Infrared radiation in the processing of plastics: Precise adjustment–the key to productivity

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AbstractInfrared radiation plays a large role in many areas of plastics processing, whether in the heating of thermoplastics for purposes of subsequent forming or in noncontact temperature measurement. This paper sets out to deepen our understanding of the plastics‐specific problem associated with infrared radiation. First of all, a brief outline is given of the necessary fundamental physical principles, before going to to discuss measurement results in terms of the radiation‐related properties of plastics. The influence of pigmentation and crystalline structures is investigated, together with the temperature dependence of absorption behavior. Linking up the radiator characteristics and absorption properties of plastics, a physical model is then presented which can be used to calculate energy efficiency and temperature homogeneity in the heating of plates. The results are presented in diagrams. In addition, the special problems of infrared heating in stretch blow molding are examined. Here, we attempt to attain a high level of penetration into the thick‐walled parisons by means of short‐wave radiation and thereby guarantee uniform and rapid heating. A program for establishing the intensity distribution of radiation on a semifinished product has been developed for geometerical configurations generally found in thermoforming machines and this will run on a personal computer. It will allow the optimization of uniform or deliberately nonuniform temperature distributions over the surface. If the stretching process is to be selectively influenced, it is essential to have knowledge not only of the temperature distribution in the semifinished part but also of the stretching behavior of the material. A highly informative testing procedure was developed to this end, which reveals the suitability of the material in question for a stretching process. A further section covers the infrared temperature measurement frequently applied in plastics processing for process analysis, monitoring, and control. The different types of measuring devices and their advantuges and drawbacks are discussed here. An analysis is also conducted of disturbance variables and possible means of correction are indicated.