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Hot runner system heating method
Jun 08, 2018

Hot runner systems generally fall into two categories based on how the heat flow guide plates are heated.

1, insulated

Insulation runners have oversized runners made of stencils. The runner is not heated, but the size of the runner must be large enough to maintain the melt within the runner by using the thermal insulation provided by the plastic condensing in the runner wall under operating conditions, combined with the heat of each shot. Smooth.

This kind of system is earlier and simpler in the two categories. The advantage is that the design is not so complicated and the manufacturing cost is low. The disadvantage is that condensation sometimes forms at the gate; in order to maintain the molten state, a very short working period is required; in order to reach a stable melting temperature, a long preparation time is required. Another major problem is that it is difficult to obtain the consistency of injection molding, or that it cannot be guaranteed. Also because there is no heating in the system, a high injection pressure is required, which often results in deformation or bending of the cavity plate.

2, heated

The heated runner system also has two designs: the inner heating runner and the outer heating runner: the inner heating runner: The inner heating runner is characterized by an internally heated annular runner. Heating is provided by probes in the flow path and a heating shuttle (also known as distributor tube). This system uses the thermal insulation effect of molten plastic to reduce heat transfer and loss in other parts of the mold.

In spite of the annular heater inside the distributor tube, there is still material condensation between the heating shuttle and the flow path wall. The material must flow continuously between the heat-insulating wall and the heating shuttle. This, together with the annual flow effect, will cause the pressure within the system to drop. Therefore, the importance of balance is critical.

Taking into account this issue, the internal heating system is best suited for processing large-scale materials and equal-distributed flow paths to gates. This system is not suitable for the use of heat sensitive plastics.

Internal heating provides improved heat distribution relative to the insulation system, but the system is more costly and more complex to design. This system requires careful balance and complicated thermal control.

External heating system: Another design of the hot runner is an external heating system. This design consists of a ring with internal flow channels

Heating manifolds. The header design has a variety of thermal insulation structures that are isolated from other parts of the mold. The advantage of this system is better temperature control, but the cost is higher and the equipment is more complex.

The latest technology development has reduced the size of the header and made installation easier. External heating systems can also be balanced by diameter rather than by length.

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