1. Lubrication • Lubricant Application • Lubrication Programs
Chapter 8
Lubrication
Lubrication • Lubricant Application • Lubrication Programs

2. Objectives Describe lubrication. Explain the coefficient of friction.
Describe gas lubricants.
Describe liquid lubricant and their properties.
Describe semisolid lubricants and their properties.
Describe solid lubricants and their properties.
Identify common types of lubricant application and contamination.
Explain why lubrication programs should be established within an organization.

3. Fluid lubricants, which include gas, liquid, and semisolid lubricants, must create a film between material surfaces to prevent contact with each other.
In addition to reducing friction, a lubricant is used to prevent wear, act as a coolant for moving parts, act as a barrier under load pressure, prevent adhesion or galling of materials, and prevent corrosion. Machines and tools depend on lubrication to ensure smooth and safe operation. Lubricants are classified as gas, liquid, semisolid, or solid. In many cases, a lubricant is a mixture of the different classes. Fluid lubricants, which include gas, liquid, and semisolid lubricants, must create a film between material surfaces to prevent contact with each other. See Figure 8-1.

4. The coefficient of friction is the measure of the frictional force between two surfaces in contact.
Greater force is required to move a body from rest (static condition) than the force required to keep it in motion (kinetic condition). However, once a lubricated body is in motion, less force is required to keep it in motion than if it were unlubricated. Generally, a static condition between two solid objects means neither object is moving. However, a static condition relating to coefficient of friction refers to the forces required to start a solid object in motion. See Figure 8-2.

5. Cleaned, unlubricated metals contain a degree of lubrication from elements in the atmosphere, such as oxygen and moisture.
Boundary lubrication occurs when molecules are adsorbed on metal surfaces through an exchange of electrons. This process occurs with metals that are either lubricated or unlubricated. Unlubricated metals are metals without the addition of a lubricant. However, even metals that have been cleaned of all foreign material contain a degree of lubrication. This lubrication is in the form of water vapor, adsorbed gases, or contaminants from handling. These lubricants affect the material’s coefficient of friction. See Figure 8-3.

6. Oxides that form on sliding metals are considered boundary lubricants and are thickened and strengthened by the addition of certain chemicals.
Chemicals are added to a lubricant to enhance its qualities or to blend with certain chemicals in the lubricant to create chemisorption. Chemisorption is a chemical adsorption process in which weak chemical bonds are formed between liquid or gas molecules and solid surfaces. This produces a thicker boundary layer and forms a solid, low shear-strength film. See Figure 8-4.

7. All animals and plants release hydrocarbons that, when absorbed into the earth’s surface, combine to form pools of gas and crude oil.
Petroleum is formed by an evolutionary process that takes many millions of years. This process begins with oil vapor given off into the atmosphere by plants. The oil vapor, sometimes seen as a blue haze over heavily vegetated areas, settles or is washed to the ground by rain or snow. The oil works its way deep into rock voids where it is concentrated and processed under high temperatures and pressures. See Figure 8-5.

8. Crude oil must be processed to become a uniform and dependable product.
Crude hydrocarbons are found in various physical forms ranging from a light gas such as methane to a heavy tar. To maintain a consistent, stable, uniform, and reliable lubricating liquid, the crude oil is processed in steps of heating, distilling, and filtering. The final step of processing a petroleum lubricant is the application of certain additives for individual and special applications. New compounds are being developed daily to handle average consumer needs. Recent submarine, subterranean, and outer space equipment applications have added to the research and development process. See Figure 8-6.

9. Shear stress is stress in which the material on one side of a surface pushes on the material on the other side of the surface with a force parallel to the surface.
Shear strength is the ability of a material to withstand shear stress.
Shear stress is stress in which the material on one side of a surface pushes on the material on the other side of the surface with a force parallel to the surface. See Figure 8-7.
Shear strength relies greatly on the liquid’s viscosity. As the viscosity of a lubricant decreases or as forces increase, the shear strength of a lubricant is weakened or broken and metal to metal contact is made.
A liquid lubricant’s shear strength may be weakened when the liquid’s viscosity decreases because of increasing temperatures.

