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IntroductionThe Pakistan Steel Mills is the producer of long
rolled steel products in Karachi, Sind, Pakistan. The Pakistan
Steel Mill is the country's largest industrial undertaking having a
production capacity of 1.1 million tons of steel. The enormous
dimensions of the project can be visualized from the construction
inputs which involved the use of 1.29 million cubic meters of
concrete, 5.70 million cubic meters of earth work (second to
Tarbela Dam), 330,000 tones of machinery, steel structures and
electrical equipment. Its unloading and conveyor system at Port
Qasim is the third largest in the world and its industrial water
reservoir with a capacity of 110 million gallons per day is the
largest in Asia. A 2.5 km-long sea water channel connects the sea
water circulation system to the plant site with a consumption of
216 million gallons of sea water per day.
History of Pakistan Steel MillsAfter independence in 1947, it
did not take long for Pakistan to come to the realization that
progressive industrial and economical development would be
impossible without the possession of a self reliant iron and steel
making plant. The dependence on imports would cause serious
setbacks to the country along with an extortionately high import
bill which would be impossible to support. In 1968, the Government
of Pakistan decided that the Karachi Steel Project should be
sponsored in the public sector, for which a separate Corporation,
under the Companies Act, be formed. In pursuance of this decision,
Pakistan Steel Mills Corporation Limited was incorporated as a
private limited company to establish and run steel mills at
Karachi. Pakistan Steel Mills Corporation concluded an agreement
with V/o Tyaz Prom export of the USSR in January, 1969 for the
preparation of a feasibility report for the establishment of a
coastal-based integrated steel mill at Karachi.
Founders of Pakistan Steel MillsThe real founders of Pakistan
Steel Mills are Prof. Dr. Niaz Muhammad, Wahab siddiqui and Russian
scientist Mikhail Koltokof. It was the hard work of Niaz Muhammad
that thousands of scientists and technical staff got trained by
him. His inspirations and innovations got him the highest award
from President of Pakistan, and also from Government of USSR. The
Government of Pakistan has given him Pride of Performance. He was
also nominated for Nobel prizes
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Iron Making Department (IMD)IntroductionIron Making Plant
comprises of many small and big working units, the biggest one is
Blast Furnace unit. This unit consists of two Blast Furnaces (BF-1
& BF-2) and both are in operation since 31st August 1981 and
07th August 1984 respectively, Inner volume of each furnace is 1033
Cu.M and its working volume is 893 Cu.M. Whereas the daily
production capacity is 1750 tons of Pig Iron per furnace. BF-1 had
two notches:a) Iron notch and b) Slag notch. Both notches have been
closed permanently and another iron notch has been prepared
instead. Blast Furnace No.2 still has one iron notch and one slag
notch but its slag notch is rarely operated. Each furnace has 14
tuyers through which hot blast is injected at high temperature
(1100 - 1200 C). Raw Material is charged from the top of the
furnace through charging system comprising of double bell charging
system. Hearth of the furnace is lined with carbon blocks whereas
the inner walls of the furnace are lined with refractory bricks
with embedded plate coolers of different types. The hot air blast
alongwith a calculated quantity of natural gas is fed into the
furnace through tuyeres at high pressure (up to 2.5 atm.) and high
temperature (1200 C). As soon as the blast rises up the furnace
shaft, the raw material gains heat and coke starts burning which
produces CO and Co2. These gases further react with different
oxides of the raw material and reduce them into their elementary
shape (Fe, Si Mn etc.), and different oxides (such as A12O3, CaO,
MgO) are also formed. The mixture of Fe, Si, Mn and carbon is
called pig iron whereas the mixture of A12, O3, SiO2, CaO, MgO, MnO
and other oxides is called slag. Both the molten iron and slag are
collected in the hearth of the furnace from where they are tapped
after a scheduled period through iron notch altogether. Slag is
separated from the iron in the main
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runner just before the skimmer box. The pig iron is collected in
the iron ladles and slag is separately collected in slag pots.The
working area around the furnace, where a network of iron and slag
runners is laid down is called cast house. The heavy equipment
installed in the cast house are:i. To open the tap hole. ii. To
close the tap hole after the completion of the tapping. iii. An
E.O.T Crane of 20T/5T capacity to shift the materials and
equipments from bottom house and to clean and prepare the iron and
slag runners. There are three hot blast stoves for each furnace.
One stove is on blast at a time while the other two remain on
heating regime. The stoves are lined with Dinas Silica bricks and
chequered brick work. The stoves are heated with mixture of N.Gas
and B.F.Gas. When the dome temperature reaches 1350 C, the stove is
ready to provide the hot blast to the furnace.The gases in the
furnace, after completing the chemical reaction, leave the furnace
at the top. These gases carry fine particles of raw materials with
them. These gases (called B.F. Gas) are brought down the furnace
through pipes of bigger diameter (internally lined with refractory
bricks) into a vessel called dust catcher. Due to sudden drop of
pressure in the dust catcher, the dust particles settle down at the
bottom of the dust catcher, and the semi-cleaned gas is transferred
to gas cleaning plant for further purification. All the raw
materials charged into the furnace are initially stored in separate
bins, called burden bins. Iron ore and fluxes are supplied to
burden bins by RMHD, and Coke and Sinter by CokeOven and Sintering
Plant respectively. These materials are then sieved and weighed
according to charging schedule and continually fed into the
furnace.There are two pig casting machines in Iron Making
Department. A pig casting machine consists of two metallic chains
(conveyers) containing metallic moulds. The molten metal is poured
into these moulds and due to their continuous forward movement the
filled moulds travel ahead and empty moulds take their places.
After covering 10-15 m distance, water is sprinkled over molten
pigs and the outer surface gets harder. At the end of themachine,
pigs are struck away by a metallic hammer and collected in a
railway gandola placed underneath. PCM No. of Machines - 2 Pigs
weight - 18 / 23 / 45 Kgs Capacity - 140,000 Tons/year
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Pouring time of 140 T ladle i) 45 Kg Pigs - 55-60 minutes ii) 23
Kg Pigs - 60-65 minutes iii) 18 Kg Pigs - 70-75 minutes
SLAG GRANULATION PLANTThe slag produced in the blast furnace is
separately collected in slag pots at the furnace. The slag pots are
then transported to SGP by railway locomotive for slag granulation.
