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A Report On
MIGRATION TO HYDRAULIC TAPHOLE
MACHINERY FROM TRADITIONAL
ELECTRO-MECHANICAL ONES IN BF
VISAKHAPATNAM STEEL PLANT
BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE,
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This is to certify that the project titled ‘Migration to Hydraulic
machinery from traditional electro-mechanical ones’ is a bonafide
record of work done by Reetam Das, student of mechanical
engineering at BITS-Pilani Hyderabad campus under my guidance in
fulfillment of Project based training program offered by the Technical
Training Institute (TTI) of VSP during the period of 19th
May to 14th
June 2014. This is an original work and has not been submitted to
any other University or organization before.
I have ensured that the above mentioned has taken sufficient safety
precautions during his visit to the shop floor.
Dr. E.V.V. Gopala Krishna
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At the outset, I would like to thank Dr. E.V.V Gopala Krishna,
AGM(BF), VSP who gave me an opportunity to make the
project. His sincere support and helpful guidance helped in
the successful completion of the project.
I would also like to thank Mr. Raju, Mr. Venugopal, and Mr.
Amit Ranjan who helped me out in understanding the
operations of the plant.
I sincerely thank all the operators and employees of the three
Blast furnaces who took the effort to show me around.
Finally I would like to thank the Technical Training Institute
(TTI) of VSP to provide such opportunities for undergraduates
to explore and gain experience in the Steel Plant.
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TABLE OF CONTENTS
1. Introduction about Vizag steel plant
1.1 Background history
1.2 Journey through years
1.3 Product and plant facilities
1.5 Modern technologies
2. Blast furnace
2.1 Furnace operation and burden handling
2.2 Hot blast stoves
3. Tapping equipment
3.1 Taphole Drill
3.2 Technical details of drilling machine
3.3 Clay Gun
3.4 Technical details of the clay gun
4. Hydraulic System
4.2 Circuit diagram
5. Justification for migrating from Electromechanical System
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1.1 BACKGROUND HISTORY
Sri Tenneti Viswanatham was one of the founding fathers who
envisioned the establishment of the Vizag steel plant. He was an
outstanding poet, patriot, scholar and statesman. He took part in the
freedom struggle under the leadership of Mahatma Gandhi and was
imprisoned for eight years. Sri Tenneti Viswanatham had the all-
party agitation in 1966 demanding 5th integrated Steel plant for
Andhra Pradesh at Visakhapatnam. Struggle of thousands and lakhs
of such selfless people has paved a way for establishing such a big
The decision of the government of India to set up and integrated
steel plant at Vizag was announced by then Prime Minister Smt.
Indira Gandhi in Parliament on 17th
April 1970. The site near
Balacheruvu creak was chosen by the selection committee, and the
formal inauguration was done on 20th
January 1971 by the then
The activities kicked off by appointing site selection committee in
June 1970 and subsequently the committee‘s report was approved
for site. On 20th Jan 1971 the then Prime minister of India had laid
the foundation stone. Consultants were appointed in Feb 1971 and
feasibility reports were submitted by 1972. The first block of land
was taken over on 7th April 1974.
M/s M.N. Dastur & Co was appointed as the consultant for preparing
the detailed Project report in April 1975 and in Oct 1977 they had
submitted the report for 3.4 mtpa of liquid steel production.
With the Government of erstwhile USSR‘s offer for assistance, a
revised project concept was evolved.
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Detailed Project Report (DPR) for a plant capacity of 3.4 Mtpa was
prepared by M/s M.N. Dastur & Co in Nov 1980. In Feb 1981 Contract
was signed with Soviet-Union for preparation of working drawings
for Coke ovens, Blast Furnace and Sinter plant. The blast furnace
foundation was laid with 1st mass concreting in the project in Jan 82.
The construction of township also started.
Since Steel Authority of India Ltd. (SAIL) was unable to allocate funds,
a new company Rashtriya lspat Nigam Limited (RINL) was formed on
18th Feb. 1982. VSP was separated from SAIL and made a corporate
entity of RINL in April 1982.
The Project was estimated to cost Rs.3897.28 crores based on prices
as on 4th
quarter of 1981. But during the implementation of VSP it
has been observed that the project cost has increased substantially
over the sanctioned cost, mainly due to price escalations and under
provisions in DPR estimates; in view of this and the critical fund
situation, alternatives for implementation of VSP with rationalization
of approved concept were studied in 1986. The rationalization has
basically been form the point of view of obtaining the maximum
output from the equipment already installed, planned for
procurement, achieving higher levels of operational efficiency and
labor productivity over what was envisaged earlier Under the
rationalized concept, 3.0 million tons of liquid steel had to be
produced in a year and the project was estimated to cost Rs. 5822.17
crores bases as on fourth quarter of 1987.
