Secondary Extruders for Tandem Foam Sheet Lines

4 Secondary Extruders for Tandem Foam Sheet Lines 

The secondary extruder is typically larger in diameter than the primary machine, and it rotates at a lower screw speed. For example, a midsized tandem line would be constructed using a 114.3 mm diameter primary extruder and a 152.4 mm secondary extruder. The primary extruder would operate at a normal screw speed (50 to 70 rpm) and could generate the pressure required to run the downstream equipment. The secondary extruder would operate at a lower screw speed (10 to 15 rpm) so that the entry and exit pressure for the extruder are about the same. 

Cooling water flow to the barrel jacket coolers for the secondary extruder removes the excess energy in the resin dissipated by the primary extruder and also the energy dissipated by the screw in the secondary machine. For a properly designed line, the performance of the secondary extruder determines the overall rate of the process. 

A typical pressure and temperature profile for a secondary cooling extruder is shown in Fig. 15.17 for a PS resin. 

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