US1555312A - Pure iron product - Google Patents

Description

manta Sept. 29, 1925.

UNITED STATES PATENT OFFICE. Y

cnmns E. rAnsoNs, or NEW YORK, N. 1., m1) SAMUEL rmcocx, or wnmmo, wns'r VIRGINIA, nssrenons r mun. nnsmcn coiarom'rlon, or mw Yonx,

N. Y., A. CORPORATION OF DELAWARE.

-- roan moi: rnonuc'r.

No Drawing. Orlglnalappllcatioiz filed October 17, 1923, Serial No. 669,111. Divided this application filed October 22, 1928. Serial llo. 870,097.

certain new and useful Improvements in Pure Iron Products; and we do hereby declare the followin to be a full, clear, and exact description 0 the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to pure iron prod- 1 nets and has for its object to produce such iron in large masses with a greater purity and at a less cost than has heretofore been possible.

With these and other objects in view the invention consists. in the novel product constituting the article of manufacture, all as will be more fully hereinafterdisclosed and particularly pointed out in theclaims.

. This application constitutes a division of our copending a plication Serial No.

669,111, filed Oct. 1 1923, andentitled Process of and apparatus for producing pure iron from its ores. In order that the invention may be clearly so understood it is said :In carrying out the procedure for making the pure iron product of this invention, one employs a temperature of reduction whichdoes not rmit the iron ore to sinter, and therefore, 1t does not collect impurities, such as slag, silica, etc. As

is .well known should these impurities become embedded in the fused mass of the iron, the subse uent step of separating out. the pure iron irom the gangue wduld fail 40 to remove all the impurities, and therefore,

upon the later fusion of the pure iron, after passing the magnetic separator, such impurities would remain .with the metal andv later cause more or less metalloids to form 46 and thus lessen the purity of the resulting product.

It is also known that unless pure iron is produced above a given temperatureflt will constitute when formed what is known as 50 pyrophoric iron, which is chemicall very active, and therefore, not sultable or the purposes in hand. It is therefore necessary in carrying out this. p ocess, to heat the iron oxide above 1500 which will prevent the presence of pyrophoric properties in the iron; and it is also necessary to so control the' aemperature that it wil not go above 1800 F., for otherwise its purity will be decreased.

In order that the invention may be the more clearly understood it should. further be said that the metallurgy of iron and steel as usually practised at thls time, consists in reducing iron oxide usually with carbon or carbon monoxide, producing a crude iron carbide and treating such crude metal b various methods to remove impurities. Sue refining processes consist largely in puddling or kneading the crude metal to separate .out the relatively low melting point impurities, or in burning with air and slagging out the metalloids. All these processes are costl and are not technically efl'ectual. The pu dling process does not clear the metal of slag, but gives a product containin relatively very small quantities of occlude gases and oxidation product, nitrogen compounds, etc. The air processes of the Bessemer and open hearth type of furnace are capable of removing more or less slag and the metalloid impurities forced into the metal by the blast furnace process, but in doing so they charge the metal with dissolved ases, iron oxidation products, in solid so ution in definite proportions, and undetermined forms of nitro en compounds.

It is possible, it is true, wit elaborate and costl refinin o rations, to greatl minimize the obje c tio ble effects of the; refining treatments, but a positively homogeneous metal is substantiall never realized, thus giving rise to an inevitable uncertainty as to the performance of such refined iron when used industrially.

, By the process to be disclosed below these objections are removed as will presently appear, and an iron is produced in masses of a larger weight and a greater purity thanhas heretofore been attainable in so far as we can find out. Further, the so-called I00 pig iron or blast furnace smelted iron varies considerably in composition, depending upon the ores and coke employed and the method of working-the furnace. An approximate general analysis showing the impurities in such iron may be stated as follows:

All these impurities are forced into the crude metal by the nature of the blast furnace smelting, in which the ore and its accompanying impurities such as silica and alumina are mixed with a flux to slag the silica, etc., and by the coke to supply heat. This mixture is charged into a closed system furnace such as a blast furnace, and the whole mass exclusive of fuel carbon is melted down together. All components of this furnace mixture, together with the necessary fuel, are charged into the furnace as solids and can only escape as liquids or gases. As a result very high temperaturesmust be employed and the furnace must be operated constantly under positively reducing conditions, and there are no practicable means of separating impurities, except by the difference in densities of the melted or gaseous products.

