Grinding MCQ Quiz in తెలుగు - Objective Question with Answer for Grinding - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Explanation:

• The Grinding wheel is a multipoint cutting tool having abrasive particles bonded together and so forming a structure.
• Generally abrasive properties like hardness, toughness and resistance to fracture uniformly abrasives are classified into two principal groups:

Natural abrasives: The natural abrasives are emery and corundum. These are impure forms of aluminium oxide.

Artificial abrasives: Artificial abrasives are silicon carbide and aluminium oxide.

Additional Information

• Silicon Carbide: It is less hard than diamond and less tough than aluminium oxide. It is used for grinding of materials of low tensile strength like cemented carbide, stone and ceramic, grey cast iron, copper, brass, bronze, aluminium, vulcanized rubber, etc.
• Aluminium Oxide: Aluminium oxide is tough and fracture resistant. It is preferred for grinding of materials of higher tensile strengths like steel; high carbon and high-speed steel and tough bronze.

Concept:

A grinding wheel consists of the abrasive that does the cutting, and the bond that holds the abrasive particles together.

A standard marking system is used to specify and identify grinding wheels.

The following is the sequence of arrangement:

Abrasive type – Grain size – Grade of bond – Structure – Bond type

Let us understand it with an example

• Abrasive type: ‘A’ for aluminium oxide, ‘C’ for silicon carbide
• Grain size: They are indicated by a number ranging from 10 (coarse) up to 600 (very fine)
• Grade of bond: It shows the hardness of the grinding wheel. The grades range from ‘A’ indicating light or ‘soft’ bond to ‘Z’ indicating a firm or ‘hard’ bond
• Structure: This structure is indicated by a number from 1 to 12. The higher numbers indicate a progressively more open structure. It is the optional specification.
• Bond type: V – Vitrified, S – Silicate, B – Resinoid, R – Rubber, E – Shellac, O – Oxychloride

Explanation:

Loading

• The grinding wheel is said to be loaded when the metal particles get embedded in the wheel surface blocking the interspaces between cutting grains.
• Loading is generally caused during the grinding of soft and ductile materials.
• A loaded, grinding wheel cannot cut properly. Such a grinding wheel can be cleared and sharpened by means of a process called dressing.

Additional Information

Truing

• Truing is the operation of changing the shape of the grinding wheel as it becomes worn from an original shape, owing to the breaking away of the abrasive and bond.
• Truing is done to make the periphery of the wheel concentric with its axis and to make its side true and this way to recover the lost shape of its face. Truing is in fact done on glazed wheels.
• Wheel truing is defined as the act of restoring the cutting face of a grinding wheel by removing the abrasive material from the cutting face and sides of the wheel so that it will run true with respect to the axis of rotation and produce perfect round or flat work.
• The wheel truing procedure involves the use of a diamond – pointed tool that is fed slowly and precisely across the wheel as it rotates.

Dressing

• Dressing of the wheel is done to recover proper cutting action of the wheel face by removing the layer of dulled grains or grains clogged with foreign material. Dressing removes the loading of the wheel.
• Wheel dressing is defined as the act of improving the cutting action. It can also be described as a sharpening operation. 

Explanation:

Truing:

• Truing is the operation of changing the shape of the grinding wheel as it becomes worn from an original shape, owing to the breaking away of the abrasive and bond.
• Truing is done to make the periphery of the wheel concentric with its axis and to make its side true and this way to recover the lost shape of its face. Truing is in fact done on glazed wheels.
• Wheel truing is defined as the act of restoring the cutting face of a grinding wheel by removing the abrasive material from the cutting face and sides of the wheel so that it will run true with respect to the axis of rotation and produce perfect round or flat work.
• The wheel truing procedure involves the use of a diamond – pointed tool that is fed slowly and precisely across the wheel as it rotates.

Additional Information

Dressing:

• Dressing of the wheel is done to recover proper cutting action of the wheel face by removing the layer of dulled grains or grains clogged with foreign material. Dressing removes the loading of the wheel.
• Wheel dressing is defined as the act of improving the cutting action. It can also be described as a sharpening operation. 

