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Table of Contents
1. Steel Scrap
1.1. Definition of Steel Scrap…………………………………………………………..2
1.1.1. Sources of Steel Scrap…………………………………………………………….2
1.2. Preparation Techniques of Steel Scrap………………………………………………4
1.3. Challenges and Recommendation on Preparation Techniques of steel scrap………..14
2. Melting Process Of Steel scrap
2.1. Explanation about Melting process………………………………………………………..
2.2. Methodology of Melting process………………………………………………………16
2.3. Process of Billet production and billet product defects……………………………….. 17
2.4. Challenges and Recommendation on Melting and Billet production process ………….18
3. Rebar
3.1. Definition of Rebar……………………………………………………………………..
3.2. Rebar Production Process…………………………………………………………………19
3.3. Heating Temperature Effect and Common defects in billet heating on Rebar Production
Process………………………………………………………………………………………….23
3.4. Challenges and Recommendation on Rebar Production process………………………….24
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1. Steel scrap
1.1. Definition of Steel Scrap
Steel scrap also known as ‘ferrous metal scrap’ is a recyclable material which is leftover during
the production of steel products and fabrication of ferrous materials or generated at end of life
of the ferrous products or consists of recyclable materials leftover from product manufacturing
and consumption, such as parts of vehicles, building supplies, and surplus materials. Unlike
waste, scrap has monetary value, especially recovered metals, and non-metallic materials are
also recovered for recycling.
1.1.1. Sources Of Steel Scrap
Steel scrap comes from several different sources and hence it differs both with respect to its
physical and chemical characteristics. It is classified in three main categories namely (i) home
scrap, (ii) new scrap, and (iii) old scrap depending on when it becomes scrap in its life cycle.
Home Scrap
Home scrap is the internally generated scrap during the manufacturing of the new steel products
in the steel plants. It is also known as runaround scrap and is the material in the form of
trimmings or rejects generated within a steel plant during the process of the production of iron
and steel. This form of scrap rarely leaves the steel plant production area. Instead, it is returned
to the steel-making furnace on site and melted again. This scrap has known physical properties
and chemical composition. Technological advancements have significantly reduced the
generation of home scrap.
New Scrap
New scrap (also called prompt or industrial scrap) is generated from manufacturing units which
are involved in the fabricating and making of steel products. Scrap accumulates when steel is cut,
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drawn, extruded, or machined. The casting process also produces scrap as excess metal. New
scrap includes such items as turnings, clippings and stampings leftover when parts are made
from iron and steel during the manufacturing processes. It is usually transported quickly back to
steel plants through scrap processors and dealers or directly back to the steel plant for re-melting
to avoid storage space and inventory control costs. The supply of new scrap is a function of
industrial activity. When activity is high, more quantity of new
scrap is generated. The chemical composition and physical characteristics of new scrap is well
known. This scrap is typically clean, meaning that it is not mixed with other materials. In
principle new scrap does not need any major pre-treatment process before it is melted, although
cutting to size may be necessary.
Old Scrap
Old scrap is also known as post-consumer scrap or obsolete scrap. It is steel that has been
discarded when industrial and consumer steel products (such as automobiles, appliances,
machinery, buildings, bridges, ships, cans, and railway coaches and wagons etc.) have served
their useful life. Old scrap is collected after a consumer cycle, either separately or mixed, and it
is often contaminated to a certain degree, depending highly on its origin and the collection
systems. Since the life time of many products can be more than ten years and sometimes even
more than 50 years (for example products of building and construction), there is an accumulation
of iron and steel products in use since the production of the steel has started on a large scale.
Since the old scrap is often material that has been in use for years or decades, chemical
composition and physical characteristics are not usually well known. It is also often mixed with
other trash. Due to these reasons, old scrap is the most difficult and costly form of steel to reuse.
Incorporation into recycled products may require cleaning, sorting, removal of coatings, and
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other preparation prior to use. The large number of sources and forms of steel scrap requires the
use of numerous scrap sorting and preparation processes to remove the contaminants and/or
recover other valuable materials (i.e. non-ferrous metals) prior to entering the steelmaking
process.
