Foundry basics

Samskruti College of Engg. & Tech.
Dept. of Mechanical Engineering
J. VISHWAS
ME
UNIT-III
FOUNDRY
SUB: Advanced Workshop Technology

CONTENTS
• INTRODUCTION
• ADVANTAGES & LIMITATIONS OF CASTING OVER OTHER
MANUFACTURING PROCESSES
• FOUNDRY EQUIPMENT
• SANDS
• Properties of moulding sand
• Types of moulding sand

INTRODUCTION
•The foundry industry is probably the oldest branch of engineering, and It is certainly one of the
most important.
•It was practiced by the craftsmen of ancient greek and roman civilizations and even earlier.
•This technique was used for some of the metallic objects in the form of knives, coins, arrows,
household articles and armoury, guns and war materials.
•Copper and bronze were common in ancient times, but now a days all the metals can be cast.
•Some of the items manufactured by foundry.
1. Jewellwery
2. Machine tools
3. Sports
4. Machine frames
5. Power transmission elements.

•A foundry is a place where castings are produced.
•Castings are made from patterns which are exact replicas of the article
to be produced.
•The patterns are pressed into sand, and when removed leave their
impression.
•Into this sand impressions or mould, molten metal is poured and
allowed to cool or solidify.
•When it is removed it will be of the same shape as the mould. Only
slightly smaller owing to the contraction of the metal.

ADVANTAGES OF CASTING OVER OTHER MANUFACTURING
PROCESSES
1.Casting can produce very complex geometry parts with internal Cavities.
2.It can be used to make small (few hundred grams) to very large size part (thousand of kilograms).
3.Any intricate shape can be Produced.
4.Any Material can be cast ferrous & non-ferrous.
5.It is economical, with very little wastage: the extra metal in each casting is re-mental and re-used.
6.Cast Metal is isotropic. It has the same physical and mechanical properties along and direction.
7.It is a process highly adaptable to the requirements of mass production large number of a given casting can
be produced quickly.
For Examples:In the automotive industry there is massive production of cast engine blocks and transmission
cases.
8.Necessary tools required for castings are Cheaper & simple.
9.Certain metals & alloys are produced only by castings.
LIMITATIONS/DISADVANTAGES
1. It gives poor surface finish and mostly requires surface finish operation.
2. Casting defects involves in this process.
3. It gives low fatigue strength compare to forging.
4. It is not economical for mass production.

FOUNDRY EQUIPMENT- Hand moulding tools
The tools are:
1. Shovel 2. Riddle
3. Rammers 4. Trowels
5. Strike-Off Bar 6. Vent Wire
7. Lifter 8. Slick
9. Swab 10. Bellow
11. Gate Cutter 12. Sprue pin
13. Draw Screw 14. Mallet
15. Gagger 16. Rapping Plate
17. Clamps 18. Sprit Level
19. strike-off bar 20. moulding board and bottom board
21. Moulding boxes

1. Shovel:
A shovel is used for mixing the sand with other ingredients. It is
also used for handling the sand from one place to another in the
foundary shop. It consists of a square metal pan fitted with a
wooden handle
2. Riddle:
A riddle is used for cleaning the moulding sand. It removes the
unwanted material like metal scrap, iron and other metal parts,
pebbles etc.,
3. Rammers:
A rammer is a wood or metal tool used for ramming or packing
the sand in the moulding box. It has two parts peen and butt.
Rammers are available in different designs and constructions.
The popular and widely used rammers are peen-rammer,
bench-rammer, and floor-rammer etc.,

4. Trowels:
A trowel is used for finishing and repairing a mould. It consists
of a metal-flat with different shapes and wooden handle. It is
also used for smoothen the mould surfaces, shaping the square
corners, finishing the parting surfaces. It is available in different
shapes like rectangular, triangular, square, round etc.,
5. Strike-Off Bar:
A strike-off bar is used for striking off the excess sand from the
mould to provide a smooth surface. It is a straight bar of wood
or steel and usually have rectangular cross-section
6. Vent Wire:
A vent wire is used to form vents or holes in the rammed sand
to provide easy escape of gases or steam formed during pouring
of molten metal. It is a circular or rectangular long needle tool,
pointed edge at one end and handle at the other end

7. Lifter:
A lifter is used for picking up the unwanted dust and damaged
parts of the mould. It is a L- shaped steel tool with long holding
shank and a small toe. It is available in thin sections of various
width and lengths, according to the shape of the mould
8. Slick:
A slick is used for repair and finishing the mould surface after
the removal of pattern. It is a double ended tool having a spoon
on one end and a flat on the other end
9. Swab:
A swab is used for moistening the sand around the edge before
the pattern is withdrawn. It consists of soft hair brush to hold
water at one end, and a rubber buld at the other end

10. Bellow:
A bellow is used to blow loose particles of sand from the cavity
and surface of the mould. Sometimes, a compress jet of air is
used for this purpose
11. Gate Cutter:
A gate cutter is used for cutting the gate in the mould which
acts as a passage for the hot metal. It is U-shaped piece of thin
sheet metal
12. Sprue pin/Cutter:
A sprue cutter is used for creating a run-through or sprue for the
molten metal in the cope. It has tapered cylindrical shape and
made from wood

