WCA September 2015

46 / 108

44 Wire & Cable ASIA – September/October 2015
❍ Redesign work from Frigeco has been extensive
Graphics bigstockphoto.com Artist Olechowski
Technologynews
WHILE the extruder is the melt supply device in most
extrusion processes, the basic design has not evolved much
over the last few years. Its purpose is to supply molten
material at a constant melt temperature and at a constant
volumetric rate.
The typical extruder is made up of three geometric sections:
The feed section or solids conveying, the transition or melting
section, and the metering or pumping section.
Frigeco has redesigned a number of areas on the Frigeco
extruder, including the feeding zone; extruder barrel and
screw profile; thermoregulation; stable and reactive
electronics; and increased output and lower energy
consumption.
The actual melting takes place in the feeding zone. Most
plastics are poor conductors of heat and are melted by
shearing the material against the barrel rather than by heat
conduction.
Consistent flow of material into the extruder barrel is
obtained by controlling the temperature of the feed throat.
However, you cannot rely on plant water supply which can
vary from 38ºF (3ºC) in the winter to 75ºF (24ºC) in the
summer. These fluctuations in temperature will affect melt
temperature and cause product variations.
Therefore, controlling the temperature of the feed throat is
essential to constant solids conveying. The Frigeco grooved
feed throat, integral cooling jacket and closed loop water
temperature control circuit provide a constant feeding zone
temperature. The next section is the transition zone, where a
large amount of heat will be generated.
Much of the heat necessary to plasticise the material comes
from the rotation of the screw. The faster the screw rotates,
the higher the surface speed of the screw, the greater
amount of shear in the material and therefore an increase in
melt temperature.
The combination of rotational speed, adequate cooling and
accurate temperature control will keep the shear rate down
and prevent localised overheating.
Frigeco – Italy
Website:
Frigeco engineers
redesign extruders