Now let’s examine the viscosity of these oils from minus 20 degrees C (minus 4 degrees F) to 100 degrees C (212 degrees F). However, one of these oils (Oil A) has a VI of 95 (mineral oil), while the other (Oil B) has a VI of 150 (synthetic). Let’s take a look at two different oils that share one common property - they’re both ISO VG 150. However, the vast majority of lubricants on the market will have VIs in the range of 90 to 160. Other lubricants can have VIs ranging over 400. Lubricants with VIs as low as minus 60 are available today. Better yet, you can enter a single known viscosity (and temperature) and VI (commonly found on a lubricant’s product data sheet) to calculate the viscosity of the same lubricant at any other temperature (say, a machine’s operating temperature). For instance, if you know the viscosity of a lubricant at two different temperatures, you can use the calculator to give you an estimation of the VI. You can use these calculators in a variety of ways. The temperatures used to determine the VI are 40 degrees C to 100 degrees C.Īn Internet search on “viscosity index calculator” will direct you to several Web pages. The higher the VI, the more stable the viscosity across a range of temperatures (more desirable). Halfway in between was a VI of 50, and so forth. If it was similar to Texas Gulf crude, it was assigned a VI of 0. If a lubricant was similar to the Pennsylvania crude, it was assigned a VI of 100. Based on the methodology, Pennsylvania crude (paraffinic) was set as a benchmark at one extreme, representing low viscosity changeability relative to temperature.Īt the other extreme was Texas Gulf crudes (naphthenic). It is an empirically derived, unitless number. The viscosity index was developed for this purpose (ASTM D2270) by E. Most importantly, for any candidate oil, you need to know how viscosity changes relative to a change in temperature. Remember, the ISO Viscosity Grade system only reports viscosity at a single temperature: 40 degrees C. That said, because machines require a certain viscosity, and temperature is known to have a dramatic influence on viscosity, it is imperative that you take the average operating temperature and temperature range into account when selecting viscosity. You may recall that the well-known Stribeck curve doesn’t have a temperature variable. Instead, a machine’s viscosity requirement is based on such things as component design (e.g., bearing), loads and speeds. Minimum, maximum and optimum viscosity requirements demanded by machines don’t take temperature into account. Conversely, machines don’t care about temperature as it relates to viscosity (loosely speaking). If you are requesting multiple posters, please add that request to the additional comment section.However, a lubricant’s viscosity is meaningless unless the temperature is noted, i.e., the temperature at which viscosity is measured. Order your FREE Viscosity Cup Conversion Chart here!įill the form below or call 80 or 30 to request your Viscosity Cup Conversion Chart Poster today. This chart is not meant to take the place of making the actual measurement. This chart is a guide to convert the efflux time, in seconds, measured with a given viscosity cup to the efflux time an alternate cup would measure using the same fluid. efflux time, and suggested standard oils for each cup. The poster also includes instructions for using the chart, standards, specifications, viscosity equations, centistokes vs. The Viscosity Conversion Chart poster compares the efflux times of the BYK-Gardner Zahn cups, S90 Signature Zahn cups, EZ Zahn cups, Ford cups, Din Cup 4mm, and ISO cups. If you interested in ordering a free poster, BYK-Gardner Laboratories Blog has included the form to order your viscosity poster at the bottom of this post. BYK-Gardner has a free Viscosity Cup Conversion Chart Poster that is available for your offices, labs or facilities around the world.
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