workshop theory and practice-i

Dr. Ikbal Bahar Laskar

Workshop Theory and Practice-I

Prepared By:

Ikbal Bahar Laskar

Department of Mechanical Engineering

Jorhat Engineering College (JEC), Jorhat, Assam, India


01-08-2021 Jorhat Engineering College, Jorhat, Assam, India

PATTERN MAKING AND FOUNDRY

Pattern making and sand casting – Pattern materials – Types – Pattern allowances. Core prints.

Moulding sand – ingredients – classification – sand additives – properties of moulding sand –

sand preparation and testing. Green sand mould preparation. Cores and core making – Types of

cores.

Syllabus Module 6



Casting

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of

the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of

the mold to complete the process.

Casting



Casting

Casting Product

Step of sand casting



Casting process

1. Sand casting

2. Investment casting

3. Die casting

4. Low pressure casting

5. Centrifugal casting

6. Gravity die casting

7. Vacuum die casting

8. Squeezing die casting

9. Lost foam casting

10. Continual casting

Lost foam casting product



Pattern In casting, a pattern is a replica of the object to be cast, used to prepare the cavity into which molten material will be poured during the

casting process.

Patterns used in sand casting may be made of wood, metal, plastics or other materials. Patterns are made to exacting standards of construction,

so that they can last for a reasonable length of time, according to the quality grade of the pattern being built, and so that they will repeatably

provide a dimensionally acceptable casting.



Pattern



Pattern material

The selection of pattern materials depends primarily on the following factors

1. service requirements, eg. Quantity, quality and intricacy of casting i.e., minimum thickness desired, degree of accuracy and finish required.

2. Type of production of castings and type of moulding process.

3. Possibility of design changes.

4. Number of castings to be produced, i.e possibility of repeat orders



Pattern material

The wide variety of pattern materials which meet these characteristics are wood and wood products; metals and alloys; plasters; plastics and

rubbers; waxes.

Wood: wood is the most common material for pattern as it satisfy many of the aforesaid requirements. It is easy to work and readily available.

Wood can be cut and fabricated i8nto numerous forms by glueing, bending and curving.

Wooden patterns



Pattern material

Metal: metal is used when large number of casting are desired from a pattern or when conditions are too severe for wooden pattern. Metal

patterns do not change their shape when subject to moist conditions. Another advantage of metal pattern is freedom from warping in shortage.

Metal patterns are very useful in machine moulding because of their accuracy, durability and strength.

Commonly, a metal pattern is cast from wooden pattern called master pattern



Pattern material

Plastics:

Plastics are now finding their place as a modern pattern material because they do not absorb moisture, are strong and dimensionally stable,

resistant to wear, have a very smooth and glossy surfaceand are leight in weight. because of its glossy surface it can be withdrawn from the

mould very easily without injuring the mould and dry or liquid parting compound is necessary.



Pattern material

Rubbers:



Types of pattern

1. Single piece pattern

2. Split pattern

3. Match plate pattern

4. Cope and drag pattern

5. Gated pattern

6. Loose piece pattern

7. Sweep pattern

8. Skeleton pattern

9. Segmental pattern

10. Shell pattern

11. Built up pattern

12. Bo9xed up pattern

13. Lagged up pattern

14. Left and ri8ght hand pattern



Types of pattern

Single piece pattern:

A pattern that is made without joints, partings or any loose pieces in its construction is called a single piece or solid pattern.

A single piece pattern is not attached to a frame or plate and is, therefore , sometimes known as loose pattern.

These patterns are cheaper. When using such patterns the moulder has to cut his own runners and feeding gates and risers.

These operation takes more time, and they are not recommended except for limited production. Single piece patterns are usually used for large

castings of simple shapes.



Types of patternSplit pattern

This is a pattern that is made in two halves split along the parting line. The two halves are held in register by pins called pattern

dowels. The pattern is split to facilitate molding.

The dowels hold the two halves of the pattern together in close accurate register, but at the same time are free enough that the

two halves can be separated easily for molding. Like the pins and guides of the flask.

The dowels are usually installed off center in such a manner that the pattern can only be put together correctly.

A dowel is a solid cylindrical rod, usually made of wood, plastic or metal. In its original manufactured form, dowel is called dowel

rod.



