7. Mechanical engineering is a discipline
of engineering that applies the principles of
physics and materials science for analysis,
design, manufacturing, and maintenance of
mechanical systems.
Mechanical Engineering
8. Manufacturing
Manufacturing basically implies making of
goods or articles and providing services to meet
the needs of mankind.
Manufacturing process is that part of the production
process which is directly concerned with the change of
form or dimensions of the part being produced.
11. • Began about 5000 to 4000 B.C with the production of various
articles of wood, ceramic, stone and metal
• Derived from Latin word manu factus – meaning “made by hand”
• The word manufacture first appeared in 1567
• The word manufacturing appeared in 1683
• Production is also used interchangeably .
Evolution of Manufacturing
14. Casting since about 4000 BC…
Ancient Greece; bronze
statue casting circa 450BC
Iron works in early Europe,
e.g. cast iron cannons from
England circa 1543
15. Casting Process
• Casting process is one of the earliest metal
shaping techniques known to human being.
• It means pouring molten metal into a refractory
mold cavity and allows it to solidify.
• The solidified object is taken out from the mold
either by breaking or taking the mold apart.
• The solidified object is called casting and the
technique followed in method is known as casting
process.
16. Casting Process
• The modern casting process is divided into two
main categories:
• Expendable
• Non-expendable casting.
• In expendable casting, it includes sand casting,
shell casting, plaster mould casting, investment
casting, and evaporative-pattern casting.
• In non-expendable casting, it includes permanent
mould casting, dies casting, semi-solid metal
casting, centrifugal casting, continuous casting.
17. Basic steps in Casting
1.Pattern making
2.Mold making
3.Melting of metal and pouring
4.Cooling and solidification of metal
5.Cleaning of casting and inspection
19. Six basic steps in this process:
• Place a pattern in sand to create a mold.
• Incorporate the pattern and sand in a gating
system.
• Remove the pattern.
• Fill the mold cavity with molten metal.
• Allow the metal to cool.
• Break away the sand mold and remove the
casting.
23. Casting Terminology
• Pattern: An approximate duplicate or true replica of
required product of casting
• Flask/Box: The rigid metal or a wooden frame that
holds the moulding material
• Cope: Top half of the moulding box
• Drag: Bottom half of the moulding box
• Core: As and shape that is inserted into a mould to
produce internal features of a casting such as holes.
24. Continue…..
• Riser: A vertical opening in the mould
• Act as a vent for gases
• Helps to confirm that the mould is completely
filled
• Act as a reservoir of molten metal to feed and
compensate for shrinkage during solidification
of a casting
25. Continue….
• Gating System: Channels used to deliver the
molten metal to the mould cavity
• Sprue: The vertical passage in the gating
system
• Runner: The horizontal channel of the gating
system
• Gate: Channel which connects runner and
mould
26. Advantages
• Product can be cast as one piece and hence the
metal joining process is eliminated.
• Very heavy and bulky parts can be manufactured
• Metals difficult to be shaped by other
manufacturing processes may be cast (eg: Cast
Iron)
• Casting can be employed for mass production as
well as for batch production.
• Complex shapes can be manufactured
29. • VERSATILE: complex geometry, internal cavities, hollow sections
• VERSATILE: small (~10 grams) very large parts (~1000 Kg)
• ECONOMICAL: little wastage (extra metal is re-used)
• ISOTROPIC: cast parts have same properties along all directions
30. Disadvantages of Casting
• Casting process is a labour intensive process
• Not possible for high melting point metals
• Dimensional accuracy, surface finish and the
amount of defects depends on the casting
process
• Allowances required.
39. Pattern
• Pattern is the principal tool during the casting
process.
• A pattern is a model or the replica of the object (to
be casted)
• It may be defined as a model or form around which
sand is packed to give rise to a cavity known as
mold cavity in which when molten metal is poured,
the result is the cast object.
• A pattern prepares a mold cavity for the purpose of
making a casting.
40. OBJECTIVES OF A PATTERN
• Pattern prepares a mould cavity for the purpose of making a
casting.
• Pattern possesses core prints which produces seats in form of extra
recess for core placement in the mould.
• It establishes the parting line and parting surfaces in the mould.
• Runner, gates and riser may form a part of the pattern.
• Properly constructed patterns minimize overall cost of the casting.
• Pattern may help in establishing locating pins on the mould and
therefore on the casting with a purpose to check the casting
dimensions.
• Properly made pattern having finished and smooth surface reduce
casting defects.
41. Pattern Materials
• Wood: Inexpensive, Easily available, Light weight, easy to shape, good
surface finish, Poor wear resistance, absorb moisture, less strength, not
suitable for machine moulding, easily repaired, warping, weaker than
metallic patterns.
• Eg. Shisam, kail, deodar, Teak wood, maogani.
• Metal: less wear and tear, not affected by moisture, metal is easier to
shape the pattern with good precision, surface finish and intricacy in
shapes, withstand against corrosion and handling for longer, excellent
strength to weight ratio,
• metallic patterns are higher cost, higher weight and tendency of rusting.
• preferred for production of castings in large quantities with same pattern.
• Eg.: cast iron, brass and bronzes and aluminum alloys
42. • Plastic:-Plastics are getting more popularity now a days because
the patterns made of these materials are lighter, stronger,
moisture and wear resistant, non sticky to molding sand, durable
and they are not affected by the moisture of the molding sand.
• fragile, less resistant to sudden loading and their section may
need metal reinforcement.
• Eg.:phenolic resin, foam plastic
• Plaster: Intricate shapes can be made, good compressive
strength, expands while solidifying, less dimensionally accurate.
• •Wax: Good surface finish, high accuracy, no need to remove
from the mould, less strength.
43. FACTORS EFFECTING SELECTION OF
PATTERN MATERIAL
1. Number of castings to be produced. Metal pattern are preferred
when castings are required large in number.
