Foundry.pdf .

Department of Mechanical & Manufacturing Engineering, MIT, Manipal 2 of 63
CHAPTER 1
FOUNDRY
MANUFACTURING TECHNOLOGY

Introduction:
 A foundry is a factory that produces metal castings.
 Casting is the process of producing metallic parts by
pouring a molten metal in to the mould and allowing
the metal to solidify.

Introduction:
Basic steps involved in casting process (Sand
Casting)
 Pattern making
 Core making
 Moulding
 Melting and pouring
 Solidification of metal
 Removal of solidified metal

Introduction:
Basic steps involved in casting process (Sand
Casting)
 Post Casting Operations
 Clean Up

Introduction:
 The most common metals processed are aluminium
and cast iron.
 However, other metals, such as bronze, brass, steel,
magnesium, and zinc, are also used to produce
castings in foundries.
 In this process, parts of desired shapes and sizes
can be formed..

Moulding:
 Consists of all operations necessary to prepare a
mould for receiving the molten metal.
 Involves
 placing a moulding aggregate around a pattern
held within a supporting frame.
 withdrawing the pattern to leave the mould
cavity.
 setting the cores in the mould cavity and
finishing and closing the mould.

Moulding:

Types of Moulding Sand:
Moulding Sands are classified according to their use
into number of varieties:
Green Sand: It’s a mixture of silica sand with 18 to
30% of clay, 6 to 8% of water. Also known as
tempered sand.
Dry Sand: Green sand is dried, suitable for big
castings.
Facing Sand: Facing sand forms face of the mould
and covers the pattern all around, thus it comes in
direct contact with the molten metal. Consists of
bituminous coal.

Backing Sand: Backing sand (or) floor sand used for
back up of the facing sand. The sand which have
been repeatedly used may be employed for this
purpose. It is also known as black sand due to its
colour.
System sand: Used in mechanical sand preparation
and handling units. The used sand is cleaned and
reactivated by the addition of water binders & special
additives. Also known as unit sand.

Parting Sand: Parting Sand is used to keep the green
sand from sticking to the pattern - consists of dried
silica sand, sea sand or burnt sand. This sand is
applied on the faces of the pattern.
Core Sand: Sand used for making cores - It is the
silica sand mixed with linseed oil or any other oil as
binder.

Constituents of Moulding Sand:
The main ingredients of any moulding sand are:
 Silica sand
 Binder
 Additives
 Water
Silica Sand:
• Granular particles of sand, that is silica, comprise
of 50 to 95 percent of the total material in a
moulding sand.

Silica Sand:
• Purest silica sand consists of 99.8 % of SiO2 and is
considered the most refractory and thermally
stable.
• Along with silica, small amounts of iron oxide,
alumina, lime stone, magnesia, soda and potash
are present as impurities.
• The shape and size of the sand grains has a
remarkable effect on the physical properties of the
foundry sand.

Silica Sand:
• Sand grains may have smooth or rough surface.
• Smooth is preferred for moulding since such a
surface renders high permeability and plasticity, but
needs higher amount of binder.
• Grains may have different shapes, like: round, sub-
angular, angular and compound.
• Rounded grains – do not bind together, hence
higher permeability but reduced strength
• Sub-angular – relatively stronger bond, reduced
permeability

Silica Sand:
• Angular grains – much stronger bond, but much
lower permeability
• Compound grains – are ones which do not
separate when screened and are not preferred.
They may consist of combination of above three
shapes.

Silica Sand:

Binder
 To impart sufficient strength and cohesiveness, so
as to capable of retaining its shape after the pattern
is withdrawn.
 Organic binders-Resins, cereal oil, phenol, etc.
 Inorganic binders-Clay binders- Kaolinite or fire
clay and Bentonite
Additives
 These are added to improve certain existing
properties and to impart certain new properties

Additives
 Coal dust - prevents oxidation by reacting
chemically with oxygen present in the sand pores,
thereby producing a reducing environment.
 Soft coal – Restricts mould wall movement.
 Corn floor/ wood flour – reduces expansion defects
by promoting mould wall movement, improves
strength, toughness, collapsibility of the mould but
decreases flowability and permeability.
 Silica flour - Increases hot strength.
 Dextrin – increases dry strength of the sand.
 Pitch – improves hot strength.

Water
 2 to 8% of water is added according to the
requirements
 Imparts desired strength to the sand and also helps
in binding.

