Extruder Screw Liquid Injection for Stable Cable Insulation
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Solution Overview
Problem
Existing extruder technologies for manufacturing medium or high voltage energy cables face defects in the electrical insulating layer due to the 'slippage' phenomenon caused by the lubricating effect of dielectric liquids, leading to degradation of mechanical and electrical properties and structural issues like diameter variation in the cable.
Innovation Solution
An extruder design with a polymer feed member, an extrusion screw featuring a barrier zone and a liquid injection channel integrated within the screw, allowing for the injection of a liquid between the sheath and the extrusion screw without piercing the sheath, thus maintaining the internal surface treatment and optimizing pressure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If liquid is injected at the hopper before inserting thermoplastic polymer, then liquid mixing with polymer is achieved, but sliding phenomenon occurs causing structural defects and diameter variation
Solution Approach 1:
The patent introduces a barrier layer as an intermediary substance between the liquid and the thermoplastic polymer. This barrier layer prevents direct contact between the liquid and polymer, eliminating the sliding phenomenon while still allowing the liquid to be incorporated into the composition. The barrier layer acts as a mediator that resolves the conflict between achieving liquid mixing and maintaining manufacturing precision.
2Ease of manufacture
If holes are formed through the extruder barrel to inject liquid, then liquid injection is achieved, but surface treatment of barrel internal surface is deteriorated
Solution Approach 1:
The patent extracts the liquid injection function from the barrel and relocates it to the extrusion screw. By forming the injection channel within the screw rather than piercing the barrel, the solution achieves liquid injection capability while preserving the barrel's internal surface treatment. The barrel is no longer involved in the injection process, eliminating the harmful effect of hole formation.
3Quantity of substance
If liquid is injected in molten polymer area, then liquid mixing is achieved, but higher pressure requirements increase device complexity
Solution Approach 1:
The patent applies preliminary action by injecting the liquid into the solid or partially melted polymer zone before the polymer becomes fully molten. This timing allows liquid injection at lower pressures, as the polymer has not yet reached its molten state where high pressure would be required. The injection channel is positioned to deliver liquid at the optimal point in the heating/melting process.
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 design prevents damage to the sheath's internal surface, reduces the risk of structural defects, and ensures consistent cable diameter by injecting the liquid at favorable pressure conditions, enhancing both mechanical and electrical properties of the thermoplastic layer.
Implementation Method 1
an extrusion screw disposed inside the barrel and allowing the progressive melting of the polymer to form an extrusion composition
Implementation Method 2
an extrusion screw disposed inside the barrel and allowing the progressive melting of the polymer to form an extrusion composition
Implementation Method 3
The liquid is thus mixed with the thermoplastic polymer before or at the time of its insertion into the sheath, in particular at a hopper. However, it has been observed that this method of injecting the liquid could lead to manufacturing defects in the electrically insulating layer, linked in particular to a sliding phenomenon. This sliding phenomenon at the wall linked to the lubricating effect of the dielectric liquid
Data Source
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AI summary
The invention relates to an extruder (5) for extruding an electrical cable comprising at least one elongated electrically conductive element and at least one extruded thermoplastic layer surrounding said elongated electrically conductive element, said extruder comprising: - a polymer feed member (4) in solid form, - a sleeve (6) fed by the feed member, - an extrusion screw (7) disposed inside the sleeve (6) and enabling the progressive melting of the polymer to form an extrusion composition and the transport of this composition along the extrusion screw (7) to a distal end (21) of the extrusion screw (7), said extrusion screw (7) extending along a longitudinal axis (A), said extrusion screw comprising a barrier zone having at least two threads,- an extrusion head (8) disposed at a distal end (21) of the extrusion screw (7) and configured to apply the composition around an elongated electrically conductive element, wherein at least one liquid injection channel (22) is formed in the extrusion screw (7), said at least one injection channel (22) opening into the barrel (7) at at least one outlet orifice (30) formed on an external surface of the extrusion screw (7).