2. Type of mould material used.
3. Kind of molding process.
4. Method of molding (hand or machine).
5. Degree of dimensional accuracy and surface finish required.
6. Minimum thickness required.
7. Shape, complexity and size of casting.
8. Cost of pattern and chances of repeat orders of the pattern
44. TYPES OF PATTERN
• Single-piece or solid pattern
• Solid pattern is made of single piece without joints, partings lines or loose
pieces.
• It is the simplest form of the pattern.
• Typical single piece pattern is shown in Fig.
• Simplest type, inexpensive used for limited production
• It is used to cast stuffing box of steam engine.
45. • Two-piece or split pattern
• When solid pattern is difficult for withdrawal from the mold cavity, then solid
pattern is splited in two parts.
• Split pattern is made in two pieces which are joined at the parting line by
means of dowel pins.
• The splitting at the parting line is done to facilitate the withdrawal of the
pattern.
• A typical example is shown in Fig.
• The split patterns are commonly used for
the casting of steam valve bodies, small pulleys,
wheels and cylinders etc.
46. • Cope and drag pattern
• In this case, cope and drag part of the mould are prepared separately. This
is done when the complete mould is too heavy to be handled by one
operator.
• The pattern is made up of two halves, which are mounted on different
plates. A typical example of match plate pattern is shown in Fig.
• These types of patterns are used in flange pipe manufacturing.
48. • Loose-piece Pattern
• used when pattern is difficult for withdrawal from the mould.
• Loose pieces are provided on the pattern and they are the part of pattern.
• The main pattern is removed first leaving the loose piece portion of the
pattern in the mould.
• Finally the loose piece is withdrawal separately leaving the intricate mould.
• Used in production of axle pin, cast rotor hub.
49. • Match plate pattern
• This pattern is made in two halves and is on mounted on the opposite sides
of a wooden or metallic plate, known as match plate.
• The gates and runners are also attached to the plate.
• This pattern is used in machine molding. A typical example of match plate
pattern is shown in Fig.
• Used to cast piston rings.
50. • Follow board pattern
• When the use of solid or split patterns becomes difficult, a contour
corresponding to the exact shape of one half of the pattern is made in a
wooden board, which is called a follow board and it acts as a molding
board for the first molding operation as shown in Fig.
• Used for casting master pattern for many purposes.
52. • Gated pattern
• In the mass production of casings, multi cavity moulds are used. Such
moulds are formed by joining a number of patterns and gates and
providing a common runner for the molten metal, as shown in Fig.
• These patterns are made of metals, and metallic pieces to form gates and
runners are attached to the pattern.
54. • Sweep pattern
• Sweep patterns are used for forming large circular moulds of symmetric
kind by revolving a sweep attached to a spindle as shown in Fig.
• Sweep is a template of wood or metal and is attached to the spindle at one
edge and the other edge has a contour depending upon the desired shape of
the mould.
• The pivot end is attached to a stake of metal in the center of the mould.
55. • Segmental pattern
• Patterns of this type are generally used for circular castings, for example
wheel rim, gear blank etc.
• Such patterns are sections of a pattern so arranged as to form a complete
• mould by being moved to form each section of the mould.
• The movement of segmental pattern is guided by the use of a central pivot.
A segment pattern for a wheel rim is shown in Fig.
56. • Shell pattern
• Shell patterns are used mostly for piping work or for
producing drainage fittings. This pattern consists of a thin
cylindrical or curved metal piece parted along the center line.
• The two halves of the pattern are held in alignment by dowels.
• The outside surface of the pattern is used to make the mould
for the fitting required while the inside can serve as a core
box.
58. PATTERN ALLOWANCES
• The size of a pattern is never kept the same as that of the desired casting
because of the fact that during cooling the casting is subjected to various
effects and hence to compensate for these effects, corresponding
allowances are given in the pattern.
• These various allowances given to pattern can be enumerated as, allowance
for shrinkage, allowance for machining, allowance for draft, allowance for
rapping or shake, allowance for distortion and allowance for mould wall
movement.
59. • Shrinkage Allowance
• In practice,all common cast metals shrink a significant amount when they are cooled
from the molten state. The total contraction in volume is divided into the following
parts:
• 1. Liquid contraction, i.e. the contraction during the period in which the temperature of
the liquid metal or alloy falls from the pouring temperature to the liquidus temperature.
• 2. Contraction on cooling from the liquidus to the solidus temperature, i.e. solidifying
contraction.
• 3. Contraction that results there after until the temperature reaches the room
temperature. This is known as solid contraction.
• The first two of the above are taken care of by proper gating and risering. Only the last
one, i.e. the solid contraction is taken care by the pattern makers by giving a positive
shrinkage allowance. This contraction allowance is different for different metals.
60. • The contraction allowances for different metals and alloys such as Cast
Iron 10 mm/mt.. Brass 16 mm/mt., Aluminium Alloys. 15 mm/mt., Steel
21 mm/mt., Lead 24 mm/mt. In fact, there is a special rule known as the
pattern marks contraction rule in which the shrinkage of the casting metals
is added.
• The pattern must be made over size to compensate for contraction of
liquid metal on cooling. This addition to the dimension of the pattern
is known as shrinkage allowance.
61. • Machining Allowance
• It is a positive allowance
• given to compensate for the amount of material that is lost in machining or
finishing the casting.
• If this allowance is not given, the casting will become undersize after
machining.
• this allowance depends on the size of casting, methods of machining and
the degree of finish.
• value varies from 3 mm. to 18 mm.
• pattern must be made over size for machining purpose
• This extra amount of dimensions provided in the pattern is known as
Machining allowance.
62. • Taper allowance
• positive allowance
• given on all the vertical surfaces of pattern to make withdrawal easier.
• taper on the external surfaces varies from 10 mm to 20 mm/mt. On interior
holes and recesses which are smaller in size, the taper should be around 60
mm/mt.
• These values are greatly affected by the size of the pattern and the molding
method
• In machine molding its, value varies from 10 mm to 50 mm/mt.
63. • Rapping or Shake Allowance
• Before withdrawing the pattern it is rapped and thereby the size of the
mould cavity increases.
• by rapping, the external sections move outwards increasing the size and
internal sections move inwards decreasing the size.
