Thermoplastic Insulating Layer Impregnation for Energy Cable Extrusion
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Solution Overview
Problem
The production of energy cables with thermoplastic insulating layers faces challenges due to the instability caused by dielectric fluids during the extrusion process, leading to structural defects and increased complexity in manufacturing, especially when high extrusion speeds are required for medium or high voltage cables.
Innovation Solution
Impregnating thermoplastic materials with dielectric fluid before feeding them into a single-screw extruder, eliminating the need for mechanical homogenization steps in the molten state and allowing for higher production speeds without compromising the quality of the insulating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If dielectric fluid is added to thermoplastic polymer in the extruder, then the insulating layer gains dielectric strength, but the extrusion process becomes unstable and produces structural defects
Solution Approach 1:
The dielectric fluid is added to the thermoplastic polymer granules before extrusion, allowing the fluid to be absorbed and distributed throughout the polymer matrix in advance. This preliminary impregnation ensures homogeneous distribution of the dielectric fluid without disrupting the extrusion process stability, as the fluid is already integrated into the polymer structure when extrusion begins.
Solution Approach 2:
The thermoplastic polymer acts as an intermediary carrier that absorbs and transports the dielectric fluid uniformly throughout the insulating layer during extrusion. This intermediary approach allows the dielectric fluid to be distributed homogeneously without directly contacting the extrusion machinery, thereby maintaining process stability while achieving the desired dielectric properties.
2Stability of the object's composition
If mechanical homogenization steps are added to distribute dielectric fluid, then homogeneity of the insulating layer improves, but manufacturing complexity increases
Solution Approach 1:
The thermoplastic polymer granules self-absorb the dielectric fluid through their inherent capillary action and affinity, eliminating the need for external mechanical homogenization devices. The polymer matrix automatically distributes the fluid uniformly throughout its structure during the feeding and extrusion process, simplifying the manufacturing line while ensuring homogeneous composition.
Solution Approach 2:
The patent replaces mechanical homogenization systems (such as mixers or kneaders) with a chemical/physical absorption mechanism where the polymer granules naturally absorb and distribute the dielectric fluid. This substitution eliminates complex mechanical homogenization equipment while achieving uniform distribution through the polymer's inherent properties.
3Productivity
If extrusion speed is increased for industrial production, then productivity improves, but the lubricant properties of dielectric fluid cause irregularities in material movement
Solution Approach 1:
The dielectric fluid is pre-absorbed by the polymer granules before extrusion, creating a uniformly impregnated material that flows consistently during high-speed extrusion. This preliminary impregnation prevents the dielectric fluid from acting as a lubricant during material movement, as it is already integrated into the polymer matrix, thereby maintaining flow regularity even at high extrusion speeds.
Solution Approach 2:
The patent changes the physical state and distribution of the dielectric fluid from a free liquid phase to an absorbed phase within the polymer matrix. This parameter change eliminates the lubricant effect that would otherwise cause flow irregularities, allowing high extrusion speeds to be maintained with consistent material flow and composition stability.
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 process enables the production of energy cables with improved dielectric strength and reduced manufacturing complexity, achieving higher extrusion speeds while maintaining the thermomechanical properties of the insulating layer, making it more attractive from an industrial perspective.
Implementation Method 1
impregnating a thermoplastic material in subdivided solid form with a dielectric fluid to obtain an impregnated thermoplastic material
Implementation Method 2
intimately admixed with a dielectric fluid... intimately and homogeneously admixed with the polymeric matrix
Implementation Method 3
extruding the impregnated thermoplastic material onto said at least one electrically conductive core
Implementation Method 4
feeding said impregnated thermoplastic material in subdivided solid form to a single-screw extruder; and extruding the impregnated thermoplastic material
Data Source
AI summary
A process for producing an energy cable including at least one electrically conductive core and at least one thermoplastic electrically insulating layer, includes the steps of: impregnating a thermoplastic material in subdivided solid form, having a melting enthalpy equal to or lower than 70 J/g, with a dielectric fluid to obtain an impregnated thermoplastic material; feeding the impregnated thermoplastic material in subdivided solid form to a single-screw extruder; and extruding the impregnated thermoplastic material onto the at least one electrically conductive core, so as to form the at least one thermoplastic electrically insulating layer, whereby the impregnated thermoplastic material is not subjected to any mechanical homogenization step in a molten state. Energy cables having a large amount of the dielectric fluid in the electrically insulting layer, e.g. higher than 10 wt %, are obtained without showing any morphological defects in the layer itself and any drawbacks in the extrusion process, even when the rotation speed of the extruder screw, and therefore, the cable production speed, are high (e.g. higher than 20 m/min for medium voltage cable).