Csting of metals complete process

1. LECTURE NO. 26-27
Casting
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2. LECTURE OBJECTIVES
To learn about:
Casting
Process
Casting Defects
2

3. Casting
 Casting is manufacturing process by which a liquid material is poured into a
mould which contains a hollow cavity of the desired shape.
 Then it allowed to solidify, Solidified part is also called casting.
 Casting Material are also usually metals or various cold setting materials that
cure after mixing two or more components together.
 Casting is more often used for making complex shapes that would be otherwise
difficult or uneconomical to make by other methods.

4. Examples
Epoxy
Concrete
Plaster
Clay

5. Foundry
A Foundry is a factory that produces metal casting. Metals are
cast into shapes by melting them into liquid, pouring the metal
in a mould and removing the mould material or casting after the
metal has solidified as it cools.
Please see the following videos
https://www.youtube.com/watch?v=ImPWnJ44xio
https://www.youtube.com/watch?v=jHMn92SAlgY

6. The most common metals processed are Aluminum and cast iron.
Other metals are:
 Bronze
 Steel
 Magnesium
 Copper
 Iron
 zinc

7. Advantage Of Foundry
Casting
 Casting is most economical method for producing complicated shapes in
quantity.
 Casting reduces machining time. Dies are produce so close to final
dimensions that the little of subsequent machining is required.
 Large casting are produced as one unit which would require machining,
welding or riveting, if fabricated from the plate.
 The smooth flowing lines in sand casting often have prove to be important
scale advantage.
 Casting is the only method that can be used for forming engine blocks from
white or grey cast iron, when the properties of these low cast material are
suitable for such applications.

8. Molding Sand Characteristics
Many casting are spoiled due to use of unsuitable moldings, to avoid it, the
learner should know what makes the moldings sand fit for use, to be fit for
molding purpose.
Plasticity: It is the property of molding sand which allows the pattern to form
a certain shape in mole, when the pattern is removed.
Permeability It is the property of molding sand which allows the gases to
escape when the molten metal is poured into the molts. It is influenced by the
size and shape of silica grains.

9. Adhesiveness: it is the property of molding sand which makes it to stick itself with
another body
Cohesiveness: it is the property of molding sand which allows the sand particals to
stick together it is greatly influenced by the binding agent used in the molding sand
Refractoriness: it is the most important property of the molding sand , which prevents
the fusion of the molding sand when the molten metal is poured.
Durability: it is the property of molding sand when enables it to make similar addition
of new sand. The destruction agent us the high temperature causing burning of clay to
improve it Coal dust, saw dust and straw is added.

10. Composition of molding
sand
Molding sand consists of the following:
1. Silicon=80-90%
2. Clay=6-9%
3. Alkalies=below 3%

11. Basic Features
Pattern and Mould
 A pattern is made of wood or metal, is a replica of the final product and is used for
preparing mould cavity.
 Mould is hollow container with a particular shape into which soft or liquid
substances are poured, so that when the substance becomes hard it takes the shape
of the container.
 Mould material should posses refractory characteristics and with stand the pouring
temperature
 When the mould is used for single casting, it made of sand and known as
expendable mould.
 When the mold is used repeatedly for number of castings and is made of metal or
graphite are called permanent mould.
 For making holes or hollow cavities inside a casting, cores made of either sand or
metal are used.

12. Process
Melting and Pouring
 Several types of furnaces are available for melting metals and their selection
depends on the type of metal, the maximum temperature required and the rate
and the mode of molten metal delivery.
 Before pouring provisions are made for the escape of dissolved gases. The
gating system should be designed to minimize the turbulent flow and erosion
of mould cavity. The other important factors are the pouring temperature and
the pouring rate.

13. Solidification and Cooling
 The properties of the casting significantly depends on the solidification
time / cooling rate.
 Shrinkage of casting, during cooling of solidified metal should not be
restrained by the mould material, otherwise internal stresses may develop
and form cracks in casting.
 Proper care should be taken at the design stage of casting so that
shrinkage can occur without casting defects.

14. Removal, Cleaning, Finishing and Inspection
 After the casting is removed from the mould it is thoroughly cleaned and
the excess material usually along the parting line and the place where the
molten metal was poured, is removed using a potable grinder.
 White light inspection, pressure test, magnetic particle inspection,
radiographic test, ultrasonic inspection etc. are used

15. Casting Defects
Defects may occur due to one or more of the following reasons:
 Fault in design of casting pattern
 Fault in design on mold and core
 Fault in design of gating system, etc.
 Improper choice of moulding sand
 Improper metal composition
 Inadequate melting temperature and rate of pouring
 Etc.

16. THANKYOU
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