Since most bearing dimensions are expressed in millimeters (mm) the following is a more usual formula: Take, for example, a 150 hp motor with a 313 size bearing that has the following dimensions: In this example, utilizing the foregoing formula, we calculate G = 0.00018 × 140 × 33 = 0.83 ounces of grease required for the bearing. When it comes to selecting lubricating oils for manufactured equipment, it’s easy to determine which products meet the original equipment manufacturer (OEM) requirements. Armed with a little bit of knowledge and a few widely available tools, it is possible to rest easier knowing that the right grease is being used. If your supplier is unsure of the compatibility, ask that an ASTM 6185 compatibility test be performed. Selecting a grease can be a delicate process. Let me try to demystify grease a bit. You may have put a lot of effort and money into selecting the best quality grease in the pursuit of lubrication excellence. The third portion is the fluid, which can be selected from mineral oils, various types of synthetics, polyglycols or a never‑ending combination of fluids. Cannot be used in presence of water and limited to 250 F. Lithium/Polymer with same density as base oil specially designed to avoid separation due to centrifugal forces. Most users are aware of the importance of selecting the right lubricant for a given application. NDm = rpm * (( bearing bore + outside diameter) / 2). Table 1 provides a general guide to selecting NLGI grade based on speed factor and operating temperature. However, there are applications that might benefit from the use of a synthetic base oil. The grease manufacturer provides this information. Using this information alone, one could select the right consistency and thickener type. For example, the term car grease is very common and it can refer to different types of greases in general. Be sure to calibrate all of your grease guns and use one particular type per application. This is where the grease quality factors in. When in doubt, always consult your lubricant supplier. A common mistake when selecting a grease is to confuse the grease consistency with the base oil viscosity. This can be done by using a postage scale and weighing out 10 shots of grease and calculating ounces per shot and then equating this to shots per ounces. Removing the mystery This article has been written to help take the mystery out of the topic of grease and to give you some techniques to improve the selection and application of grease in your facility. 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. In the Water Spray-Off Test, competitive greases lost almost six times more grease. Simple lithium soaps are more widely used because of their lower costs, but lithium complex greases, because of their inherently better properties, are faster growing. 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. Common Grease Types and Characteristics Aluminum Complex Grease. A common OEM grease specification might be to use an NLGI (National Lubrication Grease Institute) No. Grease of choice for electric motors and sealed-for-life applications. Figure 2 shows some common additive requirements by application. This converts the thickener to a soap‑salt complex, hence the term complex grease. The bearings have wide, deep axial grooves, extending about 80% along the bearing. Relubrication frequency…Once we have calculated the right amount for a rolling element bearing, we then have to establish lubrication frequencies for that bearing. For bearings, speed factor and operating temperature can be used to determine the best consistency or NLGI grade for a given application. This certainly doesn’t apply to electric motor bearings, where over-greasing is very common. The NLGI has established a scale to indicate grease consistency which ranges from grades 000 (semifluid) to 6 (block grease). 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. Proper grease specification requires all of the components of oil selection and more. Paul Grives, Global Services & Grease Marketing Manager, ExxonMobil Fuels & Lubricants. LMT. Rolling bearings are a major component lubricated with grease—in fact, most of them are. In order to help the layman understand them, we've included a chart here that compares NLGI Grades to something everyone can relate to - food. Telephone: (281) 257-1526. Figure 1 assumes the base oils’ viscosity index. For this reason, it is important to weigh each property’s significance relative to the intended applications to select the best overall fit. Like lithium complex, polyurea has good high-temperature performance as well as high oxidation stability and bleed resistance. An STLE-Certified Lubrication Specialist and Oil Monitoring Analyst, he conducts extensive training in a number of industries. Paul Grives, Global Services & Grease Marketing Manager, ExxonMobil Fuels & Lubricants. But don’t confuse the quality of the lubricant with the quality of the specification. When changing grease thickener types in an application, always consult your lubricant supplier on the compatibility of a proposed product with one that’s being replaced. t = K [ 14,000,000 _ 4d ] n dt = relubrication interval in hoursd = bearing bore diameter, mmn = speed, rpmK = 1 for spherical or tapered roller bearingsK = 5 for cylindrical or needle bearingsK = 10 for radial ball bearings. 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. A more complex structure can be formed by using a complexing salt.
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