Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/704613
BACK PAGE BASICS lubricant, mechanical/operational issues or excessive heat from the production process or environment. The higher the lubricant temperature, the more prone the lubricant is to oxidize and the shorter its life will be. Temperature is also a factor in the generation of varnish and sludge, additive deple- tion, and the shortening of machine component life. Machines have a range of normal operating temperatures that must be identified and controlled. Temperature transducers, heat guns and thermographic technologies are essential tools for monitoring machine and lubricant temperatures. Other indirect instruments may also be used. It is critical to recognize when abnormal condi- tions exist and to determine their root cause. Machines must dissipate generated heat to the environment or to cooling systems, so the possible solution will be at this point. The goal is to main- tain the operating temperature as low as possible to extend machine and lubricant life . Varnish Varnish is the result of a number of factors acting independently or in combination to generate microscopic compounds in the oil. These compounds initially remain dissolved due to the lubricant's natural solvency properties. However, if the concentration of particles continues to increase, they eventually become insoluble and migrate to machine component surfaces. The insoluble compounds in the oil are referred to as varnish potential. The higher the lubricant's solvency properties, the more the compounds will remain dissolved without becoming varnish. Also, solvency is highly temperature-dependent. Cool oils and cool machine surfaces are more prone to varnish issues. Several elements influence an oil's varnish potential, including microdieseling, oil sparking, lubricant oxidation, thermal failure, entrained air and contamination with other lubricants or substances. Depending on the root causes, different types of varnish compounds may be generated. You could say that varnish is just a generic expression of the various possible compounds. Varnish may be deposited in several compo- nents within the lubrication system and can reduce heat-transfer properties, produce filter plugging, decrease lubricant film thickness, lessen flow rates or cause obstruction of lubri- cation lines or valves. Membrane Patch Colorimetry (MPC) is a common test used to monitor varnish poten- tial. It reports the concentration of varnish potential by color and provides a score. Other tests that can identify or characterize varnish include ultracentrifugation and FTIR. Your first course of action should be to determine the root causes of varnish in order to eliminate or minimize them. A formal root cause analysis may be needed along with exception laboratory tests to measure the concentration of varnish and to characterize its type. There are also products available to help correct the problem, although the y may not eliminate the root cause. These include detergent additives, base oils that enhance lubricant solvency and high-quality oils such as polyglycols. Regardless of the type of contamination, the lubricant should be kept clean, cool and dry. It must also be applied in the right place, in the right amount and at the right frequency. If all of these goals are main - tained consistently, you will be better able to maximize the performance and lifespan of your turbomachinery. About the Author Alejandro Meza is a senior technical consultant with Noria Corporation. He has more than 20 years of experience in the lubricant industry, technical services, quality assurance, training, consulting and development in the United States, Brazil, Mexico and the Americas region. Contact Alejandro at ameza@noria.com. 6 Contamination Control Tips 1. Contaminants frequently affect a lubri- cant's foam tendency and stability as well as water separability. If you detect more foam than normal or demulsibility issues, it may be an indicator of lubricant contamination. 2. Cross-contamination with other lubri- cants, solvents, cleaning agents or assembly oils may generate varnish and lubricant performance issues. 3. Contaminant removal methods can also remove some of the oil additives. In most cases, this is not a concern, as the benefit of cleaning the oil is much greater than the potential of additives being removed. Of course, there are exceptions. If possible additive depletion is suspected as a result of purification methods, a study should be conducted with the support of oil analysis. 4. Oil sample contamination can result in a false positive report but is not actually contamination of the in-service lubricant. 5. To confirm oil analysis results, resample and retest. Also, be prepared to interpret the results. Some differences can be expected due to the various factors involved in testing protocols. 6. Synthetic lubricants may offer better options for resisting higher operating tempera- tures, reducing fluid friction and providing better solubility. 56 | July - August 2016 | www.machinerylubrication.com These images show the results of an MPC test on four different oils. The one on the far left is considered to be at the warning level, while the other three are in the critical range.