Copper-Coated Steel Wire Roughness Ratio for Interface Crack Suppression
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Solution Overview
Problem
Copper-coated steel wires used in applications with cyclic stress, such as canted coil springs, often experience cracks at the interface between the core wire and the coating layer, leading to decreased conductivity or material breakage.
Innovation Solution
A copper-coated steel wire with a core wire made of steel having a pearlite structure, containing specific compositions of C, Si, Mn, and other elements, and a surface roughness ratio between 25% and 70% of the coating layer thickness to enhance bonding strength and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper-coated steel wire is used in applications with cyclic stress, then conductivity and strength are achieved, but cracks occur at the interface between the core wire and coating layer
Solution Approach 1:
The patent applies local quality by creating a specific rough surface structure at the interface between the core wire and coating layer. The surface roughness Ra is controlled to be 25-70% of the coating layer thickness, which locally enhances the bonding strength at the critical interface region without affecting the overall conductivity of the copper coating. This localized structural modification prevents crack formation while maintaining the electrical conductivity function.
Solution Approach 2:
The patent implements preliminary action by pre-forming a rough surface structure on the core wire before applying the copper coating. The surface roughness is created in advance through controlled rolling or other surface treatment methods, ensuring that when the coating is applied, it adheres to a pre-optimized surface topology that prevents future crack formation under cyclic stress conditions.
2Strength
If the surface roughness Ra is increased to improve bonding strength, then interface crack resistance improves, but coating layer thickness must be increased
Solution Approach 1:
The patent applies parameter changes by establishing a specific quantitative relationship between surface roughness Ra and coating layer thickness. The surface roughness is controlled to be 25-70% of the coating layer thickness, which optimizes the bonding strength while minimizing the required coating thickness. This parameter optimization prevents excessive material usage while ensuring adequate interface strength to prevent cracking.
3Strength
If steel composition is optimized for strength with high carbon content, then core wire strength improves, but surface roughness control becomes more difficult
Solution Approach 1:
The patent applies parameter changes by specifying precise compositional ranges for the steel core wire: carbon content of 0.3-1.0%, silicon content of 0.01-2.5%, and manganese content of 0.03-0.9%. These controlled compositional parameters ensure both adequate strength and favorable surface properties that facilitate roughness control during manufacturing. The balanced composition prevents excessive carbide formation that would complicate surface finish control.
Data Source
AI summary
A copper-coated steel wire includes: a core wire made of steel having a pearlite structure; and a coating layer covering a surface of the core wire and made of Cu or a Cu alloy. The steel contains C by greater than or equal to 0.5% by mass and less than or equal to 1.0% by mass, Si by greater than or equal to 0.1% by mass and less than or equal to 2.5% by mass, Mn by greater than or equal to 0.3% by mass and less than or equal to 0.9% by mass, and the balance consisting of Fe and inevitable impurities. In a cross section perpendicular to a longitudinal direction, a value of surface roughness Ra of the core wire is greater than or equal to 25% and less than or equal to 70% of a thickness of the coating layer.