Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/544388
6 | July - August 2015 | www.machinerylubrication.com The Importance of Saving the Oil The importance of saving the oil is best assessed by the Overall Lubricant Criticality (OLC). The OLC defi nes the signifi cance of lubricant health and longevity as infl uenced by the probability of premature lubricant failure and the likely consequences (for both the lubricant and the machine). The proposed method for calcu- lating the OLC is shown above. Like many such methods, this approach is not an exact science but nevertheless is grounded in solid principles in applied tribology and machine reliability. The Lubricant Criticality Factor (LCF) defi nes the specifi c economic consequences of lubricant failure separate from machine failure consequences. The LCF is infl uenced by the cost of the lubri- cant, the cost of downtime to change the lubricant, fl ushing costs and system disturbance costs (e.g., the fi shbowl effect). For instance, machines that use large volumes of expensive, premium lubricants will understandably have high LCF values. Studies have shown the true cost of an oil change can far exceed 10 times the apparent cost (labor and oil costs). The Degradation Occurrence Factor (DOF) defi nes the proba- bility of premature lubricant failure. The conditions that infl uence this probability are shown below. Lubricant Robustness — Synthetics and other chemically and thermally robust lubricants lower the DOF. Operating Temperature — Lubricants exposed to high operating temperatures, including hot spots, can experience accelerated oxidation and degradation. The presence of such conditions will raise the DOF. Contaminants — Contaminants such as water, dirt, metal parti- cles, glycol, fuel, refrigerants, process gases, etc., can sharply shorten lubricant service life. The presence of such exposures will raise the DOF. Lubricant Volume and Makeup Rate — Lubricant volume relates to the amount of additives available to fi ght oil degradation, the estimated runtime to complete additive depletion and the density of contaminants. In normal service, it can take years to burn through the additives in systems containing thousands of gallons of lubricant. The makeup rate refers to the introduction of new additives and base oil. New additives replenish depleted addi- tives, and new base oil dilutes pre-existing contaminants. High oil volume and a high makeup rate will reduce the DOF. 37% of lubrication professionals say machines at their plant are selected for oil analysis based on the amount of lubricant they hold, according to a recent survey at MachineryLubrication.com The proposed method for calculating the Overall Lubricant Criticality