subject: Mechanism Of Screw Extruder [print this page] A typical extruder screw comprises a root and a single screw extruder and twin screw extruder flight helically extending about the root. The flight forms with the interior cylindrical surface of the barrel a helical channel along which the thermoplastic polymer is conveyed. The screw typically has a feed section, a tapered transition section and a metering section. The feed section is for conveying bulks of raw unmelted polymer from the hopper into the barrel. The tapered transition section is to compensate for the volume decrease as the bulk polymer is compressed and to force the polymer tight against the barrel inner wall for good heat conduction and efficient melting by mechanical shearing. Typically, the polymer begins to melt in the transition section. The necessity for good compaction is especially important in this transition section of the screw to ensure uniform melting of the polymer. The metering section is for advancing the melted polymer to the discharge end of the extruder.
In one aspect, the present invention is an extruder screw for use in a barrel of an extruder for forwarding at least one thermoplastic polymer from a first end to a second end of the extruder comprising a transition section, said single screw extruder comprising at least one flight, wherein one flight extends substantially along the entire length of the twin screw extruder and forms a spiral channel through which the polymer is transported; and a dam positioned at the point where the rapid melting of the solids starts to slow down and the rate of solid bed width decrease approaches zero.
In another aspect, the present invention is a single screw extruder for use in a barrel of an extruder for forwarding at least one thermoplastic polymer from a first end to a second end of the extruder comprising:
a feed section, a transition section, and a metering section, said extruder screw comprising at least one flight, wherein one flight extends substantially along the entire length of the extruder screw and forms a spiral channel through which the polymer is transported; and a dam positioned at the point where the rapid melting of the solids starts to slow down and the rate of solid bed width decrease approaches zero.