The first Blast furnace was blown on 28th Mar 1990.
On 3rd May 1990 the then prime minister dedicates ‘Godavari’ to the
nation. The year 1990 is marked in the history of VSP with
commissioning of major units. A few of them include Converter No.1
CCM and No. 3 of SMS in Sept’90, Billet production in LMMM, rolling
of Wire Rods from 21 Nov’90 and commissioning of Turbo Generator
no.3 in Dec’90.
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In the year 1991 CCM no. 1 & 4, Converter No. 2 of SMS, Lime
Calcining plant and Dolomite Calcining plant, Bar mill of LMMM,
Coke oven battery No. 2 and Sinter machine No. 2 were
The year 1992 was a spectacular year for VSP. On 20th March, 1992
Medium merchant and structural mill was commissioned and on 21st
March’92 the second blast furnace ‘Krishna’ was commissioned.
Remaining units were also commissioned. Coke Oven battery No. 3
which was commissioned on 30th July’92 marked the completion of
commissioning of all units of the 3 Million tonne plant.
1.2 JOURNEY THROUGH THE YEARS
Vizag Steel Plant, the first coastal based steel plant of India is located
16 KM southwest city of destiny i.e.Vizag. Bestowed with modern
technologies, VSP has an installed capacity of 3 Million Tons per
annum of Liquid Steel and 2.656 Million tons of saleable steel.
VSP has the distinction to be the 1st
integrated Steel Plant in India to
become a fully ISO – 9002 certified company. VSP by successfully
installing and operating efficiently Rs. 460 crore worth of pollution
Control and Environment Control Equipment’s and converting the
barren landscape by planting more than 3 million trees has made the
Steel Plant, Steel Township a greener, cleaner and cooler place,
which can boast of 3 to 4o
c lesser temperature even in the peak
summer compared to Vizag City. VSP exports Quality pig Iron & Steel
products to Sri Lanka, Myanmar, Nepal, Middle East, USA & South
East Asia (pig iron). RINL VSP was awarded “Star Trading House”
status during 1997-2000 for having established a fairly dependable
export market. VSP plans to make a continuous presence in the
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Having a total manpower of 17250 VSP has envisaged a labor
productivity of more than 230 tones per man per year of Steel which
is the highest in our country and comparable with the international
levels. VSP is the only integrated steel plant in the country to be
Certified for ISO 9001-2000, ISO-14001: 2004 and OSHAS
1.3 PRODUCTS AND PLANT FACILITIES
VSP produce angles, channels, bars, wire-rods billets for re-0rolling.
The plant also produces pig iron and around 1.44 million tons per
annum of granulated slag beside normal by-products from the coke-
oven and coal chemical plant.
VSP has the following major production facilities :
- 3 Coke oven batteries of 67 ovens each having 41.6 m3
- 3 Sinter machines of 312 m2
- 2 Blast furnace of 3200 m3
volume and one of 3800m3
- Steel melt shop with three LD converters (2 Operating and one
stand by) of 150 T capacity each and 6 No’s of 4 strand
continuous bloom casters.
- Light and Medium Merchant Mills of 710,000 tons per year
- Wire Rod Mills of 850,000 tons per year capacity.
- Medium Merchant & Structural Mills of 850,000 tons per year
Extensive facilities have been provided for repair and maintenance as
well as manufacturer of spare parts. A Power Plant Oxygen plant,
acetylene plant, compressed air plant etc. also form part of the plant
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1.4 MODERN TECHNOLOGIES IN STEEL MANUFACTURING
Vizag Steel Plant is the most sophisticated and modern integrated
steel plant in the country. Modern technology has been adopted in
many areas of production, some of them for the first time in the
country. Among these are:
- Selective crushing of coal
- 7 meter tall coke ovens
- Dry quenching of coke, using Nitrogen
- On ground blending of Sinter base mix.
- Conveyor charging and bell less top for blast furnace
- Cast house lag granulation for blast furnace
- 100% continuous casting of liquid steel
- Gas expansion turbine for power generation utilizing blast
furnace top gas pressure.
- Hot metal desulphurization
- Extensive treatment facilities of effluents for ensuring proper
- Computerization for process control.
- Sophisticated, high speed and high production rolling mills.
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2.1 FURNACE OPERATION AND BURDEN HANDLING
Hot Metal is produced in Blast Furnaces; the furnace is so named as
it is run with blast of air at high pressure & temperature. The air blast
is obtained from the captive Thermal Power Plant and heated in
stoves. Raw Materials such as sinter/Iron Ore Lumps, Fluxes
(Limestone/Dolomite) and Coke are charged from the top and hot
blast at around 1200deg C is blown from the bottom. The furnaces
are designed for 80% Sinter as the burden.