1.2. Preparation Techniques of steel scrap
Home scrap hardly need any preparation except that the larger pieces of the scrap may have to be
lanced or gas cut to make the size suitable for its charging in the steelmaking furnace. Same is
also true for substantial quantity of the new scrap. However some of the new scrap may need
processing. Large items such as ships, automobiles, appliances, railway coaches and wagons, and
structural steel need to be cut to allow them to be charged into the steelmaking furnace. This can
be done using shears, hand-held cutting torches, crushers or shredders. Manual sorting obviously
involves the removal of components from the scrap by hand. It is most suitable when
miscellaneous attachments are to be removed from the scrap (i.e. radiators from scrapped
automobiles, plastic end tanks from radiators etc.). The separation of metallic from non-metallic
is also often accomplished manually. Wide range of equipment and processes are available for
the reduction of the size of large scrap material into pieces small enough to enable consolidation,
transport and subsequent feeding into the steel-making furnace. The equipment and processes
used to accomplish this are described below.
Mechanical processes
The mechanical processes which are normally employed to prepare the steel scrap include
namely (i) baling, (ii) briquetting, (iii) shearing, and (iv) shredding. Chemical processes are also
used in certain cases. Lets see in detail:-
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Baling – In baling process, the scrap material is compressed in a powerful mechanical or
hydraulic press, to produce dense, cubical blocks called bales. In baling press, loose scrap which
has a high surface area and low density (i.e. lathe turnings) is compacted. A baling press is a
heavy piece of processing equipment which uses up to three hydraulic rams to compress the
scrap that requires higher density for charging in the steel-making furnace. With 600
horsepower, the largest baling press can take three flattened autos without engines and in less
than two minutes produce a bale of weight 2.5 tons and a size of 1 m x 0.5 m X 2 m. The
advantages of baling process are (i) more weight can be loaded on a truck thus reducing the
transport cost, (ii) more material can be stored in a given space, (iii) handling and storage of the
scrap becomes easier, quicker, and systematic which in turn reduces the cost of handling and
storing of the scrap, and (iv) a denser furnace charge is obtained.
Briquetting – In a briquetting machine, small scrap is compacted into pockets as it passes
between two counter rotating drums. Compaction can be assisted with heat depending on the
material.
Shearing – In the shearing process, the scrap material is chopped to length by a powerful blade
of a shearing machine. The hydraulic guillotine shear slices heavy pieces of steel including Ibeams, ship plates, pipes, and sides of railway wagons. Shears vary in size from 300 tons to more
than 2000 tons of head force. The cheapest shearing machine is an alligator shear which can cut
heavy melting scrap of 200 mm in thickness. Larger shears are even more powerful.
Shredding – It is used for steel scrap which may contain other materials (glass, plastic, rubber,
any non-ferrous metals, etc.) such as automobiles and household appliances. Hardened steel
hammers or knives, driven by electric motors of enormous power, reduce the object to small
pieces which can then be sorted, mainly by the magnets which remove the steel scrap and leave
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all other materials. Shredders usually have high capital and operating cost and are only justified
when large amount of steel scrap is available on a regular basis to feed the shredding machine for
processing. Shredding machines are also known as fragmentizers. They can reduce bulky scrap
into first-sized pieces using massive hammer mills. A medium-size shredder uses 36 hammers
weighing around 120 kg each to pound the scrap to pieces. Although the predominant raw
material for the shredder is automobile bodies, ‘white goods’(household appliances such as
stoves, washers, dryers, and refrigerators) and other large items can also be shredded. Depending
on its size, a shredder can process from 1500 tons to more than 20000 tons of scrap per month.
The shredding process produces three types of materials namely (i) ferrous metal (iron and steel),
(ii) light fraction shredder residue, and (iii) heavy fraction shredder residue. The two residue
fractions, either singularly or collectively, are often referred to as shredder residue (SR).
