Nickel-chrome plating is a labor-intensive, time-consuming process of imparting a very hard, bright metal finish to an object. A popular process in the finishing of metal parts of trucks, cars, and motorcycles, as well as household fixtures such as faucets and knobs, it’s a process that's materials and processes include significant health and environmental hazards. It’s not an activity to be undertaken as a weekend hobby, but it can be a profitable business for those willing to work patiently and adhere to the standards for safe handling and disposal of the many hazardous materials involved.
Nickel-chrome plating produces a hard finish that can be highly polished, leaving a bright, aesthetically-pleasing appearance, as well as providing a some rust and corrosion resistance to the object being plated. While some alternative, less hazardous processes, such as powder coating, can produce similar-appearing results, they cannot be used on objects subject to high temperatures in normal operation, such as motorcycle exhaust pipes or engine pistons.
There are many steps involved in nickel-chrome plating. First, the surface to be plated must be thoroughly prepared — it must be chemically and microscopically clean. To achieve this state, mechanical means such as grinding and buffing are used, as well as acid baths to remove any surface contaminants. If there’s any foreign material at all on the surface, it won’t take the plate.
Nickel-chrome plating actually consists of at least two separate plating processes: the item is first plated with nickel, and then plated with chrome. In addition, nickel plates particularly well on copper, so in many plating operations, the surface is first plated with copper. Although it takes significantly longer, a nickel-chrome plate on copper is extremely durable. After every step in the plating process, the workpiece must be cleaned and polished, because any imperfections in the surface will show through on the finished piece. Some metals, particularly aluminum, require extensive special preparation before they can be plated.
The plating process molecularly bonds very thin coats of nickel and chrome to a metal surface. The thickness can range from 1 mil to 20 mils or so (1 mil = 0.001 inch, or 0.0254 mm.) A human hair is about 1 mil, and a household plastic garbage bag is 3 mils thick. Although different parts of the process may be slightly tweaked to speed the process somewhat, one should expect a plating thickness of about 1 mil for every hour of the process. This usually takes place in a chemical bath through which an electric current is passed from an anode to the workpiece, which acts as the cathode. For the nickel plating portion of the process, the anode itself is made of nickel, and when the current is turned on, the nickel slowly leaves the anode and migrates through the chemical bath to the cathode — the workpiece. For the chrome plating step, the anode is made of lead and the chromium is one of the ingredients of the bath itself, in the form of chromic acid mixed with sulfuric acid and water.
The electroplating chemical bath requires exacting attention to detail. The different ingredients must be precisely measured, and the bath itself must be heated for optimal results. In addition, to keep the temperature constant throughout the mixture and keep refreshing the solution in contact with the workpiece, the bath must be continually agitated. This agitation is usually accomplished by pumping air through a perforated plastic tube, producing a stream of bubbles, although other means, such as keeping the workpiece in motion or placing a small propeller in the bath, can also be used.
Many forms of chromium are known carcinogens, and the entire nickel-chrome plating process is subject to strict regulations in most jurisdictions. Indeed, the regulatory burden imposed by some municipalities amounts to a de facto outlawing of nickel-chrome plating. In jurisdictions where it’s permitted, the area where the nickel-chrome plating process is taking place must be properly ventilated, because chromium is present in the vapors produced in the process, and can easily be absorbed through the lungs. In addition, not only is the chemical bath itself considered a hazardous material that's handling is regulated by law, the waste water produced in the process of cleaning and rinsing workpieces and equipment is also considered hazardous waste, as is everything it comes in contact with. These wastes cannot simply be disposed of in the plumbing system; they must be contained and disposed of in accordance with regulations.