Investigation of shaft and segment failure in co-rotating twin-screw extruder

Abstract

This research is focused on identifying the reasons behind the failure of the shaft and screw segment associated with the ABS plastic material co-rotating twin-screw extruder. These steel parts failed during production and after only 12 days of operation. To understand the failure causes, their chemical composition was examined initially. The results showed that the chemical composition of the analyzed parts meets the design and standard of BS EN 4957 (2018). Subsequently, a detailed study of the fracture cross-section of both pieces was conducted, along with microscopic and mechanical tests, to gather comprehensive information on the failure reasons. The findings indicate that the initiation of the cracks is linked to the presence of coarse carbide deposits, leading to micro-cracks on the surface of the shaft. Under torsional-bending cyclic loading, these cracks expanded as low-cycle fatigue fractures. When the fatigue crack reached its critical extent, rapid and abrupt crack propagation and failure ensued. Furthermore, defects like holes and coarse sediments within the segment also contributed to the conditions conducive to rapid crack growth and failure. In conclusion, to prevent future accidents and issues with comparable equipment, various safety measures and recommendations were introduced.