Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/680544
F or certain machines, deviations in lubricant quality can lead to disastrous consequences. This punctuates the need to confirm the quality of new lubricant deliveries, especially when the need for reliability is particularly important. Likewise, a quality-minded lubricant supplier will appreciate receiving feedback, both good and bad, from users who run such tests. Another important benefit for testing new lubricants is to estab- lish a baseline for routine used-lubricant analysis. Even when new lubricants are well within acceptable quality limits, there may be considerable variations in physical and chemical properties (batch to batch). For instance, viscosity can vary plus or minus 10 percent from the ISO viscosity grade (VG) midpoint and still be "in grade." Cautionary limits are sometimes set at plus or minus 5 percent from new lubricant viscosity. Hence, the specific new lubricant viscosity must be known. By taking an active role in testing new lubricants and giving constructive feedback to your supplier, incremental improvements in lubricant quality are bound to result. Lubrication excellence is a collaborative process. Lubricant quality is a measurable property. If it's important, measure it. Overgreasing can have many of the same negative side effects as undergreasing, plus the added cost of high lubricant consumption. Greasing can be thought of as a purging or filtering of contami- nants from the bearing, but you should not exceed a calculated amount of grease when performing greasing activities. The calculated quantity of grease for a bearing is based on its geometry and dimensions, which provide the ideal amount for relu- brication. The misconception is to apply more grease than needed to purge out contaminants. The right approach is to apply a frac- tion of the calculated quantity at a shorter time interval. This helps eliminate overgreasing at a given interval but still supplies the benefit of purging contaminants out of the bearing, just like auto- matic grease systems. One of the most common ways to overgrease is to use an auto- matic grease system without proper calibration, maintenance and interval calculations. The premise and benefits of automatic grease systems are to provide a small amount of grease very often to promote a more continuous grease application. In order for this to work and be beneficial, the technician must know how much grease to add at the right time and calibrate the automatic grease system accordingly. If it is not calibrated correctly, it is likely that too much grease will be supplied too often, which can result in a bearing failure and high grease-consumption costs. You don't have to remove what you don't allow in. Indeed, it's hard to question the logic of controlling water ingression. But because moisture is everywhere, achieving bone-dry through exclu- sion alone may not be practical or even necessary. Lubricating oils have different degrees of hygroscopicity (water-loving tendencies), making the control of all dissolved water an almost futile exercise. However, for many applications, it's the free and emulsified water that is the most destructive and, hence, the central target for control. Exclusion relates to the process of preventing (excluding) the ingress of water from environmental, machine and process sources. Common points of water ingression include: • Water from makeup oil (some supply tanks can collect inches of water below the oil level) • Turbine gland steam seals (improper pressure regulation) • Defective vapor extraction system (too high can suck in steam while too low can fail to keep up with ingress) • Process water in-leakage from pulp and paper production, water treatment plants, sewage treatment plants, etc. • Oil cooler leaks • In-leakage of water past seals from washdown sprays, rain and flooding conditions • Reservoir and sump headspace vent/breather ingress The top-line priority is to squelch ingression points through tight and well-managed ingression control. Deferring mainte- nance of worn seals, defective breathers and coolant leaks creates more expensive maintenance events in the future, including the possible cost of premature oil changes, flushing, oil dehydration and replacement of water-damaged parts. Monitoring and promptly closing off ingression sites are by far the wiser use of maintenance resources. There are many factors that influence the decision of when to change oil. And in many cases, the oil may never need to be changed. 1 Test New Lubricant Deliveries (from March-April 2003) 2 Avoid Overgreasing (from July-August 2011) 3 Achieve and Sustain Dry Oil (from May-June 2009) ML www.machinerylubrication.com | May - June 2016 | 13 4 Consider a Condition- based Oil Change Strategy (from May-June 2001)