Applications
The production of synthetic fibers represents a significant share— about 15% of global polymer production —with applications ranging from textiles to technical yarns.
In fiber melt spinning processes the polymer is melted, dosed, and transformed into continuous filaments. In this application, accurate pressure and temperature control is critical: minimal variations affect the viscosity of the melt, the stability of the process, and the final quality of the fiber.
Requirements:
Thermoregulation
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Melt temperature measurement
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Flow control with melt pump
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Spinneret pressure control
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Winder tension
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Requirement:
Thermoregulation
Stable rheological behavior and the resulting dimensional consistency of the extrudate are achieved through proper temperature control.
It is essential to ensure thermal stability in these areas so that the system can respond quickly to changes in thermal load or process, avoiding potential defects (surface instability, thickness variations, or alterations in the optical quality of the product).
Solution:
Gefran technology for the thermal control of extruders is based on staticrelays , PID controllers and thermocouples:
- Each resistance is managed in a closed loop via PID regulation, integrated in the PLC or entrusted to dedicated controllers such as the 1850, which allows the melt temperature to be maintained within ±0.5°C of the setpoint, ensuring constant viscosity and the absence of surface or dimensional defects
- The compact GRP-H solid-state relay with integrated heat sink ensures precise current control up to 120 A. IO-Link communication also reduces the number of I/O cards required, thanks to integrated management of commands, alarms, and current consumption.
The solution is scalable and compatible with PIDs integrated in PLCs or remote modules. Recipe storage and historical trend functions support rapid production changes and continuous quality improvement.
Requirement:
Melt temperature measurement
The actual temperature of the molten polymer is a critical parameter in the extrusion process, as it directly affects the viscosity of the polymer and its final mechanical and optical characteristics.
Measuring the temperature in direct contact with the melt, rather than limiting it to the surface of the cylinder, provides a more accurate representation of the actual conditions of the material, offering a significant advantage in terms of rheological control.
Solution:
Gefran offers TCM and TRM thermocouple specifically designed with a protective sheath in stainless steel or other materials compatible with the type of polymer (e.g., Hastelloy for corrosive polymers) for direct measurement of the melt, with two thermocouple technologies:
- Type K (NiCr-NiAl) are the most widely used for extrusion: they operate up to 850°C, offer a fast response and are suitable for most technical polymers
- Type J (Fe-CuNi) are suitable for slightly lower temperatures (up to 400°C) and less aggressive environments
TCM/TRM sensors can be installed independently or integrated in combination with melt pressure sensors in a compact configuration to reduce space and simplify wiring.
Requirement:
Flow control with melt pump
In fiber production, it is essential to have a constant melt flow rate at the spinneret, regardless of pressure variations in the screw.
The melt pump acts as a stabilizing element between the extruder and the head. The pump is regulated by closed-loop control based on upstream and downstream pressure readings.
Solution:
Gefran uses high-precision ME series mercury-filled melt sensors with flanged connections to regulate pump speed and maintain stable pressure and constant flow rate of the molten polymer. Melt pressure sensors are ideal for critical environments such as synthetic fiber spinning plants:
- Thermal stability even at temperatures above 400 °C
- High measurement accuracy for dynamic controls and high-precision adjustments
- Atex certification and HART protocol available in the configuration
Requirement:
Spinneret pressure control
In the spinning section, the compact size of the heads and the presence of micro-filaments make the process particularly sensitive.
It is necessary to precisely control the pressure entering and leaving the spinning pump to ensure filament uniformity and prevent breakage. Installation requires sensors with a small footprint and high performance.
Solution:
The ME series mercury-filled melt sensors, with M10 process connection and compact diaphragm, are designed for installation in spinning heads, where space is limited and temperatures exceed 300 °C. In addition, compatibility with the HART protocol and Atex certification make the product adaptable to different plant layouts.
Main features:
- Compact design for critical installations
- High metrological stability
- Option with integrated temperature sensor
Thanks to this integration, ME sensors guarantee the precise control required in high-quality spinning applications.
Requirement:
Winder tension
In the final stage of spinning, the solidified filaments are wound onto rollers using winding systems that must operate at a controlled speed synchronized with the upstream process. Incorrect tensioning can cause dimensional variations in the yarn, winding instability, or breakage.
Continuous tension monitoring allows the correct balance between pulling speed and mechanical resistance of the filament to be maintained, ensuring product uniformity and process stability even at high operating speeds.
Solution:
One or more TR force sensors installed on the winders allow direct and continuous measurement of the filament pulling force, providing a reliable reference for tension control.
Main features:
- Dual function: accurate measurement of tension force and mechanical support of rotating parts
- Signal and communication: analog force signals are processed by dedicated amplifiers, with stable, linearized, and filtered output, ready for integration into the control system
- Dynamic control: the system allows rapid tension adjustment via motor drives, maintaining constant winding conditions
Thanks to this configuration, Gefran solutions enable precise and reliable control of winding tension, reducing process defects and ensuring the quality of the finished filament.
Operating principle:
In the melt spinning process, the polymer (typically PET, nylon, or polypropylene) is metered and mixed, feeding the extruder where the plastic material is melted and homogenized. A metering pump ensures a constant flow of the melt to the filtration system, eliminating impurities that could compromise the integrity of the filaments.
The molten material is then conveyed to the spinning heads, where it passes through the spinneret, composed of thousands of micro-holes that define the number, diameter, and section of the filaments.
At the end of the production line, the filaments are rapidly cooled (quenching) to solidify the polymer structure and fix its molecular orientation. Finally, they are wound onto a winder, which completes the production cycle.
Requirements and technology:
Fiber melt spinning is a processthat is extremely sensitive to pressure and temperature variations. Deviations of a few bars or a few degrees can alter the viscosity of the polymer, causing flow instability, filament defects or production interruptions.
Melt pressure and temperature sensors are therefore essential for monitoring the polymer as it exits the extruder, in the melt pump and in the final spinning phase.
The compact size of the spinning heads, the high operating temperatures, and the need for repeatable measurements require reliable sensors with low thermal drift and small mechanical dimensions.
Gefran meets these requirements by offering specific measurement solutions for pressure and temperaturecontrol, even in the most critical conditions.