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Taphole machinery  reetam das Taphole machinery reetam das Document Transcript

  • Page 2 of 44 CERTIFICATE 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 AGM(BF), VSP
  • Page 3 of 44 Acknowledgement 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. Thank you. Reetam das
  • Page 4 of 44 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 4.1 Components 4.2 Circuit diagram 5. Justification for migrating from Electromechanical System
  • Page 5 of 44 INTRODUCTION 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 plant. 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 Prime Minister. 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.
  • Page 6 of 44 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.
  • Page 7 of 44 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 commissioned. 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 export market.
  • Page 8 of 44 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 18001:1999. 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 volumes. - 3 Sinter machines of 312 m2 area - 2 Blast furnace of 3200 m3 volume and one of 3800m3 volume - 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 capacity. - Wire Rod Mills of 850,000 tons per year capacity. - Medium Merchant & Structural Mills of 850,000 tons per year capacity. 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 facilities.
  • Page 9 of 44 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 environment protection. - Computerization for process control. - Sophisticated, high speed and high production rolling mills.
  • Page 10 of 44 BLAST FURNACE 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 manganese ore. 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
  • Page 11 of 44 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 m3 /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 plant.
  • Page 12 of 44 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.
  • Page 13 of 44 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 /hr. capacity each are provided for the purposes. Water cooling arrangement has been provided for cooling of hot blast valves and burner cut off valves.
  • Page 14 of 44
  • Page 15 of 44 TAPPING EQUIPMENT 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:  Slewing drive  Jib arm  Cable track  Chain feed drive  Hydraulic Hammer
  • Page 16 of 44
  • Page 17 of 44 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 machine.
  • Page 18 of 44 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 track) 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 conserving power. Drill bits:
  • Page 19 of 44 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  Percussion energy - 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  Slewing angle-1700 Flushing (Nitrogen)  Operating pressure: 6-7 bar  Consumption (flow): 3,5 m3 /min Flushing (water)  Water supply pressure: 3-5 bar
  • Page 20 of 44  Water flushing flow max: 4l/min  Impurities: <200mg/l Spatial arrangement in the Plant:
  • Page 21 of 44 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 plugging unit. Salient features:  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 covers.  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 independently.
  • Page 22 of 44  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.
  • Page 23 of 44 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. Main components:  Steering device consisting of jib arm, plugging unit and the regulation unit.  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.
  • Page 24 of 44 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
  • Page 25 of 44 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.
  • Page 26 of 44 HYDRAULIC SYSTEM 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 electric motor.  Valves, piping, filters etc. for guiding and controlling the system.  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 larger force.
  • Page 27 of 44 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. 4.1 COMPONENTS Hydraulic Pumps: 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 reduce vibration. Common types of hydraulic pumps to hydraulic machinery applications are:  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).
  • Page 28 of 44  Vane pump: cheap and simple, reliable. Good for higher-flow low-pressure output.  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 small flows. Control valves: 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.
  • Page 29 of 44 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.
  • Page 30 of 44  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. Actuators: 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. Reservoir: 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
  • Page 31 of 44 particulate will generally settle to the bottom of the tank. Heat exchangers are also used to cool the oil to the right temperature. Accumulator: 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.
  • Page 32 of 44 Hydraulic Fluid: 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 applications. 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: 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 once. Tubes, Piping, Hose: Hydraulic tubes are seamless steel precision pipes, specially manufactured for hydraulics. The tubes have standard sizes for
  • Page 33 of 44 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.
  • Page 34 of 44 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 obstructing wall.
  • Page 35 of 44  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.
  • Page 36 of 44 4.2 CIRCUIT DIAGRAM Taphole Drill:
  • Page 37 of 44 Clay Gun:
  • Page 38 of 44 Justification for migrating from Electromechanical System 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.
  • Page 39 of 44 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
  • Page 40 of 44 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 heat exchanger. The bottom line: Electrical systems consume more energy than that of hydraulic systems. OVERLOAD CAPACITY 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.
  • Page 41 of 44 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. PERFORMANCE 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.
  • Page 42 of 44 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. OPERATIONAL SAFETY 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.
  • Page 43 of 44 OPERATION COMPLEXITY 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 damage. 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. MAINTAINANCE 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 properly. 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
  • Page 44 of 44 functional chain to fail — the end result being downtime of the entire machine. NOISE 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.