The process of treating iron in the cupola cannot be extended beyond the point of melting and a certain limited. amount of superheating. Any additional operation such as refining, is entirely out of the question and can be performed only in some other kind of furnace. The cupola is not a refining furnace. However, it often happens that from the double standpoint of raw materia! and product, a certain amount of refining is desirable and even necessary. Refining is the principal foundation upon which is built the reputation of the electric furnace as a metallurgical apparatus, and it is truly claimed that from even the cheapest raw materials the electric furnace can produce steel of the highest quality. With no less truth, the same can be said of preparing cast iron in the electric furnace. Essentially the electric furnace is a purifying furnace and certainly it supplies the very complement that the cupola furnace most needs.

Electric Furnace as a Refiner

In considering the electric furnace in relation to refining it is preferable to consider separately the acid-lined and the basic-lined furnaces. The acid-lined furnace is simpler in operation but also much less efficacious as a refining unit. It refines entirely through maintaining a constant reducing atmosphere in contact with the metal. The refining in an acid furnace is one of deoxidation coupled with a freeing of the bath from included gases and slag. However, the acidlined furnace is hardly to be compared with the basic for refining, and its use in a duplex process should be for plain superheating and for mixing, but not where any considerable degree of refining is desired.

One must turn to the basic-bottom electric furnace to find potentiality in refining at its greatest. The possibilities of this furnace are bounded only by economical considerations. Almost any metallurgical reaction may be conducted in it, including oxidation, reduction, dephosphorization, desulphurization, decarburization, carburization, mixing with ferroalloys, superheating, and others. The duplex process for cast iron is chiefly concerned with reduction, desulphurization and mixing.

Normally, the conditions in the electric furnace are strongly reducing and the exposure of cupola melted iron to them seems to have a distinctly beneficial effect. Whether iron can be oxidized in the cupola under ordinary conditions is a question upon which the authorities are not all agreed nor is there unanimity of opinion as to the benefit or harm of oxygen in cast iron. Personally. the author believes a deleterious oxidation can at times occur in the cupola, and his experience strongly indicates that cupola iron thoroughly deoxidized as it is in the electric furnace, exhibits an improvement in general physical properties that is hard to account for on any other grounds than of deoxidation. Also it is his experience that thoroughly deoxidized iron has perceptibly more life than has the untreated iron at the same temperature.

Desulphurization in Electric Furnace

Desulphurization is an extremely satisfactory reaction when performed in the basic electric furnace. It is not only easy to perform but it takes place during the same time that the iron is being superheated, involving no extra consumption of power. Another factor tending to fit the operation into this process is the fact that desulphurization depends for its success upon maintaining reducing conditions in the furnace. The chemical reaction by which the sulphur is removed is essentially as. follows:

FeS + CaO+C=Fe + CaS + CO.

From this reaction it is seen that carbon is essential to its completion and therefore the large amount of carbon in the iron, and the carbon electrodes themselves, have a most beneficial influence upon the removal of sulphur from the bath. It is understood that the necessary basic slag is present in sufficient quantity and of the proper quality.

Sulphur is unavoidable in cast iron made by the usual methods and it is the custom to pass it over as a necessary evil. If the bare truth be spoken, the only good that can be said of it is that sometimes it is of assistance to the founder in obtaining chilled castings. The damaging fact about sulphur is that whether united with iron or with manganese in the form of sulphide, it composes an insoluble, non-metallic structural

component in cast iron that cannot do aught but unfavorably affect the good physical properties of the metal.

May Reduce Sulphur to Low Figure

Standard pig iron containing a maximum of 0.05 per cent, sulphur contains from 0.07 to 0.11 per cent after coming from the cupola, the degree of contamination depending upon the quality of coke, the condition of the cupola and its accessories, and the skill and knowledge of the cupola tender. The same iron from the cupola may subsequently have its sulphur reduced to about one-third or one-fourth by 30 or 40 minutes refining in a basic bottom electric furnace. The average of a great number of "duplexed" heats of gray iron was .088 per cent sulphur in the melt from the cupola, while in the final product from the electric furnace the average was 0.036 per cent. As low as 0.009 per cent sulphur in occasional heats has been produced in gray iron under everyday working conditions.

