This document discusses grinding and grinding machines. It begins by defining grinding as a process of removing material using an abrasive wheel. It then describes the components of a grinding wheel, including the abrasive, bond, grit size, and grade. It discusses different types of abrasives, bonds, and grinding machines for rough and precision grinding. It covers topics like dressing, truing, wheel selection, and defects in grinding like glazing and loading. Overall, the document provides an overview of grinding wheels, bonds, grit sizes, defects and remedies, and common grinding machine types.

1. Grinding and Grinding Machine

2. Grinding:
Grinding is a process of removing material by abrasive action of
a revolving wheel on the surface of a work-piece in order to
bring it to required shape and size
The wheel used for performing the grinding operation is known
as grinding wheel
It consists of sharp crystal called abrasive held together by a
binding material or bond
The wheel may be a single piece or solid type or may be
composed of several segments of abrasive blocks joined
together.

3. Wheel Materials
1. Abrasive: it is that material of grinding wheel which does the
cutting action
(a) Natural Abrasive:
The common natural abrasives are sand stone, emery (50-
60%crystalline AL2O3+iron oxide) corundum (75-90%
crystalline aluminium oxide+iron oxide), and diamond
The sand stone is used only for sharpening some wood-working
tool
Diamond is used for dressing the grinding wheel and acts as an
abrasive material for hard material

4. Artificial abrasive:
These are manufactured under controlled conditions in closed
electric furnaces in order to avoid the introduction of
impurities and to achieve the necessary temperature for
chemical reactions to take place
Example: Silicon carbide(Sic), Aluminum oxide(Al2O3)
Artificial diamond:
The diamond produced through artificial means are quite
comparable to the natural diamond in their grinding
characteristics and give better result than the latter.

5. Advantages and use of artificial Abrasive
The artificial abrasives have lately superseded the natural
abrasive for following reason
1. The controlled conditions in the electric furnace enable
uniformly in the product
2. The quality of production and supply can easily be varied
according to the demands
3. They have largely abolished the dependence on natural means
to meet the growing demand of more abrasive material in the
modern manufacturing process
Bond is the substance that acts as a binder to hold the abrasive
grains together

6. Material to be ground Recommended abrasive
Cast Iron Silicon carbide
Soft brass and bronze
Glass and stone
Aluminium
Copper
Rubber
Leather
Plastics
Heat treated carbon and alloy
steel
Aluminium Oxide
Malleable Iron
Hard brass and bronze
Mild steel and Wrought Iron

7. A bond is a substance that is employed to hold abrasive grains
together in the form of sharpening stones or grinding wheels.
Several types of bonding materials used for making grinding
wheels,
1-Vitrified bond
2-Silicate bond
3-Shellac bond
4-Resinoid bond
5-Rubber bond
6-Oxychloride bond
These bonds may be used with either silicon carbide or aluminum
oxide.

8. 1-Vitrified bonding process: vetrified wheels are made by
bonding clay melted to a glass like consistency with
abrasive grains.
• The clay and abrasive grains are thoroughly mixed with
sufficient water to make uniform mixture.
• The fluid mixture is then poured in to the mould and allowed
to dry.
• After cooling , the material trimmed to more perfect size and
shape.
• It is then heated in a furnace to a temperature 1260 deg .
• When the burning proceed, the clay vitrifies --that is it fumes
and forms a porcelain or glass like substance that surrounds
and connects the abrasive grains.
• It gives good strength and porosity to allow high stock
removal
• It is affected by heat, cool water or acids.
• Denoted by “V”

9. • 2-Silicate bonding process:
• Silicate bonding wheels are made by mixing
abrasive grains with silica of soda or water
glass.
• The mixture is packed in to moulds and allowed
to dry.
• The mould shapes are baked in a furnace at a
temp of 260 deg for several days.
• The silicate bondded wheels are water proof.
• Denoted by “S”

10. 3-Shellac bonding process: shellac bond wheels are
also known as elastic bonded wheels.
• In this process, the abrasive and shellac are mixed
in heated containers and then rolled or pressed in
heated moulds.
• Later the shapes are baked at a temp 150 deg.
• The elasticity in this is grater than in other two
types and it has considerable strength
• It is not for heavy duty.
• Used for finishing chilled iron, cast iron and steel
rolls
• Denoted by”E”

