US3648761A

US3648761A - Apparatus for distributing molten steel in a mold for a continuous casting

Info

Publication number: US3648761A
Application number: US58525A
Authority: US
Inventors: Georg Speith; Helmut Landgraf; Herbert Forster
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1969-07-29
Filing date: 1970-07-27
Publication date: 1972-03-14
Anticipated expiration: 1989-03-14
Also published as: DE1939170B2; JPS4926418B1; FR2053235B1; ZA705062B; DE1939170A1; GB1305295A; FR2053235A1; NL7010806A

Abstract

A mold for continuous casting of steel is charged through a pipe into which steel is poured. The pipe terminates in a chamber underneath the surface level of molten steel in the mold. The chamber has two upwardly and oppositely directed ducts of converging cross section but having exit openings larger than the pipe''s diameter for directing branch flows toward a region that is somewhat below the surface level where meeting the sidewalls of the mold. The chamber itself provides for sudden enlargement of cross section as to down flow of steel in the pipe and the bottom operates as flow redirecting baffle.

Description

United States Patent Speith et al.

[ 1 Mar. 14, 1972 mut Landgrat, Rumeln/Moers; Herbert Forster, Dusseldorf, all of Germany Mannesmann Aktiengesellschalt, Dusseldorf, Germany [22] Filed: July/27,1970

[21] Appl.No.: 58,525

[73} Assignee:

{ 30] Foreign Application Priority Data July 29, I969 Germany ..P 19 39 170.9

152] US. Cl. ..l64/281, 164/82 [51] Int. Cl i ..B22d 11/10 [58] Field otSearch ..l64/82, 133,281,283, 337

[56] References Cited UNITED STATES PATENTS 3 340,924 9/1967 Ludwig ..l64/28l 3,371,704 3/1968 Astrovetal. ..l64/28l 3,465,81 I 9/1969 De Castelet 3,517,726 6/1970 Mills et al. 164/82 FOREIGN PATENTS OR APPLICATIONS 228,418 7/1963 Austria 164/281 843,137 7/1952 Germany ..l64/28l 361,888 6/1962 Switzerland ..l64/283 Primary Examiner-R. Spencer Annear Attorney-Smyth, Roston & Pavitt and Ralf 1'1. Siegemund [57] ABSTRACT A mold for continuous casting of steel is charged through a pipe into which steel is poured. The pipe terminates in a chamber underneath the surface level of molten steel in the mold. The chamber has two upwardly and oppositely directed ducts of converging cross section but having exit openings larger than the pipes diameter for directing branch flows toward a region that is somewhat below the surface level where meeting the sidewalls of the mold. The chamber itself provides for sudden enlargement of cross section as to down flow of steel in the pipe and the bottom operates as flow redirecting baffle.

3 Claims, 1 Drawing Figure APPARATUS FOR DISTRIBUTING MOLTEN STEEL IN A MOLD FOR A CONTINUOUS CASTING The present invention relates to apparatus for distributing molten steel in the mold of a continuous casting apparatus so as to reduce the content of nonmetallic impurities and inclusions in the casting. The invention relates particularly to redirecting a free falling flow of steel as poured into the mold, to be divided in branch flows and redirected underneath the surface level of the molten steel as contained in the mold.

it is an object of the invention to particularly control the flow pattern in the mold so as to reduce penetration of the free falling stream, as a means for controlling the reduction of impurities; particularly here, number and size of such inclusions is to be reduced by permitting the impurities to rise to the surface in the mold under favorable conditions of flow.

The problem as posed is solved in accordance with the preferred embodiment of the invention, in that a tubular or pipe member is provided underneath a ladle from which steel to be cast is poured into the mold. The pipe has an inner diameter larger than the diameter of the pour opening in the ladle. The pipe projects into the mold and terminates in a chamber underneath the surface level of the molten steel in the mold. The chamber is provided with exit ducts, that are submerged accordingly. The chamber itself is essentially defined by two back to back, oppositely and upwardly directed ducts which, in turn, are defined as follows.

The pipe guiding descending flow of steel terminates at a more or less horizontally extending upper wall portion of chamber and ducts; the bottom of chamber and ducts are defined by wall sections inclined to each other to establish the upward component of the ducts, causing redirection of the vertical influx of steel into the chamber by about I to 150. Also, the two ducts divide the flow of steel in two branch streams directed toward opposite sides of the mold. The cross sections of the exits of the ducts are larger than the inner cross section of the pipe.

