Applications
The extruder is an industrial machine used in the continuous transformation of thermoplastic materials, converting them from solid to molten state and generating a homogeneous flow of plasticised material.
The extrusion process is applied in several stages of the useful life of plastic and rubber, from polymerisation to the creation of pellets with specific characteristics through mixing, up to the shaping of the final product.
Requirements:
Enhancing Production Data
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Control of the extrusion process
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Temperature control
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Melt temperature measurement
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Flow control through the melt pump
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Dirty filter detection
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Requirement:
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.
Solution:
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 algorithm 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
Requirement:
Temperature control
Stable rheological behaviour and the consequent dimensional consistency of the extruded material 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).
Gefran technology for the heat process control of extruders relies on solid state relay, 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 1850 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 relay, 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 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 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.
Solution:
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.
Requirement:
Flow control through the melt pump
In some specific applications, such as pipes, precision profiles or 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. This also allows dynamic decoupling between screw and final exit.
Solution:
Gefran employs two high-precision MELT sensors (upstream and downstream of the pump) to regulate 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.
Requirement:
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 intervention or starting automatic filter change systems.
Solution:
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.
Operating Principle
The plastic material is introduced through a hopper, which doses the raw material.
The extruder contains a cylinder (or “barrel”), which in turn houses a rotating screw (or multiple screws, in the case of twin-screw extruders). The screw has three fundamental purposes: transport of the material, melting through the combined effect of friction and heat and homogenisation of the molten material.
The screw is divided into functional zones (feeding, compression, dosing), each with a shape and surface optimised to modulate the pressure, temperature and viscosity of the material during the process.
The heat necessary for fusion is provided both by electrical resistors (external to the cylinder) and by the mechanical energy generated by the shear stress internal to the mass.
The process develops following specific recipes, i.e. predefined sequences of materials and processing parameters, adapted to the characteristics required by the end product.
Lastly, the plasticised material is pushed towards the end of the cylinder, where it crosses an extrusion head equipped with a shaped die, which gives the plastic flow the desired form (see Flat Head Extruder and Blown Film Extruder).
Requirements and Technology
The extrusion process requires the centralised and synchronised control of interdependent variables such as screw speed, temperature and melt pressure, in order to guarantee process stability, the rheological quality of the product and operational efficiency. It is essential to maintain precise temperature control in each heating zone to ensure the correct viscosity and reduce surface or dimensional defects. The accurate measurement of the melt temperature, via direct immersion probes, is fundamental to obtain a true representation of the conditions of the material. Furthermore, flow control via a melt pump and the timely detection of dirt in the filter make it possible to stabilise the process and prevent anomalies.
Other critical factors in process control include:
- Integration of certified security logics
- Resistance of components to loaded or recycled materials
- Continuous monitoring of rheological properties with rheometers
Gefran offers a complete range of control platforms, melt pressure and temperature sensors and modular solutions that can be easily integrated into any plant, ensuring efficiency, safety and constant quality in the extrusion process.
