Topics Introduction Types of Lubricants Viscosity Viscosity Ratings Terminology Types of Lubricant Additives Types of Lubricating Oils Types of Greases Note: Please refer to chapter 4 Lubrication in the text.

Introduction Purpose of lubrication: 1. To reduce friction 2. To cool down moving parts 3. To prevent corrosion (component wear from chemical reaction with the air and moist) 4. To prevent contamination Note: The cost saving achieved from selecting and applying the proper lubricant is far greater than the saving from using an inferior lubricant. Lubricants function by forming a thin film that acts as a barrier between the moving parts. The low coefficient of friction that greases and oils have reduces the friction between the machine components. Example 1: (Refer to figure 3-1 on page 38) what is the coefficient of static friction between two components made of hard steel in the case when there is no lubricant present (dry) and when there is a lubricant? Answer: 0.78 when dry, drops to 0.11-0.23 when lubricated

Coefficient of Friction Lubricants function by forming a thin film that acts as a barrier between the moving parts. Coefficient of friction (µ) - the ratio between the force necessary to move one surface horizontally over another and the pressure between the two surfaces. CoF is unitless and has been established primarily through extensive testing. Page 38 in your book gives a list of material/surfaces and the CoF between them. The low coefficient of friction that greases and oils have reduces the friction between the machine components.

Example 1: (Refer to figure 3-1 on page 38) what is the coefficient of static friction between two components made of hard steel in the case when there is no lubricant present (dry) and when there is a lubricant?

Example 1: (Refer to figure 3-1 on page 38) what is the coefficient of static friction between two components made of hard steel in the case when there is no lubricant present (dry) and when there is a lubricant? Answer: 0.78 when dry, drops to 0.11-0.23 when lubricated

Forms of Lubricants Lubricants may be: - Liquid lubricants such as automotive engine oils (i.e. motor oils) - Semisolid lubricants such as greases (usually mineral oil based) - Solid (dry) lubricants: such as graphite powder and molybdenum disulfide. They can function at very extreme temperatures as high as 2000 oF and as low as -395 oF. They also can withstand very high loads (more than 25,000 psi) (essentially used when other lubricants have failed) - Gas lubricants: such as a stream of pressurized nitrogen gas (used between smooth surfaces with very small clearances)

Viscosity Viscosity: A measure of the fluid’s resistance to flow. The best lubricant is that which has the lowest viscosity possible while maintaining a film that separates the metal parts. Viscosity Index (VI): a measure of the change in viscosity with temperature. The higher the VI, the smaller the changes seen with temperature. Kinematic viscosity: is the measure of inertial force to viscous force - specifically the kinematic viscosity measures the resistance to flow of a fluid under the influence of gravity only. Units of kinematic viscosity are: m2/s (the SI unit) the Stoke (1 m2/s = 10,000 stokes ) Saybolt Universal Seconds (SUS) Source: Wikimedia Commons.

Viscosity Measurement Viscosity of a liquid may be approximated using a Viscometer in units of Saybolt Seconds, accuracy is 90-95% Use the viscometer to approximate the viscosity of some Oils. In this instrument the viscosity of a liquid is compared to the viscosity of an oil.

Viscosity Ratings SAE viscosity rating: Society of Automotive Engineers established a rating for engine oils Other lubricant grade standards are those by the International Standards Organization (ISO), American Gear Manufacturers Association (AGMA). Figure 4-1 on page 60, provides a viscosity grade comparison chart and gives a break down of these ratings. The higher the viscosity rating number, the thicker the fluid. Most motor oils have to run at both high and low temperatures, therefore, they are blended for thermal stability (single-grade or multi-grade)

Viscosity Ratings Example: What is the viscosity in SUS of a SAE 30 weight oil (Refer to Figure 4-1 on page 60 of the text)? Answer: About 500 SUS. A SAE 5W-30 oil acts like a 5 weight oil in cold temperatures (100 oF and less) and a 30 weight oil in high temperatures (around 210 oF). The “W” defines the “winter weight” of the oil. A multi-grade oil A single-grade oil

There are 11 viscosity grades used by SAE: 0W, 5W, 10W, 15W, 20W, 25W, 30, 40, 50, 60 Example: Arrange the automotive engine oils shown below by thickness from high to low at high temperatures. Then arrange them by thickness from high to low in cold temperatures. Answer: at high temperature: d, then a and b, then c at cold temperatures: b, then a and d, then c (a) (b) (c) (d)

