Today's KNOWLEDGE Share
Hot Runner Manifold and Gate Balancing
The term "balanced" on paper may still refer to a situation in which one cavity flashes while another cavity short-shots in multi-cavity molds. The solution is not magic. Rather, it is science that we can put to use on the production floor.
In order to achieve a balanced hot runner manifold and gates, we use the following strategy. That involves using pressure drop, shear rate, and fill-time targets:
1. Establish a single fill-time target (here is where your quality window would begin).
2. Convert it into flow rate per gate, which is the amount of melt that each gate is required to supply.
3. Check shear rate. A shear rate that is too high may cause material stress, burn, and splay risk. A shear rate that is too low can result in poor packing response. Smaller gates provide a rapid increase in shear.
4. It is necessary to calculate the pressure drop for each flow channel. This includes the sprue, manifold branches, nozzle, and gate.
5. To get balance, make sure that ΔP and shear are the same throughout all drops. You may do this by changing the diameters of the channels, the quality of the corners, the size of the gates, the length of the land, or the timing of the valves.
6. It is important to validate the "balance" using a short-shot study and cavity pressure so that it is not theoretical but rather actual.
The mold becomes much simpler to start, much simpler to maintain stability, and a great deal more repeatable when these three factors – fill time, shear, and pressure drop – are in harmonious alignment.
source : PlastiConnect.
#polymers #InjectionMolding #HotRunner #MoldDesign
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