#CALCULATING VISCOSITY INDEX ISO#

If the oil was similar to the paraffinic oil, a VI of 100 was assigned if it was similar to the naphthenic oil, a VI of 0 was assigned. Lube oils were then compared to these benchmarks. Their VI was indicated with 0 – this was the worst possible VI. Oils with significant viscosity change (LVI-oils, refined from Texas gulf crudes, naphthenic oil) represented the low end. Their VI was indicated with 100, which represented the best VI. Oils with low temperature-dependent viscosity change (HVI-oils, refined from Pennsylvania crudes, paraffinic oil) were on the high end of the scale. For the VI scale, two limit points were set. At this time, no multi-grade oils and no synthetic oils were available. For this purpose, the viscosity index 12 for base stocks and lube oils was developed by Dean and Davis from Standard Oil in the year 1929. For any oil used under changing temperature conditions, it is important to know the change of viscosity in relation to the change of temperature. Temperature is the most influential parameter for the viscosity change of oil. Viscosity is just one of many properties used to analyse lubricants and assess suitability for different applications.The viscosity of lube oil does not give any relevant information unless the temperature, at which it was measured, is known. A holistic approach to lubricant analysis Most lubricants offer Vis ranging from between 90 to 160, though some can be as low as -60 or as high as 400. Today, ASTM D2270 Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 ☌ and 100 ☌ is one of the most widely used methods to calculate VI. Viscosity Index helps operators make informed decisions to prepare for these changes and minimise the risk of unplanned downtime. Temperature changes can and do occur, triggered by anything from weather patterns to mechanical overheating. VI allows operators to compare how different lubricants behave when exposed to temperatures outside normal operating conditions. This is usually a mistake as VI can have a big impact on how a lubricant performs when in circulation and exposed to temperatures other than the standard 40☌ used to calculate viscosity. Why Viscosity Index mattersĪs mentioned earlier, Viscosity Index is often disregarded during the lubricant selection process. A higher VI number indicated more stability when exposed to temperature changes. Pennsylvania crude was given a VI of 100 while Texas Gulf crudes were given a VI of 0. Using Pennsylvania crude as a benchmark for low viscosity and Texas Gulf crudes for high viscosity, the team developed a method for calculating changes in internal resistance to flow relative to temperature. The concept of Viscosity Index was first developed in the 1920s by a pair of American chemists. VI is an independent parameter and is used to calculate how viscosity will change when exposed to temperatures higher or lower than 40☌.

#CALCULATING VISCOSITY INDEX ISO#

Viscosity Index vs ISO Viscosity GradeĬontrary to popular belief, Viscosity Index is not part of ISO Viscosity Grade, which calculates viscosity at a standard temperature of 40☌. While VI is often an overlooked parameter when selecting lubricants, it can offer valuable insight into how the lubricant will behave when in use. Temperature-triggered changes in the viscosity of a lubricant is known as Viscosity Index (VI). Viscosity can vary enormously between different lubricants and temperature often plays a key role in changing internal resistance to flow.

Calculating viscosity index