‘Shredder fluff’ is the term given to the low density or light materials, which are collected during
the shredding process for cyclone air separation. Each ton of steel that is recovered produces
about 300 kg of SR, comprised of plastics, rubber, glass, foam and textiles, contaminated by oil
and other fluids. The ferrous metals are recovered by the shredder operator using magnetic
separation. The SR heavy fraction contains primarily aluminum, stainless steel, copper, zinc and
lead. The non-ferrous and ferrous metals are recovered from the SR heavy fraction. Heavy media
separation and eddy current separation are the technologies primarily used to recover the metallic
material from the SR heavy fraction.
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Fig. Processes for scrap preparation
Magnetic separation process
Magnetic separation is used when a large quantity of ferrous scrap is to be separated from other
materials. Permanent magnets and electromagnets are used in this process. The latter can be
turned on and off to pick-up and drop items. Magnetic separation process can be of either the
belt-type or the drum-type. In the drum type process, a permanent magnet is located inside a
rotating shell. Material passes under the drum on a belt. A belt separator is similar except that the
magnet is located between pulleys around which a continuous belt travels. Magnetic separation
process has some limitations. It cannot separate iron and steel from nickel and magnetic stainless
steels. Also, composite parts containing iron are collected which can contaminate the steel melt.
Hand sorting is often used in conjunction with magnetic separation to avoid these incidences.
Eddy current separation process
Eddy current separation process is used to separate non-ferrous metals from waste and SR. The
process generally follows the primary magnetic separation process, and it exploits the electrical
conductivity of non-magnetic metals. This is achieved by passing a magnetic current through the
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feed stream and using repulsive forces interacting between the magnetic field and the eddy
currents in the metals. Inclined ramp separator represents the simplest application of the process.
It uses a series of magnets on a sloped plate covered with a non-magnetic sliding surface such as
stainless steel. When a feed of mixed materials is fed down the ramp, non metallic items slide
straight down, while metals are detected sideways by the interaction of the magnetic field with
the induced eddy current. The two streams are then collected separately. Variations of the eddy
current separation process include the rotating disc separation, in which magnets are arranged
around a rotating axis. There is also another process which uses a conveyor with a head pulley
fitted with magnets. Both of these processes rely on the varying trajectories of materials either
affected or unaffected by magnetic fields, to make the separation.
Heavy media separation process
Recovery of recyclable materials is often achieved using a heavy-medium separation (HMS) for
the recovery of non-ferrous metals from shredder residue. This process utilizes a medium
normally consisting of finely ground magnetite or ferrosilicon and water. By varying the relative
proportions of the solids, the specific gravity of the medium can be adjusted. The specific gravity
of the medium is typically half way between the densities of the two materials being separated.
Once separated, the products/materials are allowed to drain, and the medium is recovered is then
returned to the process. Any medium still adhering to the product/material is removed by a water
spray. The resultant solution is passed through magnetic separators to recover the medium. The
effluent is then reused as spray water. HMS process is generally conducted in an open bath to
achieve a separating force equal to the force of gravity. For smaller particles, the forces of
medium viscosity tend to work against the separating force. In these cases, cyclonic separators
are used which result a separation at several times the force of gravity.
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Separation by physical and chemical characteristics
Separation by physical and chemical characteristics utilizes color, density, magnetic, spark,
chemical and spectroscopic testing. Scrap materials are typically identified by skilled operators
(sorters) using a limited number of physical and chemical tests. These tests rely on object
recognition by color, apparent density, reaction with chemical reagents, chemical analysis,
magnetic properties, nature of spark pattern when ground by an abrasive wheel, and
spectrographic analysis. Physical properties such as color, density and relative hardness can be
used to quickly separate certain classes of materials. For example, copper and brass can be
identified by color, while lead can be recognized by both its density and relative softness.
Differentiating between alloys of similar grades and compositions can be difficult. In such cases,
magnetic testing, spark testing method, and chemical and spectroscopic analysis are often used.
