Feeding System Design is a critical point in plastic mold design.It significantly affects the apperance, physical properties, dimensional accuracy, and molding cycle time of a plastic part.A feeding system consists of sprue,runners and gates.
Melt plastic flows out of the nozzle of plastic injection molding machine into the mold.For a single cavity mold, the plastic flows through the sprue into its cavity. For a multi-cavity mold, the plastic flows through the sprue and through runners to reach individual cavities.
While the melt plastic passes the sprue, runner and gates, it fills out the cavity at elevated temperature and reduced pressure,due to friction.The melt plastic material gradully cools off in the cavity by heat transfer.
Although the design of runner and gate has a great impact on the part’s molding, and quality.It is difficult to calculate and design an optimal feed system with a simple formula.Because it is difficult to mldel the acceleration of the flow inside the cavity,going through the gate at an elevated temperature due to friction. In practice, the decision on the gate and runner design is based on the shape and size of the plastic part and its material properties. Ideally, the runner and gate should be an integral effort in the plastic part design and plastic mold design process.
In selecting a feeding system, the primary principle is to maintain the temperature and pressure s it flows out of the nozzle and fill out the cavity easily.Commonly, it usually prefers a short and thick sprue, runner and gate.Also it is related to the machine injection volume,plastication ability, part’s apperance, machining, dimension precision, physical properties, cycle period, and material waste.Therefore, they could be thin and short as well. In addition, all areas around the feeding system must be fully polished.