Field of the Invention

The invention concerns a submerged nozzle for intake of steel to the mould during continuous casting of steel especially for continuous casting of round blooms.

Background of the Invention

Submerged nozzles are used for supplying of liquid steel stream from tundish beiow the levei of molten metal in the mould in order to protect the cast stream from the secondary oxidization, forbid metal splashing, stop entraining casting powder from the mould level into the volume of solidifying metal, facilitate flowing out inclusions and supply steel to the mould in such a stream, which makes the metal distribution across the moulds section more equal. In view of the nozzle mouth under the metal level in the mould the submerged nozzles can be classified as submerged nozzles with or without pressure stream outlet.

When using pressure nozzles that are characterized by one central outlet hole the stream of melted steel is directed inside the solidifying blank with significant depth of penetration into its liquid core. But this creates less favorable conditions for subsequent flowing out of nontnetallic inclusions to the melted casting powder in the mould.

This drawback is eliminated by pressure free submerged nozzles that are characterized by a side outlet holes in the lower part of the nozzle, e.g. four side outlet holes inclined upwards at the angle 10 - 20°. When they are applied the steel coming out from the side holes flows toward the mould walls, collides with the wall of solidifying blank and divides into the stream moving along the mould walls down inside the solidifying blank and the stream moving along the mould walls to the bath level . Pressure-free submerged nozzles compared with the pressure submerged nozzles have favorable effect on flowing out of inclusions but the dynamic effect of the stream coming out from the side holes toward the mould walls is strong and has negative influence on crust solidification in the mould, thus cracks, sinks and even breaks of solidified crust leading to subsequent breakthrough can originate. Particularly dangerous is the application of these nozzles for round blanks casting.

Summary of the Invention

Above stated disadvantages are eliminated by a submerged nozzle for feeding steel to the mould during continuous casting of steel, especially for continuous cas-ting of round bloom blanks consisting of the basic body of the nozzle, in which an internal flow channel is created leading to the set of side outlet holes arranged in the lower exit part of the basic body of the nozzle according to the invention which principle consists in the fact that the lower exit part of the basic body of the nozzle with the side outlet holes in the area of their mouths is covered from below by an extended end piece with dish-shaped lower bottom, which is equipped in the upward direction with curved surfaces guiding steel flow from the internal flow channel to the side outlet holes.

By elaboration of the invention idea the outer edges of guiding curved surfaces of the dish-shaped lower bottom of the extended end piece form the lower output edges of the side outlet holes exceeding advantageously the outer shape of the basic body of the nozzle.

Similarly advantageously there is arranged between the lower bottom and guiding curved surfaces in the extended end piece at least one braking retarder of steel flowing speed from the internal flow channel to the side outlet holes created for example by an overflow lip.

The braking retarder decreasing the speed of flowing out stream of steel from the side outlet holes reduces the dynamic impact of the- stream approaching the mould walls and thereby assisting in minimization of turbulence at the division line of the steel surface and melted casting powder.

In some advantageous constructions of the submerged nozzle made in accordance with the invention the side outlet holes are axisymmetric, their axes in the projection plane perpendicular to the axis of the internal flow channel make an angle of 90° with the axis of the internal flow channel .

In other advantageous implementations of the submerged nozzle made in accordance with the- invention the side outlet holes are asymmetric being screw-like curved toward their mouths.

Screw-like curved asymmetric side outlet holes ensure rotational movement of streams coming out of them and thus help inclusions to flow out and reduce dynamic effect of the stream flowing to the mould walls. On the contrary the submerged nozzle with axisymmetric arrangement of side outlet holes is easier to be- manufactured and better mechanical-thermal-dynamic stability of its basic body during casting is achieved. The side outlet holes in individual implementations of the submerged nozzle made in accordance with the invention are advantageously funnel-shaped toward their mouth from the basic body of the nozzle.

For production reasons the guiding curved surfaces of steel flow from the internal flow channel to the side outlet holes are advantageously shaped as a part of spherical cap, nevertheless various modifications of their basic shape can be constructed, e.g. ensuring such circumferential speed further eliminating the impact of steel outflow on the mould wall.

The submerged nozzle according to the invention ensures optimal required overall character of flowing in the mould and provides better conditions for inclusions flowing out. By this the nozzle provides better results of oxide micropurity compared with the steel cast by means of pressure nozzle. By application of the submerged nozzle according to the invention better results in steel micropurity are achieved compared with the application of pressure free nozzles but it can be advantageously applied for casting of round blanks as the steel streams coming out of the outlet holes do not influence negatively the solidification of the round blank.

