Mould core shaft passage should have what conditions

For cable extrusion cosmetics cosmetics packaging hose production molds for the uniformity of coating layer thickness, mold core axis flow channel size is very important. Must meet the following conditions.
1. Along the annular aperture on the melt in mouth mold should be a constant flow rate and same pressure drop.
2. The melt at various points along the flow channel has a constant shear rate.
3. Melt at various points along the flow channel to stay roughly the same time.
the flow distribution system design on the mold core shaft are diverse, mainly have threaded mold core flow channel and heart-shaped curve flow channel. With mostly heart-shaped curve port, the melt is divided into two stocks of material flow, material flow around a share about half of the mold core, meet again until the two strands of the melt, the course of these two should be equal.