Piston Ring Hard Coating for Scuffing Resistance
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Solution Overview
Problem
Piston rings in large two-stroke turbo-charged uniflow-scavenged internal combustion engines face challenges with scuffing due to high pressures and varying engine loads, leading to wear that causes sharp transitions and potential scraping of the cylinder oil film, increasing the risk of scuffing.
Innovation Solution
A piston ring design with a hard coating applied over the full outer circumferential face, where the medial surface area is harder than the peripheral areas, allowing the softer peripheral regions to wear faster and form a wedge-shaped recess that guides cylinder oil, reducing the risk of scraping and scuffing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hard coating is applied over the full outer circumferential face to increase wear resistance, then the durability and scuffing resistance is improved, but the peripheral areas do not wear faster to form the desired wedge-shaped recess, reducing oil distribution effectiveness
Solution Approach 1:
The patent applies different hardness properties to different regions of the piston ring. The medial portion has a hard coating (500-2500 HV) for wear resistance, while the peripheral portions have a softer material (100-400 HV) that wears faster to form the wedge-shaped recess. This local differentiation resolves the contradiction by providing both scuffing resistance and proper oil distribution geometry.
Solution Approach 2:
The piston ring uses a composite structure combining a hard coating layer on the medial portion with a softer peripheral material. This composite approach allows the hard region to prevent scuffing while the softer region shapes the oil-guiding wedge recess through differential wear, simultaneously achieving both contradictory requirements.
2Ease of operation
If the peripheral areas are made softer to form wedge-shaped recesses for oil guidance, then the oil distribution is improved, but the overall wear resistance and scuffing protection is reduced
Solution Approach 1:
The patent implements local quality differentiation where peripheral portions have softer material for oil guidance while the medial portion maintains hard coating for wear resistance. This resolves the contradiction by providing both functions in their respective locations without compromising overall reliability.
Solution Approach 2:
The piston ring is segmented into functional zones: peripheral portions for oil distribution (softer material) and medial portion for wear resistance (hard coating). This segmentation allows each zone to optimize its specific function while contributing to overall system performance.
3Reliability
If a rounded edge transition is used to distribute cylinder oil, then the oil film protection is improved, but the scraping effect needed to prevent excessive oil consumption is reduced
Solution Approach 1:
The patent creates local quality differences through differential wear of hard and soft regions, forming a wedge-shaped recess that provides controlled oil distribution. This resolves the contradiction by providing both rounded protection and controlled scraping effects through the geometry created by differential wear.
Solution Approach 2:
The piston ring is pre-formed with a barrel shape and differential hardness zones before operation. During initial wear, the softer peripheral areas recede to create the wedge-shaped recess, preliminarily establishing the optimal geometry for oil distribution and scraping balance.
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 design ensures durability through hard-coated medial areas while allowing peripheral regions to recede, forming a wedge-shaped recess that directs cylinder oil effectively, reducing the risk of scuffing and maintaining efficient lubrication.
Implementation Method 1
The medial portion of the outer circumferential face is provided with a hard coating and has a hardness of 500-2500 HV
Implementation Method 2
The first and second peripheral portions extend axially beyond the hard coating and have a hardness of 100-400 HV. The hardness of the first and second peripheral portions relative to the hardness of the medial portion is selected such that the surfaces of the first and second peripheral portions become, due to wear during use, receded relative to the surface of the medial portion
Implementation Method 3
forming a wedge-shaped recess that directs cylinder oil effectively
Data Source
Figure 1~2
Figure 3
Figure 4~12
AI summary
A piston ring (34,36) for use in a piston ring pack in an annular ring groove (33) in the sidewall of a piston (10) of a large two-stroke turbocharged uniflow-scavenged internal combustion engine with crossheads to seal against the pressure in the combustion chamber (32). The piston ring (34,36) comprises a ring body (50) with first- and second side faces (46,47) axially distanced by a ring height (Hr), an outer circumferential face (41) extending axially over the ring height (Hr), an inner circumferential face (42), and first- and second end portions (38,39) at a ring partition that allows expansion and contraction of the piston ring (34,36). A first transition between the outer circumferential face (41) and the first side face (46) is rounded, a second transition between the outer circumferential face (41) and the second side face (47) is rounded. A medial portion of the axial extent of the outer circumferential face (41) has a first hardness. A first peripheral portion of the axial extent of the outer circumferential face (41) that extends from the medial portion to the first transition has a second hardness. A second peripheral portion of the extent of the outer circumferential face (41) that extends from the medial portion to the second transition has the second hardness, and the first hardness is greater than the second hardness. Said first peripheral portion extends axially over a first height (HI) and is formed by material of the ring body (50), and said second peripheral portion extends axially over a second height (H2) and is formed by material of the ring body (50).