Types of patternMatch plate Pattern

When split patterns are mounted with on one half on one side of a plate and the other half directly opposite on other side of the

pattern, the pattern is called a match plate pattern. A single pattern or a number of pattern may be mounted on match plate. The

pattern is made of metal and the plate which makes the parting line may be either made of wood or metal. When the match plate

is lifted off the mold all patterns are drawn



Types of patternCOPE AND DRAG PATTERN

In the simplest sand casting procedure, the drag is placed upside down on a board, around a pattern of the part to be cast. The pattern

is a model of the desired casting. Talcum powder is often dusted over the pattern to aid in the removal of the pattern. Sand is sifted

over the pattern until the model is covered by a few inches of sand. More sand is then dumped into the drag, and rammed with a

wooden wedge, or mechanically vibrated to pack the sand down. The sand is then struck level with the top edge of the cope, using a

wooden or metal strake. A board is then placed on top of the drag and the drag is flipped over.

Then, the cope is placed on the drag, and dowels (or pins) are put in the sand to make holes for the sprue and one or more risers.

Talcum powder and sand are again sifted over the pattern, and rammed to fill the cope. The pins are then carefully pulled out of the

sand. The critical part of the operation is to separate the cope and drag to remove the pattern. The pattern may be vibrated with a

powered vibrator, or the pattern, and maybe the cope and drag flask, will be lightly tapped with a small hammer. The pattern is lifted

from the sand, leaving a molding cavity. A passageway for metal to enter the mold, called a "gate", is then cut from the sprue hole to

the void left by the pattern, and a runner is cut from the sand to allow metal to flow into the riser

https://en.wikipedia.org/wiki/Pattern_(casting)

https://en.wikipedia.org/wiki/Screed

https://en.wikipedia.org/wiki/Sprue_(casting)

https://en.wikipedia.org/wiki/Riser_(casting)



Types of patternCOPE AND DRAG PATTERN



Types of patternGated pattern

Gated patterns



Types of patternLoose piece pattern



Types of patternSweep Pattern



Types of patternSkeleton pattern

Skeleton pattern



Types of patternSegmental pattern



Types of patternShell pattern

Shell pattern is used largely for drainage fittings and pipe work. The

pattern is usually made of metal, mounted on a plate and parted

along the center line, the two sections being doweled together.

These short bends are usually moulded and cast in pairs. The shell

pattern is a hollow construction li8ke a shell and the outside shape is

used as a pattern to make the mould, while the inside is used as a core

box for making cores.

Sometimes, a pattern of the entire shape of casting is termed a shell

pattern, and a pattern that is of the required shape outside, but

having the inside cored out is termed a block pattern.



Types of patternBuilt up pattern

As the name implies, built up pattern or parted patterns are composed of two or more pieces.

Patterns for special pulleys are built up segments of wooden strips.

These segments are made by cutting strips of wood strips of wood to the curvature required, and the thickness desired is built up by gluing

them in layers.

Flanges are also made similarly. The built up is sometimes necessary because it is difficult to make an intricate shape on a block of wood for

constructing a pattern, but it is easier to build up the shape by glueing or joining number segmental pieces together.



Types of pattern

Lagged up pattern

Cylindrical works such as cylinders pipes or columns are built up

with lag or stave construction which ensures permanence of form.

“Lags” or “staves” are longitudinal strips of wood which are

beveled on each side to make the joint tight outside, and glued and

nailed or screwed to the end pieces of wood called “heads”. The

Fig.12 shows the staves fastened to heads that are half a regular

polygon, the object being to make a cylinder or barrel that is to be

parted longitudinally through the center. Such a construction gives

the maximum amount of strength and permits building close to the

finished outline of the pattern so that there is comparatively little

excess stock to be removed to bring it to the required form.Lagged up pattern



Types of patternLeft and right hand patterns

Many pattern are required to be made in pairs, and when their form is such that they cannot be reversed and they have the centers

of hubs, bosses, opposite and in line, they must be made right and left hand. J hangers for overhead shaft line, legs for wood turning

lathe, or garden bench or paddle type sewing machine, and brackets for luggage racks in the railway carriages are few examples.



Pattern making allowances

Patterns are not made the exact same size as the desired casting for several reasons. Such a pattern would produce castings

which are undersize.

Allowance must be therefore be allowed for shrinkage, draft, finish, distortion, and rapping

Shrinkage allowance:

As metal solidifies and cool , it shrinks and contracts in size. To compensate for this, a pattern is made larger than the

finished casting by means of a shrinkage or contraction allowance. In laying measurements for the pattern the

patternmaker allows for this by using shrink and contraction rule which is slightly longer than the ordinary rule of the

same length.



