G S AND

MO LDI N
 MOLDING SAND
➢ Molding sand are the most commonly used for
making all types of molds irrespective of
whether they are used for producing casting of
ferrous or non-ferrous metal
 Most sand casting operations are used silica
sand.
 Sand used to manufacture a mould for casting
process is held by mixture of water and clay.
 A typical mixture by volume could be 89%
sand,4% water and 7% clay.
 CHARACTERISTIC OF MOLDING
SAND

 Molding sands are refractory in nature and can withstand

temperature of metal being poured without fusing.
➢The molding sand do not chemically react with molten

metal.
➢The sand have high degree of permeability

and thus allow gases formed during pouring to escape.

➢These strength , permeability and hardness of the sand mix

can be varied by changing the structure of sand .

 TYPES OF MOLDING SAND
1. Green sand:

 It is sand used in the wet condition for making the

mould. It is mixture of silica sand with 15- 25 per cent
clay and 6-8 per cent water
 As explained earlier green sand moulds are not dried
and metal is poured in them in the wet condition
Being damp the sand can be easily worked with hand
 to give it any desired shape
This sand is used for producing small to medium sized
 moulds which are not very complex
GREEN SAND
2. Dry sand:
➢Dry sand is the green sand that has been dried or baked

after preparing the mould.

➢Drying sand gives strength to the mould so that it can be

used for larger castings

3. Loam sand:
 Loam sand is sand containing up to 50 % clay which has

been worked to the consistency of builder mortar.

 This sand is used for loam sand moulds for making very

heavy castings usually with the help of sweeps and skeleton

patterns
4. Parting sand:
 This sand is used during making of the mould to ensure

that green sand does not stick to the pattern and the cope
and drug parts can be easily separated for removing the
pattern without causing any damage to the mould.
 Parting sand consists of fine grained clay free dried silica

sand, sea sand or burnt sand with some parting

compounds.
 The parting compounds used include charcoal, ground

bone and limestone, groundnut shells, talc and calcium

phosphate.
PARTING SAND
5. Facing sand:
 Facing sand is the sand which covers the pattern all

around it. The remaining box is filled with ordinary floor

sand.
 Facing sand forms the face of the mould and comes in

direct contact with the molten metal when it is poured.

 High strength and refractoriness are required for this

sand.
 It is made of silica sand and clay without the addition of

any used sand.

 Graphite, mollasses etc. may be added to the facing sand.

Thickness of the sand layer varies from 20 to 30 mm

FACING SAND
6. Backing sand:
 Backing sand is the bulk of the sand used to back up the

facing sand and to fill up the volume of the flask.

 It consists mainly of old, repeatedly used molding sand

which is generally black in color due to addition of coal

dust and burning on contact with hot metal.
 Because of the color backing sand is also sometimes

called black sand.

 The main purpose for the use of backing sand is to reduce

the cost of molding.

BACKING SAND
7. System sand:
 This is the sand used in mechanized foundries for filling the

entire flask.
 No separate facing sand is used in a mechanized foundry.

 Sand, cleaned and reactivated by the addition of water and

binders is used to fill the flask. Because of the absence of

any fresh sand, system sand must have more strength,
permeability and refractoriness compared to backing sand
SYSTEM SAND
8. Core sand:
 Core sand is the sand used for making cores. This is silica

sand mixed with core oil. That is why it is also called oil sand.
 The core oil consists of linseed oil, resin, light mineral oil

with some binders.

 For larger cores, sometimes pitch or flour and water may

also be used to save on cost.

 PROPERTIES OF MOLDING SAND

➢ Strength
1. GREEN STRENGTH:
o Adequate strength and toughness for making and
handling the mold.
2. DRY STRENGTH:
 Dry sand must have strength to resist erosion and also
the mettalo static pressure of the molten metal or else
the mold may enlarge.
3. HOT STRENGTH:
 Hot molten metal

 Metalloid static pressure of the liquid metal bearing

against the mold walls may cause mold enlargement, or

if the metal is still flowing, erosion, cracks, or breakages
may occur unless the sand posses adequate hot strength.
 PERMEABILITY:
 Steam and other gases
 The mold must be permeable, i.e. , porous to permit the

gases to escape.
 THERMAL

STABILITY:
 Heat from the casting causes rapid expansion of the sand
surface at the mold-metal interface.
 The mold surface may crack, buckle, or flake off (scab)

unless the molding sand is relatively stable

dimensionally under rapid heating.
 REFRACTORINESS:

 The absence of melting, softening, or adherence of the

sand to the casting makes for better casting surface

and easier cleaning of the casting.
 FLOWABILITY
: sand should pack well/flow under load.
 The

 Sands of low flowability may result in non-uniform

hardness.
 Soft molds --- enlargement of the casting or roughness of

the casting surfaces.

