sand casting (me181056)

Title: Sand Casting
Location: Hussain Engineering Works Pvt. Limited
Sand Casting
MANUFACTURING PROCESSESS LAB – I
Student’s Name: MUHAMMAD SHEHRYAR IMTIAZ Registration Number: ME181056
Max. Marks: 30
A. Introduction
CASTING
In casting process, the liquid material is poured into a cavity (mold cavity) that corresponds to
the desired geometry. The shape obtained in liquid state is stabilized usually by solidification and
then removed from the mold as solid-state component. Usually machining and drifting
allowances are also considered in mold design. Casting is the oldest known process to
manufacture metallic and nonmetallic complements. For example, it is applied for metals,
plastic, porcelain, etc.
A "foundry" term usually applied to the collection of necessary material, tools and equipment
required to produce castings. Furthermore, "foundry man" term also applied to people produce
castings.
SAND CASTING
In sand casting the molten metal is poured into prepared sand mold, dimensioned, and contoured
to match the desired casting. Internal shapes in castings are obtained by placing backed
core/cores consisting of silica sand and a binder in the mold cavity. The molten metal is poured
into the pouring basin and flows to the mold cavity through a gate or system of gates. After
filling the mold cavity, the melt enters the risers, which act as a reservoir of excess metal to
compensate for shrinkage during solidification. A new mold must be made for each casting. The
mold box can be designed to manufacture multiple components to increase productivity.
Molding sand: The fundamental requirement of sand is to resist high temperature, strength to
retain the mold shape, withstanding the mechanical load from liquid metal, permeability (to
permit the escape of gases, and collapsibility (to permit shrinkage). Molding sand consists of:
1. Sand material (resist the high temperature and permeability), commonly used are silica (SiO2)
or quartz sand (cheaper). Olivine sand also used for steel castings, Zircon and synthetic sands
also used but more expensive.
2. The binder (give the strength), e.g. Clay (bentonite, kaolin.), Cement, Sodium silicate (for Co2
process), Oil, Resin (shell molding).
3. Additives (gives collapsibility).
4. Water 4-8% (to activate the binder).
Sometimes the mold is baked in oven 100-300C, for several hours to obtain dry sand that helps
reduce gas holes, blows or porosity in castings.

Title: Sand Casting
Molding Sand Properties:
The basic properties required in molding sand and core sand are described as under.
(a) Refractoriness: Refractoriness is defined as the ability of molding sand to withstand
high temperatures without breaking down or fusing thus facilitating to get sound casting.
(b) Permeability: It 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 mold 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.
Permeability of mold can be further increased by venting using vent rods
(c) Cohesiveness: It 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.
(d) 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 mold. 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. The green strength also depends upon the grain shape and size, amount
and type of clay and the moisture content.
(e) Dry strength: As soon as the molten metal is poured into the mold, 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 mold wall during the flow of
molten metal.
(f) Flowability or plasticity: It 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, flow ability increases with decrease in
green strength, an, decrease in grain size. The flow ability also varies with moisture and
clay content.
(g) Collapsibility: After the molten metal in the mold gets solidified, the sand mold 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 this 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 desired in cores.
Sand mold production: The common method of producing a sand mold is through using a top
flask (called cope), and a bottom flask (called drag). To improve productivity of this molding

Title: Sand Casting
technique, different molding machines were developed to provide vibration compression and
shaking on both cope and drag of sand mold to produce uniform mold strength. Fig. 1 shows the
traditional molding technique using cope and drag and a split patterns.
Fig:1 Traditional sand molding techniques using cope/drag and split pattern system
Applications: Sand casing is a common method of producing relatively cheap complements
made of steel, casting, brass, aluminum, etc. Numerous molding techniques employ sands to
produce sand molds, e.g. green sand molding (commonly used), dry sand molding (similar to
green sand molding but baked sand), core sand molding, shell sand molding, etc. The typical
component weight is in the range of 500 grams to 50 Kg or even several tons e.g. machine tool
frames. Wall thickness generally between 5 to 50 mm. Example products are engine blocks,
crankshafts, connected rods, machine bed, turbine housing, etc. Sand casing produce rough

