Classifications of Lubricating Oil Base Stocks

    Paraffinic  – predominantly straight chained hydrocarbons
    Naphthenic – predominantly ring shaped hydrocarbons
    Synthetic – manufactured hydrocarbons and compounds
                     with predictable and repeatable structures
    Intermediates/blends – combinations of these

Paraffinic

• Relatively high wax content (1-10%)

• Contains some naphthanes and aromatics

• Most widely used for standard lubricants

STRAIGHT CHAIN HYDROCARBON

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Naphthenic

• Relatively wax free (trace)

• Contains some paraffins and aromatics

• Widely used for electrical insulating oils

NAPHTHENIC RING HYDROCARBON

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Synthetic

• 7 – 10 % of current lubricant market and growing

• High oxygen stability

• Low internal friction

• Good high and low temperature properties

Different synthetics are manufactured for different applications

• pao (poly-alpha-olefin) – most common

• esters

-- diesters (dibasic acid esters)

-- polyol esters

-- phosphate esters

• pag (polyalkyeneglycols)

• silicones, silicates, siloxanes

• fluorocarbons

• other, specialty lubricants

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Intermediates/blends

• Provides some of the advantages of both blended products

• Can lower the cost of some synthetics, yet still provide adequate protection

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Functions of Lubricating Oils

                                              Reduce friction / reduces wear
                                              Remove heat
                                              Inhibit corrosion or rust
                                              Remove wear particulates
                                              Minimize contaminants
                                              Transfer energy

Reduce friction / reduces wear

Lubricating oil provides a fluid film between two metal wear surfaces to prevent them from touching. Metal surfaces moving in relative opposite directions touching each other produce a tremendous amount of friction and heat. The heat produced can be in the 1000’s of degrees. While it is localized, it is enough to melt bearing, gear, and other surfaces.

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Remove heat

As lubricant relatively moves away from the near metal contact, the heat generated due to locally pressurizing that point stays with the lubricant. While oil is not a great transferor of btu’s, in normal operating conditions it provides enough heat transfer to prevent thermal runaway. In many cases, the lubricant must be cooled with an exchanger before being used to lubricate again.

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Inhibit corrosion or rust

Oxygen is the main corrosive element found in lubrication systems. Oxygen will combine with certain metals and organics to create corrosive acids, oxidize the lubricant, and react with iron to form rust (FeO, Fe₂O₃, and Fe₃O₄). Hydrogen, when combined with chlorine (common additive in some lubricants) and water form hydrochloric acid which when unabated will attack metal surfaces. Some lubricants are called vapor phase lubricants, because they contain alkaline amines that will vaporize at certain temperatures and coat metal surfaces with a rust-preventing layer of organics.

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Remove wear particulates (through filtration)

Some lubricant additives will coagulate particulate matter so it will drop out in the sump or be removed through filtration. Other additive packages will attach themselves to particulates so their combined specific gravity is at or near the specific gravity of the lubricant. This will prevent the particulate from falling out of suspension and depositing in unwanted places. Some are heat dependant so that when the oil is hot it will disperse the particulates, but when the oil looses a few degrees it will coagulate them and allow them to fall out of suspension or be filtered out. Others are time dependant, i.e., at first they will suspend the particulates but gradually they will coagulate them to allow the coagulated masses to drop out in the sump or be removed by filtration.

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Minimize contaminants (seals, for instance)

Lubricants can provide an intermediate fluid to absorb and/or reject contaminants, depending upon the application. A good seal lubricant will readily absorb gases as well as readily release them when heated or scrubbed with air or glycol. Many lubricants are designed to release water easily, usually in the sump or the filter. Other lubricants have additives that will coagulate particles so they can be filtered out. Some lubricants have a combination of these characteristics. When selecting a specific lubricant for a specific application, you should discuss the application with your lubricant supplier.

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Transfer energy (hydraulics)

Because liquids are virtually uncompressible, you can exert a pressure on one liquid surface and apply it to all the other corresponding surfaces. Without getting into a four day discussion on hydraulics, you can move a liquid surface one inch, restrict a corresponding surface by 50%, and move that surface two inches. In order to do this consistently and concisely, the fluid used to do the work must be clean so as not to leave a deposit anywhere in the system, which would change the dynamics of the hydraulic calculations. The cleanliness level of the lubricant in question can be established by "particle count analysis", which is reported in ISO (International Standards Organization) standards. Cleanliness levels are very important in numerical control systems, high speed turbines, and hyper-compressors.

