Affect of EP Additives in Oil on Copper Base Alloy Gears

[Carburize]

Posted this in the tribology area but since it is suggested as a corrosion issue I will try here as well.

I have heard reports that there can be serious corrosion problems in copper based alloy gears in the presence of EP packages containing sulfur and phosphorus compounds. Can anybody provide any references to these issues?

 

[rorschach]

I'm not sure about copper, but if the alloy has any nickel in it (say Ampco 45 aluminum nickel bronze) then sulphur might form a low temperature alloy with the nickel which could lead to liquid metal embrittlement.

 

[TVP]

Copper itself suffers general corrosion...in sulfur compounds. [Uhlig's Corrosion Handbook, 2nd edition]

The ammonium ion is generally considered to be the specific corrodent to produce SCC in Cu-base alloys. Evidence has also been presented that citrates, tartrates, nitrites, sulfur dioxide, carbonates, oxides of N2 and phosphates, among others, may also produce SCC in some Cu-base alloys. [Uhlig's Corrosion Handbook, 2nd edition]

Some sulfur-chlorine-phosphorus additives are corrosive to bronze and nylon cages... [ASM Handbook Volume 18 Friction, Lubrication, and Wear Technology]

 

[SMF1964]

Rorschach:
Nickel-Sulfur reaction is typically at temperatures far higher than expected for oil lubricated gears, but if there is moisture present, you can end up with the EP additive dropping out into the moisture, rather than remaining in the oil, and your lubrication goes to... the Dark Side.

 

[rorschach]

I was thinking of very localized heating (due to asperities etc.) on the gear faces. I don't have my nickel alloys textbooks here with me so I can't get hold of a nickel-sulfur phase diagram, but I seem to recall that the use of sulfur bearing machining fluids are verboten because the temps generated in machining were enough to cause this.