Title of Invention

"AN IMPROVED CASTING TUNDISH USEFUL FOR THE PRODUCTIION OF HIGH QUALITY STEEL PRODUCTS"

Abstract

The present invention provides an improved casting tundish useful for continuous casting of steel for production of high quality steel products comprising a tundish (3) of rectangular cross section , provided with means for free down stream flow of molten steel (1) and having an open top box (2) at its inside bottom in such a manner so as to be concentrically below the means ( 1 ) which suppresses the turbulence and vortex formation , the tundish being also provided with weirs/dams and outlets (4).

Full Text

This invention relates to an improved continuous casting tundish useful for the production of high quality steel products. The data generated by the improved continuous casting tundish are useful in steel plant for eliminating inclusions , gas entrapment slag inclusions and reoxidation products and thereby improving the quality of the products. Water modelling is extensively used for improvement of the fluid flow behavior in continuous casting tundishes thereby improving the quality of continuously cast products in terms of low levels of inclusions and uniformity of chemistry and metallurgical structure between different strands. Various configurational changes have been brought out by way of incorporation of flow control devices like dams and weirs their locations and dimensional relationship with the tundish. It has been realised that turbulent fluid flow conditions prevail at the entry regions of the downstream from the ladle irrespective of whether the downstream entry is open or submerged, also resulting in formation of large vortices either in the central region or large number of smaller vortices gyratory in nature which form and break . To the best of our knowledge no literature information is available in water modelling on the nature and effect of these vortices and how to avoid them. In our earlier copending patent application 1000/DEL/92 and 377/DEL/94 vortex suppression devices at the outlet of tundish as well as inlet of the tundish were incorporated to suppress vertices. This invention helps not only in suppression of vertices but also helps in increasing residence time and float out of inclusion. The effects of'the vortices on the quality of steel produced are, however, adverse as these vortices entrain slag inclusions which eventually find way into the products. Besides these vortices entrain air bubbles which facilitate reoxidation in the tundish and also prevent efficient float out of inclusions. A good erforming tundish should be free from vortices with smooth fluid flow effecting maximum inclusion float out. In the existing known processes of continuous casting the tundishes do not have any such arrangement for prevention of vortices at the central downstream region or the formation of small vortices around the central regions which are gyratory in nature which result in reoxidation and entrapment of air adversely affecting the quality of the continuously cast products. The main object of the present invention is to provide an improved continuous casting tundish useful for the production of high quality steel products. Another object of the present invention is to provide an improved continuous casting tundish which prevents stream turbulence, vortex formation and air entrapment thereby leading to production of high quality steel products. The improved continuous casting tundish of the present invention is shown in fig. 1 of the drawing accompanying this specification. Accordingly the present invention provides an improved casting tundish useful for the production of high quality steel products as shown in the drawing accompanying this specification , which comprises a tundish (3)of rectangular shape , provided with a means (1) for free down stream flow of molten steel , said means (1) submerged 9 cm below the water level (5) of the tundish, the said tundish having an open top box (2) at its inside bottom in such a manner so as to be concentrically below the means (1 ), the tundish being /"-is provided with known weirs/dams and outlets (4), the said tundish is characterized in the having open top box (2) at the inside bottom. In an embodiment of the present invention the tundish may be of rectangular cross section. In another embodiment of the present invention the open top box may be integrally or separately fixed to the inside bottom of the tundish. In another embodiment of the present invention the open top box may be of rectangular cross section having length in the range of 1/6 to1/3 of the length of the tundish, width in the range of 1/3 to 2/3 of the width of the tundish and height in the range of 1/20 to 1/16 of the liquid level in the tundish. The present invention provides an improved continuous casting tundish useful for continuous casting of steel which comprises of a tundish (3) of rectangular cross section, wherein water is used (5) to submerge a means (1) with molten steel flowing through the downstream directed towards a box type device (2) integrally or separately fixed to bottom of the tundish (3) which suppresses the turbulence and the vortex formation and also favourably changes the flow patterns enhancing the mean residence