Affect of EP Additives on Bronze gears

[Carburize]

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?

 

[Frederick]

I know it can happen. In 1933, Pierce-Arrow used a worm drive rear axle in an effort to lower the car. Many of these axles were ruined when extreme pressure lubricants were used and they literally ate the bronze worm wheel in the axle. It became such a problem that Pierce developed a package to replace the rear axle. The original axle, made by Timken, is now very rare. It was only used by Pierce for one year, and by Hipano and Stutz. Sorry this doesn't give technical or chemical details, but it does support the fact that sulfur compounds can do real damage to bronze.

 

[electricpete]

An oblique reference. Read it twice and you'll conclude lubricant corrosion is particularly a concern from brass parts and EP additives are especially corrosive.... addressed through sulfur scavengers.

http://www.machinerylubrication.com/article_detail.asp?articleid=616&relatedbookgroup=Lubrication2

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[electricpete]

http://www.noria.com/learning_center/category_article.asp?articleid=496&relatedbookgroup=OilAnalysis

Much more relevant than the last... put together these two excerpts. The short version:
1 EP contains active sulfur.
2 Sulferized mineral oils are corrosive to yellow metals

The long version (direct quote)

1 - "Modern EP gear oils are formulated with additives that contain active sulfur, frequently combined with phosphorus, to provide a thermally stable, noncorrosive lubricant with high load-carrying capacity."

2 - "Sulfurized mineral oil and other highly reactive forms of sulfur have the advantage of forming protective metal films at lower temperatures than other sulfur-containing additives. On the downside, they are corrosive to certain metal and metal alloys, particularly yellow metals, which contain copper as a major alloying element. "

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[OilGuy]

EP-additized oils are usually not recommended for bronze-containing gearboxes, since the sulfur-Phos additive normally used (the EP additive) can attack the bronze, at elevated temperatures and pressures (which are normally seen in such circumstances). The specific combination of metals in the bronze can either help or hurt, but they are usually not much of a factor.