Non-Round Stranded Conductors for High Fatigue Strength

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Solution Overview

Problem

Conventional stranded conductors with round individual wires suffer from reduced fatigue strength under reverse bending stresses due to compacting procedures, which also increase production complexity and weight, particularly in applications where a circular cross-section and minimal wedges are desired.

Innovation Solution

Using non-round individual wires with a pre-formed cross-section, such as triangular or Reuleaux triangular shapes, arranged around a central inner wire to form a stranded conductor that is not compacted, thereby reducing wedges and eliminating the need for annealing, resulting in higher fatigue strength and a more circular cross-section.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If round individual wires are arranged around a central inner wire and compacted to achieve a circular cross-section, then the cross-sectional shape becomes more circular and insulation thickness is reduced, but the fatigue strength under reverse bending stresses is reduced and production complexity increases

Engineering Contradiction:

Improvecircular cross-sectionVSAvoidfatigue strength

Core Design Contradiction:

ShapeVSReliability

Solution Approach 1:

The individual wires are pre-formed with non-round cross-sections (triangular, rectangular, or other polygonal shapes) before being arranged around the central inner wire. This preliminary shaping eliminates the need for subsequent compacting to achieve a circular outer contour, thereby preserving the fatigue strength of the wires while still achieving a substantially circular overall cross-section for the stranded conductor

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The cross-sectional shape parameter of the individual wires is changed from round to non-round (triangular, rectangular, or other polygonal shapes). This parameter change allows the wires to pack together to form a circular outer contour without requiring mechanical compacting, thus maintaining the original mechanical properties and fatigue strength of the wires

Inventive Principle:

Principle #35Parameter changes

2Shape

If round individual wires are compacted to achieve a circular cross-section, then the cross-sectional shape becomes more circular, but additional process steps (annealing) are required and production complexity increases

Engineering Contradiction:

Improvecircular cross-sectionVSAvoidproduction process complexity

Core Design Contradiction:

ShapeVSDevice complexity

Solution Approach 1:

The non-round cross-sectional shapes are created during the wire drawing process before the stranding operation. By performing the shaping action in advance during manufacturing, the patent eliminates the need for post-stranding compacting and annealing operations, thereby simplifying the overall production process while achieving the desired circular outer contour

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of starting with round wires and compacting them into a circular shape, the patent inverts the approach by using pre-formed non-round wires that naturally pack into a circular configuration when stranded. This inversion of the conventional process eliminates complex compacting and heat treatment steps

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If round individual wires are arranged around a central inner wire, then the conductor can be manufactured, but wedge-shaped free spaces are formed on the circumferential side increasing the weight of insulation material required

Engineering Contradiction:

ImprovemanufacturabilityVSAvoidconductor weight

Core Design Contradiction:

Ease of manufactureVSWeight of moving object

Solution Approach 1:

The cross-sectional shape parameter of individual wires is changed from round to non-round shapes such as triangles or rectangles. These geometric shapes pack together more efficiently to form a circular outer contour, minimizing or eliminating the wedge-shaped free spaces that would otherwise require additional insulation material, thereby reducing the overall weight of the stranded conductor

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9887022B2Stranded conductors and method for producing stranded conductors

Publication Date: 2018.02.06 LEONI KABEL GMBH

AI summary

A stranded conductor contains a number of individual wires. The multiple identically designed individual wires are arranged about a central inner wire as outer wires. The individual wires form a composite which is encased by insulation, and the outer wires are uncompressed and have a non-round cross-section such that when seen in cross-section, the outer wires expand radially outwards starting from the inner wire. The composite of individual wires is not compressed such that the composite has a high alternate bending strength.