10. Commercial lubricating oil is categorized by six different groups with each group designed for a specific application.
Commercial lubricating oil is categorized by six different groups with each group designed for a specific application. See Figure 8-8.
Lubricating oil is given an SAE viscosity rating based on its ability to flow at a specific temperature.
A high viscosity rating results from a small volume of oil flowing through the orifice caused by high resistance to flow. A low viscosity rating results from a large volume of oil flowing through the orifice caused by low resistance to flow.

11. The National Lubricating Grease Institute (NLGI) has established a series of nine grease consistency grades.
Grease is classified by thickener grade. The National Lubricating Grease Institute (NLGI) has established a series of nine consistency grades. See Figure 8-9.
Each group is designed for a specific temperature range and purpose.
Grades NLGI 00, 0, and 1 are recommended for centralized lubrication systems because of their relatively high flow characteristics.

12. Grease base thickeners are chosen according to the temperature and viscosity demands placed on the lubricating product.
Grease consistency varies with a change in temperature.
As temperatures increase, greases become soft enough to separate the oil from the thickener. This is known as the grease dropping point.
The grease dropping point is the maximum temperature a grease withstands before it softens enough to flow through a laboratory testing orifice.
The dropping point of greases vary according to type. Some special greases do not exhibit a dropping point. See Figure 8-10.

13. Oil lubrication may be applied to bearing elements by submersion, wick, drip, or centralized systems.
Oil lubrication may be applied to bearing elements by submersion, wick, drip, or centralized systems. See Figure 8-11.
A submersion system is a lubrication system in which the bearings are submerged below oil for lubrication.
A wick system is a lubrication system that uses capillary action to convey oil to a bearing surface.
A drip system is a gravity-flow lubrication system that provides drop-by-drop lubrication from a manifold or manually filled cup through a needle valve.
A centralized system is a lubrication system that contains permanently installed plumbing, distribution valves, reservoir, and pump to provide lubrication.

14. Greases are applied by grease guns, grease cups, or centralized systems.
For proper operation, rolling elements must be thoroughly coated with grease.
Overgreasing leads to overheating, aerating, and churning of the grease, resulting in early bearing failure. The total space available in a rolling element bearing should contain no more than 50% grease lubricant.
The grease of all open, unsealed bearings must be replenished because the oil from all unsealed greases eventually bleeds off from the thickeners.
Greases are applied by grease guns, grease cups, or centralized systems. See Figure 8-12.

15. Regreasing a motor may include purging the old grease from between the shaft and the housing.
Motors equipped with grease fittings and drain plugs must be regreased using a low-pressure grease gun. See Figure Refer to the procedure for motor regreasing on textbook page 233.

16. Oil analysis is a predictive maintenance technique that detects and analyzes the presence of acids, dirt, fuel, and wear particles in lubricating oil to predict equipment failure.
Oil analysis is a predictive maintenance technique that detects and analyzes the presence of acids, dirt, fuel, and wear particles in lubricating oil to predict equipment failure. See Figure 8-14.
The analysis commonly includes oil viscosity, particle count, wear particle concentration analysis, and wear particle analysis.
The lubricant condition rating is identified as normal, marginal, or critical based on the results of the sample, comparison with previous data, and the machine condition analyst’s experience with the particular type of equipment.

17. Review
1. Aside from reducing friction, list three additional ways lubricant helps ensure smooth and safe operation of tools and machines.
2. When do the effects of boundary lubrication mostly occur?
3. Define chemisorption.
4. What is a liquid lubricant used for and why is it the preferred lubricant?
…Continued on next slide

18. Review (Continued)
5. List three examples of lubricant additives and explain how each one protects a machine from harm.
6. What does the viscosity index scale show?
7. What are SAE viscosity ratings based on?
8. List two advantages of using synthetic fluid as opposed to petroleum-based lubricant.
9. Define semisolid lubricant.
…Continued on next slide

19. Review (Continued)
10. Explain how an increase in temperature affects grease consistency.
11. Determine why graphite is useful as a solid lubricant and explain why it is not useful when humidity is absent.
12. Explain why oil must be replenished in order to ensure all parts within a mechanical apparatus receive the proper amount of lubrication.
13. List the four systems associated with oil application.
14. Define oil analysis.
15. What does the practice of wear particle analysis focus on?