Title: Sand Casting
surfaces, and lower dimensional accuracy compared to other casting processes, hence, machining
is required for those castings. Machining and drift allowances must be considered in pattern
design.
Machinery: Equipment consists of pattern, which usually manufactured form wood (low
production batch), plastics (e.g. thermosetting plastic) and metals (for long live pattern and high
production rate). Flask and flask-less molding techniques are used to manufacture sand mold.
Core equipment also used to produce cores for the internal shape of components.
SAND CASTING PROCESSES
1) Green sand molding
See previous section. Commonly used for making cope and drag sand molding process.
2) Shell mold casting
Definition: In shell mold casting, which is a type of sand mold casting, the mold produced from
dried silica sand (fine and sharp) mixed with a thermosetting resin (phenolic).
Shell mold preparation: Summary of molding steps are given as follows:
(a) An accurate metal pattern is heated to 150-250C, and the sand mixture is dumped on the
pattern, which is placed in mold box. After a few minutes, a layer of the sand mixture is
cured, and the excess mixture is removed by inverting the mold box.
(b) The pattern and the partially cured shell are baked in an oven for a few minutes to
complete the curing process.
(c) The pattern and shell are now separated, and the mold halves assembled with clamps,
glue, or other devices. The shell mold is placed in a pouring jacket and backed up or
supported by shot or sand and sometimes using supported pins.
(d) After mold production, molten metal is poured in the mold and the metal solidified. The
component is obtained by breaking the mold. For high production multiple pattern plate
may design to have multiple patterns. Furthermore, for high production the pattern plate
is designed to have gating and sprue system.
Applications: Shell mold casting offers greater dimension accuracy and better surface finish than
the green sand casting process. Also, it offers sharp corners, internal shape contour, small holes,
etc. Hence, accurate castings can be produced using this method. Sometimes, cores are produced
using shell molding while the mold is produced using green sand mold technique, to obtain
accurate internal shapes of castings, e.g. water pump and compressor casing components. The
disadvantage of this molding technique, is the initial cost of the tooling system. For example, air-
cooled combustion engines are produced using shell mold casting. An average weight of the
components range between 10 to 20 Kg. Commonly used to manufacture core.

Title: Sand Casting
Fig:2 Shell molding process, some casting cores manufacture using shell molding process
Machinery: Equipment consists of metal pattern mounted on the pattern plate including runner,
gate and sprue system. Heating oven, flask and metal or sand shot. Sometimes, electric heating
elements are inserted in the pattern plate to control the temperature driven using temperature
controller system, also automatic injectors may be used to automate the process and increase
productivity.

Title: Sand Casting
3) Sodium silicate (NA2SiO3) sand molding
Definition: Instead of using an oil or resin that requires heat for bonding or curing like shell
molding process. It is one of the easiest modern core making processes for instructional and
small foundries to use is the sodium silicate “CO2 process”. The sand is rammed into a core
box and cured by passing CO2 through the core. Sodium silicate cores are very strong. It is
process in which the silica sand is mixed with sodium silicate with 3% weight ratio.
Application: common used in producing core.
Fig:3 Sodium silicate core making process
4) Investment casting
Definition: A process in which the molten metal is poured into a preheated mold made by means
of a disposable pattern of wax or plastic coated with a thin layer of silica, plaster, or ceramic. It is
also known as the lost wax process. This process is one of the oldest manufacturing processes.
The Egyptians used it in the time of the Pharaohs to make gold jewelry (hence the name
Investment) some 5,000 years ago.
Mold preparation: Before casting the pattern is melted by warming the mold and then inverted
to allow the wax to flow out. The molding steps are shown in Fig. 2.5. Summary of molding
stages are as follows:
(a) Production of master pattern (from metal or wood), which is required to produce the
master die for wax pattern.
(b) Production of wax patterns by pouring or injection of wax into the master die.