Rate of contraction for important cast metal: Table1: Rates of contraction for important cast metal

cast metal Dimension (mm) Contraction (mm) Remarks

Cast iron Up to 600 10.5

600-1200 8.5

Over 1200 7.5

Cast steel Up to 600 21

600-1800 16

Over 1800 136

Aluminium Up to 600 17

600-1200 13

1200-1800 12 1.5 mm less for cored

constructionOver 1800 10.5

Magnesium Up to 1200 14.5

Over 1200 13.5

Brass 16

Bronze 10.5-21 Depends on

composition

Malleable Iron 11.8 6 mm section

thickness

10.5 9 mm section

thickness

9.2 12 mm section

thickness

7.9 15 mm section

thickness

6.6 18 mm section

thickness

4.0 22 mm section

thickness

2.6 25 mm section

thickness




Draft allowance:

When a pattern is drawn from a mould, there is always possibility of

injuring the edges of the mould. This danger is greatly decreased if the

vertical surfaces of the pattern are tapper inward slightly.

This slight taper inword on the vertical surfaces of a pattern is known as

draft. Draft may be expressed in millimeter per meter on a sides or

degrees., and the amount in each case depends upon (1) length of vertical

sides (2) intricacy of the pattern (3) method of moulding. Under normal

condition draft is about 10-20 mm per meters on exterior su7rfaces and 40

to 60 mm per meter on interior surfaces.

Draft allowance




Machining allowance :

Rough surfaces of castings that has to be machined are made to dimensions somewhat over those indicated on the finished

working drawings. The extra amount of metal provided on the surfaces to be machined is called machine finish allowance

and the edges of these surfaces are indicated by V or F. the amount that is to be added to the patterns depends upon (1) the

kind of metal to be used, (2) the size and shape of the casting and (3) method of moulding




Standard Machining allowance :

Table2: Standard Machining allo0wance

Diameter of

hole/distance

from locating

point (mm)

Cast iron

(mm)

Cast steel (mm) Nonferous

(mm)

Bore Surfa

ces

Bore Surfac

es

Bore Surfac

es

200 3 3 4 4 1.5-2 1.5

200-400 4.5 4 5.5 5 2.0 1.5

400-700 6 5 7 6 3.0 2.0

700-1100 7 6 9 7 3.5 2.5

1100-1600 9 7 11 9 4.0 3.0

1600-2200 10 8 13 11 -- --

2200-3000 12 9 15 13 -- --




Distortion or camber allowance :

Some castings, because of their size, shape and type of metal, tend to warp or distort during during the cooling period. This

is a result of uneven shrinkage and is due to uneven metal thickness or to one surface being more exposed than another,

causing it to cool more rapidly.

The shape of the pattern is thus bent in the opposite direction to overcome this distortion. As an example, a casting shaped

like the letter U will be distorted with the legs diverging, instead of parallel . To compensate for this condition, the pattern is

made in such a manner that the legs converge but as the casting cools after its removal from the mould, the legs straighten

and remain parallel.




Rapping allowance :

When a pattern is rapped in the mould before it is withdrawn, the cavity in the mould is slightly increased. In every cases

where castings must be uniform and true to pattern slightly smaller than the actual size to compensate for the rapping of

the mould



Core print

Casting are often required to have holes, recesses, etc. of varipus sizes and

shapes. These impressions are obtained by using sand cores which are separately

made in boxes known as coreboxes.

For supporting the cores in the mould cavity, an impression in the form of a

recess is made in the mould with the help of a projection suitably placed on the

pattern. This projection on the pattern is known as the coreprint.

A coreprint is therefore, an added projection on a pattern, and it forms a seat

which is used support and locate the core in the mould. There are several types of

coreprints , viz., horizontal or parting line coreprint, vertical or cope and drag

coreprint, balancing coreprint, cover or hanging core-print, wing or drop core-

print.



Core print

Horizontal core print

Vertical core print

Balancing core print

Hanging or cover core print

Wing or drop core print

Balanced Core Vertical CoreHorizontal core prints




This is laid horizontally in the mould and is located at the parting line of the mould. The core print is often found

on the split or two- piece pattern. When it is important that certain core be located at a desired angular relationship

with respect to the central axis, a flat portion at one end is made to coincide with a flat portion of the core print.




Vertical core print

This stands vertically in the mould. This is why this type of core is referred to to as a vertical core print. The core

print is located on the cope and drag sides of a pattern and is constructed with considerable taper specially on the

cope side (about 10-15 deg) so that they are easily moulded. The taper on drag print is only 1.5-3 deg.

Vertical core print




This is used when a horizontal core does not extend entirely through the casting, and the core is supported at one end

only. An important feature of this core print is that the print of the core in the mould cavity should balance the part

which rests in the core seat.




Hanging or cover coreprint

This is used when the entire pattern is rammed in the drag and the core is required to be suspended from top of the mould. In

this case, the cores serve as a cover for the mould, and also as a support for hanging the main body of a core.




