Got Chrome?

Getting Inside the Chroming Process

| August 2005

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    Bumper guards fresh out of the chrome tank at Industrial Chrome Inc
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    The nickel tank. Note copper bar where parts are hung.
  • 08-05-011-IndChrome13.jpg
    An example of hard-chroming, in this case a steel driveshaft yoke from the author’s parts collection.

  • 08-05-011-IndChrome11.jpg
  • 08-05-011-IndChrome5.jpg
  • 08-05-011-IndChrome13.jpg

For those of you thinking about nickel or chrome plating your engines now, there's a thing or two you may want to know first. To find out how the process works, I went to Industrial Chrome Inc. in Topeka, Kan. Gary Sack, the shipping and receiving manager, walked me through the whole nickeling/chroming process.

Nickel plating is more or less just chrome without the chrome, so to speak, so the two go hand-in-hand. First of all, the metal to be plated needs to be stripped down to bare metal. Parts that have previously had nickel plating (such as if they were chrome to begin with) are probably better left to the professionals, as merely sanding the chrome off does not rid the metal of its nickel properties - it needs to be stripped in a special acid bath.

Once the part is down to bare metal, it is dipped in a special cleaning solution before being acid-dipped and rinsed. It is then dipped in copper (Gary says this isn't always necessary) and rinsed again. From the copper tank, the part goes to the nickel bath and is rinsed once again. Finally, the part is dipped in the chrome solution to bring a mirror-smooth shine. Then, once again, the part is rinsed. It is important that the part be rinsed between each layer of plating or the chemicals will not adhere and the plater will have to start all over again.

For the process to work, the part is hung on a cathode bar running the length of the tank. The nickel comes in small (about 2 ounces), odd-shaped pieces, hung in bags on the side of the tank. The nickel is the anode. A DC current runs through the tank and solution, and the combination of these three elements is what makes the process work. The plating tanks run about 140 degrees Fahrenheit, whereas the cleaning tanks are kept at 180 degrees or more.

Another option other than nickel or chrome plating is hard chroming. Hard chrome is decorative chrome without all the polish and prep work, leaving a more industrial finish. The piston on a hydraulic ram, for instance, is hard-chromed.

The level of thickness to be expected on any of these types of plating are as follows: Nickel plating will add roughly 0.005", decorative chrome will add another 0.0001" on top of that, and hard chroming is in an entirely different ballpark. The thickness of hard chrome depends on the customer's requirements. The thicker it is, the more durable (i.e., hard) it is. This will typically range anywhere from 0.001" to 0.006" or more. The more time the part spends in the tank, the thicker the plating.


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