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EXPENDABLE POLYSTYRENE PATTERN CASTING PROCESS:

A REVOLUTION IN FOUNDRY TECHNOLOGY

INAUGURAL LECTURE SERIES 7

Delivered at

THE FEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI

ON

WEDNESDAY, 17TH

MARCH 2004

By

OKAY EKPE OKORAFOR B.Sc. (Hons) (Unilag), M.Sc., PhD (UW – Madison)

PROFESSOR OF METALLURGICAL ENGINEERING

FEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI




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ISBN: 978-36877-1-9




1.0 INTRODUCTION

The numerous and varied application of metal castings demand for but one ultimate concern

of the foundry metallurgist, namely, to produce sound castings which meet the requirements of

certain specified set of physical and mechanical properties with minimum rejections. To achieve

this objective, usually, the foundry employs control over raw materials, composition of the

charge according to specifications and melting conditions, superheat, pre-treatments of melt,

pouring temperature, proper designing of mould and moulding material, etc., so that the feeding

of the casting and its controlled solidification are assured.

Attention has been given to virtually all the stages of processing aluminum alloy castings. In

many instances, the effects obtained have been quite significant but, as yet, the search for

improved casting methods and techniques is still a continuing activity by foundrymen. From

available information, one thing is clear, and that is, that fast freezing leads to improved structure

and, it is believed, better properties. Since solidification basically is a phase transformation that

can be described in terms of two rate parameters, nucleation and growth, it is useful to attempt to

relate the structure produced by solidification and hence properties to the rate of nucleation of grains and their subsequent rate of growth. Both the rate of nucleation and the rate of growth

depend upon the temperature at which the transformation occurs. Consequently, a rationalization

of cast structure and properties in terms of the kinetics must include a description of the effect of

the casting process on the thermal conditions during freezing.

In general, for conventional casting, an alloy is heated above its melting point, poured into

mould and allowed to solidify there. The process depends on heat extraction into and through the

mould, which, it is clear, imposes severe limitations on the rate at which solidification occurs.

But other possibilities exist, of which some are being exploited and others are under

consideration. For example, there are various continuous casting processes in many of which

heat extraction is designed to provide rapid production, but have the advantages of directionallycontrolling the solidification process and causing it to occur at high speed. Such processes,

however, can at best provide ingots or the equivalent of some later stage of the progression from

ingot to sheet, bar or wire.

The question then is whether it is possible to remove latent heat by means other than

conduction into the mould. It is, of course, a fact that whereas heat can be added uniformly to a

body, for instance, by high frequency or resistance heating, it can be extracted only at the

surface. Bearing this in mind, two possibilities arise; one is that the liquid should be supercooled

before it enters the mould, so that part of the latent heat is used to heat the melt to the melting

point. Any such possible supercooling obtained within reasonable limits would allow the

solidification of a good proportion of the melt without the extraction of any heat.

Further, in the cases where solidification from large undercoolings gives very fine grained

materials, the details of the structure and properties of alloys studied in this manner have not

been elucidated. Severe technical difficulties in applying this procedure should be that even a

single nucleant particle would cause the whole mass to solidify. Another possible technique

would be to pour a “slurry” of solid and liquid, the “slurry” preferably being a dispersion of




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small crystals such as would be formed by violent stirring of a melt in which solidification has

started. This procedure, which would require very close control of time and temperature, might

avoid macro-segregation and would produce a fine grained, finely dendritic structure.

The present work, in this context, was a program to produce aluminum alloy castings by the

expendable polystyrene pattern casting process. The growth of interest in aluminum alloys as

materials for light castings rendered it desirable that a careful investigation into the metallurgical

aspects of these castings, when prepared under controlled conditions, should be made in order to

arrive at an independent standard of what may be expected of the alloys. Since experience with

most casting processes show that both structure and properties of castings are process dependent,

a comprehensive investigation has been carried into the process and modification effects on

structure and properties of expendable polystyrene pattern castings.

The problem of fuming, fading and uncertainty of recovery in sodium modification during

founding, together with the growing interest in strontium as a modifier with little or no fading

made it desirable to use both elements for the purpose of comparison and documentation of their

modifying effects and characteristics for this particular casting process.On the basis of the foregoing, the report which follows has attempted to provide a critical

study of the relationship between the fundamental principles of solidification and experimental

observations bearing on the results of the process and modification effects with respect to the

thermal history, structure and properties of expendable polystyrene pattern aluminum alloy

castings. Due to lack of information on this subject, some of the account presented is qualitative

in nature, however, quantitative description has been supplied where necessary for clarity and

comparison, in the hope that the material may elicit the interest and constructive criticism of

those engaged in expendable polystyrene pattern casting, so that future definitions of research

problems in this field may be closely allied to topics of interest to the industry.

1.1 THE BASIC CONPECT OF EXPENDABLE POLYSTYRENE CASTING PROCESS

The expendable polystyrene pattern, also known as full mould, cavity-less, evaporative, lost

foam or gasifiable pattern casting process has been applied to the casting of a wide variety of

metallic alloys, and present commercial practice is capable of turning out highly satisfactory

castings in ferrous and non-ferrous alloys. In its present stage of development, the process offers

most attraction for use for the „one or few off‟ type of work. Further developments are bound to

include small quantity and mass production techniques to widen the scope of the process.

The process has been fully described in the literature.1 – 3

It is therefore not the intention here to

offer guidance on the process but to present a brief description of the process. The basic concept

of the process is very simple. The principle considered is that a pattern made of foam plastic is

embedded in unbonded sand and replaced by molten metal (Fig.1). The metal replaces the foam

pattern and a metal duplicate of the pattern is the result. The claim put forward for this process is

that, owing to the chemistry of the process, the cast metal tends to be free of shrinkage porosity;

and free from unsoundness, blow-holes and non-metallic inclusions whether the molten metal is




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degassed or not, provided it is cast under proper pouring conditions.

At the present time the process offers many advantages to the foundryman and yet is by no

means developed to its full potential. The advantages of the process as compared to conventional

bonded sand techniques are numerous and include features such as no cores, reusable sand, no

binders or additives, inexpensive flasks and so on.

The principal disadvantage to the manufacture of expendable polystyrene pattern castings in

unbonded sand is the comparatively overwhelming inertia of the more established methods.

These methods have been tried and proven over a period of several years and foundrymen who

have developed satisfactory ways of making castings are understandably reluctant to change

overnight to a method which still requires experimental work for perfection. However, the fact

that a separate pattern is required for each casting is considered to be a major disadvantage of the

expendable polystyrene pattern casting process.

2.0 SOLIDIFICATION PROCESSING

The pouring of molten metal into a relatively cool mould initiates the processes of solidification, during which stage the cast form develops cohesion and acquires lasting structural

characteristics. The properties of the solidified metal or alloy are determined to a considerable

extent by the phenomena associated with this transition; these may produce various

consequences, although all metals and alloys consist essentially of crystals which fall into one or

other of a few types. Despite this similarity of the fundamental unit of the solid materials, very

great variations in their grouping and arrangement may be induced by alteration in the mode of

transition from the liquid to the solid state.

The mode of freezing exercises a two – fold influence upon the final properties of a casting.

The normal metallographic structure determines many of the properties inherently available from

the cast metal. This structure – the grain size, shape and orientation and the distribution of alloying elements as well as the underlying crystal structure and its imperfections – is largely

determined during crystallization from the melt. Even in those cases where the as – cast structure

is modified by subsequent treatments it still exerts a residual influence upon the final structure.

The properties and service performance of an individual casting are, however, also a function

of its soundness – the degree of true metallic continuity. This too is established during

solidification, since the volume shrinkage accompanying the change of state must be fully

compensated by liquid feed if internal voids are to be prevented.

Structure and soundness being dependent upon the mechanism of solidification, are

influenced by many factors, including the constitution and physical properties of alloy. Other

important factors are the melt history and prior treatment, the pouring conditions, the thermal

conditions in mould and sometimes the mould material itself; and it is with the manipulation of

these conditions to achieve full control of the pattern of freezing that much of the technique of

founding is concerned.

Principles underlying the solidification behavior and other metallurgical aspects of

expendable polystyrene pattern aluminum alloy castings are nonexistent in the literature. The




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present section therefore reviews in a general term the phenomena associated with the

solidification, modification and properties of aluminum alloys.

2.1 SOLIDIFICATION: GENERAL PRINCIPLES

The process of solidification of a metal or alloy presents a complex phenomenon, whose

course is characterized by four inherent aspects:

a) Solidification, as applied to metals and alloys (but not to glasses) is a discontinuous

process.

b) The volume of the solid is almost always different from that of the liquid.

c) Latent heat of fusion is generated in proportion to the amount of solid formed.

d) The composition of a solid alloy is usually different from that of the liquid from which it

is forming.

As a result of these unavoidable characteristics, certain limitations are imposed on the

process. In the first place, the discontinuous nature of solidification implies that there is no state

intermediate between the crystalline and the liquid; a partially solidified metal or alloy, therefore,is a mixture of solid and liquid. Any given atom is either in the liquid, in a crystal or in the

interface where crystal and liquid are in contact. From this standpoint, therefore, solidification

has two stages, of which the first, known as nucleation is the formation of new crystals in the

liquid. The second stage is the growth of these crystals by the addition of atoms to them.

The “structure” of a liquid alloy4, 5

assumes great importance when consideration is given to

how nucleation takes place. X-ray diffraction shows that there is no long range order in the

arrangement of these atoms, but the evidence is clear that there is a considerable amount of short

range order. That is, many atoms are members of very small “clusters” that are structurally

similar to crystals.6

These clusters are very short – lived, as atoms join them and leave them with

great rapidity. At any given temperature there is a maximum size of cluster that is likely to occur.

At the melting point, such a cluster is much too small to survive and grow into a crystal. At

lower temperatures the clusters become much larger, until at some temperature, the largest

clusters reach the critical size beyond which they are more likely to grow into crystals than to

revert to liquid. In practice, however, the above outlined process does not occur. This is because

heterogeneous nucleation always takes place as a result of large quantities of impurities together

with other preferred sites.

