Volume 34, Issue 4 (July 2006)
A Simple Noncontact Displacement Measuring System for Online Bubble Height Measurement During Polymer Bubble Inflation at Elevated Temperature
In thermoforming process, thermoplastic materials are heated up well above their glass transition temperature and formed to the required shape by employing appropriate mold. Material is viscoelastic at that temperature, and its characterization for thermoforming applications are possible using a bubble inflation technique as well as rheology tests. Online bubble height measurement during the bubble inflation test is an important parameter for the material characterization. A simple noncontact displacement measuring system (NCDMS) has been developed and reduced to practice for online bubble height measurement during polymer sheet bubble inflation well above its glass transition temperature. The experimental design procedure and methodology is presented in this paper. The NCDMS measurements have been validated up to the displacement rate 100 mm/s. Bubble inflation has been undertaken at an elevated temperature with different inflation rates and the online bubble height captured using NCDMS. This experimental method is cost effective and shows good repeatability in measurements. This technique has been used for bubble inflation tests up to 90 1pm air flow rate that offered height growth rate of 75 mm/s.