2103 - MIDTERM Flashcards
Oil also exhibits excellent wetting characteristics because the oil film has an ability to evenly coat metal surfaces. This characteristic of oil makes it a good sealing agent between moving parts.
Seals
The same characteristic of oil that makes it a good sealing agent also provides a cushioning effect between metal parts. For example, the thin film of oil between a rocker arm and its bushing absorbs some of the hammering shock from the valve action. The cushioning action also helps reduce some of the impact force between a crankshaft and its connecting rods.
Cushions
The oil in a lubrication system also reduces engine wear by serving as a cleaning agent. As the oil circulates, it picks up foreign particles such as dirt, dust, carbon, and small amounts of water. These particles are held in suspension by the oil and carried to a filter where they are trapped and removed
Cleans
Metal engine parts which are exposed to moist air and various chemicals have a tendency to rust or form other types of surface corrosion. This is especially true for cylinder walls and crankshafts which have been hardened by nitriding. The oil film which coats internal engine parts acts as a barrier, preventing oxygen and moisture from reaching the metal surface and causing
it to corrode
PROTECTS AGAINST CORROSION
CLASSIFICATIONS LUBRICANTS ACCORDING TO PHYSICAL STATE AS FOLLOWS
Liquid Lubricants or Lubricating Oil
Vegetable Oil and Animal Oil
Mineral Oil
Blended Oil
Semi Solid or Grease
Solid Lubricants
REDUCES FRICTION AND WEAR BETWEEN TWO MOVING/SLIDING METALLIC SURFACES BY PROVIDING A CONTINUOUS FLUID FILM IN BETWEEN THEM. THEY ALSO ACT AS:
a. COOLING MEDIUM
b. SEALING AGENT
c. CORROSION PREVENTER
GOOD LUBRICATING OIL MUST POSSES
LOW PRESSURE ( HIGH BOILING POINT)
ADEQUATE VISCOSITY FOR PARTICULAR SERVICE CONDITION
LOW FREEZING POINT
HIGH OXIDATION RESISTANT
HEAT STABILITY
NON – CORROSIVE PROPERTIES
STABILITY TO DECOMPOSITION AT THE OPERATING TEMPERATURE
ARE OBTAINED BY DISTILLATION OF PETROLEUM. THE LENGTH OF THE HYDROCARBON CHAIN IN PETROLEUM OIL VARIES BETWEEN ABOUT 12 TO 50 CARBON ATOMS. THE SHORTER CHAIN OIL HAVE LOWER VISCOSITY THAN THE LONGER CHAIN HYDROCARBONS.
THESE ARE THE MOST WIDELY USED LUBRICANTS, BECAUSE THEY ARE:
A. CHEAP
B. AVAILABLE IN ABUNDANCE
C. QUITE STABLE UNDER SERVICE CONDITIONS.
HOWEVER THEY POSSES POOR OILINESS AS COMPARED TO THAT ANIMAL AND VEGETABLE OILS TILE OILINESS OF PETROLEUM OILS CAN BE INCREASED BY THE ADDITION OF HIGH MOLECULAR WEIGHT COMPOUND LIKE OLEIC ACID, STEARIC ACID ETC.
MINERAL or PETROLEUM OIL
OILINESS OF A LUBRICANT CAN BE INCREASED BY ADDITION OF AN OILINESS-CARRIER LIKE VEGETABLE OILS (E.G., COCONUT OIL, CASTOR OIL) AND FATTY ACIDS (LIKE PALMITIC ACID, STEARIC ACID, OLEIC ACID. ETC.).
OILINESS CARRIERS
THESE ADDITIVES CONTAIN CERTAIN MATERIALS WHICH ARE ABSORBED ON THE METAL SURFACE OR REACT CHEMICALLY WITH METAL, PRODUCING A SURFACE A LAYER OF LOW SHEARSTRENGTH ON THE METAL SURFACE, THEREBY PREVENTING THE TEARING UP OF THE METAL.
EXTREME-PRESSURE ADDITIVES THESE ADDITIVES
DEPRESSING ADDITIVES USED ARE PHENOL AND CERTAIN CONDENSATION PRODUCTS OF CHLORINATED WAX WITH NAPHTHALENE. THESE PREVENT THE SEPARATION OF WAX FROM THE OIL.
POUR-POINT
WHEN ADDED TO OIL, RETARD OXIDATION OF OIL BY GETTING THEM- SELVES PREFERENTIALLY OXIDIZED. THEY ARE PARTICULARLY ADDED IN LUBRICANTS USED IN INTERNAL COMBUSTION ENGINES, TURBINES, ETC., WHERE OXIDATION OF OIL IS A SERIOUS PROBLEM. THE ANTIOXIDANTS ARE AROMATIC, PHENOLIC OR AMINO COMPOUNDS.
ANTIOXIDANTS OR INHIBITORS
ARE ORGANIC COMPOUNDS OF PHOSPHORUS OR ANTIMONY. THEY PROTECT THE METAL FROM CORROSION BY PREVENTING CONTACT BETWEEN THE METAL SURFACES AND THE CORROSIVE SUB
CORROSION PREVENTERS
ARE DETERGENTS SUCH AS THE SALTS OF PHENOL AND CARBOXYLIC ACIDS. DEPOSITS ARE FORMED IN INTERNAL COMBUSTION ENGINE,
DUE TO IMPERFECT COMBUSTION. SUCH ADDITIVE DISPERSES AND CLEANS THE DEPOSITS.
DEPOSIT INHIBITORS
HAVE HIGHER SHEAR OR FRICTIONAL RESISTANCE THAN OILS AND, THEREFORE, CAN SUPPORT MUCH HEAVIER LOADS AT LOWER SPEEDS. THEY ALSO DO NOT REQUIRE AS MUCH ATTENTION UNLIKE THE LUBRICATING LIQUIDS. BUT GREASES HAVE A TENDENCY TO SEPARATE INTO OILS AND SOAPS.
GREASE or
SEMI SOLID LUBRICANTS