As soon as nucleation has occurred, and the new crystals have started to grow, the evolution

of latent heat by the growing crystal tends to raise the temperature and to inhibit the nucleation

of more crystals. Since the number of crystals that are formed at this stage may control thenumber present in the final casting, and therefore its grain size and some if its properties, a

consideration of how the nucleation process is affected by the conditions under which

solidification takes place, that is, the rate of heat extraction from the liquid is useful.

Heterogeneous nucleation occurs when the temperature of the liquid in contact with a nucleant

reaches the necessary supercooling. The time required for nucleation to occur is then very short,




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but finite. The number of crystals that form cannot, therefore, be greater than the number of

nucleant particles that are present; but it may be much less, because the evolution of latent heat

may maintain some of the liquid at a temperature that is above that required for nucleation. A

high cooling rate, on the other hand, is accompanied by a lowering of the crystallization

temperature, thus increasing the possibility of more heterogeneous nuclei precipitating out from

the liquid alloy.7

The effect of the composition of the alloy on the process of solidification merits

consideration. It is very generally, but not quite always true that a solid and a liquid alloy that are

in equilibrium with each other have different compositions. In the majority of cases, the solid

contains less solute than liquid.8

When such a solid is being formed from liquid, solute is rejected

and so the liquid in the immediate vicinity of the solid –liquid interface is “enriched” in alloying

elements or impurities. This causes the temperature at which solidification occurs to be

depressed (because the solute enriched liquid has a lower liquidus temperature) and it means

that, for continuous solidification to occur, solute must diffuse away from the interface. Since

diffusion is inherently a much slower process than conduction of heat, this means that the rate of growth of the crystal is much slower for an alloy, therefore, the temperature at which

solidification occurs is depressed, substantially more than would be expected from the

composition of the bulk liquid; and growth takes place more slowly than for a pure metal. Both

these effects are conducive to the nucleation of more crystals; and conversely, the most effective

conditions for suppressing nucleation are slow heat extraction and high purity.7

The fact that the removal of latent heat and solute by conduction and diffusion respectively,

takes place more efficiently from points than from regions of lesser curvature accounts for the

fact that crystal growth in an alloy is usually dendritic,9

that is, the crystals grow initially as a

skeleton of “spikes” or “plates” that present a “tree-like” appearance as a result of manifoldbranching. The interstices between the branches are filled with liquid which becomes enriched

with solutes and subsequently freezes. The temperature at which solidification takes place

depends, as noted above, on composition of the layers of liquid that is actually solidifying, and

this depends on how fast the process occurs in relation to the rate at which the solute is able to

diffuse away. The depression of the actual growth temperature increases with the speed of

growth,10

and so an alloy that would, under conditions of slow growth, be unable to nucleate any

new grains after the start of freezing might, with faster heat extraction, maintain a temperature at

which frequent nucleation is possible. The speed of solidification that is required depends on the

potency of the nucleants that are present and on the quantity and kind of solute that is present.

A further unavoidable result of the solidification conditions outlined above is the highlyheterogeneous distribution of solutes in the casting. There are basically two types of segregation;

there is, almost inevitably, short range or microsegregation as a result of the movement, by

diffusion, of solute that is rejected during growth.11

This can be avoided only in the very rare

cases in which the liquid solidifies congruently, including of course, pure metals. The second

type is long range, or macrosegregation, which is caused by motion of solute enriched liquid




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away from the region in which solute rejection is taking place. The motion may be due to

convection (resulting from density gradients either thermal or compositional in origin) or to fluid

motion that persists from the time the metal entered the mould. Short range segregation is often

most pronounced at the grain boundaries where it may cause brittle phases to occur that would

not exist in equilibrium. These phases frequently have a high content of impurities which, if

distributed uniformly throughout the solid, would be in solution and therefore harmless or even

beneficial. The presence of these weak or brittle layers is to a large extent responsible for the

poor ductility that is sometime regarded as being characteristic of castings.

In a closely analogous way, the shrinkage that accompanies the transition from liquid to

crystal has its long range and its short range effects. Long range, or macroscopic shrinkage

includes the obvious effects such as pipe formation and the less obvious, but equally gross and

much dangerous internal shrinkage cavities. Short range shrinkage effects take the form of

micro-porosity, that is, fine pores that occur in interdendritic regions because the interdendritic

channels are so thin and tortuous that the liquid does not have time to flow in them to the extent

that would be required to compensate for local shrinkage. The rejection of gas, which, like mostsolutes, concentrates in the liquid, can occur by the formation of bubbles. These are formed most

readily in regions of low pressure; an actual void may therefore be the combined effect of

shrinkage and gas evolution. However, the higher the gas content, the sooner are bubbles

formed; and if they are formed relatively early in the solidification process, they tend to grow

large. In the absence of gas, on the other hand, the pores are very small and numerous.

In general, it is clear that microsegregation and microporosity are bound to occur whenever

solidification takes place dendritically;12 dendritic growth takes place wherever the relationship

between the rate of solidification and temperature gradients in the liquid exceeds a critical

condition;13 dendritic growth can be avoided only by a combination of slow advance of the solid-

liquid interface with a steep temperature gradient in the liquid. The conditions are progressivelymore difficult to meet as the solute content increases, especially if the solutes have a strong

tendency to be rejected during solidification.

2.1.1 Effect of Fluid Motion

Two effects of motion of the liquid have been mentioned; occurrence of segregation and of

shrinkage at a substantial distance from the place where most of the rejection of solute and

volume change occur; a third effect of motion of the liquid is less well understood, but its

importance is evident. When liquid flows across the advancing front of a dendritically growing

crystal, a dramatic increase in the number of crystals may take place, without the occurrence of

actual nucleation in the strict sense implied above. The conditions that are required for this

“dynamic multiplication” process are not clear, but it is probable that the liquid must not be

much above its liquidus temperature, and it must be moving at more than some limiting velocity

with respect to the crystal. It is not certain whether temperature fluctuations actually participate

in “melting off” the tips of growing crystals, but it has been shown that a crystal can grow




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dendritically at a temperature substantially below the liquidus, and then melt locally as a result of

the rise of temperature when growth slows down.14

On the other hand, it is also possible to induce nucleation by subjecting the liquid metal to

dynamic stimuli. There are few reliable data concerning true dynamic nucleation. Walker15, and

Frawley and Childs16 have all shown how mechanical vibrations can cause nucleation to occur at

lower supercooling than normally required. A hypothesis advanced by Vonnegut 17, stated that

positive pressure wave generated by the collapse of an internal cavity in the liquid could be large

enough to raise the melting point for metals which contract on freezing by an amount sufficient

to increase the effective supercooling of the melt and thus to produce nucleation. Nucleation in

systems which expand on freezing would be affected similarly by the rarefaction following the

initial pressure pulse.

2.1.2 Supercooling and Solidification

Supercooling or undercooling is a well-known phenomenon in pure metals and certain alloys.

Most of what is reported in the literature on this subject has dealt with homogeneous nucleationin small isolated droplets of clean metals. Supercooling of about 18 percent of the absolute

melting point has been observed under such conditions.18

Nucleation then occurs, the droplets

solidify liberating the latent heat of fusion and temperature rises to approach the liquidus

temperature, i.e., recalescence occurs.

A number of work has also been done on supercooling of bulk sample of liquid metals in

which large effects were observed. The work of Iyer and Youdelis19, 20 shows that; (1) the degree

of supercooling increase with cooling rate, (2) the degree of primary supercooling is dependent

on the composition of the alloy from which the primary phase grows, and (3) the degree of

supercooling may increase or decrease with solute concentration depending on the specific

nucleation and crystal growth rates for a particular alloy concentration. Other authors 21, 22 indetermining nucleation catalysis by monitoring the undercooling of bulk sample as a function of

the sample composition report that the difficulty of certain solid solution dendrites to nucleate a

second phase readily accounts for a subsequent undercooling below the eutectic temperature.

Crystal multiplication and grain refinement by dendrite fragmentation resulting from

undercooling below the liquidus has been reported by McLeod and Hogan23 for Cu-2%Sn alloy.

In these studies, the addition of various grain refining agents tends to eliminate or reduce the

supercooling effect.24

Turnbull18

, has put forward a nice description of the theory of homogeneous nucleation and

supercooling. Unfortunately, the theory of heterogeneous nucleation, which is more important in

the freezing of casting is rather ill-defined. Chalmers and his associates25 have investigated the

interaction of heterogeneous nuclei and supercooling. The “constitutional supercooling” concepts

have been given a rather detailed theoretical exposition in treating the interaction of thermal

gradients, heterogeneous nuclei and diffusion barriers to freezing. The interaction of

supercooling with nucleation or grain refinement processes in commercial practice remains

rather vague. The magnitude of the effects which may occur, their relation to the final grain




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diameter of the casting and supercooling necessary or sufficient to allow the use of a given grain

refinement agent is generally unspecified.

The degree of supercooling and the cooling rate on the occasion of solidification of molten

alloys are powerful factors to influence the solidified structures during the process of founding.

The degree of supercooling depends on kinds and numbers of the nucleation catalysts such as the

inside surface of the vessel and small particles suspended in the molten metals as insoluble

impurities and oxides formed by superheating and other treatments of the liquid. On the other

hand, the cooling rate is regarded as one of the other factors controlling the degree of

supercooling, but it has not yet been satisfactorily explained. Turnbull18, however, has noted that

the rate of nucleation is sensitive to the interface energy and to the degree of undercooling and

that the rate of nucleation is as such dependent on the size of the system under investigation. As

a result of this dependence on the interface energy, there exists a region of temperature below the

equilibrium melting temperature over which crystal nuclei do not form at perceptible rate and is

schematically shown in Fig.2. Supercooling of liquidus is an obvious manifestation of the

metastability of the liquid phase. Since the mobility of atoms is high in this zone, there is norestriction to the growth and crystals once nucleated can grow readily. In many nonmetallic

melts, a zone of high viscosity is reached at higher values of supercooling where nucleation is

again inhibited. Below the metasable zone, however, the rate of nucleation is so fast that physical

transportation of the nuclei by convective fluid flow may play a dominant role in the

solidification at lower degree of supercooling.

