The manufacturer has a marking on a grinding wheel as 'A 27 K 7 V

SOLUTION

Concept:

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

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Grain size or Grit size:

• It indicates the size of abrasive particles.
• Size of abrasives = 1/ Grain Size Number(GSN)
• When 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 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

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Grades of Grinding Wheel:

• It indicates the hardness of the grinding wheel with which the wheel holds the grains in place.
• The grade of the grinding wheel is selected based on the mechanical properties of the workpiece material.
• The 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.
• The grade or amount of bond in an abrasive wheel is indicated by a letter of the alphabet.
• A – H = Soft, I – P = Medium, Q – Z = Hard
• Therefore 'K' represents a grade of grinding wheel

​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 = Ope

​Bond type:

• 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 a bonding material.
• V – Vitrified, B – bakelite, S – Silicate, E – Shellac, R - Rubber.