FURNACES AND EQUIPMENT USED IN THE MANUFACTURE AND HEAT TREATMENT OF

R. A. P. MISRA Indian Wild-Barfield Co. Ltd., Bombay

HE types of furnaces and other manufactured by a number of furnace manu- equipment used at some stage in the facturers who have incorporated their own T manufacture and heat treatment of ideas of constructional features and detail- alloy is indeed too large to be covered ed improvements. The 3-phase direct are in one paper. It is, therefore, proposed to furnace may be subdivided into the follow- only briefly touch upon the latest develop- ing three types. ments in each field. Fixed Roof Rear Door Charging Type - This design is simple and the least expensive, Crucible Furnace but the maximum capacity for which it is suitable is about 3 tons, although larger Historically speaking, this is a first furnace capacity models have been made. If steel in which small amounts of raw materials can scrap is available in small, easily handled be melted to produce high grade alloy and sizes which can be manually charged, this tool steels. Until quite recently this had type may be used for sizes up to 5 tons with- been the only process used for the manufac- out undue loss of efficiency. ture of alloy steels which are generally re- Top Charging with the Rise-and-Swing- quired in small casts. These furnaces were Aside Roof - In this design the roof of the generally coke-fired, although gas and oil- furnace together with the electrodes is firing have also been used in some cases. lifted and swung aside to enable the charge The problem of the life and cost of crucibles to be placed in the furnace from a charg- which are generally made from refractory ing basket. This design is particularly clay mixtures is a serious one. The life of suitable where the steel scrap is available the refractories which have to operate at either in relatively large pieces or in the temperatures in the region of 1600°C. is also form of small swarf and turning. The limited. Although this process has been latter type of charge is relatively light and used for a long time in all industrial countries takes a long time to manually charge in a of Europe and America, it is gradually giving furnace of the fixed roof type. way to electric melting because of the Bridge Type This is a design which has convenience and cleanliness of working been pioneered by the Ing. Leone Taglia- conditions. ferri Company of Italy and has been prov- ed over the last fifteen years. When charg- Electric Steel Melting Furnaces ing the furnace, the shell is withdrawn from beneath a gantry bridge and carries the There are two main types, the arc furnace electrode equipment. It is more expensive and the induction high-frequency furnace. in first cost than the lift-and-swing-aside Arc Furnaces - The most popular type roof furnace, but has certain very definite is the 3-phase direct arc type furnace first advantages in the large capacities, say, from designed by Heroult. This basic design is 20 tons upward.

273 274 SYMPOSIUM ON PRODUCTION. PROPERTIES & APPLICATIONS OF STEELS

Conslruclioual Feat ures of Arc Furnaces- construction, high sensitivity plus and minus An Arc Furnace is an expensive piece of I per cent and rapid response one-seventh equipment. The smallest one with a capa- of a second ensure satisfactory operation, city of I ton costs in the region of Rs. I lakh. positive control and elimination of elec- In selecting a unit, the following points must trode breakage, etc. One important feature be borne in mind : The shell of the furnace to be considered in selecting plants suit- must be of rigid construction with heavy able for India is that highly skilled main- cast steel reinforcing members round the top tenance is not easily available in all places to prevent distortion, otherwise the door will and, therefore, the control system selected not fit properly. The base of the shell must should be such that all routine maintenance be dished on all but the smallest units to and overhauls can be carried out by mecha- provide great rigidity and uniformity of nics and electricians of average ability and hearth lining thickness. knowledge. In the electro-hydraulic system, The shell of an arc furnace when fully all moving parts in the regulator box are charged weighs several tons and the method continuously operated in a bath oil and of tilting any support employed must be such maintenance required is negligible. that no distortion takes place and no undue Furnace Tilting and Roof Raising System - stresses are produced in the shell. In this This can be of the mechanical, electrical connection the provision of perforated arc- or hydraulic type. It has been the general shaped rockers on the base of the furnace experience of engineers that where large which roll on studded machined base beams forces have to be accurately controlled, the is a valuable feature. The tilting action of hydraulic system is the only real answer. the furnace is like that of a rocking chair. The water pressure for the system is usually All parts such as slagging doors, roof ring, provided by a centrifugal pump driven by which are likely to be affected by excessive an electric motor and to prevent shuting heat should be provided with adequate water- down of the equipment because of pump cooling. failure duplicate pumps are normally in- Electrode Holders Certain furnace makers stalled. As an additional safeguard an hydro- have pioneered the development of remotely pneumatic reservoir is supplied which can controlled electrode clamps. These were give a reserve of power after a complete elec- fitted as standard equipment as far back as trical failure. 1936 and form a valuable aid to the efficient operation of the furnace. By means of suit- High-frequency able mechanical and hydraulic means, the electrode clamps can be clamped and un- In this type of furnace, the furnace part clamped by means of a push-button located is relatively simple and consists of an H.F. on the control panel. Those who have tried coil which is normally composed of a copper to adjust bolt-retained clamps on top of a tube through which cooling water is circulat- hot furnace will fully appreciate the impor- ed. The coil is embedded in a refractory tance of this feature. lining which is rammed in situ with a Electrode Control Mechanism - There have fabricated steel former which is melted out been a good deal of claims and counter- when the furnace is first started after slowly claims made by various furnace manufac- drying out the lining. The furnace case turers who adopt a particular type of system. work is made from electrically inert material The electro-hydraulic system of electrode like compressed asbestos board. Large control with gravity return for the electrodes furnaces are usually arranged for lip axis has stood the test of the time. Its simple tilting. MISRA - FURNACES & EQUIPMENT USED IN THE MANUFACTURE OF STEELS 275