time and molten steel flowing out through the nozzles of the twin strands (4) whereby with suitable locations of the dams /weirs or any obstructions the fluid flow patterns are changed to produce inclusion free and air bubble free fluid could be let out, also providing a media for fluid flow studies for characterization of flow behaviour. According to a feature of the invention, the box type device may be rectangular of size 1/6 to 1/3rd the length of the tundish or 1/3rd to 2/3rd of the width of the tundish in the length and width direction placed parallel to the tundish length and width respectively. The height of the box type device may be 1/20th to 1/10th of the liquid level in the tundish. The fluid flow studies were carried out by injecting a tracer at the entry zone of the down stream and monitoring the concentration changes at the tundish outlet at regular intervals of time. The concentration profiles were statically analysed for the characterization and performance of the tundish. The liquid streaming down through the downstream (1) in submearged nozzle conditions flows horizontally across the rectangular tundish (3), passes out through the nozzle(4). The following examples are given by way of illustrations and should not be construed to limit the scope of the present invention. EXAMPLE-1 A rectangular tundish of perspex material of size 150 cm length , width of 80 cm and height of 60 cm was placed on a steel super structure . The liquid was allowed to flow from the container placed above the tundish at a height of 130 cm through the downstream tube of 2 cm internal diameter .The downstream tube was submerged 9 cm below the water level in the tundish which was 52 cm i.e height from the tundish bottom was 43 cm. The liquid was let out through the outlets from the tundish and after attaining a steady state tracer was injected into the central downstream region at the entry . The box type device was of 29 cm length 19 cm width and 2.5 cm height placed centrally at the bottom of the tundish so that the downstream is directed onto the box .Water was continuosly let into the container to keep the level constant at 52 cm .Water was let out through the outlet from the tundish and after attaining a steady state tracer was injected into the central downstream region at the entry. The tracer concentration was continuously monitored at regular intervals of 10 seconds initially and with 5-10 minutes intervals later upto 45 minutes. The concentration profiles were plotted and statistical parameters like mean residence time . Vessel dispersion Number and Standard deviations in residence time were calculated. Flow characteristics like the Plug, Mixed or the Dead volume were also calculated from the tracer profiles using conventional expressions. The data were: Plug flow fraction in the left side of tundish(Fpl) - 0.14 Plug flow fraction in the right side of tundish(Fpr) - 0.02 Dead volume fraction in the left side of tundish(Fdl) - 0.23 Dead volume fraction in the right side of tundish(Fdr) - 0.22 Mixed volume fraction in the left side of tundish(Fml) - 0.63 Mixed volume fraction in the right side of tundish(Fmr) - 0.75 Mean residence time in the left side of tundish(Tml) - 16.6 Mean residence time in the right side of tundish(Tmr) - 16.8 Vessel Dispersion number which is Inverse of Peclet Number(VDN) - 0.14 Standard deviation in residence time(STD) - 4.9 Area ratio of the the concentration profiles from the left to the right of the tundish( AR) - 1.8 EXAMPLE -2 A rectangular tundish of perspex material of size 150 cm length , width of 80 cm and height of 60 cm was placed on a steel super structure . The liquid was allowed to flow from the container placed above the tundish at a height of 130 cm through the downstream tube of 2 cm internal diameter .The downstream tube was submerged 9 cm below the water level in the tundish which was 52 cm cm i.e height from the tundish bottom was 43 cm.The liquid was let out through the outlets from the tundish and after attaining a steady state tracer was injected into the central downstream region at the entry . The box type device was of 45 cm length 30 cm width and 2.5 cm height placed centrally at the bottom of the tundish so that the downstream is directed onto the box .Water was continuosly let into the container to keep the level constant at 52 cm .Water was let out through the outlet from the tundish and after attaining a steady state tracer was injected into the central downstream region at the entry. The tracer concentration was continuoulsy monitored at regular intervals of 10 seconds initially and with 5-10 minutes intervals later upto 45 minutes. The concentration profiles were plotted and statistical parameters like mean residence time . Vessel dispersion Number and Standard deviations in residence time were calculated. Flow characteristics like the Plug, Mixed or the Dead volume were also calculated from the tracer profiles using conventional expressions. The data obtained were: Plug flow fraction in the left side of tundish(Fpl) - 0.14 Plug flow fraction in the right side of tundish(Fpr) - 0.02 Dead volume fraction in the left side of tundish(Fdl) • - 0.15 Dead volume fraction in the right side of tundish(Fdr) - 0.13 Mixed volume fraction in the