This is used when the cavity to be cored is above or below the parting line in the mould. Wing core prints are also known as

“chair”, and “tail” core prints.




Core boxes

A core box is essentially a type of pattern made of wood or metal into which sand is rammed or packed to form a core. The types of

core boxes, in common use, in foundry work, are described below.

Half box

Dump box

Split box

Right and left hand box

Gang box

Core box with loose pieces

Sweep and skeleton box



Half core box

This is the most common type of core box. The two identical halves of a symmetrical core prepared in the half core box

are shown in Fig. Two halves of cores are pasted or cemented together after baking to form a complete core.

Half core box



Dump core box

Dump core box is similar in construction to half core box as shown in Fig. The cores produced do not require pasting, rather they

are complete by themselves. If the core produced is in the shape of a slab, then it is called as a slab box or a rectangular box. A

dump core-box is used to prepare complete core in it. Generally cylindrical and rectangular cores are prepared in these boxes.



Split core box

Split core boxes are made in two parts as shown in Fig. They form the complete core by only one ramming. The two

parts of core boxes are held in position by means of

clamps and their alignment is maintained by means of dowel pins and thus core is produced



Right and left hand core box

Some times the cores are not symmetrical about the center line. In such cases, right and left hand core boxes are used. The

two halves of a core made in the same core box are not identical and they cannot be pasted together.



Strickle core box

This type of core box is used when a core with an irregular shape is desired. The required shape is achieved by striking oft

the core sand from the top of the core box with a wooden piece, called as strickle board. The strickle board has the same

contour as that of the required core.



Gang core box

Some times the cores are not symmetrical about the center line. In such cases, right and left hand core boxes are used. The

two halves of a core made in the same core box are not identical and they cannot be pasted together.

Gang core box



Loose piece core box

Loose piece core boxes are highly suitable for making cores where provision for bosses, hubs etc. is required. In such cases,

the loose pieces may be located by dowels, nails and dovetails etc. In certain cases, with the help of loose pieces, a single

core box can be made to generate both halves of the right-left core.



Core Box Allowances

Materials used in making core generally swell and increase in size. This may lead to increase the size of core. The larger

cores sometimes tend to become still larger.

This increase in size may not be significant in small cores, but it is quite significant in large cores and therefore certain

amount of allowance should be given on the core boxes to compensate for this increase the cores.

It is not possible to lay down a rule for the amount of this allowance as this will depend upon the material used, but it is

customary to give a negative allowance of 5 mm /mt



Colour coding for patterns and core boxes

All surfaces of a wooden pattern are coated with shellac to keep out moisture and important parts of a pattern and core box

are coloured for identification of their different parts. A widely accepted colour code for general use is given below.

1. Surfaces to be left unfinished are to be painted black

2. Surfaces to be machined are to be painted red

3. Seats for loose- pieces are to be marked by red stripes on a yellow background

4. Coreprints are to be painted yellow

5. Stop-offs are to be marked by diagonal black stripes on yellow base

Thin wooden patterns often need to be secured against distortion by means of a tie bar.

This tie bar is molded but must not be cast. The corresponding mold cavity must be closed off with mold material.

Such components are referred to as stop-offs and marked on the pattern by means of black diagonal lines



Colour coding for patterns and core boxes



Moulding Sands

The principal material used in the in the foundry shop for moulding is the sand. This is because it possesses the properties

vital for foundry purposes.

Sources: All sands are formed by the breaking up of rocks due to the action of natural forces such as frost, wind, rain, heat

and water current. Rocks however, are very complex in their composition, and sands contain most of the elements of the

rocks of which they are fragments. For the reason, moulding sands in different parts of the world vary considerably. Today,

sand is obtained from places which probably once were bottoms and banks of rivers and sand dunes.

In india, foundary sand are found in damodar and barakar area, santhal paragana (Bihar), Londha (Maharastra), Batala

(Gurdaspur, Punjuab), Bhavnagar (Saurashtra), Londha (Maharastra), Avadi and Veeriyambakam (Madras), Kanpur,

Jabalpur, Rajkot, Guntur and many other places.



Principal Ingredients

The principal ingredients of moulding sands are: (1) silica sand grains, (2) clay (3) moisture, and (4) miscellaneous materials

Silica in the form of granular quartz, itself a sand is the chief constituent of moulding sand. Silica sand contains from 80-90

percent silicon dioxide and is characterized by a high softening temperature and thermal stability.

Clay: clay is defined as those particles of sand (under 20 microns in diameter) that fail to settle at arate of 25 mm per

minute, when syspended in water. Clay consist of two ingredients: fine slit and true clay.

