University of Nigeria Research Publications

Aut

hor

OKONKWO, Ivan Emeka

PG/MA/03/33967

Title

The Design and Construction of Kerosene Firing

Down Draught Kiln

Facu

lty

Arts

Dep

artm

ent

Fine and Applied Arts

Dat

e

March, 2006

Sign

atur

e

UNIVERSITY OF NIGERIA, NSUKICA

DEPARTMENT OF FINEIAYPLIED ARTS

THE DESIGN A ~ V D CONSTRUCTION OF KEROSENE FIRING

DOWN DRAUGHT KILN

A PROJECT REPORT

SUBMITTED IN PARTIAL FULFILMENT FOR THE

REQUIREMENTS OF THE AWARD OF MASTER OF FINE ARTS

DEGREE (MFA) IN THE DEPARTMENT OF FINEIAPPLIED ARTS.

OKONKWO IVAN. EIMEKA

PGlMFAl03133967

SUPERVISOR: PROF. O.K. OYEOKU

MARCH, 2006

APPROVAL PAGE \ i t

This Project Report has been approved by the Department of

FineIApplied Arts.

.l. I- a .

University of Nigeria, Nsukka.

'\

.'

Prof. O.K. Oyeoltu

Supervisor

.............................

Dr. B.E. Ojo

External Examiner

Dr. Ernest C. Okoli

Head of Department

CERTIFICATION

Okonkwo Ivan :with registration number PG/MFA/03/33967 has

satisfactorily completed the requirements for course and researcl~ work for

the degree of MFA (Master of Fine Arts) in ceramics.

'The work embodied in this pro-ject report is original and has not been

. submitted in part or full for any other diplon~a or degree for this or any other

university.

..........................

Prof. O.K. Oyeoku

Supervisor

.............................

Dr. Ernest C. Oltoli

Head of Department

................................

Dr. B.E. Ojo

External Examiner

DEDICATION -.

' I

To almighty God for guiding me throughout the duration of the programme.

ACKNOWLEDGEMENT \$

A task of this iiature would not have been possible without the assistance of

' 1 a good number of people.

My gratitude goes first to God, the almighty and all-loving father for

His graces, blessing and protection, whose steadfastness never ceases.

I am indebted to our indefatigable supervisor Prof, 0 . K Oyeoltu

without whose constructive criticism, this work would not have come

through.

Am also grateful to my parents Mr & Mrs C. Oltonltwo for their moral

and financial support, and to all my friends and well wishers. May God in

his Mercy bless you all.

ABSTRACT d:

The problem 'of firing any ceramic kiln can be overcome with time and

practice as long a i the basic principles of construction have been adhered to,

and the kiln has no obvious defects in design.

Pottery and kiln building go hand in hand because it is not just a case of

piling bricks together, putting in a few pots and then fire. Any ceramist who

intends to n~ake a living from his craft needs a kiln which combines

reliability with economy. This research paper is a constructive attempt at

using 100% locally sourced n~aterials in designing and building a kiln,

aimed at fulfilling the yearnings of most ceramist in developing countries,

especially Nigeria, it will also serve as a resource materials for subsequent

researc h.

Hence, the study has been structured such that Chapter one covers the

background study, research problem, research aims and objectives, research

approaches; scope and limitation. Chapter two takes a look at different

contribution of authors on kiln building - the literature review.

Chapter three is the Research Approach and Methodology, production of

bricks and its firing. Chapter Four covers Production of Insulating and

Dense Bricks, planning, construction and burners. Chapter Five takes a look

at the kilns operation and firing.

