All lubricants begin with a base oil. This base oil forms the backbone of the lubricant, which is then combined with additives or a thickener for grease. However, the challenge lies in understanding which base oil best fits a specific application.
This article aims to demystify base oil formulations’ complexities, enabling you to make informed decisions.
A Breakdown of Base Oil Classifications
Lubricants are classified in several ways, but one of the most prevalent classifications is based on the constituent base oil. These base oils can be mineral, synthetic, or vegetable in origin. Mineral oil, derived from crude oil, can be manufactured to various qualities related to the oil’s refining process.
Synthetics are artificially created through a synthesis process and come in several formulations with unique properties for their intended purpose. Vegetable base oils, derived from plant oils, represent a small percentage of lubricants and are primarily used for renewable and environmental interests.
According to a recent survey on MachineryLubrication.com, 55% of lubrication professionals utilize synthetic and mineral-based lubricants at their plants.
Probing into Base Oil Characteristics
All base oils possess characteristics that determine how they will withstand many lubrication challenges. For mineral oil, the refining process aims to optimize the resulting properties to produce a superior lubricant. For synthetically produced oils, the various formulations aim to create a lubricant with properties that may not be achievable in mineral oil. Each base oil, whether mineral or synthetic, is designed for a specific application.
Key base oil properties include viscosity limitations and viscosity index, pour point, volatility, oxidation and thermal stability, aniline point (a measure of the base oil’s solvency towards other materials including additives), and hydrolytic stability (the lubricant’s resistance to chemical decomposition in the presence of water).
A Glimpse into Base Oil Groups
The 20th century brought about numerous improvements in the refining process used for mineral oils and the introduction of various synthetic oils.
By the early 1990s, the American Petroleum Institute (API) had categorized all base oils into five groups, with the first three dedicated to mineral oils and the remaining two predominantly synthetic ones.
Group I
Groups I, II, and III are all mineral oils with an increasing degree of the refining process. Group I base oils are developed using solvent-extraction or solvent-refining technology. This technology, used since the early days of mineral oil refining, aims to extract the undesirable components within the oil such as ring structures and aromatics.
Group II
Group II base oils are produced using hydrogen gas in a process called hydrogenation or hydrotreating. The aim of this process is similar to solvent-refining, but it is more effective in converting undesirable components like aromatics into desirable hydrocarbon structures.
Group III
Group III base oils are made much the same way as Group II mineral oils, except the hydrogenation process is coupled with high temperatures and pressures. As a result, nearly all undesirable components within the oil are converted into desirable hydrocarbon structures.
When comparing properties among the mineral base oil groups, you will typically see greater benefits with those more highly refined, including those with enhanced oxidation stability, thermal stability, viscosity index, pour point, and higher operating temperatures.
Group IV
Group IV is dedicated to a single type of synthetic called polyalphaolefin (PAO). It is the most commonly used synthetic base oil. PAOs are synthetically generated hydrocarbons with an olefinic tail formed through a polymerization process involving ethylene gas. The result is a structure that resembles the purest form of the mineral oils described in Group III.
Group V
Group V is assigned to all other base oils, particularly synthetics. Some of the most common oils in this group include diesters, polyolesters, polyalkylene glycols, phosphate esters, and silicones.
Base Oil Applications
In general, synthetics provide more significant benefits for properties influenced by extreme temperatures, such as oxidative and thermal stability, which can contribute to extended service life. When the lubricant encounters cold startups or high operating temperatures, synthetics like PAOs typically outperform mineral oils.
While PAOs are ideal for applications like engines, gear, bearings, and others, mineral oil remains the predominant oil of choice due to its lower cost and reasonable service capabilities. With over 90 percent usage in the industrial and automotive markets, mineral oil has become the most common base oil in most applications.
Understanding Base Oils: Key Takeaways
Make sure to keep in mind these four things when working with lubricants and base oils.
1. Not all oils from each base oil type are identical, as the formulations can produce unique distinctions. Thus, the properties described for each base oil type are generalized for the category as a whole.
2. Group III oils are sometimes marketed as synthetics. There is a consensus that the refining process has significantly modified the original hydrocarbon, thus synthesizing the more highly pure product.
3. Water-based fluids are an alternative when fire resistance is crucial and typical lubricant properties like viscosity or lubricity are less important.
4. Please exercise caution when switching lubricants, particularly when they have different base oils, as they may be incompatible with each other.
When choosing a base oil, tradeoffs in the lubricant properties required for the application will be inevitable. Even though understanding the manufacturing process of the oil is not necessarily important, it is crucial to know the available base oil options and the advantages and disadvantages they provide. While synthetics are understandably more expensive than mineral oil, equipment failure costs are typically much higher.
To learn more about lubricant base oils, contact Lock Saver today!