Melt pumps for pipe extrusion

Pipe extrusion with melt pumps

Pipes are often made from plastics using the direct extrusion process. In this process, the desired material is melted in an extruder and pressed through an extrusion die/pipe head nozzle, in which the actual pipe is then created. So-called polyolefins are used for pipe extrusion. These plastics are semi-crystalline thermoplastics that have very good properties and can be easily shaped and processed. The best-known polymers from this group are:

  •     Polyethelene (PE)
  •     Polypropylene (PP)
  •     Low-density polyethylene (LDPE)
  •     Linear low-density polyethylene (LLDPE)
  •     High-density polyethylene (HDPE)

In extrusion, it is important that the mould is always supplied with sufficient polymer melt and a constant pressure.

Landscape

The role of the melt pump

The melt pump has been an integral part of a wide variety of extrusion applications for years. Its use downstream of the extruder significantly improves product quality and also brings many economic advantages. For example, the service life of the extruder is increased, the throughput can be significantly increased, temperature and pressure are constant and fully controllable for the user. Monitoring is carried out by means of corresponding sensors in the housing and end plate.

Advantages of a melt pump in pipe extrusion

  • Full temperature control
  • Constant flow rate for guaranteed consistent wall thicknesses
  • Pulsation compensation of the extruder
  • Easy maintenance
  • Retrofittability in existing lines

Technical parameters

Viscosities
up to 30.000 Pas
Media
PVC · PA · PE · HDPE · MDPE · LDPE · PP
Differential pressure
up to 250 bar
Throughput
up to 2890 l/h
Further information

Exemplary structure of pipe extrusion line

  • Twin screw extruder
  • Melt pump
  • Cooling and extractor unit
  • Cutting Unit / Pipe Saw

  • Twin screw extruder ZSE MAXX

    The extruders of the ZSE series are twin-screw extruders that guarantee both high torque and high volumetric throughput. A modular system offers maximum flexibility in the configuration of the screws and barrels and the associated tasks.

  • Melt pump EXTRU series

    Pulsation and conveying or pressure fluctuations cannot be avoided in extruders due to their design. The rotating screws cause pulsation, which can have a negative effect on the downstream equipment. Melt pumps of the EXTRU series have a number of positive features and conveying characteristics that significantly improve product quality and process performance.

    •     Reduced shear and pulsation
    •     Constant pressure build-up and flow rate
    •     Low temperature input and controlled temperature control

  • Cooling and extractor unit

    Cooling and haul-off unitThe cooling and haul-off unit transports the extruded pipe to the sawing unit. The cooling distance depends on the layer thickness of the pipe and its length. The cooling water temperature must not exceed 25 °C as a rule. Watering pumps regulate the cooling water flow and keep the temperature level stable.
    unit.

  • Cutting Unit / Pipe Saw

    In this process stage, the pipe is cut to the desired length and bundled into transport and storage units. The tube sawing units can be designed in different ways, for example as cutting or non-cutting sawing units.

Process setup

This exemplary process setup shows the combination of twin screw extruder, melt pump, haul-off unit and pipe saw. This model was realised with the kind support of Leistritz. Extruders of the ZSE Maxx series in combination with melt pumps of the EXTRU series achieve highest efficiency and are a guarantee for best product qualities. 

Further information on the ZSE extruder series