• insignificant in the case of small and medium size castings,
• but it is significant in the case of large castings. negative allowance pattern
is made slightly smaller in dimensions 0.5-1.0 mm.
64. Distortion Allowance
• This allowance is applied to the castings which have the tendency to distort
during cooling due to thermal stresses developed.
• For example a casting in the form of U shape will contract at the closed
end on cooling, while the open end will remain fixed in position.
• Therefore, to avoid the distortion, the legs of U pattern must converge
slightly so that the sides will remain parallel after cooling.
65. • COLOR CODIFICATION FOR PATTERNS
• Surfaces to be left unfinished after casting are to be painted as
black.
• Surface to be machined are painted as red.
• Core prints are painted as yellow.
• Seats for loose pieces are painted as red stripes on yellow
background.
• Stop-offs is painted as black stripes on yellow base.
67. Mould
• suitable and workable material possessing high refractoriness in
nature
• material can be metallic or non-metallic
• For metallic category, the common materials are cast iron, mild
steel and alloy steels.
• non-metallic group molding sands, plaster of paris, graphite,
silicon carbide and ceramics
• molding sand is the most common utilized non-metallic molding
material because of its certain inherent properties namely
refractoriness, chemical and thermal stability at higher
temperature, high permeability and workability along with good
strength.
68. • molding sand is the most common utilized non-metallic
molding material
• because of its certain inherent properties namely,
• refractoriness,
• chemical and thermal stability at higher temperature,
• high permeability and
• workability along with good strength.
• highly cheap and easily available.
69. MOLDING SAND
• Sources of receiving molding sands
• beds of sea,
• rivers,
• lakes,
• granulular elements of rocks,
• and deserts.
70. • sources of molding sands available in India
1 Batala sand ( Punjab)
2 Ganges sand (Uttar Pradesh)
3 Oyaria sand (Bihar)
4 Damodar and Barakar sands (Bengal- Bihar Border)
5 Londha sand (Bombay)
6 Gigatamannu sand (Andhra Pradesh) and
7 Avadi and Veeriyambakam sand (Madras)
72. Natural Molding sand:
• known as green sand
• having appreciable amount of clay which acts as a
binder between sand grains
• obtained by crushing and milling of soft yellow sand
stone, carboniferous etc
• Ease of availability
• Low cost
• High flexibility
• Mostly used for ferrous and non ferrous metal casting
73. Synthetic sand
• known as silica sand
• not having binder(clay) in natural form
• desired strength and properties developed by separate addition
of binder like bentonite, water and other materials.
• More expensive than natural sand
74. Special sands
• Zicron-cores of brass and bronze casting
• Olivine-for non ferrous casting
• Chromite-for heavy steel casting
• Chrome-magnesite-used as facing materials in steel casting.
75. Types of moulding sand
(According to use)
Green sand
Dry sand
Facing sand
Backing sand
System sand
Parting sand
Loam sand
Core sand
76. Green sand
• Green sand is also known as tempered or natural sand
• mixture of silica sand with 18 to 30 percent clay, having moisture content from 6 to
8%.
• The clay and water furnish the bond for green sand. It is fine, soft, light, and
porous.
• Green sand is damp, when squeezed in the hand and it retains the shape and the
impression to give to it under pressure.
• Molds prepared by this sand are not requiring backing and hence are known as
green sand molds.
77. Dry sand
• Green sand that has been dried or baked in suitable oven after the making mold and
cores, is called dry sand.
• more strength,
• rigidity and
• thermal stability.
• mainly suitable for larger castings.
• mold prepared in this sand are known as dry sand molds.
78. Loam sand
• Loam is mixture of sand and clay with water to a thin plastic paste.
• sand possesses high clay as much as 30-50% and 18% water.
• Patterns are not used for loam molding and shape is given to mold by
sweeps.
• particularly employed for loam molding used for large grey iron castings.
• This sand is used for loam sand moulds for making very heavy castings
usually with the help of sweeps and skeleton patterns.
79. Facing sand
• Facing sand is just prepared and forms the face of the mould.
• It is directly next to the surface of the pattern and it comes into contact
molten metal when the mould is poured.
• high strength refractoriness.
• made of silica sand and clay, without the use of used sand.
• Different forms of carbon are used to prevent the metal burning into the
sand.
• A facing sand mixture for green sand of cast iron may consist of 25% fresh and
specially prepared and 5% sea coal.
• sometimes mixed with 6-15 times as much fine molding sand to make facings.
• The layer of facing sand in a mold usually ranges from 22-28 mm. From 10
to 15% of the whole amount of molding sand is the facing sand.
81. Backing sand
• Backing sand or floor sand is used to back up the facing sand
and is used to fill the whole volume of the molding flask.
• Used molding sand is mainly employed for this purpose.
• The backing sand is sometimes called black sand because that
old
82. System sand
• In mechanized foundries where machine molding is employed.
• A so-called system sand is used to fill the whole molding flask.
• The used sand is cleaned and re-activated by the addition of water and special
additives. This is known as system sand.
• Since the whole mold is made of this system sand, the properties such as strength,
permeability and refractoriness of the molding sand must be higher than those of
backing sand.
83. Parting sand
• without binder and moisture to keep the green sand not to stick
to the pattern
• to allow the sand on the parting surface the cope and drag to
separate without clinging.
• This is clean clay-free silica sand which serves the same
purpose as parting dust.
84. Core sand
• is used for making cores and it is sometimes also known as oil
sand.
• This is highly rich silica sand mixed with oil binders such as
core oil which composed of linseed oil, resin,light mineral oil
and other bind materials.
• Pitch or flours and water may also be used in large cores for
the sake of economy.
85. Properties of Moulding Sand
• Refractoriness
• Refractoriness is defined as the ability of molding sand to withstand high
temperatures without breaking down or fusing thus facilitating to get sound
casting.
• poor refractoriness
• burn on to the casting surface and
• no smooth casting surface can be obtained.
• degree of refractoriness depends on the SiO2 i.e. quartz content, and the
shape and grain size of the particle.
