Mold Concerns
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Consider gating options early in part design. Most gates leave a vestige that may be objectionable in the visible areas of many cosmetic parts. In these instances, make provisions for gates in non-visible areas.
Gates can feed the edge of a part at the mold parting plane as do the various varieties of edge gates. These can often be broken off but may require trimming to reduce the size and appearance of the gate vestige. To minimize gate blush in highly cosmetic parts, consider wide fan gates, chisel gates, and gates that extend from the side rather than the end of the runner. These gates tend to generate less gate shear and produce fewer problems with gate blemishes.
Some gate types, such as pin point gates, tunnel gates, and direct hot tip gates provide opportunities to gate at locations other than the edge. Three-plate runners can feed the part via pin point gates at multiple locations across the front or rear surface of a part. Pin point gates and direct hot runner gates usually leave a raised gate vestige and are often placed in recessed wells to keep the gate vestige below the part surface. Valve-gated hot runners avoid the gate vestige problem but leave a circular mark similar to an ejector pin mark.
Standard tunnel gates typically feed into part features that extend perpendicular to the mold face. These features can be walls, ribs, posts or even tabs that are added to the design specifically for gating. Tunnel gates are self cutting and tend to leave relatively smooth gate vestige. Curved tunnel gates permit gating into the underside of surfaces that are oriented parallel to the parting plane.
Special gates are used in parts with a central hole to avoid weld lines. Filter bowls, for example, often use a dome-shaped gate that feeds the entire perimeter of the hole. Diaphragm gates also feed the perimeter of central holes and then are punched out after molding.
Consult the mold design section of the Bayer Material Science website for more information about the various types of gates.
