Aplicaciones
Flat head extrusion is a well-established technology for manufacturing flat products such as plastic films (used, for example, for thermoformed disposable cups or trays), rigid sheets (such as plexiglass) or honeycomb cardboard (for lightweight and easily transportable containers). These materials are used in packaging, construction, automotive and other sectors that require rigidity, lightness and strength.
This extrusion technology makes it easy to mass-produce batches of products that can then be cut or wrapped around reels. A feature of the flat head is that it usually conveys multiple extruders, so it can create a product where the visible sides and the internal filling are made of different materials. The machine also allows precise control of thickness and surface quality, offering versatility for different polymers and configurations.
Necesidades:
Control of the extrusion process
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Temperature control
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Melt temperature measurement
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Sheet thickness
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Haul-Off Tension
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Flow control through the melt pump
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Dirty filter detection
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Temperature control in the stabilisation zone
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Monitoring of the hydraulic circuit
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Enhancing Production Data
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Necesidad:
Control of the extrusion process
The extrusion process requires continuous balancing between interdependent variables: screw rotation speed, multi-zone temperature, molten polymer pressure and synchronisation with auxiliary actuators. The control system must be able to handle complex recipes, support rapid changes in materials, offer integrated diagnostics and provide a rapid response if deviations occur.
Solución:
G-Mation is the platform for the complete, synchronous and integrated control of the extrusion process. The heart of the system is the G-Mation P6 CPU, supported by G3 remote modules with EtherCAT bus communication. Integrated PID regulators manage thermal control and also the drives, with no external gateways required. The user interface is managed through an integrated webserver and displayed using the G-Mation W55 browser panels, which allow the projection of customisable dashboards.
Main features of the Platform:
- Pre-configured and customisable application templates
- Docker technology for the installation of applications such as IoT dashboards, predictive maintenance or integration with MES and ERP systems
- Open architecture that is ready for edge computing
Necesidad:
Temperature control
Stable rheological behaviour and the consequent dimensional consistency of the extrudate are obtained through correct temperature control. It is essential to guarantee thermal stability in these areas, so that the system can respond quickly to variations in thermal or process load, avoiding potential defects (such as surface instability, thickness variations or alterations in the optical quality of the product).
Solución:
Gefran technology for the heat process control of extruders relies on solid state relays, PID controllers and thermocouples:
- Each resistor is managed in a closed loop via PID control, integrated into the PLC or managed by dedicated unit such as the 1250 device, which allows the melt temperature to be maintained within ±0.5°C of the setpoint, guaranteeing constant viscosity and the absence of surface or dimensional defects.
- The GRP-H solid state relays, compact and with integrated heatsink, ensures precise control of current up to 120 A. IO-Link communication also reduces the number of I/O boards through the integrated management of commands, alarms and absorbed current.
The solution is scalable and compatible with PIDs integrated into PLCs or remote modules. Recipe storage and historical trend historicisation functions support rapid production changes and continuous quality improvement.
Necesidad:
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 characteristics, both mechanical and optical. Measuring the temperature via direct contact with the molten polymer, rather than limiting it to the surface of the cylinder, provides a more faithful representation of the material’s actual conditions, which offers a significant advantage in terms of rheological control.
Solución:
Gefran offers temperature sensors 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 melt measurements, with two thermocouple technologies:
- Type K (NiCr-NiAl) are the most common for extrusion: they operate at temperatures up to 850°C, offer a rapid response and are suitable for most technical polymers.
Type J (Fe-CuNi) are indicated for slightly lower temperatures (up to 400°C) and for less aggressive environments. - The TCM/TRM sensors can be installed independently or integrated in combination with the melt pressure sensors, in a compact configuration, to reduce space and simplify wiring.
Necesidad:
Sheet thickness
A crucial step in sheet extrusion is the sizing phase of the extrudate, with millimetre-accurate sizing achieved by two calendering rollers placed downstream of the head, when the material has already begun to cool. At this stage, the position of the two rollers must be monitored with high precision, so as to ensure uniform sizing and to avoid inaccuracies.
