Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/325287
www.machinerylubrication.com | May - June 2014 29 to MPC). As the values become closer to 1-to-1, the higher the chance of varnish deposits in the system. An inverse value of a higher MPC to a lower iMPC is a clear signal that significant varnish deposits exist inside the system. An alternative to charting two different values is to add the iMPC and MPC values and divide by 2 for an average value. This practice is useful for trending and monitoring systems that employ a varnish-removal filtration system. The most important advantage of the iMPC/MPC ratio method is that it does not depend upon a statistically derived absolute value. By using a ratio system, it is more universally applicable to a wide variety of lubricant types and equipment types. It does not rely on a massive amount of sample data from the same oil type and equip- ment type. The iMPC/MPC ratio method also correlates well with other ASTM tests, including water-separation characteristics (ASTM D1401), air-release prop- erties (ASTM D3427), and foaming tendency and stability (ASTM D892). Constantly Changing Oil and Equipment The various types of equipment using R&O oils are constantly being tweaked by their design engineers for perceived improvements, such as smaller lubricant reservoirs, combined lubricant functions and increased machine output. However, these changes also place higher stress on the lubricant. As these equipment modifications are taking place, the lubricants also are undergoing changes. Unlike the equipment changes, which are well-documented, the lubricant adjustments go by relatively unnoticed. Lubricants can be modified and sold under the same trade name even though radical changes may have been made to their formulation, such as in the base stock or additive type. In the lubricant business, this is called reformulation. This reformulation is sometimes due to refinery upgrading, which makes legacy base stocks unavailable, or a newly discovered undesirable additive charac- teristic, which leads to its replacement. While reformulation is fine if equipment designs are stagnant, in the constantly changing world of equipment design, reformulation can sometimes lead to unwanted consequences, including varnish. Over the past 10 to 15 years, industrial lubricants with the same trade names have silently become composed of Group II and III base stocks, which are better suited to the automotive lubricant market. Group I base stocks are more soluble of varnish contaminants, making them better industrial lubricants for many applications, but industrial lube sales volumes pale in comparison to automotive lube sales. This quiet disappearance of Group I base stocks began to have a pronounced negative effect in certain machines and applica- tions, causing "varnish buildup." The category reformulations coupled with the expanded use of PANA-type additives led to world- wide reliability issues. At the time, the root cause of this varnish problem was unknown. Was it the changes in additives, base stocks or equipment designs? In reality, a combination of all of these factors played a role. Varnish-Removal Systems A wide variety of varnish-removal systems have been introduced during the last 10 years. Most have been aimed at removal (reac- tive), although some have been designed for varnish prevention (proactive). The three main categories are agglomeration elec- tric-charge filters, depth-media filters and precipitation electric-charge filters. An agglomeration type of varnish-removal system (Ref. ISOPur Inc.)