Compounding lines come in many shapes and sizes. Compounding can be done on single screw extruders, twin screw extruders, reciprocating single screw compounders, batch internal mixers, and continuous internal mixers. The configuration of the line will be determined by the ingredients that have to be combined in the compounding extruder. The downstream equipment typically consists of a pelletising system.
Some pelletisers cut extruded strands that are cooled in a water bath; these are called strand pelletisers. Dicers cut an extruded sheet rather than strands. The pellets from a dicer have a uniform cubic or octahedral shape. Other pelletisers cut the material right at the die exit; these are called die face pelletisers.
Compounding extruders can also be combined with direct forming systems downstream. In many cases a gear pump is placed at the discharge end of the extruder to generate the diehead pressure and to control the throughput. An example of a combination compounding/sheet extrusion line is shown here:
The plastics is introduced to the first feed port of the compounding extruder, the filler is introduced to the second feed port, and the volatiles and air entrapment are removed from the vent port. A gear pump is placed between the compounding extruder and the sheet die.
The sheet is fed to a roll stack, from there it is handled as in a normal sheet line as discussed earlier. Compounding lines will be covered in much more detail in a later session.
Profile Extrusion Lines
Many extrusion lines are used for the production of profiles. Profile lines also come in many shapes and forms. A typical extrusion line consists of an extruder, a calibrating unit, a cooling unit, a measurement device, a haul-off, and a coiler or cutter or saw.
On some profile lines a film or foil is laminated to the extruded profile. The number of profiles that are extruded is enormous; some examples of extruded profiles are shown here.
