US2929704A

US2929704A - Methods of and apparatus for degasifying metals

Info

Publication number: US2929704A
Application number: US633971A
Authority: US
Inventors: Harders Fritz
Original assignee: Dortmund Hoerder Huettenunion AG
Current assignee: Dortmund Hoerder Huettenunion AG
Priority date: 1956-01-17
Filing date: 1957-01-14
Publication date: 1960-03-22
Anticipated expiration: 1977-03-22
Also published as: GB801518A; CH346230A

Description

F. HARDERS March 22, 1960 METHODS OF AND APPARATUS FOR DEGASIFYING METALS Filed Jan. 14, 1957 s sheets-sheet 1 ATTNEYS March 22, 1960 F. HARDERS METHODS OF AND APPARATUS FOR DEGASIFYING METALS Filed Jan. 14. 1957 5 Sheets-Sheet 2 C ffy-2 5 Sheets-Sheet 3 March 22, 1960 F. HARDERS METHODS oF AND APPARATUS FOR DEGASIFYING METALS Filed Jan. 14, 1957 F. HARDERS March 22, 1960 5 Sheets-Sheet 4 Filed Jan. 14, 1957 Inventar: 5?/ rz #Akne-.es

F. HARDERS March 22, 1960 METHODS 0F AND APPARATUS FOR DEGASIFYING METALS Filed Jan. 14, 1957 5 Sheets-Sheet 5 INV E N TOR Fritz Harder@ lWETHDS F AND APPARATUS FOR DEGASIFYING METALS Fritz Harriers, Post Ergste Uber Schwerte (Ruhr), Germany, assignor to Dortmund-Border Httenunion Aktiengesellschaft, Dortmund, Germany Application January 14, 1957, Serial No. 633,971

Claims priority, application Germany February 27, 1956 4 Claims. (Cl. 75-49) however, cannot be incorporated in the ordinary steel works. The installations are complicated and their operation is time-consuming so that they interfere with continuous production.

A vacum vessel provided with an inlet and an outlet pipe in which the metal is degasied in continuous or discontinuous flow is also known but is open to the same objections. For sealing the inlet and outlet pipes, two vessels, for example two steel-works ladles, are required of which one is filled with the metal to be degasied and the other must contain a smaller quantity of metal which is necessary for the air-tight sealing of the outlet pipe. The degasilication of the metal in continuous flow has the disadvantage that in the delivery ladle in which the steel gradually cools towards the end of the charge and tends to freeze, at least the amount of metal necessary for sealing must remain behind and, at the end of the charge, a steel which is not completely degasilied and s mixed with the molten sealing metal is contained in the receiving ladle. When Working in discontinuous flow the proportion of the melt used for sealing in the receiving ladle is particularly great, because the level of the metal in the ladle must be raised to the level of the metal in the delivery ladle in order to interrupt the ow through the vacum vessel, so that the end of the outlet pipe which has to be sealed can not at the beginning of the process be arranged so as to be near the bottom of the receiving ladle. These difficulties could only be overcome by constructing the receiving ladle as an intermediate vessel from which the metal is tapped either continuously or periodically into a steel-works ladle. rl'he vacuum vessels which operate either with continuous or discontinuous flow, therefore, require a considerable amount of time and energy to operate them which impairs all the output of the steel works. Further, the dimensions of the vacuum vessel are determined by the distance apart of the inlet and outlet pipes opening into it which must be relatively great owing to the work on the ladles and pipes which takes place below the vessel.

The invention overcomes the disadvantages of the known apparatus for degasifying molten metal, especially iron and steel melts, in a surprisingly simple manner which is the result of long experiments. The invention is based on the idea that a predetermined amount of metal can be thoroughly degasified if, with reference to the degasifying process, it is not considered as a whole but portions of it are degasilled in succession, these portions being again added to the metal remaining behind as often as is necessary to obtain the desired degree of degasilication of the whole of the metal. Only by degasiication in portions in this way is it possible to use a vacuum vessel which is of particularly simple construction and is provided with only a single pipe connection and is of States Patent O fice comparatively small dimensions, and which can now be incorporated directly in a steel-works producing steel either in large quantity or of high quality.

