Precise metering of blowing agents into extruders with LEWA systems

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

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