Gas-assisted injection molding technology supplier Alliance Gas Systems Inc. has been awarded a patent for its Backspill technique to evacuate resin from molds.
Backspill involves displacing resin from the mold using gas injection or Alliance's patented water injection system, called Hydrojection. First, resin is injected into the tool, filling the cavity. The tool includes a flow path to a secondary resin reservoir, which is closed during injection and at the beginning of the injection of gas, water or another other fluid.
The gas or water, or a second resin such as with coinjection, is injected, which maintains or increases cavity pressure of the primary resin against the cavity wall. Following the gas or water, a portion of the resin is expelled by selectively timing the opening of one or more paths from the mold into the evacuation wells, either from the runner or from the part cavity itself.
Alliance said Backspill is superior to other processes - those that use a short shot followed by the gas, or that use an open aperture from the tool cavity - because it can achieve all cosmetic requirements not possible with those other methods.
Alliance Gas Systems is based in Chesterfield Township, near New Baltimore.