The cross section of the ducts along the respective axes as to flow therein reduce in direction of flow which improves the redirecting characteristics and control of mean flow of this arrangement. The chamber itself defines a flow path for the downwardly flowing steel that increases in cross section underneath the lower end of the pipe. The bottom of the chamber defines a flow redirecting baffle for establishing a collection chamber for the poured-in steel. Either provision, redirecting baffle and enlargement of cross section for the down flow reduces the kinetic energy of the falling liquid and avoids turbulence in the two branch streams as redirected through the rather wide ducts into the mold cavity.

As a consequence of the invention, a particular characteristic flow pattern was observed inside of the mold. The branch streams as directed by the two ducts toward the sidewalls of the mold are divided again; of each stream, some material flows directly down, along and near the respective sidewall of the mold in down direction, the other portion flows close to the surface towards the center of the mold, along the side of the chamber, and the material then will tend to drop. Considering the entire cross section of the mold outside of the chamber, there is produced rather uniform descending flow at approximately constant speed across the mold which corresponds to the withdrawal speed of the casting. All oxide particles that rise in the liquid steel at a speed larger than the casting speed have opportunity to rise to the surface everywhere in the mold. Additionally, the flow along the surface of the molten steel flushes oxides to the surface to be accumulated by a cover layer. Moreover, the flow pattern prevents formation of a stagnating steel layer in the upper region of the mold that could cool.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

The FIGURE illustrates a cross section through salient portions of an apparatus for continuous casting of steel improved in accordance with the preferred embodiment of the invention.

Proceeding to the detailed description of the drawing, the figure shows a casting ladle l with a bottom opening II through which molten steel pours into a mold 2, provided for continuous casting. Support and withdrawal rolls 3 guide a casting string 4 from the bottom of the mold. Additional rolls are provided further down stream for guiding and supporting the casting. String 4 as formed in the mold 2 and as withdrawn therefrom includes a still liquidous core and a solidified skin. The surface of molten steel in the mold is covered by means of a layer 6 of powder. The molten steel itself has a surface level 5 in the mold.

As steel pours in a free falling stream out of ladle 1, it enters mold 2 and continues descending flow underneath the surface level 5 to be redirected and divided in two particular branch streams. The flow of the molten steel is controlled by means of the following provisions.

A pipe 7, made of refractory material, is suspended from the bottom of ladle I and surrounds opening 11 as well as the stream of freely falling steel poured from the ladle. Pipe 7 establishes a vertical duct having width (diameter) larger than the pour opening I I of ladle I and larger even than the diameter of the stream of falling steel. The pipe 7 extends sufficiently far into the mold so as to extend and to continue underneath the surface level 5 of the molten steel. Thus, that submerged portion of pipe 7 defines a descending flow path of diameter wider than the stream as falling and as poured from the ladle.

Pipe 7 terminates in a chamber 8, made of the same material and, possibly, being integral with pipe 7. Chamber 8 is established by a horizontally and laterally extending wall portion I2 in which pipe 7 terminates from above. Chamber 8 is further defined by a particularly shaped bottom 9. Upper wall 12 and bottom 9 together with sidewalls (not shown) provide two channels or flow ducts l0 and 10a which extend essentially away from each other and establish branch flow paths of the molten steel. in essence, chamber 8 is established by these two ducts. Each duct provides a flow path for steel from chamber 8 into mold 2. The two ducts are disposed back to back with common entrance and converging cross sections towards exits I3 and 13a. The exit openings of 13 and 13a of ducts I0 and 100, respectively, are larger in cross section than the cross section of pipe 8, even though the ducts width reduces along their respective axes.

The lower portions of the ducts as particularly defined by bottom 9 of chamber 8 are inclined to each other and to the horizontal by an angle a. Angle a is shown to be equal to 30. This corresponds to an angle of about I20 as between the vertical direction of the free falling stream as entering mold and chamber, and the redirectioning as resulting from the two ducts I0 and 10a. Thus, the exit openings I3 and 13a of ducts l0 and Illa, respectively, are above lowest portion of the bottom of chamber 7. It was found that the redirecting angle should be from to lSO".

The chamber 8 provides for sudden enlargement of cross section for the flow of steel as descending in pipe 7. Moreover, bottom 9 establishes a baffle across the path of the descending steel. These two provisions establish chamber 7 as a redirecting collection chamber, in which turbulence and vorticity is reduced; the turbulence results from the rather high entrance velocity of the falling stream. Also, kinetic energy of free fall is considerably reduced in the chamber so that, as a consequence, the flow of steel out of the chamber, near and through exits I3 and 13a, is rather smooth and quiet, charging the mold throughout with steel by means of low turbulence flow.