11. 4-Resinoid bonding process: resinoid wheels are
produced by mixing abrasive grains with
synthetic resins and other compounds.
• The mixture placed in moulds and heated at
about 200 deg.
• At this temp the resin sets to hold the abrasive
grains in wheel form.
• These wheels are used for purposes which
require a strong, high speed wheel.
• Denoted by “B”

12. 5-Rubber bonding process:rubber wheels are
produced by mixing abrasive grains with pure
rubber and sulphur.
• The mixture rolled in to sheets and wheels are
punched out of these sheets on a punch press.
• These are less heat resistant and more dense then
the resinoid wheels
• Denoted by “R”

13. 6-Oxychloride bonding process: this process
consists of mixing abrasive grains with oxide and
chloride of magnesium.
• The mixing of bond and abrasive is performed
in the same way as for vitrified bond wheel.
• These wheels are used in making wheels and
wheel segments for disc grinding operation.
• Denoted by “O”

14. GRIT SIZE
Small grit sizes produce better finishes
Larger grit sizes permit larger material removal rates
Harder work materials require smaller grain sizes to
cut effectively
Softer materials require larger grit sizes
Grit size is measured using a screen mesh procedure
Smaller grit sizes indicated by larger numbers in the
screen mesh procedure and vice versa Grain sizes in
grinding wheels typically range between 10 (very
coarse) and 250 (very fine)

15. GRADE
The grade of a bonded abrasive is a measure
of its bond strength
The grade is also referred to as the hardness
of a bonded abrasive
A hard wheel has a stronger bond and/or a
larger amount of bonding material between
the grains than a soft wheel

16. Structure of a bonded abrasive is a measure of its porosity

17. Specifying of grinding wheel
To maintain uniformity throughout the country in the system of
making grinding wheel, the Bureau of Indian Standard has
devised a standard system to be followed by all manufacturer
According to the system, the various elements and characteristics
of grinding wheels are represented on all the wheels in a
definite sequence as follows:
1. Abrasive 2. Grain size 3. Grade 4. Structure 5. Bond

18. Example:
A grinding wheel carrying the marking
125 x 25 x32 W A 46 L 4 V 17
125(mm)---wheel diameter
25(mm)--- Thickness of wheel
32 (mm)---Bore diameter
W---Manufacturer’s prefix to abrasive. It is optional.
A--- Abrasive(Al2O3)
46 ----Grain size(medium)
L ---grade (medium)
4 --- Dense structure
V --- Vitrified bond
17----it is the suffix denoting the bond type of the manufacturer

22. • Major and inevitable defects in grinding are glazing of
grinding wheels. Its remedy will be discussed later. After the
continuous use grinding wheel becomes dull or glazed.
• Glazing of the wheel is a condition in which the face or
cutting edge acquires a glass like appearance. That is, the
cutting points of the abrasives have become dull and worn
down to bond. Glazing makes the grinding face of the wheel
smoother and that stops the process of grinding.
• Sometimes grinding wheel is left ‘loaded’.
• In this situation its cutting face is found being adhering with
chips of metal.
• The openings and pores of the wheel face are found filled
with workpiece material particals, preventing the grinding
action.
• Loading takes place while grinding workpiece of softer
material.

23. Dressing
The remedies of glazing and loading is dressing of grinding
wheels.
Dressing removes the loading and breaks away the glazed
surface so that sharp abrasive particles can be formed again
ready for grinding.
Different type of dressing operations are done on a
grinding wheel.
One of them is the dressing with the help of star dresser.
It consists of a number of hardened steel wheels with sharp
points on their periphery. The total is held against the face
of revolving wheel and moved across the face to dress the
whole surface.
Another type of wheel dresser consists of a steel tube filled
with a bonded abrasive. The end of the tube is held against
the wheel and moved across the face.

24. Truing
• Truing is the process of restoring the shape of
grinding wheel when it becomes worn and break
away at different points. Truing makes the wheel
true and concentric with the bore.

