purpose, a mixture of gray scrap, washed metal and steel was melted to give a composition approximately that obtained by refining a cupola iron high in sulphur but low in manganese. Bars were cast from this heat as previously and annealed. The composition was similar to the first lot prepared except that the manganese was 0.14 per cent and the sulphur 0.009 per cent. In this case where the sulphur was low to start with, it had practically been eliminated by the action of the slag in the furnace. These bars after annealing were quite a lot better than those first prepared, containing manganese over 0.50 per cent. The test wedges could be curled up more, as is shown in Fig. 1. The tensile strength of this composition is from 38,000 to 40,000 pounds, but the elongation in 2 inches is only 3.5 per cent. The molding was bad and these were very defective looking bars. The bars when polished and etched, showed an improved structure over the first set but still show some pearlite in the rim, although the center of the bar shows the typical blackheart structure. This is shown in the photomicrographs. Figs. 2 and 3. The conclusion to be drawn from this result is that evidently there is still too great an excess of manganese present for the low sulphur and some further work is planned to verify this. Conclusions Among the conclusions which the author arrived at are the following: 1-The cupola is the cheapest method for producing molten cast iron, but the process has several inherent disadvantages that have limited the use of cupola malleable to work of light sections. It produces iron high in sulphur, and variable temperature and composition. 2. The electric furnace is capable of refining this iron, reducing the sulphur to a negligible amount and superheating the metal to any desired degree without any further altering of composition. 3. Such a process as described will permit iron of any carbon and silicon desired to be made by the proper additions of steel and ferrosilicon to the bath. 4. Where this duplex process is used, the amount of scrap used in the cupola can be increased and the fuel decreased as it would not be necessary to have the iron as hot as is the practice when poured direct into the molds. 5. The mixtures would have to be kept low in manganese, no high manganese pig or spiegeleisen would be used and it is believed that by using low manganese scrap the amount of manganese burned out in the cupola would lower this element to the point desired. This will have to be worked out definitely in the future. 6. As to costs, no figures can be given as the process is not believed to be in operation as specifically outlined in this paper. However, the power required ought not be more than 150 to 200 kilowatt hours per ton on molten metal from the cupola and with continuous operation, the labor charges should not be excessive. These costs would be offset by the lower cost of melting stock, reduced amount of coke used in melting and the lower temperature of the annealing ovens for the annealing of such low sulphur iron. Relation Between Machining Qualities of Malleable Castings and Physical Tests By EDWIN K. SMITH and WILLIAM BARR, Milwaukee During the past year or so, there has been considerable discussion of the machining qualities of malleable castings. At the same time there has been a decided tendency toward raising the physical characteristics, especially the tensile strength and elongation. This naturally has brought up the question: "What effects have the higher physical properties had on machinability?" There are wide differences of opinion in regard to this, and as the subject is of importance to manufacturers, as well as to users of castings, it seemed advisable to collect the available data, in order to present at least a preliminary report at this time. On getting in touch. with various foundries, it became evident that there are two general opinions, and that practically every concern has a strong leaning toward one or the other of these opinions. One set maintains that machinability is practically independent of physical characteristics, and that castings showing high tensile strength and elongation machine quite as well as those with lower physical properties. The other group feels equally strongly that in certain lines of work, where extremely high strength is not necessary, greater ease and speed of machining can be obtained by using a metal with lower physical characteristics. There is no question as to what metal to make when great strength is the prime requisite. There is little literature on this subject. A paper presented at the American Foundrymen's association convention in Boston in 1917 recommends the manufacture of malleable with high characteristics, but admits that with such The column in Tables I, II and IV marked "Decarb" gives the depth to which the carbon was burned out in the anneal. From these preliminary experiments, we were not able to find any relation between depth of decarbonized rim, and machinability, but we believe that this suggestion is well worth further investigation. extra good material, the user may have to increase the strength of his machine tools, and decrease the cutting speed. Another noted authority wrote: "In looking over these records, it is only fair to consider, that included in them are bars from concerns in which high strength and ductility have been sacrificed, in order to secure such a character of metal, as would machine with the greatest ease, this property in these particular cases being the predominating requirement." Also "One thing is certain, that as in the case of steel, the malleable iron casting that machines most kindly, is as a rule, the one poorest in physical properties." Theoretically it would seem probable that a high tensile strength in any metal, would increase difficulty in machining, if we consider that the tensile test consists of tearing apart the particles of iron, until the bar is fractured, and that a good part of the action, of any cutting tool, consists in a similar tearing apart of the particles of iron. Results of Questionnaire In order to obtain the ideas of those whose experience would qualify them as judges, we wrote a number of malleable foundries, and the replies showed considerable difference of opinions. A few quotations will suffice: 1.-"Very high tensile strength and high elongation malleable machines quite well." 2. "Iron of 50,000 or 55,000 pounds tensile strength, with elongation 12 to 15 per cent is easily machined; 100 per cent of this iron is machined at high speed-without the least trouble." 3. "There is no quesion but that very high tensile malleable iron will not answer for the small castings on which a great deal of finishing is done-where the quantity finished per hour is a matter of prime importance. High tensile material is a necessity for car work." 4.-"Unless we were able to do this (vary our mixture) our tool cost for machining these castings would in some cases be enormously increased." It is rather significant that the product of manufacturers of light castings, especially those extensively machined, as a rule averages considerably lower in physical tests, than that of makers of heavy castings, although both classes of castings give excellent results in service. It is particularly noticeable that the majority of concerns which both make and machine certain lines of small castings, prefer a metal of medium low test, as they find Spring Square Test Bar Die Stock FIG. 1-END VIEW OF MACHINABILITY TESTING DEVICE |