• higher the SiO2 content higher is the refractoriness of the molding
• Refractoriness is measured by the sinter point of the sand rather than its
melting point.
86. • Permeability
• It is also termed as porosity of the molding sand in order to allow the
escape of any air, gases or moisture present or generated in the mould
when the molten metal is poured into it.
• All these gaseous generated during pouring and solidification process must
escape otherwise the casting becomes defective.
• Permeability is a function of grain size, grain shape, and moisture and clay
contents in the molding sand.
• The extent of ramming of the sand directly affects the permeability.
87. • Permeability: Gases evolving from the molten metal and
generated from the mould may have to go through the core
to escape out of the mould. Hence cores are required to
have higher permeability.
• Permeability Number: The rate of flow of air
passing through a standard specimen under a
standard pressure is termed as permeability number.
• The standard permeability test is to measure time taken by
a 2000 cu cm of air at a pressure typically of 980 Pa (10
g/cm2
), to pass through a standard sand specimen confined
in a specimen tube. The standard specimen size is 50.8 mm
in diameter and a length of 50.8 mm.
88. • Then, the permeability number, R is obtained by
Where V= volume of air = 2000 cm3
H = height of the sand specimen = 5.08 cm
p = air pressure, g/cm2
A = cross sectional area of sand specimen = 20.268 cm2
T = time in minutes for the complete air to pass through
Inserting the above standard values into the
expression, we get
VH
R
pAT
501.28
.
R
pT
89. • Calculate the permeability number of sand if it
takes 1 min 25 s to pass 2000 cm3
of air at a
pressure of5 g/cm2
through the standard sample.
2
5.0 /
1min 25 1.417 min
501.28
70.75
5 1.417
p g cm
T s
R
90. • Cohesiveness
• It is property by virtue of which the sand grain particles interact and attract
each other within the molding sand.
• Thus, the binding capability of the molding sand gets enhanced to increase
the green, dry and hot strength property of molding and core sand.
91. • Green strength
• By virtue of this property, the pattern can be taken out from the mould
without breaking the mould and also the erosion of mould wall surfaces
does not occur during the flow of molten metal.
• The green sand after water has been mixed into it, must have sufficient
strength and toughness to permit the making and handling of the mould.
• For this, the sand grains must be adhesive, i.e. they must be capable of
attaching themselves to another body and therefore, and sand grains having
high adhesiveness will cling to the sides of the molding box.
92. • Dry strength
• As soon as the molten metal is poured into the mould, the moisture in the
sand layer adjacent to the hot metal gets evaporated and this dry sand layer
must have sufficient strength to its shape in order to avoid erosion of
mould wall during the flow of molten metal.
• The dry strength also prevents the enlargement of mould cavity cause by
the metallostatic pressure of the liquid metal.
93. • Strength of the moulding sand depends on:
• 1. Grain size and shape
• 2. Moisture content
• 3. Density of sand after ramming
• · The strength of the mould increases with a decrease of grain size and an increase
of clay content and density after ramming. The strength also goes down if moisture
content is higher than an optimum value.
94. • Flowability or plasticity
• It is the ability of the sand to get compacted and behave like a fluid. It will
flow uniformly to all portions of pattern when rammed and distribute the
ramming pressure evenly all around in all directions.
• Generally sand particles resist moving around corners or projections.
• In general, flowability increases with decrease in green strength, an,
decrease in grain size.
• The flowability also varies with moisture and clay content.
95. • Adhesiveness
• · It is the important property of the moulding sand and it is defined as the
sand particles must be capable of adhering to another body, then only the
sand should be easily attach itself with the sides of the moulding box and
give easy of lifting and turning the box when filled with the stand.
96. • Collapsibility
• After the molten metal in the mould gets solidified, the sand mould must
be collapsible so that free contraction of the metal occurs and this would
naturally avoid the tearing or cracking of the contracting metal.
• In absence of this property the contraction of the metal is hindered by the
mold and thus results in tears and cracks in the casting.
• This property is highly desired in cores.
97. Mould Making
Moulding is the process of making a cavity similar to the product
required in sand.
Selection of mould is governed by the type of metal to be cast, size
of casting, accuracy & the surface finish of the casting.
98. Moulding sand is the most commonly used moulding
material.
Because of its certain inherent properties namely,
refractoriness,
chemical and thermal stability at higher temperature,
high permeability and workability along with good
strength.
highly cheap and easily available.
Moulding sand
99. Important ingredients of Moulding Sand
The moulding sands are Consisting of the following ingredients.
They are
(i)Silica sand grains
(ii) Clay
(iii) Moisture
(iv)Miscellaneous materials
100. Material used for making green sand moulds consists following:
Sand (70-85%): to provide refractoriness
Clay (10-20%): to act as binder, along with water, impart tensile and shear
strength to the molding sand
Water (3-6%): to activate the clay and provide plasticity
Organic additives (1-6%): to enhance desired sand properties Moulding sand
composition must be carefully controlled to assure Satisfactory and consistent
results.
Exact composition may vary slightly depending on whether casting is Ferrous
or non-ferrous.
Good molding sand always represents a compromise between conflicting
factors such as: Size of sand particles, Amount of bonding agent (such as
clay), Moisture content, Organic matter
Composition of Moulding Sand
101. • Silica sand
• Silica sand in form of granular quartz is the main constituent of molding
sand
• having enough refractoriness
• which can impart strength, stability and permeability to molding and core
sand.
• along with silica small amounts of iron oxide, alumina, lime stone,
magnesia, soda and potash are present as impurities.
• The silica sand can be specified according to the size (small, medium and
large silica sand grain) and the shape (angular, sub-angular and
rounded).
102. Binder
• In general, the binders can be either inorganic or organic substance.
• The inorganic group includes clay sodium silicate and port land cement
etc.
• In foundry shop, the clay acts as binder which may be Kaolonite, Ball
Clay, Fire Clay, Limonite, Fuller’s earth and Bentonite.
• Binders included in the organic group are dextrin, molasses, cereal
binders, linseed oil and resins like phenol formaldehyde, urea
formaldehyde etc.
• Organic binders are mostly used for core making.
