The manifold is an important component in delivering a consistent and homogeneous melt to the cavity. Today’s industry standard includes naturally balanced melt channels (both with and without level changes),

as well as contoured heating that follows the shape of both the melt channels and manifold.
Attempting to demonstrate a thermally balanced manifold by taking an external photo outside the plates is not an accurate representation because the heat sinks (touchpoints of the hot manifold within the plates) are removed. It is easy to show perfect thermal uniformity in the manifold when removed from the plates, however, it is significantly more challenging to achieve this uniformity within the plates.

As a result, some industry leaders are moving away from symmetrical heating, choosing to use the thermodynamic method. This method simultaneously assesses heat loss and heat input using thermal analysis software. The software is able to accurately predict the actual temperature of the manifold melt channel, while in the hot half plates during the injection molding process. Using this method, common problems—such as hot and cold spots—can be eliminated by analyzing the manifold. This decreases the potential for plastic degradation, speeds up color changes and has a positive impact on cavity-to-cavity balance.

Two other important factors are nozzle heaters and temperature control. Thermocouple controlled nozzles have become the industry standard. In fact, very few market segments are holding out on using percentage control for nozzles. Thermocouple controlled nozzles have become the standard because they allow molders more process control. The controller and the information provided by the thermocouple also can be used to troubleshoot, providing an inside view of the hot runner and mold that could otherwise only be seen by taking apart and inspecting the systems.

For example, if a nozzle zone does not come up to speed within the proper amount of time or lags significantly behind the other zones, there is a possibility the nozzle is touching the plates or gate insert where it shouldn’t be and drawing too much power or not reaching a set point. This can be detected by the controller if thermocouples are attached to the nozzle and manifold.

Leading hot runner manufacturers are continuously looking for better solutions to achieve accurate temperature control, such as a temperature controller that adjusts not only temperature—but depending on the specific thermodynamic and processing conditions—the controller algorithm itself is adapted to the environment the nozzle is running in. For example, a different algorithm is required depending on whether the nozzle is well-cooled in the gate area or only has limited cooling in the gate. In testing, this has yielded significantly closer set point temperatures at the nozzle tip—when comparing a non-adaptable to an adaptable controller the set point variation moved from +/-2.5 degrees °C to +/-0.5 degree °C.