MANUFACTURING – INJECTION MOULDING & PLATIC CALCULATOR
Runner Size Design
A precise tool.
What is the Runner Size Design & How does it work?
In injection moulding the runner is the conduit that delivers molten plastic from the hot‑runner manifold to the cavity. Its diameter directly influences the pressure drop, shear heating and the ability to fill the part without premature solidification. Selecting the correct runner size is therefore a balance between minimizing material waste and ensuring reliable flow.
Two of the most influential parameters are the shot weight (the total mass of plastic injected) and the flow length (the distance the melt must travel through the runner). A larger shot weight requires a larger cross‑section to keep the shear rate within acceptable limits, while a longer flow length increases the pressure drop, demanding a slightly larger runner to maintain adequate velocity.
A widely‑used empirical relationship links runner diameter (D) to shot weight (W) and flow length (L) through a material‑dependent constant (K). This relationship provides a quick first‑order estimate that can be refined with detailed simulation.
D = K sqrt{frac{W}{L}}
D = Runner diameter (mm)
K = Material‑dependent constant (dimensionless)
W = Shot weight (g)
L = Flow length (mm)
K = Material‑dependent constant (dimensionless)
W = Shot weight (g)
L = Flow length (mm)
Parameters
Result
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Frequently Asked Questions
What is a runner in injection molding?
A runner is the channel that delivers molten plastic from the hot-runner manifold to the cavity.
How does runner size affect injection molding?
Runner size influences pressure drop, shear heating, and filling ability, balancing material waste and flow reliability.
What are the key parameters for selecting runner size?
The key parameters include shot weight (total mass of plastic injected) and flow length (distance from manifold to cavity).
Why is minimizing material waste important in runner design?
Minimizing material waste reduces costs and environmental impact while maintaining efficient production.
How does shear heating affect the runner size selection?
Shear heating increases with smaller runners, so a balance must be struck to prevent premature solidification during filling.
What is the role of flow length in runner design?
Flow length affects pressure drop; longer lengths require larger runners to maintain consistent flow rates.
How does runner size impact part quality in injection molding?
Proper runner size ensures even filling and reduces defects, leading to higher part quality and consistency.
Results are for informational purposes only and do not constitute professional advice.