Magnetic testing can also be used since iron, nickel and cobalt are ferromagnetic, as are low
alloy stainless steels. Hence, while magnetic testing cannot be used to differentiate between
alloys, it can classify alloys into their series. Spark testing involves grinding an alloy on an
abrasive wheel. The color and length of the spark can be used to identify the alloy. There is a
spectrometer which analyzes the spectra given off from the spark and compares it with standards
to identify the alloy, but this unit is not truly portable and is therefore not widely used. However
experienced spark testing operators can differentiate the material by observing the color and
length of the sparks. Various optical and X-ray spectrometers are being used to identify the
composition of alloys. Thermo-electric testing involves using the See beck effect to identify
materials. These thermoelectric devices contain two probes made of the same metal, one heated
and one at ambient temperature. When they contact the scrap, a potential difference is generated
which is the characteristic of the metal being tested. Chemical spot tests are also used whereby
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reagents such as acids are dropped on the metal and the reaction is observed. Quantitative
chemical analysis is normally done to confirm the exact composition of the alloy. Based on
chemical composition scraps are classified as:
Pure steel
Steel is an alloy of iron with typically a few percent of carbon to improve its strength and
fracture resistance compared to iron.in pure ,the crystal structure has relatively little
resistance to the iron atoms slipping past one another, and so pure iron is quite ductile, or
soft and easily formed.
According to this we can assign the following type of steel at pure level.
o Steel those have thickness above 5mm and 99% iron content
o Angle iron without any coated materials.
Medium steel
Its include grade with carbon content ranging from 0.25% to 0.60% of the steel mass.
medium carbon grade are typically employed in conjucton with alloy such as chromium,
nickel and molybdenum to produce high strength ,wear resistance and toughness. Steel
like described below are damped in this campany
Those are:
o steel having iron content from 95% up to 98%
o Pure steel with slightly corrode and minimum thickness of from 2mm up to 4mm.
o Medium carbon content steel up to 0.3%.
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Low steel
Low carbon is a type of steel that has small carbon content ,typically in the range of
0.05% to 0.3%.its reduced carbon content makes it more malleable and ductile than other
steel types. Low carbon steel is also known as mild steel.
In this campany they call the following steel type are low type steel depend on the
chemical quantity and scrap property.
o High corrode steels.
o Coated and galvanized steels
o Light sheet metal
o <95% iron content steels.
High manganese steels: is a steel type with Mn content from 3 up to 27%.it is applied to
variours industries based on various properties such as high strength, low temperature toughness,
wear resistance, nonmagnetic and damping property depend on component like Mn and c relative
to this we call the following type of scraps are high manganese steels. those describe below the
materials damped in this campany as scrap. All scrap having high percentage of Mn content.
o Gears
o Different suspension steel
o Lining and jaw plates
o Different crasher hammers
High carbon steel :as their name suggests, are steels with high carbon content .the
carbon in this sample of steel strengthen it and gives it the ability to harden by heat
treatment.it also make it less ductile and weldable than ordinary steel.
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Scrap rating and grading formula
On scrap rating technique we use the chemical properties of the scraps and physical
properties by generating in this company formula. Depend on this rate our scrap by three
grades.
In this company have three grades except super and non-grade scraps.
Grade 1= (pure steel>50%) +medium steel=>90%
Grade 2= (pure steel <45%) + (medium steel >40%) + low steel or (medium steel >60%) +
low steel +additive scrap.
Grade 3 = low steel >60% + medium steel + additive scrap.
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Decoating processes
These processes are also known as scrap purification processes and are effective for the removal
of tramp elements from the scrap. Many tramp elements dissolved in steel melts, e.g. copper, tin
antimony, and lead, are not oxidized in the presence of iron during the steelmaking process
because of their low a flinty for oxygen. This means that these elements cannot be removed from
a steel scrap melt by a common pyro-metallurgical process, as is the case with silicon,
manganese and aluminum which are oxidized and dissolved in slag. In order to remove tramp
elements, scrap is required to be pre-treated at lower temperatures while it remains in the solid
state. Pre-treatment of scrap in solid state has often the advantage that the tramp elements are
present in pure state, either mingled with the ferrous portion of the scrap or existing at scrap
surfaces, a fact which should facilitate their removal. Several steel products are being used with
coating of other metal on them. Examples are galvanized sheets, tin plate etc. It is essential that
the steel scrap generated from such coated products is stripped of the coating material before it is
processed in the steelmaking furnaces. There are currently a number of processes used in
industry for decoating of the steel scrap.
