Explosion-Proof Cable With Dual-Layer Fire Protection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing explosion-proof systems for machines operating in explosive atmospheres face challenges in preventing fire spread through cables, as conventional solutions do not adequately address the risk of fire propagation and damage to the fire-preventing mechanisms.

Innovation Solution

A cable system comprising electric wires with a conductive core and insulator, an outer cover supported by a partition, a first cover made of thermosetting resin to prevent fire spread, and a second cover with higher fracture strength than the resin to protect the first cover from damage, ensuring effective fire containment and structural integrity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single-layer cover is used to protect cables in explosive atmospheres, then the structure is simple and easy to manufacture, but the fire prevention reliability is insufficient and the cover is vulnerable to damage

Engineering Contradiction:

Improvefire prevention reliabilityVSAvoidcable cover structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The cable cover is divided into two distinct layers: a thermosetting resin layer (first cover) that provides fire prevention by charring to seal gaps, and a metallic layer (second cover) that provides mechanical protection. This segmentation allows each layer to specialize in its protective function, improving overall reliability without requiring a single complex multi-functional component.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining thermosetting resin and metal materials. The thermosetting resin provides fire resistance through charring, while the metal provides mechanical strength and durability. This composite approach leverages the complementary properties of different materials to simultaneously achieve fire prevention and mechanical protection, resolving the contradiction between reliability and structural simplicity.

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If a thermosetting resin cover is used to prevent fire spread, then fire containment is improved, but the cover is vulnerable to physical damage due to low fracture strength

Engineering Contradiction:

Improvefire spread preventionVSAvoidfracture strength

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

The protective cover is segmented into two functional layers: the inner thermosetting resin layer dedicated to fire containment through charring, and the outer metallic layer dedicated to mechanical protection. This segmentation allows the thermosetting resin to perform its fire prevention function without being compromised by mechanical damage requirements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The metallic second cover serves as a protective shell that shields the thermosetting resin first cover from physical damage before such damage can occur. This prior cushioning approach prevents the vulnerable resin layer from being exposed to mechanical stresses, ensuring both fire prevention and structural integrity are maintained.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If multiple protective layers are added to the cable, then fire prevention and damage protection are improved, but the cable diameter increases and space efficiency decreases

Engineering Contradiction:

Improvefire and damage protectionVSAvoidcable diameter

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The protective structure uses a nested configuration where the thermosetting resin first cover is positioned inside the metallic second cover. This nesting approach maximizes the protective functionality within minimal radial space, as each layer contributes its protective property without requiring additional lateral expansion.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The composite structure of thermosetting resin and metal layers provides dual protection (fire and mechanical) within a compact form factor. The thin thermosetting resin layer provides fire resistance through charring, while the thin metallic layer provides mechanical strength, together achieving comprehensive protection without significantly increasing cable diameter.

Inventive Principle:

Principle #40Composite materials

4Object-affected harmful factors

If the outer cover is extended into the explosive atmosphere, then cable protection is improved, but the fire spread risk through the cable increases

Engineering Contradiction:

Improvecable protectionVSAvoidfire spread risk

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The thermosetting resin first cover is designed to char when exposed to fire, and this charring process is converted into a beneficial sealing mechanism. The charred resin swells and seals gaps between the outer cover and partition, transforming the harmful effect of fire exposure into a protective fire-blocking action that prevents fire spread through the cable.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The thermosetting resin cover is positioned to extend into the explosive atmosphere along with the outer cover, but it is designed to react preemptively to fire exposure by charring and sealing gaps before fire can spread through the cable. This preliminary protective action ensures fire containment even when the cable penetrates the partition into the explosive atmosphere.

Inventive Principle:

Principle #10Preliminary action

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

The cable system effectively prevents fire spread and damage, enhancing safety and efficiency by using a thermosetting resin to cover exposed wires and a metal cover to reinforce the first cover, allowing for reliable operation in explosive environments while maintaining space efficiency.

Implementation Method 1

The first cover includes a thermosetting resin and covers an exposed portion of the electric wires, which is not covered by the outer cover in the second atmosphere

Methodology Applied

Scientific EffectThermosetting resin:

Implementation Method 2

The second cover covers the first cover and includes a material higher in fracture strength than the thermosetting resin

Methodology Applied

Scientific EffectFracture strength:

Data Source

PatentUS10121569B2Cable and explosion-proof system

Publication Date: 2018.11.06 YASKAWA DENKI KK

AI summary

A cable includes electric wires, an outer cover, a first cover, and a second cover. Each of the electric wires includes a conductive core and an insulator covering the conductive core. The outer cover covers the electric wires and extends from a first atmosphere to a second atmosphere less explosive than the first atmosphere. An outer surface of the outer cover is supported by a partition separating the first atmosphere from the second atmosphere. The first cover includes a thermosetting resin and covers an exposed portion of the electric wires, which is not covered by the outer cover in the second atmosphere. The second cover covers the first cover and includes a material higher in fracture strength than the thermosetting resin.