Foundry Note New1

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There are several manufacturing methods for production of metallic components these include:-

1.Mechanical Forming: (Solid state deformation methods)

These methods can further be classified into Hot Working and Cold Working processes.

(a) Hot Working: This is the mechanical shaping of a metal at a temperature in excess of its recrystallization temperature. Hot working processes include hot rolling, extrusion, forging, etc

(b) Cold Working: This is the mechanical shaping of a metal at a temperature below its recrystallisation temperature. Cold working processes include cold rolling, drawing, stretch forming, coining and embossing, etc.

2.Welding (Coalescence by localized melting)

Welding is the process of joining together pieces of metal or metallic parts by bringing them into intimate proximity and heating the places of contact to a state of fusion or plasticity. This leads to interpenetration of the atoms of the metals in weld zone and a strong inseparable joint is formed after the metals have cooled. The commonly used welding methods are:

(a)Gas welding (Oxy acetylene)

(b)Are welding with consumable and non-consumable electrodes

(c)Thermit welding

(d)Forge welding

(e)Resistance welding (spot, seam and butt welding methods)

(f)Cold welding

3.Machining (Removal of excess metal)

The term machining refers to the forming or generating of shapes by means of a material removal process. The range of machining processes includes drilling, milling, turning, grinding, etc

4.Metallurgy (Sintering of metallic grains)

This is the production of shaped parts by die pressing and sintering of metal powders. Powder metallurgy is a useful process for the manufacture of parts in metals that possess very high melting points. It is both difficult and expensive to melt these metals. Another useful application of powder metallurgy is in the production of the so called hard metals. Hard metals are used for the manufacture of cutting tool tips, precision tools and die inserts.

5.Casting processes (Involving flowability in the molten state)

The main casting methods available are:

(a) Sand casting in which liquid metal is poured into a shaped cavity moulded in a sand.

(b) Pressure die Casting

(c) Centrifugal Casting

(d) Investment Casting (lost wax process)

(e) Gravity Casting

(f) Continuous Casting

Of all these processes, casting accounts for about 80% of manufactured shapes ...... evaluation. This is so as a result of the several advantages that it has over the other manufacturing methods.

1. Very complex shapes can be cast in a single step by casting. In this many way other finishing operations like Machining, Welding, etc are minimized and eliminated.

2. Hard to machine parts which could have, been difficult to produce by other means can easily be done by casting.

3. Weight range: Casting process has no limitation as far as weight is concerned. Castings ranging from as little as 0.5g to several tons can be successfully cast. The engine block which would have been difficult, uneconomical to make by other methods is done in a single step by casting .

4. Casting also offers us the opportunity of improving mechanical properties (at least in some parts of the casting) by altering the structure of the metal.

5. It is less capital intensive.

6. Adapts easily to mass production

Other processes are required before a metallic component can be cast shape, and these processes are integrated together to form the operation of a typical foundry. Foundry processes include making of moulds, preparation and melting of metals, pouring the molten metal into the mould cast extraction and cleaning of casting etc.


1. The pattern is destroyed in the process.2. The patterns are more delicate to handle.

3. It offers little opportunity to inspect the mould cavity for possible corrections.

4. The process cant be used with mechanical moulding equipment.

General Properties of Pattern Materials

The pattern determines to a large extent the degree of smoothness and soundness of casting obtained and that is the reason why some special consideration must be taken in the selection of pattern materials. These include:

1.A good pattern material should be resistant to sand abrasion. During moulding, the pattern comes into contact with the sharp silica sand grains and there is the tendency of the pattern to wear during ramming.

Therefore, patterns should be able to resist wear during ramming so as to retain their features. Patterns made of materials like brass, cast iron and steel exhibit this properly.

2. A good pattern material should be resistant to the influence of moisture. Wooden patterns tend to warp when they come into prolonged contact with moisture from the environment and also from the silica sand. Also pattern materials like iron steel chemically react with oxygen contained in the water of the green sand mould and corrode. Therefore, a pattern must have high resistance to moisture if it has to be used repeatedly. Brass patterns tend to exhibit good behaviour when in contact with green sand mould.