The molten slag is poured on a huge trough at a point where a heavy
jet of water granulates the slag and throw it away in the yard.
This granulated slag is then collected and shifted to open yard
directly on trucks for cement factory or other purposes.
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SLAG DUMP YARDAll the molten slag is not possible to pour out,
however, some slag still remains at the bottom of the pot. After
granulation, the slag pot is transported to slag dump yard far away
from the SGP. It is an elliptical open yard where railway track is
laid down at a sufficient height. The slag pot is placed at one of
the post and electrically tilted up to maximum. A metallic bob
(attached with the excavator) strikes the bottom of the ladle and
the residue falls down the ground. Now the ladle becomes completely
empty. The slag ladle coming from slag dump yard on way to blast
furnace isstationed for a while at slag ladle sprinkling unit where
a cold solution of lime water is sprinkled in the ladle so that the
slag could not stick to the inner walls of the ladle at the time of
pouring slag into it.
CENTRAL AIR SUPPLY STATIONThis is the unit where two huge fans
are installed to supply cool air to the control rooms and other
operational units ofblast furnace where sensitive electrical and
automation equipment are installed. The air is cooled by
counter-flow of chilled water in pipes (at 8C) and passed through
filters to make it clean and dust free.
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CENTRAL ASPAIRATION UNITDue to fine particles in raw materials,
a cloud of dust may appear during receiving these materials at
burden bins. Therefore to keep the atmosphere clean and clear, a
network of suction pipes is installed over conveyors and bins.
These pipes suck the dust with the help of huge fans installed at
central aspiration unit for this purpose. This dust or fine
particles are collected in an electric filter from where the dust
is supplied to sintering plant.
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Engineering Lab (ENGG. LAB)Introduction
Electric protective devicesEquipment applied to electric power
systems to detect abnormal and intolerable conditions and to
initiate appropriate corrective actions. These devices include
lightning arresters, surge protectors, fuses, and relays with
associated circuit breakers, reclosers, and so forth. From time to
time, disturbances in the normal operation of a power system occur.
These may be caused by natural phenomena, such as lightning, wind,
or snow; by falling objects such as trees; by animal contacts or
chewing; by accidental means traceable to reckless drivers,
inadvertent acts by plant maintenance personnel, or other acts of
humans; or by conditions produced in the system itself, such as
switching surges, load swings, or equipment failures. Protective
devices must therefore be installed on power systems to ensure
continuity of electrical service, to limit injury to people, and to
limit damage to equipment when problem situations develop.
Protective devices are applied commensurately with the degree of
protection desired or felt necessary for the particular system.
Protective relaysThese are compact analog or digital networks,
connected to various points of an electrical system, to detect
abnormal conditions occurring within their assigned areas. They
initiate disconnection of the trouble area by circuit breakers.
These relays range from the simple overload unit on house circuit
breakers to complex systems used to protect extrahigh-voltage power
transmission lines. They operate on voltage, current, current
direction, power factor, power, impedance, temperature. In all
cases there must be a measurable difference between the normal or
tolerable operation and the
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intolerable or unwanted condition. System faults for which the
relays respond are generally short circuits between the phase
conductors, or between the phases and grounds. Some relays operate
on unbalances between the phases, such as an open or reversed
phase. A fault in one part of the system affects all other parts.
Therefore relays and fuses throughout the power system must be
coordinated to ensure the best quality of service to the loads and
to avoid operation in the nonfaulted areas unless the trouble is
not adequately cleared in a specified time. See Fuse (electricity),
Relay
Zone protectionFor the purpose of applying protection, the
electric power system is divided into five major protection zones:
generators; transformers; buses; transmission and distribution
lines; and motors (see illustration). Each block represents a set
of protective relays and associated equipment selected to initiate
correction or isolation of that area for all anticipated
intolerable conditions or trouble. The detection is done by
protective relays with a circuit breaker used to physically
disconnect the equipment. For other areas of protection See
Grounding, Uninterruptible power system
Zones of protection on simple power system Fault detection Fault
detection is accomplished by a number of techniques, including the
detection of changes in electric current or voltage levels, power
direction, ratio of voltage to current, temperature, and comparison
of the electrical quantities flowing into a protected area with the
quantities flowing out, also known as differential protection.
Differential protectionThis is the most fundamental and widely
used protection technique. The system compares currents to detect
faults in a protection zone. Current transformers on either side of
the protection zone reduce the primary currents to small secondary
values, which are the inputs to the relay. For load through the
equipment or for faults outside of the protection zone, the
secondary currents from the two transformers are essentially the
same, and they are directed so that the current through the relay
sums to essentially zero. However, for internal trouble, the
secondary currents add up to flow through the relay.
Overcurrent protection
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This must be provided on all systems to prevent abnormally high
currents from overheating and causing mechanical stress on
equipment. Overcurrent in a power system usually indicates that
current is being diverted from its normal path by a short circuit.
In low-voltage, distribution-type circuits, such as those found in
homes, adequate overcurrent protection can be provided by fuses
that melt when current exceeds a predetermined value. Small
thermal-type circuit breakers also provide overcurrent protection
for this class of circuit. As the size of circuits and systems
increases, the problems associated with interruption of large fault
currents dictate the use of power circuit breakers. Normally these
breakers are not equipped with elements to sense fault conditions,
and therefore overcurrent relays are applied to measure the current
continuously. When the current has reached a predetermined value,
the relay contacts close. This actuates the trip circuit of a
particular breaker, causing it to open and thus isolate the fault.
See Circuit breaker
Distance protectionDistance-type relays operate on the
combination of reduced voltage and increased current occasioned by
faults. They are widely applied for the protection of higher
voltage lines. A major advantage is that the operating zone is
determined by the line impedance and is almost completely
independent of current magnitudes.
Overvoltage protectionLightning in the area near the power lines
can cause very short-time overvoltages in the system and possible
breakdown of the insulation. Protection for these surges consists
of lightning arresters connected between the lines and ground.
Normally the insulation through these arresters prevents current
flow, but they momentarily pass current during the high-voltage
transient to limit overvoltage. Overvoltage protection is seldom
applied elsewhere except at the generators, where it is part of the
voltage regulator and control system. In the distribution system,
overvoltage relays are used to control taps of tap-changing
transformers or to switch shunt capacitors on and off the circuits.
