Tundishes, unitary tundish linings with flow-control devices, ...

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BACKGROUND OF THE INVENTION

Tundishes are refractory lined metal boxes conventionally used as a reservoir to control the flow of liquid metals between metal working vessels, such as between a ladle and-a continuous caster mold. In recent years there has been an ongoing trend to practice "clean" steelmaking to produce high quality steel grades. To this end, efforts have been made to optimize the design and size of the tundish to cont~ol the thèrmal distri-bution, the quality, and the flow of steel exiting the tundish and to have expendable refractory linings in the tundish which do not contribute any impurities to the liquid steel.
In addition to the outer casing of the tundish, the steel walls and bottom are conventionally lined with at least one permanent refractory lining, usually refractory brick or castable and an inner expendable refractory lining which must be replaced after every steel pour, or at best after a sequence of up to about 20 steel pours.
In a typical tundish, metal flows into the vessel, fills it to a certain level, and exits through one or more bottom ports sometimes called tundish nozzles. In a typical unpartitioned tundish, the outer rim of the bath inside the tundish is a cooler and stagnant zone because this metal does not mix with the metal entering the tundish. Eventually, when this cooler metal leaves the tundish it can cause either skulling or quality problems downstre~m. In addition, this type of tundish design creates turbulence particularly when a shroud tube is not used on top of of the bath which causes increased heat loss and reoxidation of the liquid steel. To prevent this turbulence, weirs have been installed on either side of the inlet stream. This quiets the bath which decreases the possibility of reoxidation and allows inclusions to float to the top of the bath and to become incorporated into the slag.
One problem associated with use of weirs is that the thermally stagnant zones still exist and some of the incoming metal stream can avoid con-tainment in the tundish and rapidly exit through the bottom ports. These problems are alleviated by use of dams located in the bottom of the tun-dish in conjunction wi~h the weirs. The dams eli-minates a rapid exit from the tundish by forcing ~- - 2 ~

the steel stream to move in an upward direction.
Another method of improving the steel flow pattern in tundishes is through the use of tundish baffles in place of the weirs and dams. They com-bine the effect of dams and weirs by directingsteel flow through a series of holes in the baffles. An additional benefit of the baffles are their large surface area onto which non-metallic inclusions in the steel tend to adhere. ' The above tundish linings and flow-control devices have been constructed from magnesite tun-dish boards which were originally used as tundish liners. These are preformed shapes which often contain resin binders. U.S. Patents 4,042,229 and 4,043,543 describe this practice in detail.
However, problems arose with use of these boards because of their inadequate strength and corrosion resistance which does enable them to withstand sequential casts of several hours or more.
Another problem with the boards is hydrogen evolu-tion from their resin binder if they are not pre-heated above F.
Some facilities have tried to form the dams by using high alumina brick, but installation of brick is expensive and time consuming. Forming 2 Q ~

weirs with brick would be quite difficult.
Monolithic forming of these flow-control devi-ces is most commonly practiced. Cement bonded 60 to 90% alumina and phosphate-bonded high alumina preformed refractory monoliths are typically util-ized in service. Major disadvantages to the use of these flow control shapes are their weight and bulkiness which can result in time-consuming, difficult, and dangerous installations. `
Oftentimes, the permanent refractory linings in tundishes are in disrepair such that these preformed shapes are no longer fit into the intended locations. Another problem with the cast high alumina shapes is that they can be eroded -~
during service and inclusions of the refractory can be trapped in the steel. A further disadvantage is the relatively high cost of these preformed, flow-control shapes.
As to all preformed flow control shapes there is the problem of damage thereto in transit from the point of their manufacture to point of use, the lack of a precise fit in any given tundish shape, and the expense of their installation separate from installation of the expendable tun-dish lining.

Efforts to utilize expendable linlngs for tun-dishes which can be applied by spraying, trowelling, tamping and molding as set forth in Canadian Patent No. 1,119,662 have not been suc-cessful. Such linings contain materials which actto contaminate the iron and steel, such as resinous binders and oxidizers such as Fe203.

SUMMARY OF THE INVENTION
The present invention overcomes these problems and provides a rapid, efficient, and cost effec-tive method of providing tundishes with internal flow control devices. ~
Briefly, the present invention comprises a tundish consisting essentially of a rigid metallic outer casing, at least one layer of a heat insulating material adjacent said casing, and a unitary, integrally formed, expendable lining made of a hydrocarbon-free composition having at least one liquid metal flow control device integrally formed therewith, said lining being chemically compatible with the metal to be poured into the tundish such as a steel or iron. The invention also comprises expendable linings with at least one integrally formed flow control device and method of forming the same as set forth herein.