Concept:

• As the name implies, the work is not supported on the centres, as in cylindrical grinding machine, but is held against the face of the grinding wheel by the combined action of a supporting rest and a control wheel for regulating the wheel.
• Centreless grinders are basically cylindrical grinders only, but they differ from center-type cylindrical grinders in that the work, instead of being held between centers, is supported by a combination of a grinding wheel, a regulating wheel, and a work rest blade
• Work is revolved and traversed across the face of to grinding wheel while being supported on the work rest blade
• The cutting pressure of the grinding wheel and regulating wheel keeps the workpiece in contact with the work rest blade
• The workpiece is not only revolved but also simultaneously given an axial movement by the regulating wheel and guides to pass between the wheels.

• Centreless grinding is a high – production process for continuously grinding cylindrical surface in which the workpiece is supported not by centres (hence the term centreless) or chucks, but by a blade.

Explanation:

The code ‘V’ represents the bond.

Designation of Grinding Wheel:

Prefix / Suffix: These are the secret codes used by the manufacturers to represent the wheel by its size and shapes respectively.

Type of Abrasives / Grain type:

• It indicates materials used for the manufacturing of abrasive particles.
• Out of the abrasives B4C is giving the poor performance during machining and diamond is very costly, therefore Al2O3 or SiC is the most commonly bused abrasives in the grinding wheel.
• Al2O3 soft and tougher than the SiC whereas SiC will be hard and brittle than Al2O3
• The type of abrasive is selected based on the mechanical properties of workpiece material I.e. for machining of soft and ductile workpieces, Al2O3, and machining of hard and brittle workpiece SiC will be used.   
• A- Al2O3, B – B4C, C – SiC, D - Diamond

Grain size or Grit size:

• It indicates the size of abrasive particles.
• i.e. Side if abrasives = 1/ Grain Size Number(GSN)
• when the GSN > 600, the size of the abrasive particles becomes very very small and it cannot act as a cutting tool, therefore MRR is less.
• When GSN < 600, the actual size of the abrasive is increasing, the chip size is increasing and MRR is increasing.
• As the GSN is reducing or the size of the abrasive is increasing, the MRR is increasing first and then reducing.
• The grain size is selected based on the surface finish required on the workpiece i.e. for a rough grinding, course or medium grain size is selected and for finished grinding fine or very fine grain size will be selected.
• 10-24= Coarse, 30-60 = Medium, 80 -180 = Fine, 220 – 600 = Very fine

Grades of Grinding Wheel:

• It indicates the hardness of the grinding wheel.
• The grade of the grinding wheel is selected based on the mechanical properties of the workpiece material.
• Soft wheels are used for grinding of hard workpiece because the rubbing forces induced by the blunt abrasive particle i.e. the self-sharpening is taking place and no dressing is required.
• Hard wheels are used for grinding of the soft workpiece, the abrasive particle will be effectively utilized so that at the end of effective utilization the dressing will be carried for resharpening of grinding wheel.
• A –H = Soft, I – P = Medium, Q – Z = Hard

Structure:

• The structure is indicating the average gap between the two consecutive abrasive particles.
• As the average gap is large, the number of abrasive particle presents per unit area will be small hence it is called the open structure.
• The structure of a grinding wheel can be varied by varying the % of abrasive particles and bonding material in the manufacturing of a grinding wheel. i.e. when higher % of abrasives and lower % of bonding material is used in manufacturing it produces the dense structure and vice-versa.
• 0 – 7 = Dense, 8 – 16 = Open

Bonds:

• Bond indicates the bonding material used for the manufacturing of the grinding wheel.
• Out of the different bonding materials, vitrified is the most commonly used bonding material because it gives higher bonding strength, high temperature withstanding capability, and high thermal conductivity.
• For the manufacturing of flexible grinding wheels also called buffing wheels, shellac or rubber can be used as the bonding material.
• V – Vitrified, B – Bakelite, S – Silicate, E – Shellac, R - Rubber

The selection of a grinding wheel will depend on the following factors:

Factors affecting the selection of abrasive:

• Material of high tensile strength - Aluminium oxide
• Material of low tensile strength - Silicon oxide

Factors affecting the selection of grit:

• Great amount of stock to remove - Coarse grain
• Soft and tough materials - Coarse grain
• Fine finish - Fine grain

Factors affecting the selection of grade:

• Hard materials - Soft wheel
• Soft materials - Hard wheel
• Great area of contact - Soft wheel
• Low wheel surface speed - Hard wheel

Surface affecting the selection of structure:

• Soft and tough material - Open structure
• Fine finish - Dense structure
• Cylindrical and tool grinding - Medium structure
• External grinding - Dense structure

Explanation:

The code ‘V’ represents the bond.

