What are the functions of the metering section in an extruder?

The metering section in an extruder plays a crucial role in the overall plastic processing operation. Its primary function is to develop pressure for pumping the plastic through the system. As the materials move through this section, they are subjected to increasingly high temperatures and shear forces, which not only help in melting the plastic but also ensure that the material is adequately homogenized and measured before being pushed into the die for forming or molding.

Developing pressure is essential because it allows for the consistent and efficient flow of plastic material, ensuring that it reaches the mold cavity at an appropriate rate and with the right characteristics for processing. This pressure generation is vital, especially given the viscosity changes that occur as the material is heated and undergoes phase transitions.

While the metering section does involve some heating and movement of the material, its primary significance lies in its capacity to create the necessary pressure. This is what distinguishes the metering function from merely cooling, heating, or solidifying processes that occur at other points in the extruder. Each of those other choices represents separate and essential processes in the broader context of plastic extrusion but does not capture the specific role of pressure development exclusively associated with the metering section.