Solución:
The Gefran RK-5 sensor, which uses magnetostrictive technology, is designed to be mounted inside the hydraulic cylinders that support the calender rollers. The absence of electrical contacts guarantees reliability and long life, while the AISI 316 frame and resistance to shocks, vibrations and high temperatures make it ideal for the extrusion environment. By delivering very precise, absolute measurements, the RK-5 allows operators to control the thickness of the slabs with a high degree of accuracy.
Necesidad:
Haul-Off Tension
A crucial step in sheet extrusion is the sizing phase of the extrudate, with millimetre-accurate sizing achieved by two calendering rollers placed downstream of the head, when the material has already begun to cool. In this phase, the tension must be monitored with the high precision and maintained within optimal values, to ensure uniform tensioning and to avoid wear or breakage phenomena.
Solución:
Two Gefran TR load cells, installed on the side of the calender rollers, provide a very precise measurement of the applied force. Their mechanical and electronic integration is designed to ensure reliability and ease of installation:
- Dual function: Accurate detection of tension force and mechanical support for rotating components.
- Signal and communication: The acquired analogue force signals are processed in real time by dedicated amplifiers, which provide a stable, linearised and filtered output, optimal for integration into the line control system.
- Dynamic control: This setup allows the management system to quickly and accurately adjust the towing system tension via the motor drives.
Necesidad:
Flow control through the melt pump
In some specific applications, such as pipes, precision profiles and sheets, it is necessary to ensure a constant melt flow rate, regardless of the pressure variations in the screw. The melt pump acts as a stabilising element between the extruder and the head. The pump is regulated via closed-loop control, based on upstream and downstream pressure readings.
Solución:
Gefran employs two high-precision MELT sensors (upstream and downstream of the pump) to control pump speed while keeping the pressure stable and the molten polymer’s flow rate constant. The melt pressure sensors of the Impact series are ideal for critical environments and integration into safety logics:
- Designed with reinforced membrane, piezoresistive sensitive element and no transmission fluid.
- Thermal stability below 1% FS between 20 and 350°C, also perfect for regenerated or abrasive polymers.
- PLc certification and electrical output improve safety and reliability, while the absence of internal fluid makes the sensor suitable for medical and food applications as well.
Necesidad:
Dirty filter detection
The filter protects the die from the impurities present in the molten polymer while also preventing the presence of contaminants in the product. However, this means that the filter tends to gradually become clogged, especially in recycling processes. Clogging increases upstream pressure and can compromise product quality or damage the line.
The continuous measurement of the pressure before and after the filter can be used to calculate the pressure differential and activate alarms, guiding the operator to a manual maintenance or starting automatic filter change systems.
Solución:
Gefran offers the Impact sensor for the precise and reliable monitoring of the pressure upstream and downstream of the filter, ideal for high temperatures (up to 350°C) and harsh environments such as the recycling and processing of loaded polymers.
Main features:
- Membrane that is up to 15 times thicker than traditional sensors, without internal transmission fluid, which directly transfers pressure to the sensitive silicon chip.
- High resistance to wear and dynamic shocks, thermal stability below 1% FS from 20°C to 350°C.
- IEPLc version with electrical output and PLc certification, for integration into safety control systems and configuration of certified alarms.
Necesidad:
Temperature control in the stabilisation zone
The stabilisation zone is essential to maintain the extrudate at a controlled temperature after forming, allowing the relaxation of internal tensions and the dimensional stabilisation of the material. In the absence of adequate thermal control, deformation, thickness variations or mechanical defects may occur. To prevent this, a high-performance multi-zone temperature control system is needed, which can guarantee thermal uniformity, rapid response times and process repeatability, reducing waste and optimising the final quality.
