Lubricants : By: SAHIL BIDANI Lubricants Introduction : Introduction Lubricants are a special category of materials, usually in either liquid or semi-solid state, applied between two or more moving parts in order to reduce the friction between them as well as dissipate the heat produced in them. General Description of Lubricants : General Description of Lubricants Lubricants are solid, liquid or semi-solid materials applied between moving parts to make their movement friction free. Right from the day of their discovery, a wide variety of lubricants have been used, depending upon the requirements of the application. The most commonly used lubricants are grease, oils, graphite etc. These materials, when applied over mechanical parts, allow easy movement of another component over it. This helps to prevent the damage caused by abrasion and friction as well as uneven expansion of the components due to heat. Methods of Lubrication : Methods of Lubrication The lubricants form a thin-film or thick-film over the surface of the components between which it is applied. When the parts move, the thick film aids in easy movement by providing a smooth surface. Also, they absorb friction and heat that is generated between moving parts. The difference between thick and thin films is that thick films completely separate the two moving layers while thin-films maintain some contact between the moving parts. Thin-film lubrication is used when the loads are heavy whereas a thick-film is used for high-speed machines, especially reciprocating and oscillating types. Classification of Lubricants : Vegetable
Synthetic Classification of Lubricants 1. Classification of lubricants according to their sources: Vegetable Lubricants : Examples of vegetable lubricants are:
Animal and vegetable oils have a lower coefficient of friction than most mineral oils but they rapidly wear away steel Vegetable Lubricants Mineral Lubricants : These lubricants are used to a large extent in the lubrication of aircraft internal combustion engines
There are three classifications of mineral lubricants:
Fluid Mineral Lubricants Synthetic Lubricants : Because of the high operating temperatures of gas-turbine engines, it became necessary to develop lubricants which would retain their characteristics at temperatures that cause petroleum lubricants to evaporate and break down
Synthetic lubricants do not break down easily and do not produce coke or other deposits Synthetic Lubricants 2. Classification of lubricants according to their physical state : 2. Classification of lubricants according to their physical state Solid
Liquid Solid Lubricants : Solid Lubricants Solid lubricants e.g., graphite, are in the form of powders and can be applied on machine surfaces where they orient themselves parallel to the surface. When the machine parts move, the graphite particles or lamellas shave over each other, reducing the friction over the machine parts. In graphite lubricant sprays, a thin film of the lubricant is sprayed using the sprayer over the machine surface. After some time, the sprayed lubricant forms a thin coating or film over the surface, which protects the moving parts from friction and heat. Semi-solid Lubricants : Semi-solid Lubricants Greases are commonly used semi-solid lubricants. They are used when liquid lubricants such as lubricating oils cannot be supplied continuously during the operation of the moving machine parts. Greases of various types are available with varying operating temperatures, moisture resistance, and stability over oxidation, etc. Grease actually consists of a base lubricant such as oil, a thickening agent whose job is to keep the lubricant in semi-solid state and additives to improve the performance of the lubricant. They are used in applications requiring low viscosity and are easier to store and handle. Grease is ideal for open gears, chain and cable mechanisms, high temperature and extreme pressure applications. Liquid Lubricants : Liquid Lubricants Oil lubricants are liquid lubricants which are mainly used in automobiles and industrial machines which require a continuous and rather controlled supply of lubricants to the system. Some of them are:
Spindle Oils Slide 13: Hydraulic Oils Hydraulic Oils are used for transmission of energy and lubrication. They also serve as a sealing agent and coolant for transferring heat from one system to another. Their performance is generally enhanced with certain additives as required by the application. Slide 14: Way Oils Way Oils are produced from a base with paraffin content, with additives added for extreme pressure capability.. This reduces the problems of sticking and slipping of machine parts during the process. Slide 15: Spindle Oils Spindle Oils are high quality refined oils which are intended specifically for high speed and light load applications. They have higher oxidation stability and wear resistance. Lubricating Oil Properties : Gravity
Ash Test Precipitation Number
Corrosion and Neutralization Number
Extreme-Pressure (Hypoid) Lubricants
Chemical and Physical Stability Lubricating Oil Properties Gravity : The gravity of petroleum oil is a numerical value which serves as an index of the weight of a measured volume of this product
There are two scales generally used by petroleum engineers:
American Petroleum Institute gravity scale Gravity Flash Point : The flash point of an oil is the temperature to which the oil must be heated in order to give off enough vapor to form a combustible mixture above the surface that will momentarily flash or burn when the vapor is brought into contact with a very small flame Flash Point Viscosity : Viscosity is technically defined as the fluid friction of an oil
To put it more simply, it is the resistance an oil offers to flowing
Heavy-bodied oil is high in viscosity and pours or flows slowly Viscosity Cloud Point : The cloud point is the temperature at which the separation of wax becomes visible in certain oils under prescribed testing conditions
When such oils are tested, the cloud point is slightly above the solidification point Cloud Point Pour Point : The pour point of an oil is the temperature at which the oil will just flow without disturbance when chilled Pour Point Carbon-Residue Test : The purpose of the carbon-residue test is to study the carbon-forming properties of a lubricating oil
There are two methods:
The Ramsbottom carbon-residue test
The Conradson test Carbon-Residue Test Ash Test : The ash test is an extension of the carbon-residue test
If an unused oil leaves almost no ash, it is regarded as pure
The ash content is a percentage (by weight) of the residue after all carbon and all carbonaceous matter have been evaporated and burned Ash Test Precipitation Number : The precipitation number recommended by the ASTM is the number of milliliters of precipitate formed when 10 mL of lubricating oil is mixed with 90 mL of petroleum naphtha under specific conditions and then centrifuged Precipitation Number Applications of Lubricants : Applications of Lubricants Lubricate parts like gears, chains, wheels, bearings etc.
Lubricate the piston movement in engine cylinders.
Lubricate the vanes of turbines and blowers.
Cool engines and pumps by dissipating heat effectively.
Lubricate and cool compressors.
Lubricate spring systems and rollers.