Page 37 - Plastics News January 2022

FEATURE

a core pin that forms a the velocity and viscosity of the molten
through hole. The design, material at the precise time it impinges
or configuration, of how against the core pin. If you experience
a core pin is retained also a problem with core-pin deflection, it
has a significant affect can often be overcome by profiling the
o the maximum L/D injection velocity. Reduce the velocity just
ratio. I combined all this before the material hits the pin, and then
information and did some speed it back up to the desired velocity a
interpolating to derive a short distance beyond the pin. This can
more user-friendly chart, as increase the effective L/D ratio by two to
shown. Keep in mind, these four points. The L/D ratio guidelines
values are strictly rules of in the chart are based on the material
thumb. There is only one flowing from one direction. When a part
sources. As the diameter of a core pin way to get a more accurate design has an extremely large L/D ratio,
increases, so does its maximum L/D prediction on whether a core pin (or even for example a pen barrel or a syringe, two
ratio. A core pin that forms a blind a core) will deflect, and that is with a or more gates are typically incorporated.
hole has a much lower L/D ratio then flow analysis. A flow analysis can predict Multiple opposing gates can often allow
L/D ratios as high as 15:1 to 20:1.

36 PLASTICS NEWS JANUARY 2022 37 PLASTICS NEWS JANUARY 2022