Basic Lubrication

What Every Lube Professional Should Know

Function of Lubricants
Lubricants must be able to protect machine surfaces from degradation. They can do this in a number of ways. First, they reduce friction and, by doing so, help control wear. Lubricants also control corrosion, temperature and contaminants, which lessens the destruction of machine parts. Finally, they transmit power throughout the system. This is very common in hydraulic systems.

For lubricants to protect machine surfaces, they will be relied upon to separate machine parts with a film. This film could be a boundary film, which is formed by additives in the lubricant, or a fluid film, which is formed by the lubricant itself. The formation of these films is critical to the equipment’s longevity, as the films prevent excess friction and wear due to surface contact.
Friction
In layman’s terms, friction is a force that resists one surface from sliding or rolling over another. Therefore, it can be said that friction only occurs when two surfaces are in relative motion, such as when a crankshaft is rotating in a journal bearing or when a ball bearing is rolling along its raceway. A microscopic view of these surfaces in relative motion reminds us that each surface contains tiny, jagged asperities (rough and uneven surfaces), no matter how closely these surfaces are machined.
Factors That Affect Friction
A number of factors affect the frictional conditions at the interface between these two surfaces in relative motion. These factors are:
Surface Finish –
The number, roughness and even the directional contact points of the asperities on the surfaces can dramatically affect the frictional coefficient.
Temperature –
Both ambient and operational temperature can affect friction. For example, temperature is a critical element in whether an anti-wear or extreme pressure additive will be effective in certain applications.
Operational Load –
Friction varies directly with load. A load exceeding the designed capacity will dramatically increase the frictional coefficient.
Relative Speed –
Increasing the speed beyond that which is safely specified will dramatically increase friction.
Nature of the Relative Motion between the Surfaces –
Sliding motion versus rolling motion can affect the coefficient of friction.
Lubricant Characteristics –
These characteristics are the base oil, the viscosity of the base oil and the additives combined with the base oil for the particular formulation.

Base Oil Groups

Almost every lubricant used in plants today started off as just a base oil. The American Petroleum Institute (API) has categorized base oils into five categories (API 1509, Appendix E). The first three groups are refined from petroleum crude oil.Group IV base oils are full synthetic (polyalphaolefin) oils. Group V is for all other base oils not included in Groups I through IV. Before all the additives are added to the mixture, lubricating oils begin as one or more of these five API groups.

Group I base oils are classified as less than 90 percent saturates, greater than 0.03 percent sulfur and with a viscosity-index range of 80 to 120. The temperature range for these oils is from 32 to 150 degrees F. Group I base oils are solvent-refined, which is a simpler refining process. This is why they are the cheapest base oils on the market.

Group II base oils are defined as being more than 90 percent saturates, less than 0.03 percent sulfur and with a viscosity index of 80 to 120. They are created by using a hydrotreating process to replace the traditional solvent-refining process.  Hydrogen gas is used to remove undesirable components from the crude oil. This results in a clear and colourless base oil with very few sulphur, nitrogen or ring structures. This is a more complex process than what is used for Group I base oils. Since all the hydrocarbon molecules of these oils are saturated, Group II base oils have better antioxidation properties. They also have a clearer colour and cost more in comparison to Group I base oils. Still, Group II base oils are becoming very common on the market today and are priced very close to Group I oils. They are commonly used in automotive engine oil formulations.

Group III base oils are greater than 90 percent saturates, less than 0.03 percent sulfur and have a viscosity index above 120. These oils are again created by using a hydrogen gas process to clean up the crude oil, but this time the process is more severe and is operated at higher temperatures and pressures than used for Group II base oils. This longer process is designed to achieve a purer base oil. Although made from crude oil, Group III base oils are sometimes described as synthesized hydrocarbons. Like Group II base oils, these oils are also becoming more prevalent and more anti-oxidant.

Group IV base oils are polyalphaolefins (PAOs). These synthetic base oils are made through a process called synthesizing. They have a much broader temperature range and are great for use in extreme cold conditions and high heat applications.

Group V base oils comprise all base oils not included in Groups I, II, III or IV.  Therefore, are classified as all other base oils, including silicone, phosphate ester, polyalkylene glycol (PAG), polyolester, biolubes etc. These base oils are at times mixed with other base stocks to enhance the oil’s properties. An example would be a PAO-based compressor oil that is mixed with a polyolester. Esters are common Group V base oils used in different lubricant formulations to improve the properties of the existing base oil. Ester oils can take more abuse at higher temperatures and will provide superior detergency compared to a PAO synthetic base oil, which in turn increases the hours of use.

Oil Cleanliness Levels

NAS / ISO / SAE Code Comparison