Circular H type Runner Layout in Mold Design

It’s called H type because the runner shape from the top similar with “H”, it’ use in both circular layout and rectangle layout system, in circular type the runner doesn’t similar with H but it more similar with fork, circular type use in various type of product, like gear, cylinder shape, etc.
Total length of H circular type in each part of runner
8.801 x 16 = 140.816
7.491 x 8 = 119.856
18.83 x 8 = 150.64
Total length of runner in H circular type runner system
140.816 + 119.856 +150.64 = 410.912
Let’s compare with previous type runner system, direct runner system both circular and rectangle type,
Direct circular type = 448 mm
Direct rectangle type = 495.04 mm
H circular type = 410.912 mm
So the conclusion is from three example runner systems for these part and layout type, H circular type has the minimum length of runner,


Advantage
1.Flow length in the runner more stabile, cause we can add runner slug before branched the runner, see picture above
2.When designing the runner, runner volume is made small as possible, this type is smallest than two type runner before.
3.All the cavities fill at the same time possibility is high, balanced runner have an equal flow length and runner size form sprue to all cavities also same, so that each cavity can fill in nearly condition.

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Fill time runner balance on 6 cavity of mold

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.

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