VSP has two 3200 m3
and one 3800m3
Blast Furnaces equipped with
Paul Wurth Bell less top charging. The first two are named as
‘Godavari’ & ‘Krishna’ after the two prominent rivers of AP. The two
furnaces are capable of producing 9720 tons of Hot Metal daily and
3.4 Million Tons of low sculpture Hot Metal annually. The third Blast
furnace has a capacity of 3800m3
and it produces 7150 tons/day.
Burden materials are received in the stock houses, one for each
furnace through a junction house. Coke is handled by two conveyors
(one stand by) 1600 mm width and 350 TPH capacity; sinter and
lump ore by two conveyors (one stand by) of 1400 mm width and
800 TPH capacities. Sized ore and additives are handled by one
reserve conveyor of 15 00 mm width and 800 TPH.
Junction house has a cross over through rolling reversible conveyor
and stationary reciprocating conveyor. For each furnace, there are 5
bins for sinter, 5 bins for coke, 3 bins for lump ore, 1 bin for nut coke,
3 bins each for limestone/LD slag and quartzite/used Silica bricks and
Coke, sinter and iron ore are screened in screens up to 400 m3/hr.
capacity to remove the fines. The screened material is fed to the
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inclined conveyor for burden handling to top through a horizontal
conveyor. Conveyors for burden handling to top are of 2000 mm
Width and 62160 m3/hr. capacity and are operated continuously.
The materials are positioned in conveyor in separate batches at
certain intervals and in a certain sequence as per pre-set
programme. PLC system is provided for batching, weighing and
feeding of the burden to the furnace top.
The Paul Wurth, bell loss top system is installed for furnace charging.
The system consists of two bunkers of 47 cubic meter capacity each,
charging through a rotating chute under the Hooper.
All drives are hydraulically operated except for chute rotation and
tilting which are electrically operated. Semi clean BF gas and nitrogen
are used for pressure equalisation in charging bunkers. Nitrogen is
used for cooling rotating trough drive and for blowing off stock bin
gates and sealing valves of charging arrangement. Mechanical gauge
rods are provided for measuring stock level.
Exhaust station and air cleaning plant are provided for handling
system. The exhaust air is directed to electrostatic precipitators (2
nos.) for cleaning. The plant capacity is 3.65x103
/hr. The dust
content of air is reduced from 2.85 gm/cum to 0.1 gm/cum, 200 tons
of dust is collected every day. The dust collected is balled in
granulation plant and is automatic transported in trucks to Sinter
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2.2 HOT BLAST STOVES
There are four hot blast stoves for each furnace (BF3 has only three
stoves) with a total heating surface of 224,000 m2. The dome can be
heated to a temperature of 1450degC maximum while the waste flue
temperature is up to 400degC. The stoves are capable of giving a
blast temperature up to
1300degC. Stoves are heated by a mixture of blast furnace gas and
coke oven gas having a calorific value of 1,100 Kcal/m3
. Pressure of
mixed gas before burners is 600mm W.C. Gas mixing station is
provided to mix BF gas, CO gas in required proportion and to get the
necessary Calorific value.
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High temperature zone is lined with silica and mullite corundum
refractories; medium temperature zone, with kaoline refractories
and low temperature zone with fire clay refractories. The shell of
dome and cylindrical part is heat insulated with a heat proof gunnite
concrete in high temperature zone. Gaps between shell and walls are
filled with mats from fibrous materials. Checker-work is lined with
hexahedral refractories with round cells of 41mm dia.
Combustion chamber is in-built construction of elliptical shape. The
chimney is of 80 m high, 3.5m diameter at the mouth. It is of
reinforced concrete and fire clay lined. Stack for back drought is
made of metal with refractory lining. Air supply for burners is
centralized. Three fans (one stand by) of 120,000 m3
each are provided for the purposes.
Water cooling arrangement has been provided for cooling of hot
blast valves and burner cut off valves.
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3.1 TAPHOLE DRILL
Also known as taphole opener, it is used to open a hole into the blast
furnace to extract molten Iron.
Main components of the taphole drill are:
Chain feed drive
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The swivelling movements are carried out by means of hydraulic
cylinder. For detection of the swivel angle, Electronic measurement
systems are installed in the cylinder.
The drill carriage mainly consists of the welded carriage, hydraulic
hammer with hydraulic rotation drive, hydraulic chain-drive with a
chain tensioning arrangement, front rod guidance.
