Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/875060
44 | September - October 2017 | www.machinerylubrication.com contamination and installation issues are the most common reasons why seals leak and fail, cold starts and cold operating tempera- tures also pose a threat of seal embrittlement. Bearings Bearings with rolling elements will have reduced mobility when oil or grease becomes too viscous in cold temperatures. Viscous oil leads to churning losses and skidding of the rollers. Skidding will damage the rolling elements and cage structure. Friction increases as these components are damaged and can result in a failure. In grease applications, the oil in the grease becomes considerably challenged at low temperatures. The base oil separation rate will be insufficient at low temperatures because the viscous oil will stay trapped in the thickener held outside the raceway. During these conditions, lubricant starvation can cause early bearing failure. Avoiding Machine Failure During Cold Starts Thankfully, over the last few decades, lubricant manufacturers have become aware of the effects that cold temperatures can have on machines. This has led them to develop formulations that can handle these conditions, including during machine starts. The base oil plays a major role, as many highly refined mineral oils and synthetics are less affected by temperature swings. This is represented by the viscosity index. Viscosity index improvers can enhance this property. The higher the viscosity index, the less change in viscosity per a change in temperature. Pour point depressants can also improve the characteristics of oil in cold temperatures. These base oil and additive prop- erties, along with a correctly selected viscosity grade or multi-viscosity grade, offer viable solu- tions in cold temperatures. Nevertheless, at times lubricant formula- tions may not be enough to avoid the pitfalls of cold starts. In these cases, machines can be equipped to overcome the frigid elements through the installation of block and pan heaters, as mentioned previously, as well as pre-lube systems that prepare the machine's components for a cold start. The consequential failure that can arise from not properly preparing for cold-start conditions will be gradual and indirect. Not only can cold temperatures be the root cause of unfavorable lubricant conditions, but their presence can also trigger a chain reaction, leading to highly viscous lubricants, which introduce the opportunity for lubricant starvation, increased contamination, premature wear generation, inactive additives and other impending effects. Once machine operators and reliability engineers are aware of the risks that cold temperatures present, partic- ularly at startup, adjustments can be made to prevent these chain reactions from occurring. References Applied Hydraulics Magazine. (1956, February). 67-70. Bbehrouz, A. (2014, September). "Dead Sensor." Mechanical Engineering Magazine. Cash. W. (2016, April). "Best Ways to Combat Oil Gelation." Machinery Lubrication. Diemand. D. (1990, December). "Lubricants at Low Temperatures." Cold Regions Technical Digest. Fitch, E.C. (2002, July). "Temperature Stability of Lubricants and Hydraulic Fluids." Machinery Lubrication. Fitch, J.C. (2012, August). "The Hidden Dangers of Lubricant Starvation." Machinery Lubrication. Hochmann. M. (2013, March). "Gear Lubrication – Gear Protection Also at Low Oil Temperature." Gear Solutions. Khonsari, M. & Booser, E.R. (2007, March). "Low Temperature and Viscosity Limits." Machinery Lubrication. Manney, D. "Extend the life of your gearbox with predictive maintenance." Retrieved from www. lselectric.com/extend-the-life-of-your-gearbox-with- predictive-maintenance. "OWI-Lab invests in -40°C cold start-up test bench for wind turbine drivetrain compo- nents." Retrieved from www.owi-lab.be/content/ owi-lab-invests-40%C2%B0c-cold-start-test-bench- wind-turbine-drivetrain-components. Wikström, V. (2000, November). "Lubrication of Bearings at Low Temperatures." Retrieved from http:// evolution.skf.com/us/low-temperatures. About the Author Bennett Fitch is a senior technical consultant with Noria Corporation. He is a mechanical engi- neer who holds a Machine Lubricant Analyst (MLA) Level III certification and a Machine Lubrication Technician (MLT) Level II certification through the International Council for Machinery Lubrication (ICML). Contact Bennett at bfitch@noria.com. LESSONS IN LUBRICATION