ORIGINAL: GSJames
What are the relative merits of chrome vs nickel? I suspect that nickel is CHEAPER for the manufacturer but that it has reduced wear and probably a higher friction coefficient. Since the sleeve is brass with only a plating of the other metal, I imagine that the coefficient of thermal expansion would not be affected. Bob, what's your take???
<span lang="EN" style="font-family: Verdana; color: black; font-size: 10pt; mso-fareast-font-family: 'Times New Roman'; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">Chrome is very hard which gives it very good wear characteristics. This hardness also results in a very low coefficient of drag. This keep the heat build up down as the parts rub against each other.
In the plating process it develops micro-cracks. These cracks offer a means to relive thermal stress (both in the plating tank and in service). This result in good bond performance over the life of the plating. In our application it allows for lubrication to collect. This collected lubrication can weep out of these micro-cracks and offer some “last chance lubrication” should the equipment be subjected to lubrication failure (lean runs).
The disadvantages of chrome are mostly in the manufacturing process.
These disadvantages are:
Hexavalent chromo sulfuric acid is very toxic. This means that there are a lot of costs associated with it to meet environmental concerns.
It is what is known as a very inefficient process. This means that the chromic solution is susceptible to contamination.
It does not plate evenly. This means that to control dimensions it must be machined (ground). This lack of precise plating thickness control means that part features that don’t need to be plated must be masked to maintain their dimension.
Unlike chrome electorless-nickel plating is a fantastic plating process.
A major benefit to elctorless nickel is that it has a very low environmental impact compared to chrome.
Electroless nickel plating is what is known as a very efficient process. This is to say contaminates (within reason) do not affect the bond strength.
Electorless nickel it is very easy to control plating thickness. This means that there is no need for a second machining operation to reach the desired bore size. It is vary easy to plate to size accurate to less than 0.002mm (.0001 inches) thick. It also means that the whole cylinder can be plated removing the need and cost of masking.
The dis-advantage with Electroless nickel plating are:
It is very soft compared to chrome plating when it if first plated. It has a high coefficient of drag this results in its tendency to gall. This galling will produce heat that can cause the plating to fail debond (peel).<br style="mso-special-character: line-break" />
Happy flying, Oscar<br style="mso-special-character: line-break" /></span>