Buffer Chamber for Plastic Sheath Extrusion
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Solution Overview
Problem
Existing extrusion facilities for plastic sheaths in the petrochemical industry, particularly those using 'coathanger' or 'fishtail' mandrels, suffer from thickness variations due to non-uniform viscosity of molten plastic, leading to defects in the sheath.
Innovation Solution
A buffer chamber is introduced between the extrusion screw and the extrusion head to stabilize the apparent viscosity of the plastic before injection, ensuring uniform viscosity and homogeneous flow, which is achieved through a cylindrical buffer chamber with chicanes and deflectors to homogenize the plastic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a coathanger or fishtail mandrel is used with distribution passages, then the plastic can be distributed to form a sheath, but the viscosity of the molten plastic varies along different flow paths causing thickness variations and defects
Solution Approach 1:
The buffer chamber is installed upstream of the extrusion head to pre-homogenize the molten plastic before it enters the distribution passages. This preliminary action ensures that the plastic has uniform viscosity throughout the buffer chamber, so when it subsequently flows through different paths in the mandrel, all streams start with the same viscosity, preventing thickness variations in the final sheath.
Solution Approach 2:
The buffer chamber acts as an intermediary component between the extrusion screw and the extrusion head. It serves as a mediating zone where the molten plastic from the screw is mixed and homogenized before being distributed to the mandrel. This intermediary structure eliminates the harmful effect of viscosity variations by providing a mixing zone that equalizes the plastic properties across all flow streams.
2Productivity
If the plastic flows through distribution passages in the mandrel, then the sheath is formed, but the residence time varies for different plastic streams causing viscosity differences
Solution Approach 1:
The buffer chamber provides a preliminary mixing zone where plastic streams with different residence times are combined and homogenized before entering the distribution passages. This preliminary action ensures that even though plastic may take different paths with varying residence times through the mandrel, the starting material in the buffer chamber has already been homogenized, compensating for subsequent residence time variations.
Solution Approach 2:
The buffer chamber merges multiple plastic streams from the extrusion screw into a single homogenized flow before distribution. By combining and mixing the plastic in the buffer chamber, the system ensures that all downstream streams originate from a unified, homogenized source, eliminating viscosity differences that would arise from separate processing paths.
3Device complexity
If the plastic is injected directly into the extrusion head, then the process is simple, but the viscosity changes during injection causing non-uniform flow
Solution Approach 1:
The buffer chamber is positioned between the extrusion screw and the extrusion head to perform preliminary homogenization of the molten plastic. This preliminary action stabilizes the plastic viscosity before injection, ensuring uniform flow characteristics throughout the extrusion process without requiring complex control systems or multiple injection stages.
Solution Approach 2:
The buffer chamber serves as an intermediary structure that simplifies the overall system by providing a passive mixing zone. Instead of requiring complex active control mechanisms to manage viscosity variations, the buffer chamber mediates between the screw and extrusion head, automatically homogenizing the plastic through its geometry and flow patterns, thus maintaining manufacturing precision with minimal added complexity.
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 ensures a uniform plastic sheath with consistent thickness, eliminating defects by maintaining constant viscosity and homogenizing the plastic flow, thereby improving the mechanical properties of the sheath.
Implementation Method 1
with said viscous plastic supplied by said extrusion screw having, at constant temperature, a viscosity that is liable to change from a value μi to a constant value μicst during a given period
Implementation Method 2
a buffer chamber installed between said extrusion screw and said extrusion head to store said viscous plastic for said given period
Implementation Method 3
achieved through a cylindrical buffer chamber with chicanes and deflectors to homogenize the plastic
Implementation Method 4
the plastic is softened and/or melted under the effect of the shearing and heat as it is gradually caused to progress
Implementation Method 5
the plastic is softened and/or melted under the effect of the shearing and heat
Implementation Method 6
In the temperature-regulated screw extruder, the plastic is softened and/or melted
Data Source
AI summary
An extrusion facility (10) includes an extrusion screw (12), capable of providing a heat-softened viscous plastic material, and an extrusion (14). The extrusion head includes an annular chamber (24) that is capable of receiving viscous plastic material. The viscous plastic material, provided by the extrusion screw, has, at a constant temperature, a viscosity variable from a value μi at a constant value μcst during a given period so that μcst>μi. A buffer chamber (16) between the extrusion screw (12) and the extrusion head (14) to store the viscous plastic material during the given period in order to enable the plastic material to reach the viscosity value μcst before being injected into the extrusion head (14).