Kurfman26, has explained the cause of supercooling in terms of the heat balance associated

with the growth of suitable nuclei, and the various barriers to the growth of such nuclei. In pure

metals and dilute alloys, crystallite growth rates can be extremely high. The growth of a few

grains, perhaps initiated at the crucible wall, is sufficiently fast to liberate latent heat as fast as

the sample is cooled. However, for higher concentration alloys, freezing tends to take placebelow the equilibrium temperature. Solute is rejected, according to phase diagram relationships,

around the growing crystals. This depresses the melting point, and if freezing is to proceed it

must occur at a temperature of this solute-rich region. This can allow the bulk liquid to undercool

sufficiently for fresh nuclei to begin growing.4

If enough nuclei grow, they can liberate latent heat faster than the sample is cooled and the

temperature may actually rise, approaching the equilibrium liquidus. On the other hand, the

failure to observe supercooling in dilute alloys is attributed to the failure to achieve stable

diffusion boundaries. In grain refined melts, enough growth sites are available with nominal

supercooling to balance the rate of heat removal and permit freezing to proceed smoothly with

no recalescence effect.

2.2 SOLIDIFICATION OF Al - Si ALLOYS

Al-Si alloys considered here include additions of copper up to 4% and/or magnesium up to

0.3%. Addition of silicon to aluminum in proper amounts provides desirable casting

characteristics such as fluidity, reduced hot tearing and sounder castings. These effects have




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contributed in making silicon the most common alloying element in the commercial aluminum

casting alloys.

Review of the solidification processes in pure binary or ternary alloys is not an objective

here. Instead, freezing mechanism of commercial alloy compositions in relationship to principles

are the area of interest in this review. In this respect, casting aluminum alloys containing silicon

are classified into three groups: (1) the hypoeutectic alloys containing less than 9% silicon; (2)

the near-eutectic and eutectic alloys (10-14% Si); and (3) the hypereutectic alloys with silicon

contents ranging up to 25 percent.

2.2.1 Normal Eutectic Solidification

The so-called „normal eutectic‟ microstructure in the aluminum-silicon alloys, is a product of

a slow solidification of the eutectic with a coarse microstructure consisting of large plate-shaped

particles of Si in the Al matrix. The mechanism of freezing of Al-Si eutectic alloys has been

reviewed by Chadwick.27 However, the consensus of many reports28, views normal eutectic or

near eutectic solidification as occurring as follows:1) Nucleation and subsequent growth of the proeutectic constituent (aluminum in the

hypoeutectic alloys or silicon in hypereutectic alloys). Nucleation begins and growth

continues from the liquidus temperature down to the eutectic start temperature. Only one

solid phase is present at these temperatures.

2) Nucleation of the second phase of the eutectic at the proeutectic phase-liquid

interface. This is usually accompanied by some supercooling below the eutectic start

temperature followed by recalescence. Growth of the plate silicon-aluminum eutectic

occurs with the plates in direct contact with the melt. 29 Growth occurs as a eutectic

colony or cell.

3) Completion of eutectic solidification over a temperature range by growth of the eutecticcells. The advancing solid front of aluminum and silicon in the cell proceeds so that

liquid is in contact with both phases. Branching of the silicon plates may occur at the

points where the plate is in contact with the melt. Branching leads to interconnection of

many of the plates in a cell. Solidification is completed over the eutectic freezing

temperature range by impingement of the cells. Segregation occurs between cells.

Certain key features are clear in the above solidification mechanism. First, nucleation of the

silicon is encouraged on proeutectic aluminum a-solid solution because of Si segregation at the

a-liquid interface. The upper limit of eutectic Si nucleation in pure alloys of the Al - Si system is

said to be 578°C. However, eutectic start and arrest temperatures up to 585°C are found in

commercial alloys containing 0.25% Fe or more and other impurities. Since eutectic

solidification may commence and proceed over the range cited, the result is usually endogenous

solidification.




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2.2.2 Undercooled Eutectic Solidification

Undercooling of normal eutectic may readily occur. In Al-Si alloys, undercooling may

suppress the eutectic nucleation and growth temperature from 585°C down to 580°C.

Undercooling allows the proeutectic a-dendrites to grow larger. When the silicon nucleates and

grows, it therefore appears interdendritic, grows more rapidly, and is finer. Further undercooling

to temperatures of 580°C and below causes the development of the modified Ai-Si eutectic.

Undercooled eutectic Si may develop as a result of Na addition or without any additions if the

solidification rate is chosen to produce mainly normal eutectic with isolated patches of

undercooled eutectic.

Normal eutectic undercooling occurs most easily in near-eutectic compositions in the Al-Si

alloys. Eutectic and slightly hypereutectic (12 to 15%) Si-Al alloys almost always have much

undercooled silicon plates in their structure. In both cases, change to a definitely hypoeutectic

composition (less than 11.5% Si) makes it possible to eliminate undercooling and mixed

structures, especially if modification is practiced. Change to a strongly hypereutectic

composition can accomplish the same effect. Thus, the proeutectic constituent serves to assistnucleation of normal eutectic toward the upper limit of the eutectic temperature range.

2.2.3 Modified Eutectic Solidification

Undercooling of the Al-Si eutectic below 580°C by chilling or from chemical treatment of

the melt produces the modified Al-Si eutectic. For example, the addition of a few hundredths

percent sodium is capable of producing a modified structure. The silicon particles in the

modified eutectic are very fine and truly globular in shape. In this way they differ from coarse or

fine plates in the normal or undercooled eutectic. An essential feature of modified eutectic

solidification is that polyhedral silicon or coarse silicon plates do not nucleate on the a-solid

solution dendrites at the highest temperature in the eutectic range. Instead, the eutectic freezes bynucleation at the cooled surface and growth of a shell toward the center (exogenous

solidification). Significant features of this type of solidification are the absence of normal

eutectic or polyhedral silicon nucleation within the unsolidified core and the a-front which

precedes the thickening solidified shell and pinches off or encases the silicon particles. New

silicon particles must nucleate at the a-front as it proceeds toward the center of the section.

Continued heat removal with a falling temperature seems to be needed to complete solidification

according to the exogenous mechanism. Chill casting is the method of accomplishing this

without sodium treatment. The a-front sometimes produces wave-like patterns in the completely

solidified eutectic. Whereas exogenous solidification is common for the modified eutectic, it can

approach the endogenous mechanism if under-or over- modification occurs or the heat transfer

mechanism is unfavorable.

2.3 THE MODIFICATION EFFECT

The aluminum-silicon alloys are of industrial importance largely because of properties which

can be obtained as a result of “modification”. The structure of cast Al-Si alloys is remarkably




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altered by the addition of modifying agents before casting. Sodium, in particular, reduces the size

of the silicon particles during eutectic solidification and tends to change their shapes from plates

to nearly rounded grains. This reduction in particles size, termed “modification”, results in an

improvement in mechanical properties. Similar effects can be attained by rapid

solidification. Consideration, therefore, of the control of the solidified structure and thus the

properties of these alloys requires an assessment of their modification aspects.

The aluminum-silicon alloys of general usefulness are those containing from 5 to 25 percent

silicon. Throughout this range of composition the structure can be refined and physical properties

materially improved by the modifying process. Both the degree of improvement and the actual

properties reach a maximum, however, near the eutectic composition, at about 13 percent silicon.

In addition to the profound reduction in the practical size of silicon and the great refinement

of the structure of the “eutectic” as a result of sodium addition, other significant experimental

observations are30:

1) Both primary silicon and primary aluminum appear in the microsturcture in modified

hypereutectic alloys.2) Modification by the addition of sodium results in the lowering of the freezing point of the

eutectic. The melting point of the eutectic is not changed. This lowering of the eutectic

freezing point is not the usual supercooling phenomenon, since the temperature does not

rise again once eutectic solidification starts.

3) There is a shifting of the apparent “eutectic” composition toward a higher silicon content.

2.3.1 Theory of Modification

Over the years the nature of the change brought about by treating Al-Si alloys with sodium

has been a fascinating subject for study. The nature of this change is at first glance quite

puzzling. Numerous theories or hypotheses have been advanced to explain modification, butnone yet has received universal acceptance or completely explained the principles of the

phenomenon.

One general trend taken by these theories is that the growth of the silicon crystals is restricted

by the appearance during eutectic solidification of sodium-rich liquid phase which, enveloping

the silicon, retards its further growth. This has been expressed in many and varied forms.

Edwards and Archer31 have postulated that liquid sodium separates out when the melt is cooled

and is present in the melt as a finely dispersed colloid. This mist of sodium, they suggested,

obstructs the growth of silicon crystals by being adsorbed on them. Other investigators32

believe

the liquid causing the obstruction to be a sodium-rich composition [NaAlSi1.25] or [NaAlSi1.33].

Thall and Chalmers33, advanced a second theory in 1950, which assumes that the presence of a

concentration of sodium in the aluminum surrounding the silicon crystals decreases the surface

energy and interfacial surface tension between the solid aluminum and the solid solution. With

this lower interfacial tension, Thall and Chalmers predicted that, the solidifying aluminum would

extend around the silicon crystals and block their further growth. The work of Davies and West 34

supports this hypothesis.




12

Other investigators27, 28, 35 have proposed that sodium removes or poisons nuclei, such as

hydrogen (or hydrides) and non-metallic inclusions (e.g., AlP), and alters the nucleation pattern

for the eutectic crystallization of silicon.

2.4 SODIUM MODIFICATION PROCESS

With the introduction of the modification process, it was discovered that if an Al-Si alloy is

allowed to stand in the molten condition for too long a time after the flux treatment, the

modification effect is gradually lost, and that if a properly modified cast alloy is remelted and

again cast without further treatment, it reverts almost entirely to the normal condition. The

discovery of the metallic sodium method of modifying indicated that this reversion to the normal

condition on standing in the molten state or on remelting is due to the loss of sodium. Subsequent

experiences have demonstrated as a practical certainty that the actual loss of sodium is the

dominant factor in this reversion, although it is conceivable that there is some effect due to a

change in the distribution of sodium.

