Melting in Induction Furnaces

Transcription

1 Melting Ductile lron in the Electric Furnace 31 Melting in Induction Furnaces For Ductile lron in Sweden by Bertil Hanas and S. E. Stenkvist For many centuries, Sweden has had a reputation as a high-quality steel country. Swedish steelworks and foundries have always been advanced in metallurgy and technology. It is then natural that ductile iron has met with strong interest in Sweden, and today ductile iron castings are used in sizes varying froin very small up to 80 tons.* It is also anticipated that the production of this type of casting will expand very rapidly. During the last few years, for example, the largest manufacturer of ductile iron castings has doubled production every second or third year.. Almost all of the Swedish produclion is processed with induction furnaces; these furnaces are used for melting from cold, for the additional melting of the alloy elements, or are included as the final stage in a duplex process. At present, about 10 foundries have ductile iron in their manufacturing program, but this number is expected to rise considerably in the near future. This may be attributed to the increased demand for ductile iron, and also to the availability of simplified methods for the adding of magnesium and improved laboratories and testing facilities. This latter factor is not of the least importance for the smaller foundries. EXPERIENCE WITH INDUCTION FURNACES Since industry in Sweden already had access to electrical energy at a competitive price at a very early stage, Swedish foundries quickly adopted induction furnaces of coreless type for the melting and holding of cast iron. At present, over one quarter of the entire production of cast iron passes through such furnaces. The lack of fossil fuels in Sweden has naturally contributed towards the competitive position of electrical All weights given in short tons. BERTIL HANAS and 5. E. STENKVIST are with ASEA Electric Inc., stationed, respectively, in Vasteras, Sweden and Arrnonk, N. Y. energy, but this factor is only one of the reasons why electrical melting occupies such a dominating position today. As is well known, induction furnaces also make it possible to utilize raw materials such as chips and borings, which can only be used with difficulty in cupola furnaces. The complete metallurgical control of the melt in the induction furnace is another advantage which cannot be overestimated in view of the present-day stringent requirements on the quality and uniformity of castings. When the production of ductile iron first reached prominence about 1950, many Swedish foundries were already equipped with induction furnaces; and thus far their operating conditions and potentialities were already known. These foundries thus had at their disposal a tool for the production of ductile iron which they could fully master as well as utilize, either alone or in combination with other types of furnaces. As a result, it was very soon ascertained that induction furnaces had many advantages in comparison with, for example, cupolas. This is perhaps one of the reasons why the price of ductile iron castings is often lower in Sweden than elsewhere on the European Continent. GENERAL VIEWPOINTS In general terms, it can be said that a cupola is characterized by its rapid melting capacity combined with a high thermal efficiency, but that its efficiency drops greatly if it is used, for example, for superheating. The cupola also possesses certain disadvantages when used for the production of ductile iron, which may become rather troublesome. Variations in the analysis may be considerable, particularly in hotblast cupolas with the basic linings which must be employed to obtain required low-sulfur content. Since a high carbon content is also required, this may be difficult to achieve unless a large addition of pig iron is made. The use of coke as fuel leads not only to an increased addition of sulfur but also to the presence of other more or less undesirable impurities. The limited flexibility of the operation of a cupola is another disadvantage, which' means that sampling and adjustments of the analysis can only be made to a very limited extent. Holding and adjustment of the temperature are other requirements which cannot be fully satisfied. If electric furnaces, which usually require a higher capital investment, are considered, it is found that they produce a substantially better basic iron for ductile iron melting. Their advantages include the great flexibility in the size, analysis, and temperature of the melt, and the ability to adjust rapidly and simply, for Fig. 1-Deslogging of a 33-ton coreless induction furnace after desulfurization. example, the carbon and sulfur contents. The risk of impurities from the fuel no longer applies; this is also the case with the lining. Another advantage is the capability of the holding and storage of the molten iron. Of the various types of electric furnace available, only the induction furnace has been used in Sweden for the production of ductile iron and, indeed, for cast iron in general. It has been considered that the arc furnace is less suited for this kind of production because of the risk of local overheating in the melt and lining, poor efficiency for hold-

