True Cause for Multi-Layer Inductive Coils’ Sensitivity to Ambient Relative Humidity

For analyzing the properties of humidity-effect on the measurement of the inductance of multi-layer coils, a formula that establishes an approximate relationship between the coil’s inherent capacitance and interlayer parasitic capacitance has been derived. Such a derivation using the inductor’s equivalent circuit to include humidity effects clarifies the characterization of inductance, after more than half a century of neglect in the literature.

Barrel heating with inductive coils in an injection molding machine

Traditional injection molding machines use resistance heating (RH) bands to heat the barrel. However, RH has a low energy rate; thus, the time required to reach the target temperature is rather long. Consequently, the use of inductive techniques, with a faster heating rate and improved energy rate, has attracted growing interest in recent years. However, an inappropriate design of the inductive coils and plasticization barrel may result in a strong repulsive magnetic field between neighboring coils and a corresponding reduction in the heating performance. Thus, developing an appropriate inductive heating design is essential in improving the barrel heating performance. The present study therefore performed a simulation and experimental investigation into the magnetic field and temperature distribution for different barrel geometries and coil current designs. The simulation results showed that the application of spiral grooves to the barrel improved both the heating rate and the temperature uniformity (TU) and effectively solved the proximity effect. The results indicated that the application of induction heating together with a novel grooved barrel design yields an effective improvement in both the thermal efficiency and the TU compared to that achieved using the traditional RH method with a single- or double-section barrel.