Common Grinding Wheels: A grinding wheel is made of abrasive grains held together by a bond. These grains cut like teeth when the wheel is revolved at high speed and is brought to bear against a workpiece. The properties of a wheel that determine how it acts are the kind and size of abrasive, how closely the grains are packed together and amount of the bonding material.
Wheel shape and sizes : There are different wheel shapes that are recognized as standard:
Straight cylinders with or without recesses in their sides.
1. Tapered two sides
2. Straight cup
3. Flaring cup
4. Dish
5. Saucer
Grinding wheel: A grinding wheel is a multi tooth cutter made up of many hard materials or particles known as” abrasive”. Which have been crushed to leave sharp edges which do the cutting? The abrasive grains are mixed with a suitable bond, which acts as a matrix or holder when the wheel is in use. The abrasive wheel is usually mounted on some form of machine adapted to a particular type of work.
Wheel shape and sizes (continue): The principle dimensions that designate the size of a grinding wheel are the outside diameter, width, and hole diameter. Standard wheel shapes are made in certain sizes only, but the variety is large.
Abrasives: It is that material of the grinding wheel which does the cutting action. It is substance that is used for grinding and polishing operations. It is a hard material used for making grinding wheels. It has uniform physical properties of hardness, toughness and resistance to fracture to be useful in manufacturing grinding wheel. Abrasives are small particular bounded together in different shape. Different abrassive materials are appropriate for grinding different work material. Abrasives are hard substances used in various forms as tools for grinding and other surface finishing operations. They are also able to cut materials which are too hard for other tools and give better finishes and hold closer tolerances.
It has classified into two groups:
Natural abrasives: they are obtained directly from mines. The common natural abrasives are sand stone or solid quart, emery, corundum, diamond, almost all of the natural abrasives, except diamond, are now considered obsolete. Emery and corundum have a greater hardness and better abrasives action than quarts.
Artificial abrasives: Artificial or manufactured abrasives inclined are:
Silicon carbide: It is made from silicon dioxide, coke sawdust and self, There constitutes are mixed together and piled up around the carbon electrical. Chemical reaction: Sio2 +3c =sic+2co. Silicon carbide is denoted by “S”.
(SiC) known in trade as Carborundum and Crystalon. Harder than Al2O3 but not as tough. Used to grind: aluminum, brass, stainless steel, cast irons, certain brittle ceramics.
Aluminum carbide: this abrasive carries very hard and tough grains having sharp cutting edges. AL 2O3 manufactured by heating mineral bauxite, a hydrated aluminum oxides clay containing silica, iron oxide, titanium oxides etc. The wheels are denoted by “A”. (Al2O3) known as Alundum or Aloxide. Various substances may be added to enhance hardness, toughness, etc. Plain Al2O3 is white, and used to grind: steel, ferrous, high strength alloys.
Bond and bond materials: A bond materials is an adhesive substance that is employed to hold abrasives grains together in the form of sharpening stones or grinding wheel. Bonding materials and processes are: Vitrified bond, Silicate bond, Shellac bond, Retinoid bond, Rubber bond, Ox chloride bond. This bond may be used with either silicon carbide or aluminum oxide.
Boron Nitride: in the forms of single-crystal cubic boron nitride (CBN) and microcrystalline cubic boron nitride (MCBN) under trade names such as Borazon or Borax. Used for hard materials such as hardened tool steels and aerospace alloys.
Diamond: a pure form of carbon, both natural and artificial. Used on hard materials such as ceramics, cemented carbides and glass.
Grain size: Important parameter in determining surface finish and material removal rate. Small grit sizes produce better finishes, larger grit sizes permit larger material removal rates. Also, harder materials need smaller grain sizes to cut effectively, while softer materials require larger grit size. Grain sizes used in grinding changes between 8-250, whilw 8 is very coarse, but 250 is very fine.
Bonding materials: To get wide range of properties needed in grinding wheels, abrasive materials bonded by using organic or ingorganic materials.
Vitrified bond: IT is a clay bond, reddish brown in color. It made by bonding clay matted to a glass like consistency with abrasive grains. The clay and abrasive grain are thoroughly mixed together with sufficient water to make the mixture unified. It gives a wheel good strength as well as porosity to allow high stock removal with cool cutting. It is affected by heat, cold water or acids. In this use high temperature are used 700 degree. It is denoted by “V”.
