By Rey Parel SPE Golden Gate Section
Mold close melt inject volume to open part eject thermal profile is now know for each molding cycle. A mold eject side vent sensor profiled melt volume inject rate to final eject state. The “instant” thermal rise from convected heat released with the “crack” of mold opening is sensed. Than part melt heat conducts to the mold vent sensor with mold opening time. The vent sensor shows the differential thermal expansion of the mold and curing part. The vent sensor heat drop occurs with part ejection. This mold vent sensor thermal readout consecutive molding cycle will be presented.
Molding Cycle Vent Profile
A mold vent sensor cyclic melt inject “rise” and following drops during mold fill-pack and cure time occurs.
Mold open to back position shows a sequence of rises with short temperature drops. Peak temperature rise and following drop occurs with part ejection. The cyclic mold close to open molding cycle is shown in Figure 2.
The vent temperature “rise” combines mold cavity melt dispersing by convection during initial mold part line opening. And mold conduction of residual heat to the vent sensor during return time.
Injection Cycle Background
The mold vent sensor profiles the melt injection fill to pack and hold cycle time. Screw return melt recovery time is an added vent sensor response to machine mold clamp force. The vent sensor thermal drop continues to cure mold opening time. The mold conduction to melt differential rate sets the in-cavity part shrink rate until mold ejection site and dimension ambient state is reached.
The machine melt to mold injected volume profile shown in Figure 1.
Mold Part Heat Vent Profile
The cavity vent sensor has sharp temperature “rise” with mold opening. The molded part heat escapes by convection to the sensor. As the mold moves back to eject position a rise to a maximum temperature is seen. When the part is ejected the sensor drops until mold close.,The induced melt residence heat is conducted through the mold steel and will vary with external site and mold temperature system. The small variance shown in Figure 3 from mold opening part ejection to close is very small range.
Mold Close Melt Vent Sense
The mold close cavity melt inject vent sensor for three consecutive cycles shown in Figure 4. The machine melt inject fill to pack injection end profile time is shown.
Screw Return Vent Profile
A time of screw return “start” initiates a “rise” in molded part internal melt pressure. A decrease in melt pressure continues until screw return time ends as shown in Figure 5.
Observation
The vent sensor profiles exiting trapped gas during mold close and melt inject volume time of molding cycle. The screw return shot size and residence time to the next inject cycle is known.
Mold open “instant” is known by the vent sensor temperature rise. This melt heat released is machine clamp release and the mold cracking open. The vent sensor relates the released molded part convection and conductive heat retained while in the mold cavity (see Figure 6).
Conclusions
The vent sensor process cycles profile of a single cavity seat mold with a direct hot runner. A 1200 Ton molding machine ran the large mold. The vent sensor side placement and sensitivity of melt front gas to pack and cure is extremely sensitive. Vent sense process to product capability achieved by placement in the mold eject side vent groove.
The machine melt to mold cavity injected volume is important. The screw return pellet to melt plasticating is indicated. And mold opening tp art ejection is thermally profiled. With mold opening the molded part heat is released by convection. The conductive heat of injected melt to mold open and part ejection is thermally precise timing.
Mold cavity melt vent sensor profile is a simple means to define and refine any machine melt to molded part cycle.
1 Buja, Using Vent Temperature To Sense Mold Cavity Melt Flow, SPE ANTEC Proceedings, (2006). Mold Maker & Mold Design Paper #120909
