Ordinary runner system, also called runner system, or gating system, is necessary passage for molten plastic from nozzle of injection machine to mold cavity. Runner system includes primary runner, sub-runner, and gate.

Also called sprue or down runner, it refers to runner from part where nozzle of injection machine contacts main runner bushing of mold to runner. This part is the first part where molten plastic flows through after entering mold.

With mold design, it can be further divided into first runner and second runner. Sub-runner is transition area between main runner and gate, which can make flow direction of molten plastic be changed smoothly; for multi-cavity mold, it also has function of uniformly distributing plastic to each cavity.

Also called feed port, it is narrow opening between sub-runner and mold cavity, it is also the shortest and thinner part. Its function is to use shrinkage of flow surface to accelerate plastic. High shear rate can make plastic flow well (due to shear thinning characteristics of plastic); heating effect of viscous heating also has effect of increasing material temperature and reducing viscosity.
After molding is completed, gate is the first to be cured and sealed to prevent plastic from reflowing, to prevent pressure of cavity from falling too fast, which causes molded product to shrink and dent. After forming, it is convenient to cut off to separate runner system and plastic parts.

Purpose is to store and replenish cold plastic wavefront at initial stage of filling, to prevent cold material from directly entering mold cavity, affecting filling quality or blocking gate. Cold slug well is usually set at the end of main runner. When length of branch runner is long, cold slug well should also be set at the end.

 

1. Thickness of glue inlet is generally 1/2 of average thickness of product.
2. Width of fan-shaped glue port is generally 2 times width of runner.
3. Length of runner should be controlled within 60~80MM as far as possible, direct filling of cavity should be avoided as far as possible, and arc transition is best.
4. When hot runner enters glue, in order to facilitate installation and processing of hot nozzle, it is best to adopt a flat transition.
5. In the case that runner needs an inclined surface to transition into glue, inclined surface should be greater than or equal to 15° as much as possible.
6. In the case of clamping different parts, glue feeding balance should be controlled above 80%.
7. When product's own weight is very related, in order to facilitate adjustment of glue balance, a throttle valve should be added to runner.
8. For large parts, when surface requirements are high, it is necessary to purchase a needle valve to delay control.

 

1) Try to adopt a balanced layout;
2) Mold cavity layout and gate opening should be symmetrical to prevent uneven load caused by uneven force of mold, problem of mold flashing;
3) Layout of mold cavity is as compact as possible to reduce size of mold.

1) It can smoothly guide molten plastic to fill mold cavity, without eddy current, can smoothly exhaust;
2) Try to avoid frontal impact of plastic melt on cores and metal inserts with smaller diameters to prevent core shift or deformation.

1) The smaller heat loss and pressure drop, the better;
2) Process should be short;
3) Cross-sectional area of runner should be large enough;
4) Try to avoid bending of runner and sudden change of flow direction (change direction at an arc angle);
5) Surface roughness should be low when runner is processed;
6) Multi-point pouring can reduce pressure drop and required injection pressure, but there will be suture problems.

1) When filling a multi-cavity mold, runner should be balanced, try to make plastic fill each cavity at the same time to ensure quality consistency of molded products of each cavity;
2) As far as possible, runner should adopt a natural-balanced layout;
3) When natural balance is not possible, artificial balance method is used to balance runner.

On the premise of smooth filling without affecting flow and pressure loss, reduce flow channel volume (length or cross-sectional area) to reduce flow channel waste generation and recycling costs.

Design an appropriate cold slug well and overflow trough on runner system to supplement cold plastic wave front in initial stage of filling, prevent cold material from directly entering mold cavity and affecting filling quality.

Plastic should be smoothly guided to fill mold cavity and allow air in mold cavity to escape smoothly to avoid problem of scorching of encapsulation.

1) Avoid short shots, burrs, encapsulation, suture lines, flow marks, jets, residual stress, warpage deformation, mold core deviation and other problems;
2) When runner system has a long process or multiple pouring, warpage and deformation of finished product caused by unbalanced flow, insufficient pressure or uneven shrinkage should be prevented;
3) Appearance of product is good, it is convenient to remove and trim gate, gate mark does not damage appearance and application of plastic part.

Minimize required post-processing, shorten forming cycle and improve production efficiency.

It is necessary to consider proper ejection position to avoid deformation of molded product.

For plastics with higher viscosity or shorter L/t, avoid using too long or too small runners.