セラミックヒーターを用いたポリスチレン射出成形品のウェルドライン加熟消去
Elimination of Weldlines in Polystyrene Injection Moldings Using a Ceramic Heater
泊 清隆・原田敏彦・前川善一郎・_田泰以
Tomari, Kiyotaka / Harada, Toshihiko / Maekawa, Zenichiro / Hamada, Hiroyuki
Polystyrene injection moldings can easily exhibit weldlines which appear as cracks on the surface and which often result in serious problems. These cracks develop as a V-notch caused by entrapping air or contaminants at the merging flow fronts. The V-notch not only reduces appearance quality but also mechanical properties, especially for brittle materials such as polystyrene. The V-notch depth was measured to be several microns using surface roughness tester. In our previous study, the weldline area which influences mechanical properties was found to be several hundred microns deep, including the surface V-notch. Preheating of a mold with halogen light or a high frequency inductor can eliminate the weldline efficiently. These methods, however, reduce the safety for work and require long cooling times.
An alternate method for weldline elimination was discussed in the present study, in which a ceramic heater fixed directly on the cavity at the weldline region was heated instantaneously during the injection process. Using this approach, the effects of heating on the appearance and the mechanical properties of polystyrene injection molding with weldlines were clarified.
Key words: Weldline / Polystyrene / Injection molding / Appearance quality / Ceramic heater