The reversion from the modified to the normal condition is gradual rather than abrupt. Bypouring at various intervals of time after the proper execution of the fluxing treatment, it is

possible to obtain castings varying continuously in structure and properties from the completely

modified to the normal. Furthermore, it was early recognized that when insufficient quantities of

flux are used the castings obtained are only partly modified. The usual recommendation called

for an amount of flux equal to about 3 percent by weight of metal treated. The flux contains two

part NaF to one part NaCl.

The fact that poor modification results from the use of too much sodium as well as from too

little sodium, whether sodium be derived from the salt flux or added directly as metallic sodium

has also been established. As a matter of fact, it is possible, by the use of too much sodium, to

make the properties of the “modified” alloys inferior to those of the normal alloys.

2.4.1 Amount of Sodium Required

Probably the most important requirement for successful modification is that the molten alloy

contain the proper amount of sodium well distributed at the time of casting. The amount of

sodium required to produce the best results appears to be definite for a given alloy and for given

casting conditions. The sodium requirement varies over a wide range with the composition of the

alloy, particularly the silicon content. For a given alloy, the sodium requirement also varies with

the rate of solidification, the general rule being that less sodium is required as the rate of

solidification increases. From the standpoint of this review, it is thus probable that somewhat

larger quantities of sodium should be used where heavy section castings predominate, but this

factor has not yet had a systematic investigation.

No simple and accurate method of determining the amount of sodium actually present in a

modified casting has been developed. Such information, though interesting, would perhaps not

be of much practical use unless there were also some means of determining the sodium content

of the molten alloy before casting. From the practical aspects, the thing of interest is the quantity




13

of sodium which must be added to the molten metal. If the conditions of the modifying process

are kept constant, then the quantities of sodium present in the modified castings should be

definitely related to the quantities added although not necessarily directly proportional thereto.

The amount of sodium in the metal at the time of casting will be determined by (1) the quantity

added; (2) the efficiency of the addition; and (3) the loss before pouring into castings.

2.4.2 Sodium Reversion on Standing

It is advantageous to allow the molten alloy to stand quietly for some time after the addition

of sodium. The function of this holding period is partly to allow the escape of air and dross

stirred into the melt with the sodium. The actual benefit, however, is the possibility that during

this period there is a diffusion of sodium through the alloy, and an escape of the larger particles

of undissolved sodium by rising to the surface. Good modification has been obtained by the

addition of a small amount of sodium and casting immediately afterwards. More consistent

maximum properties, however, seem to be obtained by adding an excess of sodium and allowing

the melt to stand quietly for a certain period; this period varying between about 10 to 20 minutes.Sodium is both highly volatile and readily oxidized at metal treating temperatures. Its vapor

pressure is high at the normal modification temperature, and recovery is only about 20-30

percent of the addition. Subsequently, the sodium is lost gradually through oxidation by the

atmosphere at the melt surface during the holding period. The rate of this loss will obviously

vary with conditions, such as the temperature of the melt and the size and shape of the container.

It has been found, as would be expected, that the loss increases with metal temperature, although

no quantitative relations have developed. The problem is one whose solution is easier by

empirical than by analytical methods. The rate of loss is believed to be reduced by leaving the

modifying flux on the surface of the melt or by lowering the iron or silicon content to a certain

extent.

2.5 PERMANENT MODIFICATION AND MODIFYING ELEMENTS

It has been stated28 that the effect of a modifying element, is: to eliminate, first, coarse

polyhedral silicon; secondly, coarse plate silicon and, finally to increase the percentage of

modified eutectic in the microstructure.

To our knowledge, sodium is a highly efficient modifying element. It refines much more

easily when the melt cools faster. Then again a drop in silicon (hypoeutectic alloys) facilitates

the modification. To maintain refinement in a melt it is necessary to renew the sodium

inoculation about every half hour. This is not very convenient. Now, it is interesting for

production casting to obtain persistent refining. This problem of sodium reversion is a very big

setback in such casting processes as the low pressure casting where, by the nature of the process

molten metal may have to stand for a length of time.

The effect of a number of elements on the modification of the Al-Si alloy system has been

observed. The observations suggest that nucleation of the silicon phase in modified structures

appears to be influenced by some factor related to the periodic properties of the chemical




14

element and that Group IA elements, with the exception of lithium, would effect modification,

with sodium being most effective for a given addition. The modifying element must be such that

it has a greatly different k value36 in the two phases, so that when the lamellae try to grow side-

by-side the buildup of solute at the interface of each will be different, such that the phase with

the smaller k value for comparable liquidus slopes, will be retarded with respect to the lamella of

the other phase. On the other hand it has been observed that the following elements, Be, Ti, Li,

Mg, and Pb are not effective for stabilizing Na; and that additions of Te, Sr, K, Ca, S, B, U, and

Th as modifying elements showed no interesting results. However, Sr, had an effect analogous to

sodium and addition of 0.2%Sb. to the hypoeutectic alloys (chill or permanent mould cast)

assured permanent refining. In the presence of Na, Sb and Na tend to neutralize each other,

perhaps to form an Na3Sb compound.

The modification of hypoeutectic Al-Si alloys by the use of rare earth metal halides has also

been reported. The authors37 observed that, alloys containing 6-13 percent Si can be modified

with a mixture of REM halides, which convert the acicular Si crystals into fine particles, but the

improvement in mechanical properties is relatively minor and the alloy becomes less sound;moreover, its fluidity in the molten state is poorer. In addition, they point out that the structure

and properties of aluminum alloys can be significantly improved by introducing relatively small

amounts of the transition metals Mo, Cr, Ti, Zr and V.

2.5.1 Strontium Modification

For some time now, Sr has been known to be an effective modifying agent for the Al-Si

constituent in hypoeutectic Al-Si alloys. However, the early work involved the addition of

element Sr or Sr salts, and difficulties were encountered in getting the desired amount of Sr in

solution. The high cost of Sr metal was also a disadvantage. An Al-10%Sr master alloy has been

available for some time, but this, too, was rather costly. Recently, an Al-16%Si-10%Sr masteralloy has been put on the market, which is less costly, making the addition of Sr practical from

an economic standpoint. This major breakthrough, combined with the major problems with

sodium modification, namely, fume generation and poor and uncertain recovery plus the

tendency of Na to come to the top of the melt and burn during addition, has aroused recent

interests in Sr as a modifier for the Al-Si constituent in hypoeutectic Al-Si alloys. In foundry

evaluations, additions of Sr master alloy affected improvements in mechanical properties,

namely a 20-100% increase in elongation and significant increases in tensile and yield strengths

of separately cast and machined test bars. Strontium maintained high mechanical properties in

the Al-Si alloys over prolonged holding periods, whereas the effects of treatment with sodium or

sodium salts were largely lost within the first 30 minutes after treatment.38

Considering all types of Sr master alloys and other Sr compounds, Al-16%Si-10%Sr master

alloy is the most convenient and economical form of adding Sr. The most suitable amounts of Sr

content, when added as Sr master alloy, are in the range of 0.04 to 0.1%,40 the optimum amount

being about 0.05 to 0.06 percent Sr.39, 41




15

An evaluation of strontium modification made by Hess and Blackmun38 shows that addition

was convenient and recovery was satisfactory, though a somewhat greater initial content of Sr

was required than for Na. However, there is a continual loss of Sr during holding. Despite this

continual loss, investigateors38, 40, 42 have reported the degree of modification actually improved

with holding time, provided a minimum amount of Sr remained in the alloy. In other words, an

initial incubation period is required for maximum modification effects. It appeared from the

reports that a retained Sr content greater than 0.008% is required for acceptable modification

regardless of holding time or remelting.

2.6 SOLIDIFICATION AND CASTING SOUNDNESS

Increased demand for quality castings has made it essential to produce castings free from

unsoundness. The lack of uniformity in castings is due in part to differences in freezing rates. In

order to produce a sound casting these differences must be established. The situation is, however,

clear when the mechanisms for freezing and feeding in alloy compositions for foundry use are

examined closely.

2.6.1 Feeding Process

While the phase change from liquid to solid takes place, an important fact occurs on the

liquid side of the casting, that is to say, the mushy zone is fed by liquid metal in order to

compensate its volumetric contraction.43 The feeding process can be divided into two stages; in

the former stage of solidification there is a mass feeding. Mass feeding is associated with the

movement of liquid, carrying even solid particles, normally under the influence of atmospheric

pressure or gravity, and is operative during the greater fraction of the solidification process. In

other words, there is the movement of a liquid-solid pasty mass, while the dendrites are growing.

When in the casting there takes place a solid network infiltrated by liquid (in this stage thereis a close resemblance between the casting and a sponge saturated with water), freezing proceeds

from the dendritic branches to the liquid surrounding them. One reaches the most critical stage of

freezing, that is to say, the stage when it is necessary to compensate the volumetric contraction of

the dendrites by the flow of feeding liquid through the already formed system of small channels.

The movement of remaining liquid during the final stage of solidification therefore, takes place

down tortuous channels between the freezing dendrites, producing a strong tendency to

microporosity.

2.6.2 Elimination of Unsoundness in Castings

In the final stage of solidification, it is comprehensible that feeding takes place less readily

than in the initial stage, and its effectiveness increases when the zone to be fed is small. Both

these factors depend upon the casting temperature; the higher the temperature gradient is, the

more favorable the conditions of a good feeding in the last and main stage.43 In the event, as an

inadequate feeding provokes matrix continuity, so even the casting physical and tensile

properties depend on the temperature gradient.




16

The process of obtaining sound castings from an alloy with a wide freezing range is bond to

the possibility of defining a sufficiently high temperature gradient between casting and feeder,

especially during the latter feeding stage. The greater or smaller tendency of solidifying with

microshrinkage is expressed by Stonebrook 27 in these terms: An alloy which solidifies with a

freezing range, is susceptible to the best feeding possibilities if it has an eutectic residue of 40-80

percent. Of course, it is always necessary to create thermal conditions fit to a limitation of the

pasty zone.

