High-precision manufacturing of multi-layer pipes

Acoustic insulation, oxygen barrier, special optical, mechanical or thermal properties, these attributes are being demanded to an increasing amount of plastic pipes today. Such attributes can be realized in multi-layer products consisting of special materials that fulfil different functions. Such materials, however, are often highly sensitive to thermal and mechanical stress and require special process parameters compared with basic materials. With conventional die concepts, such as spiral mandrel dies, these materials cannot be processed at all, or only with difficulty.

Using CFD based flow simulation, Battenfeld Extrusionstechnik has developed a new side-fed die that allows by non-centrical melt injection an optimal melt distribu-tion into a circular ring geometry for further distribution in a short time. A geometry of twin center sleeves preceded by a coathanger manifold ensures symmetrical distri-bution of pressure inside the die. This causes the majority of mechanical forces gen-erated to cancel each other out and ensures automatic centering of the mandrel. The design includes the option of modular, consecutive connection of several distributors and thus a facility for thermal isolation of each individual layer of melt from the other layers. To further optimize melt homogeneity, the side-fed distributor is followed by a brake-up plate, the geometry of which has also been optimized using 3D flow simula-tion.

The efficiency of the new die in terms of melt distribution and residence time has been very impressively demonstrated by the first results of practical test series with a great variety of resins. The combination of a twin center sleeve with a break-up plate has yielded high mass flow rates with low shear stress and excellent thermal homo-geneity.