Molten metal

“ The molten metal is sea-green in colour, and at higher temperatures (in the electric arc) it vaporizes and burns with a green flame. G. W. A. Kahlbaum succeeded in subliming the metal in a vacuum, and H. Moissan (Compt. rend., 1905, 141, p. 853) distilled it in the electric furnace. Molten copper absorbs carbon monoxide, hydrogen and sulphur dioxide; it also appears to decompose hydrocarbons (methane, ethane) , absorbing the hydrogen and the carbon separating out. ”

“ We know that if burned in a furnace this ton of high grade fuel would generate much heat. Burned inside of the mass of molten metal it generates exactly that same amount of heat and the heat is applied with such rapidity, directness and efficiency that the molten iron which had a temperature of 2300° F., say, when charged, in nine or ten minutes 131has become steel with a temperature of about 3000° F. simply through this rapid oxidation of its 4 to 6 per cent of metalloids. ”

“ In these furnaces which consisted mainly of a shallow hearth filled with glowing charcoal, with tuyères for blast supply, the pigs of iron were heated until molten. At high temperatures the metalloids of pig iron will readily burn in a blast of air. After the air blown over and upon the molten metal has burned out most of the carbon, the main metalloid, the melting point of the purified metal becomes so much higher that the heat of the furnace is not sufficient to keep it molten. It becomes more and more pasty and stiff therefore. ”

“ In the wrought iron process most of it was furnished by the iron ore or scale which was stirred into the metal, or by the slag which covered the “bath.” In the Bessemer, or as it was first known in America, “Kelly’s air blowing process,” the oxygen of the air blown through the molten metal directly oxidizes or burns out the carbon, silicon, and manganese. The extremely rapid oxidation of these furnishes the heat. ”

“ Too, the metal for valves and fittings and other more or less complicated castings for high steam, air, ammonia, water, etc., must be uniform, of close grain, strong, yet soft enough to machine easily at the extremely high speeds which modern efficient tools and methods demand. The production of the best metal for such work requires the use of properly selected materials, judicious mixing, and clever operation of the cupola furnace, that the molten metal delivered to the foundry for the pouring of the molds may be hot and fluid and of the right composition for the particular work in hand. ”

“ If a spherical ball of any metal be plunged below the surface of a molten bath of the same or another metal, the cold ball will displace its own volume of molten metal. If the densities of the cold and molten metal be the same, there will be equilibrium, and no floating or sinking effect will be exhibited. If the density of the cold be greater than that of the molten metal, there will be a sinking effect, and if less a floating effect when first immersed. ”

“ After a few minutes’ heating to a temperature above 4000° C.—a temperature at which the lime furnace begins to melt and the iron volatilizes in clouds—the dazzling, fiery crucible is lifted out and plunged beneath the surface of cold water, where it is held till it sinks below a red heat. The sudden cooling solidifies the outer skin of molten metal and holds the inner liquid mass in an iron grip. The expansion of the inner liquid on solidifying produces enormous pressure, and under this stress the dissolved carbon separates out in a hard, transparent, dense form—in fact, as diamond. ”

“ The earthy materials of the ore with the flux form a fluid slag, while the action of the fuel, or other chemical action, produces a molten metal in some cases or, in other cases, a fused mixture of sulphides, called matte, which is much richer than the original ore in the amount of valuable metal it contains. In iron-smelting the ore, mixed with coke or coal as fuel and with limestone as flux, is fed in at the top of an enormous blast-furnace, a structure somewhat like a barrel in shape, but slenderer and much narrower at the bottom than elsewhere. ”

“ These freezing-point curves and transformation curves thus divide the diagram into 8 distinct regions, each with its own specific state or constitution of the metal, the molten state for region 1, a mixture of molten metal and of solid austenite for region 2, austenite alone for region 4 and so on. This will be explained below. If the metal followed the laws of equilibrium, then whenever through change of temperature it entered a new region, it would forthwith adopt the constitution normal to that region. ”

“ We easily fall into the habit of thinking of molten rock as we think of a molten metal, merely as a substance which has passed from the solid to the liquid condition because of high temperature. With the return of low temperature a molten metal returns to the solid state usually in the same molecular condition which it possessed before. The point of fusion and the point of solidification are the same and are rigidly fixed. If this were true of the constituents of a rock, a definite order for the solidification of the several minerals might be anticipated. ”

“ But in controversion of these suggestions, we can state as the result of experiment that pieces of cast-iron which have had their surface roughness entirely removed, leaving the bright metal exposed, still float on the molten metal, and further that when, under the influence of the great heat of the molten mass, the solid is gradually melted away, and consequently any possible surface impurities or adhering air must necessarily have been removed, the remaining portion continues to float to the last. ”

“ In pig-casting machines two endless chains carry a series of pressed-steel molds, which travel at slow speed past a trough terminating in two mouths. The molten iron from the furnace is tapped into a ladle, which is carried by a ladle-car into position to discharge into the double-mouthed trough. As each mold passes it is filled with molten iron. The endless chain of molds as it moves along descends under a tank of water, where the molten metal cools and hardens. ”

“ The freezing of molten cast iron of 2.50% of carbon goes on selectively like that of these steels which we have been studying, till the enrichment of the molten mother-metal in carbon brings its carbon-contents to B, 4.30%, the eutectic [3] carbon-content, i.e. that of the greatest fusibility or lowest melting-point. At this point selection ceases; the remaining molten metal freezes as a whole, and in freezing splits up into a conglomerate eutectic of (1) austenite of about 2.2 % of carbon, and therefore saturated with that element, and (2) cementite ”

