Brake Disc Coating Stack to Prevent Flaking and Oxidation
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Solution Overview
Problem
Brake discs made of grey cast iron or steel suffer from excessive wear and surface oxidation, leading to flaking of protective coatings, which compromises their durability and aesthetic appeal.
Innovation Solution
A method involving a nitrocarburized layer on the braking surface of brake discs, followed by a base protective coating of chromium carbide and nickel-chromium, and a surface protective coating of tungsten carbide, iron, and aluminum, applied using HVOF or HVAF techniques, enhances adhesion and reduces flaking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective coating is applied on grey cast iron or steel discs, then wear resistance is improved, but the coating is subject to flaking and detachment
Solution Approach 1:
The patent applies a preliminary nitrocarburization treatment to the disc surface before coating deposition. This creates a nitrocarburized layer that serves as an intermediate structure, improving adhesion between the base metal and the protective coating. The nitrocarburized layer is formed by diffusing nitrogen and carbon into the surface, creating a hardened, adherent base for subsequent coating application.
Solution Approach 2:
The patent creates a composite structure consisting of the base metal, nitrocarburized layer, and protective coating. This multi-layer composite approach combines the advantages of each layer: the base metal provides structural integrity, the nitrocarburized layer provides adhesion and hardness, and the protective coating provides wear resistance. The composite structure eliminates flaking by ensuring strong interfacial bonding.
2Reliability
If conventional protective coatings are applied using thermal spray techniques, then wear resistance is improved, but carbon combustion creates micro-bubbles that prevent adequate adhesion
Solution Approach 1:
The nitrocarburization treatment is performed before coating deposition to pre-harden the surface and create an adherent base. This preliminary action prevents carbon combustion issues during subsequent coating application by establishing a stable, nitrogen-enriched surface that does not contain free carbon that would combust and create micro-bubbles.
Solution Approach 2:
The patent changes the chemical composition parameters of the surface layer through nitrocarburization, creating a nitrogen and carbon-enriched layer with specific hardness and adhesion properties. This parameter change in the base layer prevents the carbon combustion problem during coating application by eliminating free carbon that would otherwise react with oxygen.
3Ease of manufacture
If grey cast iron or steel discs are used, then cost is reduced and good braking performance is achieved, but excessive wear and surface oxidation occur
Solution Approach 1:
The nitrocarburization treatment is applied as a preliminary step to enhance the wear resistance and corrosion resistance of the economical grey cast iron or steel discs. This surface treatment maintains the cost advantage of using base metal while adding protective properties through diffusion hardening and oxide layer formation.
Solution Approach 2:
The patent creates a composite structure where the economical base metal is combined with a nitrocarburized surface layer and protective coating. This composite approach maintains the cost benefits of grey cast iron or steel while adding the wear and corrosion resistance properties of the nitrocarburized layer and coating, avoiding the need to use expensive carbon or carbo-ceramic materials.
4Ease of manufacture
If grey cast iron or steel discs are used, then cost is reduced, but excessive surface oxidation leads to rust formation and aesthetic degradation
Solution Approach 1:
The nitrocarburization treatment is applied preliminarily to create a protective surface layer that prevents oxidation of the base metal. This preliminary protective action forms a dense, adherent layer that acts as a barrier against oxygen, preventing rust formation and maintaining aesthetic appearance while keeping the base material economical.
Solution Approach 2:
The composite structure of base metal plus nitrocarburized layer plus protective coating provides oxidation resistance. The nitrocarburized layer contains chromium carbide and nickel-chromium that form protective oxide barriers, preventing the base metal from oxidizing and rusting, thereby maintaining both aesthetic appearance and structural integrity at lower cost.
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 significantly reduces flaking and improves wear resistance, maintaining the integrity and appearance of the brake discs by providing enhanced mechanical adhesion and anti-corrosion properties.
Implementation Method 1
subjecting at least one of said braking surfaces to a working process designed to increase the surface roughness; nitrocarburizing the braking surface with increased surface roughness obtaining on such a surface a nitrocarburized layer
Implementation Method 2
depositing on the nitrocarburized layer a material in particle form consisting of chromium carbide and nickel-chromium with a spray deposition technique, preferably HVOF technique
Implementation Method 3
depositing on the base protective coating a material in particle form consisting of tungsten carbide, iron, chromium and aluminum with a spray deposition technique, preferably with HVOF technique or by HVAF technique
Data Source
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AI summary
The present invention relates to a method for making a brake disc, comprising the following operating steps: a) preparing a brake disc, comprising a braking band 2 provided with two opposite braking surfaces 2a, 2b, each of which defines at least partially one of the two main faces of the disc, the braking band being made of grey cast iron or steel; (b) subjecting at least one of said braking surfaces to a working process adapted to increase the surface roughness thereof; c) nitrocarburizing said braking surface with increased surface roughness obtaining on said surface a nitrocarburized surface layer 300; (d) depositing on said nitrocarburized surface layer a material in particle form consisting of: Cr3C2 and NiCr, or NiCr, Fe, Mo, Co, Mn and Al, by means of a spray deposition technique, preferably by means of an HVOF technique, or an HVAF technique or a KM technique forming a base protective coating 30 which covers at least one of the two braking surfaces of the braking band with the interposition of said nitrocarburized layer; and e) depositing on said base protective coating a material in particle form consisting of WC, Fe, Cr and Al, by means of a spray deposition technique, preferably by means of an HVOF technique, or an HVAF technique or a KM technique, thus forming a surface protective coating 3 which consists of WC and Fe, Cr and A1 and which covers at least one of the two braking surfaces of the braking band.