2 32 Proceedings of Electric Furnace Conference, 1964 ing, reduced possibilities for the melting of chips and borings, the additional cost for electrodes, etc. The relative advantages of the induction furnace and the arc furnace can, however, vary according to individual conditions. METALLURGICAL POSSIBILITIES If good and uniform yields are to be achieved when magnesium is added, it is of great importance that the sulfur content of the melt should be held as low as possible and as constant as possible from one melt to the next. This is achieved naturally with induction furnaces, when melting from cold, using charge material with a low sulfur content. -. Temp, :. - 'F 'c- D 0 25% Ca C2 added I Des!agg~_ng a -' "--- t Fig. 2-Desulfurization in two stages in a 33-ton coreless induction, furnace. motion. An optimum bath motion is closely allied with several factors, of which the- furnace input and frequency are most important. The latter is one of the reasons why line-frequency furnaces have become of such importance in this connection. Since the bath motion for a certain given frequency is a function of the power input, an excessive power input would be required in many furnaces to obtain the desired bath motion. It is possible, however, to build line-frequency furnaces so that power input can be concentrated to the upper part of the furnace, thus achieving a strong bath motion with a limited power plant and, consequently, without undesirable superheating. If a good desulfurization is to be obtained, it is normally necessary that reducing conditions should prevail in the furnace. In addition, a basic slag and lining, as well as a high temperature, are required. Sodium carbonate and lime, etc., can then be selected as the desulfurizer, while materials based on magnesium oxide or spinels of a suitable type are used for the basic lining. Many difficulties have, however, been involved in the use of a basic lining, partly due to the high penetrative ability of cast iron. To a large extent, these problems have been solved by the introduction of compound crucibles, where, for example, a combination of bricks and pulverous ceramic material is used. Such good results have been obtained in this way that the commercial application of these will prob- ably become general. quartzite to make the desulfurization so that extremely low sulfur contents are obtained. If calcium carbide is added, good sulfur yields can be obtained, while the crucible wear will be maintained within a reasonable level. The reason for the latter is that after the reaction, the carbide forms a dry slag which shows hardly any tendency to react with the furnace lining. Even if a high temperature promotes the desulfurization, a fully satisfactory desulfurization can be achieved at a relatively low temperature under the above conditions with crucible wear held at an acceptable level. The amount of calcium carbide added varies normally between 0.5 and 1% of the weight of the melt. The quantity depends in the first instance on the initial sulfur content and on the desired final content. The furnace is carefully deslagged prior to the addition, as well as after the reaction (see Fig. 1, taken froin a film strip shown at the AIME meeting). The stirring time takes about 5 min. or less,'which is often adequate to achieve even very low sulfur contents. If possible, the desulfurization should not be started at a temperature exceeding about 2650 F, since a certain temperature rise during the process itself cannot be avoided. This is of particular importance when very low sulfur contents are required. In this case, it is better to carry out the desulfurization in two stages with intermediate deslagging. An example of this is shown in Fig. 2. When calcium carbide is used in In cases where this is too expen- It is also possible in a furnace an acid crucible, sulfur contents of sive, a duplex process with a cupola having a lining of dry-rammed to 0.003% and, in certain cases, and an induction furnace might be preferable, particularly for large quantities of molten iron. Melting then takes place in the cupola, after which the iron is continuously or intermittently transferred to the induction furnace for adjustment of the temperature, analysis, and for desulfurization. This improves operating economy by permitting a certain amount of melting of cheap scrap such as small chips or large rolls in the induction furnace. Furthermore, this combination gives good holding and storage capability. Irrespective of whether the induction furnaces operate in a duplex process with other furnaces or if the melting takes place exclusively in the induction furnaces themselves, the special characteristics of the latter can be utilized in a very satisfactory manner to achieve the desired analysis and temperature. The disadvantages of the small area of the melt in relation to its volume as well as of the relatively low temperature of the slag are 1 largely eiiminated through th; bath. Fig. 3-Platform for mechanized deslagging of-coreless induction furnace in a large installation. -

