A shear pin arrangement consists of a series of pins located in 2 flanges, the pins having a calculated groove diameter, positioned on a common pitch circle. A bearing is included to control rotation after disconnection.
To ensure disconnection accuracy, the precise shear of multiple pins concurrently is required. This relies upon the true position of the pin holes in both flanges to ensure all pins have equal torsional loading. A design incorporating 4 pins with 0.1mm (0.004 inch) true position, results in contact loading of 85%. Increasing the tolerance on hole position to 0.25mm (0.010 inch), sees this reduce to 75%, thus reducing the accuracy of disconnection. The rigidity of the shear pin arrangement is resultant upon the fit of the shear pins within the holes and the robustness of the bearing arrangement. A flexible joint can cause bending fatigue upon the shear pins and an increased face run out; imposing axial thrust loads upon attached machinery.
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