1. Steps involved in making a casting:
1. Make the pattern out of Wood , Metal or Plastic.
2. Prepare the necessary sand mixtures for mould and core making.
3. Prepare the Mould and necessary Cores.
4. Melt the metal/alloy to be cast.
5. Pour the molten metal/alloy into mould and remove the casting
from the mould after the metal solidifies.
6. Clean and finish the casting.
7. Test and inspect the casting.
8. Remove the defects, if any.
9. Relieve the casting stresses by Heat Treatment.
10. Again inspect the casting.
11. The casting is ready for shipping.
2.
3. Pattern Making:
A Pattern is a model or the replica of the
object to be cast.
Except for the various allowances a pattern
exactly resembles the casting to be made.
A pattern is required even if one object has to
be cast.
4. Types of Patterns:
Single piece pattern.
Split pattern
Loose piece pattern
Match plate pattern
Sweep pattern
Gated pattern
Skeleton pattern
Follow board pattern
Cope and Drag pattern
15. The pattern material should be:
1. Easily worked, shaped and joined.
2. Light in weight.
3. Strong, hard and durable.
4. Resistant to wear and abrasion .
5. Resistant to corrosion, and to chemical
reactions.
6. Dimensionally stable and unaffected by
variations in temperature and humidity.
7. Available at low cost.
16. Types of Pattern Allowances:
The various pattern allowances are:
1. Shrinkage or contraction allowance.
2. Machining or finish allowance.
3. Draft of tapper allowances.
4. Distortion or chamber allowance.
5. Shake or rapping allowance.
17. 1.Shrinkage Allowance:
All most all cast metals shrink or contract
volumetrically on cooling.
The metal shrinkage is of two types:
1. Liquid Shrinkage:
2. Solid Shrinkage:
18. 2. Machining Allowance:
A Casting is given an allowance for machining, because:
i. Castings get oxidized in the mold and during
heat treatment; scales etc., thus formed need
to be removed.
ii. It is the intended to remove surface roughness
and other imperfections from the castings.
iii. It is required to achieve exact casting
dimensions.
iv. Surface finish is required on the casting.
19. 3. Draft or Taper Allowance:
It is given to all surfaces perpendicular to
parting line.
Draft allowance is given so that the pattern can
be easily removed from the molding material
tightly packed around it with out damaging the
mould cavity.
20. 3. Draft or Taper Allowance:
It is given to all surfaces perpendicular to parting
line.
Draft allowance is given so that the pattern can
be easily removed from the molding material
tightly packed around it with out damaging the
mould cavity.
23. 4. Distortion or cambered allowance:
A casting will distort or wrap if :
i. It is of irregular shape,
ii. All it parts do not shrink uniformly i.e., some
parts shrinks while others are restricted from
during so,
iii. It is u or v-shape
24. 5. Shake allowance:
A pattern is shaken or rapped by striking the same
with a wooden piece from side to side. This is done
so that the pattern a little is loosened in the mold
cavity and can be easily removed.
In turn, therefore, rapping enlarges the mould cavity
which results in a bigger sized casting.
Hence, a –ve allowance is provided on the pattern
i.e., the pattern dimensions are kept smaller in
order to compensate the enlargement of mould
cavity due to rapping.
26. A)Natural sand is the one which is available from natural
deposits. Only additives and water need be added to it to make it
satisfactory for molding.
B)Synthetic sand is prepared by mixing a relatively clay free
sand having specified type of sand grain, with specified type
of clay binder as well as water and other additives.
27. 1. Green sand: It is sand used in
the wet condition for making the
mould. It is mixture of silica sand
with 15-25 per cent clay and 6-8
per cent water
The sand can be easily worked
with hand to give it any desired
shape.
This sand is used for producing
small to medium sized moulds
which are not very complex
28. 2. Dry sand:
Dry sand is the green
sand that has been
dried or baked after
preparing the mould.