The hydraulic hammer creates percussion effect on the drill bit which
helps in the drilling operation. This feature along with the flushing of
the drill bit eases the operation and sets it apart from the earlier
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The supply of hydraulic oil, water and nitrogen for the complete
machine is ensured by rotary couplings and fixable pipe connections.
Areas of the machine which are exposed to splatters of slag and iron
and radiation heat are protected by guard plates (example: cable
All movements are controlled by controlling hydraulics which will be
discussed later in this report. These are controlled and monitored by
sensors and limit switches.
The drill bits used are specially designed to reduce the effort in
drilling. They have holes in the end to allow use of water or nitrogen
for flushing thus cooling drill bit and also reducing effort. The
hammering effect of hydraulic hammer also reduces effort thus
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3.2 TECHNICAL DETAILS OF DRILLING MACHINE
General technical data:
Hydraulic operation pressure- 200bar
Maximum Carriage stroke- 4500mm
Effective drill stroke- 4000mm
Drilling angle- normal, 100
Drilling angle- adjusting range 8-12o
manually by spacers
Forward feeding speed- 1 to 2 m/min
Backward feed- 1 m/sec
Max feed force- 40KN
Type of hammer drill- HS 571 GHN
Operating pressure- Hammer 180bar
- Hammering 554 Nm
- Counter-hammering 472Nm
Number of impacts
- Hammering: 1765min-1
- Counter-hammering: 1666min-1
Operating pressure- rotor Max 205bar
Torque- 680Nm at 205bar
Rotor speed- 450rpm
Operating pressure: 6-7 bar
Consumption (flow): 3,5 m3
Water supply pressure: 3-5 bar
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Water flushing flow max: 4l/min
Spatial arrangement in the Plant:
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3.3 CLAY GUN
Also known as mud-gun, the clay-gun is used for plugging the taphole
after the molten metal has been extracted. Generally tar or plastic
bonded plugging mix is used to plug the hole.
The Clay gun is operated from the control room of the cast-house or
by a remote control. Complete automation option activated by the
control panel relieves operating personnel from physical danger.
The movements that are carried out are:
Swivelling of the extension arm from work or home position
Forward and backward movement of the plugging piston in the
Exact and reproducible positioning of the Clay Gun.
Constant, controlled material flow.
Maintenance friendly and easily accessible swivel-drive so
arranged that it is behind the main boom away from heat.
Lever system driven by hydraulic cylinder ensures high swivel
angle. The drive and arms are protected from splashing by
The base frame of the clay-gun includes bearing and hydraulic
swivel joints are bolted to an intermediate frame which is
directly welded to the cast-house floor supporting structure.
The gun rests in a virtually horizontal parking position with
excellent access for clay mass charging and cleaning operations.
The contact force is adjustable, at each tapping the contact
force at the furnace and the clay pressure are adjustable
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A guide rod controls the relative movement between the clay
gun and the slewing arm. At the taphole the nozzle path is
virtually linear following the iron trough centreline.
With length adjustments on the guide rod, the nozzle tip is
adjusted precisely to the taphole position.
A manual mechanical locking mechanism prevents uncontrolled
movements of the slewing arm during maintenance.
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The clay gun is supported by the Base frame which is fastened to the
intermediate bracket by means of screw and bolt. Additional
securing plates avoid torsion of the baseplate about the intermediate
plate. The intermediate plate is welded to the foundation plate
which supports the casthouse.
Steering device consisting of jib arm, plugging unit and the
Ramming gun consisting of the mass cylinder, plugging cylinder,
plugging piston and nozzle.
The plugging mass is filled into the cylinder through the mass
cylinder lid and is pressed into the taphole using the plugging piston.
The indicator device indicates the stroke of the plugging cylinder and
consequently the quantity of plugging mix pressed out of the gun.
A direct ramming cylinder creates the necessary clay mass thrust
force. The piston rod is hard-faced to prevent wear. The ramming
cylinder piston is built with a redundant dual chevron cover seal.
Should the exterior cover seal set wear out, a screw plug is fastened
and the pressure acts on the second interior seal. So the seal need
not be replaced until the next shutdown.
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The interior surface of the clay-barrel is hard-chromed for high wear
resistance. An insulated and water-cooled heat shield protects the
clay barrel and hydraulic ramming cylinder against heat and splashes.
Two bronze alloy piston rings seal the clay barrel/piston from leakage
during ramming. The piston rings can easily be replaced from the
front end of the barrel. The ramming gun is equipped with a hinged
nozzle to facilitate easy access to the barrel.
