Lubrication can be a daunting obstacle to someone unfamiliar with its basic concepts. Even someone with experience can be confused by the technology of current machinery combined with the multitude of lubricants available on the market today. Reviewing a few of the basic principles of lubrication can make it easier to see why proper lubrication is necessary in every application.
3 Types of Lubrication:
There are 3 types of lubrication or lubrication situations that can exist between two surfaces separated by a lubricant. Whether or not these situations occur is dependent upon the ability of the lubricant to provide adequate protection to the moving surfaces.
When a fluid lubricant is present between two rolling and/or sliding surfaces, a thicker pressurized film can be generated by the movement of the surfaces (at their respective velocities). The non-compressible nature of this film separates the surfaces and prevents any metal-to-metal contact. The condition in which surfaces are completely separated by a continuous film of lubricating fluid is commonly referred to as Hydrodynamic or Full Fluid Film Lubrication.
Although hydrodynamic lubrication is the ideal lubrication scenario, in many situations it cannot be maintained. Hydrodynamic lubrication is limited by the lubricant's viscosity, the rotation speed or RPM and by component loading. An increase in speed or viscosity increases oil film thickness. An increase in load decreases oil film thickness.
Boundary Lubrication is a condition in which the lubricant film becomes too thin to provide total surface separation. This may be due to excessive loading, low speeds or a change in the fluid's characteristics. In such a case, contact between surface asperities (or peaks and valleys) occurs. Friction reduction and wear protection is then provided via chemical compounds rather than through properties of the lubricating fluid.
The third type lubrication situation is known as Elastohyrodynamic Lubrication (EHD or EHL). This situation occurs as pressure or load increases to a level where the viscosity of the lubricant provides a higher shear strength than the metal surface that it supports. As a result, the metal surfaces deform elastically in preference to the highly pressurized lubricant. This increases the contact area and decreases the effectiveness of the lubricant.
To minimize friction, an effective lubricant should be able to handle the pressures and speeds of the surfaces it will separate.
Webster defines friction as the "rubbing of one body against another," and as "resistance to relative motion between two bodies in contact." Friction can be beneficial. As we overcome this resistance to motion between two objects in contact, heat is generated. This heat is what warms our hands or starts a fire. Friction is also the principle behind the braking systems we find on our automobiles. In fact, once we were able to get a car moving, there would be nothing to stop it without friction except the effects of gravity or other objects.
However, friction can also be our enemy. The heat generated as the result of friction can cause damage. Because contact is required to generate friction, wear in the areas of contact can occur. This can lead to material failures, overheating and the formation of wear deposits.
Although there are many ways to reduce friction, the most common way is through the use of a fluid or semi-fluid material. The key characteristic of such materials is that they are not readily compressible. Fluid and semi-fluid materials allow us to minimize component contact or eliminate contact altogether. These fluids are commonly referred to as lubricants.
What Every Lubricant Must Do:
Though the ability to minimize friction is the number one function of a lubricant, there are other major functions that must be considered.
A lubricant is likely to also be required to:
Clean: A lubricant must maintain internal cleanliness by suspending contaminants or keeping contaminants from adhering to components.
Cool Moving Elements Reducing friction will reduce the amount of heat that is generated and lower the operating temperature of the components. A lubricant must also absorb heat from the components and transport it to a location where it can be safely dissipated.
Prevent Contamination: The lubricant should act as a dynamic seal in locations such as the piston, piston ring and cylinder contact areas. This minimizes contamination by combustion (blow-by) byproducts (for example) in the lubricating system. Lubricants are also relied upon to support mechanical seals found elsewhere and to minimize external contamination and fluid loss.
Dampen Shock: The lubricant may be required to cushion the blows of mechanical shock. A lubricant film can absorb and disperse these energy spikes over a broader contact area.
Transfer Energy: A lubricant may be required to act as an energy transfer median as in the case of hydraulic equipment or lifters in an automotive engine.
Prevent Corrosion: A lubricant must also have the ability to prevent or minimize internal component corrosion. This can be accomplished either by chemically neutralizing the corrosive products or by setting up a barrier between the components and the corrosive material.
U.S. NAVY Engineers Do MORE Maintenance with LESS
In Maintenance, LESS means MORE
LESS Effort means MORE Productivity
LESS Complicated means MORE Confidence
LESS Waste means MORE Profit / REDUCED Expenses
The Best Manufacturing Practices Center of Excellence was formed through a partnership between The Office of Naval Research, the U.S. Department of Commerces Bureau of Export Administration, and The University of Marylands Engineering Research Center. The BMP Program is a unique industry and government cooperative technology transfer effort that improves the global competitiveness of the U.S. industrial base. The primary objective toward this goal is simple: to identify and validate best practices, document them, and then encourage industry, government, and academia to share information about them. By fostering the sharing of best practices, BMP has become a national resource in helping organizations benchmark with the best, learn from others attempts, and avoid costly and time-consuming duplication.
A Reliability Centered Maintenance (RCM) program can eliminate waste associated with outdated procedures, overstocked and redundant inventory, as well as wasted labor, time and transportation. Improve the efficiency of the system undergoing maintenance, and all other products or processes that interact with that system. Developing an effective RCM program will optimize the maintainability of the system allowing you to anticipate the times when the system is down for maintenance, and scheduling other activities or processes accordingly. By sharing information about fleet vehicle and industrial equipment maintenance pollution prevention (P2), businesses can become more competitive, business and government can realize cost savings, and environmental quality can be enhanced.
REDUCE Equipment Down or Out of Service Time
REDUCE Lubricant Inventory Requirements
ELIMINATE Premature Equipment Failures
REDUCE Energy and Fuel Consumption
REDUCE Hazardous Waste Lubricants
STREAMLINE Maintenance Protocols
REDUCE Waste Disposal Expenses
MAXIMIZE Equipment Service Life
REDUCE Man Hour Requirements
EXTEND Lubricant Drain Intervals
REDUCE Capital Expenditures
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Can respond with a good deal of pride and satisfaction, 'I served in the United States Navy'."
Chief... MMC (SW) Retired 1991
Our mechanized society cannot function without lubricants. The dilemma is oil is both necessary for our life-style and potentially destructive to nature. Quite simply, we must select innovative, efficient products that will help reduce our dependence upon foreign oil and pollution problems...
The Society of Automotive Engineers (SAE) is the premiere world resource for the design, manufacturing, operation, and maintenance of automobiles, aircraft, space vehicles, off-highway equipment, trucks, buses, trains, marine craft, engines, and self-propelled vehicles.
You get better wear protection, lower engine temperatures, improved fuel efficiency and easier cold-weather starts. All of these benefits add up to reduced operating costs and longer engine life. And even more, you generate less waste oil, which helps preserve our environment and reduce our dependence on foreign oil.