Machinery Lubrication


Machinery Lubrication magazine published by Noria Corporation

Issue link:

Contents of this Issue


Page 26 of 80

22 | July - August 2017 | ASK the EXPERTS When it comes to open gears, spray lubrication is a common practice. However, it isn't the only option. A variety of greases are specially formulated to work on open gears. That said, there are some key practices to follow when using a spray system on an open gear. As with any lubrication system, it is important to verify that the appropriate volume and type of lubricant are being used. You must also ensure that the lubricant stays in place and is of the correct viscosity. The distance between the gear teeth and the spray system's nozzles can vary greatly. "How do you spray-lubricate an open gear? Are nozzles commonly available for this? What air pressure is ideal? What is the best distance between the nozzle and application area? Is spray lubrication the best way to lubricate an open gear?" "For gearbox applications, is it preferable to use mineral oil or synthetic oil?" Most gear oils use a polyalphao- lefin (PAO) as a base stock. This is essentially a man-made version of the naturally occurring mineral oil pulled from the earth and refined. The size of the molecules is all relatively the same. These are also saturated molecules, which makes them very stable. The benefits of synthetic oils relate to the molecules' stable nature and include a higher degree of hydrolytic stability and demulsibility, a higher viscosity index (VI) and a lower pour point. The VI and pour point allow these oils to perform better across a broader temperature range. The drawbacks of synthetic oils would include their cost and solubility concerns. PAOs generally have low solu- bility, which means they do not dissolve additives as readily as their mineral counterpar ts. Synthetic oils also have a diff icult time suspending varnish- forming degradation byproducts. While many people make the snap deci- sion to switch to synthetic oils, the cost factor should be considered. Focus on the optimum reference state (ORS), which is the state that is best for a particular piece of equipment under its specific operating conditions and environment. It should also take into account the equipment's criti- cality as well. For example, say you have two identical pumps with different functions in the plant and different levels of criticality. For one of the pumps, you might take vibration read- ings and outfit it with a desiccant breather, bottom sediment and water (BS&W) bowl, and minimess sample connection. The other pump receives none of this "special treatment." Why is that? It all comes down to a matter of cost. If the more critical pump fails, it will have a larger financial impact than the other pump. This same methodology should be applied when deciding whether to use a mineral or synthetic gear oil. If the equip- ment's operating conditions and environment are not as stressful or the financial impact of a failure would not be as significant, then you could probably get by with a mineral oil, as you are not likely to gain enough benefits from the synthetic oil to justify the cost. However, if the environ- ment is more severe, the temperature runs extremely high or low, there are extended oil drains, or the impact of a failure is considerable enough to justify the cost, then you should choose a synthetic oil.

Articles in this issue

Links on this page

Archives of this issue

view archives of Machinery Lubrication - ML_July_August_2017_Digital