3.4 TECHNICAL DETAILS OF CLAY GUN
Mass pressure on plugging piston- 200bar (20MPa)
Plugging capacity- 4.10/sec
Plugging piston stroke-1380 mm
Clay gun time forward: 50-80 sec
Clay gun time backward: 40-50 sec
Nozzle diameter- 150 mm
Ramming angle: 10o
Swivelling radius: 3900 mm
Slewing angle without wake: 109o
Slewing angle with wake: 114o
Slewing time forward: 15-18 sec
Slewing time backward: 15-18 sec
Holding force on taphole: 340KN
Total weight: 21 000 Kgs
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Layout of the Drill and Clay gun on the casthouse:
There is a central hydraulic pump house for the entire BF Casthouse
equipment’s. For 2 pairs of Drill and Gun there is a valve stand room
on the casthouse which contains all the valves and is controlled from
the control room.
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The tapping equipment discussed is completely hydraulic operated.
The Electromechanical systems of the old Blast furnace are being
replaced with New Hydraulically operated equipment’s because of
their ease of operation maintenance and lower power consumption.
The study of the Hydraulic machinery is incomplete without the
study of the underlying hydraulic system consisting of the pipes and
pistons and the valves.
A Hydraulic system drive is a transmission system which uses
pressurised hydraulic fluid to drive the machinery.
A hydraulic drive system consists of 3 parts:
The generator: Consisting of a hydraulic pump driven by an
Valves, piping, filters etc. for guiding and controlling the
Actuator: can be a hydraulic driven motor or piston cylinder
arrangement to drive the machinery.
Basic principle of operation is that the force applied at one point is
transmitted to another through an incompressible fluid. Pascal’s Law
form the basis of hydraulics: Pressure = force*area. For the same
pressure a smaller piston feels small force and a larger piston feels
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The stationary pressure generating equipment supplies the machine
with the working and control pressure necessary for its operations.
The equipment for each casthouse comprises of an oil tank, a pump
station, 2 valve blocks for drives of the taphole drill and clay gun,
Cover manipulator and accumulator station.
Hydraulic pumps supply fluid to the components in the system.
Pressure in the system develops in reaction to the load. Pumps have
a power density about ten times greater than an electric motor (by
volume). They are powered by an electric motor or an engine,
connected through gears, belts, or a flexible elastomeric coupling to
Common types of hydraulic pumps to hydraulic machinery
Gear pump: cheap, durable and simple. These pumps are less
efficient because they are constant (fixed) displacement, and
mainly suitable for pressures below 20 MPa (3000 psi).
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Vane pump: cheap and simple, reliable. Good for higher-flow
Axial piston pump: many designed with a variable displacement
mechanism, to vary output flow for automatic control of
pressure. There are various axial piston pump designs, including
swash plate (sometimes referred to as a valve plate pump) and
check ball (sometimes referred to as a wobble plate pump). The
most common is the swash plate pump. A variable-angle swash
plate causes the pistons to reciprocate a greater or lesser
distance per rotation, allowing output flow rate and pressure to
be varied (greater displacement angle causes higher flow rate,
lower pressure, and vice versa).
Radial piston pumps: normally used for very high pressure at
Directional control valves route the fluid to the desired actuator.
They usually consist of a spool inside a cast iron or steel housing. The
spool slides to different positions in the housing, and intersecting
grooves and channels route the fluid based on the spool's position.
The spool has a central (neutral) position maintained with springs; in
this position the supply fluid is blocked, or returned to tank. Sliding
the spool to one side routes the hydraulic fluid to an actuator and
provides a return path from the actuator to tank. When the spool is
moved to the opposite direction the supply and return paths are
switched. When the spool is allowed to return to neutral (center)
position the actuator fluid paths are blocked, locking it in position.
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Directional control valves are usually designed to be stackable, with
one valve for each hydraulic cylinder, and one fluid input supplying
all the valves in the stack.
The main valve block is usually a stack of directional control valves
chosen by flow capacity and performance. Some valves are designed
to be proportional (flow rate proportional to valve position), while
others may be simply on-off. The control valve is one of the most
expensive and sensitive parts of a hydraulic circuit.
Pressure relief valves are used on hydraulic cylinders, to
prevent overloading and hydraulic line/seal rupture and to
maintain a small positive pressure on the hydraulic reservoir.
Pressure regulators reduce the supply pressure of hydraulic
fluids as needed for various circuits.
Sequence valves control the sequence of hydraulic circuits; to
ensure that one hydraulic cylinder is fully extended before
another starts its stroke, for example.
Shuttle valves provide a logical <or> function.
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Check valves are one-way valves, allowing an accumulator to
charge and maintain its pressure after the machine is turned
off, for example.