3. A good pattern materials must be available at a reasonable cost. Worn out patterns which are very expensive would need extensive patching and machining before it can be used again.

4. A good pattern material must have the ability to take a good surface finish.

5. It must lend itself to easy working, shaping and joining.

6. It must be light in weight to facilitate handling and working.

7. It must be strong, hard and durable.

Choice of Removable Pattern materials

The characteristic properties of some removable patterns influence to a large extent their selection for use in the moulding operation. Some of these characteristics are here under enumerated according to their merits and de-merits.



(a) It is cheap and easily worked.

(b) It is light in weight.(c) Hardwood, like mahogany is durable and can be used repeatedly.Disadvantages

(a) Its resistance to moisture is poor (it tends to warp).(b) Its wear resistance is also poor.

2. Cast Iron

Advantages(a) It is resistant to abrasion.(b) It is cheap.(c) It gives good surface finish.


(a) Cast iron patterns are heavy and fracture easily because of its brittle nature.

3.Brass Advantages

(a) It is resistant to the abrasive action of sand.

(b) It is resistant to the influence of moisture. It does not rust.

(c) It gives very good surface finish, even better than that of cast iron.

(d) It is easily repaired.


(a) Brass patterns are very heavy.

(b) They are expensive.



(a) It is light in weight.

(b) Resists the influence of moisture.

(c) Resists sand abrasion.

(d) It is easy to cast.

(e) It is easy to machine to shape.


(a) They dent easily.

(b) They are expensive.

Types of Pattern

There are three major types of pattern

(1) Loose patterns

(2) Match plates

(3) Cope and drag patterns

The materials from which the pattern is formed does not in any way determine the pattern type. The type is determined by the physical appearance of the pattern.

Loose patterns

Loose patterns can be

(a) Solid (one piece) pattern

(b) Split pattern

(c) Gated pattern

Solid pattern These patterns usually have one flat surface and relatively simple features appearing on the other side. The flat surface coincides with the parting plane of the mould.

Solid patterns can be divided into.

(a) Regular parting solid pattern

(b) Irregular parting solid pattern

The regular parting solid pattern has one flat surface which coincides with the parting plane of the mould.

Irregular Parting Solid Pattern The irregular parting solid pattern differs from the regular parting solid pattern in the sense that the parting line is shifted from the standard position to a hand-formed position. This is done to facilitate removal of the pattern without destroying the mould.

The irregular parting solid appears to be the forerunner to the split pattern. By introducing hand made PL we have been able to do what would have been done easily using a split pattern.

Advantages of Irregular Parting Solid

(1)It provides an opportunity to cast objects that would have been impossible by using solid pattern.


It is cheaper and easier to construct a solid pattern than a split pattern


(1).It requires great skill to construct the parting line.

Match Plates

A match plate is a flat plate placed between the cope and the drag to which patterns are securely mounted.

Cope & Drag Patterns

One pattern plate has the drag pattern on it and the other the cope pattern. Cope and drag patterns overcomes the weight problem associated with match plates,

and it also increase productivity as it allow two different operators to work simultaneously one in the cope part and the other in the drag part.

Split patterns

These are used to cast complex shapes which do not have a flat surface. The pattern is made to part or split along a plane which coincides with the parting plane of the mould. In this way, a part is made in the cope and the other in the drag.Gated Patterns

Can be a solid pattern or split pattern to which gate have been added. The addition of the gate eliminates the hand cutting of the gating system.

Advantages (1)Eliminates likely errors during hand cutting of gates

(2) Reduces the skill required of the moulder.

(3).Rapid moulding.

Pattern Allowance

Pattern allowance is a vital feature in pattern design as it affects the dimensional accuracy of the casting. Thus, when a wooden pattern is produced, certain allowances must be given on the sizes specified in the finished component drawing so that the casting with the desired specifications can be produced.

The allowances usually considered in parting are :(i) Shrinkage allowance

(ii)Draft or taper allowance

(iii)Machining allowance

Shrinkage Allowance

This allowance requires that the pattern be made slightly larger than the would be casting to compensate for shrinkage as the metal solidifies and cools. Total contraction is actually volumetric but the correction for it is expressed linearly. Shrinkage allowance depends on the type of metal to be cast.

