Hard Chrome Plating

Q. We produce Gearbox for Cooling Tower and at the moment we have got a problem; in the output shaft of the gearbox is appearing a corrosion and this corrosion is damaging the seal and this way a leaking in occuring in the gearbox.

If we made a hard chrome plating in the output shaft in the location of the radial seal can we get satisfactory results?

Could you tell me what is the best way to do this hard chrome plating in a shaft with material DIN 42CrMo4 with about 260 Brinell Hardness?

A. Hard chrome plating is an excellent wear resistant coating with a typical hardness in excess of 700 Brinell, and it may be enough to solve your problem. However, if corrosion is due to exposure to salty or extreme outdoor weather environments, hard chrome alone may not be enough.

In the extreme case, you may require the added protection of a base coating of nickel then a top coating of hard chromium to get the maximum corrosion resistance and wear resistance you are seeking. The cost for this process is significant and a limited number of plating facilities offer chrome over nickel.

An alternative coating is "electroless" nickel, which can be applied directly on the output shaft without the need for an undercoating. E-nickel coats uniformly and conforms to any geometry. As a rule, it doesn't require after plate grinding. As plated, E-nickel coatings are in the hardness range of 350-450 Brinell. E-Nickel can be further hardened by heat treatment to as much as 800 Brinell. E-nickel will provide both wear resistance and corrosion resistance at a lower cost than chrome or nickel/chrome.

Randy Taylor