Dezincing process for steel scrap
The main source of zinc is galvanized steel sheet scrap. The zinc coated scrap included in the
charge results in discharge of zinc oxide in the flue dust. Due to its high vapour pressure (71
kg/sq cm at 1600
°C) most of the zinc evaporates during the steelmaking process. A zinc
balance for an EAF shows that 97.9% of the zinc input escapes with the fumes, with only 2 %
remaining dissolved in steel and 0.1% in the slag. Although the removal of zinc at the scrap
smelting stage is not problematic, it is useful if the dezincing of zinc coated scrap is done at a
scrap pre-treatment stage so as to avoid the problems associated with recycling large amounts of
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galvanized scrap. The removal of zinc using thermal methods is generally carried out by using
any of the following methods. The galvanized parts are heated to a high temperature (higher than
℃) at which the zinc evaporates. The galvanized parts are heated to a temperature suffcient to
embrittle the coating which is then removed by abrasion. The galvanized parts are heated and the
removal of the coating is subsequently done by shot blasting. Zinc removal can also be carried
out using chemical techniques in which ammonia leach or caustic soda is used to dissolve the
zinc coating from galvanized scrap. A continuous process for the electrolytic dezincing of
process scrap from automotive industry was developed by Hoogovens (Holland) and a pilot plant
has been operated in France. Galvanized scrap is immersed in a hot caustic solution where zinc
dissolves while steel remains unaffected. After leaving the dissolution reactor the dezinced scrap
is washed and compacted. The zinc-enriched solution is circulated to electrolysis cells where the
zinc is recovered electrolytically by deposition on cathode plates. The high processing costs and
the additional transport costs are disadvantages of the process. However, particularly for niche
markets determined by a regional combination of a large supply of zinc-coated process scrap and
a demand for reliable steelmaking feedstock, this dezincing process offers a real direct recycling
solution. Several other methods of dezincing the scrap have been investigated recently, too.
These include thermal treatment, treatment with Cl2-O2 gas mixtures and mechanical posttreatment after thermal treatment.
Detinning process for steel scrap
Tin, which has a lower melting point, causes zones of weakness in the hot steel, leading to ‘hot
shortness’ and other problems Tin bearing scrap (i.e. food containers and auto bearings) in steel
recycling affects the surface quality of the steel products because tin segregates to the grain
boundaries and causes surface scabs during working. Some of the processes being used for
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detinning the tin-plate scrap include electrolytic and alkaline detinning. The electrolytic
detinning of tinplate scrap has been a commercialized process for a long time. Tinplate scrap is
pressed into bundles with a density which is higher than 1.2 t/cu m. The bundles which serve as
anodes in the electrolytic process are immersed in a caustic soda bath at a temperature of 85 ℃.
Tin is deposited on a steel cathode as a sponge material which is then scraped off, pressed into
large pills for its disposal to the tin industry. After detinning, the
residual tin content which can be achieved in the scrap is as low as 0.02 %. Electrolytic detinning
is economically efficient only if the detinning unit has an annual scrap processing capacity which
is higher than 30,000 t of scrap. Also, electrolytic detinning is suitable for new scrap, but is
problematic for old scrap. The tin coating on tinplate cannot be removed by mechanical
treatment (e.g. by shredding). In the temperature range of 400 ℃ to 550 ℃, the sulphidation of
the coating with reactive gases featuring a sulphur potential and its subsequent removal as a
brittle sulphide phase has been applied successfully on a laboratory scale. At present it is
impossible to remove tin from steel scrap melts under industrial conditions. On the laboratory,
tin was successfully removed by treatment with Ca-containing slags under reducing conditions as
well as by vacuum treatment of steel melts at a pressure of1kg/sq m.
Decopperization process for steel scrap
Copper cannot be removed from scrap-based steel melts by a conventional refining method.
