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SOMILO Loulo – Mali

Pitch adjustment on Mill girth gear in Mali – SOMILO Loulo

After noticing 2 important cracks on their girth gear, our client decided to repair the cracks with clamps, following manufacturer procedures. Despite warnings from Novexa, and after repair by manufacturer, the 2 cracks were indeed stabilized but a pitch default had been generated at the 2 repaired zones (3 weeks stoppage). During restarting, important shocks appeared during meshing at the repaired zones. Risks of breakage and complete shutdown were very high.

Problems before NOVEXA intervention :

  • Positive pitch default of 0,4mm and 1mm on the 2 repaired zones
  • 2 successive shocks on every rotation at the repaired zones (2 pinions)
  • Important risk of cracks due to the shocks
  • Profile deformation of 0,45% of module on girth gear. Therefore welding repair of the 2 zones with pitch default was not possible as it is not possible to re-create a worn profile identical to the rest of the gear’s teeth

NOVEXA Intervention:

NOVEXA advised to adjust the pitch on several teeth positioned before the 2 zones with clamps, in order to spread evenly the pitch difference and therefore reduce shocks during meshing of these zones:

  • On the zone with positive pitch of 0,4mm: pitch adjustment by reprofiling the 10 teeth positioned before the repaired area (maximum pitch difference between teeth 0,05mm)
  • On the zone with positive pitch of 1mm: pitch adjustment by reprofiling the 25 teeth positioned before the repaired area (maximum pitch difference between teeth 0,05mm)
  • Complete Girth gear reprofiling (after pitch adjustment of the 2 repaired zones) to re-create an involute profile similar on all teeth and ensure optimal meshing conditions (pitch, profile and flatness accuracy within 0,05mm)

Benefits for SOMILO Loulo

  • Risk of teeth breakage avoided. Come back to a stabilised situation – no more shocks after our intervention
  • 9 to 12 months of production (necessary lead time for a new girth gear)
  • A controlled stoppage time with fast restarting – only 6 days of intervention

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