Power factor Connection - The electrical which is not accurately to specification to characteristics of the furnace with a varying start with. The arc furnace is slightly charge have to be carefully matched by the more efficient thermally since the lining means of condensers which can be brought is so much thicker than that on the induction into play at will. The most expensive furnace. part of an H.F. furnace is the motor-driven One disadvantage of the arc furnace must alternator, and a furnace with a capacity be mentioned which does not apply to the of 200 lb. of steel per charge would re- induction furnace, and that is load fluctua- quire an alternator of 100 kW. delivering tion on the §upply system during the melting- 800 volts, single-phase, A.C. supply of 2000 down period. An are furnace with a cycles per second at 3000 r.p.m. Due to the normal rating of 500 kVA. may peak to very fine clearances used, a high degree of 1000 or even 1500 kVA. momentarily. maintenance is required particularly of the This is, however, not a serious disadvantage bearings and the motor generator must be if the furnace is connected to a large system located in a separate dust-proof room and on H.T. supply of 6000 or 11,000 volts, but provided with necessary fresh air inlets and the largest size of arc furnace which can be outlets. The above furnace would cost ap- safely connected to the 400 volts, 3-phase, proximately Rs. 11 lakhs which is much 50 cycles power supply has a capacity of more expensive than a direct arc 3-phase 500 lb. and with a normal rating of 150 kVA. electric furnace of a similar capacity. It is not advisable to connect arc furnaces of a larger size than this on 400 volts supply. Choice of the Most Suitable Type