See Lightning and surge protection
Undervoltage protectionThis must be provided on circuits
supplying power to motor loads. Low-voltage conditions cause motors
to draw excessive currents, which can damage the motors. If a
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low-voltage condition develops while the motor is running, the
relay senses this condition and removes the motor from service.
Underfrequency protectionA loss or deficiency in the generation
supply, the transmission lines, or other components of the system,
resulting primarily from faults, can leave the system with an
excess of load. Solid-state and digital-type underfrequency relays
are connected at various points in the system to detect this
resulting decline in the normal system frequency. They operate to
disconnect loads or to separate the system into areas so that the
available generation equals the load until a balance is
reestablished.
Reverse-current protectionThis is provided when a change in the
normal direction of current indicates an abnormal condition in the
system. In an ac circuit, reverse current implies a phase shift of
the current of nearly 180 from normal. This is actually a change in
direction of power flow and can be directed by ac directional
relays.
Phase unbalance protectionThis protection is used on feeders
supplying motors where there is a possibility of one phase opening
as a result of a fuse failure or a connector failure. One type of
relay compares the current in one phase against the currents in the
other phases. When the unbalance becomes too great, the relay
operates. Another type monitors the threephase bus voltages for
unbalance. Reverse phases will operate this relay.
Reverse-phase-rotation protectionWhere direction of rotation is
important, electric motors must be protected against phase
reversal. A reverse-phase-rotation relay is applied to sense the
phase rotation. This relay is a miniature three-phase motor with
the same desired direction of rotation as the motor it is
protecting. If the direction of rotation is correct, the relay will
let the motor start. If incorrect, the sensing relay will prevent
the motor starter from operating.
Thermal protectionMotors and generators are particularly subject
to overheating due to overloading and mechanical friction.
Excessive temperatures lead to deterioration of insulation and
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increased losses within the machine. Temperature-sensitive
elements, located inside the machine, form part of a bridge circuit
used to supply current to a relay. When a predetermined temperature
is reached, the relay operates, initiating opening of a circuit
breaker or sounding of an alarm.
EarthingIt is common knowledge that Earthing, and especially
Bonding, plays a most dominating role when it comes to personnel
Safety and prevention of Fire and Explosions. What is seldom
appreciated is that EARTHING plays a fundamental role in preventing
over-voltage conditions. Hence it impacts on the short and long
term LIFE of electrical equipment, such as the motors, lights
fittings, etc. and electronic systems. At the low cost of
implementation there is no measure that is more cost-effective.
DIFFERENTIAL PROTECTIONIt is a very reliable method of
protecting generators, transformers, buses, and transmission lines
from the effects of internal faults.
Figure: Differential Protection of a Generator In a differential
protection scheme in the above figure, currents on both sides of
the equipment are compared. The figure shows the connection only
for one phase, but a similar connection is usually used in each
phase of the protected equipment. Under normal conditions, or for a
fault outside of the protected zone, current I1 is equal to current
I2 . Therefore the currents in the current transformers secondaries
are also equal, i.e. i1 = i2 and no current flows through the
current relay.
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If a fault develops inside of the protected zone, currents I1
and I2 are no longer equal, therefore i1 and i2 are not equal and
there is a current flowing through the current relay.
Differential Protection of a Station BusThe principle of the
differential protection of a station bus is the same as for
generators. The sum of all currents entering and leaving the bus
must be equal to zero under normal conditions or if the fault is
outside of the protected zone. If there is a fault on the bus,
there will be a net flow of current to the bus and the differential
relay will operate.
Figure: Single Line Diagram of Bus Differential Protection
Differential Protection of Three Phase Transformers Differential
protection of three phase transformers must take into account the
change in magnitude and phase angle of the transformed
current.Transformers Connected Y-Y or Delta-Delta
In these two connections, the primary and secondary currents are
in phase, but their magnitudes are different. The difference in the
currentmagnitude must be balanced out by the current transformer
ratios.
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Figure: Differential Protection for a Y-Y Connected Transformer.
If the transformer ratio is
The secondary currents of the current transformers are
During normal operating conditions or when the fault is outside
of the protection zone,
Therefore, the ratios of the current transformers on the two
sides of the power transformer must be
.
.
Sometimes standard current transformers with the ratios that
satisfy the above equation are not available. In that case
auxiliary transformers between one of the current transformers and
the relay are used.
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Transformers Connected Y-D or D -Y.The primary and secondary
currents have different magnitudes and they also have 30 phase
shift. Both, the magnitude and the phase shift must be balanced by
appropriate ratio and connection of the current transformers. The
phase shift on a Y-D bank is corrected by connecting the C.T.s on
the D in Y, and on the Y side in D.
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Cold Rolling Mill (C.R.M)
INTRODUCTIONCold rolling is a metalworking process in which
metal is deformed by passing it through rollers at a temperature
below its re crystallization temperature. Cold rolling increases
the yield strength and hardness of a metal by introducing defects
into the metal's crystal structure. These defects prevent further
slip and can reduce the grain size of the metal. Cold rolling is a
method of cold working a metal. When a metal is cold worked,
microscopic defects are nucleated throughout the deformed area.
These defects can be either point defects (a vacancy on the crystal
lattice) or a line defect (an extra half plane of atoms jammed in a
crystal). As defects accumulate through
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deformation, it becomes increasingly more difficult for slip, or
the movement of defects, to occur. This results in a hardening of
the metal.
If enough grains split apart, a grain may split into two or more
grains in order to minimize the strain energy of the system. When
large grains split into smaller grains, the alloy hardens as a
result of the Hall-Petch relationship. If cold work is continued,
the hardened metal may fracture. During cold rolling, metal absorbs
a great deal of energy. Some of this energy is used to nucleate and
move defects (and subsequently deform the metal). The remainder of
the energy is released as heat.
While cold rolling increases the hardness and strength of a
metal, it also results in a large decrease in ductility. Thus
metals strengthened by cold rolling are more sensitive to the
presence of cracks and are prone to brittle fracture. In C.R.M. we
get input (feeding) from Hot Steel Making (H.S.M) unit. In C.R.M
the sheet gets thinned forcefully.