Several approaches to reduce the Cu content of steel have been proposed, namely, improvement
of scrap sorting, dilution of contaminated charges by directly reduced iron as well as mechanical
or chemical scrap pre-treatment aiming at impurity removal. Significant research efforts have
been made to develop pyro-metallurgical decopperization techniques. It has been confirmed on a
laboratory scale that copper can be removed by treatment with sulphide fluxes but a more
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promising method is the treatment of steel melts at reduced pressure of the gas phase. This
method which consists of the selective vaporization of copper has been successfully tested on the
laboratory scale. At present, investigations are being carried out to optimize the shredder
operation with respect to the copper content of the shredder scrap. Preliminary results show that
the copper content can be controlled by varying the degree of the shredder’s grid opening. With
respect to sorting of scrap, it has been found that copper is most effectively removed my manual
hand picking.
Incineration
Incineration process is often used for the removal of the combustible materials including oil,
grease, paints, lubricants and adhesives.
1.3. Challenges and Recommendation on Preparation Techniques of steel
scrap
- Lack of appropriate equipment and best available technology as evolved from time to time for
the activities defined viz shredding, shearing, baling, slitting etc.
- Lack of material handling machines to minimize human intervention and create safe work
places.
- The company did not engaged competent and trained manpower to process the End of Life
goods and other scraps.
So my recommendation is the company should solve those problems. Because the preparation
process of scrap factors the quality of final product.
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2. Melting Process of Steel scrap
2.1.Explanation about Melting process
Melting is a transition process that changes metal material status from solid sort to liquid sort by
providing enough heat. The melting steel process loosens the tight packing of metal molecules.
As the result, the melting gives metal liquid out of the solid material. The pure and solid metal
melting occurs at a certain fixed temperature called the melting point while impure metal
materials, it is melting at a different temperature that varies depended on the type and impurity
percentage. As the heart of the foundry, the melting metal process provides molten fluid that can
be used to pour into the mold and solidifies into a range of shapes as required. Metal melting is a
high energy-consuming work that takes accounts for 55% of the energy consumption of the
metalworking industry. It is a very crucial step because metal melt not only provides the material
for the casting process but also affects greatly on physical and chemical of the final casting
products.
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2.1. Methodology Of Melting process
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2.2. Process of Billet production and billet product defects
Billet Product Defects are imperfection results from over melting the scrap, impurity in molten
metal such as shrinkage, cracks, porosity and etc. Clearly, the micro-shrinkage concentrated in a
central hollow of the cross-section as the result of steel shrinkage on passing from the liquid in to
solid state. These defects are appear because the high casting temperature, the high rate of
solidification and by the strongly secondary cooling.
2.3. Challenges and Recommendation on Melting and Billet production
process
-Occurrence of defects like central crack, porosity, shrinkage
-Lack of melting temperature controlling system
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-Shortage of safety control
In order to produce qualified product the above problems must be solved. Because they have
impact on the quality of product.
3. Rebar
3.1. Definition of Rebar
Rebar is a steel bar used as a tension device in reinforced concrete to strengthen and aid the
concrete under tension. This device is essential for ensuring safe, durable structures that will be
reliable for years. Without them, the natural expansion and contraction of the concrete will cause
weak areas to develop, which will ultimately collapse in the long run. Rebar typically consists of
carbon steel, as this material allows for a stronger bond and tensile strength.
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3.1. Rebar Production Process
Scrap Preparation and Induction Furnace
The raw materials are required to be weighed and arranged on the operating floor near the
furnace before starting a heat. The raw materials to be charged are stored in suitable containers
and are to be ready for charging by the chosen method. The carburizer and additives are to be
weighed accurately and handled properly to avoid wastages during handling. The material is
charged into the empty furnace up to the upper edge of the furnace coil. Immediately after the
tapping of the previous heat, the condition of the lining material need to be inspected and then
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the scrap charging is to start. With the start of scrap charging, the heat cycle starts. As soon as
the first lot of scrap is charged in the furnace, power is switched on and current starts flowing at
a high rate and a comparatively low voltage through the induction coils of the furnace, producing
an induced magnetic field inside the central space of the coils where the crucible is located. The
induced magnetic fluxes are thus generated through-out the available charge in the crucible. As
the magnetic fluxes generate through the scrap and complete the circuit, they generate and
induce eddy current in the scrap. This induced eddy current, as it flows through the highly
resistive bath of scrap, generates tremendous heat and melting starts.