Terminology Flash point: the lowest temperature at which vapor combines with oxygen and produce a flash when an ignition source is applied. Fluid is considered flammable if flash point is less than 60º C. Fire point: The lowest temperature at which a flame ignites the lubricant vapor. Note that at the flash point, ignition stops when the igniting source is removed but continues at the fire point (flash point is a flash burst, while fire point produces vapor that will sustain a fire). Pour Point: The lowest temperature at which the lubricant will flow by the effect of gravity and still be used – machines that run in low temperatures, need lubricants with low pour point. Color: the color of the lubricant changes due to oxidation and presence of contaminants. Demulsability: The ability of oil to separate from water – water in the lubricant can disrupt the lube film. Consistency: (for greases only) the degree to which grease resists deformation. Classified and tested by penetration depth procedure set by the National Lubricating Grease Institute (NLGI) – softer the grease, lower the number. Bearings use a 1 or 2 grease. Dropping Point: a term used for greases only, it is the maximum temperature before the grease falls through an orifice.

Types of Lubricant Additives Oxidation inhibitors: prevent reaction between lubricant and oxygen from occurring. Oxidation results in oil breakdown and formation of acids. Extreme Pressure (EP) additives: these additives are used to increase the ability of the lubricant to carry high loads, such as in gear lubricants and bearings carrying heavy loads. Defoamants: additives that facilitate the breakup of foam bubbles. Film strengtheners: form films that are attached to the metal surfaces. Detergent Dispersants: they are added to hold dirt particles and suspend them to prevent them from forming engine deposits. Anti-rust additives Viscosity index improvers: most commonly used in making engine oils, they increase the viscosity at high temperatures without changing the viscosity at low temperatures. Pour Point Depressants: to decrease the pour point temperature in cold environments. Demulsifier additives: added to repel water Solid additives

Types of Lubricating Oils There are three types of lubricating oils: Animal/Vegetable Oils: rarely used as additives Mineral/Petroleum Oils: extracted from petroleum Synthetic Oils: synthesized from pure carbon and hydrogen gases in a controlled process. Their viscosity changes very little with temperature.

Types of Lubricating Greases Greases are composed of oils and thickening agents in about 9 to 1 ratio of oil to thickening agent. There are several types of lubricating greases: Lithium Soap – most widespread grease used in industry Calcium Soap: water resistant grease, working well in wet environments Sodium Soap: can be washed away with water, but have good adhesion and sealing properties. Complex Soap – made of mixtures, and created for special and specific applications. Synthetic Greases: fire resistant and can be used over a wide temperature range (-60 to 450 oF) Mineral/Petroleum Oils: extracted from petroleum

Methods of Lubricant Delivery There are five main methods of applying lubricants: Manual methods: such as using a manual grease gun (see figure 4-7 page 76 in text) Drip Methods: use gravity to supply oil drops. Automatic Grease Lubricators: a reservoir is used to supply grease. The grease is put under pressure by the action of a spring to supply grease at a precalculated amount.

Methods of Lubricant Delivery There are five main methods of applying lubricants: Bath method: such as in lubricating chains. Splash and submersion methods: such as in gearboxes, where splashing is performed by the rotating gears. Pressurized lubrication systems: such as in automotive engines.

Review Questions The main purpose of lubricants is to reduce _______ between contacting solids. What are the four forms of lubricants? Liquid, semisolid, solid, and gas lubricants. Name some units for measuring kinematic viscosity: Stoke m2/s Saybolt Universal Seconds (SUS) friction

Review Questions The picture below shows a lubricant case, what type of thickening agent is used in the grease? What does dropping point mean? A complex agent containing lithium soap Dropping point is the maximum temperature that the grease can withstand before it falls through an orifice.

Review Questions What are synthetic lubricants? Which form of lubricants is grease? The picture below shows a lubricant case, what does NLGI stand for? Lubricants that are synthesized from purified carbon and hydrogen gases. Semisolid form NLGI stands for National Lubricating Grease Institute, which classifies greases into grades by their penetration index.

Exercise Refer to the table in figure 4-1 p. 60 in the book, What is the viscosity range for each of the automotive oils shown in the pictures in room temperature? SAE 10W: 165 to 240 SUS SAE 30: 400 to 580 SUS