The 1700 hot strip mill operates on slabs produced at the steel
making plant. It produces hot rolled sheets, coils and strips
suitable for ship building and the manufacture of pipes of small,
medium and large diameter, bodies of cars, buses and other
vehicles, railway wagons, transformers, boilers, big tanks,
machinery and formed sections. The hot rolled sheets are also
utilized for the production of cold rolled sheets. It has a
designed capacity of 445,000 tons. The cold rolling mill is a cold
reversible mill with 200,000 tons capacity, from which 10,000 tons
are turned into cold formed sections. The cold rolling mill
operates on hot rolled sheets and coils produced at the hot strip
mill. Cold rolled sheets are used for the production of bicycles,
steel fabrication, steel containers, drums, barrels, vehicle and
bus bodies, steel furniture, machinery parts, products and
appliances, oil and gas appliances etc. Cold rolled sheets are also
used for the production of galvanized sheets, and black plates and
tinplates. Galvanized sheets are used for containers, trunks,
boxes, packets, steel shuttering, desert coolers, construction and
roofing, ducting equipment, appliances, paneling, utensils,
air-conditioners, water heaters and fresh water tanks.
Cold and hot-formed sections are used for steel fabrications,
furniture, vehicle and bus bodies, building construction,
miscellaneous machinery and equipment/parts, steel doors and
windows. The combined slitting units and hot rolled coil conveyor
section of the cold rolling mill and the combined shearing unit and
profile bending units were put into operation. The operation of
the
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main cold rolling mill units marked the completion of the first
phase of a 1.1 million tons production of steel products.
The main products and specifications from the plant are as
follows: Hot rolled sheets have coils of thickness 1.6-10mm and
width 630-1500 mm, with a weight of 14.5 tons. Cold rolled sheets
have thickness of 0.30-2.5 mm, width 600-1500mm and length 1-4
meters. The weight of the coils is between 14.5 tons and 90 tons.
Galvanized sheets and coils have thickness 0.35-1.5 mm with width
700-1500 mm. The weight of the coils will vary between 6.5 tons and
100 tons.
The plant also produces formed angle sections with the following
dimensions: between 80x80 mm and 150x150mm. The lengths available
are up to 12 meters.
Semi-finished products such as blooms and slabs are reheated at
high temperatures in the reheating furnaces to make the metal
malleable and then rolled into finished products at the rolling
mills. PSMC currently has a Billet Mill, a Hot Strip Mill and a
Cold Rolling Mill.
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UNITS OF C.R.M:-
C.P.U(CENTRALISED PROCESSING UNIT)
REVERSIBLE ROLLING MILL
ANNEALING UNIT
TEMPER MILL UNIT
SHEARING Unit
SLITTING UNIT
GALVANIZING UNIT
COMBINE SHEARING AND SLITTING UNIT SECTION
FORMING UNIT(PROFILE BENDING UNIT)
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1) C.P.U(CENTRALISED PROCESSING UNIT):A central processing unit
(CPU) or processor is an electronic circuit that can execute
computer programs. This term has been in use in the computer
industry at least since the early 1960s (Week 1961). The form,
design and implementation of CPUs have changed dramatically since
the earliest examples, but their fundamental operation has remained
much the same. Early CPUs were custom-designed as a part of a
larger, sometimes one-of-a-kind, and computer. However, this costly
method of designing custom CPUs for a particular application has
largely given way to the development of mass-produced processors
that are made for one or many purposes. This standardization trend
generally began in the era of discrete transistor mainframes and
minicomputers and has rapidly accelerated with the popularization
of the integrated circuit (IC). The IC has allowed increasingly
complex CPUs to be designed and manufactured to tolerances on the
order of nanometers. Both the miniaturization and standardization
of CPUs have increased the presence of these digital devices in
modern life far beyond the limited application of dedicated
computing machines. Modern microprocessors appear in everything
from automobiles to cell phones and children's toys. Here the sheet
gets cleaned and is also cut from sides.
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2) REVERSIBLE ROLLING MILL:Reversible cold rolling mill is that
one stand of mill is laid out in the line, and strip will pass the
mill reciprocally till termination product. This line is
characteristic with low cost, small occupation and flexible
production. Here sheet gets thinned.
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3) ANNEALING UNIT:It is a process of heat treatment by which
glass and certain metals and alloys are rendered less brittle and
more resistant to fracture. Annealing minimizes internal defects in
the atomic structure of the material and leaves it free from
internal stresses that might otherwise be present because of prior
processing steps . Ferrous metals and glass are annealed by heating
them to high temperatures and cooling them slowly; copper and
silver, however, are best annealed by heating and cooling quickly,
then immersing in water. Large masses of metal or glass are cooled
within the heating furnace; sheets are usually annealed in a
continuous-process furnace. They are carried on a moving table
through a long chamber in which the temperature is carefully graded
from initial heat just below the softening point to that of room
temperature at the end. Annealing time, especially of glass, varies
widely according to the thickness of the individual piece; window
glass, for example, requires several hours; plate glass, several
days; and glass mirrors for reflecting telescopes, several months.
Annealing is required as an intermediate step in metal-forming
processes such as wire drawing or brass stamping in order to
restore the ductility of the metal lost because of work hardening
during the forming operation The output from annealing unit goes
into temper mill.
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4) TEMPER MILL UNIT:A temper mill is a steel sheet and/or steel
plate processing line composed of a horizontal pass cold rolling
mill stand, entry and exit conveyor tables and upstream and
downstream equipment depending on the design and nature of the
processing system. A typical type of temper mill installation
includes entry equipment for staging and accepting hot rolled coils
of steel which have been hot wound at the end of a hot strip mill
or hot rolled plate mill. Also included in a typical temper mill
installation are pinch rolls, a leveler (sometimes two levelers),
and a shear for cutting the finished product to pre-determined
lengths, a stacker for accumulating cut lengths of product into a
bundle.
Sometimes a temper mill installation includes a re-coil line
where the finished product is a coil instead of bundles of cut
lengths of product. Maximum product flexibility capability could be
attained if the installation was arranged to produce both coils and
bundles of cut to length product.
