Foamcore pipe is a type of Structured Wall pipe used for pressureless applications. It resembles a standard solid wall pipe but incorporates a low-density core. Essentially, it is a sandwich pipe where foam replaces structures like the honeycomb often used in rigid plates.
Foamcore pipe typically consists of an inner and outer solid PVC skin, with a foamed PVC core in between. This design allows for weight savings. Production is demanding and requires a highly uniform melt temperature for even gas expansion in the core. The combination of formulation, extruder, and die must be carefully balanced.
Foamcore formulations for PVC often include additives like CaCO3 (Calcium Carbonate), sometimes up to 15-20 phr (parts per hundred resin), to compensate for the foam's lower stiffness. This allows the total wall thickness to remain similar to, or even thinner than, a solid wall equivalent while meeting stiffness requirements. Higher filler levels can also permit adding more blowing agent without creating blisters, leading to even higher cost savings per pipe length. Amorphous polymers like PVC generally foam more easily than crystalline polymers. ABS scrap/rework, compatible with PVC, can be added in micronized form to enhance melt elasticity and achieve a fine foam structure.
Standards for foam core pipe include ASTM F891, JIS 9798, and SANS 160119. ASTM requires closed cells to prevent axial leakage through the foam.
Benefits of foamcore pipes include:
Low-density cores in foamcore pipes carry risks, including skins acting independently if the core lacks shear resistance, difficulty complying with rubber ring chamber tolerances, and potential axial leakage if cells are not closed.