US3127642A - Process and apparatus for the casting of steel - Google Patents

Description

April 7, 1964 J. ZAEYTYDT 3,127,642

PROCESS AND APPARATUS FOR THE CASTING OF STEEL Filed March 16, 1961 5 Sheets-Sheet 1 El@ giu- F7116- SHIHH; HHHI n AJ April 7, 1964 J. ZAEYTYDT 3,127,642

PRocEss AND APPARATUS FOR THE CASTING oF STEEL Filed March 16, 1961 I 5 Sheets-Sheet 2 Jimmuun'A 15./jj g J2e/w Zz gig/Z;

ATTORNEYS April 7, 1964 .1. zAEYTYDT 3,127,542

PROCESS AND APPARATUS FOR THE CASTING OF STEEL 4 Filed March 16, 1961 5 Sheets-Sheet .3

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INVENT OR ATTORNEYS PROCESS AND APPARATUS FOR THE CASTING OF'4 STEEL Filed March 16, 1961 J. ZAEYTYDT April 7, 1964 5 Sheets-Sheet 4 fed/7a Za @fig/2ER /Mzw .@'QQ M f ,a-4 i ATTORNEYS April 7, 19.64 J. ZAEYTYDT 3,127,642

PRocEss AND APPARATUS FOR THE CASTING oF STEEL Filed March 1e, 1961 5 Sheets-Sheet 5 INVENTOR Jaz lagig/l ATTORNEYS United States Patent O 3,127,642 PRCESS ANI) APPARATUS FR THE CASTEIG F STEEL .lean Zaeytydt, Montignies-sur-Samhre, Belgium, assigner to Centre National de Recherches Metallurgiques, AS-

soeiation sans l3nt Iiucratif, Brussels, Belgium Filed Mar. 16, 1961, Ser. No. 96,330 Claims priority, application Belgium Mar. 24, 1960 1l Claims. (Cl. 22.-57.2)

This invention relates to a process and casting apparatus for the casting of steel.

It is well known that ingots of unkilled steel produced by continuous casting have internal cavities, chiefly pipes and blowholes, of various physical forms and at various depths in the ingot. However, under certain conditions of production, there is formed a superficial layer of metal which is free of blowholes `and whose presence is extremely important for the production of rolled products. Commonly this compact blowhole-free l-ayer is termed skin.

The thickness of the skin increases directly with the `eewescence of the steel during solidification, and this effervescence is chiefiy due to the evolution of carbon dioxide and carbon monoxide owing to the reaction together of the carbon and oxygen in solution in the steel during the cooling. The thickness of the skin and the degree of effervescence can he controlled by controlling this chemical reaction.

Since the intensity of effervescence depends mainly on the amounts `of carbon and of oxygen dissolved in the metal just at the moment of teeming, it follows that, especially in the case of mild and extra mild steels, an excessive oxygen-carbon ratio at the end of refining often has to be reduced by adding carbon or manganese as a deoxidant. However a desire for economy often causes the amount of these additions to be limited to `such an extent that the oxygencarbon ratio of the steel remains too high and carbon dioxide and monoxide are produced from the dissolved oxygen and carbon in excessive quantities as soon as solidification begins. If the effenvescence is too intense even in the ladle, it is checked by adding aluminum which `does not lead to evolution of gas. The amount of `aluminum added, however, must be limited in order to ensure sufficient effervescence in the mold.

Various methods have already been proposed for controlling the effervescence and killing of steels in order to guarantee a sufiicient thickness of skin lin the ingots. Some such methods :include operator observation of the steel in the ladle. However, the additions must then be made by rote, that is to say much depends on how Well the operator knows his job and some inaccurate dosing of the steel with deoxidant may be expected. This is a great disadvantage since the control `of effervescence by additions should `be suiiiciently precise to `obtain the correct structure in 100% of the ingots after solidilication.

One object of my invention is to make possible a process of continuous casting which avoids these disadvantages so that rigorous and rapid detenmination of the trimming action can be carried out and an accurate adjustment of rimming tendency thereby made possible.

Given in the form of a summary one form of this inventive process for controlling the addition of deoxidant in continuous casting may comprise measuring the degree of compactness of an ingot in the course of the continuous casting, deriving trom ythis measurement precise indications on the structure of the ingot, and acting on these indications to regulate the addition of deoxidant to the -steel in order to produce the desired degree of killing.