The following allowances are commonly used.


cast iron











These allowances are incorporated into the pattern by using special shrink rules which are larger than a standard rule by the desired shrinkage allowances.Sometimes double shrinkage allowances are provided in the wooden pattern if it is to be used to cast metal pattern which in turn would be used to cast other castings. Thus, the total shrinkage allowance on a wooden pattern to be used to cast an aluminium pattern which in turn would be sued to cast iron casting is 2.3%.Wooden pattern

Aluminium Pattern cast iron castings 2.3%

1.3% + 1%

Draft (Taper) Allowance

Draft is the angular difference between the sides of the pattern and an imaginary straight line to the parting line. It is usually expressed in degrees

Functions of DraftDraft allows the pattern to be drawn from the moulding medium easily, without rupturing it. The main features that determine the mount of draft are.

(i)Depth of the draw face

(ii)Type of moulding medium (type of foundry sand used)

(iii)Texture of the pattern material

(iv)Complexity of design

Draft may be external or internal

External Draft-Draft provided on the external of a pattern, it may be two-sided or one-sided.

Two sidedIt is always desirable to reduce the amount of draft as this means extra metal and extra clean-up to be done.

Interior draft -this is used when the draw face is in the interior of the pattern when the interior area of the hole is large enough for the sand to support itself.

Allowance for Machining: This is an extra allowance provided on surfaces to be machined.

Pattern colours:

Colour makings have been recommended for wooden patterns as an aid for the best use in the foundry. These are as follow:

(1)Black : Black shows the body of a casting which remain in this condition resulting from the cleaning operations (surfaces needing no further work apart from the cleaning operations)

(ii)Red: Surfaces to be machined

(iii)Yellow: This shows the pattern of core prints and seals for loose core prints.

(iv)Red strips: Red strips marked on a yellow background show core seats and loose pieces from the pattern.



A major factor in the production of casting (sand casting) is the use of sand mould and the amount of sand used is usually large and must be controlled to make good casting. Actually the sand mould is the tool which forms the casting. Therefore a great deal of attention must be paid to the detailed sand operations of preparing of preparing, controlling, handling and using of the moulding sand. From the general point of view the sand must be readily mouldable and capable of producing defects free castings.

If silica sand mould is of quality as a good one it must have the following properties

(i)Ample strength (Green strength, Dry strength and Hot strength).

(ii)Good gas permeability

(iii)Flowability (plasticity)




Green Strength: Green sand is that sand for which water is added and mixed for develop strength. Green strength is needed of a green sand to enable it withstand handling during the making of the mould.

Dry Strength: As molten metal is poured into the mould cavity the sand layer adjacent to the molten metal quickly dries up loosing is water. The dry sand must possess dry strength to enable it withstand mould erosion and metallostatic pressure of the molten metal. Other wise the mould would enlarge.

Hot Strength: After the sand has lost most of its water and is now dry, it is still in contact with the dry hot molten metal and is required to possess hot strength at elevated temperature (above 100oc). If the sand does not develop hot strength, the molten metal may cause enlargement of the mould, or while still flowing may cause erosion.Gas permeability: Molten metal always contain some dissolved gas which are upon solidification and cooling. As heat from the casting causes the moulding sand to evolve a great deal of gases (green sand). If these evolved gases do not have the opportunity to escape through the mould they remain trapped in the molten metal causing gas defects (pin holes, blowholes, etc.)Flowability: Flowability is also referred to as plasticity. High plasticity is required of a moulding sand to obtain a good impression of the pattern in the mould. Flowability of a moulding sand refer to its ability to acquire a predetermined shape under pressure and to retain this shape when the pressure is removed.Collapsibility: Some degree of collapsibility is required of a good moulding sand. That is its ability to decrease in volume to an extent under the compressive forces exerted by the solidifying and cooling metal. Poor collapsibility may lead to cracking of the casting

Effects of Clay and Other Binders to Moulding Sand

When greater mechanical properties are required of a moulding sand, binding agents are usually added. Sometimes the binder is provided by nature with sand. A binder is any material that imparts cohesiveness to the sand grains. In this way much properties are improved.