Drying sand gives
strength to the mould
so that it can be used
for larger castings
29. 3. Loam sand:
Loam sand is sand
containing up to 50 % clay
which has been worked to
the consistency of builder
mortar.
This sand is used for loam
sand moulds for making
very heavy castings usually
with the help of sweeps
and skeleton patterns.
30. 4. Parting sand:
-This sand is used during making of the
mould to ensure that green sand does not
stick to the pattern and the cope and drug
parts can be easily separated for removing
the pattern without causing any damage to
the mould.
-Parting sand consists of fine grained clay
free dried silica sand, sea sand or burnt
sand with some parting compounds.
-The parting compounds used include
charcoal, ground bone and limestone,
groundnut shells, talc and calcium
phosphate.
31. 5. Facing sand:
-Facing sand is the sand which covers
the pattern all around it. The
remaining box is filled with ordinary
floor sand.
-Facing sand forms the face of the
mould and comes in direct contact
with the molten metal when it is
poured.
-High strength and refractoriness are
required for this sand.
-It is made of silica sand and clay
without the addition of any used sand.
32. 6. Backing sand:
-Backing sand is the bulk of the
sand used to back up the facing
sand and to fill up the volume of
the flask.
-It consists mainly of old, repeatedly
used moulding sand which is
generally black in colour due to
addition of coal dust and burning
on contact with hot metal.
Because of the colour backing sand
is also sometimes called black sand.
33. 7. System sand:
-This is the sand used in
mechanized foundries for filling
the entire flask.
-No separate facing sand in used in
a mechanized foundry.
-Sand, cleaned and reactivated by
the addition of water and binders
is used to fill the flask. Because of
the absence of any fresh sand,
system sand must have more
strength, permeability and
refractoriness compared to
backing sand.
34. 8. Core sand:
-Core sand is the sand used for
making cores. --This is silica sand
mixed with core oil. That is why it
is also called oil sand.
-The core oil consists of linseed oil,
resin, light mineral oil with some
binders.
-For larger cores, sometimes pitch
or flour and water may also be
used to save on cost.
36. 1. Green strength: The green sand, after water has been mixed into it,
must have adequate strength and plasticity for making and handling of
the mold.
2. Dry strength: As a casting is poured, sand adjacent to the hot metal
quickly loses its water as steam. The dry sand must have strength to
resist erosion, and also the pressure of the molten metal, or else the
mold may enlarge.
3. Hot strength. After the moisture has evaporated, the sand may be
required to possess strength at some elevated temperature.
4. Permeability/Porosity. Heat from the casting causes a green‐sand
mold to evolve a great deal of steam and other gases. The mold must
be permeable, i.e. porous, to permit the gases to pass off, or the
casting will contain gas holes.
5. Thermal stability. Heat from the casting causes rapid
expansion of the sand surface at the mold‐ metal interface. The
mold surface may then crack, buckle, or flake off (scab) unless
the molding sand is relatively stable dimensionally under rapid
heating.
37. 6. Refractoriness. Higher pouring temperatures, such as those for ferrous
alloys at 2400 to 3200 F, require greater refractoriness of the sand. Low‐
pouring‐temperature metals, for example, aluminum, poured at 1300 F, do
not require a high degree of refractoriness from the sand.
7. Plasticity or flow-ability : It is the measure of the molding sand to flow
around and over a pattern during ramming and to uniformly fill the flask.
8. Cohesiveness: It is the property of sand which hold grains together.
9. Collapsibility. Heated sand which becomes hard and rocklike is difficult to
remove from the casting and may cause the contracting metal to tear or
crack.
10. Adhesiveness: This is the property of sand mixture to adhere to another
body (here, the molding flasks). The molding sand should cling to the sides of
the molding boxes so that it does not fall out when the flasks are lifted and
turned over
11. Offers ease of sand preparation and control.
12. Removes heat from the cooling casting.
13.Produces good casting finish
14.It is reusable.
38. Core-Core prints :
When a casting is required to have
a hole, through or blind, a core is used
in the mould to produce the same.