The heart of the temper mill is the cold rolling mill stand
which produces the temper pass. It will include electric powered
drive motors and speed reduction gearing suited to the process
desired. The design of the rolling mill can be a 2-high or 4-high
(even 6-high in some cases). The mill stand can be work roll driven
or back up roll driven. The mill can be designed with hydraulic
work roll bending and/or back up roll bending. Installations
typically have a single rolling mill stand, but may have two. Pinch
rolls provide back tension for the pay off reel in the entry
section and entry and exit tension for the temper pass. The primary
purpose of a temper mill is to improve the surface finish on steel
products
The process goal is physical property enhancement through cold
forming of the steel product in the bite of the work rolls. The
physical properties that are enhanced by the temper pass due to
elongation of the product include: Dimensional trueness and
repeatability Suppression of yield point elongation Improved
product surface finish Improve product shape and flatness Decrease
coil memory
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Increase product yield strength Develop proper stiffness or
temper
Typical elongation produced in the product is 0.5% to 2%.
Product dimensions vary. Thicknesses include typical sheet metal
gauges up to 3/4" thick plate. Widths vary from 36" to 125". The
finish of the rolled product is controlled by using rolls having a
variety of surface finishes designed to impart the desired finish
to the product. Roll finishes range from ground and polished rolls
to impart a bright finish, to shot-blasted or electric-discharged
textured rolls that produce a dull, velvety finish on the steel
surface.
Typical auxiliary equipment includes PLC based controls,
overhead traveling cranes, roll changing equipment, roll grinding
equipment, hydraulic power unit(s), bundle lifting devices, Coil
handling devices, etc.
The output from temper unit goes into either sharing unit or
slitting unit.
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5) SHEARING UNIT:Shearing is a process for cutting sheet metal
to size out of a larger stock such as roll stock. Shears are used
as the preliminary step in preparing stock for stamping processes,
or smaller blanks for CNC presses. Material thickness ranges from
0.125 mm to 6.35 mm (0.005 to 0.250 in). The dimensional tolerance
ranges from 0.125 mm to 1.5 mm (0.005 to 0.060 in). The shearing
process produces a shear edge burr, which can be minimized to less
than 10% of the material thickness. The burr is a function of
clearance between the punch and the die (which is nominally
designed to be the material thickness), and the sharpness of the
punch and the die Material selected for shearing should be standard
stock sizes to minimize the extra costs associated with special
slitting. Burrs and hold down marks which are inevitable, should be
considered in the design of the end product. Burrs should be kept
away from handling areas, preferably folded away, or in some
obscure area. The same can be done with hold down marks too.
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6) SLITTING UNIT:The slitting mill was a watermill for slitting
bars of iron into rods. The rods then were passed to nailers who
made the rods into nails, by giving them a point and head. The
slitting mill was probably invented near Liege in what is now
Belgium. The first slitting mill in England was built at Dart ford,
Kent in 1590. This was followed by one on Kinnock Chase by about
1611, and then Hyde Mill in Kinder in 1627. Others followed in
various parts of the England where iron was made. However there was
a particular concentration of them on the River Stour between
Stourbridge and Stourport, where they were conveniently placed to
slit iron that was brought up (or down) the River Severn before it
reached nailers in the Black Country. The slitting mill consisted
of two pairs of rolls turned by water wheels. Mill bars were flat
bars of iron about three inches wide and half an inch thick. A
piece was cut off the end of the bar with shears powered by one of
the water wheels and heated in a furnace. This was then passed
between flat rolls which made it into a thick plate. It was then
passed through the second rolls (known as cutters), which slit it
into rods. The cutters had intersecting grooves, which sheared the
iron lengthways.
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7) GALVANIZING UNIT:In this unit iron is painted with a
suspension of zinc particles in an organic solvent, so that a zinc
coating remains following evaporation of the solvent. The principal
method of making steel resist corrosion is by alloying it with
metal, zinc. When steel is submerged in melted zinc, the chemical
reaction permanently bonds the zinc to the steel through
galvanizing. Therefore, the zinc isn't exactly a sealer, like
paint, because it doesn't just coat the steel; it actually
permanently becomes a part of it. The zinc goes through a reaction
with the iron molecules within the steel to form galvanized steel.
The most external layer is all zinc, but successive layers are a
mixture of zinc and iron, with an interior of pure steel. These
multiple layers are responsible for the amazing property of the
metal to withstand corrosion-inducing circumstances, such as
saltwater or moisture. Zinc also protects the steel by acting as a
"sacrificial layer." If, for some reason, rust does take hold on
the surface of galvanized steel, the zinc will get corroded first.
This allows the zinc that is spread over the breach or scratch to
prevent rust from reaching the steel. The degree of galvanizing is
usually represented as the zinc's weight per surface area rather
than the thickness of the zinc, because this gives a better
representation of how much metal has been applied. Steel often gets
galvanized after individual parts have been formed, such as braces,
nails, screws, beams, or studs. However, raw galvanized steel in
sheets will withstand some bending and forming without flaking.
Galvanized steel can be found almost everywhere. You might be
living in a steel frame house. You are no doubt surrounded by steel
parts in your car that allow it to emerge from rainstorms
unscathed. Many people work in an office with metal roofing made of
galvanized steel. Besides being inexpensive and effective, this
metal is popular because it can be recycled and reused multiple
times.
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8) COMBINE SHEARING AND SLITTING UNIT:Input from Hot Steel
Making (H.S.M) also goes into this unit.
9) SECTION FORMING UNIT (PROFILE BENDING UNIT):Rolling is a
fabricating process in which the metal, plastic, paper, glass, etc.
is passed through a pair (or pairs) of rolls. There are two types
of rolling process, flat and profile rolling. In flat rolling the
final shape of the product is either classed as sheet (typically
thickness less than 3 mm, also called "strip") or plate (typically
thickness more than 3 mm). In profile rolling the final product may
be a round rod or other shaped bar, such as a structural section
(beam, channel, joist etc). Rolling is also classified according to
the temperature of the metal rolled. If the temperature of the
metal is above its re crystallization temperature, then the process
is termed as hot rolling. If the temperature of the metal is below
its re crystallization temperature, the process is termed as cold
rolling. Another process also termed as 'hot bending' is induction
bending, whereby the section is heated in small sections and
dragged into a required radius. Heavy plates tend to be formed
using a press process, which is termed forming, rather than
rolling. Output from Combine Sharing and Slitting Unit go
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DIGRAMATIC EXPLANATION
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Steel Making Department (SMD)
IntroductionSteelmaking is the second step in producing steel
from iron ore. In this stage, impurities such as sulfur,
phosphorus, and excess carbon are removed from the raw iron, and
alloying elements such as manganese, nickel, chromium and vanadium
are added to produce the exact steel required. Basic oxygen
steelmaking is a method of primary steelmaking in which carbon-rich
molten pig iron is made into steel. Blowing oxygen through molten
pig iron lowers the carbon content of the alloy and changes it into
low-carbon steel. The process is known as basic due to the pH of
the refractorycalcium oxide and magnesium oxidethat line the vessel
to withstand the high temperature of molten metal.
