Investigation Into the Effects of Leveling Roll Diameter Variation on Coupling Shear Pin Breakage of a Hot Plate Leveler

摘要

A4,216-mm hot plate leveler, which was designed in 1968, has nine leveling rolls with nominal diameter of 240 mm, and two auxiliary rolls at the entry and delivery sides of the leveler with nominal diameter of 300 mm. The leveling rolls and auxiliary rolls are integrated driven by a single 660 kW DC motor via a gear reducer and 11 universal shafts each with a torque rating of 720 kg-m. To protect the universal shaft and the whole driving train, safety devices are installed on the couplings between roll ends and the universal shafts. Four shear pins with a neck diameter of 9.5 mm are used to connect the couplings and the flanges on universal shaft hubs. Recently, the shear pins have experienced a number of unexpected failures, and, in many cases, the failures occurred in very light leveling load conditions. Eighty percent of the failures occur in the couplings of Roll 7 (numbering of the leveling rolls is shown in Figure 1). Since Roll 7 is in the delivery side of the leveler, its load is normally less than that of the leveling rolls in the entry side. Therefore, the failures are not caused by overloading the machine. The shear pin failures severely restricted the capacity of the leveler, caused production losses and increased maintenance costs. Quad Engineering Inc. was retained to perform an engineering analysis to determine the cause of the problem and recommend possible solutions.