US3570713A

US3570713A - Pouring of melts

Info

Publication number: US3570713A
Application number: US815954A
Authority: US
Inventors: Kristof Tromel
Original assignee: Schloemann AG
Current assignee: Schloemann AG
Priority date: 1969-04-14
Filing date: 1969-04-14
Publication date: 1971-03-16
Anticipated expiration: 1988-03-16

Abstract

In pouring superheated metal melts from a pouring vessel into an ingot mould or a chill mould, the molten metal is passed through a teeming tube of relatively small cross-sectional area into the mould, and during this passage the whole of the superheat and part of the heat of fusion is withdrawn from the melt, and measurements of the temperature of the melt are made at certain points in the teeming tube and employed for controlling the flow of the molten metal.

Description

United States Patent [72] Inventor Kristof Tromel Buederich near Duesseldorf, Germany [21] Appl. No. 815,954 [22] Filed Apr. 14, 1969 [45] Patented Mar. 16, 1971 {73] Assignee Schloemann Aktiengesellschaft Duesseldorf, Germany [32] Priority Mar. 9, 1965 [33] Germany [31] Sch 36656 Continuation-impart of application Ser. No. 532,638, Mar. 8, 1966, now abandoned.

[54] POURING OF MELTS 10 Claims, 6 Drawing Figs.

[52] U.S. Cl 222/1, 222/54, 222/146, 222/566, 164/122 [51] Int. Cl B67d 5/62 [50] Field ofSearch 222/1, 54, 146 (H), 146 (C), 566; 164/122, 337; 266/38 [56] References Cited UNITED STATES PATENTS 770,130 9/1904 Trote 164/270 958,613 5/1910 Forgo 65/25 Harrison Alexanderson Jones Seigfried Steigerwald Eliot Brick et a1.

Miller et al. Woodburn, Jr... Calderon Primary Examiner-Robert B. Reeves Assistant Examiner-H. S. Lane Att0rney Holman, Glascock, Downing & Seebold PATENTED MAR] 6197! SHEET 1 BF 3 3 mm n Em? a Tx m N o J T 0 m.- K p. v B

PATENTEDHARIBIBH 3570.713

, SHEET 3 or 3 Fig. 6"

INVENTOR. KRISTOF TROMEL BYMMW M,

POURING OF MELTS This application is a continuation-in-part of my application Ser. No. 532,638 filed Mar. 8, 1966, now abandoned.

According to the present invention, the pouring or casting output in the pouring of a metal melt into an ingot mould or into a chill mould is increased by withdrawing from the metal melt, on its way to the ingot mould or chill mould, its superheat, and also part of its heat of fusion. The molten metal is passed through a teeming tube, which is of small cross-sectional area in comparison with the ingot mould or chill mould, the pouring tube being cooled, and being traversed by the molten metal in turbulent flow, with a coefficient above its critical Reynolds number. Under these circumstances temperatures which correspond to the temperatures of the melt are measured at least at two positions located one behind the other in the direction of flow of the melt, and are compared with one another.

The present patent application is a continuation-in-part of the US. Pat. Application Ser. No. 532,638, dated Mar. 8, 1966, now abandoned according to which it had already been proposed to withdraw the superheat from the metal melt, on its way to the ingot mould or chill mould by cooling, and to measure the temperature of the pouring jet at the end of the cooling operation, and to control the speed of pouring and/or the cooling power by corresponding measurement of temperature. Amongst other things it had also already been proposed to employ a thermocouple in the pouring tube in the neighborhood of the surface of the bath in the mould.

The present invention relates to further measures for increasing the cooling power, which consist in the feature that the molten metal is passed through a teeming tube the crosssectional area of which is small compared with that of the ingot mould or chill mould, wherein the whole of its superheat, and also a part of its heat of fusion, are withdrawn from it in the teeming tube by cooling, while it is flowing through the teeming tube in turbulent flow with a coefficient above the critical Reynolds number and temperatures corresponding to its temperature are measure at least at two places following one another in the direction of flow of the melt, and are compared with one another. In this way it is possible to adjust the thermal content of the molten metal with great precision at its entry into the ingot mould or chill mould. Since the melt in the teeming tube is in a condition of turbulent flow, a small part of its heat of fusion can in fact be withdrawn at this position, so that it may already contain to a certain extent presolidified metal particles, without this leading to the teeming tube freezing up. In this case it is possible to withdraw about to percent of the heat of fusion from the melt. The turbulent condition of flow not only has the result that upon a withdrawal of part of the heat of fusion, freezing is still not possible, but in addition it also renders possible a better utilization of the cooling power of the teeming tube. By comparing the values of the measured temperatures, as is still to be explained in detail, to fix exactly what part of the heat of fusion should be withdrawn at each moment of the teeming operation.

