Hannover-based KraussMaffei Berstorff GmbH has developed an innovative system solution for TPE-V production by merging its engineering capabilities in rubber processing and compounding. Precise feeding of the rubber compound into the twin-screw compounding extruder is achieved by using a short single-screw rubber processing extruder with downstream gear pump.
The single-screw extruder and gear pump combination provides outstanding high-precision feeding performance. Bale rubber cut into strips can be processed directly instead of having to use pellets. Process efficiency and cost-effectiveness are substantially improved since time-consuming and expensive pre-pelletising of the rubber is no longer necessary. The benefits offered by the new KraussMaffei Berstorff system are especially significant in the production of soft TPE-V types. In many cases, soft TPE-Vs are produced using oil-extended EPDM rubber, which is rather difficult to pelletise owing to its sticky surface and because separating agents must be used.
The single-screw extruder ensures reliable feeding and pre-compounding of the rubber. A pressure-based control system adjusts the extruder speed in such a way that the downstream gear pump is always completely filled. The gear pump is designed to achieve precise volumetric feeding of the rubber into the twin-screw compounding extruder.
Inside the twin-screw compounding extruder, the rubber is mixed with the thermoplastic material, and the cross-linking reaction of the rubber phase takes place to form the TPE-V required. The phase morphology and the physical properties of the finished TPE-V are determined by the configuration of the twin-screw extruder. The first extruder section is designed for the compounding and mixing of the main recipe components, usually EPDM and PP, and for the incorporation of additives and processing oils. Dynamic cross-linking takes place in the downstream mixing zones of the extruder. The last extruder section is used for vacuum degassing.
The new system can also be used with an internal mixer. In this case, rubber, fillers, plasticiser oils and additives are pre-mixed in the internal mixer and fed into the extruder in the form of strips. With this solution, the twin-screw compounding extruder is merely required to mix in the thermoplastic material and, if necessary, the cross-linking agent and to perform the dynamic vulcanisation process.
Owing to their superior material properties, thermoplastic elastomers (TPEs) are becoming increasingly important. TPEs can be easily processed, dyed and recycled. Component weight, energy consumption and manufacturing costs are significantly lower than with cross-linked rubber (e.g. pure EPDM). Moreover, TPEs can be easily combined with other thermoplastic materials such as polypropylene (PP) or polyamide (PA), which enables easy integration of hard/soft components.
