Lubricants and Coolants MCQ Quiz - Objective Question with Answer for Lubricants and Coolants - Download Free PDF

Explanation:

Function of Coolants in Metal Cutting or Machining Operations

Definition: Coolants are essential fluids used in metal cutting or machining operations to manage the heat generated during these processes. The primary function of coolants is to enhance the efficiency of the cutting operation by maintaining the temperature within manageable limits, ensuring the longevity of the tool, and improving the quality of the finished product.

Working Principle: During metal cutting or machining, friction between the tool and the workpiece generates significant heat. Excessive heat can lead to tool wear, deformation of the workpiece, and poor surface finish. Coolants act by absorbing this heat and carrying it away from the cutting zone, reducing the temperature of both the tool and the workpiece. This cooling effect is crucial for maintaining the integrity of the tool and the quality of the machining process.

Benefits of Using Coolants:

• Decreased Adhesion Between Chip and Tool: Coolants reduce the adhesion between the chip and the tool, which is the primary function of coolants in metal cutting. This reduction in adhesion minimizes the chances of built-up edge (BUE) formation on the tool, resulting in a smoother surface finish and better dimensional accuracy of the workpiece.
• Reduced Tool Wear: By effectively managing the heat generated during cutting, coolants reduce the wear and tear on cutting tools. This leads to longer tool life and fewer tool replacements, contributing to reduced operational costs.
• Improved Surface Finish: The cooling action of coolants helps in achieving a better surface finish on the workpiece. This is because lower temperatures reduce the chances of thermal deformation and ensure cleaner cuts.
• Enhanced Machinability: Coolants help in reducing cutting forces, making the machining process smoother and more efficient. This improved machinability allows for higher cutting speeds and feeds, increasing productivity.
• Lubrication: Besides cooling, coolants also provide lubrication between the tool and the workpiece. This lubrication reduces friction, further contributing to the reduction in heat generation and tool wear.

Applications: Coolants are widely used in various machining operations such as turning, milling, drilling, and grinding. They are indispensable in industries where precision and surface quality are critical, such as aerospace, automotive, and manufacturing sectors.

Explanation:

For machining yellow metals and free-cutting steels, water soluble oils are used as cutting fluids.

Reason: When it comes to machining yellow metals (such as brass and bronze) and free-cutting steels, the choice of cutting fluid is crucial to ensure efficient machining, good surface finish, and prolonged tool life. Water soluble oils, also known as emulsifiable oils, are widely preferred for these materials due to their excellent cooling and lubricating properties.

Properties of Water Soluble Oils:

• Water soluble oils are a blend of oil and emulsifiers that allow the oil to mix with water, creating a stable emulsion.
• They provide superior cooling by dissipating heat generated during the cutting process, which is essential for maintaining the integrity of both the tool and the workpiece.
• The lubricating properties of the oil reduce friction between the cutting tool and the workpiece, minimizing wear on the tool and improving the surface finish of the machined part.
• Water soluble oils are also effective in flushing away chips and debris from the cutting area, preventing them from interfering with the machining process.

Advantages of Using Water Soluble Oils:

• Enhanced cooling capacity due to the water content, which helps in maintaining lower temperatures during machining.
• Improved lubrication compared to water alone, reducing friction and wear on cutting tools.
• Better chip evacuation, which helps in maintaining a cleaner cutting zone and reducing the risk of chip-related damage.
• Cost-effective as they can be diluted with water, reducing the overall consumption of oil.
• Environmentally friendly compared to pure oils, as they are less likely to cause pollution and are easier to dispose of.

Applications: Water soluble oils are commonly used in various machining operations, including turning, milling, drilling, and grinding, especially when working with yellow metals and free-cutting steels.

Analysis of Other Options:

Option 2: Germicides and Water

While germicides and water might be used in certain industrial processes for sanitation purposes, they are not suitable as cutting fluids for machining yellow metals and free-cutting steels. Germicides are primarily used to kill bacteria and other microorganisms, and they do not provide the necessary lubrication and cooling required for machining operations. Additionally, water alone does not offer adequate lubrication and can lead to increased tool wear and poor surface finish.

Option 3: Water

Water, by itself, is not an ideal cutting fluid for machining operations. Although it provides excellent cooling due to its high specific heat capacity, it lacks the lubricating properties needed to reduce friction between the cutting tool and the workpiece. This can result in increased tool wear, higher cutting forces, and poor surface finish. Therefore, water is typically used in combination with soluble oils or other additives to enhance its lubricating properties.