Binders can be classified into 3 broad groups: (i) Organic and (ii) inorganic binders (iii) clay-type binders.

1.Clay-type binders

Clays originate in three ways: (i) some are formed by the decomposition of rocks and are called residual clays.

(ii)Others are formed by the alteration of rock of igneous origin by underground waters.(iii)Others are deposited as sediments and are called sedimentary claysThe commonly used clay binders are fireclays (kaolinite), bentonites, illites montmorillonite, etc.

2.Organic BindersOrgan binders are those binding agents that contain carbon as the major constituent element. The commonly used organic binders are:

(1)Cereal binders

(2)Resins and Gums



(5)Drying oils

Cereal binders: These are derived from the common cereal, e.g corn. They are frequently produced as flourlike dry materials and occasionally as fluid materials such as molasses. Many of the cereal binders are susceptible to souring in use and may develop odours. They have been used in foundries for thousands of years to give green strength to cores in the green state .Cereal binders are also used in moulding sands, iron and steel foundries to give a rubbery state to the foundry sand to enable the molten metal move over the sand and not burn in or penetrate the mould itself. Most cereal binders burn out at approximately 400oC, but then they would have fulfilled their functions. Resins and Gums:

Natural resins are called gums while synthetic resins are simply called resins. Gums are not usually used as primary binders while synthetic resins are used as primary binders.

Thermoset Binders:

When phenolic resin comes in contact with heat for the first time, they go through 3 stages.

First the resin melts into a liquid, then it changes into a rubbery state and finally, the rubbery solid changes into a hard strong almost insoluble material. This procedure is often referred to as the shell process and is commonly used in the foundry.

Shell Process: A heated match plate (metal pattern) is damped to a dump box containing a mixture of foundry sand and phenolic resin.

The box is inverted and the mixture is dumped on the match plate. The phenolic resin now goes through the three stages earlier mentioned. Thereafter the dump box is returned to its original position and is further treated by baking it in an oven to produce the shell of the pattern.

Euran Binders ________________________________

3.Inorganic Binders

(i)Cement bonded mould

(ii) The CO2 process

Special sands

Silica sand has found extensive application in the foundry industry because it is readily available and inexpensive. However the so-called specially sands are also used commonly for certain reasons: (i)Better stability at elevated temperatures hence better cast surfaces are obtained.(ii)Strength

Commonly used special sands are olivine, zirconite and chromite. Because they are expensive they are commonly used as facing sand, and sometimes as total mould.

Silica sand is much less expensive than specially sands. In fact, olivine is about 10 times the cost of silica sand, while chromite and zirconite cost twice as much as olivine.Additives to Moulding Sand

Sand additives are those materials added to sand which do not act as binders but impact certain important properties.

The commonly used additives are

(i)Pulverised coal (ii) graphite (iii) peat (iv) wood flow and other organic matter.

Upon contact with the molten metal these additives burn and form gases which do not allow intimate contact between the metal and the mould. This gas jacket do not only prevent intimate contact between the mould materials and the metal but also makes the mould more collapsible as the metal shrinks.Pulverised coal, graphite and charcoal are used as additives to prevent burn-on and metal penetration. They are finely grind and applied in the mould surface in the form of dust coating (blacking).Peat and wood flow are added to mould and to improve their plasticity and collapsibility.

Dry sand moulds are coated with whitening which has high refractoriness. Whitening eliminates the possibility of burn- on and enables castings with smooth surfaces to be obtained. Whitening for grey cast iron consists chiefly of graphite, while silica flow is used for steel castings.



Moulding machines or hands are used for the production of moulds. The hand moulding is used for small work while the machine moulding is preferred for mass production work.Moulding Procedures: The most extensively used types of hand moulding procedures are:(1)Floor moulding flasks

(2)Pit moulding

(3)Sweep moulding

Pit moulding

In pit moulding, all the work in making the mould is done on the foundry floor pit moulds may be either open or covered.

