Analysis of the Common Causes of Papermaking Cast Iron Dryer's Defects and the Study of Test On-Line

Abstract

The existing researches only put forward the stress concentration portion and design improvements from the perspective of stress analysis, or conducts safety assessment on dryers with the methodology of fracture mechanics, without non-destructive testing methods. Based on over 3,400 tests on cast iron dryers in Hangzhou, an ultrasonic testing technology with longitudinal wave double crystal probe is developed in the present investigation. This study illustrates how to identify the volume defects through testing on the air holes, shrinkage cavities and inclusions in the dryer cylinder and small R transition zone with longitudinal wave double crystal probe at a small angle (5°), as well as plane defects with deep cracks through testing on the dryer cylinder and small R transition zone with longitudinal wave double crystal probe at a large angle (42°). It addresses the issues of how to measure the thickness in regular online testing for cast iron dryers, to calculate the intensity or compare with the design value, to identify low hardness value, to determine the key parts in online testing, and how to conduct safety assessment on the cast iron dryers with small cracks. This technique may resolve various problems in cast iron dryer testing.