Option 4: Insoluble Oils

Insoluble oils, also known as neat oils, are used in certain machining operations, but they are not the best choice for yellow metals and free-cutting steels. These oils provide good lubrication but lack the cooling properties of water-based fluids. They can lead to higher cutting temperatures, which may negatively impact the machining process and the quality of the finished part. Insoluble oils are more commonly used in operations where cooling is less critical, such as in heavy-duty cutting of ferrous materials.

In conclusion, water soluble oils are the most suitable cutting fluids for machining yellow metals and free-cutting steels due to their excellent combination of cooling and lubricating properties, which enhance tool life, improve surface finish, and ensure efficient machining operations.

Explanation:

There are 3 systems of lubrication.

Splash feed system: 

• It is also known as the Ring Oiling system. 
• In this method the shaft, or something attached to it, actually dips into the oil and a stream of lubricant is continually splashed round the parts requiring lubrication.
• This method is employed for the gears and bearings inside all gear drives, the lower parts of the gears actually dipping in the oil.
• A common method of employing splash lubrication is known as ‘ring oiling’.

Gravity feed system: 

• There are numerous ways of employing this principle, varying from the simple oil hole to the more elaborate wick and glass-sided drip feed lubricators in which the flow of the oil may be controlled and observed through the glass.

Force feed system: 

There are various systems of lubrication employing a pressure feed to the lubricant, and the most important of such systems may be classified roughly into the following:

• Continuous feed of oil under pressure to each bearing concerned. In this method an oil pump driven by the machine delivers oil to the bearings and back to a sump from which it is drawn by the pump.
• Pressure feed by hand pump in which change of oil is delivered to each bearing at intervals (once or twice a day) by the machine operator.
• Oil or grease gun method in which the oil hole leading to each bearing is fitted with a nipple and by pressing the nose of the gun against this and the lubricant is forced into the bearing.

Explanation:

• For effective cutting of steel with a hand hacksaw, the most suitable coolant would be Cutting oil.
• Cutting oil is commonly used as a coolant during metal-cutting operations.
• It provides lubrication to the cutting process, reducing friction and heat generation.
• The use of cutting oil helps in extending the tool life, improving cutting efficiency, and obtaining smoother cuts.
• It also helps in clearing away metal chips or swarf from the cutting area.
• While options such as grease, lard oil, and kerosene oil may have certain lubricating properties, they may not be as effective as cutting oil specifically formulated for metal-cutting purposes.
• Therefore, cutting oil is generally the preferred coolant for hand hacksaw operations on steel.

Explanation:

Coolants (Cutting fluids):

• Coolants (Cutting fluids) play an important role in reducing the wear of cutting tools.
• Coolants (Cutting fluids) are essential in most metal-cutting operations.
• During a machining process, considerable heat and friction are created by the plastic deformation of metal occurring in the shear zone when the chip slides along the chip tool interface.
• This heat and friction cause the metal to adhere to the cutting edge of the tool, and the tool may break down.
• The result is poor finish and inaccurate work.
• The reason why cast iron can be machined without using coolants is that the graphite in the cast iron acts as a lubricant in itself.
• So it is generally dry for its self-lubricating property.

Recommended cutting fluids for various metals:

A lubricant is a substance, which reduces friction between mating parts. Lubricants are grouped into three categories.

1. Liquid lubricants: Some of the most commonly used liquid lubricants are mineral oil, fatty or vegetable oils, synthetic oils.
2. Semi-liquid lubricants: Greases are most commonly used lubricants with a higher viscosity than oils. These are employed for slow speed and heavy pressure operations like drawing, rolling and extrusion processes.
3. Solid lubricants: Graphite is the commonly used solid lubricant. Other types of solid lubricants are soapstone, talc, French chalk etc.

Concept:

There are 3 systems of lubrication.

Splash feed system: 

• It is also known as the Ring Oiling system. 
• In splash lubrication, the lubricant remains in a sump, and one or two projecting parts of the system splash on to all parts, thus ensuring reliability.

• Gravity feed system: Oil holes, Oil cups, and wick feed lubricators

• Force feed system: Oil, grease gun and grease cups and Oil pump method

Explanation:

Pour point 

• The temperature at which the lubricant is able to flow when poured or
• It is the temperature below which the liquid loses its flow characteristics.

Dynamic viscosity (μ)

• It is the property of a fluid that offers resistance to the movement of one layer of fluid over the adjacent layer of the fluid.
• Shear stress between two layers of fluid is directly proportional to the rate of change of velocity with respect to perpendicular distance from a fixed point.
• Unit – kgm^-1s^-1

Kinematic Viscosity (ϒ):

• It is the ratio of dynamic viscosity to the density of fluid flowing
• \({\rm{Kinematic\;Viscosity\;}}\left( {\rm{\gamma }} \right) = {\rm{\;}}\frac{{{\rm{Dynamic\;viscosity\;}}\left( {\rm{\mu }} \right)}}{{{\rm{density\;}}\left( {\rm{\rho }} \right)}} \)
• Unit is – m²s^-1

Important Points

With the movement of the two mating parts of the machine, heat is generated. If it is not controlled the temperature may rise resulting in total damage to the mating parts. Therefore, a film of a cooling medium with high viscosity is applied between the mating parts which are known as a lubricant.