TABLE OF CONTENTS

Title Page ....... .- ............................................................................. i . . Approval page ..... :I ........................................................................ 11

... Certification ................................................................................. 111

Dedication ................................................................................... iv

Acltnowledgement ......................................................................... v

......................................................................................... Abstract vi . . ........................................................................... Table of contents vii

CHAPTER ONE

Introduction ............................. ... ............................................. 1

Historical background ................................................................... 1

.................................................... 1.1 Statement of the Problem 4

............................................................ 1.2 Research Objectives 4

.............................................................. J .3 Scope 'of the Study 5

.................................................... 1.4 Significance of the Study 5

1.5 Limitation of the Study ........................................................ 6

CHAPTER TWO

2.1 Literature Review ................................................................ 9

CHAPTER THREE

3.1 Research ApproacWMethodology ....................................... 13

3.2 Sourcing for Materials ........................................................ 1 3

3.3 Line Blend Test ................................................................... I 8

3.4 Procedure ............................................................................ 20

... V l l l

CHAPTER FOUR

Production' of Insulating and Dense Bricks ......................... 26

Construction I! ....................................................................... 28

Fire Box ........................................................................... 30

Floor and Wall .................................................................... 32

Crown and Arches ........................................................... 32

Flue Box ............................................................................. 33

.............................................................................. Chimney 33

Burners ................................................................................ 33

Iron Work and Extra ............................................................ 37

CHAPTER FIVE

5.1 Firing .................................................................................. 38

5.2 Conclusion .......................................................................... 42

5.3 Reference .......................................................................... 43

5.4 Appendix ............................................................................. 46

CHAPTER ONE

INTRODUCTION

Ceramic3 has an extremely long and varied history.

Archaeological discovery of fragments from clay vessels of prehistoric

human activities across Eurasia about 70,000BC to 35,000BC proved that

those people had knowledge of fire. They lined their twig basket with

clay to make them hold water or food and one day those vessels were

accidentally put on fire, leaving a hardened clay vessel. (Peterson 1992).

Consequently, it becomes apparent that the process of firing clay to

make it hard and durable is an agc long tradition.

The history of the kiln is actually the evolution over a long period

of time from the simple shallow pits into a fixed structure designed to

direct and contain the heat of the fire. Kiln actually is not an invention

but rather the outcome of a series of small improvements from open firing

to the development of Electric Kilns, and this happened soime 70 years

ago.

Before the development of the electric kiln, pots were fired in

different flame burning kilns using fossil fuels like coal, wood oil,

kerosene or gas. Electric kilns offer the straight test forward and trouble

free method with obvious advantages over the other fuel burning Kilns.

They are portable, relatively light and compact; it requires no chimney

and can be operated without special skill or knowledge. One needs only ..it,

to turn on the switchcs and turn them off whcn tllc dcsircd tcmpcraturc is -.

attained. It fires uniformly with little variation in result. ' 1

With such an impressive list of advantages one might ask, why

have these electric kilns not flooded our scl~ools, pottery centers studios

and industries1? Or why has it not supplanted all other types? The answcr

is, that electric ltiln costs three times as much for a large gas, kerosene or

oil kiln. Thcn comes, the cost of electric power, which is very high in

developing countries. For example, Nigeria has the problem of power

failures, power fluctuations and no power a t all. The other more serious

disadvantage is the size limitation. Rhodes (1981) notes that Electric

Kilns do not perform too well if the inside measurement exceeds 2 !h feet

across. This size limitation does not permit the firing of large pieces.

Other necessary accessorics like elenlents, pyrometers and switches etc

though costly, are not readily available in Nigeria. Another fault is the

life expectancy of electric kiln-good elements last only for a period of

five years without accident. The greatest wear occurs if the kiln is used

for reduction firing. Electric Iciln is selective in the type of ceramics,

which can be fired in it because of the ~~nchanging nature of the chamber.

Wood, charcoal, coal, diesel kerosene and & I are other sources of

heat. Wood and charcoal are the ancient traditional materials for firing

pottery and are still used extensively in areas wherc wood is available. Its

kiln needs large space and because it creates a lot of smoke it has to be .\

located in relatively isolated areas. -.

Coal can be used to replace wood. It is a combustible rock which i 1

has its origin in the accumulation and partial decomposition of

vegetation. (Adams 1995). Nigeria is blessed with this cheap source of

fuel but management problem has very much affected the industry and

supply of it. Wood and coal l dns are specially designed to fire heavy

.industrial products.

Gas is the ideal fuel for kilns. The flow to its burners is continuous

and easily controlled. It is noted for its cleanliness and its kiln is easy to

build. Nigeria is endowed with this mineral but to construct a gas kiln in

this country is highly uneconomical. Oil is an excellent fuel for I<ilns.