3 Melting Ductile Iron in the Electric Furnace. 33 even lower, can be achieved. This is possible in the line-frequency coreless furnace, thanks to the previously mentioned bath motion. No additional means, such as mechanical stirring or injection of the d.esulfurizer with a carrier gas, are necessary to obtain a good contact between the melt and the desulfurizer. As a general value for the sulfur yield, it can be estimated that removal of each pound of sulfur requires' about 10 lb of calcium carbide. In this connection, it is worth mentioning a factor which is of particular importance for larger coreless furnaces. Because of the pronounced radiation from the melt during the deslagging, it may often prove difficult for the furnace per- shown in Fig. 4 and recorded simultaneously in the foundry office. In addition to the correction of the sulfur content, it is often necessary also to adjust the silicon and carbon contents. For natural reasons, the phosphorus content, should it be too high, cannot be easily reduced as long as acid conditions prevail in the furnace. When a basic crucible and a basic slag are adopted, a certain degree of adjustment is feasible, but this is probably not justifiable from the economic viewpoint. The silicon content can be raised very easily with the addition of ferrosilicon. Because of the excellent bath motion, the alloying time will be very short and the silicon yield, practically speaking, 100%. Fig. 4-Large wall-mounted instruments connected to pressductor load cells indicate the charge weight for correct calculation of additions. Operator has an additional instrument with individual zero adjustment at the tilting panel for weighing smaller pours. A common feature of carburizers is, however, that they are very light and thus make only a very limited contact with the surface of the melt. The good bath motion of the linefrequency furnace proves very useful in this respect, and, when correctly utilized, can provide extremely high and uniform carbon yields. As is the case with desulfurization, it is particularly advantageous if furnace power input can be concentrated to the upper part of the furnace so that the best possible bath motion on the surface is created during the addition of carbon. When graphite is added in coreless furnaces, carbon yields of 90 to 95% are usually obtained within a period of about 5 min. This applies also when a relativelv high carbon con- " - - ~- tent is required. The description hitherto has dealt with induction furnaces of crucible type. In channel type furnaces, the conditions are somewhat different since the bath motion, developed in the channels, only gives limited stirring effect on the bath surface. Nevertheless, heavier alloy elements can be relatively well dissolved. and distributed within the melt. But if desulfurization has to be performed in these furnaces, the injection of calcium carbide with a carrier gas is probably the best solution. Very good carbon yields can also be obtained in a channel furnace, usually in acceptable carburizing times, if the furnace is turned so that the inductor or inductors will be almost horizontal, as shown in Fig. 5. From this illustration it can be seen how the bath motion formed on the surface changes from more uniform to pointed waves. The latter bath motion yields a noticeable improvement in the carbon pick-up. Furthermore, the illustration shows the difference in the carbon yields and carburizing times, while the improved carbon pick-up is confirmed by a markedly lower temperature rise. sonnel to remove the slag from the furnace platform with the tools that are normally used. Fig. 3 shows an example of how this operation can be mechanized for larger installations. Another important factor for economic operation is that the weight of the melt must be accurately known to enable correct additions of alloy elements and of slag-forming material. This is possible if the furnace structure is placed upon pressductor load cells, whose operation is not affected by the tilting angle of the furnace. The total charge weight is then indicated on large wall-mounted instruments as Furthermore, the good bath motion ensures that the homogenization of the melt will be complete. The same remarks apply, largely speaking, to all ferroalloys. When it is desired to increase the carbon content, graphite chips, which are normally obtained as a by-product during the manufacture of carbon electrodes, are used. Coke breeze can also be utilized in certain cases, but its higher sulfur content means that this material can increase the sulfur content and other undesirable impurities. Furthermore, its higher ash content results in a considerably inferior and more uneven carbon yield. MELTING INSTALLATIONS FOR DUCTILE IRON Table I lists the Swedish foundries possessing induction furnaces which are used for the melting and processing of ductile iron. Svenska Kullagerfabriken (SKF) SKF, one. of the world's leading manufacturers of ball and roller bearings, employs a duplex process for the production of ductile iron based on hot-blast cupolas and linefrequency coreless furnaces. The iron produced in the cupolas, each having a capacity of about 4.5 tph, is accumulated in a forehearth and is then transferred to one of three

