ZDDP - Scuffing vs Fatigue Effects

[JAG]

http://www.tribologia.org/ptt/tribv35.htm

Quote:

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6-2004 Tibologia

Witold Piekoszewski, Waldemar Tuszyński
Instytut Technologii Eksploatacji - PIB, Zakład Tribologii, Radom, Poland.
Scuffing and Rolling Contact Fatigue as Effects of the Chemistry of Lubricating Oils
Zacieranie i powierzchniowe zużycie zmęczeniowe jako efekty kompozycji chemicznej olejów smarowych
Key-words: Four-ball tester, scuffing, rolling contact fatigue, AW additives, EP addi-tives, SEM, EDS, GDOES, FTIRM

Summary

The aim of the research was to establish a relationship between the re-sistance of a tribosystem to scuffing and surface fatigue as a result of the type and concentration of AW/EP additives in lubricating oils.
Lubricating oils of various chemical composition were tested. A base mineral oil was blended with commercial packages of lubricating addi-tives of AW and EP type, at different concentrations. The AW additives contained ZDDP, and EP ones - organic S-P compounds.
The tests were performed in two different four-ball testers. The first one (denoted as T-02) was used to determine extreme-pressure (EP) properties at sliding friction - a new method for testing scuffing and sei-zure was employed. The second instrument (denoted as T-03) was used to assess the surface fatigue (pitting) life at rolling movement.
It is shown that AW additives not only improve EP properties but - at a small concentration - are also beneficial for the fatigue life. An in-crease of the content of AW additives leads to an improvement of EP properties but may reduce the fatigue life.
EP additives - even at a small concentration - significantly improve EP properties. A small concentration of EP additives gives no influence on the fatigue life. An increase of the content of EP additives leads to a further improvement of EP properties. However, this is accompanied by a much decrease in the fatigue life.
By using a scanning electron microscope (SEM), energy dispersive spectrometer (EDS), glow discharge optical emission spectrometer (GDOES), and Fourier transform infrared microspectrophotometer (FTIRM) for analysis of the worn surface, the authors identified mecha-nisms of action of various lubricating additives under different friction conditions. It must be emphasized here that GDOES is mainly used to analyze flat surfaces; results for small wear scars on non-flat surfaces (balls), like in this study, are published very rarely.

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[Leo]

Call me dumb but I'm not sure what they are referring to as 'fatigue life'?

 

[goodvibes]

Sounds like more of a good thing isn't better. Without knowing which adds and at what concentrations this doesn't tell us a great deal especially with a test that may not represent what happens in a motor.

 

[Thatwouldbegreat]

This sounds like we can't just experiment with adding a little VSOT, SLOB, or SX UP without possible risk.

I wonder if some forum member can come up with a rule of thumb that defines when it is worth the risk to add extra Moly or ZDDP etc. ... and when it isn't?

Also, I wonder what the consequences of these 'fatigue effects' are?

Maybe this study illustrates that 'more isn't always better' but maybe the harm isn't that great?

I wonder if the formulations from major oil companies are already designed with this 'scuffing vs fatigue effects' factored in?

Or is this really a new theory?

 

[MolaKule]

"EP additives - even at a small concentration - significantly improve EP properties. A small concentration of EP additives gives no influence on the fatigue life. An increase of the content of EP additives leads to a further improvement of EP properties. However, this is accompanied by a much decrease in the fatigue life."

Sounds contradictory to me or the translation missed something.

Someone is running a test with ZDDP and an EP additive but from this abstract, it is difficult to tell how the experiment was conducted and what the definitive results, if any, were.

 

[oilyriser]

I understood it as:
low EP/AW - good EP properties, same fatigue life
high EP/AW - better EP properties, but lower fatigue life

 

[JAG]

oilyriser got it, at least that's my understanding. Fatigue in this case was causing pitting. My guess is the ZDDP concentrations that increased pitting were very high, as in much higher than used in HDEOs and maybe even hihger than all racing oils. So I'm thinking maybe >2000 ppm, as that's about the highest I've seen in some racing oils.

I found two things most interesting. More ZDDP gave more scuffing protection. That is, the protection against scuffing did not plateau above some small concentration. I always figured that and never bought the balogney that protection is good as long as Zinc is >600 ppm or whatever small number it is. And it's well known that ZDDP breaks down during use (though used oil analysis cannot track that since they are for elements, not molecules), so starting with low amounts isn't my cup of tea.

The other interesting thing was another instance of super high ZDDP levels causing pitting. Just interesting to me from a geek point of view, not a practical one since I'll never be using that much ZDDP anyway.