Title: Sand Casting
(c) Assembling the pattern assembly with a thin layer of investment material (dipping in a
thin slurry of fine-grained silica).
(d) Production of final investment by placing the coated pattern assembly into flask and
pouring investment material around.
(e) Drying and hardening for several hours.
(f) Melting the wax pattern assembly by warming the mold and inverting it to allow the wax
to flow out.
(g) Heating the mold to higher temperatures ( 850-1000C), to drive off moisture.
(h) Preheating the mold to 500-1000C to assist the flow of molten metal to thin sections and
to obtain accurate part geometry.
(i) Pouring the molten metal, either by gravity, or pressure.
(j) Removal of castings after solidification by breaking the mold.
(k) Summary of molding procedure is shown in Fig.4.
Applications: In investment casting no draft allowance is required and very complex shape, e.g.
pump impellers, compressor diffusers, turbine plates or wheels, etc, are common components
produced using investment casting. Therefore, the part complex geometry is limitless in case of
investment casting process. Investment casting applied for both ferrous and non-ferrous metals
also used to manufacture metals difficult to machine or un-machinable metals e.g. radioactive
metals. Hence, an accurate components are produced with tolerances of +/-0.075% for
components having dimensions up to 15 mm. Low surface roughness is obtained using
investment casting (1.5-3 Ra).
Machinery: Equipment for producing the ceramic mold consists of slurry tank, baking oven. The
equipment for making the wax pattern are also needed.
Fig:4 Procedure of mold preparation on investment casting.

Title: Sand Casting
C. Lab Discussion
1. What are the main ingredients and properties of good moulding sand? [3]
The fundamental requirement of sand is to resist high temperature, strength to retain the mold
shape, withstanding the mechanical load from liquid metal, permeability (to permit the
escape of gases, and collapsibility (to permit shrinkage). Molding sand consists of:
1. Sand material (resist the high temperature and permeability), commonly used are silica
(SiO2) or quartz sand (cheaper). Olivine sand also used for steel castings, Zircon and
synthetic sands also used but more expensive.
2. The binder (give the strength), e.g. Clay (bentonite, kaolin.), Cement, Sodium silicate (for
Co2 process), Oil, Resin (shell molding).
3. Additives (gives collapsibility).
4. Water 4-8% (to activate the binder).
Sometimes the mold is baked in oven 100-300C, for several hours to obtain dry sand that
helps reduce gas holes, blows or porosity in castings.
2. What is meant by foundry? [2]
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting
them into a liquid, pouring the metal into a mold, and removing the mold material after the
metal has solidified as it cools. The most common metals processed are aluminum and cast
iron. Ferrous foundries produce iron and steel castings.
Also, Foundry processes can be divided into two types:-
Ferrous foundries and non-ferrous foundries. Foundry processes involve making the mould
and the core, melting and pouring the metal into the mould, and finally removing the mould
and core and finishing the product.
3. What is the purpose of ladle in a foundry shop? [3]
Ladle is a tool used to carry hot molten metal from the furnace to the molds. Industrial ladles
have different weighed buckets which are designed to carry as hot temperature as 1800⁰C.
Also, ladles have different sizes depends on their weight.
4. What is meant by core and core print? [3]
Core is a separate part which is inserted in the mold cavity for shape. Core is generally put
inside cavity to made hollow part on the extracted casted parts. It acts as the secondary mold
which is put after whole mold is prepared. It is placed to produce internal features of casting
such as holes, or passage for water cooling.