4 34 Proceedings of Electric Furnace Conference, ton line-frequency coreless furnaces. Both the cupolas and the induction furnaces have acid lining. This combination of furnaces has been selected because manufacture of ductile iron is combined with that of several other qualities of cast iron. Furthermore, the preparation of molds and the casting takes place along the same mechanized line. This factor necessitates a high degree of flexibility with regard to the storage of different grades of cast iron. It was considered unsuitable to base all melting and holding on cupolas because of the temperature drop in conjunction with the desulfurization and treatment with magnesium. Desulfurization prior to the addition of magnesium was felt to be highly desirable, since this would satisfy both the quality and economy requirements of the process. A hot-blast system was justified by the desire to use a high proportion of steel scrap in the charge without reducing the high carbon content. The acid lining i s relatively cheap and leads to a lower loss of silicon, while at the same time a subsequent desulfurization was considered necessary under all circumstances. In addition to the duplex process, special grades of ductile iron are melted directly in line-frequency furnaces, where the charge contains up to about 30% of ductile iron chips. Desulfurization takes place with calcium carbide in the line-frequency furnaces with acid lining and in conjunction with pouring from the ladles. The furnace is first charged to about 20%, after which a Fig. &Batch duplexing of molten iron into a coreless induction furnace. Note funnel for addition of calcium carbide for desulfurization. further 60% of molten metal is charged along with the calcium carbide (see Fig. 6). After the furnace has been charged with the remaining 20% of. the molten metal, the power is switched on so as to produce the bath motion. The process is terminated at about 255O0F, when the carbide slag is withdrawn. The sulfur content is reduced in this manner from about 0.08 to about 0.01%, with about 10 Ib of calcium carbide being consumed for each pound of sulfur removed. The magnesium treatment takes place according to the Pontla-Musson method in 2200-lb pressure chambers in which 0.25% magnesium is added. The temperature before and after the addition is 2700 F and 2600 F, respectively. Inoculation is made by adding ferrosilicon in conjunction with tapping into the casting ladle, after which pouring takes place within 20 min. The following data are the mean values obtained during the period June-July 1964 and can serve as an example of the physical characteristics achieved. I As cast, ferritic condition Heattreated, ferrltlcpearlitlo conditlon, Car ' "lo - Carbon Temp (S1=1 SOX) ' 3.45 I I 335 I OC OF ) I ' 320 I I W M i I I mln mln I L---_ -- fie1_d_22 "!e----, -- Y~eld -- - Fig. 5-Carbon 95' A increase in a channel induction furnace., Tensile strength, psi 80,000 92,000 Yield streneth at 0.2% offset, psf Elongation, % 57, Brine11 hardness No Akers Styckebruk Akers Styckebruk, one of the most well-known European manufacturers of cast iron rolls and drain pipes, was one of the first companies in Sweden to base its melting program on induction furnaces (1942). Since then, their furnace plant has been expanded to include both medium-frequency and large line-frequency furnaces (33 tons). At present, practically all melting takes place in the medium-frequency furnaces, this applying to both ductile iron and grey iron. The line-frequency furnaces are used for the holding and adjustment of the analysis of the molten iron, but also for a certain amount of melting, for example, in conjunction with the melting of large scrapped rolls.

5 Melting Ductile lron in the Electric Furnace 35 tated partly by the ease with which the analysis and temperature could be adjusted and the ability to melt particularly large and small scrap in addition to the use of the duplex process with the blast furnace. With regard to the operational economy, this latter factor was a particular advantage. Fig. 7-A Guldsmedshytte Bruk Guldsmedshytte Bruk is one of the leading Swedish manufacturers of molds for steelworks as well as smaller rolls of both grey iron and ductile iron. Iron is tapped from a blast fur- nace at a temperature of about 2370 F and is transferred to one of the 33-ton line-frequency furnaces. Desulfurization is done in this furnace with calcium carbide or before that in a shaking ladle. The carbon content is adjusted in the induction furnace with the addition of steel scrap, the silicon content with ferrosilicon, etc. Then the magnesium treatment takes place during the tapping into the casting ladle. This is accomplished in such a way that one-third of the melt is tapped into the ladle together with the addition of NiMg, while the line frequency coreless furnace installation. inoculant is charged into the furnace. The furnace power is switched on for a few seconds to permit stirring, after which the remaining part of the melt is tapped into the ladle and mixed there with the already overtreated iron. An older, small line-frequency furnace is also available for the treatment of melts of up to 7 tons by means of overtreatment in a 3300-lb pressurized ladle. The desired magnesium content has been set at a value of 0.06%, which is obtained with a yield