“ The earthen mould is closed directly it is filled with metal, after which the compressed gas is admitted to it from a reservoir of liquid carbonic acid, and in this way the space above the molten metal is filled with gas under very high pressure. A tendency to the formation of flaws and cavities, which nearly all metals are subject to—meaning, in the case of railway plant, broken bridges and fractured crank axles—is in this way completely avoided. ”

“ To remove these it is not only necessary that some substance should be added which has the power of combining with them, but of one which is capable of forming a compound which shall become fusible by the heat of the furnace, so that the molten metal as it sinks through it by reason of its greater specific gravity, and falls to the bottom of the furnace, shall be protected in doing so from contact with the air. ”

“ When a ladle or pot of molten iron is drawn from the melting furnace and allowed to stand at rest, the surface presents a most remarkable and suggestive appearance. Instead of remaining calm and smooth it is the scene of a lively commotion: the thin coat of scoria or molten oxide which forms on the otherwise bright surface of the metal is seen, as fast as it forms at the circumference of the pot, to be swept by active convergent currents towards the centre, where it accumulates in a patch. ”

“ There are many ways by which Metals are brought to light, viz. by huge Fires: if by Accident and Carelesness of Shepherds, a Wood catcheth fire, the Earth by reason of the intollerable heat Gapes, and the molten Metal flows forth and is detected: sometimes also vehement Earthquakes discover them.
Besides, the Veins of Metals are found out when deep Wells and Pits are digged, or by the Plowing in the Fields, they are sometimes dig’d up, and their Veins discovered: strong Rivers washing away the Earth and Sand, do sometimes open their Veins ”

“ The mould must have a good surface and be composed of the right kind of iron. The best metal for the purpose appears to be one high in silica and low in combined carbon, thus securing a soft iron which will not crack when the molten metal strikes it. ”

“ When two dissimilar metals are to be joined, the one which melts at the higher temperature must be acted upon by the flame first and when it is in a molten condition the heat contained in it will in many cases be sufficient to cause fusion of the lower melting metal and allow them to unite without playing the flame on the lower metal to any great extent. ”

“ Molten silver, for example, is capable of absorbing from the atmosphere more than twenty times its volume of oxygen, which it expels on solidification, thus producing what is called the “spitting of silver.” Platinum again can absorb and retain when solid, or occlude, a large volume of hydrogen, that can be expelled by heating the metal in vacuo. In like manner molten rock under pressure can absorb much steam. It appears that many igneous rocks contain gases locked up in their pores, not set free by pulverization, yet capable of expulsion by strong heat. ”

“ For, of course, as there cannot be abrupt variations in the constituent elements of a molten metal which is uniform, it must follow that a process of reservoiring which in the continuous operation of a plant will obtain a uniform metal must necessarily exclude abrupt variations in the quality of the metal. ”

“ He only heard a little hissing as the metals battled for the precious oxygen.
There was no explosion, there was no violent scattering of molten particles, and there were no noxious life-destroying gases such as come from the explosion of gunpowder, dynamite, or even the burning of coal. And yet the seething, molten metals in the crucible reached a temperature second or third to the highest ever registered by man. Five thousand four hundred degrees—think of it!—more than half as hot as science tells us is the sun which makes this world of ours habitable. ”

“ It oxidizes the carbon also, which escapes in purple jets of burning carbonic oxide. As the melting point of the metal is gradually raised by the progressive decarburization, it at length passes above the temperature of the furnace, about 818 1400° C., with the consequence that the metal, now below its melting point, solidifies in pasty grains, or “comes to nature.” These grains the puddler welds together by means of his rabble into rough 80-℔ balls, each like a sponge of metallic iron particles with its pores filled with the still molten cinder. ”

“ Such parts as may be subjected to extreme heat and the fretting action of molten material, as the tuyere and slag breasts of blast furnaces, and the fire bridges and bed plates of reverberatory furnaces, are often made in cast iron with double walls, a current of water or air being kept circulating through the intermediate space. In this way the metal, owing to its high conductivity and low specific heat as compared to that of water, is kept at a temperature far below its melting point if the water is renewed quickly enough. ”

“ In consequence of the extremely high temperature which we can command, either in the Bessemer or open-hearth process, it is possible to obtain in a molten state a metal practically free from carbon, or containing carbon to any required amount. All of the products have been called steel, although they constitute in effect a new metal, having qualities considerably different from those of steel. ”

“ Waves of light, tongues of leaping flame, passed over the polished surface of the metal, here darting off in long zigzag streaks, there forming a sort of pool of molten, quivering fluorescence, as the physicists call it, varying in size and color, then vanishing utterly. Much the same appearance Una remembered having seen on the surface of a copper kettle when subjected to intense heat. ”

“ These two things are done simultaneously by heating and melting the ore in contact with coke, charcoal or anthracite, in the iron blast furnace, from which issue intermittently two molten streams, the iron now deoxidized and incidentally carburized by the fuel with which it has been in contact, and the mineral matter, now called “slag.” This crude cast iron, called “pig iron,” may be run from the blast furnace directly into moulds, which give the metal the final shape in which it is to be used in the arts; but it is almost always either remelted, following path 1 of fig. ”

“ The process consists in forcing through molten cast iron, held in a vessel called a converter, a stream of cold air under pressure. The combination of the oxygen in the air with the silicon and carbon in the metal raises the temperature of the latter in a spectacular way and after "blowing" for a certain period, eliminates the carbon from the metal. Since steel of various qualities demands the inclusion of from 0.15 to 1.70 percent of carbon, the blow has to be terminated before the elimination of the whole carbon content ”