left side of tundish(Fml) - 0.71 Mixed volume fraction in the right side of tundish(Fmr) - 0.84 Mean residence time in the left side of tundish(Tml) - 18.4 Mean residence time in the right side of tundish(Tmr) - 18.7 Vessel Dispersion number which is Inverse of Peclet Number(VDN) - 0.12 Standard deviation in residence time(STD) - 11.4 Area ratio of the the concentration profiles from the left to the right of the tundish(AR) - 1.0 EXAMPLE-3 A rectangular tundish of perspex material of size 150 cm length , width of 80 cm and height of 60 cm was placed on a steel super structure . The liquid was allowed to flow from the container placed above the tundish at a height of 130 cm through the downstream tube of 2 cm internal diameter .The downstream tube was submerged 9 cm below the water level in the tundish which was 52 cm.The liquid was let out through the outlets from the tundish and after attaining a steady state tracer was injected into the central downstream region at the entry. The box type device was not incorporated. Water was continuosly let into the container to keep the level constant at 52 cm i.e height from the tundish bottom was 43 cm. Water was let out through the outlet from the tundish and after attaining a steady state tracer was injected into the central downstream region at the entry. The tracer concentration was continuoulsy monitored at regular intervals of 10 seconds initially and with 5-10 minutes intervals later upto 45 minutes. The concentration profiles were plotted and statistical parameters like mean residence time. Vessel dispersion Number and Standard deviations in residence time were calculated. Flow characteristics like the Plug, Mixed or the Dead volume were also calculated from the tracer profiles using conventional expressions. The data obtained were: Plug flow fraction in the left side of tundish(Fpl) - 0.07 Plug flow fraction in the right side of tundish(Fpr) - 0.10 Dead volume fraction in the left side of tundish(Fdl) - 0.39 Dead volume fraction in the right side of tundish(Fdr) - 0.40 Mixed volume fraction in the left side of tundish(Fml) - 0.53 Mixed volume fraction in the right side of tundish(Fmr) - 0.50 Mean residence time in the left side of tundish(Tml) - 12.2 Mean residence time in the right side of tundish(Tmr) - 11.9 Vessel Dispersion number which is Inverse of Peclet Number(VDN) - 0.14 Standard deviation in residence time(STD) - 10.4 Area ratio of the the concentration profiles from the left to the right of the tundish(AR) - 1.1 The dead volume reduces the efficency of tundish operation. It is evident from example 3 that a large dead volume fraction (Fdl - 0.39, Fdr - 0.40) is present without our improved device. Example 1 & 2 indicate that the dead volume fraction reduces with the incorporation of the device, i.e. Fdl - 0.23 , Fdr - 0.22 & Fdl - 0.15, Fdr - 0.13 respectively. The main advantages of the present invention are: 1. by the use of the present device vortex- free flow of steel is obtained whereas this is not possible in the existing devices where vortex formation is encountered either in the central downstrem region or around the central regions which are gyratory in nature forming and breaking with certain periodicity causing breakage of the slag layer which protects metal from oxidation. 2. by the use of the present device there is no entrapped gas/air in the exit stream while continuously casting of steel and reoxidation of metal due to vortex formation is not encountered. 3. by the use of the present device turbulence in the region of the downstream entry is avoided whereas turbulance exists in the existing practice. 4. by the use of the present device the nature of the fluid flow is changed, favourably increasing the mean residence time thereby helping in the float of inclusions. We Claim: 1. An improved casting tundish useful for the production of high quality steel products as shown in the drawing accompanying this specification , which comprises a tundish (3) of rectangular shape , provided with a means (1) for free down stream flow of molten steel , said means (1) submerged 9 cm below the watey level (5) of the tundish, the said tundish having an open top box (2) at its inside bottom in such a manner so as to be concentrically below the means (1 ), the tundish being —; provided with known weirs/dams and outlets (4), the said tundish is characterized in the having open top box (2) at the inside bottom. 2. An improved casting tundish as claimed in claims 1 wherein the open top box is of rectangular cross section having length in the range of 1/6 to 1/3 of the length of the tundish, width in the range of 1/3 to 2/3 of the wjdth of the tundish and height in the range of 1/20 to 1/16 of the liquid level in the tundish. 3. An improved casting tundish useful for the production of high quality steel products substantially as herein described with reference to the drawing accompanying this specification and the examples.

Documents:

1190-del-1999-abstract.pdf

1190-del-1999-claims.pdf

1190-del-1999-correspondence-others.pdf

1190-del-1999-correspondence-po.pdf

1190-del-1999-description (complete).pdf

1190-del-1999-drawings.pdf

1190-del-1999-form-1.pdf

1190-del-1999-form-19.pdf

1190-del-1999-form-2.pdf

1190-del-1999-form-3.pdf