A foaming agent, usually as a so-called master batch granule, is added to the plastics granules. By heat addition a volatile component of the foaming agent is separated, this leads to a foaming-up of the melt. The production of foams is generally based on cross-linking of a polymer with simultaneous formation of gas. For polyurethane e.g. CO₂ or pentane acts as a foaming agent, which is generated during the reaction of water with isocyanate from carbamic acid formed as an intermediate product.

The main components, polyol mixture and isocyanate, are fed by the axial piston pumps working in a closed loop to the high pressure mixing head via high pressure mixing nozzles. Then they are mixed according to the counter flow injection principle and, with a special application nozzle, applied to the lower cover layer. Additional components are either added in the dynamic pre-mixing station or in the high pressure supply line for polyol where they are mixed in a static mixer.

Metering of all components is done in continuous operation this means without use of intermediate vessels so that possibly required changes of the mixing ratio can be carried out immediately during the production and the desired effect is shown instantly also.

LEWA manages the handling of critical melts in heated and insulated metering systems without product damage also at low flows. Of course with LEWA’s known reliability and precision.