of about 50%. The inoculation is then maae with 75% ferrosilicon in additions of between 0.6 and 0.9%. These additions are often made direct to the pouring stream from the ladle with the aid of a funnel. The choice of the 33-ton line-frequency coreless furnaces was dic- Table I. Induction Furnaces For Ductile lron Production in Sweden Medium- Line- When frequency, frequency, duplexing, Company, City coreless coreless melting in AB Akers Styckebruk, Akers Styckebruk x 13,000 2 x 66,000 Medium-frequency coreless ASEA, Vasteras 2 x x 66,000 Kohlswa Jernverks AB, Bjorneborgs Jarn- 2 X 3300 verk, Bjorneborg 2 x 1100 Grangesbergsbolaget, Guldsmedshytte Bruk, 2 x 66,000 Blast furnace Guldsrnedshyttan AB Svenska Kullagerfabr~ken (SKF), Ka- 2 X 12,000 trineholm 1 x x 11,000 Hot-blast cupola AB Jarnforadling. Halleforsnas 3 x 12,000 Hot-blast-cupola AB Volvo, Skovde 4 X 6600 AB Davy Robertsons Maskinfabrik, Gothen- 2 X 2200 berg 2 x 11,000 Lidkoplngs Mekaniska Verkstads AB. Lid- 1 X 6600 koping AB Nordiska Armaturfabrikerna (NAF), Lin- 1 X 4400 koping Bjorneborgs Jernverk Bjorneborgs Jernverk manufactures medium-sized machine castings, of which about 1700 tons per year are of ductile iron in weights up to about 1000 lb. The charge of selected scrap is melted in 1.7-ton medium-frequency furnaces, whereupon desulfurization is made with calcium carbide. The bath motion is not sufficiently effective, however, at this frequency to ensure an adequate immersion of the carbide. Therefore, the bath motion is supplemented by manual stirring. The sulfur content is reduced from about to 0.005% within about 4 min at a temperature of about 2550 F. It has been found that the crucible wear resulting from the desulfurization has increased only very insignificantly, and a crucible life of 180 to 190 melts is norn~ally obtained. The magnesium treatment is accomplished afterwards according to the Pont-a-Musson method in a 2200-lb ladle. GENERAL CONSIDERATIONS Experience in Sweden has shown that coreless induction furnaces constitute an excellent aid in the ever-growing production of ductile iron, satisfying the need for castings of a better and more uniform quality at a competitive price. Furthermore, these furnaces offer great metallurgical flexibility for varying market demands. The steady improvement of lining materials has very positively contributed to today's reliable and economical operation of induction furnaces of increasing sizes. Large furnace units of 30 tons and more enable mechanization of charging systems, deslagging to a much bigger extent, and the possibility of controlling the analysis, temperature, and weights. Indeed, the entire cycle will undoubtedly in the near future lead to full automation with computer control. The great progress made in foundry technology has also enabled considerable savings in material and labor. The generally higher degree of precision in alloying technique and temperature control has also resulted in savings in heat treatment, better yields, less rejects, etc. The cleaner working conditions associated with the operation of induction furnaces, and their limited maintenance, are other factors of special significance to the personnel.

6 36 Proceedings of Electric Furnace Conference, 1964 Discussion EDWARD OLDFIELD (American Hoist and Derrick Co., St., Paul, Minn.) : Are the returns you charged cleaned of sand before they go into the induction furnace? BERTIL HANAS: Mostly not, but it would be advantageous to clean them because a big part of the slag that we have to handle before the calcium carbide treatment is caused by the sand in these returns. When I said 50% returns, they were not only returns with sand; these returns consist to -a large extent of chips and borings from ductiles. That is what is left from the machining of the semi-finished castings. EDWARD OLDFIELD: DO these chips have cutting oil or anything of that nature on them? BERTIL HANAS: Sometimes they do to a great extent. D. E. DORNEY (Bethlehem Steel Co., Bethlehem, Pa.): Have you ever tried magnesium treatment in the furnaces? BERTIL HANAS: Occasionally, and it is possible, but for practical reasons it is done in either pressure chambers or in ladles. I think the pressure chamber with the Pont-a- Musson method is used in Sweden more than in the United States. D. E. DORNEY: YOU did say you were able to plunge in the furnace and magnesium-treat this way. Would you expect unusual losses of magnesium? BERTIL HANAS: NO, but there may be a rising of the temperature, causing a risk of local wear of the lining where we have this heavy reaction with magnesium. We are working with a fairly thin lining, as you know, and that is the reason it has not been general practice. D. E. DORNEY: DO YOU have your coil located up close to the top one-, third of the furnace where you : might not get so much stirring? If i you did not have that coil, were the losses reduced? 