In open pit moulding, the upper part of the mould in pit is open; in the covered pit moulding the top is finished off with cores or with sand rammed in an open flask.

Pit moulding requires that the earth floor at the moulding site be horizontal and sufficiently permeable to gases. Therefore, the place must be properly prepared before hand. This is called bed making the mould.

Preparation of the mould bed.This involves covering the rammed bottom of the pit with a 50 to 80mm layer of coke to improve the gas permeability of the mould. This is particularly done for large castings. A bed of sand is sufficient for smaller castings.

Vent pipes are then run from the coke layer to the surface (at the dives) and the coke is covered with backing metal.

Open pit moulding

This method is used to cast simple shapes in which the upper surface is flat (plates, grald, bars, pards, etcPattern 1 is placed face downwards on the sand bed and then sunk gently into the bed with the help of gently hammer blows administered through a board placed on the pattern. The horizontal position of the pattern is checked using the spirit level (4). Next the pattern is covered at the sides with facing sand and then consolidated and then backing sand is added. After this the pattern is checked again with the spirit level, and then excess sand is removed. The sand around the pattern is smoothed with trowel and vent holes (3) are provided. Runners 6 and 7 are cut- to admit and drain excess metal. After all the preceding operations, the pattern is withdrawn with the help of the draw spike. The impression of the pattern, i.e. the mould cavity, remains in the sand. Parts of the sand mould damaged during pattern withdrawal are repaired and smoothed down. The mould surfaces are then coated with graphite dust and the molten metal poured in. Immediately after pouring the surface of the molten metal is covered with charcoal and a layer of dry sand to ensure uniform cooling of the casting and to prevent oxidation of the metal.

Covered Pit moulding:

In covered pit moulding, parts of intricate shapes are made. An example of covered pit moulding is illustrated in the fig. below. Here the lower part of the pattern is placed in a previously prepared pit and bedded into it to a certain depth. Next, all the processes listed in the preparation of the open pit moulding are followed and then the upper part (cope part) of the pattern is aligned with the drag part and the cope placed over it. Pattern for runners and risers are located and the cope part is filled and rammed. Next, the cope is separated from the drag followed by withdrawal of pattern and subsequent assemblage (including the core made separately).

The mould is then ready for pouring.

Pit moulding is practiced in place or job production

Flask moulding:

This is the most widely employed process both in hand and machine moulding procedures. Various flask moulding procedures are employed depending on the shape size and complexity of the casting be made. These are:(1)Two- part moulding with an unsplit pattern

(2)Two-part moulding with a split pattern

(3)Multiple part moulding

(4)Moulding with pattern having loose pieces

(5)Stack moulding

(6) Snap or removable flask moulding etc.Two-part moulding with unsplit and split patterns-refer to my handout (national diploma)

Multiple part moulding

The shape of a casting may be so complex. It mould be difficult to make it using two flasks. In such cases three or more flasks may be required (each flask housing a part of the casting). Where three flasks are used, the middle part is called the check.

Stack moulding:

Stack moulding is used to make small light casting. One advantage of this process is that it requires much loss floor space in the foundry.

Two types of stack moulding procedures are employed in the foundry

(i)The upright and

(ii)The stepped procedures

In upright stack moulding from 10 to 12 flask sections are arranged one above another; having a common down sprue through which all of them are fed with molten metal.In stepped stacking, the flask sections are arranged in steps with each flask section having is own sprue. Each successive mould is offset from the other by the width of the pouring basin. Thus each mould is poured separately.

Snap flask moulding

Snap flask moulding utilizes matched plates. The match plates are designed to have an offset parting plane to avoid shifting of the cope and drag and to prevent molten metal from breaking out through the parting plane during pouring.

In this procedure the drag (2) is placed on the metal match plate (4) which is placed on an overturned cope and filled with sand and rammed in the usual manner.