Pilot controlled Check valves are one-way valve that can be
opened (for both directions) by a foreign pressure signal. For
instance if the load should not be held by the check valve
anymore. Often the foreign pressure comes from the other
pipe that is connected to the motor or cylinder.
Hydraulic fuses are in-line safety devices designed to
automatically seal off a hydraulic line if pressure becomes too
low, or safely vent fluid if pressure becomes too high.
This is the effecting end of the circuit which causes the required
movement either linear force or torque application. The piston
cylinder arrangement causes the arm to extend.
The hydraulic fluid reservoir holds excess hydraulic fluid to
accommodate volume changes from: cylinder extension and
contraction, temperature driven expansion and contraction, and
leaks. The reservoir is also designed to aid in separation of air from
the fluid and also work as a heat accumulator to cover losses in the
system when peak power is used. Design engineers are always
pressured to reduce the size of hydraulic reservoirs, while equipment
operators always appreciate larger reservoirs. Reservoirs can also
help separate dirt and other particulate from the oil, as the
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particulate will generally settle to the bottom of the tank. Heat
exchangers are also used to cool the oil to the right temperature.
Accumulators are a common part of hydraulic machinery. Their
function is to store energy by using pressurized gas. One type is a
tube with a floating piston. On one side of the piston is a charge of
pressurized gas and on the other side is the fluid.
At the event of loss of power, the accumulator ensures that the
actuator stays in that current position. Operator can also exploit the
stored pressure to perform some emergency maneuvers.
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Also known as tractor fluid, hydraulic fluid is the life of the hydraulic
circuit. It is usually petroleum oil with various additives. Some
hydraulic machines require fire resistant fluids, depending on their
In addition to transferring energy, hydraulic fluid needs to lubricate
components, suspend contaminants and metal filings for transport to
the filter, and to function well at high temperatures.
Filters are an important part of hydraulic systems. Metal particles are
continually produced by mechanical components and need to be
removed along with other contaminants.
Filters may be positioned in many locations. The filter may be located
between the reservoir and the pump intake. Blockage of the filter
will cause cavitation and possibly failure of the pump. Sometimes the
filter is located between the pump and the control valves. This
arrangement is more expensive, since the filter housing is
pressurized, but eliminates cavitation problems and protects the
control valve from pump failures. The third common filter location is
just before the return line enters the reservoir. This location is
relatively insensitive to blockage and does not require a pressurized
housing, but contaminants that enter the reservoir from external
sources are not filtered until passing through the system at least
Tubes, Piping, Hose:
Hydraulic tubes are seamless steel precision pipes, specially
manufactured for hydraulics. The tubes have standard sizes for
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different pressure ranges, with standard diameters up to 100 mm.
The tubes are supplied by manufacturers in lengths of 6 m, cleaned,
oiled and plugged. The tubes are interconnected by different types of
flanges (especially for the larger sizes and pressures), welding
cones/nipples (with O-ring seal), and several types of flare
connection and by cut-rings. In larger sizes, hydraulic pipes are used.
Direct joining of tubes by welding is not acceptable since the interior
cannot be inspected.
Hydraulic pipe is used in case standard hydraulic tubes are not
available. Generally these are used for low pressure. They can be
connected by threaded connections, but usually by welds.
Hydraulic hose is graded by pressure, temperature, and fluid
compatibility. Hoses are used when pipes or tubes cannot be used,
usually to provide flexibility for machine operation or maintenance.
The hose is built up with rubber and steel layers. A rubber interior is
surrounded by multiple layers of woven wire and rubber. The
exterior is designed for abrasion resistance. The bend radius of
hydraulic hose is carefully designed into the machine, since hose
failures can be deadly, and violating the hose's minimum bend radius
will cause failure. Hydraulic hoses generally have steel fittings
swaged on the ends. The weakest part of the high pressure hose is
the connection of the hose to the fitting. Another disadvantage of
hoses is the shorter life of rubber which requires periodic
replacement, usually at five to seven year intervals.
Tubes and pipes for hydraulic applications are internally oiled before
the system is commissioned. Usually steel piping is painted outside.
Where flare and other couplings are used, the paint is removed
under the nut, and is a location where corrosion can begin. For this
reason, in marine applications most piping is stainless steel.
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Seals, fittings and connection:
Components of a hydraulic system [sources (e.g. pumps), controls
(e.g. valves) and actuators (e.g. cylinders)] need connections that will
contain and direct the hydraulic fluid without leaking or losing the
pressure that makes them work. In some cases, the components can
be made to bolt together with fluid paths built-in. In more cases,
though, rigid tubing or flexible hoses are used to direct the flow from
one component to the next. Each component has entry and exit
points for the fluid involved (called ports) sized according to how
much fluid is expected to pass through it.