It is made up of sand ,wood, or metal
body, which is left in the mould during
casting and it remove after casting.
This core has to be properly seated
in the mould extra projections are
added on the pattern surface at proper
places. These projections are known as
core prints.
39. Use of chaplets to avoid shifting of cores
Possible chaplet design
and casting with core
43. Casting Terms:
2. Pattern: It is the replica
of the final object to
be made. The mold
cavity is made with
the help of pattern.
3. Parting line: This is the
dividing line between
the two molding flasks
that makes up the
mold.
Pattern
44. 4. Pouring basin: A small funnel shaped cavity at the
top of the mold into which the molten metal is
poured.
5. Sprue: The passage through which the molten
metal, from the pouring basin, reaches the mold
cavity. In many cases it controls the flow of metal
into the mold.
45. 6. Runner: The channel through which the molten metal
is carried from the sprue to the gate.
7. Riser: A column of molten metal placed in the mold
to feed the castings as it shrinks and solidifies. Also
known as feed head.
8. Gate: A channel through which the molten metal
enters the mold cavity.
46. 9. Core: A separate part of the mold, made of sand and
generally baked, which is used to create openings and
various shaped cavities in the castings.
10.Chaplets: Chaplets are used to support the cores
inside the mold cavity to take care of its own weight
and overcome the metallostatic force.
11. Vent: Small opening in the mold to facilitate escape
of air and gases.
47. Furnaces
• Melting is an equally important parameter for
obtaining a quality castings. A number of
furnaces can be used for melting the metal, to be
used, to make a metal casting. The choice of
furnace depends on the type of metal to be
melted. Some of the furnaces used in metal
casting are as following:.
• Crucible furnaces
• Cupola
• Induction furnace
• Eclectic arc furnace
52. Cupola
Cupola furnaces are tall, cylindrical furnaces
used to melt iron and ferrous alloys in foundry
operations. Alternating layers of metal and
ferrous alloys, coke, and limestone are fed into
the furnace from the top. This diagram of a
cupola illustrates the furnace's cylindrical
shaft lined with refractory and the alternating
layers of coke and metal scrap. The molten
metal flows out of a spout at the bottom of the
cupola. .
53. Description of Cupola
The cupola consists of a vertical cylindrical steel sheet and lined
inside with acid refractory bricks. The lining is generally thicker in
the lower portion of the cupola as the temperature are higher than
in upper portion.
There is a charging door through which coke, pig iron, steel scrap
and flux is charged
The blast is blown through the tuyeres
These tuyeres are arranged in one or more row around the
periphery of cupola
Hot gases which move up from the bottom (combustion zone)
preheats the iron in the preheating zone
Cupolas are provided with a drop bottom door through which
debris, consisting of coke, slag etc. can be discharged at the end of
the melt
A slag hole is provided to remove the slag from the melt
Through the tap hole molten metal is poured into the ladle
At the top conical cap called the spark arrest is provided to prevent
the spark emerging to outside
54. Operation of Cupola
The cupola is charged with wood at the bottom.
On the top of the wood a bed of coke is built.
Alternating layers of metal and ferrous alloys,
coke, and limestone are fed into the furnace
from the top. The purpose of adding flux is to
eliminate the impurities and to protect the
metal from oxidation. Air blast is opened for the
complete combustion of coke. When sufficient
metal has been melted that slag hole is first
opened to remove the slag. Tap hole is then
opened to collect the metal in the ladle.
58. The Electric Arc Furnace (EAF) uses only scrap metal. The
process was originally used solely for making high quality
steel. Modern electric arc furnaces can make up to 150 tones
of steel in a single melt.
The electric arc furnace consists of a circular bath with a
movable roof, through which three graphite electrodes can be
raised or lowered. At the start of the process, the electrodes
are withdrawn and the roof swung. The steel scrap is then
charged into the furnace from a large steel basket lowered
from an overhead travelling crane. When charging is
complete, the roof is swung back into position and the
electrodes lowered into the furnace.
