Investigation on acoustic emission characteristics of a paper dryer

摘要

Cracking in dryers has long been a challenge in the pulp and paper industry. The acoustic emission (AE) technique, which is capable of supplying information regarding the cracking behaviour of metal objects, can be used to reduce or prevent dryer failure. This study applies AE testing to a paper dryer made of grey cast iron in China. To realise this task, the AE characteristics of the cast iron dryer were examined by accomplishing three main work parts: (ⅰ) in the lab part, basic AE signatures from the dryer shell material were characterised; (ⅱ) in the artificial crack test part, AE features from the crack were obtained and the AE location of the crack in the dryer was tested; (ⅲ) in the field part, the basic procedure for testing the paper dryer under hydrostatic test conditions was verified based on the analysis of parts Ⅰ andⅡ. The results indicate that grey cast iron is a good AE emitter. The tensile test revealed that the AE responses are active and the AE sources include the deformation of pearlite, decohesion and fracture of several graphite flakes and microcrack growth. The AE attenuation in the dryer is not severe and the cracks in the dryer during hydraulic testing exhibit an active AE response. Additionally, an accurate crack location was obtained by using the cylindrical location method. These results can provide useful information for AE inspection on structures made of cast iron.