ABSTRACT
This study explored the possibility of producing Iron Oxide based arc welding electrodes
using mill scales from Dana rolling mill. The performance of the weld joints using the
produced electrodes and a foreign electrode was also examined. It is estimated that 4000-5000
tons of mill scales are produced annually without any immediate industrial application. The
mill scales were collected prepared and analyzed using the Oxford 800 X Supreme XRF
machine. The report of the analysis shows the presence of predominantly Iron Oxide, which is
an important constituent in electrode coating. The flux compositions were generated using the
Hadamard multivariate chemical model. Using this model, twelve different flux compositions
emerged within given ranges of the constituent flux elements. Four of the flux compositions
were used to produce electrodes using sodium silicate as binder. The electrodes were produced
manually by means of a wooden mould. The produced electrodes (E6020, E6027, E6024 and
E6030) and a foreign electrode were used to carry out weld on some prepared samples. The
welded joints were tested for tensile, hardness, and impact tests. The results of the tests
conducted on all the welded joints using the produced electrodes and the foreign electrode
shows that all the produced electrodes with the exception of electrode type E6030 compete
well with the foreign electrode (Oerlikon). Electrode type E6020 gave the highest tensile and
hardness test results of 453N/mm2 and 457.1N respectively. The maximum impact energy was
found to be 94.9 joules on the sample welded with the electrode type E6030. The micrographs
of the weld joint using electrode type E6027 revealed a coarse pearlite (black matrix) and an
elongated ferrite (white matrix). To this end, this study established the need to maximize the
use of mill scales (an industrial waste) for the production of arc welding electrodes and by so
doing conversion of waste to worth would have been achieved.
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TABLE OF CONTENTS
Cover Page i
Title Page ii
Declaration iii
Certification iv
Dedication v
Acknowledgement vi
Table of Contents vii
List of Tables xi
List of Figures xii
List of Plates xiii
Abstract xv
CHAPTER ONE
1.0 INTRODUCTION 1
1.1 Overview of Welding 1
1.1.1 Types of welding 2
1.1.2 Types of arc welding 3
1.1.3 Development of welding 5
1.2 Statement of Problem 6
1.3 Present Research 7
1.4 Aim and Objectives 8
1.5 Justification 8
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Contents Pages
1.6 Research Scope 9
CHAPTER TWO
2.0 LITERATURE REVIEW 10
2.1 Electrode Overview 10
2.2 Types of Arc Welding Electrodes 12
2.2.1 Consumable electrode s 12
2.2.2 Non consumable electrodes 12
2.3 Classification of Electrode Coatings 12
2.3.1 Gas forming component 13
2.3.2 Slag forming component 13
2.3.3 Reducing component 13
2.3.4 Stabilizing component 13
2.3.5 Binding component 13
2.4 Types of electrode coatings 13
2.4.1 Gas shielded (cellulosic) electrodes 14
2.4.2 Rutile electrodes 14
2.4.3 Iron oxide electrodes 14
2.4.4 Basic electrodes 14
2.5 Review of Related Researches 14
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CHAPTER THREE
3.0 MATERIALS AND METHODS 22
Contents Pages
3.1 Introduction 22
3.2 Materials 22
3.3 Equipment 25
3.4 Experimental Procedure 26
3.4.1 Chemical composition formulation process 28
3.4.2 Production process 34
3.4.3 Mechanical tests 36
3.4.4 Production cost determination 37
3.4.5 Estimated cost for the produced electrodes 37
3.5 Sample Preparation 39
3.5.1 Tensile test samples 39
3.5.2 Hardness test samples 41
3.5.3 Impact test samples 42
3.5.4 Metallographic examination 42
CHAPTER FOUR
4.0 RESULTS 45
4.1 Introduction 45
4.2 Results of Mechanical Tests Conducted 45
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CHAPTER FIVE
5.0 DISCUSSION OF RESULTS 53
5.1 Elemental Analysis of Mill Scales 53
5.2 Performance Evaluation of Welded Joints 53
Contents Pages
5.3 Micrographs of Weldments and Heat Affected Zone 56
CHAPTER SIX
6.0 CONCLUSION AND RECOMMENDATIONS 58
6.1 Conclusion 58
6.2 Recommendations 59
References 60
Appendices 64
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CHAPTER ONE
1.0 INTRODUCTION
1.1 Overview of Welding
Welding is a production or a fabrication process of joining two or more materials
together, usually metals or thermoplastics to achieve coalescence. Welding is performed by
the application of heat and pressure to melt the work piece together often with the addition of
filler material to form a pool of molten material which form the welded joint after
solidification (www.metal_processing/welding.cfm). Many welding processes are
accomplished by heat alone, with no pressure applied; others by a combination of heat and
pressure; and still others by pressure alone, with no external heat applied.
