METAL CASTING TECHNOLOGY

DIGITAL ASSIGNMENT – 2

METAL CASTING TECHNOLOGY

Submitted to: Prof. SRINIVASAN NARAYANAN

DONE BY: PALLI GOUTHAM REDDY

17BME0720

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1. Classify various continuous casting processes with the help of

simple sketches.

CONTINUOUS CASTING
Continuous casting, also referred to as strand casting, is a process used in
the manufacturing industry to cast a continuous length of metal Molten metal is
cast through a mold, the casting takes the two-dimensional profile of the mold
but its length is indeterminate. The casting will keep traveling downward, its
length increasing with time. New molten metal is constantly supplied to the mold,
at exactly the correct rate, to keep up with the solidifying casting. The industrial
manufacture of continuous castings is a very precisely calculated operation.

1. Molten metal, from some nearby source, is poured into a tundish.

2. This particular casting operation uses the force of gravity to fill the mold
and to help move along the continuous metal casting.
3. The tundish is placed about 80-90 feet above the ground level.
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4. The tundish is constantly supplied with molten steel to keep the process
going.
5. The whole process is controlled to ensure there is smooth flow of
molten steel through the tundish.
6. Further, the impurities and slag are filtered in tundish before they move
into the mold.
7. The entrance of the mold is filled with inert gases to prevent reaction of
molten steel with the gases in the environment like oxygen.
8. The molten metal moves swiftly through the mold and it does not
completely solidify in it.
9. The entire mold is cooled with water that flows along the outer surface.
10. The metal casting moves outside the mold with the help of different sets
of rollers.
11. While one set of rollers bend the metal cast, another set will straighten
it.
12. This helps to change the direction of the flow of the steel slab from
vertical to horizontal.

Advantages of continuous casting:

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 The process is cheaper than rolling.

 100% casting yield.
 The process can be easily mechanized and thus unit labor cost is less.
 Casting surfaces are better.
 Grain size and structure of the casting can be easily controlled.
 High production rates.

Disadvantages:
 Continuous and capable cooling of mould is required.
 Just simple shapes can be cast.
 Last capital investment is necessary to set up process.
 Not proper for small scale production.
 Require large ground space.

APPLICATION OF CONTINUOUS CASTING

o A great tonnage of continuous casting is done using cast steel.
o Other metals that are continuous casting are copper, aluminum, grey cast
iron s, white cast irons, aluminum bronzes, oxygen-free copper, etc.
o Metals are cast as ingot for rolling, extrusion, or forging, and long shapes of
simple cross-section are cast as round, square, hexagonal rods, etc.

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2. What is meant by slush casting? Explain the process with the help
of line sketches.

Slush Casting

Slush Casting is a traditional method of permanent mold casting process, where

the molten metal is not allowed to completely solidify in the mold. When the
desired thickness in obtained, the remaining molten metal in poured out. Slush
casting method is an effective technique to cast hollow items like decorative
pieces, components, ornaments, etc.

Process:
Mostly pewter is casted using the slush casting technique. Firstly, a pattern is
made using plaster or wood. Now the pattern is placed on a cardboard or wooden
board. A mold box is kept around the pattern. The unwanted space that is formed
is the mold box can be eliminated by placing a board. Once the pattern is set the
molding material is poured on the pattern and allowed to set with the molding
aggregate. When the mold is set, the pattern is withdrawn from the mold.

The metal melted completely and poured into the mold which is shaped in the
desired form. Rotate the mold to coat the sides. When the metal settles in the
mold, remaining liquid metal is poured out of the mold. Thus, a hollow skin metal
is formed inside the mold.

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If the cast needs to be thicker, once again molten metal is poured into the mold
and poured out. This process is repeated until the desired thickness is achieved. In
some slush castings, bronze molds are used. When the metal hardens, the mold is
broken to remove the castings. The inside of each cast retains molten textures
while the exterior is smooth and shiny. Bowls and vases are serially produced by
this technique that ensures no two are ever the same.

Similarly, to cast metals a bowl, a new process designed to capture the beauty of
Pewter and its unique characteristics. Recycled molten Pewter is swirled inside
mould to form a fine skin. The inside of each cast retains molten textures whilst
the exterior is smooth and shiny. Bowls are serially produced by a technique that
ensures no two are ever the same.

Application:
Some casting of pewter is cast using slush casting method. Using pewter and
other metal s mainly hollow products are casted. Decorative and ornamental
objects that are casted are as vase, bowls, candlesticks, lamps, statues, jewelries,

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animal miniatures, various collectibles, etc. Small objects and components for
industry like tankard handle, handles for hollow wares, etc.

Advantages:
Slush casting is used to produce hollow parts without the use of cores.
The desired thickness can be achieved by pouring our the left over molten
metal.
A variety of exquisitely designed casting can be casted for decorative and
ornamental purpose.

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3. Give advantages, limitations and application of electro-slag

casting.
Electro-slag casting

Electro-slag melting and refining:

 This process was developed originally in the erstwhile USSR in 1930.

 Electro-slag melting is also known as Electro-flux melting is a process of
melting and refining steel and super alloys for mission-critical applications.
 Its principle is based on the electro-slag welding process.
 It dispenses completely with the rising and gating system and also with the
need for separate melting units, pouring ladle and transportation
arrangements.
 Graphite and ceramic mold have been used in place of metallic ones.
 Consumable steel electrodes are used.

