Multilayer Molding Technology for Electro-Fusion Fittings [PE]

Electro-fusion (EF) fittings are used in the joining of polyethylene (PE) gas pipes. However, the cost of fittings for large-diameter pipes is high compared with that for small-diameter pipes. Accordingly, the multilayer molding method was developed, with the aim of reducing the cost of EF fitting for large-diameter pipes. In this method, the wall thickness of the fitting is divided into a number of stages (injections). Hence the wall part formed at each stage is thinner, thus allowing reduction of the time required for cooling inside the mold. In this way, it was planned to increase the production efficiency of fitting. With this type of formation of the wall of the fitting, a resin layer is formed at each injection, but there are fears regarding the reliability of the adhesive strength between layers. Hence, using tensile test and the full notch creep test (FNCT) on the part between resin layers, it was verified that performance is the same as for an article with a single layer.