1 BERTIL HANAS: The coil is divided in three sections, and it goes all the way from below the bottom of the helt up to the top of the melt. When I talked about the top coil, it is just the coil connected electrically. During the melting cycle, the two bottom coils are connected instead. We could thus get the stirring at any point we wanted for the magnesium treatment. D. E. DORNEY: Are you only, utilizing this top coil now in your regular practice when you are desulfurizing with a calcium carbide treatment? BERTIL HANAS: In operational practice, yes, but there is also another problem when it may be more important to have it, and that is for good sintering at the furnace when the lining is new. Then this total coil is electrically connected and we get electrid heating of the template to the top. (Showing Slide) : There are hoods here, above the furnaces, as parts that come with or from the oil in the chips might burn. The furnace as such does not create any smoke at all, so there is no smoke problem in the furnace or in the foundry, but we have found it desirable to take out this "oil" smoke from it directly, and that is why it is installed. E. A. PIPER, (Pholman Foundry Co., Buffalo, N.Y.): You talked a great deal about making ductile iron from the crucible type of furnace. What are the pro and con of making ductile iron in the channel type of furnace? BERTIL HANAS: I would not say that is not possible, but one main reason is that the desulfurization is very easy to do in the crucible type furnace, It is not practical in a channel furnace partly because of a more difficult slagging condition in the channel type. In case of duplex you should make the desulfurization after the.cupola and then enter into the channel furnace as an iron low in sulfur. E. A. PIPER: What about if you just cold-melt in a channel type and had basic lining? You would not have need to go to desulfurization then, would you? BERTIL HANAS: NO. Then you have to concentrate on scrap low in sulfur, so you would not get the flexibility of utilizing the cheapest scrap. J. M. FULTON, (Farrell Corp., Ansonia, Conn.) : First of all, in scrap preparation, should it be kept rust free? BERTIL HANAS: It is, of course, an advantage to keep it under roof, but not necessary. J. M. FULTON: HOW much slag would you generate from a cold charge in inches in a furnace of this type-a foot, 6 in., 3 in.? BERTIL HANAS: 1 cannot answer that in inches, but I would say that is fairly little. Of course, it depends on the rust. If you have thin scrap and it is stored outdoors, it will get wet and too rusty. In our own foundry, the scrap is stored outdoors right under the rain, with the exception of the chips. They are in containers, but the rest of the scrap is taken right from outdoors and put on the furnace floor and from there it is taken by chutes into the furnaces. There are no special problems with the slag. Possibly there are 3 in. on top when it is melted that have to be skimmed. J. M. FULTON: Some of the people in this country who have induction furnaces have had problems with a great deal of slag on top. This is the reason I asked the question. That is from a cold melt? BERTIL HANAS: Yes. The same problem does not exist to the same extent in Sweden. J. M. FULTON: In your removal of slag, is the rake water-cooled or is this just a steel rake? BERTIL HANAS: It is just a steel rake. If the furnace is on the platform level, we sometimes utilize an overhead crane for taking off the slag. The rake is taken down from the bath, raised with the help of a crane, and then moved away. This is, of course, somewhat elaborate but there is no problem with it. There are foundries like Akers Styckerbruk who make the complete melting in induction furnaces, but they have no problem with the slag. MEMBER: DO YOU have any typical operating figures for a 25- or 30- ton furnace with regard to running life, turns per hour, and total watts? BERTIL HANAS: Yes. A typical 30- ton furnace has a power input of 4300 kw here at 60 cycles per sec, and it produces roughly 10 tph. From that you have to take away the time that is lost at the deslagging and the pouring or handling, and so on, so this is a theoretical value. The lining life varies very much, depending upon the working conditions, and I can mention that we are right now putting together correction curves for normal lifetimes with regard to rusty scrap, temperature, special elements as titanium, and for other factors that influence the lining life. A normal figure for duplexing, for instance, from one of the installations mentioned here, is 540 charges per lining, but that is at a fairly low temperature. MEMBER: HOW about cold melting? BERTIL HANAS: That de~ends very much upon the number bf shifts. - Chairman BORIS: The sliding

7 Melting Ductile Iron in the Electric Furnace 37 off operation that you have seen here is nothing unusual, I might add that we do this for all of our heats in our Amsted Research Laboratories, or in the Washington Steel, or Eastern Stainless, so this is not unusual, and we are doing it on steel. When your sulfurs are as low as 0.003, do you actually need magnesium? BERTIL HANAS: I am not a specialist on that, but as far as I understand it,, we do. May I add to a previous question here regarding the use of channel furnaces? Of course, this way of duplexing from cupola to forehearth and then to channel would be very possible. It is just a question of economics which way you choose. One reason for choosing a crucible type furnace as we do in Sweden is to give the flexibility of melting from cold.