Externally heated Hot drops
With this type of hot drop, the polymer is totally enclosed by a heated up tube. Most of surfaces with the melt channel ID are kept inside the preferred melt heat. Heat run out of outside to the facility effects with a homogeneous melt temp across the melt channel “dia”. This enables for excellent heat manipulation, minimizing the potential for polymer degradation or crystallized polymer caused by poor heat manipulation. Excellent thermal manipulation at the tip of the hot drop is essential to proper operation of this model of technique. There is known as a fairly tiny distance between the underside from the hot drop, kept at the required melt temperature, as well as the cavity surface, which need to be cooled off to the required mould tool temperature.
Heat switch out of the heated drop towards the surrounding tool stainless steel is minimized with an insulated gap in the annular space between the hot drop as well as the custom mold steel. Several techniques allow the molten polymer to move directly into this gap and serve as the insulating polymer. This is not recommended with Eastman polymers, as this polymer can diminish and result in black specks or brown streaks within the casted parts. A more desirable solution is to employ a high heat insulating polymer such as Vespel to fill this gap. A cooling circuit or water jacket in close proximity towards the gates is also wanted for heat removal.
Plumbing this circuit independent from a few other impressions cooling channels can be beneficial, as standalone water heat manipulation can be utilized to optimize molding performance in either the gates region and also the mould impressions. Several manufacturers offer distinctive thermal tip styles for this kind of hot drop strategy. Generally speaking, full-flow open-tip styles are suggested for most Eastman polymers. Styles which includes a ‘spreader tip’, blueprint can be problematic with a number of with the faster crystallizing polymers. Discuss with with supplier’s Blueprint Services for thermal tip suggestions for specific material grades.
Internally heated Hot drops
Internally heated up probe-type methods are not suggested for all the polymers. With this category of hot drop, the polymer flows down the annular space among the OD of the heater probe and the ID from the melt channel. Heat generated through the internal probe moves out through the probe into the melt.
A thin layer of polymer freezes about the colder metal on the melt channel ID. Higher probe heat setpoints are normally demanded to keep the melt channel from freezing completely. The combination of the frozen layer and higher heat setpoints can result in material degradation and problems maintaining consistent processing condition setpoints. Degraded polymer generally outcomes in black specks or brown streaks within the molded parts with this kind of strategy.
Link to this article：Externally and Internally heated Hot drops
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