The arrows on the drawing shown here represent the plastic flow from the sprue, runner system, point gate, and into the cup shape cavities. A 3 plate mold system automatically degates the part and sprue. The 3 plate mold separates the runner system, as well as the part from the cavity side, and ejects everything from the mold base. This design requires a trapezoidal runner system with sucker pins to break the gates.
The small cross-sectional opening of the point gate becomes a problem with respect to resin filled plastic. This style gate could be a problem with low viscosity, long fiber, or bead filled resins. The small gate restriction could raise the melt temperature and affect heat sensitive resins. Ignoring these factors could result in high mold maintenance.
Enlargement “A” shows a very small scar left after the gate pulls free of the part. On this part design the scar area is lower than the highest surface not affecting the part function. Some designs allow gating into a very small concave dish on the part surface to insure that the scar break is below a flat surface.
Page 6 of 12