The invention will now be further explained by way of illustration but not of restriction, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 shows a thermal-content diagram of a metal melt;

FIG. 2 shows a teeming tube with a cooling jacket;

FIG. 3 shows a teeming tube with a cooling coil;

FIG. 4 shows the arrangement of the teeming tube between a pouring vessel and an ingot mould or chill mould;

FIG. 5 shows the flow profile of a metal melt inside the teeming tube; and

FIG. 6 shows a circuit arrangement for regulating the teeming operation.

In MG. 1 the dependence of the thermal content I of a metal upon a temperature T is represented. During the cooling, first of all that quantity of heat is withdrawn which corresponds to the course of the curve f,. The external characteristic here is a fall of temperature, at first only as far as the melting point S. Upon further withdrawal of heat the temperature T remains constant, whereas the thermal content I diminishes further by withdrawn portion of the heat of fusion the amount Q With this amount Q it is a question of the heat of fusion. At this juncture the state of aggregation changes from liquid to solid. Following upon this, a reduction of the thermal content again leads to a fall of temperature corresponding to the curve to. Since the withdrawal of heat depends upon the thermal conductivity of the cast material, the, thickness of the cast workpiece or ingot, and the difference of temperature, for a given cooling power of the ingot mould or chill mould, it is to be a first approximation to be regarded as constant, and the known equation is here applicable, where: t

d the layer already solidified in the ingot mould or chil mould; t= the time that has so far elapsed; and k a solidification constant incorporating the aforementioned pertinent magnitudes. I

Whether the solidification of the melt sets in exactly at the melting point depends upon whether sufficient crystallization nuclei are available. If not, then an activating energy or seedforming energy is necessary for the formation thereof, which, however, in the case of a turbulent flow of the molten metal, is to be regarded as present.

Practical experience in filling ingot moulds or chill moulds with a melt shows clearly, as is well known, particularly in continuous casting, that this can only be effected at a speed which corresponds to the cooling power of the ingot mould or chill mould, the main influence upon the speed of pouring being given by the thermal content of the melt. The upper limit with respect to the permissible speed of pouring and temperature is known, by h the occurrence of longitudinal cracks in the solidified workpiece or ingot. They occur owing to the solidification being efiected too slowly for a given cooling power of the casting mould or chill mould in comparison with the thermal content of the melt and the heat subsequently delivered; for the relatively thin solidified marginal layer that occurs shrinks, rises out of the casting mould or chill mould, and cannot withstand the liquid pressure with which it is burn butdened, so that it fractures. As a countermeasure, the speed of teeming is usually reduced, or, if possible, the temperature of the melt is lowered. The lower limit with respect to the speed of teeming and the temperature is known from the occurrence of scabs on the solidified workpiece or ingot. They arise from the fact that the solidification was effected too quickly for a given cooling power of the casting mould or chill mould, in comparison with the thermal content of the melt and the heat delivered subsequently. The solidification in the marginal zone of the cast workpieces or ingots is here effected so quickly that the after-flowing melt can no longer unite with the portion already solidified. Regular separations of material occur. The present invention, in order to obviate such disturbances, provides a special form of construction, hereinafter to be set forth, of the thermal insulation of the melt that has entered the chill mould with a low heat content.

For carrying out the method according to the invention it is characteristic that in the heat content temperature diagram an operating point W is aimed at, which is located in the portion O of the curve in FIG. i. This operating point W lies, as FIG. 1 shows, in the upper portion of the curve Qs, so that the amounts to about 5 percent thereof.

- In FIGS. 2 and 3, the teeming tube is marked 1, and the chill mould is marked 2. The teeming tube l, which is represented in longitudinal section, is preferably of noncircular cross section, so that the surface area acted upon by the cooling medium is considerably increased. Thus the teeming tube may be made with an oval or a rectangular cross section. A number of other cross sections of the teeming tube, to be likewise acted upon by the cooling medium, are also possible. With this formation of the cross section of the teeming tube it is important to provide a sufficiently large area for the withdrawal of the quantity of heat to be removed.

