Continuous production of elastomer compounds on corotating twin-screw extruders

For more than fifty years, the co-rotating twin-screw extruder has been used for continuous processing

and mixture of highly viscous products. Thermoplastic polymers, including thermoplastic

synthetic elastomeres, are its most important application. Through its modular construction and

various degrees of freedom within the process configuration, the twin-screw extruder can be well

adapted to different processing tasks.

The technical reliability and the high economic efficiency in its classical operational areas led quite

early to considerations, to also use the twin-screw extruder for the continuous production of elastomer

compounds.

These are traditionally produced discontinuously on internal mixer. Scientific investigations in laboratories

prove that it is basically possible to produce elastomer compounds on twin-screw extruders,

capable of cross linking.

Furthermore first positive experiences with industrial standards have already been made. Basically

the main advantages of continuous compared to the discontinuous mixing process, lie in the

steady operating method, which leads to a constant product quality and a constant low power demand.

The quality of a continuous mixing process decisively depends on the accuracy of feeding the raw

materials. Most additives are available as a well free-flowing bulk materials or as a liquids and can

be easily fed to the mixing process with help of commercially available gravimetric solid metering

units and pumps.

In contrast, dosing of rubber often causes difficulties. Granular elastomeres often is expensive and

tends to agglomeration. Meanwhile, a system consisting of a single-screw extruder and a gear

pump has been developed that is able to convey reliably and inexpensively roughly chopped bale

rubber or rubber slabs into the twin-screw extruders.

Therefore, good conditions exist to use the continuous mixing process economically effective on

co-rotating twin-screw extruder in the rubber industry.