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The process was developed in 1948 by Robert Durer and
commercialized in 19521953 by Austrian VOEST and AMG. The LD
converter, named after the Austrian towns Linz and Donawitz (a
district of Leoben) is a refined version of the Bessemer converter
where blowing of air is replaced with blowing oxygen. It reduced
capital cost of the plants, time of smelting, and increased labor
productivity. Between 1920 and 2000, labor requirements in the
industry decreased by a factor of 1,000, from more than 3
worker-hours per ton to just 0.003. The vast majority of steel
manufactured in the world is produced using the basic oxygen
furnace; in 2000, it accounted for 60% of global steel output.
Modern furnaces will take a charge of iron of up to 350 tons and
convert it into steel in less than 40 minutes, compared to 1012
hours in an open hearth furnace. Steel making department is one of
the most important departments in whole steel mill. Because of this
department it is called steel mill. Here iron is converted into
steel. Steel making department converts pig iron into steel that is
transferred from iron making department to SMD through locomotive
railway in ladle. The pig iron in molten form is first transferred
into mixer. Then from mixer it is transferred to converter where
other raw materials are also transferred to converter. Then it is
heated and after oxidation steel and slag becomes separate. Then
they are taken out separately. After than steel is given several
shapes as needed.
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Converter in Pakistan Steel Mill:The Steel Making Plant Complex
has two Linz. Donawitz converters. Each converter has a capacity of
130 tons of steel for which there is one bloom caster and two slab
casters. Molten metal from the blast furnace is taken to the steel
making plant where further reduction of impurities is done in an
oxygen furnace (Linz Donawitz converters). The crude steel in
liquid form is taken in a ladle for further refining, where
ferroalloys are added to the liquid steel.
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Casting Method:PSMC employs continuous casting technology to
cast the liquid steel into semi-finished products (i.e. cast
billets, blooms and slabs). Cast billets are sold without any
further processing whereas blooms and the slabs are further
processed at the Billet Mill and the Hot Strip Mill respectively.
Bloom 260 x 260 mm sizes are used for making billets which are
utilized for manufacturing various steel products. The slabs of
150-200 mm thickness and 700-1500 mm width sizes produced at the
Steel Making Plant are fed to the hot strip mill where they are
rolled into stripes, sheets and coils.
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Electronic lab
SMD has a separate lab to control and monitor whole process of
steel making. Because movement of whole machine is controlled
through electronics. This lab is also responsible to repair things.
The electronic section deals with the solid state electronic
devices on the plant. It is subdivided into four categories for
convenience. a) b) c) d) Analog lab Digital lab Misc.lab Electro
drive lab
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a) ANALOG LABThis lab is responsible for the repair and
maintenance of the analog devices of the plant such as regulated
and un-regulated power supply, automatic summation sub-units etc
This lab has following systems: a) Analog gauge system (AGS):
interlink the primary and secondary devices. b) Face code converter
system: generator, register, memory, 3 phase amplifier, comparator,
counter, galvanic separator and transformer. c) Force measurement
panel: shaper card, power supply. d) Selling: mechanical to
electrical. e) Tension system card: sheet level and angle.
b) Digital lab:This lab is concerned with the digital equipments
on the plant which includes the entire process computerized system.
In this lab checking stands are available in order to check the
digital cards that are used in the control rooms. This lab is
mostly concerned with the following equipments: 1) 2) 3) 4) 5) 6)
7) 8) A/D converter D/A converter ROM+RAM Microprocessor Phase code
converter Timer Digital display Force analog lab(primary) a) Selcin
(Mechanical to electrical) b) AGS (analog gauge control system) c)
Checking stand(face code converter system) 9) 3 phase generator 10)
Comparator 11) Galvanic separator
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12) Counter 13) Transformer 14) Memory
c) Misc.lab:This lab deals with the miscellaneous devices on the
plant which includes: a) b) c) d) e) Controllers Timer Relay
Counter and converters Other miscellaneous devices etc
D) Electro-drive lab:It deals with all types of motors that are
used on the plant. It also deals with the high power supply to this
heavy machinery. It deals with the following equipments: a) b) c)
d) Thyristor Synchronous motors Asynchronous motors Dc motors
Any other equipment related to motors
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PLC in SMD:A programmable logic controller (PLC) or programmable
controller is a digital computer used for automation of
electromechanical processes, such as control of machinery on
factory assembly lines, amusement rides, or light fixtures. PLCs
are used in many industries and machines. Unlike general-purpose
computers, the PLC is designed for multiple inputs and output
arrangements, extended temperature ranges, immunity to electrical
noise, and resistance to vibration and impact. Programs to control
machine operation are typically stored in batterybacked or
non-volatile memory. A PLC is an example of a hard real time system
since output results must be produced in response to input
conditions within a bounded time, otherwise unintended operation
will result. The functionality of the PLC has evolved over the
years to include sequential relay control, motion control, process
control, distributed control systems and networking. The data
handling, storage, processing power and communication capabilities
of some modern PLCs are approximately equivalent to desktop
computers. PLC-like programming combined with remote I/O hardware,
allow a general-purpose desktop computer to overlap some PLCs in
certain applications. Regarding the practicality of these desktop
computer based logic controllers, it is important to note that they
have not been generally accepted in heavy industry because the
desktop computers run on less stable operating systems than do
PLCs, and because the desktop computer hardware is typically not
designed to the same levels of tolerance to temperature, humidity,
vibration, and longevity as the processors used in PLCs. In
addition to the hardware limitations of desktop based logic,
operating systems such as Windows do not lend themselves to
deterministic logic execution, with the result that the logic may
not always respond to changes in logic state or input status with
the extreme consistency in timing as is expected from PLCs. Still,
such desktop logic applications find use in less critical
situations, such as laboratory automation and use in small
facilities where the application is less demanding and critical,
because they are generally much less expensive than PLCs. In more
recent years, small products called PLRs (programmable logic
relays), and also by similar names, have become more common and
accepted. These are very much like PLCs, and are used in light
industry where only a few points of I/O (i.e. a few signals coming
in from the real world and a few going out) are involved, and low
cost is desired. These small devices are typically made in a common
physical size and shape by several manufacturers, and branded by
the makers of larger PLCs to fill out their low end product range.
