1.

Explain any four types of patterns used in foundry with a neat sketch
Single Piece Pattern

Single piece pattern, also called solid pattern is the lowest cost casting pattern. It is very
suitable for simple process, and small scale production and the large casting manufacturers
prefer it because this kind of casting pattern make casting process just needing simple shapes,
flat surfaces like simple rectangular blocks. One flat surface is used to separate planes.

Two-Piece Pattern

Two-piece pattern also called split piece pattern is a common casting pattern for intricate
casting. This kind of pattern has parting planes which may have flat or irregular surface, and the
exact position of the plane was decided by the shape of the casting. There are two pieces of the
split piece pattern. One of the parts is molded in drag and another is molded in cope. And the
cope part always has dowel pins. With the dowel pins, the two halves of split piece pattern can
be aligned.

Multi Piece Pattern

Multi piece pattern is a good solution for complex designs which is hard to make. This kind of
pattern includes 3 or more pattern which helps you achieve mold making.

Take the three-piece pattern as an example. The pattern is made of the top, bottom, and middle
parts. The top part is cope, the bottom part drag, and the middle parts are called as checkbox.

Match Plate Pattern

Match plate pattern has a metallic plate to divide the cope and drag areas into the opposite face
of the plate. This kind of pattern nearly has no hard work and can provide high output. It is
widely used in the manufacturing industry, and usually has an expensive cost, precise casting
and high yield. And this kind of casting pattern is widely used in metal casting like aluminum.

Gate Pattern
Gate pattern can consist of one or more patterns into a pattern molding pattern. It is designed
for the mold which makes multiple components at one casting process. The gates are used to
combine the different patterns, and runners to create a flow way for the molten materials. When
the gates and runners have already attached, the patterns are loosing. This kind of pattern is
expensive, and it is usually used for small castings.

2. What are pattern allowances? Explain any two pattern allowances with a neat sketch.
A pattern is a slightly larger version of a casting that is used to make a mold
cavity. This pattern change is caused by the fact that when the cast solidifies,
it shrinks to a certain extent due to the metal shrinkage property during
cooling. As a result, a pattern is made slightly larger to compensate. Pattern
allowances refer to these minor changes in the pattern.

3. Explain the constituents of moulding sand

The most common casting process used in the foundry industry is the sand cast system. Virtually all sand
cast molds for ferrous castings are of the green sand type. Green sand consists of high-quality silica
sand, about 10 percent bentonite clay (as the binder), 2 to 5 percent water and about 5 percent sea coal
(a carbonaceous mold additive to improve casting finish). The type of metal being cast determines which
additives and what gradation of sand is used. The green sand used in the process constitutes upwards of
(1)
90 percent of the molding materials used.

4. What are the types of moulding sand and explain any two type of moulding sand.
Molding sands can also be classified into various types according to their use are backing sand, core sand, dry sand, facing sand, green sand, loam

sand, parting sand, system sand.

2.1 Backing sand or floor 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.

2.2 Core sand

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.

2.3 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.

2.4 Facing sand

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. The layer of facing sand in a mold usually ranges between 20-30 mm. From 10 to 15% of the whole

amount of molding sand is the facing sand.

2.5 Green sand

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.

2.6 Loam sand

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.

2.7 Parting sand

5. Explain the 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.

3.1 Adhesiveness

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.

3.2 Cohesiveness

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.

3.3 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.

3.4 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.
3.5 Flowability or plasticity

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.

3.6 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. Also, the sand grains must have the property known as cohesiveness i.e. ability of the sand grains

to stick to one another. By virtue of this property, the pattern can be taken out from the mould without breaking the mould and also erosion of mould wall

surfaces does not occur during the flow of molten metal. The green strength also depends upon the grain shape and size, amount and type of clay and

the moisture content.

3.7 Permeability

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.

7. Explain the three types of core binders.

Today, the most commonly used core binders are plastics of the urea- and phenol-formaldehyde groups, and furan resins. There are three

categories of resin binder processes: cold-setting, cold-box/gas-hardened, and hot-curingmethods.

Cold-setting processes begin to harden after the last additive has been stirred into the sand, like cement does. They are chemically self-setting

processes. Common examples are furan resins and phenol-formaldehyde resins which are acid-catalyzed. They begin to cure after sulfonic acid is

stirred into the sand. Timing is important to these processes—the sand cannot set so slowly it interferes with production, nor so quickly that it is

hard to manage the reaction.

Cold-box, or gas-hardened processes introduce a gas to the core box which reacts chemically to harden the core binder. For example, sands

enriched with furan resins or epoxies can be hardened by introducing SO . Water glass, or sodium silicate, can be hardened using the CO
2 2
process.
Hot-curing methods rely on the introduction of heat to set the core sands. Linseed core oil, the traditional core binder, is set with a hot curing

process. In the shell process, the foundry does not need to do chemistry: sand comes premixed or coated from the distributer and the chemicals in

the sand cause it to create a hard shell when baked. Usually, these do not need to cure all the way through. Hot-box and warm-box methods use

furan or phenolic resins and a catalyst acid-salt which set when the core box is heated.

10. Explain the squeeze jolting machine with sketch.

The working principle of a squeezer type moulding machine is shown in Fig. . The pattern plate is clamped on the machine table, and a flask is put

into position. A sand frame is placed on the flask, and both are then filled with sand from a hopper.

Next, the machine table travels upward to squeeze the sand between the pattern plate and a stationary squeeze head. The squeeze head enters

into the sand frame and compacts the sand so that it is level with the edge of the flask. These machines rammed the sand harder at the back of the

mould and softer on the pattern face. Squeezer machines are very useful for shallow patterns.
11. Explain ceramic mould casting with a neat sketch.

Ceramic mold casting, also known ambiguously as ceramic molding,[1] is a group of metal casting processes that use ceramics as the mold material. It is a

combination of plaster mold casting and investment casting.[2][3] There are two types of ceramic mold casting: the Shaw process and the Unicast process.[4]

These casting processes are commonly used to make tooling, especially drop forging dies, but also injection molding dies, die casting dies, glass molds, stamping dies,

and extrusion dies.