Rectangular Insulated Wire Coating for Crack-Resistant Bending
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Solution Overview
Problem
Insulated wires with rectangular cross-sections are prone to cracking during bending due to their brittle corner portions, which compromises the space factor and dielectric breakdown strength, especially in applications requiring high bending workability and downsizing.
Innovation Solution
The insulated wire features a thermoplastic resin insulating coat layer with specific thickness ratios and compositions that enhance edge-wise and flat-wise bending workability, maintaining dielectric breakdown strength and preventing cracks, even after extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a rectangular wire is used to increase the space factor, then the space factor is dramatically increased, but the corner portion becomes extremely brittle to bending working and the coated film cracks
Solution Approach 1:
The insulating coat layer is designed with different thicknesses at different locations: a first thickness at the corner portion, a second thickness at the side surface, and a third thickness at the flat surface. This local differentiation allows the corner portion (which experiences higher stress during bending) to have sufficient insulation thickness to prevent cracking, while other areas maintain optimized thickness for space factor.
Solution Approach 2:
The invention specifies precise thickness parameters for the insulating coat layer at different locations. The thickness ratio relationship (first thickness : second thickness : third thickness) is controlled within specific ranges to optimize both bending workability and space factor. By changing the thickness parameters locally, the wire achieves improved reliability during bending while maintaining high productivity through increased space factor.
2Reliability
If the insulating film is thickened to increase the partial discharge inception voltage, then the insulating property is improved, but the space factor is lowered
Solution Approach 1:
Instead of uniformly thickening the insulating film across the entire wire surface, the invention applies different thicknesses at different locations. The corner portion receives a greater thickness (first thickness) to enhance partial discharge inception voltage where electrical stress is highest, while side surfaces and flat surfaces have optimized but thinner coatings (second and third thicknesses), thereby maintaining higher space factor.
Solution Approach 2:
The invention controls the thickness parameters of the insulating coat layer with specific numerical relationships. By setting the first thickness (at corner) to be greater than the second and third thicknesses within defined ratios, the design achieves improved partial discharge inception voltage at critical locations without proportionally increasing the overall insulation thickness, thus preserving space factor.
3Productivity
If the insulating film is thinned for downsizing, then the space factor is increased, but the insulating film tears easily when the corner portion is grazed
Solution Approach 1:
The insulating coat layer is designed with location-specific thicknesses to address the vulnerability of thinned films. The corner portion maintains a greater thickness (first thickness) compared to side surfaces (second thickness) and flat surfaces (third thickness), providing enhanced mechanical strength and tear resistance at the most vulnerable location, while allowing overall downsizing and improved space factor.
Solution Approach 2:
By precisely controlling the thickness parameters of the insulating coat layer and establishing specific ratio relationships between different locations, the invention enables film thinning for downsizing while preventing tear failure. The first thickness at the corner is maintained at a higher level relative to other areas, ensuring sufficient strength to prevent tearing during handling and installation, even as overall insulation thickness is reduced for improved space factor.
Data Source
Figure 1~3
AI summary
An insulated wire having an insulating coat layer comprising a thermoplastic resin on the outer peripheral surface of a conductor having a rectangular cross-sectional shape and also having a long side, a short side, and a corner portion having a curvature radius Rc, wherein a thickness t1 (µm) of the insulating coat layer covered on the surface which is continuing in an axial direction of the conductor, and which layer includes a long side of a transverse section of the conductor, a thickness t2 (µm) of the insulating coat layer covered on the surface which is continuing in the axial direction of the conductor, and which layer includes a short side of the transverse section of the conductor, and a corner portion thickness t3 (µm) of the insulating coat layer satisfy the relationship of formula (1): t3/t1+t2/2≥1.2 wherein the t1 (µm) and t2 (µm) are each independently 20 µm or more and 50 µm or less, and wherein a ratio of a cross-sectional area Sc (mm2) of the conductor to a cross-sectional area Sw (mm2) of the insulated wire satisfies the relationship of formula (2) 1.0>Sc/Sw≥0.8; as well as a coil and an electric or electronic equipment using the same.