Starting from these considerations the invention relates to a process of degasifying metal melts, for example molten iron and steel, in a vacuum vessel disposed over a container for the molten metal and into which the metal is drawn up through a pipe, degasied and then allowed to run out again. The novel feature of this process is that only a portion of the amount of metal to be degasified which is present in the container, for example a ladle, is introduced each time into the vaccum vessel through the pipe which opens into the vacuum vessel and after the portion has been degasilied is returned through the same pipe to the metal remaining in the container or ladle these operations being repeated a number of times until the whole amount of metal to be treated has reached the desired degree of degasitcation. The filling and emptying of the vacuum vessel in portions can take place most simply by altering the depth to which the pipe dips into the metal. For this purpose either the vacuum vessel or a container arranged below it for the metal melt is so arranged that their distance apart can be periodically varied. An installation having a fixed vacuum vessel which is charged from a truck having a platform of which the height is adjustable and which carries the ladle has proved satisfactory, the ladle filled with the melt to be degasiiied being carried on the platform.

When the vacuum vessel is lilled and emptied in portions by altering the depth to which its pipe extends into the container, the vacuum pumps effects degasication continuously. There may, however, be some condi.- tions when this is not desired. In this case a stationary vacuum vessel which is charged from a simple truck carrying a ladle can also be lilled and emptied with portions, the pressure in the vacuum chamber being periodically altered, for example, by admitting gas before the chamber is emptied.

The method of the invention and means for carrying it out will now be described, by way of example, with reference to the accompanying drawings. In the drawings Figure l illustrates diagrammatcally a vertical section through the degasifying apparatus,

Figures 2 and 3 show similar views of the apparatus under different conditions,

Figure 4 is a diagram how the degasiiication process proceeds, and

Figure 5 is a diagram to explain some experiments with a model.

Referring to Figures L3, the apparatus consists of a lixed vacuum vessel 1 which is mounted on a platform B. The vacuum vessel is lined with refractory brick-Work 2 and is enclosed air-tightly by a metal jacket 3. The etiective space 4 within the Vessel may be relatively small.

A pipe 6 which is lined on the inside with refractory brick-work 5 opens into the bottom of the vessel l. The end of the pipe is surrounded by refractory brickwork 7 and a conical sheet metal body S is placed on the end of the pipe, the object of the body 8 being to displace to the side any slag on the surface of the steel melt S when the pipe 6 is introduced into the melt.

A pump 9 is mounted on the platform B beside the vacuum vessel 4 and is connected by a pipe 10 to the space 4 within the vacuum vessel.

The metal to be degasied is brought to the vacuum vessel 1 on a truck 11. A ladle 12 containing the melt stands on a platform 13 which can be raised and lowered by a hydraulic cylinder 14. Figure 1 shows the positreatment.

steel.

out of the pipe from the vacuum vessel when the ladleY steel melt occupy before VVthe, beginning ofthe vacuum Figure 2 shows the conditions afterY a vacuum has been established in the chamber 4 of the vessely 1 and the ladle lzlstanding on the platform 13 ofthe truck 1t has been raised, so that the pipe 6 is immersed more deeply in the molten steel S. The conical body 8 shown Vin Figure l has meanwhile been melted and a part of the steel content of the ladle has been Vraised about 1.4 m. by the atmospheric pressure. The space inside' the vacuum vessel is thenrlilled to ther extent Yindicated .in

the drawing. Y

After this part of the steel to be treated Lhas been ldegasiied for about 30 seconds the ladle 12.V is lowered without altering the vacuum in the vessel A and is brought into the position illustrated in Figure 3. The metal, except for a portion remaining inthe pipe- 6, then ows back into the melt remaining in the ladle 12. The raising and lowering of the ladle andthe inlet andoutlet of a portion of the molten metal into and out of the Yladle 12 caused thereby is repeated untilV the entire `contents of the ladle have been degasified to the Vdesired extent. The diagram illustrated in Figure 4'and which has been drawn from the results of a practicalY experiment ywith thedegasification process of the invention confirms ,the unexpected result thatvby a repeated introduction of only a part of the molten metal Vto be degasifed intoVV .this melt, 4` tons of the steel were introduced thirty .times in succession into the vacuum vessel, degasied in it and then returned to the melt remaining in the ladle. The suction output of the pump amounted at a pressure Vof Torr. to 2,000 cubic metres per hour.