This process on'the other hand, obviates the necessity of introducin these impurities in the product, and there ore, itavoids the difficulties and, expense incident to their removal.

Further, the carbon itself is initially burned to carbon monoxide, thus utilizing scarcely more than one third of its heating power so far as the melting zone of the furnace is concerned. Unfortunately, elemental iron readily forms compounds with metalloids, hence silicon from; the silica, and carbonfrom the coke together with the highly objectionable sulphur and phosphorus in the furnace charge tend to ultimate in the crude iron. Iron ore generally contains very little sulphur, but the coke necessarily employed contains from one to two per cent andof the total sulphur in the furnace charge about 90% comes from coke. This sulphur must be as completely removed as possible, and this is usually done by adding a relatively large proportion of lime to the furnace charge, which requires stillmore coke for its conversion to a fusible slag, so

"that at best, sulphur elimination is never more than partial. By the procedure of this invention these objections are likewise eliminated as will presently appear.

- In addition to the foregoing objections,

the fuel proportion is greatly augmented, under the prior procedures, because to form and melt a pound of slag requires seven times as much coke as is necessary to re duce from the oxide and melta pound of iron. The inefliciency of the blast furnace process is indicated by the fact that while somewhat less than one third of a pound of coke is technically sufficient to reduce and melt a pound of iron from iron oxide, more than one pound is required in actual practice and the result is a very crude iron product of minor industrial value, unless it is further refined. These last named objec-. tions are likewise obviated by the procedure disclosed below. Again, although pig iron refined by the kneading or puddling process gives a moderately uniform product, yet, the operation is entirely too costly for general industrial application. And the Bessemer and open hearth processes, while almost universally employed, give a very uncertain product. In fact, Sir Roberts Austin experimentally determined that steel made by such methods, contains from six to eight times its volume of gasses, which high temperatures alone will not remove, and ample evidence supports the belief that these dissolves gases are seriously objectionable, although elaborate and costly processes have been devised for their removal as an industrial procedure. It results that most of the methods involve adding further impurities, and none of them are positive in refining effect. Also in these smelting processes, from the blast furnace through the open hearth furnaces or converters, a considerable proportion of rejected materials are produced, which generally contains too much iron to discard as waste and which must be reworked in the blast furnace. In fact, it is safe to say that practically over 25% of the total iron smelted in a blast furnace connected with steel making is reworked metal which must bear again and again the cost and losses of smelting.

The process of this invention again avoids these objections as will appear more fully hereinafter.

According to this invention, on the other hand, pure iron may be produced direct from the ore b the following procedure which consists simply in reducing iron oxide at about 1500 F. in a stream of a reducing gas which has previously been desulphurized by any suitable means. The gas which may 1 gases in excess and maintaining in the reducing chamber a partial pressure of carbon dioxide, or water vapor, never .in excess of 5 centimeters, practically a quantitative reduction of iron oxide maybe' realized. The ore prior to reduction is thoroughly dried and passed through rolls to evenly size the particles of mineral and prevent clumping.

It is not practicable to completely reduce ferric oxide, or the magnetic oxide with a theoretical quantity of carbon monoxide only in the presence of the catalytically reacting pyrophoric elemental iron in contact with carbon monoxide, because therewill result the following reaction:

cess, but this reaction will deposit carbon on the metal, pyrophoric metal, if present, and it would be difficult to later remove it.

But, if once deposited and not removed,

the carbon would ultimate as iron carbide whenthe iron is melted thus destroying its purity. Above 1200 F., however, the car bon deposition (reaction velocity from the gas is greatly reduced'and at about 1400 F. a reversion of the pyrophoric properties of the iron commences; But. there is always possible a momentar temperature 'drop which may deposit car on upon the reduced pyrophorlc metal and thus upon fusion, introduce iron carbide into the end product of iron. But this is avoided by providing in the apparatus a positive temperature control which prevents the iron from' reaching a point below a predetermined degree. Probably equally undesirable is the presence of a small, even minute quantity of ferrous oxide which may accompany the carbon deposition, and which would dissolve into the iron upon fusion. Therefore, to avoid these objections the temperature ranges'employed must be strictly maintained within narrow limits not above 1800 F. and not below 1500 F. y Y

Coal gas may be used as a reducing agent containing about 47% hydrogen. A gas of this type contains by volume approximately:

00.18%. C0 =3%. CH,=32%. C H,=5%. H :47%.

sired tem rature. By this means, the ore 06"; and reducing agents may be kept above the No great conis then suitabl 7 Its positive freedom temperature at which pyrophoric iron can exist and at which the CD can deposit carbon.

