Applications
Hydraulic injection machines are the most widespread in the plastics industry because of their robustness and ability to handle high clamping forces. They use a hydraulic circuit to move all the main actuators, i.e. injection unit, injector, ejector and closing platens. They are appreciated for their reliability and versatility, and are used in sectors ranging from automotive to packaging. The architecture of the machine favours the optimisation of production cycles and the reduction of waste, offering a versatile solution for both mass and medium-small batch productions.
Requirements:
Control of plastic pellets
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Injection unit position
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Injector position and movement
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Position of the moving platen
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Ejector position
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Monitoring of the hydraulic circuit
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Management of the Hot Runners
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Temperature control of the barrel
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Control of the moulding process
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Tie bar deformation
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Deformation of the moving platen
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Enhancing Production Data
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Requirement:
Control of plastic pellets
Before the injection phase, the plastic pellets must be heated and dehumidified to eliminate residual moisture. Failure to do so may allow bubbles to form inside the product during the moulding process, compromising both product aesthetics and functionality.
In addition, there is the risk that wet pellets could damage the heating elements of the extrusion cylinder, greatly increasing the risk of unexpected machine downtime. Stable thermal control is therefore essential.
Solution:
The use of smart solid state relay device with soft-start feature allows the progressive heating of the pellets, avoiding thermal shocks and ensuring the complete elimination of moisture. The integrated diagnostic system detects any partial breakage of the load, improving reliability and reducing machine downtime.
Requirement:
Injection unit position
The injection unit must be able to approach and rest correctly on the injection plate, without displacements caused by the opposing forces that develop during the injection phase. It must also be able to retract in a controlled manner so that the cylinder may be purged. Precise and stable position measurement is therefore essential to ensure production continuity, item quality and the protection of mechanical components.
Solution:
The WPA magnetostrictive sensor uses Hyperwave technology, which guarantees a resolution of up to 0.5 μm and the absence of wearable components, making it ideal for applications subject to high stress and requiring extreme precision and repeatability. The floating sliders make installation easy: the aluminium bar is fixed to the base of the machine and the slider easily attaches to the injection unit, ensuring stable and long-lasting contact. The sensor can be connected via analogue, digital, CANopen or Real-Time Ethernet outputs, ensuring maximum flexibility of integration with different control systems.
Requirement:
Injector position and movement
The injector must have a precise and repeatable stroke to always inject the correct amount of material into the mould cavity. The stability and repeatability of the position are essential to avoid defects in the item, waste of material and stress on the mechanical components. Small variations in stroke can compromise product quality and slow down production, which make a reliable, high-resolution sensor essential.
Solution:
The WPA sensor is installed with an aluminium bar fixed to the machine and a slider connected to the injector. It can measure position and speed in real time, so as to start the motor quickly and slow it down progressively when coming close to the set point, achieving a soft stop.
- Wear-free components reduce maintenance and the risk of failure.
- Flexible outputs: analogue, digital, CANopen or RTE.
- High repeatability for optimal injection cycle quality.
- Protects the mechanical components as the injector advances and recedes.
Requirement:
Position of the moving platen
The central platen, pushed by the toggle, must move back and forth with precision. Controlled speed is fundamental: the platen starts fast and slows down, approaching the mould to close correctly. Accurate position detection stops the injector from working without proper contact, preventing damage or leakage of the material. The repeatability of the movement ensures the quality of the item and the protection of the machine and the mould.
Solution:
The WPA sensor continuously provides feedback to the PLC regarding platen position and speed, allowing for a soft and safe stop by controlling the drives.
- Quick and accurate position detection.
- Speed control for a soft approach.
- Prevents premature injection and mould damage.
- Analogue, digital, CANopen or RTE outputs.
- Simplified installation with bar and slider.
Requirement:
Ejector position
The ejector usually requires two strokes to completely eject the piece from the mould and return to the initial reference position. The repeatability of the movement is essential to avoid damage to the mould or item and to ensure production continuity. Position monitoring allows the operator to optimise ejector timing and manage the ejector stroke, reducing mechanical shocks and stresses and ensuring that the ejector moves precisely.
Solution:
The WPA sensor is fixed with an aluminium bar to the machine body while the slider is connected to the ejector, detecting position and speed in real time.
- Continuous measurement of position and speed.
- Allows for soft stop and repeatable stroke.
- Reduces mechanical shock and stress.
- Analogue, digital, CANopen or RTE outputs for maximum flexibility.
- Wear-free components, minimal maintenance.
Requirement:
Monitoring of the hydraulic circuit
In the process of moulding plastic or rubber components with hydraulic machinery, the hydraulic circuit is involved in all or part of the movements. 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 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:
Management of the Hot Runners
The design of the material distribution channels in the mould is often one of the most critical jobs. It is essential to put as many of these channels as possible to try to obtain the most uniform distribution in the form, but, at the same time, the channels must not be too many or too small, because material that solidifies inside the form is difficult to restore to a molten state. For this reason, the management of hot runners can help in many moulding situations, heating the channels inside the mould to keep the material in a semi-liquid state.
