Crosslinkable Polyethylene Cable Insulation With Low Methane Formation
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Solution Overview
Problem
Current cable manufacturing processes face challenges with premature crosslinking and volatile decomposition products from crosslinking agents, leading to issues like 'scorch', unevenness, and increased production costs due to the need for degassing steps, which also affect the quality and safety of high-voltage cables.
Innovation Solution
A polymer composition with a specific amount of vinyl groups and a controlled amount of crosslinking agent, such as peroxides, is used to minimize premature crosslinking and volatile decomposition products, allowing for improved processability and reduced methane levels, thereby eliminating the need for extensive degassing and ensuring safer, higher-quality cable production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a crosslinking agent is added to the polymer composition to improve heat and deformation resistance, then the thermo-mechanical properties are enhanced, but premature crosslinking occurs during extrusion leading to scorch and surface unevenness
Solution Approach 1:
The polymer composition is prepared with a crosslinking agent in advance, but the actual crosslinking reaction is delayed until the extrusion process is complete. The composition is formulated to remain stable during storage and transport, then undergo crosslinking during the extrusion process itself, preventing premature reaction while ensuring proper crosslinking occurs at the right time
Solution Approach 2:
The extrusion temperature is carefully controlled and optimized to balance two requirements: high enough to ensure proper melting and homogenization of the polymer composition, but low enough to minimize decomposition of the crosslinking agent. This parameter optimization prevents premature crosslinking while maintaining manufacturing quality
2Ease of manufacture
If the extrusion temperature is increased to improve melting and homogenisation, then the processability is enhanced, but the decomposition of crosslinking agent increases leading to premature crosslinking
Solution Approach 1:
The extrusion temperature is optimized to a specific range that simultaneously achieves adequate melting and homogenization of the polymer while minimizing crosslinking agent decomposition. This parameter optimization resolves the contradiction between processability and preventing harmful decomposition
3Productivity
If crosslinking is performed at elevated temperature to increase crosslinking speed, then the production efficiency is improved, but volatile decomposition products such as methane are generated
Solution Approach 1:
The volatile decomposition products, particularly methane, are deliberately directed toward the flame zone where they are combusted and converted into useful heat energy. This converts the harmful volatile products into a beneficial source of additional heating, accelerating the crosslinking process while eliminating the harmful effects of methane accumulation
Solution Approach 2:
The flame zone provides a high-concentration oxygen environment that accelerates the oxidation and combustion of volatile decomposition products. This strong oxidizing condition rapidly converts methane and other volatiles into CO2 and H2O, preventing their harmful accumulation while utilizing the released energy
4Manufacturing precision
If a degassing step is added to remove volatile decomposition products, then the cable quality is improved, but the production time and cost increase
Solution Approach 1:
Instead of removing volatile decomposition products through a separate degassing step, the invention converts them into useful heat energy by directing them to the flame zone for combustion. This eliminates the need for time-consuming degassing while maintaining cable quality, as the volatiles are rapidly consumed in the flame zone before they can affect the cable
Solution Approach 2:
The crosslinking process and volatile removal are merged into a single integrated process. The flame zone serves dual purposes: providing additional heat for crosslinking and simultaneously consuming volatile decomposition products. This eliminates the need for a separate degassing step, reducing production time while maintaining quality
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 solution results in cables with enhanced sagging resistance, processability, and thermo-mechanical properties, reducing methane levels and enabling shorter degassing times or eliminating the need for it, thus improving production efficiency and cable quality.
Implementation Method 1
the crosslinking agents decompose generating free radicals
Implementation Method 2
the crosslinking agents decompose generating free radicals
Implementation Method 3
crosslinking of polymers, e.g. polyethylenes, substantially contributes to an improved heat and deformation resistance
Implementation Method 4
crosslinking agents where the crosslinking agents decompose generating free radicals
Implementation Method 5
the decomposition of the crosslinking agents, e.g. peroxides, during the crosslinking, will further also result in formation of peroxide decomposition products. Some of the peroxide decomposition products are volatile
Implementation Method 6
The peroxide decomposition products remain mostly captured within the polymer composition of, for example, a cable, after crosslinking. This causes, e.g. problems in view of the cable manufacturing process as well as in view of the quality of the final cable
Data Source
AI summary
The invention relates to a cable comprising layer(s), which layer(s), is/are obtained from a polymer composition, wherein the polymer composition comprises a polyethylene and a crosslinking agent, wherein the polymer composition contains a total amount of vinyl groups which is B vinyl groups per 1000 carbon atoms, and B1 ≤B, wherein B1 is 0.88, when measured prior to crosslinking according to method ASTM D6248-98; and wherein the crosslinking agent is present in an amount which is Z wt%, prior to crosslinking, based on the total amount (100 wt%) of the polymer composition, and Z ≤Z2, wherein Z2 is 0.60, the cable, e.g. being a power cable, and processes for producing the cable; the cable useful in different end applications, such as wire and cable (W&C) applications.