This measurement of the compactness can conveniently be performed by passing electromagnetic radiation of a given wave length, preferably gamma radiation, through ice the ingot and comparing the intensities of the incident and emergent rays. This technique is based on the fact that the absorption of radiation by two sections of a body of the same thickness depends on the presence of discontinuities in structure, and, in the case of metals, in the presence of blowholes in the path of the rays.

In the present process I prefer to use an emitter such as cobalt 6() or caesium 137 which has a long half-life and emits low energy radiation.

One particularly advantageous form of the process includes Ithe projection `of a beam of penetrating radiations through the ingot in `such a way that .the axis of the steel is preferably related to incident and emergent parts of a beam of penetrating radiation projected through the ingot. Thus the two can be related manually, automatically, or by other known means. The killing agent can be added in solid form, for instance as a filament, or as a liquid.

The improvements will now be made more readily understood with reference to Ithe following description when considered in connection with the accompanying drawings, in which in all figures like reference numerals represent like parts throughout and in which FIGURES la to lg are transverse sections of the ingots,

FIGS. 2 and 3 are diagrammatic views showing the course `of a beam of penetrating rays through the crosssection of an ingot,

FIGS. 4 and 5 are diagrammatic views showing the ingot in oblong representation,

FIG. 6 is a diagrammatic view showing the penetration of an ingot by two beams of radiation,

FIG. 7 is a diagrammatic Iview showing an ingot lwith the means for passing a beam of radiation obliquely through one corner thereof,

FIG. 8 is a diagrammatic view showing the projection of `a beam through a cylindrical ingot,

FIG. 9 is a cross-section showing a device for directing a penetrating beam through an ingot,

FIG. 10 is a plan view of a portion of the device of FIG. 9,

IFIG. 1l is a plan view of another portion of the device of FIG. 9 with various parts in section,

FIG. l2 is a vertical section of a device for adding molten aluminum `to the steel during ycontinuous casting,

FIG. 13 is a vertical section of a modified device for adding the molten aluminum,

FIG. 14 is a Vertical section of a `further modified device for adding the molten aluminum, and

FIG. l5 is a vertical section of a still further modified device `for adding the molten aluminum.

The first FIG. la represents an ingot which was teemed with dead-killed steel so that it solidified Without any effervescence. It can be seen from the FIGS. 1b to 1g that to obtain a skin of sufficient thickness, more intense effervescence is required than that in the ingot shown in FIG. 1d. However, there is an upper limit to the intensity of effervescence since when very strong it hinders casting, brings about the ejection of large pieces of metal which represents a substantial loss of material, and results in serious surface flaws in the ingots.

Thus if eifervescent steel is to be cast, it is essential to produce ingot structure of the types shown in FIGS. le or lf. The structure shown in FIG. 1g is somewhat less acceptable as steel may be thrown out of the mold.

It is therefore necessary to regulate the effervescence of a steel to make sure of producing ingots of the structures shown in the two FIGS. le and 1f, corresponding,

in practice to an estimated thickness of the skin of l5` Referring to FIGS. 2 and 3, it can be seen that the ingot 29 is traversed by a beam of penetrating rays 35 parallel to one side 36. In the case of the ingot of FIG. 2 the beam passes through a compact region constituting skin while in the next FIG. 3 it passes through one containing blowholes 33.

Suppose I0 is the intensity of the incident radiation 30, I the intensity of the emergent radiation 31 as shown in FIG. 2, and I the intensity of radiation 34 emerging from the ingot in FIG. 3, then the value of the fraction 1710 will therefore vary as the compactness of the zone through which the beam 35 passes. This value is sensed by a detector 39 of the usual type, for example, a scintillation counter, a Geiger counter, or an ionisation chamber. The signal received by the detector is amplified and transmitted again through customary devices, which are not shown, to suitable relays which actuate either an indicating or warning device, if the adjustment of the feed of deoxidant is to be made manually, or a mechanism for automatically regulating it, if automatic control or adjustment of the latter is desired. In the particular case where the deoxidant is in filament form (for example, aluminum wire) the relays could control the speed of unwinding of a supply bobbin carrying the wire, and consequently the rate at which the deoxidant is introduced into the liquid steel.

In the case of the ingot 29 of rectangular section shown in FIGS. 4 and 5, the internal course of the rays is parallel to the small side 37. In this case, as in the case of ingots of square cross-section, the axis of the incident radiation 3i) is spaced by a distance 38 from the side 37 of the ingot 29 which is at least equal to the minimum thickness of the skin desired. That is to say the beam passes through the deepest part of a flat surface stratum of the ingot of depth 38.