Electro-slag melting furnaces

Work of ESM furnace:

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 The electro-slag melting process is used to melt and refine steels and
various super-alloys, resulting in high-quality ingots.
 Electric current (generally AC) is passed between the electrode and new
ingots, which is formed in the bottom of a water-cooled copper mold.
 The new ingot is covered in an engineering slag that is superheated by the
electric current.
 These metal droplets travel through the slag to the bottom of the water-
cooled mold and slowly freeze as the ingot is directionally solidified
upwards from the bottom of mold.
 Solidification takes place without any contact with the atmosphere.
 The slag pool floats above the refined alloys, continuously floating upward
as the alloy solidifies.
 The molten metal is cleaned of impurities that chemically react with slag or
otherwise float to the top of the molten pool as the molten droplets pass
through the slags.
 Electro-slag melting uses highly reactive slags to reduce the amount of
sulfide present in bio-metal alloys.
 ESM furnaces can be designed for the melting of round, square and
rectangular ingots.

Slag used and its properties:

 Slag for electro-slag melting is usually based on calcium fluoride (Caf2), lime
(Cao) and alumina (Al2o3). magnesia (MgO), titania (Tio2) and silica (Sio2)
may also be added, depending on the alloy to be melted.
 To perform its intended functions, the slag must have some well-defined
properties, such as:
o It's melting point must be lower than that of the metal to be melted.
o It must be electrically efficient.
o Its composition should be selected to ensure the desired chemical
reactions.
o It must have suitable viscosity at the melting temperature.

New development in ESM process:

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Melting is carried out under vacuum as in VAR, however, using a slag.

Problems of oxidation of the melt do not arise. In addition, dissolved gases
such as hydrogen and nitrogen can be removed.
The danger of white spots, as encountered during VAR, is reduced to a
minimum. That is of interest to super-alloys or titanium melting.
Low gas content in the final material, then the VAR process is chosen.

Advantages:

 Uniform mechanical properties in the longitudinal and sectional direction.

 Very large ingots such as 3000mm diameter and more than 200ton weight
can be produced.
 Homogeneous, sound and directionally solidified structure.
 The high degree of cleanliness.
 Free of internal flaws.
 Free of macro-segregation.
 Smooth ingot surface resulting in a high ingot yield.

Disadvantages:

 Slag treatment to achieve the lowest hydrogen in Ingot.

 Closed melting to avoid hydrogen pick-up from the atmosphere.
 Melt rate adjusted according to slag system, alloy composition, and furnace
size.
 Gases (like nitrogen & hydrogen) need to be adjusted to the lowest level in
the electrode.
 Adjustment of slag chemistry and composition of the electrode.

Application

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4. What is single crystal casting? Explain it briefly.

Single Crystal Casting and Rapid Solidification

Single Crystal casting:

The advantage of single-crystal growing techniques is well illustrated by
describing the developments in the casting of gas turbine blades, which are
generally made of nickel-base superalloys. The procedures involved can also be
used for other alloys and components. The conventional casting of turbine blades
involves investment casting using a ceramic mould. The liquid is poured into the
mould and begins to solidify at the ceramic walls. The grain structure developed is
polycrystalline, and the presence of grain boundaries makes this structure
susceptible to creep and cracking along those boundaries under centrifugal forces
at elevated temperatures. In the directional solidification process, the ceramic
mould is preheated by radiant heating. A water-cooled chill plate supports the
mould. After the liquid is poured into the mould, crystals begin to grow at the
chill-plate surface and upwards. The blade is thus directionally solidified, with
longitudinal but no transverse grain boundaries. Consequently, the blade is
stronger in the direction of the centrifugal forces developed in the gas turbine.

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COLUMNAR CRYSTALS
SINGLE CRYSTAL
POLYCRYSTALS CHILL PLATE
Three methods of casting turbine blades: conventional casting with ceramic
mould, directional solidification, and single-crystal blade Single-crystal blades: The
mould has a constriction in the shape of a corkscrew, the cross-section of which
allows only one crystal through. A single crystal grows upward through the
constriction and begins to grow in the mould. The strict control of the rate of
movement is necessary. The solidified mass in the mould is a single-crystal blade.
Although more expensive than other blades, the lack of grain boundaries makes
these blades resistant to creep and thermal shock. Thus they have a longer and
more reliable service life. With the advent of the semiconductor industry, Single-
crystal growing has become a major activity in the manufacture of
microelectronic devices. There are several methods of crystal growing that are
used world-wide.

Rapid solidification

Rapid solidification involves cooling of fluid at rates as high as 10 6 Kelvin/s,

whereby the molten material does not have sufficient time to crystallize along
with the “long” distances. During rapid solidification, crystals can grow at rates of
up to 250 m/s however this fast growth in all directions reaches the level of the

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nucleation rates. They typically contain Fe, Ni, and Cr, which are alloyed with C, P,
B, Al, and Si. Among other effects, rapid solidification results in a significant
extension of solid solubility, grain refinement, and reduced micro-segregation.
Amorphous alloys exhibit excellent corrosion resistance, good ductility, and high
strength Consequently, the melt chills rapidly (splat cooling) and forms an
amorphous solid. A further method of rapid solidification is Twin Belt Caster
Technique. Typical aspects of this production process include melt feeding, belt
stabilization and control, heat transfer control, mould tapering, etc. Products
include sheets, strips, tubes etc.

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