In production process of plastic products, runner system of mold is like blood vessels of human body, which determines whether material can "flow" smoothly to every corner. However, seemingly simple runner design hides a complex game of material properties, process parameters and product structure. Today, we will reveal scientific code of runner selection and talk about how to use "golden parameters" to make mold run efficiently!

 

Runner is a channel connecting injection molding machine nozzle and mold cavity, responsible for transporting molten plastic to various parts of product.
Key role:
Uniform filling: Avoid defects such as lack of material and pores in product.
Control cooling: Affects product shrinkage and dimensional accuracy.
Improve efficiency: Reasonable design can reduce waste and shorten production cycle.
For example: Poor quality runners may cause material retention, uneven cooling, weld lines or even cracks on the surface of final product, while optimized runners can make plastic flow efficiently like a "highway".

Runner design is not a "snap decision" and requires following scientific parameters:
Material fluidity (melt index, MFR)
High-flow materials (such as PP, ABS): suitable for slender runners to reduce pressure loss.
Low-flow materials (such as PC, PEEK): short and thick runners are required to avoid insufficient filling due to too fast cooling.
Material thermal properties
Thermosensitive materials (such as PVC): runners need to avoid high temperature areas to prevent decomposition.
High-temperature materials (such as nylon PA66): require higher mold temperatures and runners need insulation design.
Product structure and wall thickness
Complex thin-walled parts (such as mobile phone cases): use multi-level split runners to balance filling path.
Thick-walled parts (such as tool boxes): increase runner size to avoid shrinkage and depression.
Mold type
Cold runner: Low cost, but easy to produce waste.
Hot runner: No waste, suitable for mass production, but requires precise temperature control.
Production efficiency and economy
Runner volume ratio: Small parts require micro runners, large parts can be appropriately relaxed.
Demolding difficulty: U-shaped runners are easy to demold, circular runners are more efficient but costly.

According to characteristics of different materials, runner design needs to be "appropriate":

Case analysis:
Automobile bumper (PP material): Use fan-shaped diverter channel to balance filling pressure of multiple cavities.
Medical catheter (silicone): Surface coating treatment of runner to reduce risk of sticking.

Misunderstanding 1: The thicker runner, the better?
→ Too thick runner wastes materials, prolongs cooling time and increases costs.
Misunderstanding 2: Are all products suitable for hot runners?
→ Hot runner maintenance costs are high, and small batch production is not cost-effective.
Misconception 3: Ignore difference in material shrinkage?
→ For example, if nylon shrinks a lot, compensation space needs to be reserved.

With popularization of CAE simulation technology and AI algorithms, runner design is moving towards precision:
Mold flow analysis software(such as Moldflow): predict filling effect in advance and optimize runner layout.
3D printing conformal cooling runner: achieve efficient temperature control of complex structures.
Conclusion:
Runner design is a combination of science, experience and technology. Whether you are an engineer or a newcomer in industry, mastering these "golden parameters" can make mold "blood flow" and produce more perfect products!