• Among all the above binders, the bentonite variety of clay is the most
common. However, this clay alone can not develop bonds among sand
grains without the presence of moisture in molding sand and core sand.
103. Moisture
• The amount of moisture content in the molding sand varies generally between 2
to 8 percent.
• This amount is added to the mixture of clay and silica sand for developing
bonds.
• This is the amount of water required to fill the pores between the particles of
clay without separating them.
• This amount of water is held rigidly by the clay and is mainly responsible for
developing the strength in the sand.
• The effect of clay and water decreases permeability with increasing clay and
moisture content.
• The green compressive strength first increases with the increase in clay content,
but after a certain value, it starts decreasing.
• For increasing the molding sand characteristics some other additional materials
beside basic constituents are added which are known as additives.
104. Additives
• Dextrin
• carbohydrates
• increases dry strength of the molds.
• Corn flour
• It belongs to the starch family of carbohydrates
• is used to increase the collapsibility of the molding and core sand.
• Coal dust
• To avoid oxidation of pouring metal
• For production of grey iron and malleable cast iron castings.
• Sea coal
• sand grains become restricted and cannot move into a dense packing pattern.
• Pitch
• form of soft coal (0.02 % to 2%)
• Wood flour:0.05 % to 2%
• To avoid expansion defects.
• increases collapsibility of both of mold and core.
• Silica flour
• added up to 3% which increases the hot strength and finish on the surfaces of the molds and cores.
• It also reduces metal penetration in the walls of the molds and cores.
105. Sand Testing
• Molding sand and core sand depend upon shape, size composition and distribution
of sand grains, amount of clay, moisture and additives.
• The increase in demand for good surface finish and higher accuracy in
castings necessitates certainty in the quality of mold and core sands.
• Sand testing often allows the use of less expensive local sands. It also ensures
reliable sand mixing and enables a utilization of the inherent properties of molding
sand.
• Sand testing on delivery will immediately detect any variation from the standard
quality, and adjustment of the sand mixture to specific requirements so that the
casting defects can be minimized.
• It allows the choice of sand mixtures to give a desired surface finish. Thus sand
testing is one of the dominating factors in foundry and pays for itself by obtaining
lower per unit cost and.
106. • 1. Moisture content test
• 2. Clay content test
• 3. Grain fitness test
• 4. Permeability test
• 5. Strength test
• 6. Refractoriness test
• 7. Mould hardness test
107. • Moisture Content Test
• Moisture is the property of the moulding sand it is defined as the amount of water present in
the moulding sand. Low moisture content in the moulding sand does not develop strength
properties. High moisture content decreases permeability.
• Procedures are:
• 1. 20 to 50 gms of prepared sand is placed in the pan and is heated by an infrared heater bulb
for 2 to 3 minutes.
• 2. The moisture in the moulding sand is thus evaporated.
• 3. Moulding sand is taken out of the pan and reweighed.
• 4. The percentage of moisture can be calculated from the difference in the weights, of the
original moist and the consequently dried sand samples.
• Percentage of moisture content = (W1-W2)/(W1) %
• Where, W1-Weight of the sand before drying,
• W2-Weight of the sand after drying
109. • Clay Content Test
• Clay influences strength, permeability and other moulding properties. It is responsible for bonding
sand particles together.
• Procedures are:
• 1. Small quantity of prepared moulding sand was dried
• 2. Separate 50 gms of dry moulding sand and transfer wash bottle.
• 3. Add 475cc of distilled water + 25cc of a 3% NaOH.
• 4. Agitate this mixture about 10 minutes with the help of sand stirrer.
• 5. Fill the wash bottle with water up to the marker.
• 6. After the sand etc., has settled for about 10 minutes, Siphon out the water from the wash bottle.
• 7. Dry the settled down sand.
• 8. The clay content can be determined from the difference in weights of the initial and final sand
samples.
• Percentage of clay content = (W1-W2)/(W1) * 100
• Where, W1-Weight of the sand before drying,
• W2-Weight of the sand after drying.
110. • Grain fitness test:
• The grain size, distribution, grain fitness are determined with the help of the fitness
testing of moulding sands. The apparatus consists of a number of standard sieves
mounted one above the other, on a power driven shaker.
• The shaker vibrates the sieves and the sand placed on the top sieve gets screened and
collects on different sieves depending upon the various sizes of grains present in the
moulding sand.
• The top sieve is coarsest and the bottom-most sieve is the finest of all the sieves. In
between sieve are placed in order of fineness from top to bottom.
• Procedures are:
• 1. Sample of dry sand (clay removed sand) placed in the upper sieve
• 2. Sand is vibrated for definite period
• 3. The amount of same retained on each sieve is weighted.
• 4. Percentage distribution of grain is computed.
112. • Flowability Test
• Flowability of the molding and core sand usually determined
by the movement of the rammer plunger between the fourth
and fifth drops and is indicated in percentages.
• This reading can directly be taken on the dial of the flow
indicator.
• Then the stem of this indicator rests again top of the plunger of
the rammer and it records the actual movement of the plunger
between the fourth and fifth drops.
114. • Permeability Test
• Permeability test:
• The quantity of air that will pass through a standard specimen of the sand at a
particular pressure condition is called the permeability of the sand.
• Following are the major parts of the permeability test equipment:
• 1. An inverted bell jar, which floats in a water.
• 2. Specimen tube, for the purpose of hold the equipment
• 3. A manometer (measure the air pressure)
115. • Steps involved are:
• 1. The air (2000cc volume) held in the bell jar is forced to pass through the sand
specimen.
• 2. At this time air entering the specimen equal to the air escaped through the specimen
• 3. Take the pressure reading in the manometer.
• 4. Note the time required for 2000cc of air to pass the sand
• 5. Calculate the permeability number
• 6. Permeability number (N) = ((V x H) / (A x P x T))
• Where,
• V-Volume of air (cc)
• H-Height of the specimen (mm)
• A-Area of the specimen (mm2
)
• P-Air pressure (gm / cm2
)
• T-Time taken by the air to pass through the sand (seconds)
117. • Refractoriness Test
• The refractoriness of the molding sand is judged by heating the American Foundry Society
(A.F.S) standard sand specimen to very high temperatures ranges depending upon the type of
sand.
