Composite Brazing Alloy for Plate Heat Exchangers With Low Erosion
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Solution Overview
Problem
Brazing materials used in plate heat exchangers often result in either porous joints or erosion of the base material due to melting point depressants, which can lead to 'burn-through' and reduced joint strength, especially when using nickel or stainless steel with Silicon, Boron, and Phosphorous as melting point depressants.
Innovation Solution
A brazing material blend comprising grains of melting and non-melting alloys, where the melting alloy has a solidus and liquidus temperature lower than the brazing temperature and the non-melting alloy has temperatures higher than the brazing temperature, with a ratio that ensures the formed alloy has a solidus temperature below and liquidus temperature above the brazing temperature, utilizing Boron as a melting point depressant and matching the composition of the heat exchanger plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a stainless steel based brazing material with melting point depressants (Silicon, Boron, Phosphorous) is used, then the brazing temperature is reduced, but the melting point depressants migrate into the base material causing erosion and burn-throughs
Solution Approach 1:
The brazing material is divided into two distinct components: melting grains (providing low melting point depressants) and non-melting grains (resisting erosion). This segmentation allows each component to perform its specific function without the harmful effects of the other - the melting grains lower the brazing temperature while the non-melting grains prevent migration-induced erosion
Solution Approach 2:
Different regions of the brazing material have different properties: the melting grains are designed to decompose and provide melting point depressants locally at the brazing interface, while the non-melting grains maintain structural integrity and prevent erosion. This local differentiation of material properties resolves the contradiction between achieving low brazing temperature and preventing base material damage
2Object-affected harmful factors
If the amount of melting point depressants is reduced so the brazing material does not melt, then erosion is minimized, but the joint becomes porous and weak
Solution Approach 1:
The invention merges two types of brazing material grains with opposite characteristics into a single composite brazing material. The melting grains provide the necessary melting point depression for strong diffusion bonding, while the non-melting grains prevent erosion. Together they achieve both low erosion and high joint strength that neither component could achieve alone
3Adaptability or versatility
If nickel is used as a brazing material, then copper-free brazing is achieved, but the melting point depressants produce brittle brazing joints
Solution Approach 1:
The brazing material is formulated as a composite system containing nickel base alloy with a controlled mixture of melting and non-melting grains. This composite structure allows the use of necessary melting point depressants (like Boron and Silicon) for achieving low brazing temperatures compatible with ammonia refrigerant applications, while the non-melting grains prevent excessive concentration of these depressants that would cause brittleness
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 approach reduces porosity and erosion of the base material while maintaining joint strength, as the melting brazing material's rapid diffusion and high melting point decrease effect are controlled, resulting in a strong and pore-free brazing joint with minimal base material erosion.
Implementation Method 1
the melting brazing material grains comprising boron as a melting point lowering element... the ratio between the melting and non-melting brazing materials is such that an alloy formed by the melting and non-melting brazing materials
Implementation Method 2
heated to a temperature between the solidus and liquidus temperatures of the formed alloy
Implementation Method 3
the brazing material is melted whereas the materials to be joined are not
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A brazing material for brazing a brazed plate heat exchanger comprising a number of heat exchanger plates being provided with a pressed pattern of ridges and grooves adapted to provide contact points between neighbouring heat exchanger plates, such that the heat exchanger plates are kept on a distance from one another and such that interplate flow channels for media to exchange heat are formed between the heat exchanger plates comprises a brazing alloy comprising at least one melting point depressing element and metals resembling the composition of the heat exchanger plates. The brazing material comprises a mixture between grains of a melting brazing material having solidus and liquidus temperatures lower than a brazing temperature and a non- melting brazing material having solidus and liquidus temperatures above the brazing temperature. The ratio between the melting and non-melting brazing materials is such that an alloy formed by the melting and non-melting brazing materials has a solidus temperature lower than the brazing temperature and a liquidus temperature higher than the brazing temperature. To be published with Fig 1.