Coolants are fluids used during machining.

These improve surface finish.

There is a reduction in rejection. Makes

manufacturing cheap.


Use Cutting fluid during machining operations such as

(i) turning

(ii) drilling

(iii) reaming

(iv) grinding

(v) stamping

(vi) milling.

It reduces friction. Also, reduces power requirements. It cools the tool and the work piece.  Cooling of the cutting tool maintains its cutting ability and hence increases the tool life. It increases the rate of production. Cooling of the work piece saves it from thermal deformation and improves the surface finish. Thus reduces number of final rejections.  The value of product is increases because of improved surface finish.

Different types of cutting fluids

(i) water

(ii) soap solution

(iii) oils

(iv) oil-water emulsions

(v) pastes

(vi) gels

(vii) aerosols

(viii) air or other gases

 Used in different machining operations. Water is cheap and best but causes rust. Therefore add something to water to make it a better cooling cutting fluid.

Functions of a Cutting Fluid

  • Does effective cooling

  • Provide good lubrication

  • Prolong cutting-tool life

  • Assure rust protection

  •  permit less heat production

  •  reduce power consumption

Desirable Qualities of a cutting fluid

  1. Good cooling capacity

  2. Good lubricating qualities

  3. No bad odor

  4. Transparent

  5. Low viscosity

  6. should be Nonflammable

  7. Non decomposable

  8.  Non- corrosive

  9. Non-toxic

  10. Easy separation from work piece and chips

  11. Quick setting of grit and fine chips make their recirculation difficult with the coolant

  12.  It should be safe to use.

  13. Resistant to fungus growth.

  14. Resistant to bacteria and mold growth.

  15. Requires no additives to preserve a fresh, clean product.


  1. Reduces rusting

  2. Reduce power requirements for machining

  3. Increases tool life

  4. Improves surface finish on the work piece

  5. Reduce heat generation during cutting

  6. It breaks the chips into small pieces.

  7. Removes the chips away from the tool.

  8. Reduces work piece rejections

  9. It permits higher speed which reduces machining time

  10. Increases rate of production

  11. Decreases cost of production

  12. Easy separation of chips from the work piece

  13. Quick setting of grit and fine chips avoid their recirculation with the cooling fluid

Examples of cooling fluids

  1. Straight oils

                   Petroleum oils

  1. Soluble oils

          These oils form an emulsion with water. In this, a base mineral oil emulsifiers produce a stable emulsion. Use these in a diluted form (usual concentration is 3 to 10%). These are in common use. They are least expensive among all cutting fluids. These are available as Apex 9900, Apex 9800, Apex 9500

  1. Synthetic fluids

        Form synthetic fluids from alkaline inorganic and organic compounds along with additives for corrosion inhibition. Use these in a diluted form (usual concentration is 3 to 10%). Synthetic fluids have the best cooling performance among all cutting fluids.

  1. Semi-synthetic fluids— Semi-synthetic fluids are the combination of synthetic and soluble oil having properties of both. Their cost is in between the cost of synthetic and soluble oil fluids.

  2. Lord oil with mineral oil  used with steels.

  3. Sulphur brass oil with mineral oil  used with alloy steels.

  4. Soluble oil with 90 to 95% of water  used with copper.

  5. Mineral oil with soluble oil  used with aluminum.

  6. No cutting fluids  used with cast iron.


Refractometers measure the concentration of emulsions. pH meters measure the pH value. Biocides added to reduce bacteria growth. Particulate matter separated with a centrifuge. These degrade with the passage of time reject these. Before disposal, treat these with chemicals harmless to the living beings and the environment.

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