Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/957021
L ubricated components fail for a variety of reasons. ese reasons can be cate- gorized based on the type of failure, specifically early failures, random or event-dependent failures, and condition-based failures. An early failure event may be the result of inadequate lubrication. When a system is at rest, unless the bearing has hydrostatic lubrication applied, the sliding surfaces will be in contact. As the components begin to rotate, the surfaces remain in contact until the lubricant film is established. During this time, the highest incidence of failure persists. As a film is formed and surface-active additives begin to protect, a lubrica- tion regime is established. Prior to this occurring, surface asperities and particulate will contribute to surface wear and possible part failure. When there is an imbalance or non-uniform tolerances between part surfaces or the wrong materials or components are used, there is the possibility for premature wear. Poor maintenance practices, workmanship and installation can all lead to an early failure event. Various particles can indicate these scenarios. Another failure class is random or event-dependent. ese types of failures can occur at any point during the system's life cycle. They are caused by too much speed or over- loading a component. As speed and load increase, there is an opportunity for the sliding or rolling surfaces to come in contact, generating heat, as well as for particulate to contact the surfaces. In both situations, the surfaces and particles produce wear. Condition-based failures are primarily due to contamination – both internally generated from wear debris (normal or accelerated) or external sources such as dirt or processed product. The contam- ination can also be liquid or gas. Gases like hydrogen sulfide or pure oxygen can produce severe corrosion, which generates wear particles. Liquids such as fuel and coolants will contribute to system failures in engines. Water is the most prev- alent contaminant that causes metal oxidation and lubricant degradation in oil-lubricated systems. These fluids compromise the viscosity of the oil, resulting in surface contact or oxidation product development. is leads to an increase in the opportunity for failure. When Early Failure Occurs Each asset has a lifespan. Often it isn't until premature failure occurs that an in-depth investigation will ensue. Whether inadequate lubri- cation, component defects or poor maintenance practices are to blame, routine oil analysis combined with wear debris analysis can indicate a pending failure. A lthough it is not realistic to perform wear debris analysis on every asset, it is reasonable to test critical assets for wear debris on a scheduled basis. It is also recommended to perform wear debris analysis when beginning an oil analysis program. is will help establish which assets may be most vulnerable to failure. When to Perform Wear Debris Analysis e lubricant can provide insight into what is occurring within a system without having to disas- semble and inspect the machinery. Prior to an oil sample being drawn for wear debris analysis, it is prudent to consider overheating, vibration and high system pressure. ese may indicate if the oil should be analyzed for wear debris. Once an oil sample is tested, certain indicators will encourage the use of wear debris analysis. e first indication will be an increase in wear metals like iron, aluminum and copper. Second, check to see ML www . machinerylubrication.com | March - April 2018 | 11