A high frequency preheater using dielectric heating is used to raise the resin temperature. Dielectric heating is a phenomenon in which dielectric material consisting of dielectric dipoles undergo rotational motion when a high-frequency electric field is applied to this dielectric material and internal heat is generated by mutual friction.
The electrode structure of the high frequency preheater consists of parallel-plate electrodes and a roller electrodes. Parallel-plate electrodes are suitable for cases where there are many heating materials and the temperature distribution can be controlled by using auxiliary electrodes.
In this example, evaluations of the influence on the material (tablet) temperature distribution with and without auxiliary electrodes are shown.
The generated electric field is affected greatly by the distance between the electrodes. The distance between an electrode and the tablet is fixed whether or not an auxiliary electrode is used.
Dielectric Loss Density
Fig. 2 shows the dielectric loss density distribution and Fig. 3 shows the electric field intensity distribution.
From Fig. 2, it can be seen that when there is no auxiliary electrode the loss near the edge but inside the tablet is high, and when there is an auxiliary electrode the loss inside and towards the center of the tablet is high.
From Fig. 3, it can be seen that from adding an auxiliary electrode the electric field inside the tablet concentrates toward the center. Dielectric loss is affected by physical properties, frequency, and electric field. In this example, since physical properties and frequency are both factors, the differences in the electric field appears as differences in dielectric loss.
The differences also appear in the temperature distribution with and without the auxiliary electrodes. In this way, it is possible to control the temperature distribution of the tablet using the auxiliary electrodes.