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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a elevational sectional view of an unpartitioned tundish of the prior art without any internal flow-control devices;
Figure 2 is an elevational sectional view of a tundish with weirs;
Figure 3 is an elevational sectional view of a tundish having weirs and dams; and Figure 4 is an elevational sectional view of a~`
tundish with bafflesO

DETAILED DESCRIPTION
This invention provides forming of flow control devices in situ in an efficient and cost effective manner by using spray mixes. The dams, weirs, and/or baffles are formed in situ at the same time the expendable working lining is formed by spraying.
Figure 1, depicts a conventional unpartitioned tundish 10 with a metal outer casing formed by metal walls 11 and metal bottom 12 with a heat insulating lining 13 which is usually formed of refractory brick and is considered to be a per-manent lining. A conventional inner expendable lining 15 is placed over the permanent lining.

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Lining 15 can be a magnesite tundish board or other lining as discussed~above. The tundish depicted has four nozzles 14, although it will be obvious that the number of nozzles used in commer-cial practice varies widely.
In this figure and also in Figures 2, 3, and 4, the steel inlet stream~into thè tundish is depicted as is the general flow o the steel in solid lines in each tundish showing the general effect of the weirs, dams, and baffles.
To form the weirs as shown in Figure 2, pat-terns 20 approximating the shape of the weir and preferably made of a rigid material such as styro-foam, cardboard, wood, or steel are placed across walls 21 of the tundish 22 against the permanent layer 23 in the place where the conventional precast weirs would be installed. The face of the pattern is then sprayed to a given thickness and, if desired, the space between the two walls of pat-terns 20 filled by pumping with the material beingsprayed to form the weir shape. The side walls and bottom of the tundish are sprayed at the same time to form a unitary lining. After the sprayed flow control devices have been dried out, each pattern 20 (if not filled in) can be removed for reuse or left in place and burned out when the liquid steel enters the tundish or during pre-heating of the tundish or dumped out with the expendable lining when the pour or pours are completed. It will be evident that there can be any number of dams, weirs and baffles, and com-bination thereof and their location in the tundish is dependent upon the desires of the user.
After a pour or pours of steel is finished the`
tundish~can be tilted to dump out the expendable lining and the process repeated to form a new lining.
The dams 30 depicted in Figure 3 can be formed in the same manner.
The baffles 40 shown in Figure 4 may be formed by inserting forms, which have provisions for the desired holes, into the tundish before spraying and then spraying to coat the baffles in the same manner as weirs 20 and dams 30.
The sprayed or pumped dams, weirs, and baffles may be formed to any practical thickness and may incorporate a network of steel re-enforcing bars or steel plate for added strength.
The advantages of sprayed or pumped in situ formed tundish flow control devices are their 2 ~

relative ease of forming once the pattern of the desired shape has been installed. Spraying or pumping to the desired thickness only takes several minutes and with expenditure of minimal effort. Another advantage of in situ spraying or pumping is that shape thickness can be varied; if a long sequence of casts are expected, greater thickness can be formed and if more aggressive slags are expected, a thicker slagline can be formed. Also, the flow control devices are formed at the same time as the lining eliminating any damage to the lining.
As to the refractory spray mix composition used to form the unitary expendable lining conven- -~
tional hydrocarbon-free silica/fireclay-based or high alumina~based spray mixes which have high insulating values can be used with some grades of steel, but it is preferred to use a hydrocarbon-free magnesite-based spraying mix since magnesia is chemically compatible with clean steel prac-tices.
It would not be recommended to us a gunning mix to form the flow control devices because of the inherent high rebounds associated with these mixes, particularly magnesite gunning mixes.

Magnesia is reIatively inert against molten steel. An additional advantage~of using a magnesite spray mix is the absence of hydrogen pick-up by the steel. This has been reported to S bç a disadvantage of using tundish boards, which are bonded with a hydrocarbon that liberates hydrogen when in contact with molten steel.
Hydrogen is known to be an undesirable contaminant in steel. ~`
Any hydrocarbon-free magnesite-based sprayable composition contaiing at least about 60~ by weight magnesite can be used. Such composition can con-tain other oxides, such as silica and alumina, and minor amounts of oxides such as lime and iron oxide. Such composition also contain minor amounts of accessory oxides. Particularly pre-ferred are sprayable compositions containing at least 75% by weight magnesia. Dossolite -72 being a specific Example and having the properties and composition shown in Table I below.

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TABLE I
Properties of Dossolite -72 PhYsical Properties:
Bulk Density, After Drying 100 pcf . Thermal Conductivity, BTU/HR
Ft2 F/In. ~250F 3.1 650 3.1 ~ 3.4 3.9 4.2 Chemical Analysis:
% by Wt.
Silica tSi02) 16%
Alumina tA123~ 1.5 Iron Oxide tFe203) 3 Lime (CaO) 1 -~
Magnesia (MgO) 75 Accessory Oxides 1.5 Loss on Ignition, % 2 2 ~ Q ~

While the inveDtion has been described in con-nection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but, on the contrary, it is intended to cover such alter-natives, modifications, and equivalents as may be included within the spirit and scope of the inven-tion as defined by the appended claims.

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