UHMWPE Sheet Ram Extrusion Back Pressure Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for producing ultra high molecular weight polyethylene (UHMWPE) sheets and panels via ram extrusion face challenges such as distortion, warping, and surface irregularities due to the high friction and volume contraction of UHMWPE, making it difficult to achieve commercially acceptable quality, especially for large widths and high aspect ratios.
Innovation Solution
Implementing a process where UHMWPE is extruded from a slit die at a temperature below the crystalline melt temperature, with the use of a back pressure device that applies adjustable pressure zones across the width and sides to maintain contact with the die, ensuring uniform crystallization and minimizing movement, thereby controlling thickness and flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If UHMWPE is extruded above crystalline melt temperature, then the material flows more easily through the die, but the sheet experiences severe distortion and warping due to volume contraction during cooling
Solution Approach 1:
The die is pre-cooled to below the crystalline melt temperature of UHMWPE (e.g., to 100-150°C) before extrusion begins. This preliminary cooling action ensures that the sheet solidifies quickly upon exiting the die, maintaining dimensional stability and preventing warping, while still allowing the material to flow through the die at the required temperature
Solution Approach 2:
The patent changes the temperature parameter of the die from conventional high temperature (above melt point) to below crystalline melt temperature. This parameter change fundamentally alters the extrusion mechanism, allowing the material to be extruded in a semi-solid state that minimizes volume contraction and maintains sheet flatness
2Device complexity
If conventional ram extrusion is used, then the process is simple and equipment is basic, but the sheets exhibit thickness variations and surface irregularities
Solution Approach 1:
The patent introduces temperature as a critical control parameter, cooling the die to below crystalline melt temperature. This simple parameter change in the existing ram extrusion equipment dramatically improves thickness uniformity and surface quality without requiring complex additional equipment
Solution Approach 2:
The patent implements monitoring of sheet characteristics (thickness, flatness) with feedback control that adjusts process parameters to maintain product specifications. This feedback mechanism ensures consistent quality while working within the constraints of relatively simple equipment
3Ease of manufacture
If UHMWPE is extruded at high temperature, then the material viscosity is lower and extrusion is easier, but friction against die walls increases causing surface defects
Solution Approach 1:
The patent optimizes the temperature parameter by cooling the die below crystalline melt temperature, creating a temperature gradient that reduces material viscosity near the die wall. This minimizes frictional stress and prevents surface defects like scratching and marking, while still maintaining adequate flow through the die
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 approach results in UHMWPE sheets with improved uniformity and reduced defects, achieving constant thickness and flatness specifications, such as ±0.050 inch variation over 80% of the panel width, surpassing the quality of traditional ram extrusion methods.
Implementation Method 1
inducing back pressure by means of a back pressure device
Implementation Method 2
the panel has been cooled to a temperature below the crystalline melt temperature
Implementation Method 3
ensuring uniform crystallization
Data Source
AI summary
UHMWPE panels of large width may be ram extruded from a slit die in a stable process, by restraining a panel which exits the die below the crystalline melt temperature against movement away from the die by a back pressure device, so as to exert a back pressure between the back pressure device and the die, the back pressure device preferably constructed of a plurality of differentially adjustable elements so as to be able to compensate for changes in processing characteristics over time. Vertically restraining UHMWPE panels as they further cool also greatly improves product characteristics.