Baily, (1946) classified it as the oils that together with bitumen, make up

the residue aftcr crudc oil has been distilled to give off petrol, paraffin,

oil, gas, diesel and motor oil. The price of oil, which used to be

comparably cheap, has gone up in this country, 111aking its use less

economical for the ceramist. The problem with oil is to break it down

into fine droplets or mist, SO that air can mix with i t for rapid combustion.

The most efficient burners using pressure and heat can reduce oil to a

vapous, which burns in a manner similar to gas.

1.1 STATEMENT OF THE PROBLEM 1-7..

In the past twenty years, potters and entrepreneurs in Nigeria have \.

set up many studio potteries. A good number of these potteries have not ' I

survived partly due to difficulties in procuring a functional l t ih and

sourcing for cheap and readily available fuels for firing.

Firing is considered a crucial stage and the turning point in the

process of pottery making. The researcher therefore considers i t a

challenge to develop a refractory body suitable for the constr~~ction of

kerosene kiln. Consideration is given to the fact that Iterosene is cheap to

procure and diesel is readily available.

Furthermore, it is high time we look inwards and harness our local

materials and technology.

1.2 RESEARCH OBJECTIVE

1. To source materials locally for the construction of a down draught

2. To source for kerosene in the immediate environn~ent as fuel for

down draught kiln.

3. To use these sourced materials in f'dbricating refractory and

insulating bricks for the construction of the kiln

4. To design and construct a f~~nctional down draught kiln

5 . To design and construct burners from discarded and scrap metal

pipes

6. To test-fire the down draughts kiln using kerosene

1.3 SCOPE OF THE STUDY \

In most cases kiln design must be adopted to a particular type, size, I I

and specific needs of the potter. This project shall cover only a down

draught kiln of moderate size. The lciln has been chosen for temperature

of 1 2 5 0 " ~ range, size, firing technique and cost. It is important to

mention here that the burners shall be fabricated from scrap pipes and

, discarded metal. Secondly, this research revolves around the use of

kerosene, diesel or other similar oils in the firing of a down draught kiln.

It strives to produce burners capable of burning these fuel types. It is an

exploration into the use of locally sourced materials. Burners and kilns

go hand i11 hand. A kiln is not just a case of piling bricks together. It

. needs thought, care, planning and application, which shall coinbine

reliability with economy.

1.4 SIGNIFICANCE OF THE STUDY

It is hoped that the research will contribute to the development of

eel-amics both academically and as an industrial input in Nigerian

economy. It is also intended to make potters and ceramists earn a living

from this craft. It is also bound to reveal and project t l~osc neglected,

rejected and condemned materials with a view at re'suscitating then1 from

slumber into life for functional purposes for the potter. On the other

hand, this rcsearch hopes to contribute a landn~arl< for present and

upcoming ceramic and other artists who might have lost hope i n the use \:,,

of clay because of the I~andicap caused in the non-availability of kilns. \

Thus, it will activate artists, ceramists, schools and industries to become ' I

more determined to overcome the probleins with kilns and also make

them generate interest i n the study, development and construction of kilns

from locally sourced materials.

1.5 LIMITATIONS OF THE STUDY

I n the course of executing this study, the researcher was faced with

the following inherent limitations.

1 ) Dearth of literature on the recycling of waste products or

2) Lack of analytical equipments has made the researcher seek

assistance from experts in the analysis of the raw materials

proposed for use in the construction of the kiln. Areas covered

are, classification of the various clays-Fireclays, Kaolins, Silica

minerals etc: the chemical and structural composition of some of

then^, and blending of the analyzed n~aterials. The inaterials

technologists, laboratory technicians and chemical engineers at

Project Development Agency (Proda) Enugu have being very

3) Another aspect that poses some difficulties is the curving and

fashioning of the collected scrap metals and pipes. No furnace

was readily available so the researcher rely on I<erosene blowers .:v.

to cure the pipes and sort for the services of a sculptor friend, to

assists in drilling the pipes, forming shaping and welding them, ' 1

according to the researcher's directions.

4) Sourcing and collection of the raw materials was not easy. The

location of the clays were far away from Nsukka. For instance,

fire clay and stone ware clay were located at the coal mines and

independent layout respectively, i n Enugu and had to be

transported to Nsuklta. So also was the silica (builders sand).