A bottom board (3) is then placed on the drag and the whole mould is then turned over and then the cope is filled and rammed as usual. Then the cope is lifted off and the match plate pattern. Both cope and drag moulds are repaired and then assembled. After this the cope and drag sections of the flask are removed simultaneously from the mould. This of course presents no difficulty because of the tapered nature of the flask. The mould is then taken to the pouring section, where a steel jacket is worn over to provide rigidity.

Snap flask mould is extensively used for producing small casting on a large scale. Knock-out is much easier in this method and significant economy is attained in the cost of flasks. Moulding sand consumption, however, is somewhat higher.

Sweep moulding:

This procedure is resorted to when the part to be cast is of large size and the casting has to be done in a short time. In-other words, the cast of pattern and the time required to make it has been greatly reduced. Sweep moulding excludes the use of expensive pattern, and therefore reduces cost about 11/2 times.

Sweep moulding may be performed by 2 methods.

(1)By using a turning sweep (template) rotating either about a vertical or horizontal axis to form surfaces of revolution (in moulding cylinders, bowls, etc). (2)By using a drawing sweep pushed along a guide frame.

Moulding Machines

The commonly used ones are

(i) Jolting machine


(iii)Jolt squeeze

(iv)Sand slingers

These machines not only ran and consolidate the sand they also draw the pattern from the mould.

The use of moulding machines enables labour productivity to be sharply increased, more accurate castings to be produced, costs to be reduced and a higher quality of products to be maintained.

Moulding machines pack the sand and draw the pattern from the mould. According to the method by which sand compaction is achieved moulding machines are classified as above.

Squeeze Moulding Machines

These are operated by compressed air at a pressure from 5 to 7 atmospheres.

A schematic diagram of a top squeeze machine is shown in figure below.Fig. 3. Top Squeeze Machine

The pattern plate with pattern is clamped on work table and flask is placed on the plate. The sand frame is placed on the flask and the machine. Next the table lift mechanism is switched on and the flask together with the sand frame and pattern is lifted up against platen of the stationery squeeze head, the platen enters the sand frame and compact the sand down to the upper edge of the flask (shown by dash line). After the squeeze, the work table returns to the original position.The principle of a bottom squeeze machine is shown in fig.4. The pattern plate 2 with the pattern is clamped on work table 1. Flask 3 is placed on frame 4 of the machine and is filled with sand from a hopper. Next, the squeeze head 5 is brought against the top of the flask and the lift mechanism is switched on. Table 1 and 2 and the pattern are pushed up to the lower edge of the flask (shown by the dash line). After this the table returns to the initial position.

In squeeze moulding machines, maximum hardness is achieved in areas around the squeeze head.

Fig.4 Bottom squeeze machine

Jolt Moulding Machines The schematic diagram in fig. 5 illustrates the principle of a plain schockless jolt moulding machine.In the operation of the jolt moulding machine, table 1with pattern plate and pattern 2and 3, filled with moulding sand lifted by plunge 4 to a definite height when compressed air is admitted through hose 5 and channel 6. Next, the table drops since compressed air is released through hole 7.

While falling, the table strikes the stationary cylinder guide 8 and this impact packs the sand around the pattern in the moulding flask. Spring 9 by cushioning the table blows, reduce noise and prevent damage to the mechanism and foundation.

In jolting, maximum mould hardness is achieved towards the bottom, against the pattern surfaces.

Fig 5 Jolt Moulding MachineJolt-Squeeze Machines These machines utilise the advantages of the jolt and squeeze moulding techniques.

The Sand Slinger

The sand slinger impels moulding sand into the flask with sufficient force to pack it around the pattern to the desired hardness.

