Melt pumps for extrusion

An example from the upstream process stage in fibre production.

Extrusion for the production of fibres

Synthetic fibres are used in a wide range of products. As fishing lines in the form of PE-UHMW fibres for the consumer sector, as nonwovens for the manufacture of clothing or as synthetic fibres in carpets, the fibres are used in many products. The fibres are versatile and extremely robust. The areas of application for fibres are just as versatile as the types. In the course of a rethinking towards circular economy, fibres are nowadays not only made from so-called virgin polymer, but also from recycled plastics.

For example, fibres are made from recycled PET bottles (PET post-consumer bottle flakes) in various production processes. In addition to the use of extruders, filters and degassing units, as well as various other process equipment, melt pumps are also used to increase the pressure. Depending on the process, the melt pumps are used upstream or downstream of the filter units. Upstream of the filter unit, they enable extremely fine filtration due to the high pressure.

Landscape

Melt pump as booster pump in extrusion and fibre production

The melt pump plays an important role not only in processes with recycled material. Melt produced from post-consumer material must be cleaned after melting and homogenisation in the extruder in order to avoid unwanted contamination in the material. Impurities would have a negative effect on the later course of the process and on the quality of the product. Fine-mesh filter units cause high pressure losses after the filter. At this point in the process, the pressure loss can be reliably compensated by using a melt pump. If the melt is used to produce fibres, the melt pump conveys them to the spinning beam with the required process pressure.

Advantages of melt pumps in fibre production

  • Sufficiently high process pressure after filtration
  • Constant temperature window for maintaining viscosity
  • Reliable pumping of even shear-sensitive melts
  • Pump integrates seamlessly into the process

Process data

Pump size:
EXTRU-IIB 176-70-70
Medium:
PET
Throughput:
up to 1000 kg/h
Inlet pressure:
approx. 30 bar
Outlet pressure:
approx. 220 bar
Temperature range:
280 to 295 °C

Technical parameters

Pump size
EXTRU-IIB 176-70-70
Housing:
1.6582
Friction Bearings
1.2379
Gear shafts
1.2344
Sealing type
Threaded shaft seal, cooled
Further information

Melt pump in the extrusion process

  • Filter unit / Backwash screen changer
  • Extruder
  • Degassing / Vacuum unit
  • Online viscometer
  • Melt pump

  • Filter unit / Backwash screen changer

    In the processing of post-consumer material, the melt is usually contaminated. To prevent the material from becoming scrap later on and downstream process equipment from being damaged, it is recommended to use a filter after the extruder. In this process setup, an RFSgenius backflush screen changer from Gneuss is used. In this process, the RSFgenius filters up to 1100 kg/h of melt. The upper limit is 13,000 kg/h.  Cleaning is carried out by the finest screens, which rotate in the filter unit and are cleaned continuously during operation by a high-pressure system so that they do not become clogged.

  • Extruder

    MRS extruder from the company Gneuss.

    The extruder is a single-screw extruder with the special feature that the extrudate is fed into a rotating drum in which 8 small rotating satellite screws are arranged. The rotation of the screws is in the opposite direction to the rotation of the barrel. The advantage is a disproportionate surface exchange of the melt for a highly efficient degassing. The melt is thus cleaned of volatile contaminants such as oils, gases and water. Pre-drying of the washed post-consumer material is thus eliminated.

  • Degassing / Vacuum unit

    The degassing unit works with a low-maintenance and robust water ring pump system. The required vacuum is generated by a paddle wheel rotating in a water ring. This draws unwanted substances and gases out of the melt.

  • Online viscometer

    The online viscometer is used to monitor the melt quality. It can be used to precisely measure the polymer properties. Both the melt pressure and the melt temperature are recorded. These values provide information about the shear rate and viscosity and thus provide a reference to the strength of the end product.

  • Melt pump

    The melt pump compensates for pressure losses and fluctuations in the volume flow that can be caused by the upstream equipment before the pump and by the extruder. They also build up the required differential pressure for the downstream equipment and keep the melt within the required temperature window by means of a sophisticated temperature control system. Melt pumps are extremely stable. Special types of gearing can be used for particularly shear-sensitive media.

Exemplary process structure

This process setup was realised with the kind support of Gneuss. WITTE has been supplying the established EXTRU melt pump for integration into the Gneuss extrusion lines for many years. A large number of joint projects have already been realised. In addition to a WITTE gear pump of the EXTRU type, the following components are installed in the Gneuss extrusion lines.

Extruder MRS

The MRS series extruder can process between 350 and 450 kg of polymer melt (MRS 90) per hour, depending on the polymer type.

Further information

Degassing / Vacuum unit

Degassing is an essential process step in extrusion. The solvent is drawn out of the melt by means of the vacuum unit.

Further information

RFS Genius Melt Filter

Filters are used to increase product quality in order to eliminate possible impurities and resulting quality losses.

Further information

Online viscometer

The viscometer is used to monitor the pressure and temperature as well as the melt quality and the required product properties.

Further information