Metallic Foil Surface Roughness for Honeycomb Body Brazing
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Solution Overview
Problem
Existing metallic foils for producing honeycomb bodies in exhaust-gas systems of internal combustion engines face challenges in high-temperature corrosion resistance, adhesion of catalytically active coatings, and stability due to inconsistent connecting techniques, particularly diffusion connections at contact points.
Innovation Solution
A metallic foil with a high-temperature-resistant material having a mean surface roughness of greater than 0.3 μm and an oxide coat thickness of 60-80 nm, specifically γ-aluminum oxide, is used to enhance brazing and prevent unwanted diffusion connections, allowing for selective and stable connections through high-temperature vacuum brazing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective oxide coat is formed on the foil surface for high-temperature corrosion resistance, then corrosion resistance is improved, but adhesion of catalytic coatings deteriorates
Solution Approach 1:
The patent applies local quality by creating different surface properties in different regions: the rear side maintains a thick protective oxide coat for corrosion resistance, while the front side has a reduced oxide coat thickness to enable good adhesion of catalytic coatings. This spatial differentiation resolves the contradiction between corrosion protection and coating adhesion.
2Stability of the object's composition
If foils are connected at all contact points for high stability, then structural stability is improved, but elasticity under thermal loading deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the connection strategy into two distinct segments: brazed connections at selected regions for structural stability, and non-brazed contact points for elasticity and thermal movement accommodation. This segmented approach resolves the contradiction between stability and adaptability.
3Manufacturing precision
If diffusion connections are prevented at certain contact regions for controlled connectivity, then connection precision is improved, but manufacturing complexity deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-forming the oxide coat on the foil surfaces before the brazing process. This preliminary oxide layer serves as a barrier that prevents unwanted diffusion connections at non-brazed contact points, thereby achieving connection precision without requiring complex post-processing or additional manufacturing steps.
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 improved high-temperature corrosion resistance, enhanced adhesion for catalytic coatings, and stable connections in honeycomb bodies, preventing unwanted diffusion connections while allowing targeted connection formation, ensuring durability and elasticity under thermal fluctuations.
Implementation Method 1
an oxide coat which has a thickness from 60 to 80 nm, preferably from 70 to 75 nm, in particular consisting substantially of γ-aluminum oxide... preventing unwanted diffusion connections
Implementation Method 2
Brazed connecting points, in particular high-temperature vacuum-brazed connecting points, are disposed between the adjacent foil layers only in selectively predetermined regions
Data Source
AI summary
A foil for producing a metal honeycomb or catalyst carrier body, has an average surface roughness of more than 0.3 μm (micrometers) on both surfaces in at least one measurement direction. Preferably, the foil is rolled and has an average surface roughness of more than 0.3 or 0.5 μm, especially approximately 0.6 μm, in the rolling direction and/or transverse thereto. The foil can have an oxide coating with a thickness between 60 and 80 or between 70 and 75 nm (nanometers) on both surfaces. Despite the roughness, an even thickness of the oxide coating with a tolerance of less than 10% or 5% is advantageous on both surfaces. The foil allows production of durable honeycomb bodies, especially for exhaust systems of internal combustion engines, requiring an exactly defined distribution and quality of compounds in the interior thereof. A honeycomb body and method of production using a foil, are also provided.