The saw dust was sourced from timber market at Nsukka.

5) It took the researcher a while to find someone to agree to weld

the frame together because of the technicalities involved.

6) Carpenters disappointed the researcher at very crucial period.

7) The hardness and toughness of the raw materials have to be

mentioned. There are no crushers and grinding equipment to

reduce the lumps to a fine powder. All the crushing and grinding;

hanunering, mixing and moulding were done manually.

8) Firing of the raw bricks caused a lot of trauma. I t was extremely

unpleasant. The institutes kiln got broke down and the researcher

had to transport tl~ein to various far away places to be fired.

9) It is very costly to set up.

. .-- .. ..-. .

Development of kilns i ,--- -. . -

%mpk updraft kiln 1 Firellolcs foi nlulr~ylo 8 [~eding of fucl .-. - --Z -

low biscuit firing in lowcr chalnber

la11 chimney increased I draft

Downdraft Wln

CHAPTER TWO

b LITERATURE REVIEW

" ~ i t h o ~ ~ t ! the knowledge of fire the potters craft will not exist."

(Rhodes 198 1). Here he shares his continual explorations into

understanding the managenlent of fire. He so shares his experiences

during his travels, of the fascinating evaluation of the earliest kilns in the

Orient, China, Korea and Japan.

The discovery that fire hardcns clay was made thousands of years

ago in widely separated parts of the earth. Peterson (1992) believes that

much of the earliest potteries discovered had basket woven or corded

designs on its surface were because clay was first used to line baskets and

accidentally fired. These early and pre-historic potteries played vital

roles in the evaluation of civilization and is an invaluable source of

archaeological information.

The origin of pottery and firing has been linked to the hearth and

basket theories. According to Ahuwan (1987), the hearth theory was

based on the fact that early man was exposed to harsh weather conditions

especially cold weather; as a result he was forced to warming himself up

around a hearth. While putting off the fire with water, he discovered that

the ground hardened.

Wangboje (1982) agree with the Basket theory that the origin of pottery \-v,

was by accident rather than by design. Thus: Early man used reed

baskets linked with mud for storing food items and water. When it ' !

accidentally burnt off the clay did not burn, instead it became hard, strong

and rock like. Man then began to think of a better and more effective

way of improving on his new discovery leading to new methods of

making containers and firing them.

It could be agreed that firing was as a result of domestic tragedy

which enabled man to have such knowledge about firing techniques.

As ceramists it is inevitable that we look at pieces from the past in

a unique way. Like other crafts, pottery developed in Jericho between

8000 and 7000 BC. Excavations in Anatolian Plateau (Turkey) was at

about 7000BC; That of Egypt was 500 BC and by 3000 BC the Egyptians

had developed glazes. In China the first pottery was probably made at

about 3000BC but by 1400BC clay work became highly developed in the

Yellow River Valley of the north who was already producing stonewares.

(Peterson 1992).

Rhodes (1981) says kiln is an early invention, a rational process

where certain techniques were used to achieve a desired practical result.

He explained that primitive firing was carried out in the open bonfires or

in shallow pits holding the fire. Soon they began to enclose their wares in

bricks, caves, stone boxes and low mud walls, which allowed a greater \..,,

control and higher temperatures.

en& (1976), Blandino (2003) and Flight (1989), traced the ' !

developmental stages of kiIn; they all agree tliat tlie bonfirc firing, later

metamorphosed into the Up-draught kiln, Oriental kilns, Climbing kiln,

then the liiglier temperature down draught kilns, multiple chambered kilns

etc, to the more recent electric kilns.

Billington (1969) says that the one indispensable itel11 of

equipment to a potter is a Idn and i t must be efficient or i t will spoil his

work, waste time and materials and be a serious liability. He says that

kilns are expensive and that there are various types of kilns, each has its

liniitations and its uses. He also mentioned tliat so n~ucli depends on

local conditions and on tlie type of fuel available.