Welding processes are used to produce joints with properties similar to those of
materials being joined, these materials are called parent materials.Welding process usually
involves raising the materials at the joint to elevated temperature (Ibhadode, 2001). There are
three main components to create a weld and these components are:
1 A heat source: A heat source is an important component in the creation of weld, a
heat source include an electric arc, a flame, pressure or friction. However, the most
common heat source is the electric arc.
2 Shielding: Shielding is the use of gas or another substance to protect the weld from
atmospheric contamination of the molten weld.
3 Filler material: They are used in joining two pieces of materials together, usually
metals.
Welding is extensively used in fabrication and has found application as an alternative method
for casting or forging and as a replacement for bolted and riveted joints. It is also used as a
repair medium, for example to reunite metals at a crack, to build up a small part that has
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broken off, such as gear tooth or to repair a worn surface such as a bearing surface(Khurmi
and Gupta, 2005).
The objective of welding is to join pieces of metals together by means of suitable
heatsource(Lancaster, 1993).Advantages of welding as a joining process include high joint
efficiency, simple set up, flexibility and low fabrication cost (Armentani et al., 2007).
Today, many process of welding have been developed and probably there is no industry which
is not using welding process in the fabrication of its product in one form or other, hence
welding process can be broadly classified, as fusion welding and solid phase welding.
1.1.1 Types of welding
Fusion welding: This type of welding operation involves joining two pieces of metals together
by the application of heat. The two materials or parts to be joined are placed together and
heated, often with the addition of filler metal, until they melt and solidify on cooling. Types of
fusion welding include electric arc welding, electrical resistance welding, gas welding etc.
Solid phase welding: This type of welding operation is achieved by bringing the clean faces of
the materials to be joined into intimate contact to produce a metallic bond. Solid phase
welding can be performed with or without the application of heat. However pressure
application is important so as to induce plastic flow (Jain, 2008). Heat or temperature
distribution that occurs during welding greatly affects the microstructure of the weld, and
hence the weld properties (Kou, 2003). At the end of a welding operation, the complete weld
metal and metal pieces having been joined should now to all intents, be one piece of metal
(Somksy, 1986).
After welding, a number of distinct regions are identified in the weld area, the weld
itself is called the fusion zone, and it is a portion where the filler metal was laid during the
welding process. The property of the fusion zone is dependent on the filler metal used and its
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compatibility with the base materials, the fusion zone is surrounded by the heat affected zone.
The heat affected zone is the area that had its microstructure and properties altered as a result
of heat during welding. The fusion zone and the heat affected zone microstructure properties
depend on the base materials behavior when subjected to heat(Cary and Helzer, 2005). The
properties and microstructure of heat affected zone depends on the rate of heat input and
cooling and also the temperature at which the zone is raised during welding (Kalpakjian and
Schmid, 2006).
Arc welding is one of the several fusion processes of joining metals. By the application
of intense heat, metal at the joint between two parts are melted and caused to intermix directly
or, more commonly with an intermediate molten filler metal, which when solidify a
metallurgical bond results which is called weldment. In arc welding, the intense heat needed to
melt the metal is produced by an electric arc, and the electric arc is formed between the work
pieces to be welded and an electrode that is manually or mechanically moved along the joint
(Hwaiyu, 2004). An electric arc is obtained when an electric current flows between two
electrodes separated by a short distance, in electric arc welding, one electrode is the welding
rod and the other is the work piece being welded (Ibhadode, 2001).