• The heated sand test pieces are cooled to room temperature and examined under a
microscope for surface characteristics or by scratching it with a steel needle.
• If the silica sand grains remain sharply defined and easily give way to the needle. Sintering
has not yet set in.
• In the actual experiment the sand specimen in a porcelain boat is p1aced into an e1ectric
furnace.
• It is usual practice to start the test from l000°C and raise the temperature in steps of 100°C to
1300°C and in steps of 50° above 1300°C till sintering of the silica sand grains takes place.
• At each temperature level, it is kept for at least three minutes and then taken out from the
oven for examination under a microscope for evaluating surface characteristics or by
scratching it with a steel needle.
118. • The refractoriness is used to measure the ability of the sand to withstand the higher
temperature.
• Steps involved are:
• 1. Prepare a cylindrical specimen of sand
• 2. Heating the specimen at 1500 C for 2 hours
• 3. Observe the changes in dimension and appearance
• 4. If the sand is good, it retains specimen share and shows very little expansion. If
the sand is poor, specimen will shrink and distort.
119. • Strength Test
• Green strength and dry strength is the holding power of the various bonding
materials.
• Generally green compression strength test is performed on the specimen of green
sand (wet condition).
• The sample specimen may of green sand or dry sand which is placed in lugs and
compressive force is applied slowly by hand wheel until the specimen breaks.
• The reading of the needle of high pressure and low pressure manometer indicates
the compressive strength of the specimen in kgf/cm2.
• The most commonly test performed is compression test which is carried out in a
compression sand testing machine
120. • Measurements of strength of moulding sands can be carried out on the universal
sand strength testing machine. The strength can be measured in compression, shear
and tension.
• The sands that could be tested are green sand, dry sand or core sand. The
compression and shear test involve the standard cylindrical specimen that was used
for the permeability test.
122. • Mould hardness test:
• Hardness of the mould surface can be tested with the help of an “indentation
hardness tester”. It consists of indicator, spring loaded spherical indenter.
• The spherical indenter is penetrates into the mould surface at the time of testing.
The depth of penetration w.r.t. the flat reference surface of the tester.
• Mould hardness number = ((P) / (D – (D2
-d2
))
• Where,
• P- Applied Force (N)
• D- Diameter of the indenter (mm)
• d- Diameter of the indentation (mm)
127. • Various molding methods are:
– Bench molding
– Floor molding
– Pit molding
– Machine molding
a) Bench molding
• Molding is carried out on a bench of convenient height.
• Small and light molds are prepared on benches.
• The molder makes the mold while standing.
• Both green and dry sand molds can be made by bench molding,
• Molds, both for ferrous and (especially) non-ferrous castings are made on bench molds.
• Both cope and drag are rammed on the bench.
MOLDING METHODS
128. b) Floor molding
• Molding work is carried out on foundry floor when mold size is large and molding cannot
be carried out on a bench.
• Medium and large-sized castings are made by floor molding.
• The mold has its drag portion in the floor and cope portion may be rammed in a flask and
inverted on the drag.
• Both green and dry sand moulds can be made by floor molding
129. c) Pit molding
• Very big castings which cannot be made in flasks are molded in pits dug on the floor.
• Very large jobs can be handled and cast easily through pit molding.
• The mold has its drag part in the pit and a separate cope is rammed and used above the (pit) drag.
• The depth of the drag in pit molding is much more than that in floor molding.
• In pit molding, the molder may enter the drag and prepare it.
• A pit is of square or rectangular shape.
• The sides of the (pit) drag are lined with brick and the bottom is covered with molding sand .
• The cope (a separate flask) is rammed over the pit (drag) with pattern in position.
• Gates, runner, pouring basin, sprue etc. are made in the cope.
• The mold is dried by means of a stove(heater) placed in the pit.
• Cope and drag are then assembled. A crane may be used for lifting and positioning the cope over
drag.
• Cope can be clamped in position.
• Mold is ready for being poured.
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130. d) Machine molding
• In bench, floor and pit molding, the different molding operations are
carried out manually by the hands of the molder, where as in machine
molding, various molding operations like sand ramming, rolling the mold
over, withdrawing the pattern etc. are done by machines.
• Machines perform these operations much faster, more efficiently and in a
much better way.
• Molding machines produce identical and consistent castings.
• Molding machines produce castings of better quality and at lower costs.
• Molding machines are preferred for mass production of the castings
whereas hand molding (bench, pit and floor) is used for limited production.
• Machine molding is not a fully automatic process; many operations can
though be performed by machines, yet some others have to be carried out
by hands.
• A few different types of molding machines are listed below:
– Jolt machine
– Squeeze machine
– Jolt-squeeze machine
– Sand Slinger
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131. MOULDING MACHINES
• When large number of castings is to be produced, hand moulding consumes
more time, labour and also accuracy and uniformity in moulding varies.
• To overcome this difficulty, machines are used for moulding.
• Based on the methods of ramming, moulding machines are classified as follows:
1. Jolt machine
2. Squeeze machine
3. Jolt-squeeze machine
4. Sand slinger
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132. 1. Jolt Machine
• A jolt machine consists of a flat table mounted on a piston-cylinder
arrangement and can be raised or lowered by means of compressed air.
• In operation, the mould box with the pattern and sand is placed on the
table. The table is raised to a short distance and then dropped down under
the influence of gravity against a solid bed plate. The action of raising and
dropping (lowering) is called 'Jolting'.
• Jolting causes the sand particles to get packed tightly above and around the
pattern. The number of 'jolts' may vary depending on the size and hardness
of the mould required. Usually, less than 20 jolts are sufficient for a good
moulding.
• The disadvantage of this type is that, the density and hardness of the
rammed sand at the top of the mould box is less when compared to its
bottom portions.
