Contactless measurement of PET bottles' thickness

The tuning of Injection Stretch Blow Molding (ISBM) process for PET bottles is crucial to lower the production costs, reduce the environmental impact and assure a sufficient quality of the final product. Among the parameters defining PET bottles quality, the thickness is of primary importance for the appearance and mechanical resistance of the final product. Up to date, tuning of the process is demanded to the operator skills through a trial and error process, iterated until the wanted configuration is achieved. Moreover, the process is not controllable because the PET bottles characteristics are not currently measured. This work describes a method for PET bottles thickness measurement; the method could be implemented as part of an active control of the ISBM process. A noncontact method based on infrared transmittance measurement has been developed to evaluate the wall thickness of PET bottles. The method uncertainty is 6% when the nominal thickness ranges between 0.2 and 0.5 mm. A prototype of the measurement system has been developed and validated testing PET specimens with different geometry, pigmentation and composition.