The teeming tube 1 extends further, as illustrated in the drawings, preferably right to the surface level of the bath in the interior of the chill mould or casting mould. This has the advantage, on the one hand, that by the teeming tube a comparatively long cooling tract is provided, whereas on the other hand, an atmosphere of protective gas can be thereby easily maintained above the surface level of the bath in the chill mould, so that for instance a disturbing reoxidation of the molten steel is obviated.

It is particularly advantageous to provide the teeming tube at its lower end with a cover 3, which screens from the exterior the free cross section of the casting mould or chill mould, which is considerably larger than that of the teeming tribe. This constructional feature is of particular importance with the present invention, because the molten metal is brought into the chill mould 2 with a considerably lower thermal content than is usual, and in the event of no such screening being provided, there would be the risk of the formation of the socalled matt welding," or scabs.

The teeming tube 1 consists of materials which are stable to the melt, and which also have the ample thermal conductivity requisite for the cooling. For the teeming of molten steel it is advisable, at least on the inside of the teeming tube, to employ graphites or silicon carbide.

According to FIG. 2 the teeming tube 1 has a cooling jacket 6, whereas in FlG. 3 it is provided with a cooling coil 7. In both cases a cooling liquid 12, water for instance, is admitted into the cooling device, preferably at the point 8 in the lower part, and leaves the cooling device at the top, at the point 9, as indicated by arrows in the drawings. The cooling device thereby worlcs on the known countercurrent principle, thus giving rise to a tendency to maintain as constant a fall of temperature as possible throughout the length of the cooling tract.

The quantity of cooling medium, and its speed of its flow, are preferably controlled, as already described, to correspond to the requisite cooling power. The speed of pouring of the teeming jet, represented by the arrow 5, in the interior 4 of the teeming tube ll, is likewise adjusted by known means, for instance by a ladle plug, or else by a pressure produced in the pouring vessel above the surface of the melt.

The aforementioned means for varying the cooling power and the teeming speed include, according to FIG. 4, a regulating valve V fitted into the connection 13 for the cooling medium 12, and a bottom plug 15 for the bottom aperture 16 of a pouring vessel 17. By this means an outlet cross section V of variable magnitude is provided for the molten metal. Both the plug 15, represented in FIG. 4 only by its lower portion, but in reality projecting above the pouring vessel, and also the valve V for the connecting branch 33, may be actuated either manually or by motor means. Adjusting it by motor means above all enables the teeming to be controlled automatically.

The speed profile of the flow. is diagrammatically represented in FIG. 5. For the turbulent state of flow it is important to exceed the critical value of the Reynolds number, which is formed in a known manner, and should if possible be above 2,300. The turbulent flow has, in the direction of the cross section s, as indicated by the arrow in FIG. 5, a substantially constant speed v, as can likewise be gathered from FIG. 5. The turbulent jet is largely equalized in the direction of the cross section sin every respect, and particularly by a temperature which is practically homogeneous over the cross section, so that without incurring the risk of freezing up, it can to a certain extent carry along with it even solidified metal particles, as corresponds to the withdrawal of a part of the heat of fusion. Insofar as solidified metal particles are formed in the immediate neighborhood of the internal wall surface of the teeming tube 1, that is, in the so-called boundary layer, they are caught by the flow and distributed over the cross section 5. In order to meet reliably the risk of the formation of objectionable deposits on the wall surface of the teeming tube 1, the speed of teeming, and the cooling power can according to the invention be so adjusted to one another throughout the entire teeming operation that a cycle is established, in which the temperature difference between two temperature measurements located one behind another in the direction of flow in the neighborhood of the exit 10 from the teeming tube I from time to time is intermittently zero and different from zero. In the case in which the temperature difference differs from zero, it is found that one is certainly not yet in the vicinity of the heat of fusion. The molten metal therefore then runs for a short time somewhat superheated into the chill mould. Insofar as any deposits should have formed on the outlet 10 from the teeming tube 1, these are now detached. In conjunction with this, that is, when the temperature difference between the said measurements of temperature is zero, heat of fusion is again withdrawn, so that for the melt, in the middle of the withdrawal of the heat of fusion according to the invention, this is given, even if, in the manner mentioned, this is renounced for a short time during the melting.

