Melt Extrusion or profile extrusion is a
basic method of polymer processing. Melt extrusion essentially is a
continuous process, typically used for mixing and designing materials that
can be molded. It can be either used as the primary method of forming or as
a technique of transporting and subsequent metering of the molten plastic
before its formation. To understand the basics of melt extrusion process is
to visualize how we extrude toothpaste onto our toothbrush. In processing of
plastics a screw extrusion is used.
The basics of Melt extrusion or simply profile extrusion as used for
extruding materials like thermoplastics starts with an Extrusion line.
A typical extrusion line consists of the following items, as described in
the image above.
- Material feed hopper
- Basic extruder (drive, gearbox and screws)
- Extrusion die
- Calibration units
- The haul-off
- Saw or any other cutting device
- Treatment devices to be used for final finishing and handling
The Melt Extrusion Process
A basic melt extrusion process functions like this. A hopper is used for
holding the raw plastic material. This plastic material can either be in the
form of powder or granule. The hopper feeds this continuously into the
extruder. The extruder has a heated barrel that contains a rotating screw.
The screw is used for transporting the polymer to the die head.
Consequently, the material undergoes the stages of heating, mixing,
pressurizing and metering. At the stage of the die, the polymer is able to
take up roughly the shape of the article. The melt plastic material
(extruded) is then cooled. For cooling, air or water is used and gives the
final shape. And finally, as the polymer cools, it is drawn along by using
haul-off devices. Then depending on requirement of soft or hard it is either
coiled or cut to length.
Advantages of Melt Extrusion Processes
The Melt extrusion process offers the following advantages:
- Small equipment
- Economic and continuous process
- High efficiency in mixing
- Quick processing time
- Process parameters can be easily controlled
Potential Application of Melt Extrusion
Not withstanding some of the weaknesses of Melt extrusion a wide variety of
industrial applications utilize melt extrusion profitably. Fluoropolymer
tubing manufactured via a melt extrusion process is utilized in applications
involving fluid handling for a number of reasons. The main benefits are
perfect clarity, resistance to UV, flexibility and chemical resistance. PFA
and FEP tubing are used to retrieve ground water for purposes of analysis.
Other fluid applications include transferring of deionized water or
chemicals, which cannot infiltrate or break down a fluoropolymer tubing.
Industries like semiconductor, biotech, and pharmaceutical also utilize melt
extrusion process.
Various mechanical applications also utilize Fluoropolymer tubing produced
through melt extrusion. Standard tubing, convoluted tubing, and other heat
shrinkable products are commonly utilized for insulating wiring, bundling of
cables, fiber optics etc. The advantages include:
- Low friction
- Light weight
- High temperature characteristics
- Insulation properties
