A hot runner internal heating system is an advanced technology that maintains the temperature of molten plastic by placing a heating element in the center of the runner. Its core lies in utilizing internal probes and distributor tubes for heating, relying on the plastic's own insulation to reduce heat loss. This system is suitable for processing a wide range of non-heat-sensitive materials and equidistant gate layouts, but it requires high runner balance and is prone to material solidification and pressure drop issues.
I.Working Principle and Structural Characteristics
The internal heating system places the heater in the center of the runner, with the molten plastic flowing in an annular gap. Due to the temperature gradient, the melt in the outer annular region tends to solidify due to its proximity to the cooler mold wall, leaving only the inner annular region as an effective fluid cross-section. Heat is provided by probes and heating shuttles (also called distributor tubes) within the runner. By precisely controlling the heating power, the melt remains in a uniform molten state throughout the entire transport process.
The system mainly consists of the following parts:
Heating probe: Located in the center of the flow channel, directly transferring heat.
Distributor tube: Guides melt flow and assists in heat transfer.
Temperature control device: Works with thermocouples to achieve temperature control accuracy of ±1℃~±3℃.
Insulation structure: Utilizes the thermal insulation properties of the molten plastic to reduce heat loss.
II. Applicable Scenarios and Limitations
|
Characteristics |
Advantages |
Limitations |
|
Processing Materials |
Suitable for non-heat-sensitive plastics such as PP and PE |
Not suitable for heat-sensitive materials such as PC and PVC. |
|
Flow Channel Design |
Suitable for equidistant, balanced multi-cavity molds |
Poor adaptability to asymmetrical or complex flow channels. |
|
Energy Consumption Performance |
Utilizes the material's own insulation, resulting in less heat loss |
Requires higher initial heating power. |
|
Maintenance Difficulty |
Compact structure, small footprint |
Cleaning and maintenance are relatively difficult. |
III. Comparison with Other Heating Methods
External heating systems use heating coils wrapped around the outside of the flow channel for heating. The flow channel is unobstructed, without any hindrance to melt flow. Compared to internal heating, external heating is more suitable for heat-sensitive materials, and the resulting products have lower stress and stricter tolerances. However, internal heating systems still offer irreplaceable advantages in certain specific applications, such as precision molding where extremely high temperature uniformity is required.
Tip: When choosing between internal and external heating, factors such as material properties, product precision requirements, mold structure complexity, and production costs should be considered. For high-precision, high-volume production of non-heat-sensitive plastic products, internal heating systems remain a worthwhile technical solution.
