From the days of Ancient Egypt, when the first engineers ingeniously used vegetable oil to reduce wear and tear on chariot wheels, to the present, the need to lubricate parts in motion has been a constant in human history. At their most basic level, lubricants reduce the frictional force between two surfaces when in repeated contact. Without lubrication, moving parts generate heat that can cause damage and reduce performance, even leading to equipment failure. In a very literal sense, industrial lubricants keep the world moving smoothly, connecting us to a long-standing engineering tradition.
Today, selecting a suitable lubricant for a specific use requires more than just a trip to the store. Based on the context they’re used in, various industrial lubricant products may prioritize different things, such as maximizing performance, minimizing corrosion, or prolonging equipment life. To help operators make the right choices, industry standards set by organizations like the US Society of Automotive Engineers (SAE) and the American Gear Manufacturers Association (AGMA) provide a solid framework. These standards, which include measuring viscosity as the most effective way to categorize different types of lubricants, give operators the reassurance and confidence they need to make informed decisions.
What is Viscosity?
We’ve all heard the phrase “swimming through peanut butter” to convey the frustrations of trying to move in a constrained environment. If someone were to attempt this, peanut butter’s high viscosity would make swimming in it quite tricky. Thinning the peanut butter would lower the viscosity and thus make it easier to swim in, which is easier to visualize than the following more technical definition:
Viscosity is the ratio of shear stress to shear rate. It defines how fast a fluid will flow through an opening at different temperatures. It is the attribute used to determine a lubricant’s grade.
Why Are There Multiple Grading Systems for Industrial Lubricants?
The simple answer is that various groups developed grading systems at different times. For example, the US Society of Automotive Engineers (SAE) released its first oil grades (10W and 20W) in 1938. The American Petroleum Institute (API) maintains a system for engine oils, and the American Gear Manufacturers Association has a system for gear oils. These grading systems are not merely arbitrary classifications; they serve as a guide to optimize the performance of specific lubricants, ensuring the use of the correct lubricant for each application.
The International Standards Organization (ISO) released its standards in 1975, covering lubricants used in enclosed gear systems. ISO standards are worldwide standards that are updated to reflect technological advances. The ISO system uses the acronym ‘VG’ to indicate a lubricant’s viscosity grade. However, temperature, pressure, shear rate, and additives can alter oil properties, so knowing the test conditions is crucial to understanding the grading systems.
Other lubricant grading systems include:
- Food-grade lubricants: Industrial lubricants are used on equipment in the food-processing industry.
- Readily Biodegradable lubricants: Products that degrade by 60% or more of their original volume within 28 days are considered biodegradable.
- Synthetic, mineral-based, and re-refined lubricants: Synthetic oils use a highly refined base, while mineral and re-refined lubricants use a moderately refined base.
Allegheny Petroleum‘s Industrial lubricant line is marketed under our Altra brand. These products use a synthetic or high-quality mineral base that offers enhanced fuel economy, lower viscosity, and lower operating temperatures while meeting original equipment manufacturer requirements.
How is Grading Performed?
Because oil properties can change based on temperature and additives, each grading system stipulates the conditions under which the tests are performed. Once the correct conditions are established, viscosity can be measured.
Temperature
Oil viscosity changes with temperature. The higher the temperature, the lower the viscosity. Most manufacturers will provide an optimal operating range that engineers may adjust based on operating environments. ISO standards test oil at 40 degrees Celsius or 104 degrees Fahrenheit. SAE grades are based on a test temperature of 100 degrees Celsius or 212 Fahrenheit.
Additives
Oil additives can influence lubricant viscosity. While the base oil used in the product contributes most to the overall viscosity, additives can alter the oil’s performance by degrees that, while small, impact the outcome enough to warrant further consideration. Viscosity Index Improvers have allowed engineers to achieve desired viscosities regardless of the base oil. These additives play a significant role in ensuring the oil maintains its viscosity under varying conditions, enhancing its performance.
Viscosity Index Improvers are added to oils to provide more consistent lubrication over a wider temperature range. The higher the index, the less the viscosity changes based on temperature.
As one of the largest additive manufacturers in North America, Allegheny Petroleum produces industrial lubricants and custom blends that can improve the performance of industrial lubricants.
How is Oil Viscosity Measured?
Viscosity can be dynamic or kinematic. Dynamic viscosity calculates lubrication for rolling element bearings and gears. It is measured in centipoise (cP) and is considered the internal friction of a fluid.
Kinematic viscosity refers to the relative flow of oil under the influence of gravity, which we measure in centistokes (cSt). In SI units, this would be mm2/s (1cSt = 1 mm2/s). Kinematic viscosity can be calculated by dividing the oil density by the dynamic viscosity.
Other measuring units include Redwood, Saybolt, and Engler, although these are not widely used.
How to Select the Right Grade of Industrial Lubricant
When deciding what grade of industrial lubricant is suitable for a particular application, companies should evaluate the following:
- Equipment specifications and OEM recommendations.
- Industry-specific standards and regulations.
- Operating conditions such as temperature, speed, and load.
Once customers understand how oil grades are determined, they can select the appropriate grade for their machines, enhancing equipment efficiency, maximizing performance, and extending lifespan.
Consulting a lubrication engineer can ensure the oil grade matches your operational needs. If a custom blend is needed to meet your specific requirements, contact Allegheny Petroleum for expert advice.