Fracture Characteristics of Tensional–Torsional Fatigue Failure of the Archimedes Helix

“Archimedes helix” (Fig. 1) is very widely applied in worm gear systems (Fig. 2) and is a critical component of transportation systems of raw material in the ceramic industry. Failures of such components from mineral processing plants (production of ceramics) have been addressed in our lab during the last two years. The helixes are manufactured from of ferritic–perlitic steels that are usually protected during service by a hard surface coating. In the recent years, uncoated material is progressively replacing the more expensive hard coated materials primarily for economic reasons. The uncoated material frequently fails owing to the fracture of the component into two pieces (Fig. 3). A serious economic consequence of such failures is the stoppage of the production line until the broken component is replaced, while the cost of the component itself is negligible. Failure analysis was conducted, and it revealed that the primary mechanism of fracture tensional–torsional fatigue. The use of penetrant testing–non destructive testing (PT–NDT) makes it possible, in many cases, to detect the fatigue phenomenon at its early stages and to replace the part during the normal service of the machine, thereby avoiding unexpected plant shutdown.