Zakin (1990) and Gade (1997) sliare the same view with Billington

011 the diffcrcnt kilns tliat existed. They went further to discuss the

various fuels for firing a kiln; tliat wood is a surprisingly versatile fuel,

while liquid and gaseous fuel have become favourcd among

contcrnporary ceramists because they allow ceramists to use widc variety

of glazc typcs.

Leach (1978) in his contribution confirms that kiln is a chamber

where successful heat action can be carried out, fed with flames by one or

more fire places and out of which a chimney draws heat and sniol<e.

Igwilo (1982) reports that studio ceramic artist need kiln for <!J.

ceramic wares to complete their circle. \.

Many other authors and scholars agree that Electric kilns are the ' !

easiest to manage but costs high. They all agree that electric ltilns are not

yet f ~ ~ l l y developed. They say that electric kilns do not lend then~selves

to the rich effects of reduction fire that characterize fuel burning Icilns.

Rhodes (198 1) devoted an entire book to the construction of Icilns.

The various develop~nental stages were explained from early Idns to the

more recent electric ltilns. Rhodes discussed the development, design,

construction and operation of Itilns starting with the earliest methods of

open firings and its gradual development into a tool capable of exacting

controls and the achievement of high temperatures to thc more recent

electric Icilns invented in the 1930's and 1940's.

Dressier (1937) i n the boolt, "Industrial Ceramics", discussed

"recalculating radiant gas tubes". He describes the use of recalculating

radiant gas tubes for decorating Icilns. Bailey (1946) made mention of old

rubber tyres which are waste products being used for firing in Mexico.

The researcher to this extent is quite motivated by Dressler and

Bailey's view on the use of discarded materials. They hope to usc some

scrap metals (discarded) and other components purchased to construct

Kerosene burners.

CHAPTER THREE

WSEARCH APPROACHIMETHODOLOGY

This study is quite exploratory in the gathering and utilization of

locally soul.ccd matcsiuls lor tllc Jcsig~l allti constsuctio~l ol' i\ licl.os~llc

firing down draught kiln. The researcher is aware that kilns of some sort

1inve been built since pottcry began. Thc first priniitivc firing took placc

in bonfires and went through various stages in design and construction.

The most radical change is in the use of gas and electricity which are not

readily available in Nigeria.

The researcher carried out various field surveys in locating and

sourcing for materials to be used. The location, description, structure and

analysis of collected samples were carried out. The requirement of

ceramic kiln building generally involve knowledge about the following

properties: Refractoriness; the ability of that materials to behave as an

insulant; Resistance to thermal shock; Abrasion and inipingenient

resistance; Resistance to slag, f ~ ~ m e s etc; and good constructional

properties.

SOURCING FOR MATERIALS

The need for understanding the sources and propcrties of the

materials is very important. The exact choice of refractories for

constructing ccramic kiln will depend primarily on the maximum

temperature to which the ware is to be fired. The researcher is planning \i:

to build a kiln that will withstand a temperature up to 1 2 5 0 ' ~ rangc.

Materials h;gh in aluminosilicate, silica and inagilesite etc will bc

' 1 sourced. Test of the refractory n~aterials will be carried out.

Investigations already carried out reveal that the following areas have

good materials for such refractory and insulating bricks.

Material ( Location/source I State

/ Ukpor (kaolin) / Ozubulu I Anambra I / Nsu (kaolin) / Osu nibano 1 Imo I

I I

Fire clay I Coal mine Enugu / Enugu

Ugwuogba (kaolin)

Bata River (Kaolin)

I Silica 1 Nsude / Enugu I 1 Un~uchu clay I Umuchu ( Anambra I

Nsuldta

Benin

Enugu

Edo

Nafula (kolin)

Kaukare

Uturu day

1 Okija clay / Ihiala I Anambra I

Jos

Jos

Nnewi clay

I Silica I Abeokuta I Ogun I

Plateau

Plateau

Okigwe

I I I I

Source: Raw material and Research center Federal Secretariat Enugu.

11110

Umudim

The list of sources of refractory materials is very extensive but one

Anambra

might ask, what distinguishes a refractory from other materials?

Substances with melting points or fusing temperatures above 1 5 8 0 ' ~ are <I?,

termed refractories while others with lower fusing points are sonictinies -.

processed to remove fluxing impurities make them meet up with the ' 1

refractories.

