A review and evaluation of melt temperature sensors for polymer extrusion

Melt temperature is one of the key variables in polymer extrusion which determines process thermal stability and hence melt quality. Therefore, melt temperature is commonly measured in polymer processing and point/bulk melt temperature measurement methods are widely used in the present industry. Some thermal profile measurement methods have also been attempted in research. This study presents a review of melt temperature measurements in polymer extrusion in research and industry, and describes the results of an experimental evaluation carried out to explore the performance of five melt temperature measurement techniques. In addition, an investigation was carried out on the fully developed melt temperature profile of a cylindrical rod die. Moreover, the existing challenges and possible future applications for extrusion thermal monitoring are discussed. The results confirmed that melt temperature varied significantly at different radial locations within the die. Point/bulk melt temperature measurements were found to provide relatively limited information on process thermal quality close to the die wall. Hence, information provided by these sensors is less representative of actual thermal conditions as they are unable to capture thermal information from the whole melt flow cross-section. Therefore, the importance of the development of industrially compatible thermal profile measurement techniques is emphasised.