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Study of PET Spectral Absorbance in Designing Infrared Heating Control of Vacuum Forming Machine

Heating process is the first step in vacuum forming that transforms the plastic sheet from its glassy state to rubbery state, pliable enough to be formed to mold’s shape. Infrared ceramic heaters with zoning control are commonly used in thermoforming industry, in which temperature distribution and its consistency throughout processing time become very important in determining the thickness and properties of manufactured parts. Compared to other thermoplastics, Polyethylene Terephthalate (PET) with its crystallization characteristics is known to have narrower process window. Slight uneven temperature distribution and overheating will degrade PET as well as cause visible defects in final product. In order to obtain proper parameter setting of infrared ceramic heater in PET vacuum forming, a numerical approach that considers PET spectral absorbance was deployed and two methods to control temperature were compared. The experiment resulted in a reliable temperature distribution by means of voltage potentiometer control for pre-heating and implanted thermocouple inside ceramic emitter for main heating in PET vacuum forming machine.