Q & A

Solid versus Chemical EP Additives

“In a recent Lube-Tips Q&A, you mentioned that many oils with EP additives contain sulfur phosphorus additives which can be corrosive to yellow metals. When I mentioned this to our lube supplier, he told me that the EP oil we are using contains “solid” EP additives that are less corrosive. -What are solid EP additives?”

Some EP oils obtain their EP protection from solid particles suspended in the oil. Some of the more commonly used solids include molybdenum disulfide (often referred to as “moly”), borates, graphite and fluorinated polymers (e.g., Teflon).

Unlike conventional EP oils where the EP additive chemically reacts with the surface under high load/temperature conditions, solid EP additives plate out on the surface and adhere by physical attraction. Since this physical attraction does not involve the formation of strong chemical bonds with the surface, solid EP additives are usually less chemically aggressive and hence less corrosive in many applications, although they do have other disadvantages.

Both solid EP additives and chemical EP additives produce the same effects of protecting heavily loaded bearings and gears operating under conditions of boundary lubrication, they simply work in different ways.

Today's Tip

• Protect new bearings against contamination and condensation. New bearings should be kept in their original wrappings as long as possible, and stored away from moisture where the temperature can be kept reasonably constant. It is typically not a good practice to flush the original lubricant from a new bearing. This could introduce contamination.
  

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Book Bits

Many open gears, whether operating outdoors or indoors, are exposed to dusty and dirty conditions. Abrasive dust, adhering to oil wetted surfaces, will form a lapping compound that causes excessive wear of the teeth. When viscous lubricants are used, the dirt may pack in the clearance space at the roots of the teeth, forming hard deposits. Packed deposits between gear teeth tend to spread the gears and overload the bearings.

For more information about the book "Lubrication Fundamentals" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=2

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