In any case, the alloy is more subjected to microporosity when there is a scarce eutectic

quantity. It can also be noted that when the crossing speed of the solidification range is high the

quantity of eutectic residue is larger. Therefore, high cooling rate affects microporosities in a

double way - it reduces the extent of the pasty zone and increases the eutectic residue. Although

feeding behavior is largely a function of alloy constitution, the problem of shrinkage porosity is

in some cases diminished by grain refining techniques, since a suspension of fine crystals flows

more freely during the mass feeding stage than does an interlocking structure of coarse dendritic

grains.

2.6.3 Gas Porosity

A further contributing factor to unsoundness in Al-alloy castings is the precipitation of

dissolved gases (H2 in particular) due to changes in gas-metal equilibria on freezing. This form

of porosity (pin-hole porosity) is noted for its spasmodic occurrence, which is usually attributed

to variations in atmospheric humidity, but could also be due to variations in foundry processes. It

is well known that certain variations of these processes increase the possibility of pinhole

porosity. For instance, certain aluminum alloys, and foundry processes, e.g. thin section castings

made in green sand, are more prone than others to pinhole porosity. This suggests that not only

must the gas content of the alloy be considered, but also the chemical composition, sectionthickness and type of mould material. These considerations suggest that some reaction in the

alloy which is forming gas holes is operative/non-operative depending on variations in

atmospheric humidity, or foundry process. Hydrogen is probably the most troublesome gas in

aluminum founding. Mould materials which contain even a small percentage of moisture must be

regarded as potential sources of hydrogen. Furthermore, high hydrogen levels occur in aluminum

at times of high humidity, when outbreaks of pinhole porosity occur.

In general, the driving forces for the creation of pores can be either gas or solidification

shrinkage or both. On the other hand, increased soundness could be obtained by chilling or

artificial nucleation to promote mass feeding, after proper degasification of the melt has been

carried out to minimize the hydrogen content.44

2.7 MOULD MATERIAL EFFECT ON SOLIDIFICATION

A better understanding of the scientific aspects of the production of quality casting has

attracted a good deal of attention in recent years. The casting quality is dependent on such

variables as, the nature of the metal or alloy cast, properties of mould materials employed, and




17

the casting techniques. In any case, the thermal properties of mould materials will determine to a

large extent the rate of heat extraction for a given casting and thus the influence of mould

material on quality of the casting.

A knowledge of the influence of mould materials on solidification time of expendable

polystyrene pattern castings is extremely useful for the production of quality castings and in the

efficient design of the gating and risering system. Dieter45 has reported that expanded

polystyrene patterns can be moulded in green sand, CO2 sand, furan sand, or in some cases in dry

unbonded fluid sand. There is, however, no mention of the effect of such moulding materials on

the solidification mode or casting properties.

In the past several years several investigators have studied the influence of mould material

properties on the casting characteristics of pure metals and alloys. The results of the experiments

conducted by the technical sub-committee of the IBF46 on cast iron, regarding the effect of

mould materials on its cooling rate and physical properties, showed that increased mould density

increased tensile strength in castings, as a result of increased cooling power, provided other

variables are kept constant. Lee and Volkmar

47

have reported that for dry sand moulds, relativelycoarse sand will increase heat transfer characteristic and mould density as well as minimize the

use of binder. It is noted also, that for a given casting shape and a given metal or alloy, the

cooling conditions may be more or less favorable by changing the mould materials. In the

various reports48 there is agreement on, the improvement in mechanical properties of castings

with increased mould density; and the solidification time of castings is influenced by the

volumetric heat capacity of the moulds.

2.8 EFFECT OF SOLIDIFICATION STRUCTURE ON MECHANICAL PROPERTIES

The importance of structure in cast alloys lies mainly in the structure-sensitive properties

which can be utilized in engineering. The properties are determined primarily by the influence of the microstructure on the behavior of dislocations in the lattices of the individual crystals. Unlike

wrought materials, in which further opportunities exist for changing both structure and

dislocation density, the initial microstructure is frequently the main vehicle for the control of

properties, although subsequent heat treatment plays this role in some cast alloys. The two most

significant variables affecting cast structure are alloy composition and cooling rate, and their

effects on tensile properties for a series of aluminum alloys have been reported by Watkins and

Kondic.49

The search for factors responsible for low mechanical properties of cast aluminum alloys led

directly to studies of alloy solidification. Of particular interest were the compounded ill-effects

of dissolved hydrogen, solidification shrinkage, and unfavorable mechanism of freezing on size,

shape, and distribution of microporosity in cast structures. A review of the literature 50 suggests

some of the factors which lower mechanical properties of cast aluminum alloys as follows:

1) Interdendritic porosity resulting from hydrogen evolution during solidification.

2) Interdendritic porosity resulting from shrinkage during “mushy” or “pasty” type

solidification.




18

3) Weak or brittle materials present at grain boundaries (intermetallic compounds or dross).

4) Grain size.

Gas porosity has often been designated as the chief cause of low mechanical properties of

cast aluminum alloys. The high solubility of hydrogen in molten aluminum and very low

solubility in solid aluminum cause gas evolution during solidification. 50 Further, the mushy type

solidification traps the gas interdendritically, resulting in small voids sometimes invisible even

on a machined surface. These small voids are extremely damaging to mechanical properties.

The high thermal conductivity and wide temperature range of solidification in aluminum

alloys result in a mushy type solidification. The extent of progressive solidification in aluminum

alloy casting is limited. In general, nucleation occurs nearly simultaneously over large portions

of the casting and growth continues until isolated interdendritic pools exist throughout the

casting. The liqiuid-soild shrinkage of these pools leads to interdendritic voids, and the pressure

of gas serves to enlarge these voids.

Any techniques which reduce the mushy zone during solidification will benefit mechanical

properties. The most important condition for achieving this is a high temperature gradient duringsolidification. An extensive survey on the effect of temperature gradients within a solidifying

plate casting on the strength of Al-4.5%Cu alloy has been published by Ruddle.51

Ruddle was

able to show a definite correlation between temperature gradients and tensile properties. He also

observes, a marked drop in tensile properties occurred for pouring temperatures greater than

700°C.

A high thermal gradient within a solidifying casting usually means high freezing rate. It has

been shown9 that fineness of the dendritic structure within grains of an aluminum alloy casting is

dependent on cooling rate. When solidification results in finer grains, not only is the grain size

uniform throughout the cross-section but the casting has reduced risk of hot tearing or cracking

in the mould. The tendency towards shrinkage is also reduced as a result of the better feedingcharacteristics when solidification proceeds simultaneously from a very large number of

nucleation centers. In an aluminum alloy containing insoluble impurity elements, the

solidification process leads to grain boundary and interdendritic segregation of a brittle

intermetallic phase. The combination of a brittle constituent and voids reduces mechanical

properties. High cooling rates or grain refining treatment tend to produce fine dendritic structures

and, therefore, give relatively fine distribution of brittle intermetallic phase. The fine distribution

of brittle constituent resulting from high cooling rates or addition of grain refiners has been

advanced as a reason for improved mechanical properties with high rates of freezing52

or

nucleation.53 Ordinarily, in most aluminum alloys the cast grain size is markedly coarsened

particularly by substantially superheating the melts or by prolonged holding above liquidus

temperature. The grain size is, however, relatively independent of the superheat and the pouring

temperatures in melts which have been specially rendered capable of solidifying into intrinsically

fine grains but are otherwise of similar composition.




19

Mechanical properties of cast Al-Si alloy can also be markedly affected by modification.

Modification increases strength and ductility. The improved properties resulting from modified

structure is due to the grain refinement of the silicon phase. Commercially, modification of

castings may be obtained by addition of modifying agents such as sodium or sodium salt and

strontium.

In summary, it should be emphasized that fine grain size is usually beneficial to mechanical

and foundry properties. Within the individual grains, both dendrite and eutectic substructure are

significant and often outweigh even grain size in importance.29 In dendritic structures, dendrite

cell size and secondary arm spacing frequently determine the form and distribution of second

phase constituents and the pitch of the composition fluctuations due to microsegregation, so

exercising the function in other cases of the primary grain size.

3.0 THE FOUNDRY INDUSTRY

The scope of the foundry industry encompasses a major segment of any industrialized

economy. In the USA it had been described, over four decades ago, as an 8.5 billion dollarindustry, employing directly and indirectly 475,000 people; one which produces about 14 to 18

percent of all ferrous production annually and feeds castings into 90 percent of all machine

shops, produces about 18 million tons of salable casting annually, and itself sustains the

subsidiary businesses of foundry equipment and material supplies. The industry‟s product,

castings, enters into every field in which metals serve man. Castings are used in transportation,

communication, construction, agriculture, power generators, in aerospace and atomic energy

applications, and in other activities too numerous to describe. Because of their widespread use,

castings are produced almost everywhere that manufacturing occurs.

3.1 FOUNDRY AND NIGERIA’S INDUSTRIALIZATION

Castings in iron, brass, aluminum or other metals are an essential part of most engineering

products and a foundry in which to make them is needed by any developing industrial society. It

goes without saying that foundry is a necessary antidote to the perennial lack of industrial spares

to keep our industries running. This is so because foundry creates both the forward and backward

linkages necessary for the industrial development in both the manufacturing and consumer goods

industries. Moreover, it helps to save or conserve the foreign exchange which could be channeled

into other sectors of the economy.

The present low level of foundry activities in Nigeria is also responsible for our technological

backwardness. As a result there have been persistent calls for the establishment of more

foundries. Several technical and opinion papers have been presented to this effect at different

fora.

Considering the interplay of economic forces, it must be noted that, the world which left

Nigeria and other third world countries with economies burdened with huge foreign debts, high

inflation rates, high unemployment rates, import dependency, etc., are in no hurry to change the




20

scenario. Consequently, these third world countries have no alternative than to initiate

programmes and policies that will be geared towards industrialization.

The metallurgical industry may be defined as the productive practice of arts and sciences of

extracting metals from their ores, of blending metals with both metals and nonmetals in various

percentage combinations to form alloys and of working, machining and fabricating metals and

alloys.

The development of the metallurgical industry has been the basis of man‟s civilization, from

the golden to the silver and the bronze ages. The importance of the metallurgical industry in the

cultural and technological evolution of man has been universally accepted down the ages. Even

now the technological achievements of the nuclear age are based on the development of new

materials, for which the metallurgical industry can rightly claim credit also.