Properties of lubricant

Explanation:

A lubricant is a substance, which reduces friction between mating parts. Lubricants are grouped in three categories.

1. Liquid lubricants: Some of the most commonly used liquid lubricants are mineral oil, fatty or vegetable oils, synthetic oils.
2. Semi-liquid/solid lubricants: Greases are most commonly used lubricants with a higher viscosity than oils. These are employed for slow speed and heavy pressure operations like drawing, rolling and extrusion processes.
3. Solid lubricants: Graphite is the commonly used solid lubricant. Other types of solid lubricants are soapstone, talc, French chalk etc.

Explanation:

• A lubricant is a substance used to reduce friction between surfaces in mutual contact
• It will reduce the interlocking of the irregularities (Friction) of the surfaces
• The property of reducing friction is known as lubricity (slipperiness)
• They can be grouped as:
  • Liquid Lubricants: Mineral Oil (paraffin, naphthalene, and aromatics), Fatty and vegetable oils (Animal oils, tallow, lard, castor oil, olive oil, rosin oils, etc), Synthetic oils
  • Semi-Liquid Lubricants: Greases, calcium, sodium, etc
  • Solid Lubricants: Graphite, soap-stone, talc, French chalk, etc.

Explanation:

Lubricant:

• With the movement of two mating parts of the machine, heat is generated.
• If it is not controlled, the temperature may rise resulting in total damage to the mating parts.
• Therefore a film of cooling medium with high viscosity is applied between the mating parts which are known as a ‘lubricant’.
• A ‘lubricant’ is a substance having an oily property available in the form of fluid, semi-fluid, or solid-state.
• It is the lifeblood of the machine, keeping the vital parts in perfect condition and prolonging the life of the machine.
• It saves the machine and its parts from corrosion, wears, and tears and it minimizes friction.
• The primary purpose of the lubrication system is to lubricate sliding surfaces and reduce friction losses in the engine while others are coming under secondary purposees.
• Purpose of using lubricants
  • Reduces friction
  • Prevents wear
  • Prevents adhesion
  • Aids in distributing the load
  • Cools the moving elements
  • Prevents corrosion
  • Improves machine efficiency

Explanation:

• Cutting fluids and compounds are the substances used for efficient cutting while cutting operation take place.
• Types of cutting fluids:
  • Straight mineral oil
  • Chemical solution (synthetic fluids)
  • Compounded or blended oil
  • Fatty oils
  • Soluble oil (Emulsified oil-suds)

Soluble oil (Emulsified oil)

• Water is the cheapest coolant, but it is not suitable because it causes rust to ferrous metals. 
• An oil called soluble oil is added to water which gets a non-corrosive effect with water in the ratio of about 1 : 20.
• It dissolves in water giving a white milky solution.
• Soluble oil is an oil blend mixed with an emulsifier.
• It is most common type of cutting fluid used in almost all the machining operation.

Explanation:

Cutting fluid

Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases.

Various functions of cutting fluids are

1. Cutting fluid cools the workpiece and tool by carrying away the heat generated during machining
2. It acts as a lubricant at the friction zones, hence tool life increases
3. It prevents the corrosion of chips and machine
4. As friction get reduced, the forces and electric power consumption decreases
5. Using cutting fluids produces a better surface finish to the workpiece
6. It causes to break the chips into small pieces
7. It washes away the chips from the tool
8. Improves dimensional accuracy and control on the workpiece

Explaination:

Lubricant grease:

• Lubricant grease is a solid to semi solid dispersion of a thickening agent in a liquid lubricant.
• Grease normally used under the condition of lubrication for which oil is not suitable or convenient.
• Grease is considered to a liquid lubricant gelled by a dispersed solid.
• The term dropping point is used to define the temperature at which grease passes to a liquid state through either gross melting or separation of the oil phase.
• Electron microscope is an extremely useful tool in the study of grease structure. 

Explanation:

• A system, which controls the temperature, is known as a cooling system. 
• Types
• There are two types of cooling systems:
  • Air cooling system 
  • Water-cooling system
• To know the leakage point in the cooling system, we need to increase the pressure of the fluid (air or liquid), i.e. for inspection of the cooling system, we required dynamic tests.