When alloy steel has to be melted, one is Submerged Are Furnaces often called upon to decide between an induc- tion and an arc furnace. The correct This type of furnace is used for the produc- choice depends upon the raw materials avail- tion of ferro-alloys such as ferro-manganese, able and the finished charge required. If ferro-silicon, ferro-chrome, etc. This type selected scrap of known analysis is available, of furnace is also used for the production of such as in the works of a too] steel maker, to calcium carbide and pig . These fur- which known quantities of alloying additions naces, sometimes called electro-blast fur- can be made and it is desired to produce naces, are normally of the non-tilting type alloy steels of the highest grade of purity and consisting of a heavy circular steel shelve controlled composition in small casts, the fitted with tap-holes. A roof is provided answer is the induction furnace in spite of only when gas recovery is required. The its higher capital cost. charge is hand-loaded into small furnaces If, however, only normal commercial scrap and mechanically charged in the case of is available which is to be corrected after an larger types. The operating platform is analysis of the melt, then an arc furnace is usually arranged to be flushed with the shell indicated. top. In some furnaces, a rotating hearth It should be clearly understood that it is which completes one revolution in about 24 hr. not possible to carry out refining in an induc- is used to avoid the formation of (lead pots tion furnace. It is essentially a furnace for and ensure uniformity of the products. melting down and alloying known consti- The electrodes are of the continuous form- tuents. The arc furnace, on the other hand, ing Soderberg type and dip deeply into the is capable of carrying out a refining process charge and lower voltages than those nor- to give the required alloy from a raw material mally employed with arc furnaces are used 276 SYMPOSIUM ON PRODUCTION, PROPERTIES & APPLICATIONS OF STEELS with consequent heavy secondary currents. be used. The operation of this furnace is A complete installation usually includes the well known and covered in detail in techni- building designed specially to accommodate cal literature. So no further remarks are the auxiliary equipment allowing space for necessary. the manufacture of electrode shells which can be welded to existing electrodes while Soaking Pits the furnace is in operation. A hoisting mechanism for electrode control is usually These furnaces are storehouses for large provided. The transformers are similar to ingots which are kept (as a rule under- those employed with the normal arc furnaces, ground) at a uniform temperature after but no reactance is required and the tap casting until they can be handled by the mill. changer is of the ' onload ' type. They are, as a rule, gas-fired. The electrical load provided by this type Due to the lower tonnage handled in the of furnace is reasonably steady and does not case of alloy steels and the smaller size of fluctuate much. ingots cast from the smaller electric furnaces, The term small or large furnaces for this soaking pits are not used if the ingot size is type of plant is merely relative and a furnace small but allowed to cool down. of 2000 or 3000 kVA. would be considered small and the usual size of an economic unit Billet Reheating Furnaces is from 8000 to 12,000 kVA. A furnace alone with its electrical equipment of 8000 kVA. If ingots or billets have to be reheated for would cost about Rs. 15 lakhs, but a com- reduction in a mill or under a hammer or plete plant consisting of two such furnaces, press, fuel-fired furnaces are used. They are buildings, etc., and all other ancillary equip- generally gas or oil-fired, but pulverized coal ment may cost in the region of Rs. 13,300,000 is also used where the large size of the furnace ( one crore thirty-three lakhs of rupees ). makes its use economic. Apart from the cast of the pulverizing equipment, even the Indirect Arc Type Furnaces finest pulverized coal particle has to travel about 20 ft. in a straight line before combus- In this type of furnace the arc is struck tion is complete. This is because the coal between a pair of electrodes forming the axis particle is like a football compared to a of a refractory-lined drum which is rotated. -- in. ball when the ball represents a gas Due to the lower temperatures attainable, molecule. this type is used for melting cast and The design of the furnace depends on the non-ferrous metals but not steel on a commer- nature of the charge and the output required. cial scale. Another disadvantage is that Heavy blooms and billets are generally heated the furnace requires a single-phase supply in batch type furnaces of the fixed hearth and the load is not balanced unless three fur- type with mechanical handling of the billets. naces are operated at the same time. The Very heavy charges like turbine rotors, ships electrodes are often manually controlled on propeller shafts are heated on bogie hearth small sizes, although automatic arc control is furnaces to facilitate mechanical handling the rule on larger sizes. of these large charges which are, as a rule, forged under large hydraulic presses. Basic Open-hearth Furnace Where a large number of small or medium size billets have to be heated continuously Where alloy steel casts are required on a to feed a rod mill, they are pushed through tonnage basis the open-hearth furnace can the furnace on water-cooled skids located in