There are a number of standardized methods in use to attach the
hose or tube to the component. Some are intended for ease of use
and service, others are better for higher system pressures or control
of leakage. The most common method, in general, is to provide in
each component a female-threaded port, on each hose or tube a
female-threaded captive nut, and use a separate adapter fitting with
matching male threads to connect the two. This is functional,
economical to manufacture, and easy to service.
Fittings serve several purposes;
To join components with ports of different sizes.
To bridge different standards; O-ring boss to JIC, or pipe
threads to face seal, for example.
To allow proper orientation of components, a 90°, 45°, straight,
or swivel fitting is chosen as needed. They are designed to be
positioned in the correct orientation and then tightened.
To incorporate bulkhead hardware to pass the fluid through an
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A quick disconnect fitting may be added to a machine without
modification of hoses or valves.
Hydraulic systems are far more costly than their electromechanical
counterparts (approx. 4 times) but their maintenance requirement is
very less. One need to only ensure seals are in proper condition, the
fluid is free from particulate matter, filters are regularly cleaned and
temperature of oil is properly maintained.
On the contrary electromechanical systems have motors which need
to be frequently rewired, gears wear out, and constant greasing is
required. Also it consumes more power.
In Blast Furnace 1 the electromechanical system has been replaced
by the Hydraulic ones. The electromechanical system had completed
their life of 24 years so they anyway needed replacement.
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4.2 CIRCUIT DIAGRAM
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Justification for migrating from
Various factors need to be considered for justifying migration to
Hydraulic system from the electro-mechanical alternatives. Clients
demand a combination of rapid acceleration and deceleration, tight
positioning control, long life, and, of course high reliability.
The larger the mass that needs to be moved, the more likely it is that
motion bases will use hydraulics. Manufacturers have been able to
increase the capacity of electromechanical actuators, so they present
them as preferable to electrohydraulic systems.
However, many of the arguments minimize the advantages of
hydraulics over electromechanical systems and exaggerate the
disadvantages of hydraulics. Different motion bases have application
advantages based on their particular design.
Different arguments can be used depending on a variety of
situations; here we will focus our attention to the application of
casthouse machinery i.e. Clay Gun and Taphole drill.
SIZE AND POWER
Let us compare how an electromechanical actuator fares with that of
a hydraulic one in an experimental setup. Assume we need to lift and
hold a 20,000 lb payload for extended periods of time. This force can
be thought of the force that we put on the clay to extrude it through
nozzle (an overestimation nevertheless). Different types of kinematic
arrangements can be used but it is assumed that this result is based
on the optimal setup.
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The observation during experimentation is that the installed power
requirement is 20% more for an electric motion based system, and
consumption is greater. The most telling issue is when the motion
base operates near its mid-stroke position, with no motion being
commanded. In this case, the hydraulic valves feeding the cylinders
close, and the variable-displacement pump in the hydraulic power
unit (HPU) throttles to near zero displacement. This allows the HPU’s
motor pump to operate in a low energy consumption mode. The
electromechanical unit, on the other hand, must continue consuming
energy equal to the entire weight of the payload, generating heat.
In this case, the hydraulic system generates heat that requires about
3.2 tons of refrigeration (38,000 btu/hr or 11.1 kW) to stabilize
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temperature. However, the electric unit generates heat requiring 13
tons of refrigeration (156,000 btu/hr, or 45.7 kW). This point is
important because electrical systems are air cooled, so the
generated heat migrates to the surrounding environment, typically
occupied by people. Hydraulic systems reject less heat, and that heat
can be dissipated in a separate room through an air- or water-cooled
The bottom line: Electrical systems consume more energy than that
of hydraulic systems.
Both electric and hydraulic motion bases are typically designed for a
specific application with a clearly defined payload. If the payload
should increase, say, by 20%, an electromechanical system probably
would become overloaded. Electrical systems depend on precise
sizing of their motors. Suppliers rarely oversize these systems
because doing so would increase cost, which would jeopardize the
supplier winning the contract. If payload increases, the solution is
generally to scrap the old system and order a newer, larger, and
more expensive motion base.
A hydraulic system, on the other hand, can accommodate a much
wider range of operating parameters. Typically, a properly designed
hydraulic system can be overloaded up to 50% or more and still
operate effectively. But you don’t get something for nothing;
if you increase the operating pressure to handle larger payloads,
then you must re-stroke the HPU’s pump to avoid overloading the
motor. Doing so would sacrifice some dynamic performance to
handle the larger payload. However, installing a larger motor-pump
assembly could provide performance comparable to the original,
even with the higher payload.
