Slot Die Gap Control for Polymeric Melt Swelling
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Solution Overview
Problem
Existing polymeric web forming processes using slot dies face challenges in achieving a flat web profile during startup operations, leading to significant waste due to the inability to accurately adjust the melt outlet profile before reaching steady state, as the swelling or 'clam shelling' of the die lips causes thickness variations across the web.
Innovation Solution
A system that includes a slot die with a polymer reservoir and actuators to adjust the gap profile based on pressure and flow rate data, using a control unit with algorithms to correlate pressure and flow rate signals to generate actuator control signals, ensuring a uniform gap profile between the die edges, thereby compensating for swelling and achieving a flat polymeric web profile before steady state operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If repeated iterative measurements and manual adjustment of the die are performed, then the web profile can be adjusted, but the process time increases significantly and waste increases during startup
Solution Approach 1:
The patent replaces manual mechanical adjustment with an automated control system that uses actuators driven by control signals from a processor. The system automatically adjusts the die gap based on pressure sensor feedback, eliminating the need for repeated manual measurements and adjustments during startup, thereby reducing both time and waste.
Solution Approach 2:
The patent implements a feedback control mechanism where pressure sensors continuously monitor the pressure of polymeric material in the die, and the processor uses this information to automatically adjust the actuators. This closed-loop feedback system enables real-time compensation for die swell without requiring manual intervention or iterative measurements.
2Measurement precision
If cross web scanning devices are used to measure web profile, then measurement capability is provided, but the devices take time to traverse across the web requiring more time to determine true web profile
Solution Approach 1:
The patent performs preliminary compensation for die swell during startup operations by automatically adjusting the die gap before the material exits the die. This preliminary action ensures that the web profile is corrected in advance, eliminating the need for time-consuming post-extrusion scanning and measurement processes.
Solution Approach 2:
The patent replaces physical cross-web scanning devices with a pressure-based control system that uses pressure sensors and actuators to automatically adjust the die gap. This substitution eliminates the need for mechanical scanning across the web, providing real-time control without the time delay inherent in physical measurement traverses.
3Manufacturing precision
If the die gap is adjusted manually, then the profile can be modified, but the process cannot accurately adjust the melt outlet during startup operations
Solution Approach 1:
The patent replaces manual die adjustment with an automated control system that uses pressure sensors and actuators to precisely control the melt outlet profile during startup. The system automatically compensates for die swell based on real-time pressure data, providing accurate control without the complexity of manual adjustment procedures.
Solution Approach 2:
The patent implements feedback control during startup operations by continuously monitoring pressure in the die and automatically adjusting the actuators accordingly. This feedback mechanism enables accurate melt outlet profile control during the complex startup phase without requiring manual intervention or complex operational procedures.
4Productivity
If flow rate of polymeric melt is increased, then production capacity increases, but the melt profile forming lips swell causing thickness variations
Solution Approach 1:
The patent uses pressure sensors to monitor the pressure of polymeric material in the die and feeds this information back to the processor, which automatically adjusts the actuators to compensate for die swell. This feedback mechanism enables the system to maintain uniform web thickness even when operating at high flow rates and production capacities.
Solution Approach 2:
The patent dynamically changes the die gap parameter in response to pressure variations caused by changes in flow rate. The actuators adjust the die gap opening based on real-time pressure data, allowing the system to maintain optimal web thickness uniformity across varying production capacities and flow rates.
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 system effectively adjusts the gap profile in real-time, reducing waste and enhancing the quality of the polymeric web by maintaining a consistent thickness across the web, even during startup, and accelerating the control to a flatter profile in less time than traditional methods.
Implementation Method 1
A pressure sensor is in communication with the reservoir. The pressure sensor measures the pressure of the polymer melt in or just prior to the reservoir.
Implementation Method 2
Each of the actuators has an extendable member and a drive unit that is in communication with the extendable member. The extendable member moves a portion of the second edge relative to the first edge in response to forces generated by the drive unit to adjust the profile of the gap.
Implementation Method 3
The polymer melt within the polymer reservoir begins to solidify into a partially formed polymeric melt as it exits the melt outlet.
Data Source
AI summary
A system for adjusting a gap in a slot die for producing a polymeric web. The system includes a slot die that has a polymer reservoir that extends between a polymer inlet and a melt outlet. The melt outlet has a first edge and a second edge that each extend longitudinally along the melt outlet. The second edge is opposite the first edge. A plurality of actuators move the second edge along a plurality of positions along a length of the second edge. The first edge is spaced apart from the second edge by a gap that has an adjustable profile. A pressure sensor communicates with the reservoir and measures the pressure of the polymer in the reservoir. A control unit with an algorithm correlates the profile of the gap to the pressure in the reservoir. The algorithm is configured to generate control signals to cause the profile of the gap to be uniform.