Although the production of castings on a large scale is a sophisticated and capital-intensive

venture, there is need for small-scale foundries producing castings for building and domestic

products, machinery parts and spare parts for other equipment. It is obvious that our

developmental problem stems from our inability to exploit the abundant natural resources andtalents within the confines of our borders, and to recognize the principle of self-reliance by

creating modalities for creation of basic core industries.

3.1.1 Foundry Plants in Nigeria

Though foundry in Nigeria is very recent, it has attracted so much interest in the industrial

sector. Presently, there is an estimated total capacity of 16,500 tonnes/year which is held

between an estimated 50 operational foundries, majority of which are cottage-level industries. A

broad classification is as follows:

Estimated Total Capacity

Present operational Foundries - 16,500 tonnes/yearFoundries under construction - 8,500 tonnes/year

Foundries on the drawing board - 46,100 tonnes/year

Of these, the major ones include:

Estimated capacity

1. Delta Steel Company Limited - 1,200 tonnes/year

2.Castings (Nigeria) Ltd, Otta - 8000 tonnes/year

3.Nigeria Foundries Ltd, Ilupeju - 3,000 tonnes/year

4.Nigeria Railway Corporation Foundry, Lagos - 5,000 tonnes/year

5.Adebowale Foundries and Machine shop, Otta - 4,500 tonnes/year

Of the existing 16,500 tonnes/year capacity, about 62% is under private sector control, while

the government sector controls about 38%.




21

Castings requirements of industries are enormous and inexhaustive. Types of castings

required by some listed industries are shown in Table 1.

Table 1: Industries and Types of Castings Produced*

INDUSTRY REQUIRED TYPE OF CASTINGS

CEMENT INDUSTRIES Step liners, manhold surrounds, collar gratt

plates, impellers, joint preces (thicker conveyor

and pot packet) machinery spares, crusher

balls.

TEXTILE INDUSTRIES Pulleys, gears, reed frames, spinning mules,

spindle rails, spinning drive cylinders, sewing

machine parts, tricot beams.

MANUFACTURERS OF CUSTOMER

DURABLES

Electric iron base, dishwasher housings, food

mixer housings, lawn mower housings,

refrigerator and freezer evaporators, stove/gascooker parts, ceiling and table fan parts.

AUTOMOTIVE INDUSTRY Crankshafts, gears, pinions, rollers slide,

steering knuckes, disc brake calipers, rocker

arms, brake drums, carburetors, brake discs or

bodies, connecting rod, pistons, fuel pumps,

intake manifolds, master cylinder pistons,

transmission housings, valve rocker arms,

water pump bodies, cylinder heads, flywheel

housings, axle housings, crankcases, hubs,

spring brackets, engine block, cylinder head.

METAL PRESS INDUSTRY Bolsters, punch plates, rings, press plants, Ram

body.

TOOL INDUSTRY Housings for power drills, chain saws, butting

machines, power shears, hydro press form

blocks, hydro stretch form dies, jigs and

fixtures, machine and table vices.

SHIP BUILDING Pumps, housings, gears, valve bodies,

propellers, cylinders, engine blocks, blower

housings, water jackets, pistons, pulleys,sheaves, generator housings.

FURNITURE INDUSTRY Door locks, base for chairs (rotating).

BUILDING & ROAD CONSTRUCTION

INDUSTRY

Manhole covers, grates, pipe fittings, valve

street lamp housings, door hangers.

ARCHITECTURAL DESIGNERS Ornamental hardware, architectural fittings




22

RAIL-ROAD EQUIPMENT Brake shoes, gratings and stocker parts.

ELECTRICAL EQUIPMENT Motor frames and heads, refrigerator

compressor parts, part for power lines cast

resistor grids, electric motor base, change over

switch bodies, gear switch bodies, gland

(ducting).

MINING, QUARRYING AND CEMENT

MANUFACTURERS

These castings require alloying resulting in

high chromium and nickel chrome iron casting,

e.g, ball mill liner, roll crusher sleeves, dred

pump liners, grinding balls, conveyor casting.

CERAMIC AND REFRACTORY

INDUSTRY

Wearing parts for clay mixer, extrusion press

dies and impellers, ceramic press arm store-

polishing spiral, dies for tiles and bricks.

TEXTILE MACHINERY & MACHINE

TOOLS

Small machine beds, machine tool parts, small

mill rolls, metal forming dies.AGRICULTURAL EQUIPMENT &

AGRO-ALLIED

Parts for mowers, ploughs and cultivating

equipment, corn mills parts & plates, oil

expeller parts, water pumps, hand pumps (bore

well & for oils) agric. diesel engine parts.

GENERAL Dead weights, weighing machine parts,

mooring anchors, conveyor parts, plumber

blocks, bearing, housings, laboratory stands for

schools.

*SOURCE: National committee on foundry development (strategies for the development of

foundry industry in Nigeria) an unpublished report

3.2 THE CHALLENGES OF FOUNDRY TECHNOLOGY IN NIGERIA

In the early years of our independence, we expanded our basic infrastructure and social

services. Our government dashed for modernization, copying but not adapting the Western

models. The result was poorly designed public investments in industry, too little attention to

agriculture and most importantly, too little effort to set up core industries like the foundry and

forges. Consequently, the economy started faltering in the midst of plenty and suddenly went

into decline. The result of this is that today most Nigerian families are not better than they were

43 years ago.Even with the introduction of SAP, industrial output has remained low and poor, the rate of

real investment has stagnated and the disparities between us and the developed nations 22 have

continued to widen. As one economist said, Nigeria had obtained and expended billions of

dollars realized over the years in oil revenues that could have been used for investment purposes.

Such a sum if properly used could have catapulted Nigeria into the ranks of the industrializing




23

nations of the world. Poor Nigeria! The slow growth of industrial output in the last decade for the

country has been attributed to lack of raw materials and spare parts.

It is not hidden fact that very little attention has been paid to the development of foundry and

allied industries. It is well known all over the world that founding is the basic ingredient for rapid

industrialization of any nation. It provides an effective linkage and is essential to the production

of basic equipment and machine tools.

The manufacture and development of final goods and equipment in the country require the

simultaneous growth of the foundry and allied industries. It is therefore very necessary to take

stock of what has transpired within the Nigerian Foundry Industry. This paper will try to show

how far it has developed and point out the constraints militating against it.

3.2.1 Foundry Industry outside Nigeria

To understand the sordid situation of foundry development in Nigeria, it is important to

quickly peep into the foundry industries in some of the developed and developing countries.

Fig.3 shows the production of ferrous castings in USA, Japan, Germany, United Kingdom,France, Czechoslovakia and Italy, while Fig.4 shows the ferrous castings for China, Brazil and

Korea.

According to Foundry International Trade Journal of March 1991, Japan has about 1,513

Foundries in 1989, with a total output of 7.81 million tonnes. Thus, in terms of annual castings

output per foundry, the product breakdown is indicated as follows:

Iron Casting - 6,949 tonnes

Cast Iron pipes & Fittings - 22,678 ”

Malleable Cast Iron - 7,346 ”

Steel Castings - 3,993 ”Non-Ferrous Metal Casting - 1,219 ”

Die Casting - 4,005 ”

Precision Castings - 283 ”

The actual number of foundries in USA is not given but total production figure for 1989 is

put at 9.544 million tonnes and the breakdown is as follows:

Grey Cast Iron - 4.241 million tonnes

Ductile Iron - 2.554 ” ”

Malleable Iron - 0.257 ” ”

Steel - 1.031 ” ”

Non-Ferrous - 1.461 ” ”

By 1980, according to statistics in the World Foundry Directory, the production figures for

casting in India from about 7000 foundries were as follows:




24

Grey Cast Iron - 2,350,000 tonnes

Malleable Iron - 21,300 ”

Special Grade Iron - 6,900 ”

Steel - 75,000 ”

Non-ferrous - 60,000 ”

Total - 2,513,200 ”

This in annual casting output per foundry is equivalent to:

Grey Cast Iron - 3,357 tonnes

Malleable Iron - 30.4 ”

Special Grade Iron - 0.99 ”

Steel - 10.71 ”

Non-ferrous - 8.57 ”

In comparison with Japan, it follows that there are so many cottage foundries in India even

though the rate of industrial development is not as high as in Japan. There is no doubt; therefore,

that in terms of the material and technological progress of man, foundry may as well be taken as

an index of the state of industrial development or as a barometer of the state of the economy of a

society.

3.2.2 Nigerian Situation

Now, let us see how Nigeria fits into the production graph. In the first instance there are no

past statistical figures, for easy reference. However, a field survey conducted in 1991 by the

National Committee on Industrial Development (NCID) project team revealed a total of aboutmere 50 (fifty) foundries in Nigeria with a total installed capacity of 35,350 tonnes of cast iron;

1350 tonnes of steel and 4,270 tonnes of non-ferrous. These are scattered in 10 (ten) states of the

Federation.

According to the report of the Strategic Consultative Group on Foundries & Forges, the

average capacity utilization of our foundries stands at about 15 percent. Consequently, the annual

production of foundry castings in the country is as follows:

Grey Cast Iron - 5,302 tonnes

Steel - 202.5 tonnes

Non-ferrous - 604.5 tonnes

In annual casting output per foundry, it is equivalent to:

Grey Cast Iron - 104 tonnes

Steel - 4.1 tonnes

Non-ferrous - 12.8 tonnes




25

This clearly shows that the foundry subsector in the country is still very under-developed. We

therefore do not need any other barometer to place us properly in the map of developed,

developing and under-developed countries.

