What is the importance of viscosity index improvers in lubricating oils used in industrial machinery?

Viscosity index (VI) improvers are additives used in lubricating oils to minimize the change in viscosity with temperature. Viscosity is a measure of a fluid's resistance to flow. Ideally, a lubricating oil should maintain a relatively constant viscosity over a wide range of operating temperatures to provide effective lubrication. Without VI improvers, lubricating oils tend to thin out significantly at high temperatures and thicken considerably at low temperatures. This can lead to inadequate lubrication at high temperatures, resulting in increased wear and potential equipment failure, and difficulty in starting equipment at low temperatures. VI improvers are typically polymers that are long-chain molecules. At low temperatures, these polymers are coiled up and have minimal impact on the oil's viscosity. However, as the temperature increases, the polymers uncoil and become more extended. This increases the oil's viscosity, compensating for the thinning effect of temperature. The result is a lubricating oil that maintains a more consistent viscosity across a wide temperature range. This is particularly important in industrial machinery that operates under varying temperature conditions, such as hydraulic systems, gearboxes, and engines. For example, a hydraulic system operating outdoors in a cold climate requires a lubricating oil that remains fluid enough to allow for easy starting. However, when the system warms up during operation, the oil must not thin out too much, as this can lead to internal leakage and reduced performance. A lubricating oil with a high viscosity index, achieved through the use of VI improvers, provides the necessary viscosity characteristics for reliable operation under these conditions.