25. Selection of Grinding Wheel
1.Properties of the material to be machined i.e hardness,
toughness, strength
2. Quality of surface finish required
3. Grinding allowance provided on the work-piece i.e the amount
of stock to be removed
4. Dimensional accuracy
5. Method of grinding i.e wet or dry
6. Rigidity, size and type of machine
7. Relative sizes of wheel and job
8. Type of grinding to be done
9. Speed and feed of wheel

26. Types of grinding Machine
Grinding machines according to quality of surface finish, may be
classified as
1. Rough /Non-precision grinding
2. Precision grinding
Rough/Non-precision grinding
To remove more stock than other grinding
a)Floor stand and bench grinders
(b)Portable and flexible shaft grinders
(c)Swing frame grinders
(d)Abrasive belt grinders

27. Floor stand and bench grinders
Used for snagging and off-hand grinding of various materials and
cutting tools in tool rooms, foundries and general repair shops
It carries a horizontal spindle having grinding wheels mounted on
both ends
It can be suitably bolted on a bench at convenient height
The floor or pedestal grinder is nothing but a bench grinder of the
above type mounted on a steel stand or pedestal of suitable
height
The horizontal spindle carrying the grinding wheel is normally an
extension on both side of the armature shaft of the motor
These grinder are also be used for polishing by replacing the
grinding wheel by polishing wheel

30. Precision grinders: according to the type surface
generated or work done they may be classified as:
• (a)cylindrical grinding machine
• (b) surface grinding machine
• (c) Internal grinding machine
• (d) Tool and cutter grinding machine

31. Surface grinding machine
Horizontal spindle and reciprocating table
Vertical spindle and reciprocating table
Horizontal spindle and rotary table
Vertical spindle and rotary table

32. Horizontal spindle reciprocating table surface grinder

35. Cylindrical Grinders
The wor-kpiece is hold on centre by a chuck or in a suitable
holding fixture, rotating it about its axis and feeding a fast
revolving grinding wheel
If the work surface to be ground is longer than the face width of
the grinding wheel, the work is traversed past the wheel or the
wheel past the work.
Traversing of wheel or work is done either by hydraulic or
mechanical power or by hand
Feed is given to the work or the wheel at the end of each
traversing movement

37. In case of width of wheel face is more or equal to the length of
work surface to be ground, the wheel may be fed in with no
traversing movement of it or that of work.
This is known as Plunge Grinding
The simplest and quite commonly used type of cylindrical grinder
is tool post grinder used on lath
When wheels of large diameters are used, they can be mounted
directly on the motor shaft
For mounting small wheels, an auxiliary shaft is provided, which
runs at a relatively much higher speed than the motor
Both external and internal cylindrical grinding can be done on
lathe by this equipment

38. Types of cylindrical grinding:
1. Plain cylindrical grinding
2. Universal cylindrical grinding
3. Centreless grinders

39. Centreless Grinders
Here the work is supported by a combination of grinding wheel,
regulating wheel and a work rest blade
The relative movement of work-piece and two wheels shown in
figure
It is used for both external as well as internal grinding
Many hollow cylindrical and tapered workpiece, like bushes,
pistons, valves tube and balls etc either do not or cannot have
centre are best ground on centreless grinder

40. It carries a heavy base and two wheel heads, one carrying the
grinding wheel(large one) and the other regulating
wheel(smaller)
The workpiece rests on the blade of the work rest between these
two wheel
Each head carries a separate wheel trueing mechanism for the
wheel it carries
A housing is provided on one side of the machine body to house
the main driving motor
There are two control panels on the front
The left hand panel carries controls for speed adjustments of two
trueing mechanism and the infeed grinding mechanism
The right hand panel carries control for hydraulic mechanism,
speed adjustment of regulating wheel, automatic working
cycle switch, start and stop switch etc

41. In operation, grinding operation is performed by grinding wheel
only while the function of regulating wheel is to provide the
required support to the work piece while it is pushed by
cutting pressure of grinding wheel
It helps the work-piece to remain contact with the grinding wheel
At the same time, required support from bottom is provided by
work-rest as the work-piece while rotating rests on the blade of
worksheet
The regulating the wheel essentially carries rubber bond and
helps in the rotation of work-piece due to friction
The methods used for feeding the work are:
I. Through feed
II. Infeed
III. End feed

45. The work-piece is supported and revolved as described above but
simultaneously given an axial movement also regulating wheel
and guides so as to pass between wheels
The axis of the regulating the wheel is inclined at 2 to 10 degree
with vertical
The amount of stock to be removed determines as to how many
time a workpiece has to pass between the wheels
The actual feed(S) can be calculated by the formula
S=πdn. sinα
S=feed in mm per minute.
n=revolutions per minute.
d=diameter of the regulating wheel in mm.
α=angle of inclination of wheel.
Through feed

