Planetary extruder used to eliminate pre-drying in PET sheet production

German extrusion machinery maker Battenfeld Extrusionstechnik has developed a new single screw sheet extrusion system that it claims will direct process PET without pre-drying while retaining flexibility to run PP and PS resins.

The new processing system is designed for companies operating extrusion lines with outputs between 800 and 1,000 kg/hr. Its novelty is the combination of a single screw extruder with a specially developed planetary degassing section. According to Battenfeld, the capital investment requirement for the new system is similar to a single-screw extruder and conventional pre-drying unit. However, maintenance costs and energy consumption are considerably lower.

Planetary gear systems are long-established in PVC processing. The technology uses several geared planetary spindles, which revolve around and are driven by a rotating central spindle. The melt is transported through the intermeshing gears, a process which continuously presents new surfaces for effective vacuum degassing.

A second short single screw conveys the degassed polymer melt from the plantary element into a melt pump, which pressurises it for delivery to the die. The first system has been running for several months in a European plant processing PET thermoforming sheet using virgin A-PET and purified reclaim bottle flakes with a maximum initial moisture content of 3,000ppm.