If it is desired to take safeguards against excessive addition of deoxidant, it is possible, as shown diagrammatically in FIG. 6, to use two parallel beams 39 and 40 the distances of the axes from the side 37 being equal to the value 38 of the minimum thickness of the skin while the other is of a value 41 equal to the greatest allowable thickness of the skin. In this set-up the rst detector will give a signal for increasing the rate of feed of deoxidant as soon as the value of l/I0 relating to the intensities of the incident and emergent radiation exceeds a critical value which has been determined empirically in advance. The second detector 42 on the other hand generates a signal for the reduction of the feed of deoxidant as soon as the value of 1710 falls below this critical value owing to the reduction in blowholes 33 so that they are not present within the layer of depth 4I.

When the thickness 32 of the ingot 29 exceeds the maximum depth of penetration of the beam 39, the setup shown diagrammatically in FIG. 7 is employed. Here the beam is not projected in the direction parallel with the side 36 of the transverse section of the ingot Z9 but is inclined thereto at an angle 43, preferably 45. The beam then passes through part of the section at a distance 44 from the corner edge 45. The former distance 44 is equal to the distance 38 multiplied by cos 45. The beam is in fact passed through a convex surface stratum of the ingot of thickness equal to the desired thickness of the skin.

FIG. 8 shows the apparatus for examination of a cylindrical ingot, and again the depth of penetration is indicated by 38. The beam 3i) can be regarded as probing the deepest part of a convex surface stratum of depth 38 of the ingot.

FIG. 9 is directed to an apparatus in which rollers are provided for centering the ingot, while FIGS. l0 and 11 are partial sections at the level of one of the rollers and of the emitter respectively.

The rollers 47 and 48 are mounted for engaging one corner edge of the ingot 29 which is of square cross section. The rollers are carried on a support 49 which is itself carried by the arm 50 and is forced towards the ingot by two helical compression springs 51 so as to keep the rollers in Contact with the ingot.

46 is the emitter while 39 indicates the detector of the emergent radiation beam from the ingot 29. The emitter and the detector are carried on a strut 54, which is attached to the support 49 by two arms of adjustable length. A radiation screen 55 is provided as shown.

The apparatus of FIGS. 9 to 11 also includes devices for measuring the intensities of incident and emergent radiation, and relays and other devices for amplifying the signals so derived for actuating indicators or servomotors, but these devices have not been shown since they are of known construction and can be obtained from commercial suppliers. In any case it is clear that the apparatus for measuring radiation intensities could be of various known types as long as they are suitable for carrying out the new methods of continuously examining ingots.

The emitter 46 and the detector 39 must be placed suiiiciently far along the ingot for the crust of the ingot 29 to have reached a thickness greater than the minimum thickness of the skin that is to be tested.

The minimum distance (d) in meters between the level 0f the exit of the ingot from the mold and the level of the emitter and detector is given by the empirical formula:

LZV d" 5 which also applies to horizontal continuous casting. L is the thickness of the skin desired in centimeters, that is to say the thickness of the peripheral zone free of blowholes, and V is the speed at which the ingot emerges from the mold in meters per minute. Thus, if the thickness of the skin is to be L=2.2 cms. and the speed of the ingot is V=0.6, the minimum distance between the emitter and detector, on the one hand, and the exit end of the mold, on the other, will be 2 #Zig-@wes m.

The delay occurring before a possible error in the rate of feed of deoxidant is detected and will therefore be known in:

TJ v

or about one minute.

In the following description the addition of aluminum as a deoxidant will be considered. for the sake of convenience, but it is understood that the improvements can equally well be applied to apparatus in which other deoxidants are added.