FIGS. 2 to 4 further show, at positions located one behind another in the direction of flow 5 of the molten metal, temperature probes 11, which may for instance be thermocouples, or, above all, resistance thermometers. It is to be noted that for each temperature probe 11 there are two contacts, which are connected either to the two limbs of a thermocouple or else to the two ends of a resistance thermometer. These temperature probes are preferably located at a short distance from the internal wall surface of the teeming tube 1, so that they will not be damaged by the molten metal, but on the other hand will show a temperature which at least stands in a definite relationship to the temperature of the melt. It is not so important to determine the exact temperature of the melt as to determine the difference of temperature between two successive measuring positions, or the ratio between the temperatures at two successive measuring points. By this means the arrangement of the temperature probes admits of being substantially less expensive, and at the same time they act more reliably. Thus for instance it is possible to use, instead of costly noble metal probes capable of withstanding high temperatures, substantially cheaper probes of base metals, since owing to their distance from the teeming metal, they need only be designed for lower temperatures.

In the arrangement illustrated in FIG. 6, the temperature probes 11 are individual temperature-measuring resistances marked 18 to 25. They are so arranged that the temperaturemeasuring resistance 18 is located near the outlet end 10 from the teeming tube 1, whereas the rest of the temperature-measuring resistances are at increasing distances, corresponding to their increasing reference numerals, from the outlet end 10 in the longitudinal direction of the teeming tube 1. The tem= perature-measuring resistances 18 to 25 are included in a circuit which is equivalent to a Wheatstone bridge. To the two contacts 28 a supply voltage is connected. Between these two contacts there are two

resistances

26 and 27 connected in series, which are exactly equal in magnitude. From the connection between these two

resistances

26 and 27 there branches off a conductor, which leads to an amplifier A. The other entry into the amplifier A is formed by two

scanning switches

29 and 30 connected with one another, which enable in each case one of a number of contacts to be selected. To the selecting contacts of the scanning switch 29 are connected the temperature-measuring resistances I9, 21, 23 and 25, whilst to the selecting contacts of the scanning switch 30 are connected the other temperature-measuring

resistances

18, 20, 22 and 24. The other contacts of the first-mentioned group of resistances are in each case connected with one another, and also with the outer contact of the resistance 27, and are fed by the same supply voltage as the resistance 27. The individual contacts of the

other resistance group

18, 20, 22, 24 are likewise connected with one another and also with the outer contact of the resistance 26, to be fed, together with the latter, by the supply voltage.

To the amplifier A, constructed in the usual manner, is connected a relay 31. When it is not excited, it keeps closed a circuit which is fed at the contact points 32, and in which there are a pilot lamp L and also a regulator C. The pilot lamp L then therefore lights up. The regulator C controls two motors M and M which in their turn actuate two valves V and V The motors M, and M are at first so controlled by the regulator C as to yield a manually adjustable ratio between the opening of the valves V and V The result is thereby obtained that at an increased pouring speed the cooling power also rises at the same extent. Upon this control is now superimposed a control signal, which is recognizable by the lighting of the lamp L, and in the case in which the lamp L lights up, it leaves unaltered the adjusted ratio in the position between the motors M and M,. if however the control signal is interrupted, the motor M, is fed in such a manner that it opens the valve V more widely, so as to provide a greater cooling power. By switching means not illustrated, on the regulator C, the result can also be obtained that simultaneously, or only in the case of the absence of the control signal, the motor M, is supplied with current in such a way that it closes the valve V more strongly, so that the teeming speed is reduced.

By the corresponding adjusting of the scanning switches 29 and 30, it is possible to select the temperature-measuring resistances the resistance. values of which are to be compared with one another. By choosing the resistance 18 with the scanning switch 30 and the resistance 19 with the scanning switch 29, the pouring jet temperatures at the last and last-butone positions at the outlet end of the pouring tube are compared with one another. The pouring operation is thus controlled in such a way that this temperature difference is zero, and therefore a comparatively small portion of the heat of fu sion is withdrawn. If however the

resistance

21, 23 or 25 is connected with the scanning switch 29, the pouring operation proceeds in such a way that along a correspondingly greater section of the scanning tube, within the melt, there is no longer any fall of temperature, and therefore a correspondingly larger part of the heat of fusion is withdrawn.

The arrangement of a measuring instrument 35 at the outlet from the amplifier A additionally renders it possible to obtain values which characterize the variation in temperature in the interior of the teeming tube 1. The knowledge of the variation in temperature may be particularly desirable when, in consequence of the spatial arrangement of the temperature-measuring resistances within the teeming tube, and in consequence of the distribution of temperature within the teeming tube and/or of the zone closeto its internal wall surfaces, an exact reproduction of the position at which the temperature of the pouring jet begins to be constant is not possible. In this case the said position admits of being found by also permitting a difference value differing slightly from zero, in order to produce the control signal.

