COOLANT AND LUBRICANTS

 A lubricant is a substance placed between two mating surfaces in order to separate them by a thin film reducing the intensity of friction & ensuring a smooth operation. 

PURPOSE OF LUBRICANT 

1. To reduce friction 

2. To prevent wear 

3. To prevent adhesion 

4. To prevent Corrosion (rust) 

5. To cool the moving elements. 

6. To cool the surfaces by washing away the metal particles resulting from wear. 

7. To ensure a speedy & noiseless operation. 

8. To extend the overhaul & services life of the machine. 

9. To aid sealing in bearing against the entrance of dirt/ dust. 

10. Sometimes as in hydraulic equipments the lubricant actually serves to transmit power one part to another part. 

11. To carry away heat generated by friction 

12. To reset oxidation 

13. To add in distributing the load

Mineral Oil: -

Mineral oils are mostly used for engine & m/c lubrication as they are cheap & durable. 

They are complex mixture of hydrocarbons & are obtained from fractional distillation of 

petroleum. They are less viscous but have more oiliness than the fatty oils. 

Vegetable: - 

Vegetable oils & Animal oils are also called fatty oils. Their viscosity does not change 

even at every high temperature, but due to excessive heat they are liable to decompose 

forming acids which are injurious to the metals of mating parts. 

Synthetic oil: - 

Synthetic oil may be defined as an organic fluid derived by synthesis or as any fluid other 

than petroleum having lubricating properties. They are specific hydrocarbons or more 

properly, the fluids with oily characteristics not usually obtained directly from petroleum. 

Semi-Liquid / Semi Solid Lubricants: -

Generally such lubricants are prepared as a mixture of mineral & fatty oils. Such lubricants have no flow at atmospheric temperature. So they are called as SEMI- LIQUID or SEMI- SOLID lubricants. All verities of greases fall in this category. This is used for the lubricants of heavy & slow speed m/ cs, gear- tooth, ball & roller brags, moving m/c parts at a high pressure & parts needing lubricants after certain time. 

 Solid Lubricants: -

French chalk, Graphite, Soap stone, Wax, Mica etc. are used as solid lubricants. A solid lubricant is used for those parts where oil-film can retain its thickness due to high pressure & temperature. They are also called in-organic lubricants. 

Properties of Lubricants: - 

A good lubricant should have following qualities for the sake of its satisfactory working. 

They are 

1. Minimum co-efficient of friction 

2. Maximum film strength 

3. Physical stability against oxidation 

4. Chemical stability against oxidation 

5. Resistance to emulsion (a mixture of oil & water which does not separate into 

component is called as EMULSION. 

6. Non-volatile 

7. High specific heat 

8. Proper fluidity at low temp.

9. High flash-point 

10. High pour-point 

11. Resistance to carbon formation 

COOLANT

Cutting fluids or coolants are liquid & gases applied to the tool & work piece to assist in the cutting operation. 

Purpose of Coolant: -

Coolants are used for the following purpose: - 

• It carries off the heat & thereby prevents a dangerous rise of temperature (400 degree F to 1100 degree F). 

• Ii lubricants the chips, work piece & tool. Thus reduce the heat friction. 

• It improves finish on the job & saves it from rusting. 

• It increases the life of the tool. 

• It flushes out chips & keeps the cutting point clear. 

• Sometimes a cutting fluid prevents the expansion of the work due to the heat. 

• It improves machine ability & reduces machining forces 

• To prevent welding of chips or tools 

Properties of Coolant: - 

• A cutting fluid should have the following properties. 
•  High heat absorption for readily absorbing the heat. 
• 
  It should have low co-efficient of friction. 
• 
  High flash point to eliminate the hazards of fire.
•  Neutral, so as not to oxide in the air. 
• 
  Odorless, so as not to produce bad smell when heated. 
• 
  Harmless to the skin of the operator. 
• 
  Harmless to the bearings. 
• 
  Non-corrosive to the work / Machine. 
• 
  Transparent, so that the cutting action of the tool may be observed. 
• 
  Low viscosity to permit free flow of the liquid. 
• 
  Low price to minimize the production cost. 
• 
  Should have low evaporation rate & should not fame.

Types of Cutting Fluids/ Coolants: - 

The detailed classification of cutting fluids is shown in the figure. The are broadly 

classified into four parts. 

(i) Neat oil 

(ii) Soluble oil 

(iii) Synthetic coolant 

(iv) Gaseous fluids 

Besides these four fluids, a true solution, which is nothing but water mixed with corrosion inhibitors, is also in use. The true solution is effective as a coolant, but extremely poor as a lubricant. The use of true solution is restricted only to grinding & even here it is not widely used. Owing to its low lubricants property, it is difficult get a fine surface finish with a true solution.

Difference between Coolant & Lubricant

Lubricant 

1) A lubricant is a substance that is used between to rubbing surfaces to reduce friction by preventing a moving part from coming into contact with its support parts. 

2) It increases the life of the m/c components 

3) It carries away the metal particles 

resulting from wear. 

 4) It carries away the heat resulting from two rubbing surfaces. 

5) Some times it works as a power 

transmitter in hydraulics. 

 6) It serves as a coolant in some cases. 

7) It provides smoothness 7) It provides better finish on the surface 

8) It is found in liquid, solid, semi-liquid & liquid state. 

Coolant

1) A coolant is a substance which brings is applied to the tool & work piece to assist in the cutting operation.

2) I increase the life of the cutting tool.

3) It carries away the chips from finished surface.

4) It carries away the heat from the tool & work piece.

5) It does not serve to transmit power.

6) It does not serves as a coolant

7) It provides better finish on the surface

8) In addition it is also found in gases state also.