Runner balance constraints

Runner balance constraints are an optional analysis input that you can set for a Runner Balance analysis.

These constraints enable you to determine the correct size for the runners so that a balanced flow to the cavities is achieved. The Runner Balance Analysis is then performed to ensure that all cavities in a multi-cavity mold fill simultaneously with equal pressure to each cavity.

Runner balance constraint guidelines

It is a common design principle that the minimum dimension of a runner cross-section be 1.5mm greater than the thickness of the part. This enables the cavity to pack evenly and produce an even volumetric shrinkage. The choice of minimum dimensions may be affected by the material and design of the part. Runner dimensions are often determined by the type of material that is used. For example, on ejection from the die, one millimeter of styrene may snap and one millimeter of nylon may flex. There should be no "reversed tapers" in the mold or runner system, which prevent the runners from being ejected.

Tip: It is useful to perform a Runner Balance analysis without runner balance constraints, and then use these new dimensions as the basis on which to set constraints. This reduces the risk of over-constraining a part and restricting the program's ability to provide a balanced runner system design.