The economical side of this great power of desulphurization attracts the attention. The founder who is able to employ this process with the basic furnace immediately finds himself to a large extent emancipated from the tyranny of low-sulphur specifications in the selection of raw materials, including pig iron, scrap and coke. The advantage is great and must be apparent to all. According to metallurgists of the iron foundry there exists today a sulphur problem which bases its gravity upon the probability that constant melting and remelting of the iron scrap of the world is causing a steady increase in the sulphur content of iron castings made from even the smaller percentages of scrap iron. Coke also is involved and the duplex process described does not necessitate the use of low sulphur cokes which not always are easily obtained. The doors of many foundries are closed to "off" grades of pig iron because of the high sulphur brand of shame attached to them. Here the basic electric furnace is a great leveler which makes high or low sulphur irons almost equally acceptable.

We have said that the electric furnace step of the duplex process is particularly good for mixing. It enables a perfect

mixing of the original raw materials, assuring homogeneity in the single heat, and it facilitates the accurate duplication of results, assuring uniformity among several heats. It simplifies and insures the perfect admixing of alloys such as ferrosilicon and ferromanganese. In the case of the latter, it is especially valuable in view of the considerable loss of manganese that is inevitable in the cupola. Under the reducing conditions prevailing in the electric furnace there is absolutely no loss of manganese. Steel scrap may be admixed in the electric furnace making attainable that carbon-diluted form of gray iron which is also known as semisteel. This method indeed produces a real alloy of gray iron and steel with the total carbon capable of the closest regulation, and the dream of the semisteel enthusiasts is realized as by no other method.

In concluding, the author would like to leave two injunctions concerning the use of the electric furnace as an adjunct to the cupola. In the first place, the duplex process just described is not intended to displace the established methods of preparing iron in the cupola for ordinary grades of iron castings; certainly they will not bear the added cost. The process is intended, however, for those extraordinary cases where ordinary iron as produced by the ordinary process has not met the demands of the occasion and where the advantages gaired justify the extra cost of production. Also, the author does not claim that the electric furnace presents an infallible cure-all. Its adoption cannot be expected to release the founder from the necessity of good foundry practice and of constant, experienced and intelligent metallurgical supervision in every department of the foundry establishment. The electric furnace is but a bit of apparatus, efficient, it is true, and in some ways almost wonderful, but it must be supplemented by human brains.

Discussion

DR. RICHARD MOLDENKE.-We are going to get all the castings made during the war back in the scrap pile before 20 years have passed and we will get scrap with up to 0.32 per cent sulphur. The question is what we are going to do with

material so full of sulphur-although sulphur is not so dangerous as we once thought it was. Mr. Elliott has found that the basic hearth electric furnace will be the solution for the high sulphur trouble. I have tried to overcome the sulphur problem but so far have failed. The last experiment I made was by blowing hydrogen through the molten metal to reduce the sulphur and deoxidize the metal at the same time. I nearly blew the place up and got a perfectly hard white iron out of gray pig. In the basic electric furnace you have the lime or magnesia bottom, which is ready to take up sulphur if you have the temperature high enough; and so Mr. Elliott has reduced the sulphur to almost nothing by melting the metal in the cupola in the ordinary way and finishing in the electric furnace. The only drawback is the high first cost of

electric furnace plant. With castings costing you from 15 to 18 cents a pound in your own shop, it does not hurt to add another 2 cent a pound by making them in the electric furnace. Where you have a casting costing you 4 cents a pound in your shop, you cannot add another half cent. Therefore the electric furnace will be popular for higher grade work, such as piston rings, etc., where you can afford to add a little to the cost to obtain molten metal yielding extra good results.

A MEMBER. I would like to ask if Dr. Moldenke has had any experience in the use of cast iron borings in the electric furnace.

DR. MOLDENKE.-I have not had any experience myself, but I think that in the basic electric furnace you ought to get first class results. The idea is that the electric furnace has heat enough for complete deoxidation and then the results will be all right.

MR. GRAGAN.-I have had a little experience with a carbon bottom electric furnace for melting scrap and converting it into gray iron. I used a 500-pound furnace, and with 85 per cent coke and 15 per cent pitch and by putting in a carbon bottom, I am now melting turnings and borings, both of steel and iron, and getting gray iron castings.