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The extensive use of decorative chrome on parts has fallen in and out of fashion in the auto industry, but currently this trend is hot…and that poses a problem. To achieve the shiny finishes car buyers covet, chroming suppliers traditionally have had to use an array of hazardous materials for surface preparation. But as government restrictions tighten on the use and disposal of hazardous chemicals, traditional methods may have to be modified or even jettisoned.
Enter Gary Goodrich, president and CEO of Goodrich Technology (Pittsburg, CA). He has patented a method of chroming parts called PermaStar that uses no hazardous chemicals and produces no hazardous by-products. The key to this process is a two-stage physical vapor deposition (PVD) technology, and a topcoat to protect the chromed surface. By using PVD, Goodrich says he can completely eliminate surface preparation chemicals, thus removing a potential environmental hazard. Further, his method does not require the meticulous polishing used in current chroming operations, thereby significantly reducing labor costs.
Goodrich began researching the possibility of using PVD to produce chrome finishes over four years ago, and traveled to Europe with the thought of replicating the PVD-based chroming methods in use there. But he deemed the resulting parts too dark for American tastes, and began developing his own variation on the theme—PermaStar.
The process begins by smoothing the part to be chromed to achieve a uniform surface roughness. It then undergoes a series of de-ionized (DI) water rinses including a non-chromate/DI water solution coating if the part is aluminum, and an iron phosphate/city water solution coating if it's steel. After being dried by high-pressure filtered air and a stint in an oven, a base coat is applied to provide a smooth surface suitable for nickel/chromium adhesion. (Goodrich recommends an organic, thermosetting powder, but the process also allows for the use of an inorganic compound, or even electroplated coatings and e-coatings.) The part is then heated to achieve an even flow of material and to crosslink and solidify the powder.
Next comes the two-step PVD phase. The part is placed in a vacuum chamber where a layer of approximately 80% nickel and 20% chromium is applied using a sputtering method. The second layer, which is crucial to the final appearance, is 99.9% chromium. Goodrich says that the layers are a mere 600 angstroms thick, (an angstrom is one hundred-millionth of a centimeter) which keeps material use to a bare minimum.
Finally, a top coat is applied to protect the chromium layer. Again, an organic thermosetting powder is preferred, with the alternatives being the same as for the base coat. The top coat is important for increasing durability and corrosion resistance, but according to Goodrich, before PermaStar no one had figured out how to stabilize the chromium layer sufficiently so that a top coat could be properly applied.
A pilot plant was set up in 2001 to prove the process in a production environment, and has produced several hundred chrome wheels for an aftermarket supplier. PermaStar products have passed standardized tests for salt spray, corrosion and chip resistance, and interest has been piqued in the automotive industry. "Ford, GM and DaimlerChrysler are all actively looking at this process," says Goodrich.