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A Gate is a small area between the runner and the part cavity.  The type, size and location of a Gate in an injection mold is critical to efficiently producing quality parts. 

    The type of gate selected depends on many factors including: 

        Gate witness marks,
         Material Type,
         Filler used (if any),
         Tooling Costs,
         Scrap Allowance,
         and the Mold  Plates used among others.
    Small restrictive gates are preferred.  Minimal sized gates provide a small witness mark, and detaching parts from the Gate/Runner is easier.
A single gate per cavity is desired,  however,  part size and the material  used may dictate multiple gates to be used.
     Locate the gate in an inconspicuous location of the part if possible. The Gate location should be at the thickest wall of the part (flow from thick ,to thin) and the thickness of the gate should be approximately two thirds the size of the wall. 

        The gate location  and the surrounding area is also the highest area of stress in the final part.  Do not position the gate at a location that part function indicates bending  or impact strength is required.
There are two general categories  of gates:
    1.  Automatic De-gating
            Automatic de-gating includes Sub gates and 3-Plate Pin gates
    2.  Manual De-gating
            All others generally fall into the Manual de-gating category.