![]() ![]() Most greases are formulated using API Group I and II mineral oil base stocks, which are appropriate for most applications. Figure 2 shows some common additive requirements by application. Most performance-enhancing additives found in lubricating oils are also used in grease formulation and should be chosen according to the demands of the application. For instance, a lightly loaded high-speed element bearing does not require extreme pressure (EP) additives or tackifying agents, while a heavily loaded open gear set does. The additive and base oil types are other components of grease that should be selected in a fashion similar to that used for oil-lubricated applications. Once the appropriate viscosity has been determined, it’s time to consider additives. To be more precise, one would need to use a chart that identifies the viscosity at operating temperature, then determine the viscosity grade from a viscosity/temperature chart for a given lubricant. Knowing the speed factor value and likely operating temperature, the minimum viscosity requirement can be read directly from charts like Figure 1.įigure 1 assumes the base oils’ viscosity index. The NDm value uses pitch diameter rather than bore diameter because not all bearings of a given bore have the same element diameter, and thus have different surface speeds. NDm = rpm * (( bearing bore + outside diameter) / 2) ![]() Speed factors account for the surface speed of the bearing elements and are determined by the following formulas: There are several common methods for determining minimum and optimum viscosity requirements for element bearings, most of which use speed factors, commonly denoted as DN or NDm. While most would not use an EP 220 gear oil for an oil-lubricated electric motor bearing, many people will use a grease containing that same oil for an identical grease-lubricated bearing. Because the majority of grease-lubricated applications are element bearings, one should consider viscosity selection for those applications. A common mistake when selecting a grease is to confuse the grease consistency with the base oil viscosity. The most important property of any lubricant is viscosity. Let’s walk through the grease selection process step by step, starting with the most important property. Understanding the need and the methods for appropriate grease selection will go a long way toward improving lubrication programs and the reliability of lubricated machinery. Other special considerations for grease selection include thickener type and concentration, consistency, dropping point and operating temperature range, worked stability, oxidation stability, wear resistance, etc. Proper grease specification requires all of the components of oil selection and more. A similar specification for an oil-lubricated application would be to use a “good quality lubricating oil.” What?!ĭue to the lack of specificity in most grease recommendations, it is important to learn how to properly select greases for each application in the plant. Using this information alone, one could select the right consistency and thickener type. Grease specifications, on the other hand, often lack the detail necessary to make a proper selection, leaving it up to the lubrication engineer to create the specification.Ī common OEM grease specification might be to use an NLGI (National Lubrication Grease Institute) No. OEM specifications for a lubricating oil normally include viscosity at operating or ambient temperature, additive requirements, base oil type and even special considerations for different environmental conditions. ![]() When it comes to selecting lubricating oils for manufactured equipment, it’s easy to determine which products meet the original equipment manufacturer (OEM) requirements. Most users are aware of the importance of selecting the right lubricant for a given application. But don’t confuse the quality of the lubricant with the quality of the specification.Ĭonsidering this lubricating oil analogy, the best quality turbine oil would most likely not make a good engine oil. You may have put a lot of effort and money into selecting the best quality grease in the pursuit of lubrication excellence. How do you know if you’re using the right grease? You might be using a high-quality grease. ![]()
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