Extruder melt pump for demanding compounding applications up to 8,000kg/h

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Gear pumps are commonly used for the precise transfer and metering of polymers, fuels and chemical additives. In extrusion applications, gear pumps (melt pumps) stabilize the process by generating a constant pressure, ensuring a constant flow of material and relieving the extruder from the pressure build-up task. The Swiss company Eprotec is specialised in the manufacturing of high-precision melt pumps for recycling, compounding and film/sheet extrusion for throughputs up to 8,000 kg/h.

Specially coated “Titanium” version with 7-year guarantee

Eprotec’s Melt-X series of melt pumps can be operated at a maximum working temperature of 320°C and maximum difference pressure of 250 bar (special versions for higher temperature/pressure ranges are also available). The pumps come with a 3-year guarantee, the specially coated “Titanium” version even with 7 years.

The working principle of the melt-x gear pump

The volumetric pumping device has two externally toothed gear wheels that mate with each other when they rotate. A small pressure in the pump inlet is sufficient to fill the tooth chambers (Fig. 1). On the discharge side, the mating of the gear teeth in each other forces the melt out of the tooth chambers (Fig 2). The forces on each of the gear shafts are taken up by two slide bearings. These are lubricated by the plastic and are maintenance-free (Fig 3).

working principle of diaphragm pump

Pressure fluctuations reduced to a minimum

The melt pump reduces pressure fluctuations caused by the extruder to a minimum. The flow-optimised inlet, outlet and smaller flow channels also lead to an increased flow velocity, reduced residence time and low shear stress. The pumps can therefore be used for the processing of thermo-sensitive, transparent and easily degradable polymers. The flow-optimised channels also contribute to a very good self-cleaning behaviour. In case of frequent colour changes, an additional bleeding valve can be used.

Design features of the Melt-X melt pump

Design features of the Melt-X melt pump (source: Eprotec)

Example: thermoforming sheet extrusion

By employing the Melt-X gear pump, the producers of thermoforming sheets can increase the regrind content up to 100%. The melt pump ensures a pressure reduction down to 20-50 bar in the pressure build-up zone of the screw which allows the melt to flow in a particularly gentle manner. The low pressure also increases the service life of the extruder’s processing unit (screw and barrel). In addition, the pressure reduction in the extruder leads to a relief of the vacuum zone and prevents flooding.

Special versions for high filler content, high pressure and thermally critical melts

Special versions of the melt pump for demanding extrusion applications are also available: a hard-coated version, the Melt-XRA, is used for maximum filler content, e.g. 80% for BaSo4, 50% for glass fibres and 83% for CaCO3. The Melt-XS version is used for thermally critical melts, while the Melt-XH is suitable for the highest discharge pressure (max. 700 bar) and high differential pressure of up to 500 bar.

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