Finally the scanning switches 29and 30 may still be controlled in such a way that they swing to and fro for instance between two successive positions, and thus have the result that the portion of the heat of fusion withdrawn changes intermittently during the entire teeming operation and lies, for instance, at 0 percent and 10 percent, whereby, in the manner already described, a formation of solidified deposits of metal at the outlet of the teeming tube is obviated.

lclaim:

l. A method of pouring superheated metal melts from a pouring vessel into a mould having a substantial cross-sec tional area, comprising the steps of: guiding the molten metal with a teeming tube having a cross-sectional area which is small compared with the cross-sectional area of the mould, withdrawing from the melt the whole of its superheat and a portion of its heat of fusion by cooling while it is flowing through the teeming tube in a state of turbulent flow with a Reynolds number above the critical value, measuring temperatures corresponding to the temperature of the melt at not less than two positions in the teeming tube located one behind another in the direction of flow of the melt, and establishing a pouring cycle in which the relationship between the pouring speed and the cooling power of the mould is such that the difference between the measured temperatures is substantial at certain times and is zero at other times.

2. The method of pouring superheated metals melts into moulds as claimed in claim 1, in which the points of measurement of the temperatures are close to the outlet of the teeming ube.

3. The method of pouring superheated metal melts into moulds as claimed in claim 1, in which the points of measurement of the temperatures are close to the outlet of the teeming tube, in which method the said relationship is established by adjusting the cooling power of the teeming tube.

4. The method of pouring superheated metal melts into moulds as claimed in claim 1, in which the said temperatures are measured at more than two points distributed along the teeming tube.

5. Apparatus for pouring superheated metal melts from a pouring vessel into a mould, comprising a teeming tube arranged between the pouring vessel and the mould, cooling means extending over the entire length of the teeming tube, means for varying the teeming speed and the cooling power relatively to one another, temperature probes located on the teeming tube at not less than two positions one behind another in the direction of flow, and an electrical comparison circuit in which the temperature probes are included, the circuit serving to emit a signal which varies as the temperature difference at said probes varies.

6. Apparatus as claimed in claim 5, in which said temperature probes are temperature-measuring resistances included in a bridge circuit.

7. Apparatus as claimed in claim 5, further comprising automatic controlling means to control the said means for varying the relationship between the coolingpower and the teeming speed by the signal from the comparison circuit so that a cycle of zero difference and substantial difference of temperature at said probes is maintained.

8. Apparatus as claimed in claim 5, in which the cross section of the teeming tube is noncircular, so as to increase the area of contact between its internal we wall surface and the cooling medium.

9. Apparatus as claimed in claim 5,. wherein the teeming tube extends right to the surface of the bath of metal in the mould.

10. Apparatus as claimed in claimS, further comprising a cover at the lower end of the teeming tube, shielding from the exterior the considerably. larger free cross-sectional area of the mould.

Claims

1. A method of pouring superheated metal melts from a pouring vessel into a mould having a substantial cross-sectional area, comprising the steps of: guiding the molten metal with a teeming tube having a cross-sectional area which is small compared with the cross-sectional area of the mould, withdrawing from the melt the whole of its superheat and a portion of its heat of fusion by cooling while it is flowing through the teeming tube in a state of turbulent flow with a Reynold''s number above the critical value, measuring temperatures corresponding to the temperature of the melt at not less than two positions in the teeming tube located one behind another in the direction of flow of the melt, and establishing a pouring cycle in which the relationship between the pouring speed and the cooling power of the mould is such that the difference between the measured temperatures is substantial at certain times and is zero at other times.

2. The method of pouring superheated metals melts into moulds as claimed in claim 1, in which the points of measurement of the temperatures are close to the outlet of the teeming tube.

7. Apparatus as claimed in claim 5, further comprising automatic controlling means to control the said means for varying the relationship between the cooling power and the teeming speed by the signal from the comparison circuit so that a cycle of zero difference and substantial difference of temperature at said probes is maintained.

9. Apparatus as claimed in claim 5, wherein the teeming tube extends right to the surface of the bath of metal in the mould.

10. Apparatus as claimed in claim 5, further comprising a cover at the lower end of the teeming tube, shielding from the exterior the considerably larger free cross-sectional area of the mould.