If hydrogen is used, as a reducing agent, the reaction is strongly endothermic requiring about 347 B. t. u., per pound of iron thus Per cent. Elemental iron 56. 8 Ferric oxide 81. 2 Silica 8. 3 Alumina 2. 5 Lime phosphate l Lime sulphate 1 Lime carbonate 3 Magnesia carbonate A Manganese dioxide 1. 2

Volatile matter The iron oxide of this ore may be separated out by an oil separation, or. by other well known ore treating operations, producing as an end product, iron oxide of a purity exceeding 99.9% or the crude iron oxide may be reduced to elemental iron, and such iron removed from the gangue material by a magnetic separation.

' After treatment with reducing gas, as described above, if crude ore is employed,

there remains in the solid form from 100 pounds of such ore, 56 pounds of elemental iron and 14 pounds of. gangue material, the latter having passed through the reducing chamber unchanged. The solid matter is conveyed out of the reducing chamber by any suitable means, and after cooling below the magnetic transformation point or substantially below 1400 F. is passed through a magnetic separator by means of which, in two or more passes, the elemental ironis completely separated from the gangue matter and isv physically in the form of a fine powder and substantially chemically ure as it has not been in contact with carn or metalloid oxides at a higher temperature than about 1500 F. The'iron powder delivered into an electric furnace of the induction or similar type, by means of which it is melted into a mass without contact with carbon electrodes or in any way subjected to carbonaceous material. The molten product is pure iron.

w from gaseous occlusions, metalloid solutions and slag inclusions of any kind preclude the presence of alloy eutectics or eutectoids, an constitutes this metal as a composition or state of matter never heretofore known in mass as an industrial product in so far as we are aware.

Its industrial usefulness is wide and varied; it has a low corrosion factor, is easily worked without strain hardening, and may be shaped as readily as zinc or tin. Its chief use, however, is in making steels free of gaseous occlusioiis and metalloid eutectoids. For such purposes it is only necessary that a suitable alloying metal or compound be added in the desired proportions to the molten pure iron. Any desired alloy effect may be positively and exactly duplicated at will, an accomplishment quite impossible under the present method of making special steels.

For making straight iron carbides for carburizing iron and steel without adding impurities, this metal brought to a high temperature such as 4000 F., in contact' with pure carbon will take up nearly 10%, of carbon. An'alloy of iron and carbon of this nature enables the manufacturer to produce a wide range of iron carbon steels of exceptional purity and of positive physical properties. There can be no blow holes in an ingot made of such materials, and practicallyno'lamination or segregations in the worked metal.

It will now be clear that by following this.

process, iron'oxide is reduced by means of a reducing gas, at a low temperature. Illustrating with carbon monoxide and with a hydrogen, the reactions may be stated thus:

be supplied in the heating chamber to regulate the combustion of the gases used for heating the charge, to avoid too high temperatures. If the hydrogen is employed as the reduction reagent, heat is absorbed and there is no dan er of" objectionably high temperatures in e reducing chamber.

According to the theory of allotropy, all allotropic substances are complex, and if ferric oxide is reduced at a temperature different from that at which the oxide was formed originally, a metallic phase different from the original metallic state will be obtained. When iron oxide is reduced very slowly at about 750 F. the elemental iron thus obtained, has very different physical properties from those of ordinary iron at 750 F. This elemental iron thus produced at such low temperature consists possibly of ferrous ions exclusively, and constitutes substantially the state of iron usually known as pyrophoric. Pyrophoric iron is extremely active, as above stated, and its presence in elemental iron produced by gaseous reducing reagents very markedly lowers the efliciency of reduction, because the partial pressure proportion of the gaseous reaction product is enormously reduced. That is, the reaction reverses at vastly lower partial pressures of carbon dioxide or water vapor than is usually observed in studying reactions with ordinary iron; This, of course, seriously involves the commercial application of producing pure iron by gaseous reducing agents; and means must be found for the elimination of the pyrophoric state in such reduced elemental iron. I

In fact, pyrophoric iron maintained at 600 F. for 48 hours, loses most of its active tendency and at 650 F. for 24 hours the pyrophoric state entirely disappears; but holding a charge of such iron for 24 hours under narrow temperature limits is a diflicult and costly industrial operation.

