Machinery Lubrication magazine published by Noria Corporation
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Machinery Lubrication PUBLISHER Mike Ramsey - mramsey@noria.com 5 Silent Assumptions of Bearing Reliability For a bearing to have a normal life expectancy, it is assumed that the following often unspoken root causes of failure (silent assumptions) will not occur at any time after commissioning. 1. Mechanical Causes — Exceeding a bearing's dynamic load rating translates to a disproportionate reduction of fatigue life. For most bearings, doubling the load can reduce bearing life to roughly one-eighth of its normal life. Mechanical assaults on bearings by misalignment and unbalance can produce similar consequences. 2. Impaired Fluid Properties — There are many vital lubricant properties that when altered or impaired can sharply diminish bearing life and reliability. These include such things as additives, acid number, lubricity, viscosity, pressure-viscosity coefficient and viscosity index. 3. Fluid Contamination — The "most wanted" fluid contamination assassins include dirt, water, fuel, glycol and soot. However, there are many others. 4. Heat — Heat is also a contaminant. Its aggressive tendencies can be viewed as both a cause and effect of most types of fluid and mechanical problems. Overlubrication is a common cause of heat in grease-lubricated bearings. 5. Starvation — A surprising number of bearings are simply starved to death. Over time, they run dry of lubricating oil or grease unless properly and frequently relubricated. constant oil flow rate through the filter(s). Should any of these conditions change, equilibrium is lost until it is re-established later at another level. It's a mass balance, i.e., particles entering from ingression must equal the particles removed from filtration. This stable state of cleanliness must be within the target cleanliness level set by the reliability team. Target cleanliness should be aligned to the machine's Optimum Reference State (ORS). For more information on the ORS, see http://www.machinerylubrication.com/Read/28659/ optimum-reference-state-. For most all machines, the correct ORS cleanliness target is driven by five important factors: criticality, environment severity, contaminant tolerance, proactive maintenance and predictive maintenance. 1. Criticality This is a combination of the cost of repair and the cost of failure (downtime, safety, machine readiness, etc.). It is the cumulative consequences of machine failure. For more information on criticality, visit http://www.machinerylubrication.com/Read/29346/ machinery-criticality-analysis. 2. Environment Severity This relates to the likelihood of contaminant invasion and the subsequent damage to critical machine surfaces. The three main considerations are the density of contaminants in the work environment, the effectiveness of the machine to prevent ingress of these contaminants, and the ability of the filter(s) to rapidly remove and retain ingressed contaminants. GROUP PUBLISHER Brett O'Kelley - bretto@noria.com EDITOR-IN-CHIEF Jason Sowards - jsowards@noria.com SENIOR EDITOR Jim Fitch - jfitch@noria.com TECHNICAL WRITERS Jeremy Wright - jwright@noria.com Wes Cash - wcash@noria.com Bennett Fitch - bfitch@noria.com Loren Green - lgreen@noria.com CREATIVE DIRECTOR Ryan Kiker - rkiker@noria.com GRAPHIC ARTISTS Julia Backus - jbackus@noria.com Terry Kellam - tkellam@noria.com Josh Couch - jcouch@noria.com ADVERTISING SALES Tim Davidson - tdavidson@noria.com 800-597-5460, ext. 224 MEDIA PRODUCTION MANAGER Rhonda Johnson - rjohnson@noria.com CORRESPONDENCE You may address articles, case studies, special requests and other correspondence to: Editor-in-chief MACHINERY LUBRICATION Noria Corporation 1328 E. 43rd Court • Tulsa, Oklahoma 74105 Phone: 918-749-1400 Fax: 918-746-0925 E-mail address: jsowards@noria.com MACHINERY LUBRICATION Volume 13 - Issue 5 September-October 2013 ( USPS 021-695) is published bimonthly by Noria Corporation, 1328 E. 43rd Court, Tulsa, OK 74105-4124. 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Machinery Lubrication is an independently produced publication of Noria Corporation. Noria Corporation reserves the right, with respect to submissions, to revise, republish and authorize its readers to use the tips and articles submitted for personal and commercial use. The opinions of those interviewed and those who write articles for this magazine are not necessarily shared by Noria Corporation. CONTENT NOTICE: The recommendations and information provided in Machinery Lubrication and its related information properties do not purport to address all of the safety concerns that may exist. It is the responsibility of the user to follow appropriate safety and health practices. Further, Noria does not make any representations, warranties, express or implied, regarding the accuracy, completeness or suitability of the information or recommendations provided herewith. Noria shall not be liable for any injuries, loss of profits, business, goodwill, data, interruption of business, nor for incidental or consequential merchantability or fitness of purpose, or damages related to the use of information or recommendations provided. Figure 1. Background contamination can mask the ability to enable early detection of abnormal wear conditions. High background particles in Case A result in a short detection time window compared to Case B. 3 September - October 2013 |3