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the hearth of the furnace by means of a Coke ( Solid ) - Generally same remarks ap- mechanical or hydraulic pusher. The ope- ply as in the case of coal with the exception ration of the discharge door is interlocked that coke ensures general freedom from with the pusher. As a rule, the billets prog- smoke, but since the calorific value is lower ress through the furnace in a line at right than coal, larger grate area is required for a angles to their own axis. certain heat output. Oil - Where this fuel is available at eco- nomic prices it is a serious competitor to coal Forging Furnaces owing to the easier control of combustion as no labour is needed for firing. Oil burners As alloy steels are mostly used for their require either a forced draught of air or high strength, they are often used as forgings steam to atomize the oil from the burner or stampings. As a rule, gas or oil furnaces to ensure combustion of heavy oils . Beaters are used for heating the general run of forg- are sometimes employed to preheat the ing billets, although induction heating has oil to reduce the viscosity to enable heavier been used successfully in special purpose fractions to be utilized with consequent installations for doing such specialized jobs economy. as forging the mouths of shells. Direct One great advantage of oil-firing in metal- resistance heating of the material is also lurgical furnaces is the luminous flame this practical in certain applications like forging fuel provides which enables the rapid heat the heads of valves for I.C. engines. transfer to take place to the work being heated and this is of special importance Choice of Fuels where steel billets are heated to high tem- perature for forging etc. Coal (Solid) -Advantages : Cheapness, easy Gas - This may be divided into several availability in industrial areas, luminous varieties : flame which is an advantage in some types (a) Coal gas or town gas of work. (b) Producer gas Disadvantages: Lack of proper tempera- (c) Blue water gas ture control; proper grade of coal must be (d) Natural gas used as many of the cheaper grades do not (e) Cracked oil gas. burn well in the solid state. Labour required Coal Gas - Owing to the relative scarcity for handling fuel; storage problem and smoke of high quality gassing coals in India, the problem. development of the gas industry in this Coal (Pulverized) - Advantages : Same country has been very tardy and India may as solid coal. Most of the disadvantages of be virtually said to have skipped the phase solid coal firing are overcome. Temperature of gas development and arrived at the elec- control is made possible by control of firing. tric era. Most iron and steelworks , however, Lower grade coal can be burnt satisfactorily have their own coke ovens and, in addition thus effecting economy. No labour requir- to the supply of metallurgical coke, they ed for charging furnace. Smoke problem have supplies of gas and valuable bypro- can be overcome through control of com- ducts of distillation. bustion. Producer Gas - This has a rather low Disadvantages: Increased cost of pulveriz- calorific value and unless enriched i t requires ing apparatus and attendant mechanical com- specially large burners, ports and passages plications. Coals of very high ash contents to enable the furnaces to be brought up to cannot be used successfully. heat- treating temperatures within reasonable 278 SY TPOS[UM ON l'IZODUCTION. PROPERTIES & APPLICATIONS OF STEELS time. To attain higher temperatures pre- or switch it off also influence the choice of the heating of air blast is almost essential. fuel. Whereas these features are more easily Blue lValer Gas - This gas has higher incorporated in electric furnaces, it must now calorific value than producer gas specially if be imagined that automatic temperature coal is used in place of coke in the pro- control cannot be provided with gas and oil- ducer bed. The calorific value and the con- fired furnaces. Generally speaking, these tent of methane CH4 is much lower than furnaces do need personal supervision when coal gas. they are lighted, although automatic switch- Oil Gas - This is an excellent fuel of a ing off can be arranged. very high calorific value, almost double that As a rule, the electric furnace is more of coal gas. Owing to the higher cost of oil suitable and convenient for all heat as compared With coal, this system has only treatment operations due to the precise been used for small-scale plants for labora- temperature control possible and reasonable tories etc. working costs. In the case of very large Electricihv -- The choice of the right fuel installations, however, the lower costs of fuel depends upon the availability and economy in a fuel-fired furnace may justify this of the particular fuel, but apart from con- installation. siderations of economy technical suitability plays an important role in determining the best fuel. The first cost of the furnace, the Normalizing Furnaces running fuel cost, supervision charges, main- tenance charges, all must be taken into This design depends on the nature of the account and compared with the relative charge and output. For small and medium convenience of using a particular fuel outputs the batch type is preferred, but before a correct choice can be made. where output justifies the higher capital When comparing the cost of various fuels, cost a rotary hearth or walking beam fur- efficiencies of utilization must be taken nace may be found suitable. into consideration to arrive at a fair assess- ment. For example, it is much cheaper to buv B.T.Us. as coal than in the form of Furnaces electricity, but the efficiency may be only 5-10 per cent in case of coal-fired furnace with The same remarks apply a separate fire box and 86-88 per cent in as for normal- izing furnaces except that the work is the case of a well-designed and insulated quenched instead of being air-cooled. electric furnace. In the case of liquid and gaseous fuels higher thermal efficiency can be achieved with proper design than with solid fuel fired furnaces, because the fuel and Furnaces air mixture can be arranged to burn inside the furnace Chamber; even so it is not usual Modern practice is to use electric furnaces to find an efficiency higher than about 15 of the forced air circulation type which are per cent even with recuperators and heat usually vertical. The centrifugal fan which exchangers to preheat the incoming air for has been pioneered by some manufacturers coin bust ion. Other factors such as the ease ensures absolute uniformity of temperature with which automatic temperature control- in the range up to 700°C. where radiation is lers and time-controlling switches can be not very effective in producing temperature arranged to bring the furnace into operation uniformity. MISRA - FURNACES & EQUIPMENT USED IN THE MANUFACTURE OF STEELS 279

