Repairing a Damaged Pinion Gear with Selective Electroplating

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Repairing a Damaged Pinion Gear with Selective Electroplating

Repairing a damaged pinion gear with Selective Electroplating

Working with large gear manufacture and repair specialists Horsburgh & Scott Co., SIFCO ASC’s brush plating solutions were used to repair two defects on the 16” diameter by 5” long bearing journal of this gear. They were caused by a seized bearing which damaged the seat and also created a gouge during the removal of the bearing.

The first defect was a 0.030” deep gouge measuring 0.75″ wide and 12″ long, while the bearing seat was 0.012″ undersized after clean-up.

This was considered a good selective plating application because the groove was relatively shallow and could be quickly filled with copper using a 100% tool contact. The undersized condition required only 0.006” thickness of nickel.

Welding to fill the defect was rejected as an option due to the heat and associated structural changes in the metal associated with the welding process. Meanwhile machining the entire diameter to remove the defect would have made the diameter 0.060” undersize, and so this was ruled out as well, as it would have made the journal too impractical for plating at such a high thickness.

For the resize deposit, the part required a deposit of approximately 30 Rockwell hardness. Nickel was chosen to meet that requirement.

First, the gouge was selectively filled with copper to bring it back to the overall OD.  The bearing journal was first plated with 0.001″ thickness of copper and then masked for the defect repair. A plating anode was used to cover the full length of the gouge which shortened the plating time. The defect was filled with three layers of copper and hand finished between layers. The final layer was dressed flush with the OD.

Once the gouge defect was repaired, the entire OD was brought back to size by plating with 0.006” thickness of nickel. After the repair of the two defects, the journal was as good as new and ready to receive a new bearing, making the excavator ready for action once again.