Designation of Grinding Wheel:

Prefix / Suffix: These are the secret codes used by the manufacturers to represent the wheel by its size and shapes respectively.

Type of Abrasives / Grain type:

• It indicates materials used for the manufacturing of abrasive particles.
• Out of the abrasives B4C is giving the poor performance during machining and diamond is very costly, therefore Al2O3 or SiC is the most commonly bused abrasives in the grinding wheel.
• Al2O3 soft and tougher than the SiC whereas SiC will be hard and brittle than Al2O3
• The type of abrasive is selected based on the mechanical properties of workpiece material I.e. for machining of soft and ductile workpieces, Al2O3, and machining of hard and brittle workpiece SiC will be used.   
• A- Al2O3, B – B4C, C – SiC, D - Diamond

Grain size or Grit size:

• It indicates the size of abrasive particles.
• i.e. Side if abrasives = 1/ Grain Size Number(GSN)
• when the GSN > 600, the size of the abrasive particles becomes very very small and it cannot act like a cutting tool, therefore MRR is less.
• When GSN < 600, the actual size of abrasive is increasing, the chip size is increasing and MRR is increasing.
• As the GSN is reducing or the size of abrasive is increasing, the MRR is increasing first and then reducing.
• The grain size is selected based on the surface finish required on the workpiece i.e. for a rough grinding, course or medium grain size is selected and for finished grinding fine or very fine grain size will be selected.
• 10-24= Coarse, 30-60 = Medium, 80 -180 = Fine, 220 – 600 = Very fine

Grades of Grinding Wheel:

• It indicates the hardness of the grinding wheel.
• The grade of the grinding wheel is selected based on the mechanical properties of the workpiece material.
• Soft wheels are used for grinding of hard workpiece because the rubbing forces induced by the blunt abrasive particle i.e. the self-sharpening is taking place and no dressing is required.
• Hard wheels are used for grinding of the soft workpiece, the abrasive particle will be effectively utilized so that at the end of effective utilization the dressing will be carried for resharpening of grinding wheel.
• A –H = Soft, I – P = Medium, Q – Z = Hard

Structure:

• The structure is indicating the average gap between the two consecutive abrasive particles.
• As the average gap is large, the number of abrasive particle presents per unit area will be small hence it is called the open structure.
• The structure of a grinding wheel can be varied by varying the % of abrasive particles and bonding material in the manufacturing of a grinding wheel. i.e. when higher % of abrasives and lower % of bonding material is used in manufacturing it produces the dense structure and vice-versa.
• 0 – 7 = Dense, 8 – 16 = Open

Bonds:

• Bond indicates the bonding material used for the manufacturing of the grinding wheel.
• Out of the different bonding materials, vitrified is the most commonly used bonding material because it gives higher bonding strength, high temperature withstanding capability, and high thermal conductivity.
• For the manufacturing of flexible grinding wheels also called buffing wheels, shellac or rubber can be used as the bonding material.
• V – Vitrified, B – bakelite, S – Silicate, E – Shellac, R - Rubber

Explanation:

Grain size or Grit size:

• It indicates the size of abrasive particles. i.e. Size of abrasives = 1/ Grain Size Number (GSN)
• When the GSN > 600, size of the abrasive particles becomes very very small and it cannot act like a cutting tool, therefore MRR is less.
• When GSN < 600, actual size of abrasive is increasing, the chip size is increasing and MRR is increasing.
• As the GSN is reducing or size of abrasive is increasing, the MRR is increasing first and then reducing.
• The grain size is selected based on the surface finish required on the workpiece i.e. for rough grinding, course or medium grain size is selected and for finished grinding fine or very fine grain size will be selected.
• 10 - 24 = coarse, 30 - 60 = Medium, 80 - 180 = Fine, 220 - 600 = very fine

Concept:

Grinding ratio is the ratio of the volume of the material removed from the workpiece divided by the volume of the material which is lost from the grinding wheel.

So, it is always desired that there is no loss of the material from the grinding wheel when the grinding is taking place.

\({\rm{G}} = \frac{{{\rm{Volume\;of\;material\;removed}}}}{{{\rm{Volume\;of\;wheel\;wear}}}} = 200\)

Volume of material removed = 200 × Volume of wheel wear

Volume of wheel wear = 0.005 × Volume of material removed