Charge Progress Recorder ( coal gas) is available. In the ' Carbodrip ' process the atmosphere is pro- With this type of furnace by suitable duced by supplying a specially prepared placing of two thermocouples and a two-point fluid to the furnace chamber which is gas- recorder it is possible not only to record and tight and contains an electrically driven fan automatically control the temperature of the with special bearings and glands. furnace, but also to record the temperature The process is reliable and quicker than of the charge at any instant. This enables the conventional box carburizing method. uniform tempering treatments to be carried Very little time is required for packing and out with full utilization of furnace capacity. unpacking of the charge. The fluid is rea- sonable in cost and consumption works out Salt Baths to about 500 gallons per year for an installa- tion of medium size. The capital cost of the They are particularly useful for heat treat- furnace due to its special construction is a ment of steels, for hardening, liquid carburizing little higher, but it is a good investment in and heat treatment of high-speed steels. This view of its high productive capacity. A process is specially useful where treatment large number of motor-car manufacturers are has to be carried out at above 700°C. as there adopting this process in view of this proved is no scaling and the surface finish is much ability to lower costs. better. is also not a serious problem, but where requirements are critical, suitable salt mixtures have been developed. Carbonitriding

Where it is not required to produce cases Furnaces of great depth and production requirements These are usually electrically heated with a are large as in the case of self-tapping screws, gas-tight box or chamber which contains the a mixture of carburizing gas and work. Ammonia gas is supplied in controlled can be introduced to give a case which con- quantity and special steels are necessary. sists of carbides and nitrides. The furnace is Due to the long duration of the process which designed to work continuously and the work requires about 80 hr. and the small case is quenched into an oil tank through a chute. depth, about 0.02 in., the process has not Due to limitations of space it is impossible to found general favour. The treatment is go into greater details or describe each and carried out round 500°C., and no every type of furnace within the confines of is required. It is, therefore, possible to treat one paper. The author will be only too pleased complicated shapes like aero-engine crank- to answer any queries about any special prob- shafts which cannot be treated by other con- lems regarding furnaces. Before concluding ventional methods due to distortion. I should like to acknowledge the help and co-operation of the following companies: ` Carbodrip ' Gas-carburizing Process (1) Indian Wild-Barfield Co. Ltd., Bom- bay 18 Although the process of gas-carburizing is (2) Wild-Barfield Electric Furnaces Ltd., not new, it is only recently that a commer- England cially reliable process has been developed (3) G.W.B. Furnaces Ltd., England which does not suffer from previous dis- (4) Ing. Leone Tagliaferri Company, Italy advantages. Following the success of the (5) Aldo Tagliaferri Company, Italy prepared town gas process, it is now possible (6) Thermic Equipment & Engineering Co. to use gas-carburizing where no town gas Ltd., England. 280 SYMPOSIUM ON PRODUCTION, PROPERTIES & APPLICATIONS OF STEELS

