Precise metering of blowing agents into extruders with LEWA systems

During the production of extruded foams, continuous and precise metering of the blowing agent in the extruder is critical for the quality of the end product.

LEWA supplies self-monitoring metering systems designed especially for the metering of blowing agents such as the LEWA ecofoam as a ready-to-use unit, which is also well suited for retrofitting existing plants.


Essential components of LEWA metering systems:

  • Precisely controllable LEWA ecoflow metering pumps
  • Flowmeter with continuous signal
  • LEWA microprocessor developed especially for fluid metering, connected with the control signal of the extruder control system

This permits very reliable operation using a continuously alternating monitoring of metering pumps and flowmeters. Here the measured values are not only compared, but also tested for plausibility.

The advantages of LEWA ecofoam metering systems

  • Compact, tested, ready to use units for all commercially available extruders
  • For all conventional blowing agents, such as CO2, propane, butane, fluorinated hydrocarbons
  • Hermetically tight systems
  • Integration in the process control of the complete system
  • Components matched to each other from a single source
  • Low maintenance costs and long service life


Process description

During the production of PPE foam (or polyethylene, polystyrene, PET) the plastic melt in the extruder has a blowing agent (e.g., pentane, CO2) added under pressures up to 350 bar. The plastic expands 20 to 50 times in volume when extruded from a hole nozzle.

An important process is the production of foamed film or foamed panels. The continuous extrusion process is usually performed with so-called cascade extruders.


While the plastic granules are melted in the first extruder, after the addition of the blowing agent in the second extruder a uniform mixing of precisely this blowing agent is done. This brings the melt to a defined temperature level.

Through the low ambient pressure relative to the vapor pressure of the blowing agent, the melt expands and is calibrated in a special device to the desired panel thickness.

Source: Wikipedia, February 2012




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