Brake Rotor Nanocrystallized Surface for Wear Resistance
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Solution Overview
Problem
Cast-iron brake rotors face accelerated wear and corrosion due to the formation of porous and fragile iron oxides from exposure to environmental substances, and existing methods of burnishing and nitrocarburizing may result in undesirable surface roughness when attempting to increase the thickness of the hardened casing for improved wear and corrosion resistance.
Innovation Solution
A method involving machining and burnishing to create a nanocrystallized microstructure on the friction surface of brake rotors, followed by nitrocarburizing, which allows for a thicker hardened casing without damaging the surface, achieving a surface roughness of less than 3 microns and enhanced wear and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If greater force is applied during burnishing to increase nanocrystallized layer thickness, then hardened casing thickness is improved, but surface roughness deteriorates (Ra > 3 microns)
Solution Approach 1:
The patent applies preliminary machining (turning) at high feed rates (0.25-1.00 mm/rev) and cutting depths (0.2-0.8 mm) to create a nanocrystallized microstructure layer before burnishing. This preliminary action prepares the surface with the desired nanocrystalline structure that will later facilitate nitrogen and carbon diffusion, eliminating the need for excessive burnishing force that would damage surface roughness
Solution Approach 2:
The patent replaces the traditional mechanical burnishing process (which relies on high contact force) with a machining-based nanocrystallization approach. By using controlled machining parameters (high feed rate and cutting depth) to create the nanocrystallized layer, the process substitutes mechanical force with a controlled material removal and restructuring mechanism, achieving both thick hardened casing and smooth surface (Ra < 3 microns)
2Reliability
If traditional burnishing is used to form nanocrystallized layer, then wear resistance is improved, but corrosion resistance deteriorates due to porous iron oxide formation
Solution Approach 1:
The patent changes the microstructural parameters of the surface layer by creating a nanocrystallized microstructure through controlled machining. This parameter change (from microcrystalline to nanocrystalline structure) fundamentally alters the material properties, enabling both high wear resistance and improved corrosion resistance by preventing porous iron oxide formation while maintaining a smooth surface (Ra < 3 microns)
Solution Approach 2:
The patent creates a composite surface structure consisting of a nanocrystallized microstructure layer with embedded nitrogen and carbon atoms formed through nitrocarburizing. This composite structure combines the wear resistance benefits of nanocrystalline iron with the corrosion resistance benefits of nitrogen and carbon enrichment, producing a surface that resists both mechanical wear and chemical corrosion
3Reliability
If friction surface is exposed to harsh environment, then operational durability is tested, but iron oxide formation accelerates wear
Solution Approach 1:
The patent changes the surface microstructure from microcrystalline to nanocrystalline through controlled machining at high feed rates and cutting depths. This parameter change creates a denser, more refined grain structure that is resistant to oxidation and forms a protective barrier against the harsh operating environment, preventing accelerated wear while maintaining operational durability
Solution Approach 2:
The patent applies local quality improvement by creating a nanocrystallized microstructure layer specifically at the friction surface through controlled machining. This localized treatment concentrates the beneficial nanocrystalline structure where it is most needed (at the friction surface subject to wear and corrosion) while leaving the bulk material properties unchanged, providing enhanced protection exactly where the harsh environment causes damage
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 method effectively increases the thickness of the hardened casing on brake rotor friction surfaces while maintaining desirable surface quality, resulting in improved wear and corrosion resistance without compromising surface smoothness, thus extending the lifespan of brake components.
Implementation Method 1
A method of burnishing the friction surface by rubbing the surface against a blunt tool to form a nanocrystallized surface layer
Implementation Method 2
diffusing nitrogen atoms and carbon atoms through the nanocrystallized surface layer by a nitrocarburizing process
Implementation Method 3
nitrocarburizing the ferrous member at a time and temperature sufficient for the diffusion of nitrogen atoms and carbon atoms through the nanocrystallized microstructure layer to form a hardened casing
Data Source
AI summary
A method for manufacturing a ferrous rotational member including the steps of turning a first portion of the friction surface at a sufficient feed rate to provide a first deformed layer on the first portion of the friction surface; fine turning a second portion of the friction surface at a sufficient feed rate to provide a second deformed layer on the second portion of the friction surface; burnishing the first and second portions of the friction surface to achieve a predetermined roughness; and nitrocarburizing the rotational member at a time and temperature sufficient for the diffusion of nitrogen atoms and carbon atoms through the deformed layer to form hardened casings having variable thickness. The ferrous rotational member may be that of a brake rotor having a hub surface and a friction surface, where the hub surface and friction surface have a variable thickness hardened casing.