46. Surface Grinder
The main objective to machine flat surface, irregular, curved and
tapered surfaces
Classification
1. According to the table movement
a) Reciprocating table type b) Rotary type
2. According to the direction of wheel spindles:
a) Vertical spindle type b) Horizontal spindle type
3) Special type and single purpose machine
a) Face grinder b) Way grinders c) Wet belt grinder

47. Reciprocating table type
A reciprocating type surface grinder may have a horizontal
spindle or a vertical spindle
The former will carry a straight wheel and latter a cup type
wheel
Hydraulic drivers are commonly used
Cutting is done on the periphery of straight wheel.
In case of horizontal spindle type and on revolving edge of the
cup wheel on vertical machine
The work-piece held on the magnetic chuck. These are used for
grinding flat surface
The longitudinal feed is given to the work by reciprocating the
table

50. In case of vertical spindle reciprocating table grinders the table,
along with the work-piece, reciprocates under the wheel
The wheels covers all or major portion of the width of the job
Cross feed to the work can be given as usual by moving saddle
A manual or power feed can be employed to feed the wheel-head
vertically
An individual motor drive is usually provided to rotate the wheel

51. Rotary type
It is two type
i) Having a horizontal wheel ii) vertical spindle wheel
A circular shaped magnetic chuck is mounted on a circular table to hold
job
The work-piece is normally arranged in a circle, concentric with the
round chuck
If it is a single piece, it can be mounted centrally on the chuck
The table is made to rotate under the revolving wheel, both rotating in
opposite direction
The vertical feed to the wheel is given by moving wheel head along
a column and cross-feed by the horizontal movement
of the wheel spindle

53. A straight wheel is used on these machines, which cuts on its
periphery

54. The relative movements of the wheel and the table of a Rotary
table vertical spindle surface grinder is shown in the fig
A cup wheel has to be used on these machine
Vertical feed to the wheel is given by moving the wheel head
The work-piece are on the round chuck in same way as in
horizontal spindle type
The table rotates in a direction opposite to that of wheel and
bring the work-piece one after the other under rotating
wheel
The table is mounted on a slide so as to give cross feed

56. Internal grinders
Used for grinding internal surface of different holes, cylindrical,
tapered etc
Types:
1. Plain internal grinders
2. Universal internal grinders
3. Chucking internal grinders
4. Planetary internal grinders
5. Centreless internal grinders

57. Plain internal grinders
It carries an individual driven wheel-head mounted on a cross-
slide
The workhead either carries a chuck or face-plate to hold the
work or latter can be mounted on a fixture attached to the
workhead spindle
The work can be swiveled to the grind tapered holes

59. Universal internal grinders
Here the work head is mounted on a cross-slide which enables a
cross feed to the workhead
The work head can be swiveled though 90 degree
It is used to grind cylindrical and tapered holes, flat surfaces,
outside the cylindrical surfaces, convex and concave
surface

61. Centreless internal grinders
The work-piece is supported between three rolls known as
pressure roll, supporting roll and a regulating roll
These rolls while supporting the work-piece also rotate the same
All rolls rotate in same direction while the work-piece and
grinding rotate in opposite direction
The grinding wheel remains contact with the internal surface of
the work-piece at the horizontal centerline of regulating wheel
It ensures that a uniform wall of thickness of the work-piece and
therefore concentricity of the ground internal hole with the
external surface
The pressure roll is so mounted that it can be swung to a slide to
allow loading and unloading of the work-piece

62. The wheel head is mounted on a slide and can be given a
reciprocating motion by hand to feed the grinding wheel in
and draw it out of the operation

64. Planetary internal grinders
To grind holes in large, irregular shaped and heavy work-piece
The work-piece remains stationary, which is mounted on a
slide
The wheel head carries a mechanism due to which the axis of
rotating grinding wheel travels along a circular path
around the axis of hole in the work piece
The longitudinal traverse obtained by
1) By reciprocating movement of the grinding wheel spindle
2) By moving the slide forward and backward on which work-
piece is mounted

65. The spindle of the grinding wheel is given a radial infeed after
completion of each planetary circle to increase the depth of cut

67. Honing: it is an abrading process mostly used for polishing bored
and reamed holes and also cylindrical surfaces using bonded
stones(called hones)
Lapping: It is finishing process and is done after grinding
Super-finishing: it is mostly done for obtaining high quality
surface finish along with an almost complete absence of
defects layers.