A powerful electric current is passed through the charge, an
arc is created, and the heat generated melts the scrap.
62. Centrifugal casting is a method of casting parts having axial symmetry.
The method involves pouring molten metal into a cylindrical mold
spinning about its axis of symmetry. The mold is kept rotating till the
metal has solidify
The rotation speed of centrifugal mold is commonly about 1000 RPM
(may vary from 250 RPM to 3600 RPM).
63. Centrifugal casting is carried out as follows:
The mold wall is coated by a refractory ceramic coating
(applying ceramic slurry, spinning, drying and baking).
Starting rotation of the mold at a predetermined speed.
Pouring a molten metal directly into the mold (no gating
system is employed).
The mold is stopped after the casting has solidified.
Extraction of the casting from the mold.
Non-metallic and slag inclusions and gas bubbles being less
dense than the melt are forced to the inner surface of the
casting by the centrifugal forces. This impure zone is then
removed by machining.
Centrifugal casting technology is widely used for
manufacturing of iron pipes, bushings, wheels, pulleys bi-metal
steel-bronze bearings and other parts possessing axial
symmetry.
64. Applications
Typical parts made by this process are pipes, boilers, pressure
vessels ,flywheels, cylinder ,liners and other parts that are axi-
symmetric. It is notably used to cast cylinder liners and sleeve
valves for piston engines, parts which could not be reliably
manufactured otherwise.
65. ISE 316 - Manufacturing
Processes Engineering
Shell Molding
Casting process in which the mold is a thin
shell of sand held together by thermosetting
resin binder
66. ISE 316 - Manufacturing
Processes Engineering
Steps in shell-molding:
(1) a match-plate or cope-and-drag metal
pattern is heated and placed over a box
containing sand mixed with
thermosetting resin
67. ISE 316 - Manufacturing
Processes Engineering
(2) box is inverted so that sand and resin fall
onto the hot pattern, causing a layer of the
mixture to partially cure on the surface to
form a hard shell
68. ISE 316 - Manufacturing
Processes Engineering
(3) box is repositioned so that
loose uncured particles drop
away
69. ISE 316 - Manufacturing
Processes Engineering
(4) sand shell is heated in oven for several minutes to
complete curing
(5) shell mold is stripped from the pattern
70. ISE 316 - Manufacturing
Processes Engineering
(6) two halves of the shell mold are assembled,
supported by sand or metal shot in a box, and
pouring is accomplished
(7) the finished casting with sprue removed
74. Procedure
1. Produce a master pattern
The pattern is a modified replica of the desired product made
from metal, wood, plastic, or some other easily worked
material.
2. From the master pattern, produce a master die
This can be made from low-melting-point metal, steel, or
possibly even wood. If low-melting-point metal is used.
3. Produce wax patterns
Patterns are made by pouring molten wax into the master die,
or injecting it under pressure, and allowing it to harden. Plastic
and frozen mercury have also been used as pattern material.
4. Assemble the wax patterns onto common wax sprues
The individual wax patterns are attached to a central sprues
and runner system by means of heated tools and melted wax. In
some cases, several pattern pieces may first be united to form a
complex.
75. 5. Coat the cluster with a thin layer of investment material
This step is usually accomplished by dipping the cluster into a
watery slurry of finely ground refractory material.
6. Produce the final investment around the coated cluster
After the initial layer is formed, the cluster can be redipped,
but this time the wet ceramic is coated with a layer of sand
and allowed to dry. This process can be repeated until the
investment coating is the desired thickness (typically 5 to 15
mm).
7. Allow the investment to fully harden
8. Melt or dissolve the wax pattern to remove it from the
mould
This is generally accomplished by placing the moulds upside
down in an oven, where the wax melts and runs out, and any
residue subsequently vaporizes.
76. 9. Preheat the mould in preparation for pouring
Heating to 550 to 1100°C (1000 to 2000°F) ensures complete
removal of the mould wax, curves the mould to give added
strength, and allows the molten metal to retain its heat and
flow more readily into all of the thin sections.
