Hot runner injection molds

Internally heated nozzle and externally heated manifold plate

Since the heat can be directly supplied to the gate end, the inner heating nozzle can effectively provide better temperature control of the gate end (less freezing layer, casting, wire drawing, etc.), in addition, because the heater is surrounded by plastic, the heating center probe heat

More naturally isolated from the mold cavity, the product in the cavity needs to be cooled. With some designs that pass the probe from the manifold plate to the nozzle, there will be an increase in the frozen layer around the runner which helps seal around the runner and reduces leakage at the junction of the manifold plate and nozzle.

A potential problem with internally heated nozzles is that because the heaters are installed in the center of the runner, they can inhibit the flow and cause flow stagnation in these areas, depending on how the heaters are installed in the melt. These factors can also lead to increased material degradation, difficult color changes, increased injection pressure, and undesired temperature changes in the melt.

Because it is the runner form of the inner heating nozzle, it is usually not suitable for heat-sensitive plastics. It should be used with caution when the mold requires cleanliness and the color of the plastic is light. If there is a point of flow stagnation, over time, many plastics will degrade, decompose, unnecessarily streak, or produce dark spots on pastel materials at that point.

The built-in heater creates an inefficient annular flow path, resulting in a much larger pressure drop across the internally heated nozzle for the same amount of melt than a completely circular nozzle. If the cavity is filled with sufficient pressure, it may not be a problem.