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133. 2. Squeeze Machine
• In squeeze machine, the mould box with pattern and sand in it is placed on a fixed
table as shown in figure
• A flat plate or a rubber diaphragm is brought in contact with the upper surface of
the loose sand and pressure is applied by a pneumatically operated piston.
• The squeezing action of the plate causes the sand particles to get packed tightly
above and around the pattern.
• Squeezing is continued until the mould attains the desired density.
• In some machines, the squeeze plate may be stationary with the mould box
moving upward.
• The disadvantage of squeeze machine is that, the density and hardness of the
rammed sand at the bottom of the mould box is less when compared to its top
portions.
134. 3. Jolt Squeeze Machine
• Jolt squeeze machine combines the operating principles of 'jolt' and 'squeeze'
machines resulting in uniform ramming of the sand in all portions of the moulds
• The machine makes use of a match plate
pattern placed between the cope and the drag
box.
• The whole assembly is placed on the table
with the drag box on it.
• The table is actuated by two pistons in air
cylinders, one inside the other. One piston
called 'Jolt piston' raises and drops the table
repeatedly for a predetermined number of
times, while the other piston called 'squeeze
piston' pushes the table upward to squeeze
the sand in the flask against the squeeze
plate. In operation, sand is filled in the drag
box and jolted repeatedly by operating the
jolt piston.
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136. • After jolting, the complete mould assembly is rolled over by
hand.
• The cope is now filled with sand and by operating the
squeeze piston, the mould assembly is raised against the
squeeze plate. By the end of this operation, the sand in the
mould box is uniformly packed.
• The match plate is now vibrated and removed. The mould is
finished and made ready for pouring.
The Jolting and Squeezing methods will give the uniform
strength and hardness if the height of the mold is less than 200
mm.
If the height of the mold is greater than 200 mm, the top and
bottom will be getting higher strength but the middle of the
mold is at a lower strength.
137.
In Sand slinging operation, small quantities of molding sand will be
thrown into the mold with a certain amount of force so that
localized ramming action will be taking place and it gives the
uniform strength and hardness of the mold with whatever may be
the height of the mold.
The Sand Slinging equipment is costly and also when the molten
sand is thrown on to the projection, it may damages the projection
present on the pattern.
Hence this method cannot be used for producing the molds with a
pattern having projections and Extinctions.
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4. Sand slinger
139. Characteristics of Core
Green strength – sufficient strength to hold up its shape till it is baked.
Dry strength – sufficient strength to resist bending forces due to hydrostatic
pressure from the liquid (molten metal), when core is placed inside the mould
Refractoriness – core is surrounded on all sides by molten metal and should
have high refractoriness.
Permeability – gases evolved may pass through the core to escape and should
posses sufficient permeability.
Collapsibility – should get dismantled easily once the casting is completely
cooled
Smoothness – surface of core should be smooth to have better surface finish.
Low gas emission – emission of gases from core should be as low as possible
to avoid voids formed inside core
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140. Core Sand
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Core sand must be stronger than moulding sand
Core sand = Sand grains + Binders + Additives
Sand grains
Sand containing more than 5% clay is not used to make core
Excessive clay reduces the permeability and collapsibility of the core.
Coarse silica used for making steels and finer one for cast iron an
non- ferrous alloys
Binders
Organic binders tend to burn away under the heat of molten metal
and hence increases the collapsibility of the core.
Organic binder develop strength by polymerisation and cross-linking
and hence cores are baked.
Some of the binders are linseed oil, dextrin, molasses, resins etc.
141. Core Prints
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4
1 Core prints are extra projections provided on the pattern that form
a seat in the mould. Core prints support the core in the mould
cavity.
Core shifts and chaplets
Chaplets are used to support the cores
which tend to sag without adequate supports.
Chaplets are made of the same material as
that of the casting.
142. Types of Cores
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4
2
Horizontal cores –
It is held horizontally along the parting line of the mould.
Ends of core rests in the seats provided by core prints on the pattern.
Vertical cores –
Two ends of the mould sits on the cope and drag portion of the mould.
Amount of taper on the top is more than the taper at the bottom of the core.
Balanced cores –
When openings are required at only one end, balanced cores are used.
Core prints are available at one end of the pattern.
Core prints need to be sufficiently longer to support the core in case of longer
holes.
143. Types of Cores
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3
Hanging cores –
They are used when the casting is made in drag.
Core is supported from above and hangs into the mould.
Fastening wires or rods are used and hole is made in the upper part of the core so that
molten metal reaches the mould cavity.
Cover cores –
In cover core, core hangs from the cope portion and is supported by the drag.
Core acts as a cover and hence termed as cover core.
Wing cores –
A wing core is used when hole or recess is to be obtained in casting.
Core print is given sufficient amount of taper so that core is placed
readily in the mould.
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4
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Functions of Gating system
To provide continuous, uniform feed of molten metal in to mould
cavity and to reduce the turbulence flow.
Proper directional solidification
To fill the mould cavity in a less time to avoid thermal gradient
To provide minimum excess metal
To prevent erosion of mould walls
To prevent the foreign materials to enter in mould cavity
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4
7
Elements of Gating system
1. Pouring basin
It is the conical hollow element or tapered hollow vertical portion of the
gating system
It makes easier for the ladle operator to direct the flow of molten metal from
crucible to pouring basin and sprue.
It helps in maintaining the required rate of liquid metal flow.
It reduces turbulence and vortexing at the sprue entrance.
It also helps in separating dross, slag and foreign element etc.
Skim core plays very important role in removing slag.
148. 1
4
8
Elements of Gating system
2. Sprue
It is channel in cope side connected at bottom of pouring basin
which will carry molten metal to the parting plane.
In straight sprue due to vortex flow air bubbles may enter in to the
cavity this can be compensated by providing taper to it.
It is tapered with its bigger end at to receive the molten metal the
smaller end is connected to the runner.
It some times possesses skim bob at its lower end.
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4
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Elements of Gating system
3. Sprue Base Well
It acts as a reservoir for metal at the bottom of sprue in order to
reduce moment of molten metal.
The molten metal gains velocity while moving down the sprue, some of
which is lost in the sprue base well by which the mold erosion is reduced.