The essential element of the sand slingers head shown in fig.6. The slinger head consists of housing 1, which is blade 2 rotates rapidly. Moulding sand is fed by a belt conveyor through opening 3 into the head where it is picked up by the rapidly rotating blade 2and thrown in separate portions at a very high speed through outlet 4 into the flask beneath. Core-Making

Cores are compact mass of core sand that when placed in mould cavity at required location with proper alignment does not allow the molten metal to occupy space for solidification in that portion and hence help to produce hollowness in the casting. The environment in which the core is placed is much different from that of the mould. In fact the core (Fig. 10.12) has to withstand the severe action of hot metal which completely surrounds it. Cores are classified according to shape and position in the mould. There are various types of cores such as horizontal core (Fig. 10.13), vertical core (Fig. 10.14), balanced core (Fig. 10.15), drop core (Fig. 10.16) and hanging core (Fig. 10.17). There are various functions of cores which are given below

1. Core is used to produce hollowness in castings in form of internal cavities.

2. It may form a part of green sand mould3. It may be deployed to improve mould surface.

4. It may provide external under cut features in casting.

5. It may be used to strengthen the mould.

6. It may be used to form gating system of large size mould

7. It may be inserted to achieve deep recesses in the casting Cores are subject to very severe conditions since they are enveloped in all sides by the molten metal except at the ends. Therefore cores must possess

(i) Very high strength

(ii) Good gas permeability

(iii) Good collapsibility

(iv) Ample refractoriness

A lack of collapsibility in cores is very dangerous because this may lead to the formation of cracks in the casting.

Cores are made manually or with machines. Core making consists of the following sequence of operations, moulding of grain sand core, baking, finishing, and cracking. If a core is made of two or several pieces, they are assembled together after baking by parting or other moulds. Core Box

Any kind of hollowness in form of holes and recesses in castings is obtained by the use of cores. Cores are made by means of core boxes comprising of either single or in two parts. Core boxes are generally made of wood or metal and are of several types. The main types of core box are half core box, dump core box, split core box, strickle core box, right and left-hand core box and loose piece core 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. 10.17. Two halves of cores are pasted or cemented together after baking to form a complete core.

Half core-box

2. Dump core box

Dump core box is similar in construction to half core box as shown in Fig. 10.18. 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.

3. Split core box

Split core boxes are made in two parts as shown in Fig. 10.19. 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.

4. Right and left hand core box

Some times the cores are not symmetrical about the centre 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.

5. 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.

6. 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.

Reinforcement of coresCores are often reinforced to increase their strength, they are usually reinforced with annealed low carbon steel wire up to 8mm. Heavy cores with large cross section are reinforced with cast iron . Venting of cores

Provision of vent holes to improve gas permeability. Vent holes may be made by piecing the cores with stiff wire where possible. Other methods are the insertion of wax cards during core making (for slender cores) and the cutting of gates and griming them after (Heavy cores).

Core making machines

(i) Die extrusion

(ii)Squeeze and jolt machines

(iii)Sand slinger

(iv) Core blowers, etc


MELTING IN METALLUGICAL FURANCESThe commonly used melting equipment in foundry are:(i) The Crucible furnace(ii) Cupola furnace

(iii) Electric furnace

The Crucible furnace is further subdivided into three types namely

a) Lift-out Crucible

b) Fixed (bail-out) Crucible

c) Tilting Crucible

In (i) above, the crucible is placed inside the furnace shell and is lifted out when the metal is ready for pouring.Fig. Lift crucible Furnace

The fixed crucible, the crucible is fixed and is removed only for repair or replacement. The molten metal is removed from the furnace with the help of ladles. For the tilting furnace, is mounted on a pivot which allows it to tip for metal removal. The metal is usually poured into transfer ladles which are used to move the molten metal to the moulds for pouring.

Crucible furnaces provide great flexibility, changing materials and alloys to be melted is fairly simple. However, capacity is limited; the working conditions are crucible furnace has limited use. It is most often found in low production operations and in educational and experimental facilities.Electric furnace is divided into three namely

*Arc furnace

*Induction furnace

*Resistance furnaceFurther, the arc furnace is further divided into two types, which are

*Direct arc furnace

*Indirect arc furnace

The induction furnace is also further divided into *High frequency (crucible) furnace

*Low frequency (core or channel) furnaceCupola Furnace

The cupola furnace is the oldest and most widely used furnace for melting grey iron, ductile and malleable irons. The cupola provides a simple and inexpensive method of continuously melting pig iron and scrab iron. It consists basically of a refractory lined steel shell, closed at the bottom and open at the top as shown.

A charging (loading) door is located about 30-45m above the bottom of the furnace.

