Selective Electroplating Speeds Parts Repair

Returning OEM parts back to original specification — or better

Equipment lifespan and machine condition are critical considerations for driving down costs. Remanufacturing is one of the best ways to achieve this, but what does it entail? Mark Meyer, North America sales manager for SIFCO Applied Surface Concepts (ASC), explained how selective electroplating can build components back to original specifications.

Mining is an intensely demanding industry for all types of equipment. Unpredictable field conditions and harsh operating environments can combine to increase the risk of wear and tear, corrosion and damage to component surfaces. If not properly maintained, many of these components — or entire pieces of machinery — may need to be scrapped, increasing capital equipment costs and downtime.

This result is far from inevitable though, if site managers and manufacturers can find a way to head off component failure. This is where remanufacturing comes into play, returning OEM parts back to original specification — or better — for a longer, more reliable lifespan.

Extending Operational Lifespan

Remanufacturing can extend the operational lifespan of equipment, but it’s just as crucial to ensure that in doing so, downtime is also minimized. When the costs of such downtime are counted in millions of dollars, as in mining, any way to quickly, cost-effectively and sustainably enhance components, improve wear resistance and repair damage is key. Here, selective electroplating offers a vital benefit.

Selective plating is a method of repairing and restoring critical dimensions and surface properties of worn components back to OEM standards, using an array of solutions such as copper, nickel, nickel-tungsten and cobalt. Even more crucially, it can be completed on site to reduce downtime.

This is due to the focus on treating specific areas of a component by accurate, selective brush plating of materials on to localized surfaces and diameters, enabling in-situ repair and enhancement that is typically faster than alternative surface-coating methods. Compared to the other major electroplating method — tank plating — it does not require extensive masking or special fixtures and can plate deposits between 30 to 60 times faster without risk of part distortion because the process takes place at room temperature. All of this combines to make it a faster, more cost-effective and lower-risk option.

The Selective Plating Process

Given the severe and the harsh direct impacts experienced by mining components, selective plating needs to bond at the atomic level. This is not provided by traditional surface-coating methods such as thermal spray, which form mechanical bonds.

Focusing on this atomic bond, selective plating uses electrochemical principles. An electrolyte solution, containing ions of the deposit material, is introduced between the negatively charged plating surface and the positively charged tool. This is powered by a portable power pack, enabling precision control over amperage, voltage and duration.

When the tool (anode) touches the surface, a circuit is created with a cover material around the tool providing a reservoir to ensure even distribution. The current within the circuit causes the ions between the interfaces to bond, building up the plating layer, and delivering a highly adherent and dense metal deposit.

Selective plating also allows for more accurate control of deposit thicknesses, frequently enabling parts to be plated to size with no post-machining. With repairs able to be undertaken in the most appropriate location — in the shop or on the job site — this accuracy is matched by a fundamental flexibility in the process.

Rejuvenating a Pinion Gear

We’ve discussed selective plating in principle, but what happens in practice? An example that illustrates its effect is the repair of a dragline pinion gear. SIFCO ASC is a global leader in selective plating, providing brush-plating solutions to improve part performance and reduce manufacturing costs through corrosion protection, increased wear resistance, increased hardness, improved conductivity, anti-galling or slip. Recently, Horsburgh & Scott, a large gear manufacturing and repair company, called upon SIFCO ASC to repair two areas on a 16-in.-diameter by 5-in.-long bearing journal caused by a seized bearing that damaged the seat and created a gouge during removal.

With the first defect being a 0.030-in.-deep gouge measuring 0.75 in. wide and 12 in. long, and the bearing seat being 0.012-in. undersize after cleanup, this presented an ideal situation for selective plating: a shallow groove that could be rapidly filled with a copper deposit through 100% tool contact. Meanwhile, the undersize condition required only 0.006 in. thickness of nickel.

Welding to fill the defect was rejected because heat and structural changes in the metal could contribute to potential distortion or stress. Machining the diameter was also decided against, as it would have presented distinct impracticalities for plating at a high thickness. Brush plating presented the ideal solution, with a deposit of approximately 30 Rockwell hardness required, nickel was chosen.

First, the gouge was selectively filled with copper to bring the outside diameter (OD) back to round. The bearing journal was plated with 0.001 in. of copper, then masked for the defect repair. A graphite anode that covered the full length of the gouge shortened the plating time. The defect was then 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 in. of nickel. After the repair of the two defects, the component was as good as new and ready to receive a new bearing, making the dragline ready for action once again — and, crucially, in safe and efficient condition.

Dave Niederhelman, chief metallurgist at Horsburgh & Scott Co., said, “Over the years, SIFCO ASC has helped us find the most efficient ways to repair and maintain equipment, adding 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. The cost of manufacturing and material to replace the gear would have been extortionate in comparison, as well as causing weeks of downtime.”

Cutting Environmental Impact

The selective plating process fits well within concepts of sustainability in the mining industry, given its far lower impact compared to other surface coating methods. Using less solution and chemicals, and generating very little waste, along with reductions in the carbon costs of emissions, transport and shipping, it’s a more sustainable option at an ecological level. Plus, the reduction in fumes and hazardous waste to dispose of offers a safer, healthier working environment.

In a fast-moving quarter of the world’s industrial landscape, remanufacturing and selective plating present a distinct way to do things better: returning vehicles, machines, and equipment to operational effectiveness with minimal downtime required. Increased wear resistance, surface hardness and low electrical contact resistance, or corrosion protection, are just some of the benefits of the process.