Back to Lube-Tips™ Back Issues.

Machinery Lubrication Magazine Reliable Plant Magazine Motor Oil Selection Guide Synthetic Oil Resources

Q & A

"About a year ago we ran a lubricant too long in a high-duty gearbox and it oxidized and threw sludge. Ever since that incident, we've been watching the oil more closely with oil analysis. My problem is that we are now seeing acid numbers rise and oil darken after only one month of service--the lubricant used to last a full year. We keep changing the oil but the problem just repeats. Why does our gear oil have such such a short life?"

Its sounds like the gearbox was not thoroughly flushed after the oil oxidized the first time. Typically, a simple drain will leave more than 15 percent of the old oil behind - occluding to machine surfaces and trapped within the casing. This also leaves a host of reactive chemicals (pro-oxidants) behind that rapidly deplete antioxidant additives, leaving the base oil unprotected.

You refer to the gearbox as high duty, which probably means high temperature and high wear metal production. The temperature and wear particles also accelerate the rate of oxidation, especially when sludge and other pro-oxidants are in the mix. I suggest you do a thorough flushing of the gearbox. You might refer to the article on flushing that will be featured in the July - August issue of Machinery Lubrication magazine.

Today's Tip

• Things that can extend the oil drain interval in engines: high oil consumption (makeup), synthetics, highway miles, clean oil, dry oil, low sulfur fuels, low blowby, minimal idling and lugging, few stops/starts, no coolant leaks, properly serviced air, fuel, oil and sump filters, and proper rack and air/fuel settings.

Each tip published will earn the sender $10. Send your tips to webmaster@noria.com or fax to 918-746-0925.

Book Bits

From the book "Turbine Lubrication in the 21st Century":

For turbine oils, the greatest advantage Group II finished oils provide over Group I oils is superior oxidation stability. Severe hydroprocessing of feedstocks greatly reduces the aromatic, sulfur and nitrogen-containing “impurities” to give virtually impurity-free Group II base oils. These impurities are responsible for the lower oxidation stability of Group I stocks because they readily oxidize. These impurities oxidize to form benzylic, sulfuric, and nitric acids and other oxidized species. Group II base oils typically contain only trace amounts of these impurities and the finished oils can exhibit outstanding oxidation stability properties when formulated with the proper additives. The superior oxidation stability of Group II finished turbine oils is demonstrated in their RPVOT and TOST values.

For gas turbines, such as the General Electric (GE) Frame 7 series, a turbine oil with excellent oxidation stability is very desirable. The GE Frame 7 series has three journal bearings with a center bearing that can be subjected to 500 degrees Fahrenheit. Since a turbine oil also acts as a coolant, it will be subjected to high temperatures from the center bearing and it must be oxidatively and thermally stable. A turbine oil with excellent oxidation stability is necessary in many gas turbine applications.

For more information about the book "Turbine Lubrication in the 21st Century" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=59

Copyright © 2001, Noria Corporation. All rights reserved. Please do not reprint or host on your website without explicit permission. However, if you found this newsletter helpful, we grant you permission, and strongly encourage you, to e-mail it to a business associate or a friend. Thank you. The presence of advertising in Lube-Tips does not constitute an endorsement of the products or services in such ads. Further, because results will vary widely based on a number of factors, Noria Corporation cannot warrant the results, the accuracy or the completeness of any material published herein.

Lube-Tips is published by Noria Corporation. Oil Analysis and Lubrication Experts