 

As you can see, lubricating oils are called upon to perform a wide variety of functions. Add to that the wide variety of loads, temperatures, and operating environments and you can understand why there are so many different lubricants available. A manufacturer may blend hundreds of different lubricating oils, each engineered and blended to perform particular functions under particular operating conditions.

This is one of the reasons that when specifying a lubricant for any application, it is wise to consult with your lubricant supplier to select the proper oil for the proper application.

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Types of Lubrication

                                                    Hydrodynamic lubrication
                                                    Elastohydrodynamic Lubrication
                                                    Boundary lubrication

Hydrodynamic Lubrication

Adhesive properties of the oil on a turning shaft draw the oil under the shaft and create a hydrodynamic wedge or film due to its resistance to being pressed out.

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Elastohydrodynamic Lubrication

Typical of roller bearings. Deformation occurs in the contact zone increasing the surface area. Film becomes very thin and lubricant changes instantaneously to solid or semi-solid.

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Boundary Lubrication

Sliding surface lubrication such as reciprocating cylinders during starts, stops, shock loads, and directional changes.

 

Uses extreme pressure and anti-wear additives to combine with metal surface to form a sacrificial layer of protection.

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Hydraulics

Hydraulics is the transmission of force or motion using confined fluids to perform work.  Lubricating oils can provide both lubrication and force transmission (hydraulic).

                                                    Qualities of hydraulic oils
   
                                                    Lubrication Systems
                                                            Pressurized
                                                            Splash
                                                            Stream/Spray
                                                            Mist
                                                            Drip

Qualities of Hydraulic Oils

• Chemical stability and oxidation resistance

• Corrosion protection as most hydraulic systems contains a variety of metals.

• Compatible with elastomer seal material

• Light enough to prevent sluggish response, yet heavy enough to provide required lubrication.

• Good anti-foam characteristics to prevent sluggish response.

• Inhibited to prevent rust

• Certain applications may call for fire resistant fluids, good high temperature stability, or good low temperature characteristics.

• Hydraulic fluids are formulated with combination of additives and characteristics to meet various application requirements and price constraints.

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Pressurized Lubrication Systems

• Sump / reservoir / daytank

• Pump or multiple pumps

• Cooler, usually water cooled

• Filter / screen

• Collection manifold

• Oil is pumped from a sump or reservoir through coolers and filters and finally to the lubricated components. Oil is collected by a manifold and returned to the sump.

• Other auxiliary equipment may be added to the system such as bypass filtration systems, centrifuges, degassifiers, etc.

• Applicable for use in most gear and bearing systems because it allows for cooling and filtration.

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Splash Lubrication Systems

• Lubricated components partially immersed in an oil bath, and rotational movement of the component splashes oil to other parts and areas of the equipment

• Sometimes aided with a slinger ring, which rotates freely with the shaft rotation, picks up oil from the bath, and ‘slings’ it to the top of the bearing and other locations in the system.

• Applicable for use in gear, chain, and roller bearing systems which do not require cooling.

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Stream/Spray Lubrication Systems

• A stream of pressurized lubricant Is aimed directly at the component to be lubricated.

• The stream may be nebulized into a spray for better coverage.

• Used lubricant is usually collected and returned to the sump by gravity

• Applicable for use in gear and roller bearing systems.

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Mist Lubrication Systems

• Oil is atomized into sub- and one-micron droplets with clean, dry compressed air. The mist, which looks like smoke, is piped to the oil lubricated compartment at a slight positive pressure.

• The mist coalesces on the component surface to provide lubrication.

• Mist systems provide a slight positive pressure in the compartment providing a purge.

• Older mist systems were vented to the atmosphere.

• Newer systems are closed systems, allowing for reuse of the coalesced lubricant.

• Applicable for use in gear and roller bearing systems.

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Drip Lubrication Systems

• Continuous metered drops of oil are dripped onto the lubricated assembly

• Most often once-through system

• Collection cups are emptied periodically, or dumped into water/oil sewer system.

• Applicable for small, lightly loaded roller bearing systems.

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