VIt. will be seen from the diagram that each time a new portion Vof steel is admitted, the pressureY in the vacuum vessel is increased owing to the gas escaping from the steel. It will also be seen that the pressure maxima, even after two periods, continuously decrease and reach their lowest value even after about l5 minutes. From this point onwards the degasifying work of the pump takes place practically at a vacuum below 2O Torr. and continues until the entire melt has been degasied to the desired extent.

- Figure 5 `illustrates an experiment with a model to show what takes place ,when the degasied portion of the metalis returned tothe melt remaining in the ladle. The experiment was made with a glycerine-water mixlture of the same viscosity as that of ordinary liquid Figure 5a shows that a continuous stream'ows -is lowered/and `the stream reaches the bottom of the Vladle without being divided. The metal which is drawn I Vand said zone until the metalV insaid the desired degree rof purity.l

can be controlled by thespeed with which the ladle is moved. s Y Y The experiments with the model were also confirmed by practical trials. .After 80 tons of steel had beenV degasiiied by the process of theinvention, 100 kg. of nely powdered ferro-.silicon were added Vto the metal in the ladle and the contents of the ladle were treated in'portions of 4 tons as during the degasitication. YThe test samples taken on casting theV charge gave absolutely uniform silicon-contents in the steel.

In carrying out Vthe process of the invention it is advisable to heat the degasication vessel either by resistance heating, or by carbon rod heating, or by induction, arc or glow discharge heating.'`

During degasication the molten Ymetal to be treated can also be alloyed. For this purpose the vacuum vessel lis provided with, for example, a sluice-like container, which is not illustrated in the drawing, Lfrom which the alloying medium can be introduced into the vessel. .v

I claim: v Y 'Y l. A discontinuous' process for the degasii'ication of molten metals comprisingfmaintaining a substantially constant, subatmospheric pressure in a vacuum zone provided with a'molten metal interconnecting passageway, maintaining a bath of molten metal in adjustable relationship with respect toY said zone, Yiiowing said metal into said zone by immersing said lpassageway in said bath and reducing the distance between said zone and said bath to such an extent that onlya portion of the metal is drawn into said vacuum zone, degasifying said Vvmetal portion in said zone by the application of said Asubstantially constant, subatmospheric pressure thereto, increasing the distance betweensaid bath andk saidrzone to discharge the degasied metal portion.V from said zone to said bath, and successivelyrepeating the steps of decreasing and increasing the distance tetweeu said bath bath is brought to 2. A discontinuous process for the degasitication of molten metals comprising maintaining a bath of molten metal in a position to Vberraised andl lowered, maintaintimes the `liquid in the stream is still in the lower part f of the vessel, as shown in Figure 5b. If later the lowering of the vessel is accelerated and,V therefore, the kinetic energy of the' stream of liquid'owing out is increased, as shown in Figures 5c-5e, a vigorous mixing of the liquid in the receiving vessel takes" place. y be seen, therefore,that the progress of the degasication It will ing a substantially constant, subatmosphric pressure in a vacuum zoneprovided with a molten metal admission and discharge passageway above said bath, causing said metal to be drawn'into said vacuum zone Vby lowering said passageway into said bath and reducing the distance between said zone and said bath to such an extent that only -a portion of the metal is drawn into-saidvacuum zone, subjecting said withdrawn molten metal to said substantially constant, subatmospheric pressure in said vacuum zone to remove entrained gases therefrom, discharging the degasited metal into said bath by increasing the distance between said zone audsaid bath, and repeating' said distance decreasing andincreasing steps until the molten metal.v in said bath'is brought to the desired degree of purity.yV i f' s 3.'A discontinuous processffor the degasiication of molten metals comprising maintaining a bath of molten metal and a vacuum zone Vrnaintained'at a substantially constant, subatmospheric'pressure, said bath and said zone beingin adjustable, spaced relationship with respect to each other, said vacuum zfone having a molten Ametal admission and discharge passageway, causing said metal to be drawn into said vacuum zone by lowering said passageway into said bath and reducing the distance between said zone and said bath to such an extent that only a portion of the metal is drawn into said vacuum zone, subjecting said withdrawn molten metal` to said Ysubstantially constant, subatmospheric pressure in said vacuumV zone towremove entrained gases therefrom, discharging the degasied metal portion into said bath by increasing the distance between said zone and said bath,

