BASE OIL
- Lubricating oils are the major components in grease formulations and as such, exert considerable influence on BEHAVIOR of the grease.
- The oxidation resistance of a grease may be poor if its base oil component has a low viscosity index or large amounts of sulfur or polynuclear aromatic molecules.
- Paraffinic oils of high viscosity index are preferred for inherent god oxidative stability. Grease uses high quality paraffinic base oils.
SYNTHETIC OIL
- Synthetic fluids are becoming increasingly important in greases designed for special extreme-temperature applications.
- Synthetic oils have higher viscosities indexes and flash points and their pour points are considerably lower.This makes them valuable blending components when compounding oils for extreme service at both high and low temperatures.
- The DISADVATAGE of synthetics is that they are much more expensive than normal base oils.
- This limits their use to specialty oils and greases that command premium prices.
VISCOSITY
- One Centistoke = 1 mm/sec.
- When quoting a viscosity it must be accompanied by the temperature at which it was determined.
- Most certainly, viscosity differences of 20% between grade ordered and received should cause no operational problems to a modern motor vessel. Viscosity Index provides a measure of how much an oil changes viscosity as temperature changes.
- This is usually calculated by comparing the viscosity at 100 degree C and at 40 degree C. a high viscosity index means that the oil does NOT change viscosity as much as a low viscosity index oil.