Silicate bond: Its base material is silicate of soda. They are made by mixing abrasive grains with silicate of soda or water glass. The mixtures is packed into moulds and allowed to dry. It is a more rapid process than vitrified bond. In this extra hard wheels cannot be produced with this bond. In this use temperature of 260 degree centigrade
It is denoted by ‘S’.
Shellac bond: It is also known as elastic bonded wheels. In this the abrasive and shellac are mixed in heated containers and then rolled. It is not intended for heavy duty. It is cool cutting on hardened steel and thin sections. They can run safety in water but use of oil or caustic soda should be avoided denoted by ‘E’. It has use 150 degree centigrade temperature.
Reinhold bond: It is a synthetic organic compound which is enough strong and flexible. They can remove stock very rapidly. They are useful for precision grinding cams, and rolls requiring high finish. In this temperature are used 200 degrees centigrade. It is denoted by letter ‘B’.
Rubber bond: IT composed of fairly hard vulcanized rubber. They are prepared by mixing abrasive grains with pure rubber and sculpture. It is most –resilient less heat resistant. They are used where good finish is primary requisite. It wheel is denoted by letter’ R’.
Ox chloride bond: This process consists of mixing abrasive grains with oxide and chloride of magnesium. They are employed in making wheels segments for use in disc grinding operations. It is denoted by ‘O’.
Inorganic bond:
Vitrified bond: Clay bond melted to a porcelain or glass like consistency. It can be made strong and rigid for heavy grinding and not effected by water, oil, acids. Most grindig wheels have vitrified bonds.
Slicate bond: is essentially water glass hardened by baking. It holds grains more loosely than a vitrified bond and give closer cut. Large wheels can be made more easily with slicate bond. Usually used in situation where heat generation must be minimized.
Metallic bond: Cubic boron nitride and diamond abrassives are usually (but not always) embeded in metallic bonds, for utmost in strength and tendency to hold the costly long-wearing grains.
Organic bond: Rubber bond is a flexible bond, used in cutoff wheels. Resinoid bond is a high strengt bond, used for rough grinding and cutoff operations. Shellac bond is relatively strong but not rigid, used in applications that requires good finishing.
Grit or grain sizes: It’s denoted the approximate size of the abrasive particles and gives an idea of the coarseness or fitness's of the grinding wheel. Grinding wheels have the abrasive particles of same size or different sizes. Its depends upon quality of finish required, amount of stock material to be removed and physical properties of the material to be ground. A grain size is denoted by a number indicating the number of meshes per liner inch (2.54”).
COARSE. 10 12 14 16 20 24
Medium 30 36 46 54 60
Fine 80 100 120 150 180
Very fine 220 240 280 320 400 500 600
Grade: It applied to a grinding wheel refers to the tenacity or hardness with which the bonds hold the cutting points or abrasive grains in a plane. It does not refer to the hardness of the abrasive grain. it is indicated in bonds and process by a letter of English alphabet ‘A’ denoting the softest and ‘Z’ the hardest grade. A wheel from which the abrasive grains can easily by dislodged is called “soft", where as one which holds the grains more securely is called “hard”. Hard wheels are recommended for soft material and soft wheels for hard materials.
SOFT A B C D E F G H
MEDIUM I J K L M N O P
HARD Q R S T U V W X Y Z
Structure of wheels: Abrasive grains are not packed in the wheel but are distributed through the bond. The relative spacing is referred to as the structure and denoted by the number of cutting edges per unit area of wheel face as well as by number and sizes of valid spaces between grains. The structure of a grinding wheel depends on the hardness of the material being ground, the finish required and the nature of grinding operation. Soft, tough and ductile materials and heavy cut require on open structure. Hard and brittle materials and finishing cut require a dense structure.
DESE 1 2 3 4 5 6 7 8
OPEN 9 10 11 12 13 14 15 or higher
Wheel shapes and sizes: Grinding wheels are made in many different shapes and sizes to adapt them for use in different types of grinding machines and on different classes of work.
1. Straight –side grinding wheels.
2. Cylinder wheel
3. Cup wheel
4. Dish wheel.
Standard grinding wheels shapes are:
Straight wheels: Straight wheels are the kind generally used cylindrical, centre less and surface grinding operations. Wheels of this form vary greatly in sizes, the class of work for which the wheel is used and the sizes and power of the grinding machine.
