Portable Plating Process Repair Gets Crane Mining Again

By repairing the pinion gear of a mining crane in-situ with a selective plating process, a crane was able to return to service with minimal downtime and extend the working life of the gear components.


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By repairing the pinion gear of a mining crane in-situ with a selective plating process, industrial gearing manufacturer Horsburgh & Scott Co. was able to return a crane to service with minimal downtime and extend the working life of the gear components.

This in turn has improved the failure rate of the part and saved significant cost compared with alternative repair methods for the Cleveland, Ohio-based company that designs, manufactures, services and rebuilds industrial gearing and gear drives.

 

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

 

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 dragline excavator crane used in the surface mining of coal. 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 Horsburgh & Scott 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 inch in depth, 0.75 inch wide and 12 inches long, and was 0.012 inch 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 0.060-inch undersize) and then post-processing machining operations for dimensional restoration. 

Horsburgh & Scott has extensive experience in successfully repairing and rebuilding more than 90 varieties of gearing manufacturers’ brands from around the world. With a heritage dating back to the 1870s, it is well placed to identify the most cost-effective and robust methods of repair.

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 that alternatives requiring pre- and post-process machining. 

The bearing journal was first plated with 0.001-inch 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-inch thickness of nickel using an ID plater.

“Sifco ASC is a well-established partner of Horsburgh & Scott and their ability to work on-site is highly attractive,” says Dave Niederhelman, chief metallurgist for Horsburgh & Scott. “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.”

In this application, the Sifco process extended the working life of the gear and improved the failure rate due to the nature of the nickel coating on the journal. Niederhelman said 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,” says Lee Shelton, managing director of Sifco ASC. “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.”

For more information on Horsburgh & Scott Co., please visit horsburgh-scott.com. To find more about Sifco’s selective plating process, visit sifcoasc.com or email info@sifcoasc.com. Information for this story supplied by Sifco ASC.

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