Sand Preparation:
Mixing of Sand
• Mixing Clay, additives, horse manure, coal dust etc.
Tempering of Sand
• The process by which sufficient moisture is added to
the moulding sand
Sand Conditioning
• New sand should be properly conditioned before it is
used
• To ensure uniform distribution of binder around sand
grains, control moisture content, eliminate foreign
particles and increase flowability.

Properties required in moulding sand:
Refractoriness
• It is the ability of the moulding material to resist the
temperature of the liquid metal to be poured so that it
does not get fused with the metal.
• Sand fusing with metal results in slag formation on the
surface of the casting.
• The refractoriness of the silica sand is highest.
• Mainly decided by the distribution of silica and impurities
in the sand.
• Impurities like calcium, sodium and potassium react
chemically to form compounds which have low melting
temperatures thereby reducing the refractoriness of the
sand.

Permeability
• Also termed as porosity
• It is the property of the sand which allows the gases and
steam to escape through the sand mould.
• If these gases are not allowed to go out they will either
make the casting unsound or blast the mould.
• Size, shape, moisture and clay content has an impact on
the permeability of the moulding sand.
• Ramming also effects the permeability; soft ramming
increases the permeability while hard ramming reduces it.
• Permeability is increased by help of vent wires.

Flowability
• It is that property of the sand due to which it flows during
ramming to all portions of the moudling flask, packs
properly around the pattern to acquire the desired shape.
• Is also responsible for distributing the ramming pressure
evenly to all parts of the mould.
Adhesiveness
• It is that property of the sand due to which it is capable of
adhering to the surfaces of the other materials.
• Due to this, heavy sand mass successfully holds in the
moulding flask.
• Better adhesiveness allows manipulation of the mould
without any danger of fall out.

Cohesiveness
• It is that property of the sand due to which its rammed
particles bind together firmly and allows withdrawal of
pattern without damaging the mould surfaces and edges.
• The mould faces gets sufficient strength to withstand the
pressure of the flowing molten metal and do not get
washed away.
Collapsibility
• It is the property due to which the sand mould
automatically collapses after solidification of the casting to
allow a free contraction of the metal.
• In absence of this property, contraction is affected and
leads to casting defects like tears and cracks.

Green strength
• The sand after water has been mixed into it, must have
adequate strength and plasticity for making and handling.
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 metallostatic pressure
of the molten metal.
Hot Strength
• The strength of the sand that is required to hold the shape
of the cavity at high temperatures is called hot strength.
• Reduced hot strength may lead to mould enlargement,
erosion, cracking or breaking of mould due to flowing
molten metal.

Sand Tests:
 Foundry sand may account for one third of the
cost of the finished casting.
 Moulding sand must be tested periodically in
order to control its composition and to maintain
properties.
 Mechanical and chemical tests are used.
 Chemical tests are used only to determine the
undesirable elements in the sand, and in most
cases mechanical tests are employed.

Test on Moulding Sands:
 Moisture content test
 Clay Content test
 Grain fineness test
 Permeability test
 Strength test

Moisture content test:
 20 – 50 gms of prepared sand
is placed in a pan and is
heated by an infrared heater
for 3 minutes.
 Moulding sand is taken out
and reweighed.
 % moisture can be calculated
by,
%Moisture=(W1-W2)*100/W1
W1 - Initial Weight
W2 – Final Weight

Clay content test:
• The method for determining the clay-content of
moulding sands consists of agitating the sand in
water so as to separate the clay from the sand
particles and then removing the clay which
remains suspended in water.

Clay content test

Clay content test:
1. Dry a small quantity of prepared moulding sand.
2. Separate 50 gms of moulding sand and transfer to a wash bottle.
3. Add 475 cc of distilled water and 25 cc of a 3% NaOH solution.
4. Using a stirrer, agitate the whole mixture for about 10 minutes.
5. After settling down for about 10 mins, drain off the water from the
bottle.

6. Clay is dissolved in water and is removed.
7. To the left out sand add more water and stir well and allow it to
settle down.
8. Repeat the above steps until the water above the sand is clear.
9. This assures that the clay is completely removed.
10. Dry out the sand.
11. Difference in weights gives the % clay in the moulding sand.

