Piston Ring Coating Sequence for Crack-Resistant Transition Regions
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Solution Overview
Problem
Piston rings made of steel or cast steel with nitride layers are prone to chipping and cracking in transition regions between the running face and flank areas due to the susceptibility of nitrided surfaces and edges.
Innovation Solution
A method involving a steel or cast steel piston ring production process where the running face and transition regions are coated with a first chromium layer, which is then removed on the running face, and a nitride layer is applied to the running face, while maintaining the chromium layer in the transition regions, followed by a final chromium layer application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nitride layer is applied to all free surfaces of the piston ring to create wear resistance, then the wear resistance of the piston ring is improved, but the susceptibility to chipping and cracks in transition regions increases
Solution Approach 1:
The patent applies different surface treatments to different regions of the piston ring: the running face receives a nitride layer for wear resistance, while the transition regions are kept free of nitride layer to avoid chipping and cracking. This is achieved by selectively masking or removing the nitride layer from transition regions, creating locally optimized properties that resolve the contradiction between wear resistance and structural integrity.
2Reliability
If a chromium layer is applied over the nitride layer in transition regions to prevent chipping, then the protection against chipping is improved, but the complexity of the coating process increases
Solution Approach 1:
The patent applies a first chromium layer before nitriding, then removes it selectively from the running face area. This preliminary chromium layer serves as a base that prevents chipping in transition regions when removed from the running face, while avoiding the need for complex post-nitriding chromium application and removal processes.
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 creates nitride-layer-free transition regions, reducing chipping and cracking susceptibility in these areas, enhancing the piston ring's operational performance by maintaining the chromium layer in the transition regions.
Implementation Method 1
The first galvanically applied chromium layer is advantageously formed with a layer thickness of no more than 15 μm
Implementation Method 2
By way of a heat treatment process under a nitrogen atmosphere, a wear-resistant nitride layer can be generated on piston rings made of steel or cast steel
Implementation Method 3
The at least one final chromium layer is galvanically formed with a layer thickness between 5 and 20 μm
Data Source
AI summary
A piston ring is produced from a main body made of steel or cast steel and comprising a running face, an inner circumferential surface, upper and lower flank regions, and transition regions from the running face to the respective flank region, by coating the running face and the transition regions with a first chromium layer, removing this first chromium layer at the running face down to the base material of the main body, providing at least the running face of the layer-free main body with a nitride layer, and, finally, coating the running face and the transition regions with at least one further chromium layer.