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BALANCED FLOW PREVENTS MOULDED-IN STRESS
Filling phase is influenced by wall thickness variation as it introduces variation in resistance to flow in all directions from the gate. Melt is held in cylindrical shape in plasticating cylinder before injection. When the melt is injected through gate and runner system, melt streams move equally in all directions only when resistance to flow is equal in all direction.
It should be realised that variation in wall thickness, hole / slot, variation of mould surface temperature introduces variation in resistance to flow. Therefore melt moves in number of streams with different velocity in different direction and mould does not fill in balanced manner.
When melt streams reach boundary at the same time it can be called balanced filling. When some stream reaches the boundary early and some other streams reach late - this time lag to complete the filling of part results in induction of moulded-in stresses in the part.
Unbalancing flow can be corrected by using flow-leader / flow deflector and multiple gates so as to form the melt stream shape very close to the projected shape of the part.
Typical filling time animation.
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