Getting the most from Chrome Coatings

Feb. 21, 2001
Several simple steps ensure that automotive parts can be economically coated for an attractive appearance and corrosion resistance.

Linda Wing
Automotive Industry Manager
Enthone Performance Coatings
New Haven, Conn.

Edited by: Stephen Mraz

Chrome plated 14 and 15-in. wheels were once the norm in the auto industry. It is now commonplace to chrome plate 17 and 18-in. wheels, and in the future, the automakers will be probably be plating 20-in. wheels.

There's often a gap between what automotive engineers imagine designs will look like once they're made and the actual products. Design teams routinely come up with innovative, "out-of-the-box" concepts for shiny automotive trim and chrome only to be told it can't be done or it's way outside the budget.

But wait, all is not lost. OEM designers can explore new forms and materials by following a few simple rules and striking up partnerships with metal-finishing companies and coating-technology suppliers.

Working with platers
Working with a plating company is the first step in getting an attractive, long-lasting, coated automotive part. Platers can help control production and plating costs, reduce waste, and improve throughput and profitability. They also want to help designers bring their visions to life, improve product performance and durability, and eliminate failures in the field.

"A good plater can be an invaluable partner, especially in the early design stages," says Bob Biltz, president, Dayton Alloy Wheel, LLC, Dayton. "A minor change here or there can make for a successful coating down the road. It can also boost performance and strength in certain areas. And remember, changes made in the concept and design phases are much easier and less expensive to handle than modifying tooling in the manufacturing process."

The plating industry has an arsenal of techniques to help clients produce even and consistent chrome coatings and other metal finishes in difficult to reach areas. Take auxiliary anodes, for example. Placing extra anodes on various parts of the plating racks helps metal ions find hard-to-reach surfaces. It produces uniform coatings that stretch down inside doors, pockets, and other recessed areas.

Brightening up the scene
A recently developed multilayered nickel-chromium coating process is making decorative items such as nameplates and exterior trim shine brighter and last longer. It's also being used on functional components such as wheels, bumpers, door handles, and other accessories.

The multilayered process puts together layers of semibright nickel, bright nickel, and particulate nickel. To make it more corrosion resistant, platers can add a high-sulfur nickel layer between the semibright and bright nickel layers. This thin layer (often only 0.000020 in. thick), can actually double the corrosion protection of the substrate.

To make the multilayer nickel finish even more durable and blemish-free, a microporous coating is applied before the final application of chromium. This microporous nickel layer induces microporosity in the subsequent chromium layer, creating a tough barrier against corrosion.

Copper-accelerated salt-spray testing simulates service conditions in a controlled lab environment. It's also an automotive benchmark for evaluating how plated components stand up to weather and exposure. Current standards call for up to 66 hr of exposure. When multilayer nickel finish is combined with a high-sulfur-nickel layer, components can exceed 100 hr of testing before deterioration is apparent. Field tests have also proven that the combination creates a new standard in metal coatings. Now a few OEMs are asking for up to 200 hr of testing for parts on entry-level and luxury vehicles.

New trends in auto design that challenge platers and engineers include dual-function bumpers and larger components. "We've seen an increased demand for 'wrap-around' chrome bumpers from light truck manufacturers," notes Tony Barnett, vice president, Chrome Craft of Highland Park, Mich. "However, many of these bumpers, besides protecting the vehicle in crashes, have recessed rear steps that must withstand heavy traffic and abuse." Coating companies can give such customers what they need, a more durable, shiny finish, if they are included in the design process.

Dayton Alloy Wheel's Biltz also sees OEM's moving toward bigger and bolder designs that will need coatings. "Traditionally, the industry was plating 14 and 15-in. wheels. It is now commonplace to chrome plate 17 and 18-in. wheels. In the future, the automakers will be demanding mass production and plating of 20-in. wheels. And many wheels that originally were not designed to accept chrome are now being plated and held to the same performance standards."

Now is the time to start thinking about the next generation of vehicles and their functional and decorative treatments. New coating technologies and techniques are being developed by platers and the world's leading vehicle manufacturers that will make future vehicle designs even better.

Although platers and coating companies don't want to seem unreasonable in offering guidelines or placing constraints on designers, there are ways to make designs more "plating friendly."

They include:

  • Minimizing "blind holes," recesses, and joint crevices where metal shavings and polishing compounds can get trapped during the plating process.
  • Avoiding sharp edges and protrusions that are susceptible to mechanical damage.
  • Maximizing exposed and visible surfaces. They can be effectively polished using polishing methods.
  • Wheels and other parts actually increase in hardness when chrome-plated. Designs that do not take this into account often have to be structurally redesigned to pass fatigue testing.

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