The addition of aluminum in the ingot mold is generally carried out with the aluminum in the solid state, that is, in the form of granules or tablets or in the form of a continuous Wire fed in the immediate vicinity of the jet of molten steel as it passes into the mold. For ease in handling, aluminum wire is supplied on a bobbin which is unwound by an automatic mechanism which can be controlled manually so as to vary the rate of feed. In the case where the aluminum to be used as a deoxidant is in liquid form, it is of course fed from a furnace maintained at a temperature above the fusion point of aluminum. The latter is fed to the ingot mold in a molten condition by a suitable duct as shown in FIG. 12, and as illustrated the steel 1 in the ladle 2 ows in an unbroken jet 4 through the nozzle or opening 3 into the ingot mold 5 where it forms the continuous ingot 6 wherein the upper part is killed in a continuous manner by the liquid aluminum fed from the reservoir or furnace 9 heated by an electrical winding 10. The aluminum supply 8, which is kept above its melting point continually ows through the nozzle or opening 11 and through the duct 12 and forms a jet 13 which merges with the liquid steel 7 above the continuous ingot 6. The proportion of aluminum added to the steel 7 can, of course, be regulated in various ways, and an elementary method comprises varying the level 15 of the aluminum 8 in the reservoir or furnace 9 so as to vary the head 23, and therefore the rate of flow through the exit orifice 24 of the aluminum 8 into the ingot mold 5. A simpler method of regulating the feed is to provide a stopper or valve in the furnace 9 to cooperate with the nozzle 11. Another method is illustrated in FIG. 13 W-hich comprises the use of a gastight reservoir or furnace 9 having a lid 14 to which it is sealed at 13a. IThis allows the pressure at the free surface 15 of the molten aluminum 8 to be controlled at will, for example, by means of an adjustable valve 16 controlling the pressure in a duct 17 connected with the furnace interior at 18, so that the flow of aluminum into the ingot mold can be easily regulated.

Another modification is shown in FIG. 14, which involves the feeding of the molten aluminum 8 through a duct or siphon 19. The latter is primed by providing a branch 21 connected at 20 which can be placed under vacuum through an adjustable valve 22 so that molten aluminum S is drawn up into the rising and falling limbs of the siphon 19. The liow velocity depends on the head 23 comprised between the surface 15 of the aluminum bath 8 in the furnace and the lower outlet orifice 24 of the Siphon or duct 19. There is a device (not shown) provided for adjusting the aperture of this orifice 24, which is closed completely while the Siphon is being primed and thereafter used to regulate the feed of aluminum.

FIG. shows an apparatus for controlling the flow of aluminum which has been found especially successful. The reservoir or closed furnace 9 which resembles that described in relation to FIG. 13 in regard to the lid 14 and the sealing joint 13a, has a sipho-n 19 for passing the molten aluminum 8 into the ingot mold S. The flow of the aluminum is regulated by varying the pressure inside the surface 9.

Since it is clear that those skilled in the art will be able to modify the apparatus which has been described in various ways it is to be understood that the scope of invention sought is defined by the following claims which are to be taken to cover the whole range of equivalent integers and combinations.

I claim:

1. A process to continuously insure -a predetermined compactness in a superficial layer of a rimming continuously poured ingot, comprising the steps tof pouring a rirnming steel in a continuous casting mould, continuously adding deoxidant material to the poured liquid metal, and continuously measuring the apparent compactness of the superficial layer lof the ingot in a zone in which the ingot is completely 4solidified and according to said measure modifying the rate of the adding deoxydant material to the liquid steel to obtain Afor said measure, a predetermined value which corresponds to a desired apparent compactness of the layer.

2. A process according to claim l, in which the measure of the apparent compactness is performed in the supercial layer of the ingot lat a certain depth.

3. A process according to claim 1, in which the measure of the apparent compactness is performed by passing electro-magnetic radiation through the ingot and comparing the intensity of intrance radiation to the intensity of the emerging radiation.

4. A process according to `claim `1, in which the measure of the apparent compactness is performed by passing electro-magnetic radiation through the ingot and comparing the intensity of int-nance radiation to the intensity of the emerging radiation las gamma radiation.

5. A process according to claim 1, in which the measure of the apparent compactness is performed by passing continuously a first .beam of gamma radiations through the deeper part of said superficial layer, passing a second beam o-f gamma radiation through the part of the ingot immediately inside the superficial layer deriving a signal by comparing the intensities of the incident yand emergent parts of the first-mentioned beam, increasing the rate of addition `of deoxidant material when the first-mentioned signal corresponds to a compactness below the present value, and deriving a second signal by comparing the intensities of the incident and emergent parts `of the second-mentioned beam and decreasing the rate `of addition of de-oxidant when said second-mentioned signal corresponds to a compactness of said layer exceeding the preset value by a given amount.

6. An apparatus to insure in a continuously east ingot of rimming steel a desired compactness in a superficial layer comprising a continuous casting mould, a vessel pouring continuously nimming steel in said mould, means adding deoxidant material to said steel at an adjustable and continuous rate, ian apparatus emitting an electromagnetic radiation through the superncial layer of the solidified ingot, and means for adjusting the rate of addition of deoxidant material .to the ingot in respect to the value of the rati-o between the intensity of the emerging radiation and the entering radiation.