According to Shaw (1972), a material can be described as

'refractory' if it can stand up to the action of corrosive solids, liquids, or

gases at high temperatures. The various combinations of conditions in

. which refractory are used, make it necessary to manufacture a range of

materials with different properties. This involves selecting raw materials

with specific characteristics processing them and finally fabricating them

into shapes with the desired combinations of properties to meet the

particular demands of a given work condition.

The classification of the raw material proposed for use in the

construction of the kiln has already been carried out and are as stated in

tables 1, 2, 3 and 4.

TABLE 1

ENUGU FIRECLAY \

ANALYSIS OF SAMPLE (DRIED AT 1 1 O'C) ' 1

Silica (SI02) %

I

Titanic oxide (TI02) 2.15 I

Alumina (A 1 2 03) 1 14.32

Ferric Oxide (Fe203) 3.13

Magnesia (MgO)

Lime (C,O) I 0.08

Potash (K20)

Soda (Na20)

Loss (Calcined at 95000 7.37

CALCULATED PROXIMATE (RATIONAL) ANALYSIS

I 1 CLAY

3 I Quartz

2

4 1 Lime Compounds Calculated as C,O

Feldspar or Mica calculated as

Feldspar

I

6 I Magnesi~~m compounds (MgO)

I

7 / Ferric oxide

5

A

Source Nigerian coal corporation information manual.

Titanic Oxide

MATERIALS

TABLE I1

CHEMICAL ANALYSIS OF MATERIALS

Feldspars 1 0.45

kaolin I

koaling I

kaolin I Whiting

(I ime)

TI02 C,O Mgo NaiO K20 I Mno P205

PHYSICAL ANALYSIS OF SOME REFRACTORY CLAYS

TABLE 111

Ukpor

clay

Nsu

clay

Firc

Clny

EIIH~LI

'%drying

shrinkage

Green \ Plasticiry I Firing Fried

slrenglh

45.40

40.50

75.50

76.60

2 14.90

223.70

25 I .SO

314.30

156.10

102.SO

235.00

340.70

'% App

porosity

38.80

37.70

27.30

20.30

30.50

38.30

33.20

25.20

29.40

28.80

27.40

25.30

%I walcr

Absorption

22.30

22.0

13.00

9.80

TABLE IV

CHEMICAL ANALYSIS OF INDEPENDENCE (NEW HAVEN) -.

BRICK CLAY

3

4

5

6

7

8

9

Source: (

Cilica (Si02)

Titanic Oxide (Ti02)

Ferric Oxide (Fe203)

Aluinina (A 1203)

Lime (C,O)

Magnesia (MgO)

Potash (K20)

Soda (Na20)

Loss I yeoku (1988) the nature of clay

Having explored and analysed the various clay samples, the

Independent layout earthen ware clay and the coal mine fire clay, all

located in Enugu were found very ideal for the development of the kiln,

while thc Independence layout clay would be used for the dense red

bricks, the fire clay would be used to produce insulating and refractory

bsicks.

LINE BLEND TEST

Rhodes (1 998. 2 15) explains line blend as blend which establishes

n series of variation or mixes between two samples. A line blend test was

carried out for the mixtures of fire clay and sawdust see table V.

I 1 I

Fireclay / 30 140 150 0 Sawdust

For each samples, two test bars were made and labeled A to E to

find out the best combinations. The first sets were fired to 1200'~.

While the other batch was fired to 1 3 0 0 ~ ~ . The follows result was

recorded.

TABLE VI

Series I

Dry shrinkage

Plasticity

Total shrinkage

A

4.5%

Good

Warpinglcracking

Plasticity /Good I Good / Good I Good I Good

1 1.5%

B

4.5%

Good

None

Series I

Dry shrinkage

12%

D

4%

Total shrinkage

Absorption at 1 2 0 0 ~ ' ~

C

5%

Good

None

E

4%

Warpinglcraclting

D

4%

Good

13%

C

5%

A

4.5%

11.5%

2.5%

12.5%)

None

B

4.5%

None

None

I .2'%

2.5%

None

13%

5%

None

12.5%

5%

11%

3%

None None

The 'C' combination of 50-50 was found to be best in the series and was \ ?

used for the production of insulating bricks. -.