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Unfortunately, this scenario is fairly common: a customer requests a
system designed for an 8000 lb payload but ultimately loads the
machine to 12,000 lb. An electrical system would need to be
replaced, but a hydraulic system may get by with reduced dynamic
performance or a larger HPU.
Assuming equal design criteria, accelerations and velocities that can
be obtained with hydraulic and electric systems are comparable. In
theory, electromechanical systems should be capable of higher
resolution because most of these systems use an encoder, resolver,
or similar feedback transducer. In reality, though, manufacturing
tolerances and design and assembly tolerances relegate the true
resolution to that comparable to hydraulic systems. Digital accuracy
relative to computer programming and theoretical computation can
be far different from the actual accuracy once machining and
fabrication tolerances are taken into account. Hence, hydraulic and
electric systems accuracies are comparable.
DURABILITY AND RELIABILITY
Hydraulic motion bases have proven to be far more durable than
their electrical counterparts. Many hydraulic motion bases have
been in operation for more than 60 years with virtually the same
hardware in place. Control and computer systems have changed and
been upgraded, but the physical components are original or as
original. Other than servo and proportional valves, essentially the
only moving parts in each actuator are the piston, rod, and bearings.
Developments in valves have made them reliable and durable— with
operational lives exceeding 30 years in most instances.
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Electric motion systems have been in operation for perhaps 15 years.
During that time, several have been replaced with hydraulic systems
for many dead weight bearing applications. Current designs use
either lead screw, ball screw or roller screw mechanisms for linear
motion. All of these contain a multitude of components to convert
rotational motion of an electric motor to linear motion. Planetary
rollers, roller balls, and the sliding motion of lead screws all require
generous amounts of lubrication. Such lubrication problem does not
exist in case of hydraulic system as the oil itself doubles up as
lubricant and coolant also.
Electromechanical motion bases require high voltage transmitted to
their actuators. Special precautions need to be taken to ensure such
systems are safe and meet national and code requirements.
Hydraulic systems, however, only require high voltage service at a
remote HPU. It is common for the hydraulic HPU to be located in a
room with limited access. Hence, only low control voltages are
required directly at the motion base. Thus hydraulic systems provide
a safer work environment for the employees.
Hydraulic systems require pressurized hoses routed to each of the
actuators under servo valve control. Typically system pressures run
from 1000 to 1500 psig. These pressures are easily and safely
handled by two-wire-braid hoses commonly rated for working
pressures to 3000 psig and burst pressures well above that. Leaks are
virtually eliminated by using SAE O-ring, JIC, and other modern fitting
configurations. And if environmental issues are a concern, any of
several “environmentally friendly” or even food grade hydraulic
fluids can be used.
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Hydraulic systems are quite simple: actuators, servo valves,
controller and computer. Hydraulic actuators are designed to absorb
the total system energy in the event of worst case, runaway
conditions. This is accomplished by using built-in cushions at either
end of the actuator stroke. This common design feature is built into
the cylinder to protect against all control, electrical, and hydraulic
failures. Essentially, when any condition of failure occurs, the
cushions protect both the motion base and the payload from
Electrical systems, on the other hand, typically rely on a combination
of switches and control logic to protect the system. Many electrical
systems rely on a braking system to violently stop the motion.
Although these can be effective in their implementation,
Programming and additional complexity elevates installed cost and
potential for damage to either the motion base or its payload.
Hydraulic systems typically require maintenance approximately every
1000 hr of operation. This usually amounts to checking and replacing
filters, taking fluid samples, general maintenance, and running
diagnostic tests to ensure everything is adjusted and working
Electromechanical systems, on the other hand, typically require
lubrication about every 80 hr of operation, along with checking of
power wiring and a multitude of limit switches, control logic
verification, and encoder or resolver operational checks. Reliability
depends on proper operation of a serial combination of components.
Failure of one component causes all subsequent components in a
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functional chain to fail — the end result being downtime of the
Hydraulic cylinders used in the motion base are quiet, generating
levels less than 50 dB. In most applications, any sound emanating
from the cylinders is masked by ambient noise. The HPU can
generate substantial noise, but it is usually located in a separate
room or enclosure away from the motion base. This presents two
advantages: noise can easily be isolated from the simulator, and
heat-generating components are located away from the simulator.
Another advantage is that most maintenance can be conducted in
one convenient location — much of it with the motion base running.
Electric motion base systems can be noisy due to the many small,
fast-moving parts in the actuators. They generate a loud rushing
sound that is distinct and may or may be heard in the enclosure
mounted on the motion base.