In order to obtain the desired result, chamber 8 dips into the mold for a particular depth that depends upon the width Blof the mold and also upon the angle a, as that angle determines materially the direction of outflow of steel from the chamber and the degree of redirection imparted upon the vertically entering stream of steel. The relationship was found to be therefor:

h=Bl2 tan u-l-a. wherein the constant a is about 50 to 150 mm.; if Bis given in millimeters, the depth it can be calculated in this dimension.

As the free falling stream of molten steel is piped into the mold and caused to continue to flow down underneath level 5, the turbulent flow is quieted within chamber 8, divided and guided obliquely in outer direction with an upwardly directed component of flow. The channels or ducts l and 100 direct the two branch flow towards opposite sidewalls of the mold, just below the surface level 5. The constant n represents that average distance from the surface. lt should be mentioned that in view of the relative shonness of the ducts and 100, the directions of mean flow, as leaving the ducts, are predominantly determined by the inclination of the bottom portion of chamber 8.

The dotted lines with arrows show the direction of flow in the mold as resulting from charging the mold through the particularly oriented channels 10 and 100. As it can be seen, there results a particular characteristic flow pattern within the molten steel as contained in mold 2. The illustrated flow lines demonstrate that each branch flow is again divided in two components. One component flows down along the respective sidewall of the mold. The other component flows underneath surface level 5 toward the center, to be redirected again for descend. As an overall result it was found that underneath chamber 8 there is a rather uniform descending flow. Particularly, it was found that the down flow exhibits rather uniformly constant speed of descend. That speed is equal to the speed of withdrawal of the casting string. The uniformity in descend facilitates rising of oxide particles in the liquidous steel.

The several branch streams and flow components of the material are shown somewhat idealized. Various factors may contribute to deflection from the intended direction of flow. That may necessitate to raise or to lower the chamber 8 relative to level 5. It was found that for a larger casting capacity and for a relatively short length of ducts or channels ll] and [0a, the parameter a in the equation above must have value closer to its upper limit (l50 mm.), i.e., the chamber 8 must dip rather deeply into the molten steel in the mold.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

We claim:

I. In an apparatus for continuous casting of steel, wherein molten steel is poured from a ladle through a bottom opening thereof into a mold, there being a pipe-like member extending from the bottom of the ladle into the mold, to extend underneath the surface level of molten steel in the mold, the pipe member having inner diameter larger than the diameter of the bottom opening, so that a vertical flow duct as defined by the pipe member, where submerged, has larger cross section than the cross section of the stream of steel as poured from the ladle the improvement comprising, means defining a mold charging chamber underneath the pipe, the chamber includmg:

a. an upper wall, the pipe member terminating in said upper wall, the upper wall extending laterally, essentially horizontally from the pipe member toward the sides of the mold,

b. two bottom wall portions inclined to each other and to the vertical by an angle of to ISO", to define upwardly directed wall portions,

. the upper wall portions and the two bottom wall portions extending laterally beyond the inner diameter of the pipe member and forming two flow directing ducts having exits for redirecting the flow of steel in the chamber upwardly and laterally towards the side of the mold, the ducts together having cross section larger than the cross section of said pipe member. 2. Apparatus as in claim I, the chamber defining means as suspended from the pipe underneath the surface level of the molten steel in the mold having position to direct flow from the channels toward areas of the sidewall of the mold somewhat underneath the surface level thereat.

3. Apparatus as in claim 1, the exits of the ducts, each having cross section larger than the cross section of said pipe member.

Claims

1. In an apparatus for continuous casting of steel, wherein molten steel is poured from a ladle through a bottom opening thereof into a mold, there being a pipe-like member extending from the bottom of the ladle into the mold, to extend underneath the surface level of molten steel in the mold, the pipe member having inner diameter larger than the diameter of the bottom opening, so that a vertical flow duct as defined by the pipe member, where submerged, has larger cross section than the cross section of the stream of steel as poured from the ladle the improvement comprising, means defining a mold charging chamber underneath the pipe, the chamber including: a. an upper wall, the pipe member terminating in said upper wall, the upper wall extending laterally, essentially horizontally from the pipe member toward the sides of the mold, b. two bottom wall portions inclined to each other and to the vertical by an angle of 120* to 150*, to define upwardly directed wall portions, c. the upper wall portions and the two bottom wall portions extending laterally beyond the inner diameter of the pipe member and forming two flow directing ducts having exits for redirecting the flow of steel in the chamber upwardly and laterally towards the side of the mold, the ducts together having cross section larger than the cross section of said pipe member.

2. Apparatus as in claim 1, the chamber defining means as suspended from the pipe underneath the surface level of the molten steel in the mold having position to direct flow from the channels toward areas of the sidewall of the mold somewhat underneath the surface level thereat.