The viscosity of an oil refers to its resistance to flow. And this resistance is affected by many factors, but especially temperature. Oil thins or its viscosity decreases at high temperatures, and it thickens or its viscosity increases at low temperatures. In our previous blog post on high vs. low viscosity lubricants, we discussed viscosity and the factors to consider when choosing lubricants based on viscosity. In this article, we will look further into the benefits of high viscosity fluids in machinery lubrication and why most engineers choose them over those with low viscosity.
Viscosity Index (VI) and Kinematic Viscosity (KV)
To start, we must define and understand the critical concepts of viscosity index or VI and kinematic viscosity or KV.
An oil’s VI is its ability to resist changes in viscosity due to changes in its temperature. When subjected to varying temperatures, fluids with a higher VI show fewer viscosity changes than those with a lower VI. Two fluids can have similar viscosity but have different VI, which greatly impacts their performance.
Fluids such as oils and lubricants are also described by their kinematic viscosity or KV and dynamic viscosity or DV. An oil’s KV is its viscosity as it flows due to gravity. In contrast, in high-pressure systems where gravity has minimal effects, the oil’s DV is the more relevant measure of viscosity. Evaluating the KV and DV values further helps in choosing the ideal oils for a machinery lubricant or lubrication system.
Benefits of High Viscosity Fluids
Reduces Wear Even at Higher Temperatures
High viscosity fluids are thick and form a lubrication film that can coat bearings, cylinders, gear sets, and other machinery parts, providing excellent wear protection. This protection is more effective at higher temperatures than lower viscosity lubricants.
However, it is essential to consider a high viscosity lubricant with high VI for machines that need to operate in a wide range of temperatures. A high VI would ensure that high viscosity is constant even at low temperatures.
Reduces Oil Consumption
High viscosity fluids stay put when applied to bearings or machinery parts. This ability lets you save on oil consumption. Low viscosity fluids flow or run off machine parts, leading to the need for reapplication of the lubricant.
Also, the KV and DV values of most high viscosity fluids are similar to or nearer than those of most low viscosity fluids. The closer the KV and DV values are, the lesser the possibility of oil loss at high-pressure and high-temperature conditions, thus, lesser oil consumption.
Better for Heavy-Duty Applications
High viscosity fluids are the ideal choice for machines that perform heavy-duty functions involving the presence of high temperatures. Again, high viscosity fluids for these types of applications must have a high VI. This is to ensure that the viscosity remains within optimum operating conditions.
A high VI would also mean that your lubricant does not thicken significantly, even at low temperatures. Low VI means severe thickening of your lubricant, which, as observed in machines operating in colder locations, can promote more fuel consumption and wear due to high friction during start-up.
Resistant to Shear Stress or Shear Rate
High viscosity fluids are more resistant to shear stress or shear rate, which promotes thinning or a decrease in viscosity. This shear thinning then decreases the lubricant’s ability to provide a sufficient film thickness to protect the equipment or engine from wear.
Most high viscosity lubricants come with additives that increase the VI and ensure stability against temperature changes. But conditions such as shock loads, ongoing heavy loading, extremely high temperatures, and low levels or low viscosity of lubricating oils can promote high shear stress and weaken the stability and performance of lubricants.
Lubricant Choices Key to Lubrication Management
Choosing the right lubricant is an essential part of lubrication management. High viscosity fluids are not always the perfect choice for all your lubrication needs, but they have the most benefits and more manageable disadvantages. Hence, engineers and lubrication experts almost always choose high viscosity fluids over low viscosity options.
When identifying the ideal high viscosity lubricant for your lubrication system, you must consider its viscosity index and kinematic viscosity, as well as your operations’ shear stress or shear rate conditions. Keep in mind that for lubrication systems to have the highest effectiveness and efficiency, lubricant viscosity must match the lubricated parts’ requirements for speed, load, and temperature. A lubrication management software like Redlist can help you monitor and make the necessary improvements in your lubrication. Redlist is user-friendly and intuitive, allowing you access to real-time data and accurate analytics. You need this level of insight to monitor the impact of your lubricant choices and make adjustments to optimize your lubrication management.
