Lubricant

Reduce Friction 

The main purpose of lubricating oils is to reduce friction. Friction can reduce the speed of actions and also cause damage. For instance, lubrication added to gears will increase the speed in which the gears operate and reduce wear and tear on the gears.

Coolant 

Lubricating oils can be used as cooling agents.

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Rust Inhibition 

Some lubricants contain alkaline amines that inhibit rusting in metal machinery.

Particle Cleaning 

Through wear and tear, machinery often sheds particles. The particles get trapped in the lubricating oils and then drip off of the machinery.

Sealant 

Lubricating oils can block contaminants that might damage surfaces, thereby acting as sealants.

PROPERTIES

Heat Resistance

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Since two parts rubbing against each other generate friction and friction generates heat, it is essential that the oil be chemically stable under the heat of normal operation. If it is not, oxygen will react with the oil, producing a host of compounds---most notably, damaging carboxylic acids. These acids erode metallic surfaces. Even worse, oxidized motor oil with a high acid number forms sludge and varnishes that are even more damaging than the acids themselves. Another form of heat-related breakdown is compressive thermal failure. This is caused by a very limited amount of oil between hot sliding surfaces but in the absence of air. Although it is not as clearly understood, it contributes to the need for heat stability.

Suitable Viscosity Range 

Over the entire range of temperatures and conditions in which lubricating oil will used, the viscosity range should remain within specified limits to assure proper lubricity. In commercially obtained motor oils, this is generally specified by the Society of Automotive Engineers (SAE). It is commonly referred to as the "weight" of the oil. A low number means viscosity is low---a high number means viscosity is high. Numbers followed by a "W" means the measurement was made at a temperature typically found in winter---zero degrees Fahrenheit. Higher viscosity is not generally given a "W" after the number, but simply lists the number. In many modern motor oil formulations, a dual value is given. The start-up value in cold weather, followed by the viscosity under ordinary operating conditions. Thus, 5W-30 means motor oil in ordinary operation possesses a viscosity of 30, but under winter start-up conditions, it responds with a viscosity of 5.

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Corrosion Resistance and Other Properties 

Improved lubricating oils usually contain special additives, such as detergents and dispersants to prevent carbon-forming deposits, as well as antioxidants and corrosion inhibitors to protect metallic surfaces. Viscosity-index improvers, wetting

agents, extreme pressure additives and pour point depressants are added to motor oils to improve overall performance. Then there are the modified or completely synthetic motor oils--more expensive, but often delivering improved performance and having a longer functional life before needing replacement.

Five Essential Lube Oil Properties Not Routinely Reported By Your Oil Lab 

Jim Fitch, Noria Corporation Tags: oil analysis, oil oxidation

You may be surprised to learn that there are no less than five lubrication performance properties that are missing from nearly all in-service oil analysis reports. These are not esoteric properties that are of limited value or interest to those in charge of machine reliability. Instead, they represent the core foundation of a lubricant’s formulation and purpose. In other words, they relate to the essence of what we expect and need from a lubricant. And, these are the properties that are imparted by additives and commonly found on a lubricant’s product data sheet (spec sheet). Don’t get me wrong; I am not suggesting that commercial oil analysis labs are duping their clients by shortchanging testing services. Many of these missing tests cannot be practically performed on routine oil samples because they are expensive, involve prolonged test periods and/or require large sample volumes. Yet it is important that the user community fully

understand what they get and what they don’t get when they pay $35 for oil analysis.

Performance Tests Below is a list of “performance” tests that are often used to portray the quality and performance capabilities of a new lubricant. Unlike ordinary used oil analysis tests that report physical and chemical properties such as viscosity, acid number, flash point, elemental analysis and contamination, performance tests work by challenging a lubricant in some way similar to the actual machine work environment. The reported results characterize or measure how the lubricant responded to the challenge. The following are typical examples of performance tests:

Film Strength. There are numerous ASTM test methods that attempt to depict or measure a lubricant’s ability to reduce friction and control wear under wide-ranging rolling and sliding conditions. Adhesive wear, contact fatigue and two-body abrasion are examples of wear modes affected by a lubricant’s film strength. Antiwear and extreme pressure (EP) additives are added to many lubricant formulations for this purpose. These additives are subject to depletion and impaired performance as a lubricant ages and becomes contaminated. Conventional used oil analysis tests do not measure film strength. Air-handling Ability. The quality of a lubricant’s basestock and the use of certain additives can define its air-handling abilities. We want a lubricant to release entrained air rapidly

and to suppress the formation of foam. Air handling is nearly impossible to interpret from ordinary oil analysis. Water-handling Ability. Like air handling, the lubricant’s ability to efficiently shed water during static conditions is difficult to anticipate from the usual slate of oil analysis tests. Yet for most lubricants, a loss of water-handling ability not only reveals risks from oil-water emulsions but also signals faltered performance of other important properties. This property too often goes unnoticed by the used oil analysis community. Corrosion Control. Corrosion control is a fundamental lubricant formulation objective. There are many additives used to neutralize corrosive agents or form protective barriers on sensitive machine surfaces. These are sacrificial additives that lose their effectiveness over time. Nonetheless, no conventional used oil analysis test, other than the base number, reports the residual effectiveness of the corrosion-protecting qualities of an in-service lubricant. Oxidation Stability. With rare exception, nearly all lubricants are formulated with oxidation inhibitors to stem the rate of oxidation. The most robust and superior lubricants on the market today emphasize this important lubricant property. These include premium turbine oils, long-mileage motor oils and synthetic lubricants of all types. While post-oxidation byproducts can be detected and measured by ordinary oil analysis tests (after the fact), the residual oxidation stability of a lubricant is far more difficult to assess. That said, some success has been reported with techniques such as linear-sweep voltametry and infrared spectroscopy (additive spectral bands). These tests are becoming increasingly common in commercial oil analysis, although used on less than five percent of all samples tested.

Besides those properties listed above, there are numerous other performance properties that are application- and lubricant-type specific. These include volatility, resistivity, biodegradability and thermal stability. And there is a slew of properties relating specifically to grease formulation including consistency, dropping point, separability, water wash-out, pumpability, etc.