The Blog

Torsten’s Training Tips: Ejector Pin Sub-Gates

by Torsten Kruse

The design and placement of gates are crucial elements in mold design, mainly because manufacturing parts often necessitate the absence of surface marks or gate remnants. To achieve this, certain gate styles are preferable over others. While many gate systems inevitably leave a witness mark, opting for a gate that integrates seamlessly with the ejector pin and employs an automatically detachable sub-gate presents a viable solution. This approach, an ejector pin sub-gate system, offers an efficient automatic de-gating mechanism that effectively eliminates gate residue.

Ejector pin sub-gated runner systems can vary in design, offering multiple configurations such as full-round, half-round, and wedged runner systems. Specifically, the wedged design features a thicker section at the juncture with the sub-gate, tapering towards the part, which optimizes the flow and minimizes gate visibility.

Moreover, fine-tuning the dimensions of sub-gates and ejector pin gates is essential for enhancing the stability and efficiency of the molding process, ultimately leading to superior quality of the final parts. The size and style of ejector pin gates are pivotal in regulating the pressure dynamics during the filling phase. Smaller gates are associated with higher pressure peaks, increased overall injection pressures, elevated internal cavity pressures, and more significant clamp tonnages, underscoring the importance of careful consideration in gate design to achieve optimal molding outcomes.

Ejector Pin Sub-Gate Styles


Full-Round Ejector Pin-Gate System: The full-round system has the lowest pressure drop of the three designs and, therefore, the most comprehensive possible process window. However, this style creates the most significant witness mark on the part gate interface, potentially leading to minor sink marks or surface blemishes.

Half-Round Ejector Pin-Gate System: The half-round system does not have as low a pressure drop as the full-round system but has fewer possible surface appearance issues.

Wedged-Round Ejector Pin-Gate System: The wedged-round system has a greater thickness at the gate and “wedges” into a smaller thickness at the intersection of the part. This design would have the highest pressure drop of the three systems and the fewest possible surface appearance defects.


Kruse Analysis, Inc. has provided CAE simulation services to the plastic injection molding industry since 1995. By using advanced Moldex3D technology, Kruse helps customers troubleshoot from product design to development, optimize design patterns, shorten time-to-market, and maximize product return on investment (ROI). For more information, visit

Kruse Training, Inc. offers a state-of-the-art online knowledge and training solution that uses 3D process simulation technology to demonstrate the cause and effect of molding behavior. This interactive training program illustrates how “The Circle of Knowledge” between the part designer, mold designer, and process engineers works in the real world of plastic mold and design. For more information, visit

Questions, Comments or Feedback…