Why Runner Size Matters

The injection molding process is one of the most versatile and dependable manufacturing processes available.  Advances in new injection molding machines with increasingly tighter tolerances and repeatability have widened the appeal of injection molding.  Injection molding reduces production time and offers a high degree of accuracy.

There are various machines on the market depending on the end result you want to achieve.  Leading the heard for extreme dosing capability and high-response times are Sodick Injection Molding Machines.  These machines are designed to accelerate to set speed now and inject extremely fast which enables users to dramatically downsize their runners.

Runner waste is reduced as well as compressibility of material in the runner compared to previous large runner system, which improves the overall process.  Also, if runner size is reduced typically cycle time will then be reduced as you are not waiting for the large runners to cure prior to the mold open.

A Little Background

Sodick feels the feed system of an injection molding machine is responsible for the material flow from the machine nozzle to the mold cavity.  The feed system consists of a sprue, runner, and gate.  The runners in the mold are the flow channels that connect the injection unit to the injection gate.  A properly sized runner will achieve a balanced fill pattern for all cavities, balances the benefit of shear heating in the resin with the increased pressure required to fill the runner, will allow the molten plastic to increase in temperature improving flowability while not requiring expressive pressures to fill, minimize waste, and allow for easy injection and control of the cycle time.  If runners are too large they require longer cooling time, consume more material and scrap, and need additional clamping force.

Proper runner sizing is dependent on material morphology and part thickness.  Certain materials require larger runner to reduce pressure requirements and temperature rise, while other materials need a smaller runner size.


Examples of small runners.pptx

Examples of small runners.pptx

Mold Frame for LCD

12 gates are reduced to 4 gates.

Runner weight is reduced from 45g to 22g.

Examples of small runners.pptx

Bearing Retainer

Smaller runner system results in reduced waste and a smaller equipment size.

Examples of small runners.pptx

In summary, Sodick Injection Molding Machines offer extremely fast response time, extreme acceleration, they are capable of minimizing the runner, improve process control, and reduce cycle time.  A properly sized runner in a feed system is critical to reducing processing requirements and reducing part cost.


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