7. An apparatus according to claim 6, in which the electro-magnetic radiation is a long half-life and low-energy gamma emitter.

8. A plant adapted yfor the `continuous casting of rimming steel accompanied by the addition of a deoxidant, comprising means for measuring the compactness of a compact superficial layer of the steel ingot produced, means for producing a signal the value of which corresponds to the measured "compactness, means for modifying the rate of addition of the deoxidant material lin respect to the value of said measure in order to achieve formation of the compact superficial llayer at a preset compactness, and means for feeding the deoxidant agent into the steel.

9, A plant adapted `for the continuous casting of rimming steel accompanied by the addition of molten aluminum, compnising means for measuring the compactness of a compact superficial layer of the steel ingot produced, means for producing a signal the value of which corresponds to the measured compactness, means for modifying the rate of addition of the `molten `aluminum material in respect to the value of said measure in order to achieve formation of the compact superficial layer fat a preset compactness, means `for feeding the molten aluminum into the steel, including an electrically heated supply reservoir, an apertured duct for passing the molten aluminum from said reservoir into the steel, `and means lfor varying the aperture of the duct.

10. A plant adapted Ifor the continuous casting of rimming steel with the addition of molten aluminum las deoxidant, comprising means for measuring the compactness of a compact superficial layer of the steel ingot produced, means for producing a signal the value of which corresponds to the measured compactness, means for modifying the rate of addition of the molten aluminum in respect to the value of said measure and to insure to said signal a preset value which lcorresponds to a preset compactness in said superficial layer, an electrically heated reservoir for the molten aluminum, a Siphon having two limbs of which one limb is immersed in the aluminum in the reservoir, means for blocking the other limb of the Siphon below the level 4of the surface of the laluminum in the reservoir, means for priming the siphon by drawing gas out of the top part thereof, and means for adjusting the aperture of the siphon.

11. A plant adapted for the continuous casting of rimming steel fwith the addition lof molten aluminum las deoxidant, comprising means for measuring the compactums of a compact superficial layer of the steel ingot produced, means for deriving a signal proportional to the difference between the measured compactness and a preset value ooi'responding to the desired compactness, an eleotnioai-ly heated reservoir for the molten aluminum, a duet for passing the 'aluminum `from said reservoir to `tbe steel, means @or maintaining propontion-al to said signal the diierence between `the pressure above the xfree surface of the aluminum in the reservoir 'and la predetermined value of said pressure, said `value corresponding to a preset rate of adding aluminum which corresponds to the desired compactness in the steel, and said difference modifying the mate in such a manner that, decreasing said `diierence, decreases the diierenee between said r-ate and the preset mate.

Spooner Aug. 15, 1944 Hopkins May 1, 1945 3 2,566,854 Rhodes Jan. 26, 1949 2,549,790 Finkeidey etal Apr. 24, 1951 2,682,691 Harter July 6, 1954 2,882,571 Easton Apr. 21, 1956 2,748,290 Reiehertz May 29, 1956 2,764,779 Zona Oct. 2, 1956 2,959,932 Spergel Nov. 15, 1960 15 States Steel Corporation, Pittsburgh, Pla., 7th edition, reed in Sei. Lib., Ilan. 27, v1958, pages 391-397 Ielied upon. (Copy in Sc-i. Lib.)

Claims (1)

1. A PROCESS TO CONTINUOUSLY INSURE A PREDETERMINED COMPACTNESS IN A SUPERFICIAL LAYER OF A RIMMING CONTINUOUSLY POURED INGOT, COMPRISING THE STEPS OF POURING A RIMMING STEEL IN A CONTINUOUS CASTING MOULD, CONTINUOUSLY ADDING DEOXIDANT MATERIAL TO THE POURED LIQUID METAL, AND CONTINUOUSLY MEASURING THE APPARENT COMPACTNESS OF THE SUPERFICIAL LAYER OF THE INGOT IN A ZONE IN WHICH THE INGOT IS COMPLETELY SOLIDIFIED AND ACCORDING TO SAID MEASURE MODIFYING THE RATE OF THE ADDING DEOXYDANT MATERIAL TO THE LIQUID STEEL TO OBTAIN FOR SAID MEASURE, A PREDETERMINED VALUE WHICH CORRESPONDS TO A DESIRED APPARENT COMPACTNESS OF THE LAYER.

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