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5
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Elements of Gating system
4. Runner
It is located in parting plane and connects the sprue to the in-gates.
The runners are normally made trapezoidal in cross-section.
The slag trapping takes place in the runner, when runner flows full. If the
amount of molten metal coming from sprue base is more than the amount
flowing through the in-gates.
A partially filled runner causes slag to enter the mold cavity.
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5
1
Elements of Gating system
5. Gate
It is a small passage or channel being cut by gate cutter which connect
runner with the mould cavity.
It feeds the liquid metal to the casting at the rate consistent with the rate
of solidification.
Types of Gates
Top Gate
Bottom Gate
Parting Gate
Step Gate
152. Types of Gating System
1. Top Gate 2. Bottom Gate 3. Parting Line
Gate 4. Step Gate
Directional Cooling
Fast Filling
Ferrous Casting
1. Minimum Turbulence
2. Reduce Erosion
3. Used for Deep Mold
1.Gradual Filling of
MOLD
2. Heavy Casting
3. Small size of in
gates in Compare to
Runner
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5
3
6. Riser
It is a passage in molding sand made in the cope portion of the mold.
Molten metal rises in it after filling the mould cavity completely.
It compensates the shrinkage during solidification of the casting
thus avoiding the shrinkage defect in the casting.
It also permits the escape of air and mould gases.
It promotes directional solidification too and helps in bringing the
soundness in the casting.
154. Gating Ratio
• Gating ratio is used to describe the relative cross-
sectional areas of the components of a gating system.
• Pressurized Gating System:-
Area of Sprue : Area of Runner : Area of in gate ( 1:2:1)
This System is Gating Control System , because in gate
Control the Flow Rate.
Air Aspiration effect is minimum.
Casting Yield is Maximum.
Chances of turbulence.
155. Unpressurized Gating System
• Gating Ratio is:-
Area of Sprue : Area of Runner : Area of in gate( 1: 2: 2)
This System Is Choke Control System, Choke area
Controls the Flow Rate.
Area of Choke will be:-
Ac = W/ c.d.t( 2gh )
Air Aspiration effect is more than other System .
Velocity is low, so Turbulence is minimum.
Casting Yield is Minimum.
156. FACTORS CONTROLING GATING DESIGN
• The following factors must be considered while designing gating system.
(i) Sharp corners and abrupt changes in at any section or portion in gating system should be avoided for suppressing
turbulence and gas entrapment. Suitable relationship must exist between different cross-sectional areas of gating
systems.
(ii) The most important characteristics of gating system besides sprue are the shape, location and dimensions of runners
and type of flow. It is also important to determine the position at which the molten metal enters the mould cavity.
(iii) Gating ratio should reveal that the total cross-section of sprue, runner and gate decreases towards the mold cavity
which provides a choke effect.
(iv) Bending of runner if any should be kept away from mold cavity.
(v) Developing the various cross sections of gating system to nullify the effect of turbulence or momentum of molten
metal.
(vi) Streamlining or removing sharp corners at any junctions by providing generous radius, tapering the sprue, providing
radius at sprue entrance and exit and providing a basin instead pouring cup etc.
157. 1. Sprue in casting refers to.......
A.Gate
B.Runner
C.Riser
D.Vertical passage
2. The ability of the moulding sand to withstand the heat of melt
without showing any sign of softening is called as
a.strength or cohesiveness
b. refractiveness
c.collapsibility
d. adhesiveness
158. 3) Which of the following is not a requirement of a good pattern?
a.It should be light in weight to handle easily
b. It should be smooth to make casting surface smooth
c.It should have low strength to break it and to remove casting easily
d.none of the above
4) The patterns which are made in two or more pieces are called as
a.solid patters
b.split patterns
c.loose piece patterns
d.none of the above
5) Permeability can be defined as the property of moulding sand
a. to hold sand grains together
b. to allow gases to escape easily from the mould
c. to withstand the heat of melt without showing any sign of
softening
d. d. none of the above
159. 6) The sand in its natural or moist state is called as
a.green sand
b.loam sand
c.dry sand
d.none of the above
7) The sand is packed on pit moulds with.......
a. Manually b. Squeezers c. Jolt machines d. Sand slingers
160. 9) Which property of a material is used for Casting it into a desired
shape
(a)Strength
(b)Fluidity
(c)Ductility
(d)Formability
10) Muller is used for
(a)remove small pieces of metal or foreign particles
(b)remove iron particles from sand
(c)increase the flowability of sand
(d)mixing of sand
161. 11) Light impurities in the molten metal are prevented from
reaching the mould cavity by providing
(a) stainer (b) bottom well (c) skim bob (d) All of these
12)Freezing ratio or relative freezing time according to
Caine’s equation is
162. 12.Which of the following is used to improve the
directional solidification for difficult casting
geometries?
(a)Chills
(b) Chaplets
(c) Step gate
(d)Runner extension
166. Centrifugal Casting
• The mould is rotated and the
molten metal is distributed to
the mould cavity with
centrifugal force.
• This process makes hollow
product.
• Following are centrifugal
process:
1. True centrifugal casting
process
2. Semi centrifugal casting
process
3. Centrifuging process.
167. Centrifugal Casting
1. True Centrifugal casting
process:
• This process is also
classified as horizontal,
vertical or inclined at 70 to
90°.
(A)Horizontal axis machine :
• With this process better
quality casting is achieved
and speed control is also
possible.
Editor's Notes
#87:Permeability: Gases evolving from the molten metal and generated from the mould may have to go through the core to escape out of the mould. Hence cores are required to have higher permeability.
Collapsibility: As the casting cools, it shrinks, and unless the core has good collapsibility (ability to decrease in size) it is likely to provide resistance against shrinkage and thus can cause hot tears.
#88:Permeability: Gases evolving from the molten metal and generated from the mould may have to go through the core to escape out of the mould. Hence cores are required to have higher permeability.
Collapsibility: As the casting cools, it shrinks, and unless the core has good collapsibility (ability to decrease in size) it is likely to provide resistance against shrinkage and thus can cause hot tears.
