Repair of a 42CrMo M16 large gear shaft with 0.5~1.2mm tooth wear using build-up welding, heat treatment and gear grinding to restore GB grade 7 accuracy.
A petroleum machinery enterprise whose large gear shaft tooth surfaces on its drilling equipment were severely worn. Replacing the shafts with new parts is costly and has a long lead time, so the company asked for a repair route instead of a replacement.
A shaft in this condition cannot be returned to service by re-grinding alone, because the wear depth is larger than the remaining machining allowance on the tooth. Grinding away the damaged layer would change the tooth thickness and the profile beyond the original design. The repair therefore had to add material back to the tooth surface first, and then restore both the tooth geometry and the mechanical properties of the base metal.
Each step addresses a specific risk. Preheating together with a filler matching the base metal limits cracking and dilution in the weld zone. Stress-relief annealing after welding releases the stresses left in the heat-affected zone. Quenching and tempering bring the repaired zone back towards the base metal condition, so that the build-up layer and the original material behave as one part under load. Finally, turning and gear grinding restore the tooth form and bring the shaft back to the original design accuracy of GB grade 7.
The repaired shaft was returned to the drilling equipment and has been running in service, which is why the customer uses this route for worn gear shafts of the same size instead of ordering new parts.
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