Title: Sand Casting
Core print is kind of reference dimension which helps place the core inside the cavity. Also,
region added to the pattern, core or mold which is used to locate and support the core within
mold.
5. What is the purpose of CO2 in foundry shop? [3]
Co2 is used in the process of sand molding where it hardens the sand mold mixture by
blowing CO2 over the mold. This process is basically a hardening process for molds and
cores. In addition, we can get dimensionally correct and accurate casting with a fine surface
finish. This process may not be economical than green sand casting process. The CO2 gas is
passed through the sand mixture containing sodium silicate, the sand immediately becomes
strongly bonded as sodium silicate becomes a stiff gel. The gel is responsible for giving the
strength to the mold. CO2 sand casting process is ideal where speed and flexibility is prime
requirement.
6. What are the main tools used in the Foundry shop? [3]
1.Showel: It consists of iron pan with a wooden handle. It can be used for mixing and
conditioning the sand.
2. Trowels: These are used for finishing flat surfaces and comers inside a mould. Common
shapes of trowels are shown as under. They are made of iron with a wooden handle.
3. Lifter: A lifter is a finishing tool used for repairing the mould and finishing the mould
sand. Lifter is also used for removing loose sand from mould.
4. Hand riddle: It is used for ridding of sand to remove foreign material from it. It consists of
a wooden frame fitted with a screen of standard wire mesh at the bottom.
5.Strike off bar: It is a flat bar, made of wood or iron to strike off the excess sand from the
top of a box after ramming.
Its one edge made beveled and the surface perfectly smooth and plane.
6.Vent wire: It is a thin steel rod or wire carrying a pointed edge at one end and a wooden
handle or a bent loop at the other. After ramming and striking off the excess sand it is used to
make small holes, called vents, in the sand mould to allow the exit of gases and steam during
casting.
7. Rammers: Rammers are used for striking the sand mass in the moulding box to pack it
closely around one pattern. Common types of rammers are shown as under.

Title: Sand Casting
8.Swab: It is a hemp fiber brush used for moistening the edges of sand mould, which are in
contact with the pattern surface, before withdrawing the pattern. It is also used for coating the
liquid blacking on the mould faces in dry sand moulds.
9. Sprue pin: It is a tapered rod of wood or iron, which is embedded in the sand and later
withdrawn to produce a hole, called runner, through which the molten metal is poured into
the mould.
10. Sprue cutter: It is also used for the same purpose as a sprue pin, but there is a marked
difference between their use in that the cutter is used to produce the hole after ramming the
mould. It is in the form of a tapered hollow tube, which is inserted in the sand to produce the
hole.
7. What is meant by sprue? Why a tapering is provided on the sprue? [5]
A sprue is a large diameter channel through which the material enters the mould. Before
sprue a larger hole is made on the surface of the mold so that first it collects over the top and
then the fluid easily follows through the downsprue.
A tapering is provided on the sprue because when fluid flows down the sprue the velocity
becomes higher than the starting velocity so ultimately flow rate difference appears between
initial and final flow rate. This difference results in cold shuts and pin holes in the final
product. So, a tapered or narrow bottom sprue is created so that volume must be shrinked to
keep the ratio same for initial and final flow rate of the fluid. This helps reduce the damages
and enhances the quality of the product.
8. What is meant by green sand moulding? [3]
Green Sand Castings are castings made using wet sand or “green sand” molds. The sand is
not green in color nor do the molds use “greensand,” a greenish color sandstone. Instead the
sand is called “green” because it has moisture in it (like green wood) before the sand dries
out when molten metal is poured in the mold.
What gives the sand moisture and helps the sand stick together when making molds is the
clay that is mixed in the sand. Bentonite clay and the sand mixed together provide strong
molds that can be created on an automated assembly line.
A green sand mold is produced by loading green sand into a mold maker and then a pattern is
pressed into the sand. The pressure created when pressing the mold into the sand creates a
form similar to when a child presses a pattern into Play-Doh to create a shape.
The downside of using green sand molds for castings is that they do not have as tight a
tolerance as some other mold types like no-bake castings. This means if you have castings
that require tight tolerances or precise dimensions, you may find green sand castings need a
little more machining than other forms of molds to get to your end desired result. You also
get a better surface finish (a smoother surface) with other casting processes.

Title: Sand Casting
9. One cubic meter of a certain metal will be heated from room temperature to
100’C above the melting point for casting. Density = 7.5g/cm3
; melting point =
800o
C; specific heat of solid metal = 0.33J/g-o
C; Specific heat of liquid metal =
0.29J/g-o
C; Heat of Fusion = 160J/g. How much heat energy must be added
to accomplish the heating. (Assume no losses) [5]
( ) ( )
Where
= density
V = volume
Cs = Specific heat of solid
CL = Specific heat of liquid
Tm = Melting temperature
To = Starting temperature
Tp = Pouring temperature
Hf = Heat of fusion

Title: Sand Casting

sand casting (me181056)

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