PROCEDURE I ,

The design and construction of the down draught Iciln project

entails a great deal of careful planning. The desire for the use of local

sourced materials within the nation's environment is the main concern of

1 . Kiln planning

2. Production and procurement of Bricks

4. Bricklaying

I. 16111 Planning

I n planning a kiln, the first thing that will be considered is what the

kiln will be used for. Is it for earthenware, stoneware, porcelain or salt

ware etc? Is it for small, medium or large sized worlcs? Having

determined the circumstance for tlie kiln, the space available and its

location will be considered. Is the chosen site safe from tlie possible

hazard of fire and will it be environmentally friendly?

(a) Size and shape of the kiln

Tlic size and shape will depend will depend 011 the type of Itiln.

The project here is addressing the building of a down draught Iciln. The

down draught kiln works on the principle that, heat is introduced from the

fire box and the flames are deflected upwards by a bag wall into the \<;,

chamber and through a flue in the floor goes out through the chimney.

This type of kiln is more effective than the up drauglt kiln. (See fig.2)

Fig.

The space which will house the kiln will decide where the chimney

will be positioned. Benard Lcach (1962), ventured some rules on the

proportion of chi~iineys to kilns. t l c rccon~nlcnds that tlic chinmcy

diameter be 'A to 115, the diameter of the kiln. Furthermore, the height of

a chimney must be 25 times its diameter.

(b) Fuel

It is good here to discuss the con~bustion of fuel which involves the

reaction of carbonaceous matter and oxygen to release heat. In choosing

a fuel, i t is proper to consider all the capabilities of such a fuel. As a fuel,

kerosene produces good results, in that, the atmosphere can be fiil-ly well

controlled from reduction to clear oxidation and a steady advance in

temperature maintained until the bodies of the pots mature to the desired \!t,

temperature. The choice of fLel for the down draught kiln is Itcrosene.

cxtinguishcr must always bc available to avcrt disasters.

(c) Kiln Proportions and Design

There are several basic rules to consider when designing kilns, to

be able to reach the necessary temperatures for a firing. These rules are

based on practical experiences of past kiln builders. Compact cubic

shapes prove to have advantages over long-low structures, or a tall

nilrrow onc. In dcciding thc k i l n proportion and dcsign, t l ~ c rcsca~~cl~cs

considered good circulation in the chamber, adequate burners and firc

box; flue size and proportionate chimney for draught.

An evenly fired chamber from top to bottom is considered in kiln

design and building. A simple cube shape seems best both from the

packing point of view and for ease of tiring.

The flue and chimney should be of good proportions and allowance

made for changing the size of these. The height of a chimney is governed

by the width and kiln size. A general rule for the chimney height

required to induce the correct draught is I inch of stack width = I foot of

stack height (or 2.5cm to 30cm).

For the horizontal pull, each 30cm of cross-draught (horizontal

pull) needs 6Ocm of chimney height, in additions to the vertical pull. Thc

imperial rule is 30cm of vertical chin~liey for every 1.05m of horizontal kY,,

draught (Modes 1981). The chimney diameter is often equal to that of -.

flue and if anything, on the large side. A down draught kiln needs a ' 1

strong enough draught to clear the hot gasses and flame through the

chamber.

3. Production and Procurement of Bricks

commonest shapes being a rectangle of 9 x 4 % x 2 % inches 01- 22.8 x

range of special shapes and sizes for arches, bevels, domes etc will be

~i io~~lded by the researcher. (See figs 4&5)

For the purpose of this research, three types of bricks were used- <\,

densc rcd bricks, the insulating and refractory bricks. The insulating -.

bricks are referred to as the 'hot face' insulating bricks while the i I

refractory ones are known as the solid fire bricks. The 'solid fire briclts'

are made basically from fire clay and grog. They are hard, dense, volume

stable and shall withstand various temperatures. While the 'hot face'

insulating bricks are made from fire clay, and sawdust. This gives them a

cellular composition, like that of a natural brick, with their good

insulating qualities and the ability to withstand high teinperaturcs. The

dense red bricks were produced for the outside course.