Flame Retardant Cable Multilayer Sheath Design
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Solution Overview
Problem
Current flame retardant electrical cables often fail to meet stringent international standards for low-voltage applications due to inadequate flame retardancy and mechanical properties, with existing solutions compromising either performance or mechanical integrity.
Innovation Solution
The cable features a core surrounded by a mica tape and a multilayered sheath with an inner LSOH layer having a high limiting oxygen index (LOI) greater than 70% and an outer LSOH layer with a LOI between 30% to 70%, enhancing flame retardancy and mechanical properties without impairing tensile strength or workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high contents of flame-retardant inorganic fillers are added to the outer sheath to achieve suitable flame-retardant properties, then flame retardancy is improved, but mechanical properties deteriorate
Solution Approach 1:
The cable is divided into distinct functional layers: an inner sheath layer containing flame-retardant inorganic fillers (magnesium hydroxide, alumina trihydrate) for fire protection, and an outer protective layer providing mechanical strength and flexibility. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The cable employs composite material construction with the inner sheath layer combining polymer matrix (polyethylene, polypropylene, or elastomers) with flame-retardant inorganic fillers (20-60 wt%). The outer protective layer uses separate polymer materials to provide mechanical properties, creating a composite structure that achieves both flame retardancy and mechanical integrity.
2Reliability
If mica-containing tape wrapping is applied to protect the conductor metal, then flame retardant performance is improved, but gaps around the conductor may form compromising electric insulation
Solution Approach 1:
The invention replaces rigid mica-containing tape wrapping with a flexible inner sheath layer made of polymer material containing flame-retardant inorganic fillers. This flexible layer conformally surrounds the conductors, ensuring complete coverage without gaps while maintaining flame retardant performance through the filler-containing composite material.
3Reliability
If a multilayered sheath with high LOI inner layer is used to enhance flame retardancy, then certification in higher classes is achieved, but manufacturing complexity increases
Solution Approach 1:
The invention achieves flame retardant certification by controlling the limiting oxygen index (LOI) parameter of the inner sheath layer material, requiring LOI greater than 70%. This is accomplished by adjusting the type and content of flame-retardant inorganic fillers (20-60 wt%) in the polymer matrix, allowing manufacturers to meet performance standards while using conventional extrusion processes.
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 configuration significantly improves flame retardant and low heat release performances, enabling certification in higher classes of international standards while maintaining excellent mechanical properties, including tensile strength and elongation at break, even after thermal aging.
Implementation Method 1
an inner layer made of a LSOH flame-retardant polymeric material having a limiting oxygen index (LOI) greater than 70%
Implementation Method 2
a fire-resistant tape comprising inorganic material, preferably mica, wrapped around the core
Implementation Method 3
an outer layer made of a LSOH flame-retardant polymeric material having a limiting oxygen index (LOI) from 30% to 70%
Data Source
Figure 1
AI summary
A flame retardant cable (1) for low-voltage applications is disclosed which comprises at least one conductor (2) individually electrically insulated by a layer (3) of polymeric material, a fire-resistant tape (4) containing an inorganic material wrapped around said at least one individually electrically insulated conductor (2) and an multilayered outer sheath (5,6) having flame-retardant properties which encloses said at least one individually electrically insulated conductor (2) and said fire-resistant tape(4), wherein said multilayered outer sheath comprises an inner layer (5) and an outer layer(6), the inner layer (5) being made of a flame-retardant polymeric material having a limiting oxygen index (LOI) higher than the LOI of the flame-retardant polymeric material forming the outer layer (6) of said sheath. Such a cable has improved flame retardant performances, especially regarding a lower generation of droplets during burning, which render it capable of being certified in higher classes of the current international standards, for example of the European standard EN 50399:2011/A1 (2016).