Читать книгу Plastics Process Analysis, Instrumentation, and Control - Группа авторов - Страница 32

The basic filling phenomena in a gas-assisted injection molding process with flow visualization were assessed (42). Here, a high-speed video camera was used to record the mold-filling phenomena of rectangular cavities with various arrangements of gas channels. The mold-filling phenomena were compared and guidelines for layout of gas-channel ribs were drawn.

The following conclusions can be drawn from this investigation (42):

1 Gas-assisted filling, with a near-exponential velocity rise, is much faster than conventional filling, with nearly constant speed. Ribs with similar area but different geometry significantly affect the speed of gas tip and melt front advancement during the gas-assisted filling.

2 Without any rib in a gas-assisted molded plate, severe rigidity degradation will occur along the gas penetration path, especially near the thickness transition edges. Similar rigidity degradation will occur even in a plate with improper gas-channel rib layout. If there is no proper gas-channel rib along the melt front advancement in the far end, gas will penetrate into non-rib regions along the direction of melt front advancement to fill the free space.

3 With a symmetrical rib layout, the gas penetration in symmetrical ribs can never remain symmetrical.