10. Pour the molten metal
Various methods, beyond simple pouring, can be used to
ensure complete filling of the mould, especially when
complex, thin sections are involved.
11. Remove the casting from the mould
This is accomplished by breaking the mould away from the
casting. Techniques include mechanical vibration and high-
pressure water.
77. Applications
The products made by this process are vanes and blades for gas turbines,
shuttle eyes for weaving, pawls and claws of movie cameras, wave guides for
radars, bolts and triggers for fire arms, stainless steel valve bodies and
impellers for turbo chargers , While investment casting is actually a very old
process and has been performed by dentists and jewellers for a number of
years.
Developments and demands in the aerospace industry, such as rocket
components and jet engine turbine blades, required high-precision complex
shapes from high-melting-point metals that are not readily machinable.
Investment casting offers almost unlimited freedom in both the complexity of
shapes and types of materials that can be cast.
78. A mis-run is caused when the metal is unable to
fill the mold cavity completely and thus leaves
unfilled cavities.
A mis-run results when the metal is too cold to
flow to the extremities of the mold cavity before
freezing. Long, thin sections are subject to this
defect and should be avoided in casting design.
79. Metal penetration
When molten metal enters into the gaps between
sand grains, the result is a rough casting surface.
This occurs because the sand is coarse or no mold
wash was applied on the surface of the mold. The
coarser the sand grains more the metal
penetration.
80. Shrinkage Cavities
These are caused by liquid shrinkage occurring during the
solidification of the casting. To compensate for this, proper
feeding of liquid metal is required. For this reason risers are
placed at the appropriate places in the mold. Sprues may be
too thin, too long or not attached in the proper location,
causing shrinkage cavities. It is recommended to use thick
sprues to avoid shrinkage cavities.
81. Mold Shift
The mold shift defect occurs when cope
and drag or molding boxes have not been
properly aligned.
82. A condition existing in a casting caused by the trapping of gas in the molten
metal or by mold gases evolved during the pouring of the casting. The
defects in this category can be classified into blowholes and pinhole
porosity. Blowholes are spherical or elongated cavities present in the casting
on the surface or inside the casting. Pinhole porosity occurs due to the
dissolution of hydrogen gas, which gets entrapped during heating of molten
metal.
83. A cold shut is caused when two streams while meeting in the
mold cavity, do not fuse together properly thus forming a
discontinuity in the casting. When the molten metal is poured
into the mold cavity through more-than-one gate, multiple
liquid fronts will have to flow together and become one
solid. If the flowing metal fronts are too cool, they may not
flow together, but will leave a seam in the part. Such a seam is
called a cold shut, and can be prevented by assuring sufficient
superheat in the poured metal and thick enough walls in the
casting design
84. Inclusions:
• Inclusions are any foreign materials present in the cast metal.
• These may be in the form of oxides, slag, dirt, sand or nails.
• Common sources of these inclusions are impurities with the
molten metal, sand and dirt from the mould not properly
cleaned, break away sand from mould, core or gating system,
gas from the metal and foreign items picked on the mould cavity
while handling.
• Inclusions are reduced by using correct grade of moulding
sand and proper skimming to remove impurities.
85. Cuts and Washes:
• Cuts and washes are caused by erosion of
mould and core surfaces by the metal flowing in
the mould cavity.
• These defects are avoided by proper ramming,
having sand of required strength and controlling
the turbulence during pouring.
86. Metal penetration:
• If the sand grains used are very coarse or the metal poured has very
high temperature the metal is able to enter the spaces between sand
grains to some distance. Such sand becomes tightly wedged in the
metal and is difficult to remove.
• The remedy is to remove the causes mentioned above.
Hard Spots:
• Hard spots are caused by chilling action of moulding sands in
some metals like gray cast iron with insufficient silicon.
• These spots are extremely hard and often lead to machining
difficulties.
• Hard spots are avoided by providing uniform cooling and pouring
at the right temperature.