13. Draw Screw:
A draw screw is used for drawn out the pattern embedded in
the moulding sand. It is a pointed steel rod, with a loop at one
end. Wooden mallet is used for striking the draw screw, also
called draw spike.
14. Mallet:
A mallet is used to loosen the pattern in the mould so that it can
be removed easily. It is used together with draw spike
15. Gagger:
A gagger is used for reinforcing the moulding sand in the cope
part of the moulding box. These are the iron rods or thick wires
bent at one or both the ends. The bottom end of the gagger
must be kept 5 to 8 mm away from the embedded pattern

16. Rapping Plate:
A rapping plate is used for lift the large and heavy pattern from
the mould. It is a steel plate and firmly fixed to the top of the
pattern by means of bolts and screw. Rapping plates are
available in many shapes
17. Clamps:
The clamps are used for holding the top and bottom parts of the
mould so that the cope should not rise when the molten metal
is poured into the mould cavity
18. Sprit Level:
A sprit level is used to keep sand bed, moulding box and table in
horizontal position. It consists of an air bubble inside a curved
glass tube

19. Moulding board 20. Moulding box
A box type moulding box is shown in Fig. 4.10 (a) is also known
as permanent flask, these flasks should not be removed till the
pouring of molten metal is completed. These boxes are
generally made of steel and used for small and medium-
sized castings.
A moulding board is a smooth
wooden board on which the flask and
patterns are placed when mould making
is started.

Types of moulding sand
backing sand, core sand, dry sand, facing sand, green sand, loam
sand, parting sand, system 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. Backing sand is sometimes called
black sand because of old, repeatedly used molding sand is black in color due
to addition of coal dust and burning on coming in contact with the molten
metal.
Core sand is used for making cores and it is sometimes also known as oil sand.
Core sand 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.

Dry sand
Green sand that has been dried or baked in suitable oven after the making mold and cores is called dry
sand. It possesses more strength, rigidity and thermal stability. Dry sand is mainly used for larger
castings. Mold prepared in this sand are known as dry sand molds.
Facing sand forms the face of the mould. It is next to the surface of the pattern and it comes into contact
with molten metal when the mould is poured. Initial coating around the pattern and hence for mold surface
is given by facing sand. Facing sand have high strength refractoriness. Facing sand is made of silica sand
and clay, without the use of already used sand. Different forms of carbon are used in facing sand 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. They are sometimes mixed with 6-15 times as much
fine molding sand to make facings.
Green sand is also known as tempered or natural sand which is a just prepared mixture of silica sand
with 18 to 30% 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. Green sand is easily available and it possesses low
cost. Green sand is commonly employed for production of ferrous and non-ferrous castings.

Loam sand is mixture of sand and clay with water to a thin plastic paste. Loam sand possesses
high clay as much as 30-50% and 18% of water. Patterns are not used for loam molding and
shape is given to mold by sweeps. Loam sand is particularly employed for loam molding used
for large grey iron castings.
Parting sand without binder and moisture is used to keep the green sand not to stick to the
pattern and also to allow the sand to the parting surface the cope and drag to separate without
clinging. Parting sand is clean clay-free silica sand which serves the same purpose as parting
dust.
System sand
In mechanized foundries where machine molding is employed. System sand is used to fill the
whole molding flask. In mechanical sand preparation and handling units, facing sand is not
used. 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.

Properties of moulding sand
The basic properties required in molding sand and core
sand are adhesiveness, cohesiveness, collapsibility, flowability, dry strength, green
strength, permeability, refractoriness described as under.
Adhesiveness is a property of molding sand to get the stick or adhere to foreign material
such sticking of molding sand with the inner wall of molding box.
Cohesiveness is property of molding sand by virtue 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.
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 collapsibility 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 required in cores.

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.
Flowability or plasticity 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 and
vice versa. Flowability increases with decrease in grain size of sand. The flowability also varies
with moisture and clay content in sand.
Green strength
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.

Permeability 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 of the mould. Permeability of mold
can be further increased by venting using vent rods.
Refractoriness is defined as the ability of molding sand to withstand high temperatures without breaking
down or fusing thus facilitating to get sound casting. It is a highly important characteristic of molding
sands. Refractoriness can only be increased to a limited extent. Molding sand with poor refractoriness
may burn on to the casting surface and no smooth casting surface can be obtained. The degree of
refractoriness depends on the SiO2 i.e. quartz content, and the shape and grain size of the particle. The
higher the SiO2 content and the rougher the grain volumetric composition the higher is the refractoriness
of the molding sand and core sand. Refractoriness is measured by the sinter point of the sand rather than
its melting point.
Miscellaneous properties of molding sand
In addition to above requirements, the molding sand should not stick to the casting and should not
chemically react with the metal. Molding sand need be economically cheap and easily available in nature.
It need be reusable for economic reasons. Its coefficients of thermal expansion need be sufficiently low.

Foundry basics

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