PAPERS DISCUSSED

1. Segregation and Internal Weakness in Forging 10, 15 and 20 per cent respectively. In order to Ingots, by N. H. BACON. avoid panel cracking losses, they have found out 2. The Effects of Hydrogen on Alloy Steel Produc- that 11 in. sq. ingot serves the purpose best. tion, by K. C. BARRACLOUGH. For higher alloy steels the smaller the ingot, the 3. Hydrogen in Steel, by A. G. QUARRELL. better it is. 4. Oxygen in Foundry Steel-making, by A. K. DR. S. BHATTACHARYA ( Metal Factory & GUPTA. Steel Factory, Ishapur ) 5. Furnaces and Equipment Used in the Manufac- ture and Heat Treatment of Alloy Steels, by Mr. Bacon is requested to throw some light on R. A. P. MisRA. the ingot mould wall thickness to ingot diameter ratio. While manufacturing 32 in. octagonal DR. B. R. NI JHAWAN ( Dy. Director, National Ni-Cr-Mo steel ingots for ordnance purposes we Metallurgical Laboratory) experienced corner cracking along the ribs on ingots in course of forging even when the ingot was stripped May I ask Mr. Bacon if he could please indicate hot and homogenized by prolonged . the latest developments in continuous casting in This trouble could be overcome by stripping this alloy and stainless steels in the U.K. ? 5-ton ingot after 3 hr. and standing it upright in a refractory-lined ingot mould of 42 in. in dia- MR. N. H. BACON ( Sheffield) meter till the ingot had fully solidified. Stainless steel slabs in the region of 3 ft. wide, 20-27 in. broad and 7 in. thick have been MR. N. H. BACON ( Sheffield) successfully cast continuously. However, trouble The cracking is not in any way connected with is experienced on casting smaller sections. The the wall thickness of the mould. To avoid cracking trouble appears to be that if the smaller sections during forging of the ingot the ingot mould should are cooled slowly as they issue out of the mould - have sharp corners. The sharper the corners, the cooled slowly in order to obtain a good structure - better it is. The other causes of cracking are either the liquid drains out from the ingot leaving a cylin- that the metal is tapped too hot or teemed too fast. drical hollow. If the ingots are cooled rapidly, internal cracking occurs. All I can say is that MR. S. VISVANATHAN (Tata Iron & Steel continuous casting is still in experimental stage Co. Ltd.) except for certain sizes. I remember to have seen in an American paper about the use of plate at the bottom of the MR. S. C. BISWAS ( Mukand Iron & Steel Co., ingot mould to reduce the basal cone in 4 to 5 ton Bombay) ingot practice. I would like to know if Mr. Bacon We have experienced negative segregation of 3-4 agrees whether it is possible to avoid the basal cone. points carbon in the bloom of the top of the ingot MR. N. H. BACON ( Sheffield) of the feeder head in axle steels. The ingots are of I do not see how putting a carbon block at the 5 1 tons weight. I want to know why there is inverse bottom of the mould can remove the basal cone segregation. weakness. This weakness is very real and we test all heavy forging for it ultrasonically. MR. N. H . BACON ( Sheffield) I have never come across such a case and I believe MR. S. VISVANATHAN (Tata Iron & Steel there is a mix-up which sometimes occurs in the Co. Ltd.) shop or laboratory. In American practice for stainless steel making inert gas is used to avoid hydrogen pick up and MR. E. H . BUCKNALL ( Director) I do not see why the same cannot be extended to Are all the troubles reduced if the ingots are cast the of other alloy steels, provided argon in 4 to 6 in. size ? is made cheaply available by the Indian Oxygen & Acetylene Co. Talking of Oxygen Company I was MR. N. H . BACON ( Sheffield) rather flabbergasted that a couple of years ago Yes, in alloy steels very much so. At Samuel Mr. Gupta suggested using hydrogen for decarburiz- Fox, when 3 per cent Ni steel is cast in 14, 16 and ing high-silicon heats, and I gained a sort of idea 18 in . sq. ingots, the loss due to panel cracking is that bubbling hydrobgen inside the melts is being MISRA - FURNACES & EQUIPMENT USED IN THE MANUFACTURE OF STEELS 281

practised in certain parts of England. I would like Hot metal charges in the U.S.A. have been found to know whether anybody can confirm such practice. advantageous up to about 15-20 per cent in electric furnaces. When used over 20 per cent, total heat Mr. A. K. GUPTA ( Indian Oxygen & Acety- time is increased to an extent to make this advant- lene Co. Ltd.) age questionable. This is, however, based only In England a certain firm carried out experiments on limited and occasional experience ( Republic on bubbling hydrogen gas for a year and a half to steel) and is not generally followed by U.S. steel- decarburize, but now I hear that the practice has makers. been discontinued. The Battelle Institute 50 per cent hot metal MR. F. M. SCI IONWALDER ( Mukand Iron & data were calculated from theoretical considerations Steel Co., Bombay) and not from actual operating results. The discussion of removal of hydrogen in alloy The Battelle data and experience have shown that all-scrap electric furnaces (in larger size over 40 steel will not be complete without the mention of recent developments, especially in Germany, of tons capacity) are superior than all-scrap open- pouring and teeming of ingots in vacuum. hearth. The development of hot metal practice in electric MR. J. R . MILLER ( Ramseyer & Miller Inc., furnace still depends on results of actual plant ex- New York) perience. However, in recent two years interest in On Mr. Gupta',, paper on oxygen in foundry steel- hot metal electric furnace practice has been replaced making I would like to say the following: by interest in Linz Donowitz process.

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