➢COLLAPSIBILITY:

 The molding sand should also have collapsibility so that

during the contraction of the solidified casting it does not

provide any resistance, which may result in cracks in the
castings.
 Besides these specific properties the molding material

should be cheap, reusable and should have good thermal

conductivity
 Adhesiveness
 The molding sand should collapse during the

contraction of the solidified casting it does not

provide any resistance, which may result in cracks in
the castings.
 Besides these specific properties the molding material

should be cheap, reusable and should have good

thermal conductivity
 Cohesiveness

 It is the property of sand due to which the sand grains

stick together during ramming. It is defined as the

strength of the molding sand
➢ Reusability:
 Since large quantities of sand are used in a foundry it is

very important that the sand be reusable otherwise

apart from cost it will create disposal problems

 Easy of preparation and control:

 Sand should lend itself to easy preparation and control
by mechanical equipment.
➢ Conductivity:
 Sand should have enough conductivity to permit
removal of heat from the castings.
INGREDIENTS OF MOLDING SANDS
Molding sands are actually mixtures of three or more ingredients. Green
sand -- clay, water, sand (SiO 2 ).
Also a number of other ingredients/materials are added.
 SAND: Molding sand contains 50 to 95 % of the total material in a molding
sand. These sand particles may differ in the following ways:
 Average grain size, grain size distribution and grain shape. Chemical
 composition.
 Refractoriness and thermal stability.

 Generally the purest silica sand, 99.8+ percent SiO 2 is considered the most
refractory and thermally stable.
 Excessive amounts of iron oxide, alkali oxides and lime can cause objectionable
lowering of the fusion point in some sands.
 The shape of sand grains may be rounded, angular, or sub-angular depending on
their geologic history.
 Clay: 2 to 50 percent
 With a suitable water content, it is the principal source of the strength
and plasticity of the molding sand.
 Binder
 Natural molding sand ------- sand + clay in minerals Synthetic
 molding sands

 “Essentially aggregates of extremely minute crystalline, usually flake-shaped

particles that can be classified on the basis of their structure and composition
into a few groups which are known as clay minerals.
Single clay minerals Mixtures of clay minerals

Clay minerals : bentonites, fire clays (kaolinites) and special clays

(halloysite, illite)

 Water: 1.5 to 8 percent
 Activate the clay ----------- develop plasticity and

strength.
 Water in molding sand is often referred as “tempering”

water.
 Water in excess -------- free water

 The rigid clay coatings of the sand grains may be forced

together ---------- develop strength.

 Free water ----- lubricant --- makes the sand more plastic

and more moldable though the strength may be lowered.

 Control of water in sand (clay) is very important.
 SPECIAL ADDITIVES
 Cereals: finely ground corn flour or gelatinized and ground starch from corn.
0.25 to 2.00 percent
Increase green or dry strength and collapsibility.
Ground Pitch: by-product of coke making. up to 2.0 percent

improve hot strength and casting finish on ferrous castings
Sea Coal: 2 to 8 percent. A finally ground soft coal.
Grey and malleable iron molding sands.

Improve the surface finish & Improve ease of cleaning the castings.
Gilsonite: About 0.4 to 0.8 percent. A mineral
Improve casting finish
Fuel Oil: A little fuel oil is sometimes used as a replacement for a small
 percentage of water, thus lowering the total percentage of moisture present .


 SPECIAL ADDITIVES
Wood Flour: 0.5 to 2.0 percent Enhance thermal stability.
Control the expansion of sand by burning out at elevated temperature
Silica Flour: Pulverized silica, finer than 200 mesh, is called silica flour.
Up to 35 percent Increase hot strength
Iron Oxide: 0.25 to 1.0 percent To obtain added hot strength.
Perlite: An aluminum silicate mineral
0.5 to 1.5 percent
Better thermal stability of the sand Riser insulator
Molasses, Dextrin: Cane or blackstrap molasses, unrefined, and containing 60 to 70
percent sugar solids, may be used for increased dry strength.
Dextrins may also be used for the same purpose
 PROPERTIES OF GREEN SANDS
Properties depends on several factors.
i)The sand ingredients.
ii)The methods of preparing the sand for molding.
iii)The method of molding employed in using the sand.
iv)Variables related to the casting such as weight, shape, kind of casting alloy
and gating design.
Effect of the ingredients:
• Each of the ingredients can have important effects on the properties. Principal
ingredient ----- Silica Sand Grains
• Effects of the Sand Grains:
• Casting surface finish, mold permeability, sand strength, refractoriness, and
expansion characteristics are all influenced by the sand grain portion of the
mixture.
• Sand-grain contour of the mold cavity.
• Fine grains ------ smooth wall at the metal interface.
 Sand grains and permeability:
Coarser sand ---- greater permeability
Finer sand ---- lower permeability The grain size distribution has a pronounced
effect on permeability.
 Sand grains and strength:
Strength ----------- surface area of sand grains available for binding.
Fine sands present more surface area and can develop high strength, but of course
more clay is required.
Wide size distributions favor strength, while narrow distributions reduce strength.
Angular sand grains ----- more strength.
Sand grains and refractoriness: High refractoriness --sand grains of
 maximum purity and size.
Impurities which discolor silica lower its fusion point. Finer grains appear to be
more easily fused than coarser ones.
Sand grains and Expansion:

