Issue link: https://iconnect007.uberflip.com/i/1176876
OCTOBER 2019 I PCB007 MAGAZINE 37 nomena to the thermal process that the mate- rial undergoes during lamination, and all en- gineers share and agree that the cooling speed and thermal balance of the different panels in the stack play an important role. Most engineers would also agree that the ide- al way to cool down a press stack would be by maintaining the lamination pressure while the materials slowly dissipate the thermal energy naturally through the environment, exchang- ing the energy with the ambient temperature. However, this process is nonproductive, indus- trially speaking, for obvious reasons; it takes a very long time and is far too slow. Analyzing that thermal dynamics statement, and looking into the lamination press stack morphology in such "ideal" cooling conditions in detail while the material is cooling down naturally through the environment, the ther- mal energy (heat) travels from the center of the material, homogenously, to the edges of the material. This happens because the stain- less-steel separator plates have far lower ther- mal resistance than the laminated multilayers (metal versus glass and resin). This means that the edges of those metal plates in contact with the air of the environment (i.e., room tempera- ture) are exchanging the thermal energy with the environment until, after a long time, the temperature of the whole press stack becomes balanced with the ambient temperature. I have used finite element calculation soft- ware to model this behavior to simulate this thermal dynamic. A link is available that shows a fast-motion video of a single metal plate cooled down from 200°C to room temper - ature [4] . The blue col- or is the ambient tem- perature, and the white color is the separator press plate at 200°C. In conventional tech- nologies, cooling down occurs in the same way the thermal energy was conducted from the hot platens to the laminate during heat up; the platens are cooled down first, and the thermal energy stored in the materials has to be con- ducted back from the stack to the platens. This means a significant thermal delay between dif- ferent panels in the press stack as well as sig- nificant variation from panel to panel. The cooling system developed for this tech- nology emulates the natural way of cooling down previously described but boosted strate- gically to be able to speed it up for an industrial purpose: cooling down within the limits of the resin manufacturers' requirements. This meth- od of cooling down also minimizes the temper- ature delays in the height of the press stack. Once the heating section of the cycle is over, the vacuum chamber is pressurized. The devel- oped cooling system creates a specific loop of airflow with a specific ΔT that crosses through the edges of the press stack separator plates. When the cold air touches the separator stain- less steel, energy is exchanged. In other words, the air takes heat from the plates increasing the air temperature while the separator plates become a bit cooler. The air is then pulled by the blowers and conducted to a water/air ex- changer that cools down the air again before the blowers push it back to pass through the press stack again. The system recirculates in a closed-loop manner the air inside the chamber. The system uses the real material tempera- ture monitored by the temperature sensor in the middle of the press stack to regulate the airspeed (blower speed) and the air tempera- ture with the water circuits of the water/air ex- changer (Figure 14). Figure 14: Closed-loop cooling system diagram.