Mg Vapor Containment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for brazing heat exchangers using aluminum alloy brazing sheets face challenges such as the need for flux in CAB methods and the high cost and low productivity of VB methods, as well as complications with flux residue and vacuum furnace equipment.
Innovation Solution
A screen formed from a metal sheet is used to enclose a stacked body of core plates with taper portions, allowing for brazing without flux or a vacuum furnace. The screen is mounted on a base plate and positioned to maintain a precise minute gap with the core plates, ensuring effective capture of oxygen and moisture by vaporized Mg.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CAB method with fluoride based flux is used, then brazing can be performed under atmospheric pressure with short cycle time, but flux coating process and flux residue cleaning process are required
Solution Approach 1:
The invention extracts and removes the flux from the brazing process entirely. By using a vacuum furnace to create a vacuum atmosphere, the harmful fluoride based flux is eliminated, and instead magnesium is used as a brazing aid that does not require coating or cleaning processes.
Solution Approach 2:
The invention creates an inert vacuum atmosphere in the furnace to protect the brazing materials from oxidation. This vacuum environment replaces the atmospheric pressure environment with flux, allowing brazing without the need for flux coating and cleaning processes.
2Reliability
If VB method under high vacuum is used, then flux is not required, but mass-productivity is low due to batch processing and equipment cost is high
Solution Approach 1:
The invention changes the vacuum parameter from high vacuum to atmospheric pressure vacuum. This allows the use of simpler, less expensive equipment while maintaining the benefits of vacuum brazing. The magnesium is heated to vaporize and protect the brazing interface without requiring extreme vacuum conditions.
Solution Approach 2:
The invention replaces the complex high vacuum mechanical system with a simpler atmospheric pressure vacuum system using magnesium vapor. This substitution maintains brazing quality while improving productivity and reducing equipment costs.
3Reliability
If cover-shaped windscreen jig is used to enable brazing without flux, then flux drawbacks are avoided, but mechanism for raising and lowering the jig inside furnace is required making furnace complex and costly
Solution Approach 1:
The invention makes the brazing process self-service by using magnesium that naturally vaporizes when heated to protect the brazing interface. This eliminates the need for external cover-shaped windscreen jigs and their raising/lowering mechanisms, simplifying the furnace design.
Solution Approach 2:
The invention changes the approach from using physical barriers (covers) to using chemical protection (magnesium vapor). This parameter change eliminates the need for complex mechanical raising and lowering mechanisms while maintaining protection from oxidation.
4Reliability
If box-shaped cover is placed over support stand, then brazing without flux is enabled, but strict management of gaps between cover and workpiece is difficult and operation process is troublesome
Solution Approach 1:
The invention applies protection locally at the brazing interface through magnesium vapor rather than using a global physical cover. This localized approach eliminates the need to manage gaps between covers and workpieces, simplifying the operation process.
Solution Approach 2:
The invention replaces the mechanical box-shaped cover system with a vapor-based protection system. This substitution eliminates the operational complexity of managing gaps and positioning covers, as the magnesium vapor automatically protects the brazing area.
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 enables efficient brazing of heat exchangers under an inert gas atmosphere, avoiding the drawbacks of flux and vacuum furnaces, while maintaining high brazing properties and productivity.
Implementation Method 1
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 2
Heating the Mg in the furnace breaks down the oxide film on the surface of the brazing material layer of the brazing sheet, and the evaporated Mg captures traces of oxygen and moisture
Implementation Method 3
A screen formed from a metal sheet is used to enclose a stacked body of core plates with taper portions, allowing for brazing without flux or a vacuum furnace. The screen is mounted on a base plate and positioned to maintain a precise minute gap with the core plates, ensuring effective capture of oxygen and moisture by vaporized Mg.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A heat exchanger (1) is configured by stacking core plates (4) formed from a brazing sheet on a base plate (2) together with fin plates (5) and then heating and brazing these. The core plates (4) have a taper portion (4a) at the periphery. The brazing sheet contains Mg. When performing brazing, a tube shaped screen (11) overlays the heat exchanger (1) to be brazed. Due to the screen (11), Mg vaporized from the brazing sheet does not disperse into the atmosphere but remains near the core portion (3), and this Mg captures oxygen and moisture near the brazing surface which hinder brazing properties. The screen (11) is supported on the base plate (2) and is conveyed together with the heat exchanger (1) to be brazed.