runner balance is important when we works with more than 1 cavity in mold design, unbalancing runner can cause various like unfill mold (short shot), weld line, air traps, burning and others.
from previous post that talk about design of runner balance in 6 cavity, now let's prove it by simulation of filling time.
Unbalance Flow Definition
Unbalanced flow is plastic completely filling some flow paths in the mold before other flow paths have filled. we can see from result of simulation, if color is same in cavity (for example at the end and gate) that mean it have good flow.
1. Unbalance Runner System
from picture above we can consider that flow of plastic in various cavity doesn't fill in the same time, it can cause flashing, short shots, high cycle time, density differences throughout the part, warpage, air traps and extra weld lines.
flashing will occur in cavity that fill earlier, becouse cavity that fill earlier will continue receive plastic flow until other cavity filled (it depend on injection pressure and cycle time set up).
Short shots happened at cavity number that fill more slowly then others cavity then the pressure and cycle time doesn't enough to fill the last cavity.
2. Balance Runner of 6 cavity
although this runner layout is not the best for 6 cavity layout, it better in fill time than runner layout before. look at the picture below
by changing the layout we can get runner that more balance with previous, from cavity number 1 until 6 the fill time is almost same.