Why would Extreme Pressure oil additives damage Gears?

The primary reason Extreme Pressure oil additives damage Gears is because the chlorine, potassium-borate and sulfur-phosphorus extreme pressure (EP) additives, primarily used for industrial gear lubrication, protect through chemical reaction.

These EP oil additives are temperature-activated and react with the metal to form a sacrificial film.

EP oil additives can cause severe damage through chemical reaction:

• Extreme pressure additives such as the sulfur phosphorus types can be “too chemically reactive,” resulting in polishing wear. 

This type of wear reduces gear accuracy by
wearing away the tooth profiles.

If this problem is experienced, potassium-borate additives can be used to deposit EP films without a chemical reaction with the metal.

•  Because the rate of reaction of EP additives is temperature related, and the temperature is greatest at the gear tooth contact , difficulties can be experienced in low-temperature applications when operating temperatures are not high enough to fully activate the reactive EP agents. 

Anything that reduces the bulk oil temperature or the flash temperature will reduce the total contact temperature and increase the risk of wear. The viscosity of the base oil is extremely important. 

• Sulfur-phosphorus EP additives have been found to be corrosive to yellow metals, when operating at temperatures above 60 degrees C. 

In the case of Worm gearsets extreme caution should be exercised as they frequently contain phosphor-bronze materials, and for this reason gear oils using sulfur-phosphorus EP additives usually do not provide satisfactory service in worm gear drives.

• Depending upon the volume added, sulfur-phosphorus EP additives may not be compatible with lubricants containing zinc anti-wear (AW) additives. 

This is why it is not advisable to mix AW gear oils with EP gear oils. 

• Even the smallest ingress of water in the presence of chlorine or borate EP additives can reduce the efficacy or even precipitate corrosion.

Extreme Pressure oil additives should not be considered for these applications:

• The use of EP oil additives can cause severe damage when used in slow-speed gear applications (less than 10 feet per minute), causing high rates of wear known as “polishing.” 
• With Sulfur-phosphorus extreme pressure additives having an upper-temperature limit of approximately 95 degrees C, operating at temperatures above this will lead to excessive wear rates. 
• Solid lubricants such as molybdenum disulfide, graphite or tungsten disulfide are often used when the reaction rate may not be sufficient due to the operating temperatures being too high or low for the specific oil; however, these solid films have limited wear lives and may not carry the loads necessary for satisfactory gear and bearing life. 

Now that you have a better understanding of how the incorrect use of EP oil additives can damage gears, you’ll want to have a look at our top quality synthetic gear oil at Habot Synthetic Lubricants.