A novel approach of measuring the dielectric properties of PET preforms for stretch blow moulding

Abstract

Polyethylene terephthalate (PET) is the most common plastic material used in injection stretch blow molding (ISBM) process for the manufacturing of bottles. The injection-molded PET preform has to be preheated uniformly to a pliable state before the blowing stage of the process. Microwave technology offers a potentially more economical means for preheating the preform in place of the conventional infrared oven heating. For such applications, determination of dielectric properties of PET preform of a given geometry is essential. This article describes a novel approach of measuring the dielectric properties of PET preforms at microwave frequencies instead of the common experimental procedures used for such measurements. The dielectric properties are determined by using both CST Microwave Studio electromagnetic simulation software and the automatic network analyzer together. No complex mathematical solutions are required. Validation of this new approach has been made by comparing the measured dielectric properties of some polymers with those available in the published literature.

Preheating of a poly(ethylene terephthalate) preform for stretch blow molding using microwaves

“…A few successful studies on the use of Microwave Studio simulation software have been conducted. 12,[18][19][20] There is no need for calculations of complex equations or applying the trial and error method to a cavity to achieve effective results, unlike in the studies of Metaxas 17 and Sangdao et al 21 Although the Microwave Studio simulation software can make nearly precise predictions for cavity design, a good knowledge of electromagnetic filed distribution is necessary. The range of the length and diameter aspect ratio of the cylindrical cavity for the simulation trial was 0.5-2.…”

“…Details of the design work can be found in a previous work. 12 The wave guide had a short circuit at one end and a flange on the other end. The position of the preform was determined according to the electric field profile inside the wave guide with the simulation program and a network analyzer.…”

“…12 The wave guide with a sample holder, shown in Figure 3, was designed with simulation software called CST Microwave Studio. Details of the design work can be found in a previous work.…”

“…First, the dielectric properties of a PET preform exposed in a WR340 rectangular wave guide were studied. 12 The same wave guide was used to heat the preform partially. An additional cylindrical resonant cavity was designed with CST Microwave Studio simulation software to achieve a more suited profile of the electric field along its axis.…”