Cast Iron Brake Disc Surface Treatment for Graphite-Induced Corrosion
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Solution Overview
Problem
Current methods for improving the wear and corrosion resistance of brake discs, such as iDisc ™ and nitriding processes, face issues with delamination and graphite-induced corrosion, particularly in electric vehicles with varying driving cycles, where traditional coatings fail to provide long-term protection against corrosion.
Innovation Solution
A pulsed water jet process is used to selectively remove graphite inclusions from machined cavities in cast iron brake discs, followed by nitrocarburizing and oxidation to create a diffusion and oxide layer that delays corrosion, ensuring the graphite is kept distant from the diffusion zone and reducing the surface roughness to enhance adhesion and friction performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is applied to improve wear and corrosion resistance, then the corrosion and wear resistance is improved, but the coating delaminates due to thermal expansion differences causing cracks
Solution Approach 1:
The friction surface is roughened prior to coating application to create a mechanically interlocking surface structure. This preliminary surface preparation ensures that when the coating is applied later, it adheres strongly to the substrate, preventing delamination even under thermal stress during braking operations.
Solution Approach 2:
The roughening process creates localized undercuts and cavities in the friction surface that provide mechanical anchoring points for the coating. This local structural modification ensures that the coating adheres particularly well at the interface, while the bulk material properties remain unchanged.
2Reliability
If the friction surface is roughened to improve coating adhesion, then the coating adhesion is improved, but the surface becomes rougher requiring post-treatment and graphite inclusions remain as corrosion starting points
Solution Approach 1:
Graphite inclusions are selectively removed from the cavities created during the roughening process. This extraction eliminates the corrosion initiation sites that would otherwise remain in the surface structure, while preserving the mechanical interlocking features needed for coating adhesion.
Solution Approach 2:
A water jet process is used to remove graphite inclusions from the roughened surface cavities. This fluid-based method replaces traditional mechanical removal methods and effectively cleans out the harmful graphite while maintaining the beneficial surface roughness for coating adhesion.
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 process significantly improves corrosion resistance by ensuring the graphite is removed from the surface, allowing the diffusion layer to protect the cavities and preventing rapid corrosion, with the treated brake discs showing improved performance in salt spray tests, lasting up to 300 hours without visible corrosion compared to 10 hours with traditional methods.
Implementation Method 1
A pulsed water jet process is used to selectively remove graphite inclusions from machined cavities in cast iron brake discs
Implementation Method 2
followed by nitrocarburizing and oxidation to create a diffusion and oxide layer that delays corrosion
Implementation Method 3
followed by nitrocarburizing and oxidation to create a diffusion and oxide layer
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 2C~2D
AI summary
The invention concerns Method for producing a mechanically and preferably machined cast iron or grey cast iron surface, in particular on a brake disc, with increased wear and corrosion resistance, characterized in that said surface is subjected to a water jet treatment - usually according to the so-called fluid jet process, which is adjusted so that it completely or at least partially clears the cavities opened by the machining, which contain a graphite inclusion surrounded by the basic structure, so that in the latter case the level of the graphite inclusion lies below the outer surface of the basic structure surrounding the cavity, whereupon a diffusion layer is applied by nitrocarburizing and an oxide layer is applied on the diffusion layer.