Lubricants Chapter Questions and Answers | Applied Chemistry | New Topic

A lubricant is a substance that reduces friction between two moving surfaces.
Example: Engine oil, grease, graphite.

Functions of lubricants include:
A. Reducing friction and wear
B. Preventing rust and corrosion
C. Cooling engine or machinery parts
D. Cleaning away dirt or metal particles
E. Sealing gaps between moving parts

Lubricants are used to reduce friction, improve efficiency, prevent wear and tear, and extend the life of machinery.

Example: Graphite or Molybdenum disulphide (MoS₂)
Use: Applied in high-temperature or heavy-load machinery where liquid lubricants fail.

Grease is a semi-solid lubricant made by mixing lubricating oil with a thickening agent such as calcium or lithium soap. It is used where liquid lubricants cannot stay in place.

Types of lubricants:
1. Liquid lubricants: Mineral oil, synthetic oil
2. Semi-solid lubricants: Grease
3. Solid lubricants: Graphite, MoS₂

Synthetic lubricants are man-made oils designed for high performance.
Examples:
Silicone oil – used in jet engines
Ester-based oil – used in aircraft and high-speed machines

Lubricant selection depends on:
A. Operating temperature and load
B. Speed of machine
C. Type of motion (sliding, rolling, etc.)
D. Environmental conditions (dust, moisture, etc.)

Common additives:
1. Antioxidants
2. Detergents and dispersants
3. Corrosion inhibitors
4. Anti-wear agents
5. Viscosity index improvers

Additives enhance performance by reducing oxidation, foaming, and corrosion, maintaining viscosity, and improving lubrication under extreme conditions.

Effectiveness can be improved by:
1. Using proper additives
2. Maintaining cleanliness and correct viscosity
3. Regular replacement and filtration

Flash point: The lowest temperature at which oil vapors ignite momentarily.
Fire point: The temperature at which oil burns continuously for at least 5 seconds.

Grease is used in:
1. Ball bearings and roller bearings
2. Gears and joints
3. Places where continuous lubrication is difficult

Engine oil: Used in automobile engines.
Gear oil: Used in gearboxes and transmission systems.

Silicone oil: Used in jet engines and high-temperature machines.
Ester-based lubricant: Used in aircraft turbines and racing vehicles.

Graphite – used in locks, high-temperature, and high-pressure machinery.