1.1.2 Types of arc welding
ï‚· Shielded metal arc welding: Shielded metal arc welding is one of the oldest arc
welding processes. It is also the simplest and perhaps the most versatile arc welding process
used for welding ferrous based metals, because of its flexibility, simplicity and accessibility to
difficult locations (Ibhadode, 2001). Shielded metal arc welding process was invented in 1907
and is still being widely used today (Kay et al., 2010). It is a manual arc welding process using
coated electrodes. Since the electrodes melt and join the work piece, shielded arc welding is
classed under consumable arc welding method. The coating on the electrode burns along with
the core wire and produces a dense smoke which covers or shield the weld pool and thus
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prevent oxidation and absorption of nitrogen by the metal, and this type welding process is
used for steel fabrication. Fig 1.1 shows a shielded metal arc welding process with a
consumable electrode that melts and produce gaseous shield which prevent oxidation of the
molten weld metal.
Fig;1.1: Shielded metal arc welding ( Source; Parking and Flood, 1974).
ï‚· Submerged arc welding: This is an automatic process developed primarily for the
production of high quality butt welds in thicker steel plates. Submerged arc welding is
different from other arc welding processes in a way that a blanket of fusible, granular material
(flux) which consists of lime, silica, manganese oxide, calcium fluoride and other compounds
is used for shielding the arc and the molten metal. The process provides very high deposition
rate and a deep penetration and it is used for welding pressure vessels and high pressure pipes.
ï‚· Gas tungsten arc welding: Inert gases are used to keep contaminants away from
contacting the metal. Gas tungsten arc welding is faster, produces cleaner welds and can weld
metals considered to be difficult or impossible to weld, it uses a non-consumable electrode and
is used for welding stainless and light gauge materials. The equipment needed for gas tungsten
arc welding are welding torch, welding power source and a source of inert gas.
ï‚· Gas metal arc welding: This welding operation is performed using direct current
reverse polarity as it gives both good cleaning action and fast filler metal deposition rate. Gas
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metal arc welding electrode uses a consumable electrode which is fed through the electrode
holder in to the arc and at the same speed the electrode is melted and deposited in the weld.
ï‚· Plasma arc welding: Plasma is defined as a gas heated to at least practically ionized
condition, enabling it to conduct an electric current. Plasma arc refers to a constricted electric
arc which is achieved by passing through the water cooled orifice. Plasma arc is made to pass
through a small hole in a nozzle which surrounds a non-consumable electrode. This type of
welding process has a small heat affected zone and has high welding speed. It is used for
welding stainless steel, nickel alloys, refractory and metals in aerospace.
ï‚· Electron beam welding: In this process the metal to be joined are brought rather close
together and a concentrated stream of high energy electron emitted from a high voltage
(150kv) electrode gun is directed on to the surface of the work piece, causing fusion to take
place. This welding process is usually performed in the vacuum and thus no flux is required,
as there is no air present to contaminate the weld metal. Electron beam welding find
application in aerospace and automotive industries.
1.1.3 Development of welding
Welding as we know it today was not invented until the late 19th century. The earliest
form of welding was the forge welding. Forge welding was used by blacksmiths to join metals
by heating and pounding until bonding occurred. During the late 1800s gas welding, arc
welding with carbon and resistance welding were developed. The advances in welding
continued with the invention of metal electrodes which provided a more stable arc in the year
1900s.
World War1 brought a tremendous demand for a reliable and also an inexpensive
joining method throughout the United States. Many companies sprang up in America and
Europe to manufacture welding machines to meet the requirement, its first important use was
in making repairs for many equipment being chiefly as a repair and maintenance tool, arc
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welding has gradually expanded until it now constitutes an important method of fabrication in
practically every industry that uses metal. Immediately after the war the America welding
society was established to promote welding and other type of allied processes. During the
1900s automatic welding was introduced and various types of welding electrodes were
developed. Between the year 1920 and 1960, there had been a huge breakthrough in welding
with the development of several welding techniques, such as shielded manual arc welding,
stud welding, gas tungsten arc welding, electro slag welding, plasma arc welding etc. Most
recent was the development of friction stir welding, electron beam welding, laser beam
welding and electromagnetic pulse welding (Cary, 1998).
Welding has found application in the fabrication of different components, such as
pressure vessels, boilers, storage tanks, turbines etc. Today, welding is used in ship building,
construction of bridges, and joining automobile parts.
