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Lubricant functions; solid lubricants

Short answer

Lubricants reduce friction, wear, heat, seal, prevent corrosion, clean, and save energy. Solid lubricants like graphite and MoS₂ have a layered structure and are used at very high temperatures, extreme loads, in vacuum, or where oil would contaminate or cannot stay.

Write the important functions of lubricant. What are solid lubricant and specify in which conditions it is used.

Important functions of lubricants

  1. Reduces friction between moving surfaces by forming a thin film that separates them.
  2. Reduces wear and tear, which increases the life of machine parts.
  3. Acts as a coolant: carries away heat produced by friction.
  4. Acts as a seal: prevents leakage of gases, e.g. between piston rings and cylinder.
  5. Prevents corrosion by coating metal surfaces from air and moisture.
  6. Cleans by washing away dirt, metal particles and carbon deposits.
  7. Saves energy: smoother motion means less power loss and higher efficiency; also reduces noise and vibration.

Solid lubricants

Solid lubricants are solids with a layered structure that slide easily over each other, such as graphite, molybdenum disulfide (MoS₂), talc and soapstone. They are used where oils and greases fail:

  • at very high temperatures (graphite up to about 450 °C in air) where oil burns or evaporates;
  • under extremely heavy loads and very slow speeds where an oil film would be squeezed out;
  • in vacuum or at very low temperature;
  • where oil would contaminate the product (food, textile, paper machines) or collect dust;
  • as an additive or dry film on parts that cannot be lubricated often.

✓ Answer checked by Claude Opus 5.5 (high effort)

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