87. Scabs:
• Scabs are rough, irregular projections on surface of
castings containing embedded sand.
• Scabs occur when a portion on the face of mould or
core lifts and metal flows underneath in a thin layer.
• They are caused by using too fine sand grains or using
sand of low permeability or moisture content.
• They may also be caused by uneven mould ramming
or by intense local overheating.
• Scabs can be reduced by mixing additives like sea coal,
wood flour or dextrin in the sand, providing uniform
ramming and pouring with correct velocity.
88. Hot tears:
• Hot tears are ragged irregular internal or external cracks occurring immediately
after the metal have solidified.
• Hot tears occur on poorly designed castings having abrupt section changes or
having no proper fillets or corner radii. Wrongly placed chills.
• Improper placement of gates and risers or incorrect pouring temperatures can also
produce hot tears.
• Hot tears are also caused by poor collapsibility of cores.
• If the core does not collapse when the casting is contracting over it stresses will be
set up in the casting leading to its failure.
• Hot tears can be eliminated by improved design, proper directional solidification,
and uniform rate of cooling, correct pouring temperature and control of mould
hardness.
89. Shrinkage Faults:
• Shrinkage faults are faults caused by improper directional solidifications,
poor gating and risering design and inadequate feeding.
• Solidification leads to volumetric contraction which must be compensated
by feeding. If this compensation is inadequate either surface shrinkage or
internal shrinkage defects are produced making the casting weaker.
• Shrinkage faults can be reduced by providing proper gating system, pouring
at correct temperature and taking care of directional solidification.
Sand Casting Defects:
• Production of castings involves a large number of steps including casting
design, pattern making, moulding, melting, pouring, shake out, fettling,
inspection and finishing.
• It is not uncommon for one or more of these steps to be performed
unsatisfactorily due to use of defective material or equipment,
carelessness of the operator or lack of skill.
• Such unsatisfactory operations result in a defective casting which may be
rejected at the final stage.
92. -It is also called a gooseneck machine because of the shape.
-In this machine the melting pot, usually made of cast iron, is a
part of the machine.
-The gooseneck containing a cylinder and metal passage way is
kept immersed in the metal pot.
-The plunger in the gooseneck cylinder is actuated either
hydraulically or pneumatically.
-In operation the plunger is withdrawn letting the liquid metal
into the gooseneck cylinder through the port provided.
-When the die halves are closed and ready for casting the
plunger forces the liquid metal entrapped in the cylinder into
the die through the gooseneck passage and a nozzle.
-After a predetermined time interval the plunger is retracted
allowing the liquid metal in the gooseneck channel and nozzle
to fall back into cylinder.
93. The die halves are opened and the solidified casting is ejected from the die.
Hot chamber machines are designed to operate almost automatically and
fast. A press button operation will make the machine go through a complete
cycle of activities including closing the die halves, forcing the metal into the
die, holding the pressure for a predetermined time, withdrawing the
plunger, opening the die, ejecting the casting and stop ready for the next
cycle. The operator then removes the casting, inspects the dies, gives spray
lubrication to the dies and starts the next cycle. Metal injection speeds and
pressures can be controlled to suit different metals and castings.
Since the melting pot plunger and cylinder of a hot chamber die casting
machine are made of cast iron and cast iron reacts with metals like
aluminium at elevated temperatures, only low melting-point metals can
be cast by this method. There is also a limit on the maximum pressure
which can be applied. Hot chamber machines are mostly operated below
14 kPa. Alloys of lead, tin and zinc are the most common metals cast by
this process.
96. The metal in this case is melted in a separate furnace and the required quantity
of metal is ladled to the machine. A plunger operated hydraulically forces the
metal into the die. Injection pressures of 28 kPa to 250 kPa are possible in cold
chamber machines. The machine is semiautomatic in that after the metal is
ladled into the cold chamber the rest of the operation is automatic. Hot
chamber machines are made in capacities varying from 0.25 to 7.5 MN and cold
chamber ones from 1 to 10 MN.