Tapered face straight wheel: It is primarily used grinding thread gear teeth etc.
Cylinder or wheel ring: It is used for producing flat surface the grinding being done with the end face of the wheel.
Cup wheel: It is used for grinding flat surface by traversing the work past the end or faces of the wheel.
Flaring cup wheel is used for grinding in tool room.
Dish wheel: It is also used for tool room work the thickness of the wheel permits it grind the surface at narrow places.
Saucer wheel: It is generally used for sharpening of circular or band saws. The principle dimensions of a grinding wheel are the outside diameter and the width.
Segmented wheel: They are used chiefly on vertical spindle, rotary and reciprocating table surface grinders and way grinders. Grinding wheels of the straight wheel type can be supplied with a large variety of face: Flat, pointed, concave, and convex etc. these faces are used for grinding specials contours and sharpening saws.
Mounted wheels: Mounted wheels are small shaped wheels (50 mm diameter and below) mounted securely and permanently to steel spindle or mandrel by cementing or other means great care should be taken in using mounted wheel and points. Pressure between wheel and work small at no time be so heavy that any considerable springing of the spindle will result.
Form grinding wheels: Some grinding operations require special shaped grinding wheels. These grinding wheels are known as form drinking wheels.
Diamond grinding wheels: They are used to grind or cut very hard materials like carbide, glass, stone, marble, and ceramics. Diamond grains are used as abrasives. The diamond wheels are made of retinoid or vitrified bond. It are made of various shapes. Miller wheels have diamond particles throughout the wheel and lager wheel have diamond particles only on the grinding face of the wheel.
Chip formation: In grinding, the chips are small but are formed by the same basic mechanism of compression and shear. Burning chips are the sparks observed during grinding with no cutting fluid, because the chips have heat energy to burn or melt in the atmosphere. The feeds and depths of cut in grinding are small, while the cutting speed is high. Grinding may be classified as non-precision or precision, according to purpose and procedure.
Standard marking system: The Indian standard marking system for grinding wheels has prepared to designate their various characteristics, to a gives a general indication of the hardness and grit sizes of any wheel as compared with another. Each marking shall consist of six symbols denoting the following in succession:-
1. Abrasive type
2. Grain size
3. Grade
4. Structure
5. Bond type
6. Manufactures record.
Selection of the grinding wheels: In selection of a grinding wheel the following factors are considered:
1. Material to be ground.
2. The amount of stock to be removed
3. Area of content of the wheel with the work pieces .
4. Types of grinding machine and its condition.
5. Wheel speed and work speed.
Material to be ground:-
1. Soft ductile and high ----- hard grade wheel.
2. Tensile material ---- aluminum oxide wheel
----- An open structure wheel
----- Coarse grain wheel
3. Hard and brittle material---- soft grade wheel
4. With low tensile strength------ silicon carbide wheel
------ Dense structure wheel
------ Fine grain wheel
Amount of stock to be removed: This involves accuracy and finish course, grain is used for fast cutting and fine grain for fine finish, wide soaking for rapid removal and close for fine finish, resin old, rubber and shellac bond for high finish.
Area of contact: When the aired of content between the wheel and work pieces is small, a fine grained and dense structure wheel is used. When the area of content is more, a coarse grained and open structure wheel is used.
Types and condition of grinding machine: Heavy, rigid, and well maintained machine can use soft grade wheels. Light and poorly maintained machines should use hard grade wheels.
Wheel speed and work speed: When the wheel speed is more than the work speed hard grade wheels are used. When the work speed is more than the wheel speed, soft grade wheels are used. When the wheel speed is up to 2000 m/ mt. vitrified bonded wheels are used. When the wheel speed is more than 2000 m/mt. rubber, shellac and retinoid bonded wheels are used.
Work material Surface speed in m/ min. Surface speed in m/ min.
Roughing out Finish out
Cast iron 60 120
Aluminum 30 60
Soft steel 9 15
Hard steel 20 30
Condition of the grinding machine: The condition of the grinding machine has a being on the grade of the well to be selected spindle loose in their bearings and insecure or shaky foundations would necessitable the use of harder wheel than would be the case if the machine were in better operating condition.
Personal factor: The skill of workman is another variable factor which should be considered in selecting the wheel as for instance on off- hand grinding. It cans very grinding costs considerably on the same work in the same factory.
