Higher speed and higher output is the mantra at K 2007 that major extruder manufacturers of the world will chant profoundly. Speed could go up from the existing 100-250 rpm to as high as 1500 rpm. Machine manufacturers are designing output of more than double the conventional speed to provide higher profitability to the processors. In addition, the show will highlight a trend toward larger extruders for cast film, especially PET to gain output efficiency. Blown film machine builders will show new screws, dies and air rings designed to raise output 20-30% and accommodate polymer changes with greater flexibility. In pipe and profile, new systems also have more flexibility to change output and product sizes.
High-speed extruders first appeared in prototype at K-2004 from several German machine makers and have been rapidly commercialized, with over 50 such machines running in Europe, China and the Middle East. There are none so far in North America. Approximately more than 50 new machines with double or triple normal speed (400 to 500 rpm) are up and running. Most of these high-speed machines extrude thin sheet for thermoforming. A few make pipe, wire/cable; and one makes cast stretch film. The very high-speed models are all between 25 and 90 mm diameter and typically about a third longer than conventional extruders�36:1 to 38:1 L/D. They supply the same output as conventional extruders of 125 to 189 mm diameter and 24:1 to 30:1 L/D. Being so much smaller, the high-speed models offer the advantage of much faster colour and resin changes. The secret of high-speed extrusion that can turn 10-15 times faster than normal speed and not over-shear the plastic, is that it works only with low-viscosity materials�primarily PP, PS, and ABS. High-speed extrusion is under development at beta sites for PET, HDPE, and LLDPE, and does not work with heat-sensitive PVC, PMMA or PC.

Screw design is the most important part in high-speed extrusion. High rpm extruders are roughly a third longer than usual. They have deeper intake flights and a longer compression zone than normal screws and need a melting section roughly twice as long. High-rpm screws also need to mix without generating much pressure or heat, so they are very material-specific. All high-speed extruders use either a four-motor torque drive; a permanent magnet, synchronous torque motor; or a high-torque AC motor directly coupled to the screw. At least five companies have built high-speed extruders. These suppliers are still trying out different drive motors and experimenting with screw designs. Several machine builders will feature new cast film lines larger than any they have built before. Blown film co-extrusion continues to add more layers.

A patented feedblock encapsulation technology to coextrude heat-sensitive and corrosive PVDC barrier resin and keep it from touching the die will be exhibited. The same principle has advantages with EVOH, which tends to form gels in contact with the die, and with nylon, which is notoriously difficult to purge from of a nine-layer die. When encapsulated, nylon can be purged in under an hour.
In short, all major extruder manufacturers will aim for the processors to gain from higher speed & output.