| 摘要 |
The present invention relates to a method for the pelletization of plastics and/or polymers, wherein a melt coming from a melt generator is supplied via a diverter valve having different operating positions to a plurality of pelletizing heads through which the melt is pelletized. The invention furthermore relates to a pelletizing apparatus for the pelletization of plastics and/or polymers having a diverter valve which has at least one melt generator connection, at least two pelletizer connections as well as a switching gate for selectively connecting the melt generator connection to at least one of the pelletizer connections, with a respective pelletizing head being connected to the at least two pelletizer connections and a melt generator having a variable melt volume flow being connected to the melt generator connection. Finally, the invention also relates to a diverter valve for such a pelletizing apparatus having a melt generator connection, a pelletizer connection as well as a melt passage for the connection of the melt generator connection to the pelletizer connection. The present invention therefore starts from the idea of using a plurality of pelletizing heads with different passage capacities and of hereby enlarging the throughput window to be able to work largely continuously without intermediate interruptions and to shorten unavoidable start-up processes by switching in pelletizing heads having small throughput capacities or to minimize them with respect to the start-up products which occur. In accordance with an aspect of the present invention, a plurality of pelletizing heads having different throughput capacities are used sequentially for the start-up of the pelletizing process, with the melt first being supplied to a first pelletizing head having a smaller throughput capacity and then the melt volume flow being increased and the diverter valve being switched over such that the melt is diverted by the diverter valve to a second pelletizing head having a larger throughput capacity. The time and thus the amount of the start-up product until the melt generator reaches the lower throughput limit of the pelletizing head and the pelletizing process can be started are cut by the use of initially one pelletizing head having a throughput capacity which is as low as possible. No further start-up product is incurred from the start onwards of the pelletizing process at the lower throughput limit of the said first pelletizing head. The melt volume flow is increased quantitatively for so long until the diverter valve can be switched to the second pelletizing head having the larger throughput capacity with no start-up product being incurred during this time period. Moreover, the throughput window is enlarged in total so that the number of unavoidable start-up procedures with start-up product arising therein is reduced since it is possible, on a ramping down of the melting performance below the lower throughput limit of the larger pelletizing head which may become necessary for various reasons, to switch back to the first pelletizing head.
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