Chemical composition test of molten metal and Checking the pouring temperature
The melting continues till around one half of furnace volume is filled with the liquid steel. At
this point a sample is taken for the analysis. Based on the analysis result, the requirement of
further charge of scrap is determined and the charging is continued. When the liquid filling level
reaches around the upper edge of the coil, I.e. heat is about to be completed, the pouring
temperature is checked with the help of infrared thermometer.
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Making ingot and Reheating Furnace
By pouring the molten metal to the mold, the molten metal takes the shape of the mold and it is
called Ingot or Billet. The billet is heated in re-heating furnace at 1100℃. the purpose of billet
heating is to improve the plasticity of the rebar and reduce the deformation resistance to facilitate
rolling.
Rolling mill and Cooling bed
Several rolling mill stands are arranged in a row according to the rolling direction, and the
rolling pieces are rolled and deformed in several rolling mills at the same time. The rolling speed
of each stand increases with the increase of the length of the rolling pieces, and keeps the metal
in the rolling method in which the flow rate per second in each rolling mill is equal or has a
slight stacking steel relationship. Finishing the deformation process through billet rolling
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becomes the product that users need. The rolling process plays a decisive role in product quality.
The quality of rolled products includes product geometry, dimensional accuracy, internal
organization, process mechanical properties, and surface finish. In cooling bed the rebar is
cooled with the help of natural air. This cooling method generally does not affect the physical
properties of the rebar.
Mechanical properties test
Bending at half and Size cutting
The purpose of size cutting: cut off the parts that affect the use of the rebar, such as the head and
tail of the rebar; cut to the length required by the user. Rebar cutting equipment is hydrolic
machine. Bending at half is for the transportation purpose.
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3.2. Heating Temperature Effect and Common defects in billet heating on
Rebar Production Process
Heating Temperature Effect on Rebar Production Process
- Improve the plasticity of the rebar
- Reduce the deformation resistance to facilitate rolling
-Eliminate or reduce the internal structural defects of the billet.
-Effect on steel quality, rolling mill output, energy consumption, and rolling mill life.
Common defects in billet heating on Rebar Production Process
A. Overheating
When the billet is heated at a high temperature for a long time, it is very easy to overheat. The
overheating phenomenon of the steel billet is mainly manifested in the excessive growth of the
grains of the steel structure into a coarse-grained structure, thereby reducing the bonding force
between the grains and reducing the plasticity of the steel. Overheated steel is prone to cracking
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during rolling, especially at the corners. Cracks will occur on the surface of the steel when it is
slightly overheated, which will affect the surface quality and mechanical properties of the steel.
B. Overheated
When the billet is heated at a high temperature for a long time, it will become a coarse crystal
structure. At the same time, the low melting point non-metallic compound on the grain boundary
will be oxidized to destroy the crystal structure and make the steel lose its due strength and
plasticity. This phenomenon is called excessive burn. Over fired steel will cause severe cracks
during rolling. Therefore, over burning is a more serious heating defect than overheating.
Excessive burnt rebar cannot be saved except for re-smelting.
C. Uneven Temperature
This phenomenon is easy to occur when the billet heating speed is too fast or the output of the
rolling mill exceeds the heating capacity. For billets with uneven temperature, the dimensional
accuracy of the rolled pieces is difficult to control stably during rolling, and it is easy to cause
rolling accidents or equipment accidents.
3.3. Challenges and Recommendation on Rebar Production process
-No checking of the quality of billet before enter to the furnace
-Absence of heating temperature and heating time controlling system
-Occurrence of defects on the surface of products such as cracks, folds, ears, scars, delamination,
and inclusions on the surface.
-Improper cooling after rolling
# So in order to avoid above problems:
-The heating temperature and heating time must be strictly controlled
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- The acceptance of billets should be carried out in accordance with billet technical standards and
internal control technical conditions, and unqualified billets are not allowed to enter the furnace
-Improve the pre-installation accuracy of the rolling mill; timing and quantitative reverse pass.