The degradation of the material depends not only on the dwell time, but also on the temperature profile of the hot runner components.

The permitted temperature range of the processed plastics should not be exceeded to avoid a degradation of the material in the manifold.
For this reason a uniform temperate profile along the manifold is absolutely essential. In hot runner systems there is always a certain heat transfer from the heated components into the mold.

There are three types of heat transfer to the mold:
1) Radiation

2) Convection

3) Heat conduction

All these types of heat transfer have to be reduced to a minimum. In the case of radiation, this means giving the manifold a surface similar to a white emitter. With convection, it is important to keep the clearance small, and with heat conduction to ensure minimum contact surface.        

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