Popular names include PICO Controller, NANO PLC, and other names
implying very small controllers. Most of these have between 8 and
12 digital inputs, 4 and 8 digital outputs, and up to 2 analog
inputs. Size is usually about 4" wide, 3" high, and 3" deep. Most
such devices include a tiny postage stamp sized LCD screen for
viewing simplified ladder logic (only a very small portion of the
program being visible at a given time) and status of I/O points,
and typically these screens are accompanied by a 4-way rocker
push-button plus four more separate push-buttons, similar to the
key buttons on a VCR
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remote control, and used to navigate and edit the logic. Most
have a small plug for connecting via RS-232 or RS-485 to a personal
computer so that programmers can use simple Windows applications
for programming instead of being forced to use the tiny LCD and
push-button set for this purpose. Unlike regular PLCs that are
usually modular and greatly expandable, the PLRs are usually not
modular or expandable, but their price can be two orders of
magnitude less than a PLC and they still offer robust design and
deterministic execution of the logic. In SMD two types of PLCs are
used. Their names are as follows: 1) Siemens S5 2) Mitsubishi
E100
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Siemens S5The Simatic S5 PLC is an automation system based on
Programmable Logic Controllers. It is manufactured and sold by
Siemens AG. Such automation systems control process equipment and
machinery used in manufacturing. This product line is considered
obsolete, as the manufacturer has since replaced it with their
newer Simatic S7 PLC. However, the S5 PLC still has a huge
installation base in factories around the world. Most automation
systems integrators still have the ability to provide support for
the platform.
HardwareThe S5 line comes in the 90U, 95U, 101U, 100U, 105,
115U, 135U, and 155U chassis styles. Higher the number, the more
sophisticated and more expensive the system. Within each chassis
style, several CPUs are available, with varying speed, memory, and
capabilities. Some systems provide redundant CPU operation for
ultra-high-reliability control, as used in pharmaceutical
manufacturing, for example. Each chassis consists of a power
supply, and a backplane with slots for the addition of various
option boards. Available options include serial and Ethernet
communications, digital input and output cards, analog signal
processing boards, counter cards, and other specialized interface
and function modules.
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SoftwareThe S5 product line is usually programmed with a PC
based software programming tool called Step 5. Step 5 is used for
programming, testing, and commissioning, and for documentation of
programs for S5 PLCs. The original Step 5 versions ran on the CPM
operating system. Later versions ran on MS-DOS, and then versions
of Windows through Windows XP. The final version of Step 5 is
version 7.2. No further development of this product line has
occurred since that time, due to its announced obsolescence. In
addition to Step5, Siemens offered a proprietary State logic
programming package called Graph5. Graph5 is a sequential
programming language intended for use on machines that normally run
through a series of discrete steps. It simulates a State machine on
the S5 platform. Several third-party programming environments have
been released for the S5. Most closely emulate Step5, some adding
macros and other minor enhancements, others functioning drastically
differently than Step5. One allows Step5 programs to be
cross-compiled to and from the C programming language and
BASIC.
Structured programmingSTEP 5 allows the creation of structured
or unstructured programming, from simple AND/OR operations up to
complex subroutines. A STEP 5 program may, therefore, contain
thousands of statements. To maintain maximum transparency, STEP 5
offers a number of structuring facilities: Block technique - A
linear operation sequence is divided into sections and packed into
individual blocks. Segments - Within blocks, fine structuring is
possible by programming subtasks in individual segments. Comments -
Both a complete program as well as individual blocks or segments
and individual statements can be directly provided with
comments.
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Methods of representationSTEP 5 programs can be represented in
three different ways:
Statement List (STL) - The program consists of a sequence of
mnemonic codes of the commands executed one after another by the
PLC. Ladder Diagram (LAD) - Graphical representation of the
automation task with symbols of the circuit diagram Function Block
Diagram (FBD) - Graphical representation of the automation task
with symbols to DIN 40700/ DIN 40719.
Absolute or symbolic designations can be used for operands with
all three methods of representation. In LAD and FBD complex
functions and function block calls can be entered via function
keys. They are displayed on the screen as graphical symbols.
BlocksFive types of blocks are available: Organization blocks
(OB) - for managing the control program Programming blocks (PB) -
contain the control program structured according to functional or
process-oriented characteristics Sequence blocks (SB) - for
programming sequential controls Function blocks (FB) - contain
frequently occurring and particularly complex program parts Data
blocks (DB) - for storing data required for processing the control
program.
Some S5 PLCs also have block types FX (Extended Function
Blocks), and DX (Extended Data Blocks); these are not distinct
block types, but rather are another set of available blocks due to
the CPU having more memory and addressing space.
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OperationsSTEP 5 differentiates between three types of
operations: Basic operations, (e.g. linking, saving, loading &
transferring, counting, comparing, arithmetic operations, module
operations) - These can be performed in all three representations.
Supplementary operations and complex functions, (e.g. substitution
statements, testing functions, word-by-word logic operations,
decrement/increment and jump functions.) These can only be executed
in STL. System operations (direct access the operating system) -
These can only be executed in STL.
Additional functions Saving user-specific project settings
Symbol editor Automatic generation and updating of cross-reference
lists Comparison of user programs Transferring blocks to EPROM and
EEPROM memory modules for programmable controllers Rewiring inputs,
outputs, flags, timers and counters Testing and service functions
for startup and maintenance
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Electrical sectionThis section is responsible for entire
electrical system in the plant. It make sure that the electrical
equipments on the plant are maintained and working properly. It
deals with all the electrical equipments ranging from low voltage
as low voltage as low as 240 volts to very high voltage of 11 kV.
This section is also responsible for the proper distribution of
electricity to the entire plant. Electrical section has three main
branches: a) Low voltage protection 240v-1000v b) High voltage
protection 6.6kv-11kv c) Relay protection. The equipment with which
the electrical section is concerned is: a) b) c) d) e) Breakers.
