Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/655822
s oil breaks down, a variety of issues can arise, including gelation. This is when the oil is no longer fluid and resists flow. As you can imagine, this leads to poor lubrication and potential machine failure. By understanding what causes gelation and which oils are most prone to this process, you can help to prevent it and ensure your equipment will run as efficiently as possible. Defining Gelation According to ASTM International, oil gelation is defined by a rheological condition of an oil characterized by a marked increase in the flow resistance over and above the normal exponential increase of viscosity with decreasing temperature, particularly at lower shear stresses and temperatures. ASTM D5133 is one method that can be used to analyze the tendency of oil gelation. In this test, a candidate oil is heated and then gradually cooled while the viscosity is measured at different temperatures. The gelation index is a result of this test. As oil is cooled, the viscosity goes up. This value can be plotted on a chart. The slope of the viscosity line versus temperature is analyzed for changes. If the slope rapidly increases at a certain temperature, this should be noted. Once the test is completed, the full chart can be analyzed and the gela- tion index developed. The temperature at which the viscosity rapidly thickens is known as the gelation index temperature. This information becomes important as temperatures decline, especially if the equipment operates in a cold environment such as in a freezer or outside in cold climates. Oils most prone to gelation are typically motor oils, particularly those with a higher wax content than others (paraffinic base oils). This phenomenon occurs in colder conditions or in situations where the oil has experienced a gradual cooling. As the viscosity increases due to lower temperatures, certain contaminants or conditions can be achieved in which the viscosity rapidly increases and the oil gels. Gelation Standards The American Petroleum Institute (API) has established standards for the gelation index in motor oils. In most cases, the maximum acceptable gelation index is 12, with a maximum viscosity of 40,000 centi- poise. There is a certain point when an oil simply can't be pumped due to either gela- tion or to viscosity that is too high. When viscosity increases, a limited flow condition can occur. This is when the volume of oil A V i s c o s i t y BEST WAYS to Combat OIL GELATION 36 | March - April 2016 | www.machinerylubrication.com IN THE TRENCHES We s ca sh | Nori a Corpor at ioN 36% of lubrication professionals have seen the effects of oil gelation in machines at their plant, based on a recent survey at MachineryLubrication.com