Design of branch runner
Branch runner is a melt flowing way connecting the main runner and the gate, which acts as the role of diversion and turning. The branch runner system of the side gate is on the parting line surface while the branch runner of the pin point gate is on the parting line surface between the runner stripper plate and the fixed plate, which also include the vertical section on the fixed plate
In a multi cavity mold, the design of the branch runner must be considered on how to make the Plastic melt to the entire cavity at the same time to fill the cavities
If all cavities have the same volume the shape, the best runner design is with the equal distance and cross-section. Otherwise, under the same flow rate, the unequal cross section is used to change that same flow rate, so that all the cavities are filled at almost the same time. Sometimes you can change the channel length to adjust the resistance to ensure that the cavity is full
. When the molten plastic flow along the sub runner, it is required to fill the cavity as soon as possible, and the heat loss in the flow should be as small as possible. Resistant Force should be as low as possible. At the same time, it should be able to evenly distribute the plastic melt to each cavity.
Factors considered in the design
(1) The plastic flow rate and the shape of the products. For the poor fluidity plastics, such as PC, PPO, HPVC, PSF And so on, the branch runner should be as short as possible, the turning of the branch runner should be arc transition. .The cross section area should take a larger value and cross section shape should be round (side gate) or “U” – shaped (point gate). The direction and the cross section of the branch runner depend on the location and quantity of the gate, and the location and quantity of the gate are determined by the shape of the product;

(2) The number of the cavity determines the direction, length, and size of the branch runner;
(3) The wall thickness and the external quality demand determine the location and form of the gate, and ultimately determine the flow direction and size of the runner;
(4) Pressure and injection speed of the injection machine;
(5) The pull and drop of the main runner and the branch runner. If full automatic injection molding is demanded, after the mold open, the branch runner should be ensured to stay on the moveable plate and drop easily.

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