Transformer. Thyristors. Relays. Other related equipment.
All these devices or equipments are either of low voltage or
high voltage
Relays:Relays are very important for protection and switching in
an electrical system. And it is of vital concern in the electrical
section. A relay is an electrical operated switch. Many relays use
as electromagnet to operate switching mechanism mechanically, but
other operating principles are also used. Relay are used where it
is necessary to control a circuit by a low-power signal (wit
complete electrical isolation between control and controlled
circuits), or where several circuits be controlled by one signal.
The first relay was used in long distance telegraph circuit
repeating the signal coming in from one circuit and re-transmitting
it to another. Relay was used extensively in telephone exchanges
and early computers to perform logical operation. Types of relay
used in Pakistan steel are: 1) Electronic relays. 2)
Electromagnetic relays. a) Rota tic armature relay.
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b) Hinged armature relay c) Plunger or solenoid relay 3)
Induction relay. 4) Thermal relay. 5) Buchholz relay. These entire
relay are operated differently and are used according to needs,
some are of high power and some are of low power.
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Instrumentation sectionThis section deals with all types of
primary instruments that are installed on the locations from where
a parameter is to be measured. This section is responsible for the
repair, maintenance of the instrument and manufacturing of new
primary instruments. This section has following lab: a) b) c) d) e)
Pressure and flow lab. Temperature lab. X-ray lab Electric
measuring instruments lab Pneumatics lab
a) Pressure and flow lab:This lab is concerned with the
instruments that are used to measure the pressure and flow of
fluids throughout the plant. Instruments used to measure pressure
are called pressure gauges or vacuum gauges A manometer could also
be referring to a pressure measuring instrument, usually limits to
measuring pressures near to atmospheric. The term manometer is
often used to refer specially to liquid column hydrostatic
instruments. Absolute pressure is zero referenced against a perfect
vacuum, so it is equal to gauge pressure plus atmospheric pressure.
Gauge pressure is zero referenced against ambient air pressure, so
it is equal to absolute pressure minus atmospheric pressure.
Negative signs are usually omitted. Differential pressure is the
difference in pressure between two points.
Orifice plate:An orifice plate with a hole through it, placed in
the flow, it constricts the flow and measuring the pressure
differential across the constriction gives the flow rate. It is
basically a crude form of venture meter, but with higher energy
losses. There are three types of orifice:
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a) Concentric b) Eccentric c) Segmental
B) Temperature lab:This lab deals with the primary temperature
indicating instruments. There are three types of temperature
indication instruments used in Pakistan steel. 1) 2) 3)
Thermocouple RTDS Optical pyrometer
1) Thermocouple:A thermocouple is a junction between two
different metals that produces a voltage related to a temperature
difference. Thermocouple is a widely used type of temperature
sensor for measurement and control and can also be used to convert
heat into electric power. They are intensive and interchangeable
are supplied fitted with standard connectors and can measure a wide
range of temperatures. The main limitation is accuracy: system
error of less than one degree Celsius(c) can be difficult to
achieve Type B, S, R and K thermocouples are used extensively in
the steel and iron industries to monitor temperatures and chemistry
though out the steel making process. Disposable, immiscible, type S
thermocouples are regularly used in the electric arc furnace
process to accurately measure the temperature of steel before
tapping. The cooling curve of a small steel sample can be analyzed
and used to estimate the carbon content of molten steel.
2) RTDS:Resistance thermometers also called resistance
temperature Detectors or resistive thermal device (RTDS) are
temperature sensor that exploits the predictable change in
electrical resistance of some materials with changing temperature.
As they are almost invariably made of platinum, they are often
called platinum resistance thermometers
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(PRTs). They are slowly replacing the use of thermocouple in
many industries application below 600 degree centigrade due to
higher accuracy and repeatability
3) Optical pyrometer:A pyrometer is a non-contacting device that
intercepts and measures thermal radiation, a process known as
pyrometer. This device can be used to determine the temperature of
an objects surface. The word pyrometer comes from the Greek word
for fire pyre and meter meaning to measure. Pyrometer was
originally coined to denote a device capable of measuring
temperatures of object above incandescence (i.e. object bright to
the human eye) Temperature is the fundamental parameter in
metallurgical furnace operation. Reliable and continuous
measurement of the melt temperature is essential for effective
control of the operation. Smelting rates can be maximized, slag can
be produced at the optimum temperature, fuel consumption is
minimized and refractory life may also be lengthened. Thermocouple
was the traditional devices used for this purpose, but they are
unsuitable for continuous measurement because they rapidly
dissolve.
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ConclusionDuring course of my internship, I found that Pakistan
Steel Mill was set up with an objective to achieve a self reliant
and vibrant economy. Up to some extent it has been successful. But
due to ugly response of Government of Pakistan it is now in worst
condition of history. During my visits to different departments I
found that staff is very devoted to their work, they love to spend
time in mill, and they are good teachers as well. They explained
everything with good standards learned a lot about industrial
automation and instrumentation. These are core things for any
electronic engineer. By doing internship for whole 1 month I gain a
lot of confidence, learned that what professionalism is. During
this period I have overcome my many week points and mistakes.
Pakistan Steel has potential to provide a sound base for
industrialization and can provide stimuli for setting up of
downstream industries. It can also play a significant role in
purgation of technology and acquisition of new technologies. It has
also contributed billion of rupees to Gov. of Pakistan in past.,
but unfortunately this Biggest industrial unit of Pakistan is
suffering from various problems like lack of strategic direction,
weak financial position, due capital repair, lack cost control,
corruption and in efficient use of resources. After overcoming of
these problems, it can make its operation more efficient and once
again become a solid bar. May ALLAH once again give power to raise
Pakistan Steel Mill (AMEEN?)
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Suggestions Management must pay attention to the capital repair
of plant which otherwise will
prove costly for organization
Old conservative and costly employees should be replaced with
young intelligent, qualified and cheap generation
The person who are trained from abroad should not be allowed to
take VRF
Pakistan Steel should be free from politics
Proper orientation should be given to the market and sales
promotion activities
There are always need to improve working condition and safety
measures in the production unit
Pakistan steel can increase its profitability and efficiency by
promoting its downstream industries