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Runner systems

Posted by admin on July 30th, 2012
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Helping the melt flow

A runner system directs the melt flow from the sprue to the mold cavities. Additional pressure is required to push the melt through the runner system. Shear (frictional) heat generated within the melt while the material is flowing through the runner raises the melt temperature, also facilitating the flow.

Runner size considerations

Although properly sizing a runner to a given part and mold design has a tremendous pay-off, it is often overlooked since the basic principles are not widely understood.

Pros and cons of large runners

While large runners facilitate the flow of material at relatively low pressure requirements, they require a longer cooling time, more material consumption and scrap, and more clamping force.

Pros and cons of small runners

Designing the smallest adequate runner system will maximize efficiency in both raw material use and energy consumption in molding. At the same time, however, runner size reduction is constrained by the molding machine’s injection pressure capability.

Optimal runner size

C-MOLD Runner Balancing is an excellent software tool for computing the optimal runner size that conveys a balanced filling pattern with a reasonable pressure drop.

Payoffs of good runner design

A runner system that has been designed correctly will:

Achieve the optimal number of cavities

Deliver melt to the cavities

Balance filling of multiple cavities

Balance filling of multi-gate cavities

Minimize scrap

Eject easily

Maximize efficiency in energy consumption

Control the filling/packing/cycle time.

Runner Systems Overview

Author: ZHILIAN MOULD
Page Link: http://www.zhilianmould.com/blog/runner-systems/
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