A Local Authority had been investigating complaints about ground vibration from residents near a factory using rolling mills. Narrow band frequency analysis of the vibration revealed two distinct and separate types of vibration – tonal vibration at 18.25 Hz (and harmonics) plus a regular “thump”. The source of the “thump” was traced to roller backlash caused by bearing wear at the transfer gear end of a particular mill.
The tonal component was diagnosed as excessive vibration at the tooth mesh frequency of the pinion on another mill caused by worn teeth on the gear. The “thump” could be eliminated by replacing the bearings. However, as production requirements precluded immediate down-time, the interim solution recommended was to avoid running at idle and to adjust the clamping force to minimise the backlash. Inspection of the pinion gear source showed very worn pinion drive tooth flanks in mesh with “new” flanks on the driven gear. The tonal vibration was eliminated “on-the-spot” by reversing the pinion.
This case study illustrates the benefits of sophisticated diagnosis coupled with engineering expertise. A low cost solution to a complex and intractable problem was implemented within hours of arriving on site.