1.2 Statement of Problem
Examination of mill scales from Dana steel rolling mill in Nigeria, using the Oxford
800 X supreme X-ray florescence machine shows the presence of predominantly Iron Oxide
(Fe2O3) which constitute more than eighty percent of the total constituent elements of mill
scales and which is one of the most important constituents of covering on mild steel arc
welding electrodes, serving primarily as slag formers. It is estimated that 4000-5000 tons of
mill scales are produced annually with no immediate industrial application (Folayan et al.,
1992). Hence mill scales are relatively available and cheap compared to other type of slag
formers like titanium oxide (Ti02). As a result of the utilization of these waste (mill scales)
there will be actually little cost attached to the main raw material for the production of the
electrodes, hence the unit cost of the electrodes to be produced will be affordable. Moreover
the diffusible hydrogen content of weld created by rutile electrodes and most especially the
cellulosic (foreign) type of electrode is always high, hence the danger of hydrogen
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embrittlement of base metal is imminent and there is great possibility of inducing hydrogen
cracking in the weld, as the presence of hydrogen in the weld can lead to the creation of
hydrogen porosity, which reduces its ductility, strength, and fatigue resistance. Hydrogen can
diffuse out of the iron lattice when in solid state resulting in lowering of the mechanical
properties of the weld and increasing the tendency to cracking. Therefore use of mill scales as
main constituent in the production of Iron oxide based arc welding electrodes prevents the
presence of hydrogen build up and its negative consequences. Plate I shows the picture of the
Oxford 800 X Supreme XRF machine used for the elemental analysis of mill scales.
Plate I: Oxford 800 X supreme XRF machine (Chemistry department ABU, Zaria).
1.3 Present Research
The importation of electrodes has over the years undermined our efforts in the search
for local materials for the production of arc welding electrodes, perhaps due to the belief that
the materials for the production of arc welding electrodes locally are not available in Nigeria.
Therefore, this research has been conducted to investigate the feasibility of the production of
arc welding electrodes using mill scales from Dana rolling mill, and to evaluate the
performance of welded joint using the produced electrodes and a foreign electrode. The mill
scales was collected and analyzed to determine the percentage composition of Iron oxide
present in it. The produced electrodes using mill scales and other materials were used to make
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welds on different samples of mild steel and the mechanical properties such as tensile strength,
hardness, impact and the metallographic examination of these weldments using the produced
electrodes were obtained and compared with welded joints using the foreign electrode.
1.4 Aim and Objectives
This research work is aimed at utilizing mill scales from Dana steel rolling mill for the
production of arc welding electrodes and to evaluate and compare the performance of welded
joints using the produced electrodes and a foreign electrode.
The specific objectives are:
1. To obtain mill scales from Dana steel rolling mill, prepare and analyze the mill scales,
to determine the constituent elements.
2. To formulate a new flux composition for the electrodes to be produced
3. To produce various types of Iron oxide electrodes such as E6020, E6027, E6024, and
E6030 by varying the composition of the constituent elements.
4. To determine the welded joints performance of the electrodes produced and compare
them with the foreign electrodes obtained in the market.
5. To carry out the microstructural analysis of the weldments.
1.5 Justification
In Nigeria, about nine-eight percent of manufacturers in the welding electrode industry
have wound up, due to high production cost. The remaining two percent that manage to
remain operational sell their coated electrodes at exorbitant prices(Achebo and Dagwa,
2009).Consequently there is need for importation of electrodes in to the country to augment
for the shortage in the production of electrodes, as a result of this, a large chunk of our foreign
exchange is being used in the importation of arc welding electrodes and as such, production of
arc welding electrodes locally using mill scales will not only help us in conserving our foreign
exchange, but also help us in developing the technology especially as the availability of the
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locally produced electrodes has been on the decline in recent years, and in particular the low
hydrogen electrode to be produced will be cheaper when compared to the ones obtained in the
market.
1.6 Research Scope
This research work shall focus on the production of arc welding electrodes using mill
scales as slag formers. The research will also ensure that the produced electrode are used to
weld some specimen and the mechanical properties of the welds from the produced electrode
will be compare with that of existing electrodes in the market.
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