Brief Description of the Drawings

The invention will be further explained by means of drawings of individual examples of submerged nozzle made according to the invention, which illustrate:

Fig. l - overall view of the submerged nozzle Fig. 2 - cross section of the first example of manufacture of the lower exit part Fig. 3 - plan view of the first example of manufacture of the lower exit part Fig. 4 - cross section of the second example of manufacture of the lower exit part Fig. 5 - plan view of the second example of manufacture of the lower exit part Fig. 6 - actual view of the lower exit part made according to the first example Fig. 7 - cross section of the actual view of the lower exit part made according to the first example Fig. 8 - actual view of the lower exit part made according to the second example Fig. 9 - cross section of the actual view of the lower exit part made according to the second example Fig.10 - an example of steel circulation in the mould in individual phases

Description of the Preferred Embodiment

Example 1

The submerged nozzle in the first example of invention realization shown in the FIG. 1, 2 and 3 for feeding steel into the mould during continuous casting of steel consists of the basic body 1 of the nozzle with the upper entry- part Zi in which an internal flow channel 4. is created leading to the set of side outlet holes 5. arranged in the lower exit part 2 of the basic body 1 of the nozzle.

The lower exit part 3. of the basic body l of the nozzle with the side outlet holes 5. is closed in the vicinity of their mouths from below with the extended end piece S shaped closely as an inverted spherical cap of the dish-shaped lower bottom 7. equipped upwards with the curved, surfaces £ guiding the flow of steel from the internal flow channel 4. to the side outlet holes 5.. The outer edges of the guiding curved surfaces 8. of the dish-shaped lower bottom 2 of the extended end piece 6. form the lower output edges 9. of the side outlet holes 5., exceeding sideward the outer shape JLO. of the basic body l of the nozzle by the distance P.

Between the lower bottom 7. and guiding curved surfaces 8. in the extended end piece 6. there is adjusted a braking retarder .11 of the steel flowing speed from the internal flow channel 4 into the side outlet holes ϋ created by the overflow lip.

The side outlet holes 5. are in this first example of realization as it is clear especially from FIG. 3 asymmetric and screw-like curved toward their mouths in order to ensure to some extent rotational movement of the outgoing steel streams. At the same time the side outlet holes 5. are funnel-like enlarged toward their mouths from the basic body 1 of the nozzle. The guiding curved surfaces 8. of the steel flow from the internal flow channel 4. to the side outlet holes 5. are shaped as a part of spherical cap.

FIG. 6 and 7 illustrate the actual realization of the submerged nozzle respective its lower exit part 3. in accordance with this realization example.

FIG. 10 clearly shows individual phases of steel circulation in the mould when using this submerged nozzle namely at the casting speed 0.5 m/min. and the depth of submerging of 220 mm obtained by model testing at the water model . Example 2

The submerged nozzle in the second example of invention realization shown in the FIG. 1, 4 and 5 for feeding steel into the mould during continuous casting of steel, similarly as in the first example, consists of the basic body 1 of the nozzle with the upper entry part 2., in which an internal flow channel 4_ is created leading to the set of side outlet holes 5. arranged- in the lower exit part 3_ of the basic body l of the nozzle.

The lower exit part 3. is also closed in the vicinity of the mouths of the side outlet holes 5. from below with the extended end piece 6. similar as in the first example but unlike the first realization example the side outlet holes 5_ are axisymmetric and their axes in the projection plane perpendicular to the axis of the internal flow channel 4. make an angle of 90° with the axis of the internal flow channel 4..

FIG. 4 indicates also the side lap P of the lower output edge £ and outer shape iO. of the basic body 2 of the nozzle.

FIG. 8 and 9 illustrate the actual realization of the submerged nozzle or its lower exit part 3_ in accordance with this realization example.

The advantages of the submerged nozzle made in accordance with the invention was fully demonstrated in the testing of both above-mentioned specific examples of its implementation, namely in the mould of 410 mm in diameter with casting speeds from 400 to 500 mm/min. The chosen depth of submerging in this case 210 up to 240 mm, measured from the bottom of the nozzle to the steel bath level in the mould, has to ensure the condition that the vector of outgoing stream from the side outlet holes 5. was not directed to the mould walls and at the same time no turbulence appeared under the influence of the stream at the separation line between liquid steel and melted casting powder in the mould.

Field of the Application

The submerged nozzle according to the invention can be usually utilized in the machines for continuous casting of steel instead of submerged nozzles of the up-to-now known types . List of reference sign

1 basic body 2 upper entry part 3 lower exit part 4 internal flow channel 5 side outlet holes 6 extended end piece 7 lower bottom 8 guiding curved surface 9 lower output edges 0 outer shape 1 braking retarder