- MIXING Know-how
Numerous advancements have made the standard machine for base compound mixing lines even better.
When it comes to energy consumption, personnel deployment, work safety and process reliability, the conical ConvexTM twin-screw extruder is the undisputed efficiency champion among machines for discharging rubber mixtures from an interior mixer and feeding them to batch-off units. Its compact design with separate drives, the cooled screws, its robustness and a fully hydraulic calender make it a versatile and reliable machine which delivers impressive throughputs – with very good temperature control and excellent self-cleaning. The unique characteristics of the ConvexTM are guaranteed to increase the quality and performance of mixer lines – which is why it’s no wonder that it has been the standard in the tyre industry in Europe for many years now.
Fit for more applications
he latest developments now also make it attractive for other players and markets within the technical rubber goods industry. This is because the developers at Pomini Rubber & Plastics have added some new functions to the ConvexTM – functions which enable it to process sensitive raw materials and to make rapid and safe colour changes. The new Screw Inspection System, for example, makes it possible to open the extruder rapidly by means of an automatically driven mechanism, in order to exclude any possibility of contamination when changing over to very critical mixtures. Moreover, the system permits very rapid and easy inspection and maintenance of the extruder.
In addition, the engineers have developed a modular drive concept to satisfy various requirement levels. Now the customer can select from a number of different drives.
The following variants are possible:
- Four identical drives (motor + gearbox) for the two screws and the two rollers. Advantage: simplified spare parts inventory.
- Two identical drives each for screws and rollers, each with optimised power output for extruder and calender. Advantage: less expensive and more energy-efficient.
- Only one drive unit for the extruder and two for the calender. Advantage: less expensive and simpler.
- Only one drive unit each for extruder and calender. Advantage: Lowest cost with full functionality – except for the possibility of driving the calender with friction between the roller pair.
And our Italian colleagues have also optimised the temperature distribution: the already highly efficient tempering of extruder housing and extruder screws has been enhanced with an optional screw flight cooling system. It guarantees a minimal temperature rise, even at maximum discharge capacity. In addition, the so-called ASMA Cool Rollers use a combination of excellent surface tempering and special surface characteristics to minimise problems due to the adherence of sticky mixtures.
Using sophisticated screw geometries and an optimised extruder design, the developers also managed to boost the performance of the ConvexTM considerably. Now smaller models can be configured for higher efficiency, so that the discharge capacity is increased by up to 50% – with the major advantage for the customer that it is often possible to use smaller units, which are not only less expensive to purchase but also require less energy to operate.
Here is an example: the size of the extruder is selected according to the dimensions of the door top of the mixer installed above it, so the batch does not get wound up and hang there as it slides downward. In terms of that dimension alone, ConvexTM 7 is adequately sized for a BM305N. But in terms of throughput, it is the right machine only for longer mixing times (and therefore lower throughputs), such as with masterbatches. If final mixes are produced with very short mixing times, however, the ConvexTM 7 is not the right choice. Most customers install a ConvexTM 12 in this case. With the new developments, the ConvexTM 10 now becomes an attractive option for them. Its outside dimensions correspond to those of the ConvexTM 7 while its rated throughput approaches that of the ConvexTM 12 – and yet it is considerably less expensive than the latter.
Bottom line: with its new functions, the ConvexTM is attractive not only for more applications. It is now less expensive and so even more attractive, without sacrificing any of its advantages.