Copper-Coated Steel Wire Roughness Control for Twist Crack Resistance
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Solution Overview
Problem
Copper-coated steel wires experience cracking at the interface between the copper coating and the steel core when twisted, leading to degraded electrical conductivity and potential rupture of the wire.
Innovation Solution
The copper-coated steel wire features a core wire made of steel with a specific surface roughness, allowing for increased bonding strength between the core and the copper coating, thereby reducing cracking at their interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the copper coating is applied on a smooth steel core surface, then the electrical conductivity is maintained, but the bonding strength between coating and core is insufficient causing cracking during twisting
Solution Approach 1:
The patent applies different surface qualities to different regions: the bulk core wire maintains smoothness for electrical conductivity, while the outer peripheral surface is intentionally roughened to provide anchoring for the copper coating. This local differentiation of surface quality resolves the contradiction between bonding strength and electrical conductivity.
Solution Approach 2:
The core wire surface is roughened in advance before the copper coating is applied. This preliminary action creates surface irregularities that will interlock with the coating material, ensuring strong bonding before the coating process occurs, thereby preventing cracking during subsequent twisting operations.
2Strength
If the steel core wire has high surface roughness, then the bonding strength with copper coating increases, but the electrical conductivity deteriorates due to increased resistance
Solution Approach 1:
The patent carefully controls the roughness to be localized only on the outer peripheral surface where the coating contacts, while the bulk material and inner surface regions remain smooth. This selective localization ensures that roughness provides bonding strength without creating excessive resistance paths that would degrade electrical conductivity.
Solution Approach 2:
The patent optimizes the surface roughness parameters (Ra and Rz values) to specific ranges that provide sufficient bonding strength while minimizing the impact on electrical conductivity. By precisely controlling these parameter values, the patent resolves the contradiction between needing roughness for bonding and smoothness for conductivity.
3Reliability
If the copper coating layer is made thicker, then the electrical conductivity improves, but the roughness-to-thickness ratio decreases reducing bonding strength
Solution Approach 1:
The patent maintains a controlled roughness-to-coating-thickness ratio by locally concentrating the roughness effect at the interface region. This allows the coating to be sufficiently thick for good electrical conductivity while ensuring the interface region has adequate roughness characteristics for strong bonding, resolving the contradiction between thickness and bonding strength.
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
This solution effectively reduces the occurrence of cracking at the interface between the copper coating and the steel core, enhancing the durability and electrical conductivity of the copper-coated steel wire.
Implementation Method 1
the outer peripheral surface of the core wire is roughened, thereby increasing bonding strength between the core wire and the coating layer
Data Source
AI summary
A copper-coated steel wire includes a core wire made of a steel and a coating layer that covers the outer peripheral surface of the core wire and is made of copper or a copper alloy. In a cross section perpendicular to the longitudinal direction of the core wire, the ten-point average roughness Rzjis of the outer peripheral surface of the core wire is 50% or more and 250% or less of the thickness of the coating layer.