3.3 CONSTRAINTS ON FOUNDRY DEVELOPMENT IN NIGERIA

Although, as has been highlighted there is a great demand for foundry products in Nigeria,

and there exists a great potential for the foundry industry, but, the industry has only had a

fledgling start and has remained stunted in growth. It becomes necessary to identify the factors

which are responsible for the non-development of foundries in Nigeria. Among the factors

identified are:

i. High capital required for land acquisition for building, plant and machinery and lack of

easy access to venture capital;

ii. Inadequacy of experienced and skilled labour force;

iii. Absence of consulting bodies, able to solve technical problems of the industry, and most

especially the small scale foundries in order to enhanceproduct quality and market potential;

iv. Preference of multinationals to imported parts and components, even at prohibitive costs,

rather than contract them to local sources;

v. Import duty and Tariffs which favour imported finished foundry products over imported

raw materials with which the same products could be made locally;

vi. Rapid and constant change of designs of cast components in various plants operational in

Nigeria;

vii. Absence of strong local institution, possessing advanced foundry technological know-

how to solve industrial problems and provide the spring board for developing substitutes

for imported technology in such vital areas as:a) mass production facilities and techniques:

b) quality control; and

c) new product development.

viii. Inadequate technological manpower and know-how in modern

Foundry Technology;

ix. Inadequate educational and training facilities for Foundry tradesmen and technicians;

x. Non-exploitation of locally available raw materials for foundry development; and

xi. Inadequate infra-structural base especially around factories that require

foundry inputs.

4.0 MY MISSION

Expendable polystyrene casting process is a new technique offering numerous advantages

and promising possibilities. Despite the advantages and application potential for this process,

however, little is known regarding the influence of process variables on the metallurgical and

engineering characteristics of the castings produced particularly as it is related to the casting of




26

aluminum alloys. A great deal of research work has been carried out on the pattern material, the

moulding sand and on the possibilities of using this process for mass production of castings for

the automotive industry.

The development of theory in most of these areas, however, still seems to fall behind that of

practical engineering. In any case, this is to be anticipated, as most foundry works were

originally regarded as art rather than science, and this tendency has been rather extreme in the

case of expendable polystyrene pattern casting process. For example, problems relating to the

solidification processing and factors affecting the microstructure of castings made by this process

are still to be resolved, and, yet, these are critical areas for controlling quality and properties.

Consequently, an extensive programme of research was developed and directed at examining

a range of aluminum alloys cast by the expendable polystyrene pattern casting process. 54 – 66

4.1 HIGHLIGHTS OF MY CONTRIBUTION

Of the many and varied casting techniques, each is characterized by a peculiar freezing mode

which in turn controls the solidification pattern, crystal size, degree of segregation, inclusiontype and morphology and material soundness. Each of these has an influence on the end-product

properties to various degrees depending on the nature and extent of any subsequent treatments.

With regard to these characteristics and effects on aluminum alloys, and bearing in mind the

phenomena which take place during the expendable polystyrene pattern casting process are

notably different from those which take place in other processes, this section highlights my

humble contribution to knowledge with respect to such aspects of the expendable polystyrene

pattern casting process as:

i. The influence of casting and solidification processes and variables on microstructures. 54 –

56

ii. Influence of modification and holding time on solidification structures and properties.57 –

59

iii. Structure and porosity60 – 63

iv. Solidification in different moulds.64 – 66

4.1.1 Solidification and Microstructure

The results indicate that the expendable polystyrene pattern casting process can be

successfully employed in foundry practice for obtaining castings having improved

microstructures over the green sand process. In cases where dry unbonded sand was used, the

process succeeded because the expendable pattern supports the sand until it is replaced by metal.

In the process, unbonded sand is compacted around the pattern essentially by gravity, by

vibration and weighting, thus confining the sand to form a rigid structure. As the pattern is

replaced by molten metal, the resulting gas pressure, the condensed products of vaporization, the

pattern coating and the metal itself all combine to support the sand and maintain the rigid

structure of the mould.




27

For green sand and expendable polystyrene pattern casting process, a low pouring

temperature, related to a finer microstructure caused by increased cooling rates, Fig.5.

Microstructure of expendable polystyrene pattern castings are sensitive to section size. A

significant difference in the mode of freezing of Al-4.25 Cu-1.03 Si alloy in green sand and

expendable polystyrene pattern moulds is a marked degree of undercooling accompanying

solidification of casting in expendable polystyrene pattern moulds. A result of the marked degree

of undercooling was a decrease in solidification time and an increase in cooling rate for

expendable polystyrene pattern casting process on the incidence of structure is based on a

consideration of what is happening on solidification in the mould and is associated with a violent

generation of mould gases and a loss of heat from the solidifying metal to vaporize the foam

pattern. The results are: (1) turbulence resulting from gas bubbling and stirring actions, both or

each of which will disturb the top layer of the freezing liquid or fragment already growing

crystals and cause the accelerated showering of particles, and (2) a marked degree of

undercooling and the possibility that the metal may have entered the casting as liquid-solid

intermixture or slurry at low pouring temperatures.The benefits of refinement shown by the thin sections and coarser structures consequent on

slower cooling were characteristics of the general phenomenon of section sensitivity. This effect

of section size is attributed to the cooling rate of the castings through the solidification range to

the solidus temperature or the solidification time, and the mass of the castings or the volume to

surface area ratio. Apparently, the larger the mass and heat content, the slower will be the

cooling rate with resultant coarse dendrite cells in the structure.

Invariably, the fineness of the dendrite arm spacing is influenced by alloy composition and

by solidification rate, and hence by factors such as mould thermal properties, pouring

temperature and section size in as far as they influence solidification rate. A relationship exists of

the form

where Y = dendrite arm spacing in inches, and X = solidification rate in °F per sec.

4.1.2 Modification and Properties

Results of this study establish that amount of Na or Sr addition to the melt and holding of Al

6.5 Si-3.5 Cu after melt treatment directly affect the structure and mechanical properties of this

alloy when cast in expandable polystyrene pattern moulds. Examination of the microstructure of

the test castings, Figs.6 – 13, poured at different time intervals shows that the drop in tensile

properties is primarily due to a progressive increase in coarse acicular silicon flakes in the

“modified” eutectic structure with prolonged holding. The following conclusions have been

derived from the results obtained upon development of this study:

1) The expandable polystyrene pattern casting process is suitable for producing quality Al-

6.5Si-3.5 Cu alloy castings of different section sizes.

2) Strontium is as effective as sodium in modifying expendable polystyrene pattern cast Al-

6.5 Si-3.5 Cu alloy. Prolonged holding of modified Al-6.5 Si-3.5 Cu alloy in the furnace




28

lowered the tensile properties of the alloy due to volatilization and oxidation losses of Na

and Sr and the subsequent reversion to the normal condition.

3) Strontium retained its modifying action longer than sodium in spite of a continual loss

during holding.

4) The enhanced loss of the modifiers for these castings is associated with oxidation loss of

the modifiers when the pattern decomposition gases ignited and burnt in the presence of

oxygen during pouring.

5) Increased section size decreased tensile properties for normal and modified expendable

polystyrene pattern cast Al-6.5 Si-3.5 Cu alloy. Such variation in properties were

attributed to decreased dendrite interaction area, coarse microstructural features and non-

uniform distribution of microconstituents; all of which are associated with slower

solidification rates in the thick castings.

6) Modification treatment is deemed to improve tensile properties because it reduces the

effective span and stress concentration effect of coarse silicon needles.

In general, the results indicated that evaporative pattern cast aluminum-silicon-copper alloysmodified by sodium and strontium possess improved mechanical properties by promoting the

formation of fine fibrous silicon in a finely dispersed eutectic, thereby eliminating the notch

effect of the normal acicular structure. An increase in retained sodium and strontium contents, up

to about 0.01% and 0.05% respectively, led to a continuous increase in mechanical properties. A

major finding is the increased loss of sodium and strontium in the evaporative-pattern cast alloy,

which is attributed to the increased oxidation and volatilization loss of sodium and strontium

during pouring when the pattern decomposition products ignited and burnt in the presence of

oxygen.

4.1.3 Structure and PorosityThe microstructure of full mould cast Al-4.5 Cu alloy depends greatly on the pouring

temperature T, and section thickness d. At high T and d, irregular and coarse primary particles

form, while at low T primary particles form which are nearly spherical, smaller and relatively

homogenously distributed in the thick sections. A reduction in the section thickness for all values

of T tended to change the morphology of the primary particles from coarse irregular to smaller

spherical and to fine rod-like and elongated particles. Three types of porosity can result,

depending on pouring temperature T and section size d: fine trapped porosity in the primary

particles, coarse trapped porosity at the particle boundary, and fine shrinkage porosity between

the particle arms or branches, Fig.14. The main influence of section thickness on the

microstructure was a reduction in the particle size and elimination of coarse interparticle

constituents and may increase the porosity in some cases, as section thickness d decreases. The

effect of pouring temperature on the microstructural features of full mould cast Al-Cu alloys

derives mainly from its effect on the pattern decomposition process and the effect of this on the

degree of turbulence and stirring action present during the casting process. Again the combined




29

effect of low pouring temperature and small section thickness in reducing solidification time also

contribute to the variations in microstructure and porosity observed. (Fig.15)

Also as a result of the decrease in specific volume occurring in most commercially used

metallic materials during solidification and cooling, a volume deficit arises which can show up in

the form of various shrinkage defects in the solidified casting. A decisive factor for the

preferential appearance of macroshrinkage in the alloys studied is whether a strong boundary

shell forms at an early stage, as is the case in exogenous rough-wall-type and endogenous shell-

type solidifications for pure aluminum and the eutectic alloy, respectively. When a yielding

boundary shell is formed (in spongy or pasty solidification), however, the casting shows a greater

tendency towards surface sinking and internal porosity; as is the case for alloys with silicon

contents between about 4 and 8 %.

It was apparent also from the results that the feeding process of Al-4.25Cu-1.03Si alloy is

very much governed by its nucleation and growth behaviour which in turn depends very much on

the thermal conditions during freezing. The incidence of unsoundness in this alloy is a

consequence of the basic feeding mechanism, and the feeding sensitivity of the alloy may beincreased by using high thermal conductivity chills.

