---
title: "Lubricating greases and their functions"
subject: "Engineering Chemistry"
chapter: 8
key: "semester_2/engineering_chemistry:greases-functions"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/greases-functions
site: BCT Engineering
---

# Lubricating greases and their functions

Engineering Chemistry · Chapter 8: Lubricants and Paints

- Asked in: 2069 Bhadra, 1+2 marks; 2067 Mangsir, 1+1 marks; 2067 Chaitra, 2+1 marks (asked 3 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/greases-functions
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-8

## Question

What are lubricating greases? Give their functions.

## Short answer

Lubricating greases are semi-solid lubricants of mineral oil thickened with metallic soaps. They reduce friction under heavy loads, seal out dirt and water, stay in place for infrequent lubrication, protect against corrosion, and absorb shock.

## Answer

**Lubricating greases** are semi-solid lubricants made by thickening a lubricating oil (mineral oil) with a metallic soap (Ca, Na or Li soap of fatty acids). Examples: calcium (cup) grease, sodium (fibre) grease, lithium grease. They are used where liquid oil cannot stay in place, for example in slow-moving, heavily loaded or intermittently working bearings, open gears, chassis and axles, and in machines that cannot be lubricated regularly.

#### Functions of greases
1. Reduce friction and wear between surfaces moving slowly under heavy load.
2. Act as a seal that keeps out dust, dirt and water.
3. Stay in place and need less frequent refilling, so they suit hard-to-reach parts.
4. Protect metal from corrosion.
5. Absorb shock and reduce noise.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is a lubricating grease?
   A. A pure liquid oil
   B. A solid metal
   C. A semi-solid made by thickening mineral oil with a metallic soap
   D. A gas
   Answer: C. Ca, Na or Li soap thickens the oil. (Key point: Composition of grease)

2. When are greases preferred over oil?
   A. In slow-moving, heavily loaded or intermittently working parts and where oil cannot stay in place
   B. In high-speed light bearings
   C. Where cooling is main need
   D. In engines needing circulation
   Answer: A. Greases stay in place. (Key point: Where used)

3. How do greases help keep out contaminants?
   A. They dissolve dust
   B. They produce heat
   C. They are porous
   D. They act as a seal against dust, dirt and water
   Answer: D. Semi-solid consistency forms a seal. (Key point: Seal function)

## Related in Engineering Chemistry

- [Lubricants and their functions](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alubricants-functions) — Engineering Chemistry, chapter 8, asked 4×

## Related in other subjects

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- [Diesel components, lubricating and cooling functions](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-components-lube-cooling) — Power Plant Equipment, chapter 5
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