US2949637A

US2949637A - Process of making ladle stopper heads

Info

Publication number: US2949637A
Application number: US760317A
Authority: US
Inventors: Michael O Holowaty; Albert M Kroner
Original assignee: Inland Steel Co
Current assignee: Inland Steel Co
Priority date: 1958-09-11
Filing date: 1958-09-11
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23

Description

Aug. 23, 1960 Filed Sept. 11, 1958 Z 2/ WTF I M. b. HOLOWATY ET AL PROCESS OF MAKING LADLE STOPPER HEADS 2 Sheets-Sheet 1 PROCESS OF MAKING LADLE STOPPER HEADS Michael 0. Holowaty, Gary, and Albert M. Kroner, Valparaiso, Ind., assignors to Inland Steel Company, Chicago, 111., a corporation of Delaware Filed Sept. 11,1958, Ser. No. 760,317

6 Claims. (Cl. 18-47.5)

This invention relates to ladles for handling molten metals of a type having a bottom-pour delivery nozzle. More particularly, this invention is concerned with novel stopper heads for use in combination with the nozzle to prevent and regulate the flow of molten metal through the nozzle.

This application is a continuation-in-part of our pending application Serial No. 696,846, filed November 15, 1957, now abandoned.

In the manufacture of steel, the molten steel is tapped from a steelmaking furnace, such as an open hearth furnace, electric furnace, cupola furnace, oxygen vessel or Bessemer vessel, into a ceramic lined ladle. The metal is then conveyed to a pouring stand or aisle where it is bottom poured from the ladle into ingot molds or various cast shapes. Most of the ladies used in this operation have bottom-pour delivery nozzles. The capacity of these ladles can range from to 435 tons. When either ingot castings or various special type castings are poured it is necessary to control and stop the flow of molten steel through the nozzle. A stopper head, secured to the lower end of a ceramic covered rod, movable with a vertical reciprocating action from outside the molten metal, is used to seal the nozzle and stop the flow of metal from the ladle. Thus the stopper head and nozzle in combination constitute a valve.

Stopper heads now available commercially are made generally of about -25% graphite and the remainder of a high temperature hardness refractory clay of various mineralogical properties.

The stopper heads are generally made by combining the graphite and clay, previously screened to a suitable particle size, with about l5-20% water, based on the weight of the aqueous mixture, to form a mud. This material is then processed into cylindrical slugs of established diameters and lengths and containing enough material for making one head. This can be done in an extrusion machine which may also deaerate the mud prior to its entering the extrusion die.

A slug is then inserted into a mold in which the stopper head is formed from the slug by slight pressure applied by a molding piston which also shapes the inside of the green stopper head. The freshly formed green stopper head is then permitted to remain exposed to the air for .a period ranging from 1 to 7 days during which a preliminary bonding of the particles is eifected. Subsequently, the heads are dried at 180 to 400 F. to reduce the moisture content to below 4.5 percent. At this point the heads are placed in a burning kiln, properly surrounded and covered by carbonaceous materials such as a coke or anthracite fines to prevent burning out of graphite and 'fired to a temperature of between 1800 and 2500" F. (pyrometric cone equivalent O9 to 13). The firing rate varies considerably but usually does not exceed 70 F. per hour.

Stopper heads made according to this procedure have the shortcoming in that they often spall and fissure when exposed to thermal shock such as by contact with molten ice steel. This defect resembles the onion skin eflfect and is probably caused by the formation of separate mineralogical layers in the stopper head which may be due to moisture content gradients caused by the process of head pressing in the mold.

This fissuring and cracking can have serious consequences when present in stopper heads used in pouring molten metals, especially steel. The performance of a stopper head, however, cannot be known prior to pouring because it is in forced contact with the nozzle when the ladle is filled with molten metal. However, after the first or subsequent ingot is poured the performance of the stopper head can be readily observed.

Thermal shock caused by the molten metal may loosen or break away peripheral surface layers which might fall oif, or be washed 0E, when the stopper head is retracted from contact with the nozzle. The subsequent seal between the stopper head and the nozzle will then be imperfect and may permit leakage of metal out of the nozzle.

It has now been discovered that stopper heads of ex cellent properties and normally devoid of peripheral cracks can be produced by maintaining the water content at 8% or less by weight in the clay-graphite aqueous mixture prior to pressing into a green stopper head, pressing the mixture into a stopper head, water vapor curing the head and then drying and burning the stopper head.

The water content in the aqueous mixture is maintained below 8% by weight. However, suflicient minimum water is incorporated for the mixture to bind together sufficiently during pressing to withstand subsequent handling and processing. Usually not less than 1% water by weight is employed in the aqueous mixture.

The invention will now be described in conjunction with the attached drawings in which:

Figure 1 is a partial vertical section through a bottom pour ladle.

Figure 2 is an elevation of a stopper head showing peripheral fissuring of a prior art stopper head after subjection to intense heat.

Figure 3 is a top (nose) View of the same stopper head in Figure 2 again showing peripheral fissuring.

Figure 4 is a sectional side view of the stopper head of Fig. 2 showing the internal fissuring resulting from peripheral cracking.

Figure 5 is a flow-sheet of the process of making the stopper heads.

The bottom pour ladle 10 shown partly in Fig. 1 has a metal plate bottom 11 which joins the side plate 12. Both the bottom and sides of the ladle are lined on the inside with ceramic material 13, generally a fire clay brick. Afiixed to the bottom of the ladle on the out-side is nozzle plate 14 which retains nozzle 15 in position. The nozzle is further secured by clay 16 which is removable to facilitate the replacement of the nozzle after each heat.

Flow of molten metal out of the nozzle is controlled by stopper head 17 which has nose 18, of a size and shape complementary to the stopper seat 19 in the upper end of the nozzle. The stopper head is substantially semi-spherical in shape. From its upper fiat side pro,- jects collar 20. To effect vertical reciprocal movement of the stopper head into and out of sealing engagement with the nozzle, a rod 2 1 is joined to the stopper head; this is generally accomplished by a pin which is secured through hole 22 in the head as shown in Fig. 4 to the rod. However, any type of fastening may be used to secure the stopper head to the rod 21, for instance a combination of ceramic and metallic threads, a quick acting bayonet type fastener, etc. After the stopper head is connected to the pin any openings such as 23 are plugged 24 with ceramic material. The pin and rod 21 are covered with ceramic sleeves 25 which encircle the I 3 collar 20 and insulate the rod and pin from the molten metal. The rod 21 extends above the ladle. It is operated by conventional rigging.

The stopper head illustrated in Figs. 2, 3 and 4 has peripheral cracks 40 and is illustrative of this type of defect in stopper heads made by the conventional method of a high water content mixture used in pressing the stopper heads.

The graphite content of the clay-graphite blend used in the low water content process may be conventional as from 25% by weight with the remainder, not including water, of the blend a suitable high refractory clay. Thus the ratio of graphite to clay is about no greater than 0.35. The particle size of both the clay and graphite is generally below 10 mesh.

Water is added to the clay-graphite mixture in an amount not greater than 8% by weight of the final aqueous mixture. Because of the low water content the aqueous mixture is sandy in texture as distinguished from the mud or plastic like mixture obtained when water is added as in the conventional process.

The clay-graphite-water mixture is then placed in a stopper head mold. An initial vibratory action may be used to arrange the mixture, orient the particles in the mold uniformly and eliminate microscopic voids. The mixture is then subjected to a high pressure, such as 8001000 pounds per square inch, although higher pressures may be used. The pressure employed should be sufficient to produce a suitable stopper head having a final porosity of not more than 20%. (Final porosity is determined by the difference in the volume of a stopper head after burning and the volume of the head after it is reduced by grinding to particles below 100 mesh).

Following pressing, the green stopper heads are placed in a suitable water vapor curing chamber. A chamber of high humidity and high temperature and low pressure is advisably employed to get penetration into the green stopper heads and keep the curing time at a minimum. A chamber at 100% relative humidity and 200 F. is suitable for curing the stopper heads. If desired, steam such as at about 230 F. under atmospheric pressure may also be used for the curing. Steam curing above atmospheric pressure leads to deterioration of the stopper head. The time of curing may be from about 2 to 24 hours or such time as is adequate to effect a primary mineralogical cementing prior to burning.

After water vapor curing, the stopper heads are dried. A drying period of about 12 hours at a temperature up to 200 F. is suitable. However, drying should continue until the stopper heads have a moisture content of about 4.0%. The stopper heads are then placed in a conventional kiln and burned under a protective atmosphere. This should be accomplished within ten days, and advisably within 48 hours, after air drying. A protective atmosphere is obtained by enveloping the stopper heads in coke or anthracite. The stopper heads are burned at 1800-2400" F. for about 4 hours with the soaking temperature being reached from the initial firing in increments of about 50-100 F. per hour. The burning operation and temperatures employed are those in conventional use for producing stopper heads.

After burning, the stopper heads are examined carefully for obvious defects caused by handling and the defective products discarded. The perfect stopper heads are then employed as needed on the stopper-rod assem bly mechanism of a ladle.

Although this invention has been described in particular to its application in the production of stopper heads, it is equally useful for producing other predetermined shapes made from clay, graphite and water, and especially other components used in conjunction with steel manufacture.

The following example is presented to illustrate the invention but it is understood that the invention is not to '-be restricted to this specific embodiment.

Example A mixture containing 17.5% by weight of graphite particles and 82.5% of an Al O clay essentially free of lime, sodium and potassium is prepared. The clay and graphite is in particle form of a size all smaller than 10 mesh. Water is added to the clay-graphite mixture by blending or mulling until the Water content of the claygraphite-water mixture is approximately 8% by weight.

The aqueous clay-graphite mixture is inserted in a stopper head mold and pressure of 800 pounds per square inch is applied. The pressed stopper head is removed from the mold, cooled to room temperature slowly and then cured for about 10 hours in a water vapor chamber at relative humidity and 200 F.

The cured stopper head is air dried for about 12 hours and then burned in the regular manner.

Various changes and modifications of the invention can be made and, to the extent that such variations incorporate the spirit of this invention, they are intended to beincluded within the scope of the appended claims.

What is claimed is:

1. The process which comprises forming an intimate mixture of water, clay and graphite having a ratio of graphite to clay of not more than 0.35 and a maximum of 8% by weight of water in the mixture, pressing the mixture into a predetermined shape, water vapor curing the pressed shape to develop a primary mineralogical cementing bond, drying the cured pressed shape to a moisture content of not more than 4%, and burning the dried cured pressed shape at an elevated temperature.

2. The process which comprises mixing clay, graphite and water together with the water content of the mixture maintained below 8% by weight of the aqueous mixture, the amount of graphite in the clay-graphite blend being not more than 25% by weight and the particles of clay and graphite being no greater than 10 mesh, placing the mixture in a stopper head mold, applying a high pressure to the mold, removing the pressed stopper head from the mold, placing the stopper head in a high water vapor chamber for a time sufficient to cure it, removing the stopper head from the chamber and drying it to a moisture content of not more than 4%, and burning the dried stopper head in a protective atmosphere to prevent burning out the graphite.

3. In the process of making stopper heads, the improvement which comprises pressing an aqueous mixture of clay and graphite having not more than 8% water by weight into the shape of a stopper head, pressing the mixture into a predetermined shape, water vapor curing the pressed shape to develop a primary mineralogical cementing bond, drying the stopper head to a moisture content of not more than 4%, and burning the stopper head at an elevated temperature.

4. The process which comprises forming an intimate mixture of water, clay and graphite having a maximum of 8% by weight of water in the mixture, pressing the mixture into a predetermined shape, water vapor curing the pressed shape to develop a primary mineralogical cementing bond, drying the cured pressed shape to a moisture content of not more than 4%, and burning the dried cured pressed shape at an elevated temperature.

5. The process which comprises forming an intimate mixture of water, clay and graphite having a maximum of 8% by weight of water in-the mixture, pressing the mixture into a stopper head, water vapor curing the stopper head to develop a primary mineralogical cementing bond, drying the cured stopper head to a moisture content of not more than 4%, and burning the stopper head at anelevated temperature.

'6. A stopper head produced by the process of claim 3.

Handren Mar. 29, 1949 i'Leitten Now 27, 1956