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
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