and repeating said distance decreasingand increasing steps until the molten metal in said bath is brought to the desired degree of purity.

4. In an apparatus for degasifyiug molten metal, a vessel having only one molten metal receiving and discharging passageway, a lining of refractory brick-work in said vessel, said vessel and said container being in communication through only a single, downwardly extending pipe of which one end opens into said vessel and the opposite free end extends into the container for the metal to be degasied, said pipe being made of refractory brick-work and enclosed by a metal jacket and an outer ring of refractory materials protecting the lower end of said pipe, said pipe having a conical body of metal attached to the free end thereof, said body of metal being adapted to push aside the slag when said pipe is introduced into the molten metal in said container, and means `to alternately Iincrease and decrease the distance between said vessel and said container, whereby said molten metal is sequentially degasified in portions.

References Cited in the le of this patent UNITED STATES PATENTS 1,916,042 Edgar June 27, 1933 1,921,060 Williams Aug. 8, 1933 1,931,144 Gilbert Oct. 17, 1933 2,587,793 Waldron Mar. 4, 1952 FOREIGN PATENTS 138,020 Austria June' 25, 1934 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTN 51e-@em Nos 2,929,704 March 22 1960 Fritz Hamers I'b is hereby certified that error appears in the printed specification of the above numbered patent requiring correo-tion and thail the said Letters Patent should read as correo-bed below.

Column 5, line ly after "metal" insert in a container -L-e Signed and sealed this 27th day of December 1960 (SEAL) Attest: f

KARL H AXLTNE f A ROBERT C. WATSN Attesting O'cer Commissioner of Patents

Claims

1. A DISCONTINUOUS PROCESS FOR THE DEGASIFICATION OF MOLTEN METALS COMPRISING MAINTAINING A SUBSTANTAILLY CONSTANT, SUBATMOSPHERIC PRESSURE IN A VACUM ZONE PROVIDED WITH A MOLTEN METAL INTERCONNECTING PASSAGEWAY, MAINTAINING A BATH OF MOLTEN METAL IN ADJUSTABLE RELATIONSHIP WITH RESPECT TO SAID ZONE, FLOWING SAID METAL INTO SAID ZONE BY IMMERSING SAID PASSAGEWAY IN SAID BATH AND REDUCING THE DISTANCE BETWEEN SAID ZONE AND SAID BATH TO SUCH EXTENT THAT ONLY A PORTION OF THE METAL IS DRAWN INTO SAID VACUUM ZONE, DEGASIFYING SAID METAL PORTION IN SAID ZONE BY THE APPLICATION OF SAID SUBSTANTIALLY CONSTANT, SUBATMOSPHERIC PRESSURE THERETO, INCREASING THE DISTANCE BETWEEN SAID BATH AND SAID ZONE TO DISCHARGE THE DEGASIFIED METAL PORTION FROM SAID ZONE TO SAID BATH, AND SUCCESSIVELY REPEATING THE STEPS OF DECREASING AND INCREASING THE DISTANCE BETWEEN SAID BATH AND SAID ZONE UNTIL THE METAL IN SAID BATH IS BROUGHT TO THE DESIRED DEGREE OF PURITY.