Applications
The blown film extrusion line is an industrial solution for the continuous production of plastic films through an extrusion and blowing process. Unlike traditional extrusion, in this process the polymer is melted by one or multiple parallel extruders and pushed through a circular die, which generates a tube. This tube is then inflated with high pressure air, so it swells like a bubble and is stretched into film. This process is used to produce thin plastic sheets for packaging (such as bags of various sizes) or protective films.
Requirements:
Control of the extrusion process
Learn more
Temperature control
Learn more
Melt temperature and pressure measurement
Learn more
Haul-off tension
Learn more
Conveyor longitudinal and transverse opening
Learn more
Monitoring of the hydraulic circuit
Learn more
Enhancing Production Data
Learn more
Unloading the winders
Learn more
Requirement:
Control of the extrusion process
The blow film extrusion process requires continuous balancing between interdependent variables, such as 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 blown film extrusion process. The heart of the system is the G-Mation P6 CPU, supported by G3 remote modules with EtherCAT bus communication. Integrated PID controllers manage thermal control and 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 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).
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 functions support rapid production changes and continuous quality improvement.
Requirement:
Melt temperature and pressure measurement
The temperature and actual pressure of the molten polymer are critical parameters in the extrusion process, as they directly influence the viscosity of the material and its final properties, both mechanical and optical. Measuring the temperature in direct contact with the melt, rather than on the surface of the cylinder, provides a more accurate representation of the actual process conditions and, in combination with continuous pressure measurement, offers a significant advantage in rheological control.
Gefran offers an integrated solution for controlling the pressure and temperature of molten polymer, combining the precision of the Impact series pressure sensors with the reliability of Melt TCM thermocouples.
TCM sensors, with stainless steel or Hastelloy sheathing for corrosive polymers, allow direct measurement of the melt temperature and are available with thermocouples:
- Type K (NiCr-NiAl) – up to 850 °C, fast response.
- Type J (Fe-CuNi) – up to 400 °C, for less aggressive environments.
They can be integrated in a compact configuration with the Impact series, ensuring consistent measurements and simplified installation. Impact sensors, which do not require transmission fluid, ensure thermal stability <1% FS up to 350 °C and are available in the IEPLc version, which is PLc certified for safety systems.
Requirement:
Haul-off tension
A crucial step in the blown film extrusion process is the closure of the bubble itself, which is achieved by two stop rollers positioned at the top of the line. These rollers exert the necessary traction to support and tighten the film. The tension must be monitored very precisely and kept within limits to ensure the homogeneous tensioning of the film, avoiding buckling or breakage.
Solution:
Two Gefran TR load cells, installed laterally on the haul-off rolls, accurately measure the force applied during the towing of the bubble. 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 tension of the towing system via motor drives, ensuring the stability of the bubble and avoiding surface and structural defects in the film.
Requirement:
Conveyor longitudinal and transverse opening
The adjustment of the conveyor for bubble collapse generally takes place discontinuously, especially during format change operations. In addition, in large systems, the guides can open by up to several metres. It is therefore necessary to have a position detection system that can accurately monitor guide movements during the operational phases, ensuring correct positioning.
To monitor both the transverse and longitudinal opening of the conveyor, different solutions can be used, depending on conveyor size:
- The GSH-S wire position transducer, which uses Hall-effect technology, is particularly suitable for large applications such as agricultural film, because it can cover strokes of up to 18 metres while maintaining a compact design and small mechanical footprint. The sensor offers analogue output in both voltage and current.
- The WRA magnetostrictive position sensor with HYPERWAVE technology and digital or analogue output can be used to provide precise and repetitive feedback on the position of the conveyor’s side guides or on the opening of the conveyor in small applications.
Requirement:
Monitoring of the hydraulic circuit
In the blown film extrusion process, the hydraulic circuit is involved in the controlled movement of fundamental components such as the position of the rollers or the conveyor. 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.