Grain fineness test

• Grain size of a sand is designated by a number called “grain-
fineness number” that indicates the average size as well as
proportions of smaller and larger grains in the mixture.
• This test determines
a) Grain size b) distribution & c) Grain fineness
•The instrument consists of 11 standard sieves and a shaker.
•The top is the coarsest and the bottom finest.
Grain fineness test

Grain fineness test
• A given grain-fineness number corresponds to a standard sieve
of 280mm diameter.
• The test for fineness is conducted by screening sand grains by
means of a set of standard sieves that are graded and
numbered according to the fineness of their mesh
• The fineness number is then calculated from the formula:

Example

Permeability test:
Permeability is the property of moulding sand which
permits the escape of steam & other gases
generated during pouring.
 Permeability depends on:
 Grain size. Grain shape. Grain distribution, Binder
& its content, Degree of ramming, Water content
of the sand.
 Since permeability is the property of moulded
sand, a standard specimen is to prepared first.
This is done by using the Sand Rammer.

Sand specimen rammer
50.8 mm
50.8
mm

Permeability tester

Consists of:
 Inverted Bell jar, which floats in a water seal and
can permit 2000 cc of air flow.
 Specimen tube, to hold the sand specimen.
 Manometer to read the Air pressure.

2000 cc of air held in the inverted bell jar is forced
to pass through the sand specimen.
Simultaneously, measure the time ‘t’ and
pressure ‘p’ required for 2000 cc of air to pass
through the specimen.
Permeability number is defined as the volume of
air in cc that will pass per minute under a
pressure of 1 gm per cm2 through a specimen
which is 1 cm2 in cross sectional area and 1cm
deep.

2
,
volume of air passed through the specimen =2000 cc.
height of the specimen = 5.08 cm.
area of the specimen = 20.268 cm
time (mts) taken for 2000 cc to pass
V H
Permeability
Where
V
numbe
A
P
H
A T
T
r








2
through the specimen.
pressure (gms/cm ) recorded by the manometer.
P 
• The permeability number is calculated using the
following formula:

Strength test:
The following tests are conducted on foundry sands:
 Compression
 Tensile
 Shear
Strength tester machine

Shapes for strength tester

Types of Patterns
 One piece pattern
 Split pattern
 Loose piece pattern
 Match plate pattern
 Cope and Drag
 Sweep pattern
 Gated pattern
 Skeleton pattern
 Segmental pattern
 Follow board pattern

Types of Patterns
 One piece pattern

Types of Patterns
 Split pattern

Types of Patterns
 Loose piece pattern

Types of Patterns
 Match plate pattern

Types of Patterns
 Cope and Drag pattern
Cope & Drag pattern
Drag plate
Cope plate

Types of Patterns
 Sweep pattern

Types of Patterns
 Gated pattern

Types of Patterns
 Skeleton pattern

Types of Patterns
 Segmental pattern

Types of Patterns
 Follow board pattern

Types of Sand Moulding
 Bench Moulding
 Floor Moulding
 Pit Moulding
 Sweep Moulding
 Match Plate Moulding

Bench Moulding
 Bench Moulding Small moulds which can be easily lifted by a
single worker are normally prepared on a moulding bench.
 The moulding bench is conveniently designed for storing sand and
keeping moulding tools, etc

Floor Moulding
 Floor moulding Moulds for medium and large size castings are
prepared by floor moulding because large moulds are difficult to
shift or handle.
 In this case the moulding is done on the floor itself.
 The metal is directly poured into the mould cavity of the floor itself.

Pit Moulding
 Very large and heavy castings are moulded in a pit.
 The pit is formed in the foundry floor itself. Pit acts as the drag part
of the mould.
 Cope part is made separately and assembled with the pit mould as
shown.
 Gates, runner, spure and pouring basin are made in the cope.
 The sides of the pit are lined with refractory bricks.

Sweep Moulding
 Sweep moulding If the casting has similar profile with respect to
the vertical axis, sweep moulding is prepared.
 It is used for producing large castings. This mould is made on the
drag or on the floor.
 A sweep board having part of the shape is fitted on the spindle.

Match plate Moulding
 A match plate pattern is used for moulding.
 A number of patterns are fitted in the plate. Gate and runner are
also fitted in the plate.
 The match plate is placed on the drag to the bottom of the mould
portion.
 Sand is filled and rammed. By removing the plate, mould cavities,
runner and gates are formed in the drag.

Moulding Material:
 For metallic category, the common materials are
cast iron, mild steel and alloy steels. In the non-
metallic group molding sands, plaster of paris,
graphite, silicon carbide and ceramics are included.
 Moulding 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.
 Moreover, it is also highly cheap and easily
available.

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