Tuyers (air intake) are built above the slag and tapping spouts. Fig. Section through a cupola FurnaceOperation of the Cupola furnace.

The operation of the cupola involves several steps. First rags, wood, coal, coke and other combustible materials are placed on the sand floor and lit then an initial charge of coke is placed on top of the fuel .

When the initial charge of hot alternating layers of metal, coke and limestone are added and allowed to be heated. A blast of air is introduced through the tuyeres. The metal will melt and accumulate on the sand bottom from whence it is drawn at regular intervals through the pouring spout. Clay plugs may be used to stop the flows so that batches of metal may be taken from the furnace.

The cupola furnace is widely used because of its simplicity. However, there are so many difficulties connected with its operation. The chemical action within the furnace is very difficult to control. A proper balance must be maintained between metal, coke and limestone if the output is to have the desired chemical and physical properties.

Electric furnace

Electric melting is one of the major methods of melting in iron and steel foundry. Electric furnaces have proved a big asset in the production of high quality metal as they attain high melting efficiency with minimum loss.

Unlike cupola furnace, electric furnace posses greater adaptability and flexibility and provide precise control over the temperature of the molten metal. The high cost of the electric power is a limitation but this is outweighed by several overwhelming advantages its types had been mentioned above.

Direct Are Furnace

This furnace works on the principle that heat is produced when resistance is offered to the flow of electricity. In the case, it is the metal in the charge that provides the resistance of the flow of current. When the metal is molten. The slag offers resistance to the flow of current. Thus to maintain proper heating even when the metal is molten, the electrode must be raised so that they just touch the slag layer. A typical direct arc furnace is shown below with a refractory lined steel shell. It has roof which can be rotated to open the furnace for loading. Three adjustable carbon electrodes extend through the roof.Fig. Direct Arc FurnaceThe operation of eh furnace includes

Raising the electrodes. Rotating the roof to the open position. Lowering the furnace(could be molten pig iron and steel scrap or only steel scrap). Rotating the roof to the closed position.

Lowering the electrodes to their arcing position.

Turning on the power. Arcing between the electrodes and the charge creates the heat necessary for melting the metal.

Indirect Arc Furnace

The indirect are furnace may be used to melt all types of metals, but it is specially designed for non-ferrous metals.

The furnace is made up of a barrel-shaped drum, mounted horizontally and so geared that it can be rotated back and forth through an angle of 180o. The shell is lined with insulating and refractory material.Fig. Indirect Arc FurnaceTwo electrodes are used, each are entering the furnace from either end and coinciding with the horizontal axis of the cylinder. As the electrodes are brought near each other, an arc is struck between the two ends and tremendous heat is generated. The heat of the arc is radiated and reflected in all directions. Thus a part of the heat is directly absorbed by the metal and the remainder by the lining. As the shell rotates back and forth, metal flows over the heated surface and absorbs the heat energy from the walls by conduction.

Induction furnaces

Melting of metal in an electric induction furnace differs from that in the arc furnace in that instead of the bulk of the heat being generated in an arc and radiated to the charge, all the heat is generated in the charge itself.

Two basic types of induction furnaces are in use. They are the high frequency crucible type and the low frequency core or channel type. Both types operate by inducing current into the metal charge.

Basic advantages of induction furnace over the arc furnace are

There is precise control over temperature.Good quality of metal.

It adapts easily to vacuuming.High frequency crucible Induction Furnace

Crucible type has a coil of copper tubing wrapped around it. This coil carries a high frequency (up to 30.000 HZ) alternating current. As the alternating current is applied to the coil an alternating magnetic field is induced around the coil. This magnetic field in turn induces a high alternating current in the charge.

The low frequency (channel of core) furnace

The low frequency crucible works on the principle of the step down transformer but the number of turns in the primary coil is always greater than that of the secondary. That of the secondary is always a loop. The current come into channel through the primary coil and the coil step down the voltage as it passes into the secondary coil. Bottom board

Regular parting solid pattern pattern


PL (Parting Line)

Draft PL


One sided

Internal Draft



Head mace parting line



Bottom Board


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