Viscosity is defined as a fluid’s resistance to flow. In lubrication management, understanding the viscosity of a lubricant means understanding the two types of viscosity measurements: kinematic viscosity (KV) and dynamic viscosity (DV). This post focuses on DV and its implications in lubricant analysis.
What is Dynamic Viscosity?
Dynamic viscosity, also called absolute viscosity, is the measure of a fluid’s resistance to an external force. Simply put, dynamic viscosity is the viscosity value you get if you apply force to a fluid and measure the fluid’s reaction to said force.
To illustrate, if you stir an amount of water in a cup, it will react by producing a force, called torque, which resists the stirring force. Now, if you stir the same amount of honey in a similar cup, you experience more resistance as you stir because honey produces a larger torque in response.
If you measure the viscosity of the above water and honey samples, the honey will have a higher DV than the water sample. Thus, higher dynamic viscosity means that a fluid produces higher resistance to an applied force.
The Brookfield viscometer is the most common instrument that measures the resistance of fluids. This instrument works by inserting a probe into a quantity of fluid. The probe is then allowed to rotate while measuring the force that resists its rotation.
Dynamic Viscosity of Lubricants
Viscosity is a physical property critical in evaluating lubricant suitability, performance, and overall quality. When it comes to the dynamic viscosity of lubricants, it’s essential to consider the following:
DV and KV Relationship
A lubricant’s dynamic and kinematic viscosity is related to a certain degree. Ideally, a lubricant’s DV is equal to its KV multiplied by its specific gravity (the density when compared to water).
When comparing viscosity values, you can use KV to estimate DV, but other factors may affect the accuracy of your calculations. These factors include:
- Presence of Contaminants
- Additive Package
- KV and DV Testing Methods
Dynamic Viscosity Testing Conditions
The dynamic viscosity of a lubricant is called absolute viscosity, implying that no other forces affect its resistance other than the force applied. But, this is not always the case. Other testing conditions can affect the values measured for viscosity.
For this reason, standardization organizations like the ISO (International Organization of Standardization) and the ASTM (American Society for Testing and Materials) established and continue to update the standard testing methods for viscosity and other properties of materials.
When comparing DV values of lubricants, it is always wise to check and compare the methods used to arrive at these values. You can’t compare DV values measured by different methods.
Often, even similar methods can affect the precision of measurements. Every testing setup can have variations in temperature, humidity, the force of gravity, instrument, etc. These variations ultimately result in variations in KV or DV values.
DV Trend Analysis
Knowing the dynamic viscosity of a lubricant is essential, but what’s more critical is understanding how this DV changes as lubricants are stored or used. Creating a record of viscosity measurements, whether KV or DV, and performing a trending analysis helps track these viscosity changes.
Trends in DV or KV values give you useful insights into how a lubricant performs and reacts over time. These trends can help you predict and prevent lubricant failure. Hence, you can better manage any resulting damage to your machine or effects on your operations.
Lubrication Management and Viscosity Measurements
The success of any lubrication management depends on understanding why viscosity is a critical property when it comes to lubricants. It is also essential to be familiar with the basis and implications of the different viscosity measurements.
More facilities are now recognizing that lubrication management is no longer as simple as applying lubricants to machines. Lubrication management is a science requiring the careful study of lubricants’ chemical and physical properties and the factors that affect them.
A comprehensive, user-friendly, and computerized Lubrication Management Software like Redlist can help you keep up with the demands of a science-based lubrication system. With Redlist, gathering accurate and precise data is easy because it eliminates paperwork and guesswork. With real-time data analysis and cloud-based storage, data trends and other crucial information is secure and accessible whenever needed.Find out why Redlist is your all-in-one tool for results-based and successful lubrication management. Schedule a free demo today!