Wide size distribution --- dense packing of the grains --- cause expansion
problems.
Fine sands also expands more.
 Effects of Clay: Water is necessary to activate the clay.
Clay and Sand Strength: For a given clay type and content, there is an
optimum water content.
The effects of the clay on dry and hot strengths are quite important.
Too low a dry strength permits washing of the sand by the metal, and dirt in the
castings.
Too low or too high a hot strength is also undesirable.
Clay Content and Permeability: Permeability is reduced by fine material in
the sand.
Increasing clay content ------ lowers permeability.
Higher clay content also require more tempering water, and hence more steam is
formed when the metal is poured .
Clay Content & Bulk Density: Clay content also influences the bulk density
achieved by the sand during ramming.
A sand having minimum bulk density has much void space and will have a good
permeability commensurate with its sand grain characteristics.
Clay Content & Expansion:
Clay content of 10 to 14 per cent in the sand mixture are accompanied by
minimum confined-expansion value, 0.03 to 0.04 in. per in. as measured at 2500
F.
High clay contents together with the proper amount of water and ramming of the
sand thus favor thermal stability.
Clay Content & Other Properties:
High hot and dry strengths are developed by bentonite and bentonite- fire clay
mixtures ----- less collapsibility.
Combustible materials may be added to promote collapsibilty. Excess clay -----
clay balls Good mixing is required.
Effects of water: Close control of the moisture content of
molding sand.
Optimum tempering water.
Water causes ------- the clay to develop higher dry strength.
The bonding action is attributed to adsorbed water rigidly
held by the clay.
With its adsorbed water, the clay coatings on the sand grains
can be wedged together if sufficient force (ramming) is
applied.
Free water, un-adsorbed, can lubricate the coated sand grains
and permit a greater bulk density to be reached.
CORE MAKING IN THE
PROCESS OF CASTING
 INTRODUCTION
A core is a device used in casting process to produce
internal cavities and reentrant angles. The core is
normally a disposable item that is destroyed to get it out
of the piece. They are most commonly used in sand
casting.
CORE BOX
 TYPES OF CORE BOXES
Half core box: When the shape of the core required is such
that it can be prepared in identical halves, a half core box
should be used.

Dump core box : If the core produced by the core box does not
require any pasting and is complete in it, the box designed is
referred to as a dump core box.
Split core box: When the core box is in two parts and complete
cores results in single ramming, the box is split core box. For
alignment of two parts, dowel pins are fixed in one part and
corresponding holes are made in the other.
 Left and right core box: When the core is required in two
parts and they are not identical, two different core boxes
of the half core type have to be provided for each part of
the core. Such boxes are called right handed and left
handed core boxes.
Strickle core box: This is used when the core is required to have
an irregular shape, which cannot be rammed by other methods.
In this case, the desired irregular shape is achieved by striking
off the core sand from the top of the core box with a piece of
wood called strickle board. The strickle is cut to correspond
exactly to the contour of the required core.
Loose piece core box: In case where two parts of the core
are not identical they can be prepared from a single core
box with the help of loose pieces. One part of the core is
processed by placing the loose piece in the left-hand
recess, and the other part by shifting the loose piece to the
right-hand recess
 CORE MAKING PROCESES
In Hinduja Foundries, they are using three
processes. They are
1. Cold box process
2.
Carbon dioxide (CO2) core making process
3.
Shell process
 COLD BOX PROCESS
Cold box machine
Part A- Polyol- Phenolic formaldehyde resin
The usage amount of this binder varies with season.
0.8 to 1.2 %( summer season)
1.0 to 1.2 %( winter season) Part B- Polyisocyanate
The usage amount of this binder also varies season.
0.8 to 1.2 %( summer season)
1.0 to 1.2 %( winter season)
Part C
The part C is AMINE gas which is used to harden core.

Gas time 4 to 15 sec (20 sec maximum)

Initially part A and part B both are mixed with the sand
itself and this is used to fill core box and packed tightly.
The Amine gas is introduced to harden the core
SODIUM SILICATE/CO2 CORE
MAKING:
Sodium silicate core-making process
 In this process, liquid sodium silicate is mixed with the sand.
The sand is rammed into a core box and cured by passing CO2
through the core.

The core should be between 25ºC to 30ºC (75ºF to 85ºF).

 SHELL CORE MAKING PROCESS
Shell core making process
The shell core making process uses silica sand mixed
with a thermo plastic resin. This mixture is shot into a
heated metal core which is heated to a temperature of
about 230c. Shell moulds are made in halves which are
then glued or clipped together. The shell thickness is
dependent on the amount of time the sand is in contact
with the heated core box.