The pinion gear is an essential part of a gear train assembly.

 

By repairing the pinion gear of a dragline in-situ with the SIFCO Process, industrial gearing manufacturer Horsburgh & Scott Co. (H&S) was able to return the machine to service with minimal downtime and extend the working life of the gear components. This in turn has improved the time between failure of the part and saved significant cost compared to alternative repair methods.

Based in Cleveland, Ohio, H&S designs, manufactures, services, and rebuilds industrial gearing and gear drives for industry-specific needs. The company has a long-standing relationship with SIFCO ASC and has been working with them to solve various component repair issues for 20 years.

The pinion gear is an essential part of a gear train assembly. In this application, the pinion gear was part of the boom driveline of a BHP dragline used in a South African coal mine. If not maintained regularly, lubricant in the pinion gear can leak out of the seal and potentially cause the bearing to seize and gall the bearing journal. Removal of the seized bearing often results in additional gouging damage to the bearing journal surface.

When H&S approached SIFCO ASC with this problem, they worked together to look for a solution that would minimize the downtime as well as the cost of the repair. The bearing journal in question had incurred a deep gouge measuring 0.030 in. in depth, 0.75 in. wide and 12 in. long, and was 0.012 in. undersize.

Traditionally, this type of damage is rectified by component replacement or by repairing the damaged area. Typical repair options include sleeving, welding, metal spray and tank plating. Component replacement can be costly and result in a four- to six-week lead time. Welding can weaken the strength of the substrate. All of these repair processes require the part to be removed from the equipment and taken off-site for both pre-processing machining operations to remove the defects in the journal (making the journal a minimum of 0.06 in. undersize) and then post-processing machining operations for dimensional restoration.

Using the SIFCO Process, a portable plating process used to selectively electroplate localized areas, defects are typically repaired with one or more layers of copper, and then covered with a wear-resistant deposit.

In this instance, a nickel in the 30 Rockwell hardness range was selected as the final deposit because it was close to the hardness of the original base material and it provided the necessary wear properties. Copper was chosen for the fill material because it has excellent “throwing power” (the ability of the plated deposit to reach into deep grooves or other defects), it is easy to reactivate when building up multiple layers, and as a softer fill material it is easy to dress back down in between layers.

For this application, in which the gouge in the journal was filled with copper, no machining was required and only one layer of nickel was plated to achieve the desired journal dimension. This resulted in a repair that was significantly less expensive than other alternatives requiring pre- and post-process machining.

The bearing journal was first plated with 0.001 in. thickness of copper and then masked for the defect repair. The gouge was filled with three layers of copper and hand finished in between each layer. Once the gouge was repaired, the outside diameter was plated with a 0.006 in. thickness of nickel using an ID plater.

“SIFCO is a well-established partner of H&S and their ability to work on-site is highly attractive. Over the years they have helped us to find the most efficient ways to repair and maintain our customers’ equipment and this has added up to thousands of dollars, hours of downtime, and manpower time saved,” said Dave Niederhelman, chief metallurgist, H&S. “In this application, the SIFCO Process has extended the working life of the gear and improved the failure rate due to the nature of the nickel coating on the journal. The cost of manufacturing and material to replace the gear would have been expensive in comparison, as well as causing weeks of downtime.”

“We understand the inconvenience caused when critical components fail and need urgent repair. The portability of the SIFCO Process makes it a versatile solution used for numerous demanding repair and OEM applications. The localized plating process works well in an industrial environment. The plated deposits withstand considerable stress and strain, while maintaining excellent adhesion,” said Lee Shelton, managing director for SIFCO ASC.