12/18/2023 0 Comments Viscosity index astmIt can also be used to determine the viscosity index of lubricating oils.ġ. It is used to determine the kinematic viscosity of liquid petroleum products (Newtonian liquids) and the kinematic viscosity of dark petroleum products. PT-D445-265B-1 Kinematic viscosity / Reverse-flow viscosity / Viscosity index Tester is designed and made as per the national standard of People’s Republic of China GB/T265 Petroleum products-Determination of kinematic viscosity and calculation of dynamic viscosity, GB/T 11137 Black petroleum products-Determination of kinematic viscosity(reverse-flow method) and calculation of dynamic viscosity and GB/T 1995 Petroleum products-Calculation of viscosity index. Antibiotic Residues Detection Reagent Strip.Water Vapor Permeability Tester / Moisture Permeability Tester.Bacteria resistance inoculation equipment.Microbial collection and filtration equipment.Small tangential flow ultra filtration system.Vacuum Constant Temperature Drying Case.High-VI fluids can also improve the energy efficiency of a machine. But when conditions are not constant-such as in mobile equipment that must operate from winter cold to desert heat-and loads, speeds and temperatures vary, many OEMs recommend high-VI fluids that help maintain near-optimum viscosity over a wider temperature range. Here, the viscosity index is not so important: Just choose the suitable monograde viscosity recommended for the application. Too thick and the machine is hard to start and has low mechanical efficiency, and can even lead to problems like cavitation.Īlthough oil viscosity changes with temperature, that’s not so important in machines that run at constant load and speed and at constant temperatures. When viscosity is too low and fluid too thin, users will see problems like higher wear and overheating. Experts often recommend shear-stable additives to ensure high-VI fluids work as intended.Īlso remember that it’s important to use a fluid with the recommended viscosity when running a machine. Such action can, over time, break down the polymers and degrade fluid viscosity. However, viscosity improvers can be susceptible to mechanical shearing. But at higher temperatures, the polymers expand and that helps increase viscosity. At low temperatures, the polymer chains in the modifiers contract or fold and don’t have much effect on fluid viscosity. These modifiers are temperature sensitive. Synthetic oils usually have a higher VI than do mineral oils.įluid manufacturers can improve the viscosity index of base oils by using polymer additives to form multigrade-viscosity oils. Highly refined mineral oils with few contaminants tend to have higher VIs, all things being equal. Standard ASTM D2270 calculates viscosity index in part by measuring a fluid’s kinematic viscosity at 40° and 100° C. That, in turn, means consistent, high performance from a machine. The best oils with the highest VIs remain stable and don’t vary much in viscosity over a wide temperature range. Typical mineral-oil fluids used in hydraulics have a viscosity index of around 100, although products range from below 100 to well beyond 200. High-VI fluids, in contrast, are less affected by temperature changes. Thus, a fluid with a low viscosity index will experience a relatively large swing in viscosity as temperatures change. (It also applies to fluids like engine and automatic transmission oils, gear lubricants, and power-steering fluids.) The greater the viscosity index (VI), the smaller the change in fluid viscosity for a given change in temperature, and vice versa. Viscosity index is a dimensionless number that represents how the viscosity of a hydraulic fluid changes with temperature.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |