US3429486A - Tar impregnated fused silica stopper head - Google Patents

Description

Feb. 25, 1969 R, COPE ET AL TAR IMPREGNATED FUSED SILICA STQPPER HEAD Filed Jan. 10, 1966 mhw E E E o N ww w m a A T w MR mwm G T A United States Patent O 3 Claims Int. Cl. B67d 3/00, B65d 51/14, C04b 35/14 ABSTRACT OF THE DISCLOSURE Stopper-heads used for the handling of molten metal comprising ceramically bonded, tar-impregnated fused silica.

In the manufacture of steel and alloys, it is conventional to tap molten metal from a furnace into a transfer ladle in an adjacent pouring pit. The pouring pit is usually at a lower elevation than the floor on which the metallurgical furnace sets, so the molten metal may flow by gravity from the furnace to the transfer ladle. Spaced from the furnace are a plurality of ingot molds. The ladle of molten metal is moved through the pouring pit and molten metal is poured into the ingot molds to form ingots. In the new and less conventional continuous casting process, the transfer ladle is drained into a tundish ladle. The molten steel is then poured from the tundish ladle into the continuous casting apparatus. Usually, in both transfer and tundish ladles metal is poured through a nozzle which opens through the bottom thereof. The flow of hot metal through the nozzle is often controlled by raising and lowering a stopper-head over the nozzle.

Nozzles and stoppers used with ladles have been the source of many problems and difiiculties in the past. Conventionally, the nozzles are fabricated from clay which is pyroplastic at pouring temperatures. The stopper-heads are usually clay graphite compositions. The purpose of incorporating graphite in the clay-graphite stopper-heads is to prevent sticking between the stopper-head and nozzle. This addition substantially reduces the thermal shock resistance of the stopper-heads. This marginal thermal shock resistance could be tolerated in the past. However, now that increased tapping temperatures are being used the clay-graphite stopper-heads are no longer satisfactory.

Accordingly, it is an object of this invention to provide improved refractory stopper-heads.

It is a further object of this invention to provide improved vessels for handling molten metal.

And still further it is an object of this invention to provide a process of intermittently pouring hot metal from a ladle.

Briefly, according to one embodiment of this invention, there is provided an improved bottom-pour-ladle nozzle and stopper assembly. The nozzle is fabricated of conventional refractory which resists molten metal and slags and which does not materially crack or spall away in contact therewith at operating temperatures. The stopper-head is fabricated substantially from fused silica and is ceramically bonded prior to use. Up to 5% plastic clay or other plasticizer may be a desirable addition to the batch used to form the stopper-heads.

In the refractories art, the term fused silica means several things. As used in this specification, it means silica that is at least 85 amorphous or vitreous. Such silica is most often formed by electrical fusion, but may be formed by other methods. For example, vitreous silica may be formed according to Patent No. 3,314,758, assigned to the same assignee. A very finely divided form is manufactured by vapor deposition and is known in the refractories art as volatilized silica. It is preferable that the fused 'ice silica used in this invention be at least amorphous, and contain up to 3% other oxides including CaO, FeO, MgO, Na O, and K 0.

Other features and advantages of this invention will become readily apparent to those skilled in the art from a study of the following detailed description, with reference to the drawings. In these drawings:

FIG. 1 is a side elevation in partial section of a bottompour-ladle nozzle and stopper assembly according to the concepts of this invention; and

FIG. 2 is a schematic side elevation in partial section of the nozzle and stopper-head of the arrangement of FIG. 1.

Referring to the drawings, there is shown a bottom-pourladle, having a stopper and nozzle assembly, according to this invention. Such a ladle normally includes an outer metal shell 10 lined with suitable refractory composition. The sidewalls 11 are commonly lined with alumina-silica ladle brick, because they are cheap yet satisfactory in most instances. The bottom of the ladle includes an outer metal shell 12, also lined with a refractory composition 13, usually similar to that which is used to line the sides. A slag lip 14 opens through a portion of the upper periphery of the sidewall, and is usually fabricated of a refractory monolith.

Opening through the bottom, adjacent the sidewall, is a nozzle 15'. A downwardly-extending stopper-rod 16, terminating in a stopper-head 17, is axially aligned with the nozzle inlet, as is shown more clearly in FIG. 2.

Stopper-heads may be of various constructions. Their surfaces are shaped to fit over the top of a nozzle thereby sealing off the flow through the nozzle. Most often, they have a well extending downwardly thereto into which the bottom of the stopper-rod is inserted. The well may be internally threaded, thereby to mate with the external threads on the stopper-rod. Other more elegant means are also used for fastening the stopper-head to the stopperrod.

Merely by way of example, a fused silica stopper-head according to this invention was manufactured from a batch consisting, by weight, of 99% fused silica and 1% bentonite. The batch was sized so that about 15% rested on 10 mesh, 25% was 10+28 mesh, 15% was 28+65 mesh, 45% was 65 mesh, and 40% was mesh. To the batch was added a dispersant; for example, 0.2 to 0.5% sodium hexametaphosphate sold under the trade name of Calgon. The batch was tempered with about 4% water and cast with the aid of vibration into plaster molds. The cast stopper-heads were then burned at about 1800" F.

A stopper-head made according to the technique disclosed in the last paragraph is attached to a stopper-rod assembly within a ladle. The ladle is filled with hot metal which is intermittently poured from the ladle by raising and lowering the fused silica stopper-head over the pouring nozzle.

According to another aspect of this invention, the fused silica stopper-heads are tar-impregnated and baked to cokify the tar. This treatment provides additional slag and hot metal resistant without effecting other desirable properties.

The impregnation is preferably made with a cokable, nonaqueous, carbonaceous material such as tar or pitch. The tar material is heated to about 400 F. Thereafter, it

easily penetrates the stopper-heads when immersed therein. Commercially available tar or pitch of petroleum or coal base can be used for impregnation. We suggest a coal-base pitch having a softening point on the order of 150 F.

Fused silica stopper-heads have the following advantages: They have extremely high thermal shock resistance and can, therefore, be brought into contact with molten metal without shattering. This increased thermal shock 3 resistance is especially desirable for casting metals at about 3000 F. The fused silica stopper-head does not tend to stick to the nozzle. Furthermore, because of its low thermal conductivity it does not cool the nozzle thereby causing skulling or constriction of the nozzle by solidified metal.

In the past, it has not been thought feasible to use fused silica above about 2000 F. because of its tendency to devitrify. This devitrification is minimized in fused silica stopper-heads because they are heated through what we have found the most critical devitrification range (2200- 2400 F.) very rapidly. This is because hot metal at about 29003000 F. is poured around the stopper-rod assembly including the stopper-head without preheating them. Furthermore, a small amount of devitrification will not destroy the stopper-head because devitrification results in a slight volume shrinkage.

Having thus described the invention in detail and with sufiicient particularly as to enable those skilled in the art to practice it, what is desired to have protected by Letters Patent is set forth in the following claims.

We claim:

1. In a vessel for handling molten metal, comprised of a shell, a refractory lining in the shell, a stopper-head and a stopper-rod assembly operatively associated with said vessel and a pouring nozzle the improvement which comprises said stopper-head being ceramically bonded tarimpregnated fused silica.

2. The vessel of claim 1 in which the fused silica stopper-head is prepared from a batch comprising fused silica being at least 85% amorphous and having up to 3% other oxides including CaO, FeO, MgO, Na O, and K 0.

3. The vessel of claim 2 in which the batch contains in addition up to about 5% of a plasticizer.

References Cited V UNITED STATES PATENTS 3,192,582 7/1965 Cope et al. 222-566 X FOREIGN PATENTS 817,446 7/1959 Great Britain.

WALTER SOBIN, Primary Examiner.

U.S. Cl. X.R.

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