The general proposition has been confirmed that the well known iron alpha-beta transformation point about 1420 F. (770 to this process, therefore, that at all stages of the reducing operation the temperature of the elemental iron shall never fall below 1500 F. as produced, and to avoid sintering and thereby entangling particles of gangue matter in such manner as to cause the magnetic separation to fail, the reducing temperature must not exceed 1800 F.

Pureferric oxide melts at 2854: F. and sinters readily at 2300 F. The crude oxide as it occurs in iron ore, sinters appreciably at 1850 F. Therefore, for efficiency in the operation of our process the iron oxide under treatment in the reducing phase should never fall below 1500 F. nor exceed 1800 F. also in drying the ore and driving out water and organic matter, the maximum temperature employed should not exceed It is obvious that after reduction to elemental iron the material must be cooled below the magnetic transition point 1420 F.

in order to enable magnetic separation. The cooling of the finely divided elemental iron under such conditions does not restore the oxide at low temperatures, a negative catalyst' may be mixed with the oxide, such as arseneous acid in very smallproportlons;

or a few hundredths of one per cent of chlorine may be added to the reducing gases.

temperature of reduction it does not enable the use of temperatures higher than 1800 F. in the preparatory stages.

In the practical operation of our process, the iron oxide is thoroughly dried and oranic matter burned out when present.

he ore is then passed through a reducing apparatus, the temperature being positively maintained between 1500 and 1800 F. The reducing apparatus consists of three or more reducing decks upon which the ore is slowly delivered at a point on the outer circumference of the uppermost deck. Re

volving arms having plow shaped stirrers attached slowly move the ore in successive circular ridges, from the circumference of the deck .to a central aperture, when the charge falls to the deck below. On this deck the plows attached to the revolving arms work the charge in successive ridges to the circumference of the deck where apertures suitably placed enable the ore to fall to the .next lower deck; this treatment of successive ridging is continued on as many decks as the particular ore under treatment may require. One or more upper chambers may be usedfor .heating the ore when required by burning a portion of the reducing gases within such chamber or chambers. The reducing gases enter the reducing furnace at the bottom deck and pass'through and over the successive decks, in counter current to the flow of the furnace charge. charge from the reducing furnace passes over magnetic separators to eliminate gangue, and the pure iron powder is discharged into an induction furnace for fusion. The whole system from the reducing furnace to the induction melting furnace is sealed in a closed system.

The performance of the reducing furnace is the controlling factor in the process. It is known that the efliciency of deoxidation of iron oxides byameans of reducing gases The disis less a function of fineness of subdivision than of surface contact between the oxide and the reducin reagent. B means of a fi ect, fresh sur aces are constantly being exposed to gas contact.

What'is claimed is 1. The herein described new article of manufacture consisting of a mass of substantially pure iron reduced from its ore at a temperature between 1500 F. and 1800 F. I

2. The herein described new article of manufacture consisting of substantially chemically pure iron whlch has been reduced from its ore in a finely divided condition at a temperature between 1500 F. and 1800 F. and melted into a mass.

3. The herein described new article of manufacture consisting of a mass of substantially pure iron having less than 0.1% of impurities.

4. The herein described new article .of manufacture consisting of a mass of substantially pure iron having less than 0.11% of impurities and devoid of'gaseous inclu- SIOIlS.

5. The herein described new'article of manufacture consisting of a mass of substantially pure iron having less than 0.11%

of impurities and devoid of sions and metalloid solutions.

6. The herein described new article of manufacture consisting of a mass of subgaseous inclustantially pure iron havin less than 0.11%

of impurities and devoid of gaseousinclusions and eutectoids.

In testlmony whereof we aflix our signatures.

, CHARLES E. PARSONS.

SAMUEL PEACOCK.