Moisture, in requisite amount, furnishes the bonding action of clay, when water is added to clay, it penetrates the mixture

and forms a microfilm which coats the surface of flake-shaped clay particles. The bonding action is considered best if the

water added is the exact quantity required to form the film. On the other hand, the bonding action is reduced and the mould

gets weakened if the water is in excess. The water should be between 2 and 8 percent

Miscellaneous materials that are found, in addition to silica and clay, in moulding sand are oxide of iron, limestone,

magnesia, soda, and potash. The impurities should be 2 percent.



Moulding sand

Moulding sands may be classified generally into three different types: (1) natural moulding sands, (2) synthetic or high silica

sands and (3) special sands

Types of moulding sand1. Green sand2. Dry sand3. Loam sand4. Facing sand5. Backing sand6. System sand7. Parting sand8. Core sand



Green sand

The green sand is the natural sand containing sufficient moisture in it. It is mixture of silica and 18 to 30% clay with about

6-8% water. Clay and water act as a bonding material to give strength. Molds made from this sand are known as green sand

mould. The green sand is used only for simple and rough casting products. It is used for both ferrous and non-ferrous metals

Dry sand

When the moisture is removed from green sand, it is known as dry sand. The mould produced by dry sand has greater strength,

rigidity and thermal stability. This sand is used for large and heavy castings

Loam sand is a mixture of 50 percent sand and 50 percent clay. Water is added in sufficient amount. It is used for large and

heavy moulds e.g., turbine parts, hoppers etc.

Loam sand



facing sand

A sand used for facing of the mould is known as facing sand. It consists of silica sand and clay, without addition of used

sand. It is used directly next to the surface of the pattern. Facing sand comes in direct contact with the hot molten metal;

therefore it must have high refractoriness and strength. It has very fine grains.

parting sand

A pure silica sand employed on the faces of the pattern before moulding is known as parting sand. When the pattern is withdrawn

from the mould, the moulding sand sticks to it.To avoid sticking, parting sand is sprinkled on the pattern before it is embedded in

the moulding sand. Parting sand is also sprinkled on the contact surface of cope, drag and cheek

The backing sand is old and repeatedly used sand of black colour. It is used to back up the facing sand and to fill the whole

volume of the box. This sand is accumulated on the floor after casting and hence also known as floor sand

Backing or Floor Sand



System sand

The sand employed in mechanical heavy castings and has high strength, permeability and refractoriness, is known as system

sand. It is used for machine moulding to fill the whole flask. In machine moulding no facing sand is used. The system sand

is cleaned and has special additives

Core sand

A sand used for making cores is known as core sand. It is silica sand mixed with core oil (linseed oil, resin, mineral oil) and other

binding materials (dextrine, corn flour, sodium silicate). It has remarkable compressive strength.

A sand which carries molasses as a binder is known as molasses sand. It is used for core making and small castings of

intricate shapes.

Molasses Sand



Properties of Moulding Sand

Following are the important properties of moulding sand

Porosity:

Porosity also known as permeability is the most important property of the moulding sand. It is the ability of the moulding

sand to allow gasses to pass through. Gasses and steam are generated during the pouring of molten metal into the sand

cavity. This property depends not only on the shape and size of the particles of the sand but also on the amount of the clay,

binding material, and moisture contents in the mixture.

Cohesiveness:

Cohesiveness is the property of sand to hold its particles together. It may be defined as the strength of the moulding sand.

This property plays a vital role in retaining intricate shapes of the mould. Insufficient strength may lead to a collapse in the

mould particles during handling, turning over, or closing. Clay and bentonite improves the cohesiveness.




Adhesiveness:

Adhesiveness is the property of sand due to which the sand particles sticks to the sides of the moulding box. Adhesiveness

of sand enables the proper lifting of cope along with the sand.

Plasticity:

Plasticity is the property of the moulding sand by virtue of which it flows to all corners around the mould when rammed,

thus not providing any possibility of left out spaces, and acquires a predetermined shape under ramming pressure.




Flow-ability:

Flow-ability is the ability of moulding sand to free flow and fill the recesses and the fine details in the pattern. It varies with

moisture content.

Collapsibility:

Collapsibility is the property of sand due to which the sand mould collapse automatically after the solidification of the

casting. The mould should disintegrate into small particles of moulding sand with minimum force after the casting is

removed from it.

Refractoriness

Refractoriness is the property of sand to withstand high temperature of molten metal without fusion or soften. Moulding

sands with poor refractoriness may burn when the molten metal is poured into the mould. Usually, sand moulds should be

able to withstand up to 1650°C.


01-08-2021

Jorhat Engineering College, Jorhat, Assam, India

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workshop theory and practice-i

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