Gefran technology for hot-runner thermal control relies on solid state relay, PID controllers and thermocouples.
- Each resistor is managed in a closed loop via PID controller, integrated into the PLC or assigned to dedicated multiloop controllers such as the GFXTERMO4, which allows the temperature to be maintained within ±0.5 °C of the setpoint.
- 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.
Requirement:
Temperature control of the barrel
The heating cylinder of the injection machine works like an extruder, so correct temperature control is essential to obtain an optimal finished product. Temperature control is necessary to ensure the thermal stability of the cylinder, so that the system can respond quickly to variations in thermal or process load, avoiding potential defects and deformation of the polymer.
Gefran technology for thermal control relies on solid state relay, PID controllers and thermocouples:
- Each resistor is managed in a closed loop via PID controller, 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 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:
Control of the moulding process
The injection moulding process requires the correct balance between the quality, objective and speed to be derived from the material used for moulding and the design of the item to be moulded. The process control must take these characteristics into account to move the different electric or hydraulic drives while managing complex recipes. In addition, the PLC must be able to support rapid changes in materials, offer integrated diagnostics and provide a rapid response in the event of deviations.
Solution:
G-Mation is the platform for the complete, synchronous and integrated control of the injection moulding 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:
Tie bar deformation
Calibration of the mould closing force alone is not always sufficient to guarantee the quality of the process. In many cases, the tie bars are not tensioned evenly, which results in the applied force being concentrated on one of the four corners of the platen. This imbalance generates an inhomogeneous injection that can produce burrs and aesthetic defects, and over time lead to wear or breakage of the tie bars themselves.
Gefran proposes two approaches to monitor tie bar deformation:
- Continuous monitoring: “lance” sensors, such as the ML1018 models, installed in special holes in the tie bars, detect deformation in each closing cycle. It is possible in this way to obtain detailed trends and promptly intervene on the process.
- Mould change monitoring: QE2008 magnetic sensors, which can be positioned directly on the tie bars, allow quick checks during the test cycles at each format change, without the need for permanent installation.
Requirement:
Deformation of the moving platen
The force required to open and close the mould is cyclically applied to the moving platen; an imbalance of the force applied during closing can cause defects in the finished item, mechanical stress on the structures or premature failures. The accurate monitoring of the deformation of the platen pushed by the hydraulic force enables prompt intervention in the event of any imbalances, maintaining high product quality and improving the durability of both the machine and the mould.
The Gefran SL strain link sensor is an ideal solution for closing force monitoring because it is so easy to install: it is mounted directly on the back of the moving platen, with no complex operations needed. It is available in SL-VAA and SL76-VDA versions, with integrated amplifier and respective analogue or digital output, providing for easy integration into existing control systems.
Designed for industrial applications characterised by very fast cycle times, the SL sensor guarantees reliability and precision even in harsh conditions.
- Mechanical deformation amplification between the two installation areas, with stable and repeatable signal.
- Optimal in voltage mode, for accurate and responsive monitoring.
- Robust stainless steel structure with IP54 protection rating, resistant to shocks, vibrations and contaminants typical of the production environment.
Requirement:
Enhancing Production Data
Operating Principle
The heart of the hydraulic machine is the hydraulic circuit that transfers power to the different moving elements. The plastic granules are plasticised inside the heated cylinder and pushed by the injector towards the mould cavity. The pressure and injection speed are regulated by the oil under pressure, which acts on the hydraulic cylinders connected to the various mechanical elements. The moving platen, operated by toggle or direct cylinders, closes by tightening the mould with the force necessary to counteract the injection pressure. Once the material has been injected, the mould remains closed until the item solidifies; the hydraulic ejector then pushes it out. Circuit management requires the constant monitoring of oil pressure and temperature, as well as precise control over actuator position to ensure repeatable cycles and reduce waste. Mechanical components, such as linear guides and recirculating ball screws, ensure precise and fluid movements, while advanced sensors constantly monitor temperature, pressure and material flow. These data can be used by the operator to optimise the process and intervene promptly on any anomalies, reducing machine downtime and increasing overall efficiency.
Requirements and Technology
Hydraulic machines need solutions that combine robustness and precision. The main requirements are:
- Monitoring the position of the injection unit, injector, ejector and moving platen, to ensure repeatable and safe movements. Magnetostrictive transducers are ideal because of their resistance to high pressures, long life and the ability to also provide speed values in real time.
- Monitoring of pressure in the hydraulic circuit, crucial for managing injection pressure and closing force.
- Thermal management of the mould and the plasticiser cylinder, necessary to keep the viscosity of the material constant and speed up the cycles.
Gefran offers a complete range of control platforms, pressure and position sensors and modular solutions that can be easily integrated into any plant, to ensure efficiency, safety and constant quality for the injection moulding process of plastic or rubber products.