4.1.4 Solidification in Different Moulds

Fig.16 shows the plot of solidification time versus casting modulus. It can be seen that the

solidification time ts satisfied the expression;

where B and n are constants depending upon alloy cast and moulding material. The solidification

equations for the aluminum alloy plate castings in gasifiable pattern moulds with various

moulding materials are:

Dry silica sand

Wet silica sand

Dry zircon sand

A study of Fig.16 indicates that for the aluminum alloy test castings in gasifiable pattern

moulds prepared with various moulding materials, the Chvorinov‟s rule relating solidification

time and square of casting modulus is not valid. This implies that the equation ts VA2

does

not hold good for gasifiable pattern mould system and in fact, the casting technique are radically

different from the conventional moulding systems and casting techniques. The fact that the

foamed polystyrene pattern is left in the mould and vaporized by the molten metal duringpouring introduces other factors with regard to the heat transfer and extraction mechanisms in the

system. Notably, heat is obtained from the metal to vaporize the pattern and contact resistance

exists for the heat flow from the coat wall to the mould material since the contact between the

coat wall and the packed bed of moulding sand is far from perfect. Owing to these factors the

relationship between solidification time and casting modulus departs from Chvorinov‟s rule.




30

The variation of solidification constant ⁄

for small and large values and with

various moulding materials is given below:

Dry zircon sand 0.7(V/A=10mm); 0.60(V/A=25mm)

Wet silica sand 0.65(V/A=10mm); 0.57(V/A=25mm)

Dry silica sand 0.58(V/A=10mm); 0.53(V/A=25mm)

The study indicates that the “solidification constant” is not really a constant for a gasifiable

pattern mould. When a casting of small casting modulus solidifies in gasifiable pattern moulds,

the relative ratio of the portion of heat from the solidifying metal utilized to vaporize the pattern

is higher than that for vaporizing lager section thickness. Consequently, when a casting of

smaller section thickness (or smaller casting modulus) solidifies in gasifiable pattern moulds, the

solidification constant of the mould system tends to have a value higher than the solidification

constant relating to the particular moulding sand employed. However, for thicker section castings

solidifying in gasifiable pattern moulds, because a lower relative ratio of the heat from the

solidifying metal is available for vaporizing the pattern, values of solidification constants closer

to those relating to the particular moulding sand, are obtained. It is apparent from the results

obtained in the present investigation that the larger the casting thickness, the greater is the

dependence of solidification time on the thermal characteristics of the moulding material.

The effect of mould material upon the structure and properties of the Al-6.5Si-3.5Cu alloy test

plate castings is similar in the normal and modified conditions. Since the pouring temperature

and degree of superheat were kept constant, any changes in structure and properties are related to

changes in cooling rate due to changes in mould material properties. Considering the alloy cast in

dry unbonded silica sand, sodium silicate bonded silica sand and dry unbonded zircon sand

moulds the structures obtained show that mould materials can exert an appreciable effect upon

the dendrite structure, amount and size of eutectic cells, and the size and shape of silicon

particles, whether or not the alloy is modified.

The explanation of the effect of mould material on the mechanical properties and structure of

Al-6.5Si-3.5Cu alloy is associated with the cooling rate of the alloy, which is mainly influenced

by differences in the physical, thermal and chemical properties of the moulding material. In

effect, the higher cooling power of the dry unbonded zircon sand arises from the higher specific

heat and density. In fact, a relationship:

where D is the mould bulk density (kg/m3

) and t, the casting solidification time (mins) wasobtained for the dry unbonded sand moulding materials.

5.0 CONCLUSION AND RECOMMENATIONS

The scope of the foundry industry encompasses a major segment of any industrialized

national economy. The industry‟s product, castings, enters into every field in which metals serve




31

man. Castings are used in transportation, communication, construction, agriculture, power

generators, in aerospace and atomic energy applications, and in other activities too numerous to

describe. Because of their widespread use, castings are produced almost everywhere that

manufacturing occurs.

Foundry is the most basic input industry and stringent demands of quality and quantity are

being placed on it with rapid industrialization and growth in other fields of production. Up-to-

date knowledge of materials and processes for casting is necessary in order to be able to produce

sound castings economically.

In this paper, an attempt has been made to highlight the results of investigations on the foundry

characteristics of a relatively new and revolutionary casting technique, the expendable

polystyrene pattern casting process. Also the state of the art and the problems of the foundry

industry in Nigeria are examined.

The metallurgical and engineering aspects of the expendable polystyrene pattern casting

process which affect the microstructure and other casting characteristics of the casting include

the large degree of undercooling and turbulence characteristic of the process, as a result of utilization of heat from the metal to decompose the pattern and the copious evolution of gases

therefrom.

Within the limits of the actual demand for castings used in machine assembly and the level of

machining capacities, Nigeria‟s foundry industry thrives within the limits of small and medium

scale investments. New foundry capacities will have to proceed integrally with the development

of the overall engineering manufacturing industry. In which case, the overall manufacturing

engineering base in Nigeria needs to be broadened to create enough challenge and demand to

enable the foundry industry expand its scope and capabilities. The challenges of the new

millennium are enormous, so also are the problems facing Nigeria‟s foundry industry, which

include lack of foundry inputs, poor development financing, lack of adequate infrastructuralfacilities, lack of skilled labour, and serious low level of activity in the engineering

manufacturing sector. These problems will have to be addressed before there is any meaningful

industrialization in Nigeria.

The Government should address the issue of the present challenges facing the foundry

industry.

the full utilization of and expansion of existing capacities;

new investments in steel and alloy castings for the strategic industries;

the exploitation of market opportunities especially in the West African Subregion.

In view of the huge capital investment and the long gestation period associated with the

establishment of iron and steel foundries, the author recommends that the Government should

take the lead and encourage the establishment of one non-captive medium sized iron foundries.

The capacities should not be more than 4,000 tonnes per annum.




32

Something serious should be done to attract the public sector. The Government should

review the policy environment and put in place the necessary services, incentives and physical

facilities which will encourage private entrepreneurs in building and operating more foundries.

It may be necessary to restructure the existing government foundries to be more profit oriented.

Above all, the Standard Organization of Nigeria (SON) should standardize the foundry products

and enforce compliance.

Government should see to the reduction in the prices of industrial tools and other materials so

as to lessen the hardship encountered by the industrialists.

This may go a long way in reducing costs of products and consequently in raising the level of

demand and rate of refund to management.

It is also recommended that at both Federal and State levels government should provide

training for small scale entrepreneurs in manpower management and on recruitment and

selection of appropriate personnel and how to provide periodical on-the-job training for their

employees.

Government should take measures to protect the small scale foundries from competition frommodern industrial mass production.

Finally, the country should evolve a new industrial policy which must be directed towards

removing the distortions of the past so that genuine aspirations of the people can be met within a

time bound programme of economic development.




33

ACKNOWLEDGEMENT

Mr. Vice – Chancellor Sir, this lecture will not be complete if I do not acknowledge those who

have contributed in one way or the other to make it possible for me to stand here today to deliver

this lecture.

I am most indebted to my parents Late chief Ekpe Okorafor and Late Madam Awa Ekpe

Okorafor, who brought me to planet earth, loved me, saw me through thick and thin, and taught

me never to give up.

I am extremely grateful to my elder brother, Professor Apia Ekpe Okorafor, and his wife (Mom),

Mrs. Rose Odiolu Okorafor, for always being there for me. They gave me all and I love them and

their wonderful children. My younger brothers, Dr. O.E. Okorafor and Mr. N.E. Okorafor, I

acknowledge your love and prayers all these years, May the good Lord bless you and your

families.

My colleagues and students in the Department of Materials and Metallurgical Engineering, I

thank you for good comradeship and healthy competition and argumentation. You have alwayshelped sift the chaff from the wheat.

I appreciate the entire staff of the Academic Planning and Development Unit of the Office of

the Vice-Chancellor. It is fun and challenge working with you. You have been a family.

I thank all my teachers, through elementary school to the university. You were my source of

inspiration and you taught me hardwork and devotion to duty. You moulded my character. For

example, I went through the Hope Waddell Training Institution, Calabar, and came out a perfect

gentleman and I‟ll labour night and day to be a pilgrim.

My special thanks go to my numerous friends, friends I made through school and to the

present time, here in FUTO and beyond. You know yourselves and I know you and I radiate

God‟s love to you all as I pray for you. You have always assisted me in different ways to helpmake me what I am. Your love, support, trust, advice, warmth and understanding have continued

to be a source of strength and enthusiasm. Your friendship will ever be cherished. In this regard,

I appreciate the Vice-Chancellor, Prof. J.E. Njoku. He has continued to be a “friend‟s friend”

May God continue to guide and protect him and his family.

I also acknowledge all the past Vice-Chancellors of FUTO for their love and faith in me. I

have had a personal relationship with all the Deans of the School of Engineering and

Engineering Technology, I cherish them all.

I acknowledge my parents – in- law Late Chief and Late Madam Uluata Okpo. They loved me

and gave me a roommate.

Mr. Vice-Chancellor, I have the pleasure to acknowledge my roommate and mother, a

woman of great faith and patience, Mrs. Caroline Ada-Okay Okorafor. I cannot appreciate you

better than what Proverbs 31:10-31 say of the capable wife like you and you are indeed worth

more than jewels! To you our children, Ekpe, Apia, Olihe, Nwanyibekee and Okore, I thank you

and I appreciate all your support. Please continue to keep the flag flying and higher still, as you




34

continue to ensure that you dwell in the light and to be a light to others. I love you and pray God

to bless you continually.

I acknowledge the Presbyterian Church of Nigeria and her various ministers of the gospel

and members who have touched my life and those of my family in one way or the other over the

years. Your efforts would not be in vain. You left a residue of love and good will. May God bless

you richly.

I had the opportunity of working with one civilian governor and four military administrators

in Abia State. I thank them all for finding me worthy.

Finally, let me honour God with the words of Psalm 62 verse 11 and 12, “Once God has

spoken; twice have I heard this; that power belongs to God; and that to thee, O lord, belongs

steadfast love. For thou dost requite a man according to his work.” Now to him who is able to

keep you from falling and to present you without blemish before the presence of his glory with

rejoicing, to the only God, our Saviour through Jesus Christ our Lord, be glory, majesty,

dominion, and authority, before all time and now and forever. Amen.




35

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36

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37

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38

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65. O. E. Okorafor, “Production of Aluminum Castings Using Gasifiable Patterns”,

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