Solución:
The GRM-H Power Controller is a smart regulator for managing the electrical loads of stabilisation furnaces. With its advanced voltage and current control, it ensures stable and precise temperature control, avoiding critical oscillations. Integrated diagnostic functions support predictive maintenance and increase process reliability. The modularity and connectivity with the main fieldbuses allow easy integration into the extruder automation system, guaranteeing production continuity and uniformity of product quality.
Necesidad:
Monitoring of the hydraulic circuit
In the flat head extrusion process, the hydraulic circuit is involved in the controlled movement of key components such as the position of the calenders. Pressure monitoring is not only used to detect anomalies, but is a direct indicator of consistency between command and response. This feedback is therefore essential not only for process control, but for operator safety and machine protection as well.
Solución:
KS sensors offer a reliable solution for pressure monitoring in hydraulic circuits, combining compactness, precision and safety logic. In addition, Gefran pressure sensors allow pressure thresholds to be associated with machine controls, enabling cross-checks to prevent unexpected or missed movements, therefore improving the system’s safety and operational reliability.
Main features:
- Measurement range: from 1 to 1000 bar
- Outputs: analogue 4… 20 mA or 0…10 V
- Thick film technology with stainless steel membrane
- SIL2 certification, suitable for safety circuits
- KS-I version with IO-Link for advanced diagnostics
- High mechanical strength and IP67 protection rating
Operating Principle
The flat head extrusion process to produce sheets, films or honeycomb cardboard is developed through well-defined phases to ensure a uniform product with controlled thickness.
The polymer, in granules, is continuously fed into the hopper, to ensure a constant supply of material. Since there is no dispenser, the extruder is described as having a “hungry mouth,” because the screw draws in the material from the hopper continuously and evenly, ensuring uniform and uninterrupted plasticisation.
Inside the plasticisation chamber, the heated screw transforms the solid granules into a homogeneous and fluid melt, ready to be processed. Unlike control through material quantity dosing, here the flow rate of the molten material is mainly regulated through a melt pump located downstream of the extruder. This pump allows the operator to precisely manage the amount of material reaching the flat head, ensuring a constant pressure and a stable flow.
The melt coming from one or more extruders is then pushed through the flat head, a rectangular die designed to distribute the material evenly over the entire width of the product, maintaining constant thickness and flatness.
After exiting the die, the hot sheet or film passes over the cooling rollers, which solidify the material while preserving its shape and dimensions. In the case of honeycomb cardboard, a complex air blowing system expands the sheet to provide the desired shape. At the end of the cooling process, the towing system “pulls” the product with constant speed and tension, delivering it to the storage preparation point, where it can be wrapped around a reel or cut and stacked as slabs.
Requirements and Technology
Flat head extrusion requires precise coordination of process variables and mechanical actuators, with the aim of ensuring operational stability, consistent quality and the reduction of waste. The criticality lies not only in the extrusion recipe, but in the system’s ability to ensure balance between interdependent parameters such as screw speed, melt temperature, pressure and line synchronisation.
Among the main requirements are multi-zone temperature control (essential to maintain constant viscosity and prevent surface or dimensional defects) and the direct monitoring of the temperature of the molten polymer, which allows a more accurate control of rheological behaviour compared to the cylinder readings alone. Other fundamental requirements concern the control of the thickness of the slabs, obtained by precisely positioning the calender rolls, and the management of the tension applied by the towing system, to ensure uniformity without breakage or wear.
Dimensional consistency is further guaranteed by flow control via the melt pump, which stabilises the pressure downstream of the extruder, while filter monitoring preserves product quality by preventing clogging and unwanted variations. Lastly, the control of temperature in the stabilisation furnaces ensures the relaxation of internal tensions, and the monitoring of the hydraulic circuit further improves the safety and reliability of the system.
Gefran responds to these needs with a complete range of integrated solutions, from the G-Mation control platform to thermal regulators, from melt sensors to position and force transducers, which guarantee efficiency, continuity and constant quality in flat head extrusion.
