Critical Measurement
As an example of a critical measurement, we were retained to assist in the investigation of the failure of the bearings of a steel rolling mill. The roller bearings guiding the edges of the stock were failing prematurely and an excessive normal loading was suspected as the inherent cause. It was proposed that commercial load cells be placed under the bearings to determine the loading. As an alternative, we had the supporting shafts of the mill rolls bored at their ends where they passed through the supporting bearings. The material removed from the ends of the shafts was sufficiently small and at the centerline of the shafts, that the bending stiffness of the shafts was virtually unchanged.
We bonded strain gages on the inside of the hollow shafts near the bearing gaps to make direct measurements of the shear load on the shafts, which translates into the normal loads on the bearings. The strain gage installation was sensitive enough to measure down to 100 pounds of normal loading on a roller bearing with a static load capacity of 14,800 pounds. This investigation provided the necessary information to correct the problem and return the mill to normal service.