Multifunctional dosing system for combining natural fibres with polymers

Gravimetrische Synchrondosier- und Mischeinheit aus der Graviplus-Baureihe mit vier Labline-Dosiermodulen; ein Dosiermodul kann automatisch mit einem Metro-Fördergerät befüllt werden, die übrigen drei sind manuell zu befüllen. (Bild: Motan-Colortronic) / Graviplus-series gravimetric synchronous dosing and blending station with four Labline dosing modules, one of which can be automatically supplied with material by a Metro conveying unit, while the other three have to be manually filled. (Image: motan-colortronic)

Das modular aufgebaute Dosiersystem lässt sich ohne großen Aufwand mit verschiede-nen Dosiermodulen für Granulat, Mikrogranulat, Pulver und Mahlgut sowie für Flüssigkei-ten schnell an unterschiedlichste Dosieraufgaben anpassen. (Bild: Motan-Colortronic) / The modular dosing system comes with four different dosing modules and can be quickly and easily adapted for feeding granulate, micro granulate, powder, grinding stock and liquids and various dosing tasks. (Image: motan-colortronic)

Gesteuert wird das Dosiersystem über die Gravinet GP-Steuerung, deren Bedienung me-nügeführt über einen 12,1“-Bildschirm mit TFT-Touchscreen erfolgt. (Bild: Motan-Colortronic) / The dosing system is controlled by a Gravinet GP control unit, which is operated using a menu displayed on a 12.1" TFT touch screen. (Image: motan-colortronic)

The University of Rosenheim has built a system – a pilot plant unique across the whole of Germany – for developing climate and resource-friendly procedures and materials for automotive applications, timber construction and furniture manufacture as well as a wide range of other applications. The aim of this investment project is to combine the advantages of wood fibres with those of polymers in order to develop technologically innovative products made of natural fibre-polymer composites and to develop appropriate manufacturing technologies for producing the same.

MUNACU – an inter-faculty research collaboration

The interfaculty research collaboration project "MUNACU - Multifunctional Natural Fibre & Synthetics Composites" was sparked by an announcement by the Federal Ministry of Education and Research (BMBF). This announcement detailed the fact that the BMBF is offering help to universities of applied science seeking to expand their research profile or a research focus through investment projects with the acquisition and application of research equipment through its "FHInvest" funding initiative.

"Initially, we were going to combine classical wood processing methods with proven and efficient one-shot injection moulding technology", explained Peter Karlinger, professor at Rosenheim University, about the project's origins. Karlinger's specialist area is injection moulding and he conducts research in the area of injection moulding process technology, lightweight construction and clean room technology. Karlinger designed the "Multifunctional lightweight construction using raw or natural materials, with an emphasis on renewable fibres" project together with his colleagues Dr.-Ing. Michael Schemme, who specialises in fibre composites, and Dr. Andreas Michanickl from the faculty of wood technology and construction.

Integrated system configuration

In designing the pilot system, the researchers pursued an integrated concept that simultaneously meets the objectives expressed by the superordinate principle of "from the raw material to the fibres and the final component". This means that the system is correspondingly complex and comprises a number of components that are located in different departments:

- Refining system inside the university's Wood Materials & Engineering Laboratory for producing specific natural fibres
- DCIM direct compounding injection moulder in the Polymer Processing Centre
- Gravimetric synchronous dosing and blending station with four dosing modules for supplying the compounder
- Vertical clamping unit that can simultaneously be used as a stamping press
- Additional injection moulding unit (bolt-on unit)
- IMC injection moulding compounder with a continuous gravimetric dosing system
- Six-axis robot, experimental tools and test equipment

Material preparation and processing using DCIM technology

In Direct Compounding Injection Moulding (DCIM), the raw material is both prepared for processing and then moulded in a single production step.

This is achieved by employing a single-screw compounding extruder that continuously feeds material to a standard plasticizing and injection moulding machine. The tip of the extruder is fitted with a switch valve for controlling the material feed to the plasticizing and injection moulding machine. There is no need for a melt reservoir; and the injection process itself is not changed.

Directly processing material at a uniform temperature has both technical as well as economic advantages. This includes better material quality thanks to the fact that the material is not put under any significant thermal or mechanical stress (lower shear stress). This process also, for example, makes it possible to gently and uniformly integrate longer fibres, which is very important when working with natural fibres. Forgoing the production of a semi-finished product also saves costs and energy. The DCIM technology was jointly developed by KraussMaffei, Motan-Colortronic and the compound developer Exipnos.

Quadruple Labline dosing system – Precision component dosing

The compounding extruder is supplied with material by a Graviplus-series gravimetric synchronous dosing and blending station from Motan-Colortronic, Germany. The dosing system features four Labline dosing modules. One of these dosing modules can be automatically filled with material by a METRO conveyor, while the other three are designed to be filled manually. The dosing modules are equipped with dosing screws that are suitable for materials with a range of different flow properties (free flowing, average and poorly flowing). One of the dosing units has been retrofitted with a twin dosing module.

The dosing system is modular and can be quickly and easily adapted to a range of different dosing tasks, which makes it perfect for use in the planned research project. The different modules include modules for dosing granulate, micro granulate, powder, grinding stock and liquids. The dosing system also includes dosing modules with twin screws and mixers for dosing materials that do not flow easily or not at all.

The Graviplus uses the differential weighing method, which is also known as 'loss-in-weight' feeding. This is because loss-in-weight feeding is significantly more accurate than batch dosing as demonstrated by dosing tests conducted during a previous project. This aspect is particularly important when working with materials that are difficult to feed. The fact that the material is fed directly to the compounding extruder also means that it is near impossible for material to separate, which, in addition to the required level of dosing accuracy, was another reason for choosing a continuous gravimetric dosing system.

During operation, the control unit compares the actual with the specified nominal throughput rate, which means that deviations are instantly identified. These deviations are then compensated for using the dosing modules' feed speed. The material is continuously and synchronously fed into the storage container, where it is mixed to form a homogeneous blend that is then fed into the compounder's material feed. This process ensures that the material does not separate.

Thanks to the fact that the material flow is constantly monitored and controlled on the basis of its weight, bulk density fluctuations, particle size differences or changes in flow behaviour only have a marginal affect on the differential system's dosing accuracy. This aspect is also an important factor for the research project that is going to be conducted in Rosenheim, because dosing and conveying natural fibres is considered a serious challenge.

The dosing system is controlled by a Gravinet GP control unit, which is operated using a menu displayed on a 12.1" TFT touch screen. The control unit displays messages and alarms in plain text.

"Apart from needing a system with a high level of dosing accuracy and that would allow us to reproduce results, we also needed one that is easy to use. With this system, changing the test set-up and the material only takes a few minutes" explained Karlinger.

Research aims

The technologies now available to us in wood and polymer materials processing allow us to research a wide range of different material and process technologies. This research is primarily aimed at investigating and developing new materials and lightweight construction methods that will allow us to produce components from natural fibres in a more resource-friendly and cost effective way, and such that they are suitable for a wide range of applications. The researchers are also planning to conduct comparative tests with the DCIM and classical parallel double screw extruders with reference to the IMC injection compounder, which is also equipped with a Motan-Colortronic continuous gravimetric dosing system.