Selection of grinding wheel: It is a vital necessity to obtain the best results in grinding work. A wheel may be required to perform various different functions like be required to per from various different functions like quick removal of stock material, give a high class surface finish, maintain close dimensional tolerances and a single wheel will fail to meet all the requirement . It is also necessary, that proper grain sizes, bond, grade, strength, shapes and sizes of wheel be selected. It also depends on this factor:-
1. Properties of the material to be machined.-hardness, toughness, strength etc.
2. Quality of surface finish required.
3. Dimensional accuracy required.
4. Method of grinding, wet or dry.
5. Rigidity, sizes, type of machine.
6. Relative sizes of wheel and job.
7. Type of grinding to be done.
8. Speed and feed of the wheel.
Dressing: operation removes the loading and glazing from a grinding wheel. By dressing, sharp abrasive particles are made to project from the surface of the grinding wheel. Dressing is done using the tool called ‘dresser’. The dresser is guided by the tool rest. Grinding wheel is run at a slow speed. The dresser is moved crosswise along the width of the wheel. This type of wheel dresser is used for dressing coarse grain abrasive wheels. Coolant is applied while dressing. Very light cut is taken in diamond dressing. It is holder at 15 degree angle. Dressing is the conditioning of the wheel surface which ensures that grit cutting edges are exposed from the bond and thus able to penetrate into the work piece material. From time to time it will be necessary to dress a wheel in use, to open up the pores and remove any dull abrasive grain or clogging metal from the wheel face, thus presenting fresh sharp grains which will cut better and generate less heat. Dressing refers to the removing of clogs and blunt abrasive grains from the surface of the grinding wheel. Dressing exposes the cutting edges which restore the correct cutting action of the wheel. Dressing is done on a glazed or loaded wheel to recondition it.
Truing: It is the process of trimming the cutting surface of the wheel to run with the axis. By truing, the cutting surface of the wheel can be shaped to the required contour for from grinding. It is done with a diamond truing tool. The process is similar to dressing. In truing, the diamond tool must be fed across the wheel very slowly. The grinding wheel surface may become concave or convex or irregular due to uneven wear. Truing is done to correct these irregularities in the cutting surface of the grinding wheel. Turning is done periodically. Truing is the act of regenerating the required geometry on the grinding wheel, whether the geometry is a special form or flat profile. Therefore, truing produces the macro-geometry of the grinding wheel. Truing is also required on a new conventional wheel to ensure concentricity with specific mounting system. In practice the effective macro-geometry of a grinding wheel is of vital importance and accuracy of the finished work piece is directly related to effective wheel geometry. Truing refers to the shaping of the wheel to make it run concentric with the axis. When a new grinding wheel is mounted, it must be tried before use to remove the run out.
Balancing of grinding wheels: Grinding wheels rotate at high speeds. The weight should be evenly distributed throughout the body of the wheel. If it is not so, the wheel will rotate without balance. The imbalance of the wheel will develop a high unbalanced centrifugal force. This wills lead to busing of the wheel at high speed which is dangerous. So the grinding wheel should be balanced before use. The balancing of grinding wheel is done as follows. The wheel is fitted to a test mandrel. The mandrel is placed over two knife edges. The knife edges are kept parallel and they are placed on truly horizontal plane. The mandrel is gently rotated to roll over the knife edge. If there is any imbalance in the wheel, the wheel will come to rest with a particular portion at the bottom. This means that the portion which comes to the bottom is heavier than the other portion of the wheel. In balance can also be rectified by painting the particular side of the wheel with a special heavy paint. A balanced wheel will come to rest in different positions of the knife edge.
American National Standard Institude’s marking system for standard wheels:
Prefix-Abbrasive type-Abrasive grain size-Grade-Structure-Bond type-Manufacturer record Ex: 51-A-36-L-5-V-23
Prefix:Manufacturer symbol indicating exact kind of abrasive (use optional)
Abrassive type: - A:Aluminum oxide, C:Silicon Carbide, B: Boron Nitride, D:Diamond
Grain size: coarse:8-24, medium:30-60, fine:70-180, very fine: >220
Grade:Ranges from A-Z, where A represents soft, Z represents hard wheel grade.
Structure: Scale isnumerical. 1: very dense and 15:very open.
Bond type:- B : Resinoid, E : Shellac, R : Rubber, S : Silicate, V : Vitrified
Manufacturer record: Manufacturer’s private marking to idetify the wheel.
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