Solution:
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 analogue 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
Requirement:
Enhancing Production Data
Requirement long description: In modern industry, companies are seeking tools capable of maximising the value of data generated by their plants to improve overall performance. It is essential to monitor machine operation in real time, prevent failures through predictive analysis, and optimise energy use. At the same time, there is a growing need to support operators and managers with contextual information and intelligent responses that facilitate everyday decision-making. The goal is to build an industry that is increasingly connected, responsive, and sustainable.
MAX and GAIA are advanced digital solutions developed by Gefran to drive the intelligent transformation of industrial plants.
MAX is an IoT platform designed to monitor machines in real time, perform predictive analyses, and optimise efficiency, helping to reduce energy consumption and downtime.
GAIA, on the other hand, is a virtual assistant based on Generative Artificial Intelligence that provides operational support, offering contextual and intelligent responses to improve daily production management.
Together, MAX and GAIA represent the perfect synthesis of a connected, responsive, and sustainable industry.
Operating Principle
The blown film extrusion process consists in several phases: melting and plasticisation of the polymer, extrusion through the die, air blowing to stretch the tube, so it forms a film, internal and external cooling, and winding of the final film.
The granular plastic material is introduced into the hopper and transferred into the extruder, where it is transported, heated and plasticised by the rotating screw until a homogeneous, molten material is obtained. The flow rate in this type of application is directly controlled by the amount of material loaded into the hopper. The melt is then pushed through a circular die, from which a tubular film of hot material emerges. The compressed air blown into the tube inflates and stretches the film, increasing the bubble diameter and reducing the thickness of the bubble wall. The film formed in this way is cooled by external and internal air streams to stabilise the shape and mechanical properties.
After the initial cooling, the bubble is collapsed by a system of guides and rollers that transform it from a tubular structure into a flat film. Only if destined to produce bags, the bubble is also folded inwards at the sides, to optimise bulk in the reel. The upper part of the line, consisting of the conveyor and the haul-off, is mounted on a structure that rotates continuously around the axis of the bubble. This rotation makes it possible to spread the film evenly on the rollers, minimising thickness variations and ensuring the even distribution of the material over the entire useful width.
The flat film passes through a first haull-off unit, consisting of opposing calender rolls that drag it upwards by exerting controlled traction. This step determines a first longitudinal orientation of the material, essential to ensure mechanical and geometric uniformity. Subsequently, the film descends through a series of descending rollers that regulate its flatness, thickness and tension, stabilising the product before collection.
Depending on the desired type of output, the film can be wrapped in a closed form to produce bags, or cut laterally and wrapped around two separate reels to produce flat films for other processes. In the latter case, the removed side portions, known as cutting scrap, are collected by an integrated suction extraction system and reinserted directly into the extrusion process or into a recovery circuit. This minimises waste, improving production efficiency and the overall sustainability of the line.
Requirements and Technology
The blown film extrusion process requires a more precise and coordinated control of multiple parameters than traditional extrusion, since the criticality of the process no longer resides solely in the extrusion recipe but in the coordination of the various motors to obtain the desired dimensions and thicknesses. The main requirements include:
- Melt temperature control: fundamental in the extrusion head and cooling rings, where fast and stable sensors are essential.
- Monitoring of molten polymer pressure: essential to prevent overloading, breakage or flow fluctuations.
- Monitoring of the hydraulic circuit: pressure is a safety parameter. Variations not consistent with the mechanical controls indicate potential anomalies or risks for the operator.
- Towing tension: this requires the precise detection of the tension exerted by the towing system during the closing and collection of the bubble after cooling.
Other requirements include:
- Precise positioning of the bubble guide, to maintain the correct trajectory of the film.
- The position of the winder unloaders.
- Data collection for diagnostics and predictive maintenance, essential to increase availability and production continuity.
Gefran offers a complete range of control platforms, melt pressure and temperature sensors and modular solutions, which can be easily integrated into any plant, to ensure efficiency, safety and constant quality in blow film extrusion lines.
