US2833008A - Hot top for ingot molds - Google Patents

Description

May 6, 1958 w. M. CHARMAN ETAL 2,833,008

HOT TOP FOR INGOT MOLDs Filed Dec. so, 195o 1a" INVENTORS WAL ree /V CHAPMAN BywfAM/N [Ama/Vy man MSM Arme/IEW HOT TOP FOR INGOT MOLDS Walter M. Charman, Shaker Heights, and Benjamin F.

Anthony, Cleveland Heights, Ohio, assignors, by mesne assignments, to Oglebay Norton Company, Cleveland, Ohio, a corporation of Delaware Application December 30, 1950, Serial No. 203,666

6 Claims. (Cl. 22-147) This invention relates to improvements in hot tops for ingot molds, and has reference particularly to a method and means for hot topping in a highly eicient manner in order to reduce to a minimum the percentage of wasteV metal in the sinkhead as compared to that of good metal in the ingot proper. i

The conventional composite hot top comprises a cast iron casing lined with iirst quality tire brick blocks. Such bricks have a higher softening temperature than the temperature at which molten steelsv are poured, namely 2700 F. to 2950" F. They possess thermal shock resistance of an acceptable order to withstand, rst, the considerable shock attendant upon filling the hot top when molten steel comes into intimate contact with the relatively cold brick lining and second, when the hot top, the face of whose brick lining may be at a temperature as high as 2400 F., is stripped otr the sinkhead and cold air rushes up through it to wipe these very hot surfaces. These brick also possess good mechanical strength to withstand the abuse given a hot top upon stripping and handling. When a craneman pulls a hot top off a sinkhead it is rare that a straight up axial lift is achieved,

consequently any cooking action must be resisted by they brick lining. The heat losses for a hot top employing tire bricks o the first quality grade are considerable due to their high thermal conductivity and their high heat capacity. These high losses must be supplied by enough molten steel to insure adequate feeding of the molten metal needed for the shinkage cavity of the solidifying ingot. Depending on the type of steel, its pouring temperature and several other factors, a hot top must have a capacity approximating l percent of that of the combined mold and hot top volumes. Only about 4 to 6 percent of the combined volumes is necessary to feed and insure ingot soundness. Hence the balance of 9 toll percent represents waste, loss or scrap and is an item which every steel plant is trying to reduce. Any reduction so accomplished is the equivalent of adding additional steel manufacturing capacity which'today is of utmost importance to our military and civilian economies.

Various expedients have been devised to reduce the amount of steel necessary to produce a sound ingot and to keep the reduced amount molten for satisfactory feed-A ing. These include playing gas flames or electric arcs on the top surface of the ingot, exothermic reactions in the hot top, special hot top constructions and special refractory materials. The benefits attendant upon these expedients have been limited by operating and economic considerations, and as a result the great bulk of hot topping is being done today as it was twenty yearsl ago.

ln this invention we substitute for the conventional tire brick linings a lining composed of insulating fire brick. These brick depend for their insulating qualities upon high porosity caused by burn-out material incorporated in the mix and burning upon tiring of the brick. They are light in weight and quite fragile. They are also f ivice y more expensive than rst quality re brick. They are Y made in various grades, those having the best insulating qualities being adapted for use at top service temperatures very much less than the pouring temperature of steel. Such brick will not withstand the mechanical abuse nor the penetration of their porous structure by liquid metal or slag phases as will the usual lining of iirst quality tite brick. Protective washes have proved ineffective because such protection hardens to greater strength than the brick structure and then upon rapid heating and cooling, differential dimensional movements will shear through the weaker structure of the porous in sulating tire brick.

We have found that by providing a single use Protec-- tive veneer of the proper thickness we are enabledtol The thickness of the protective veneer is such that the temperature gradient across it will prevent the temperature of the internal face of the insulating fire brick from going above its rated maximum. Such thickness is of the order of one-half inch, that is to say on hot tops of average size under normal conditions for best results a one-half inch veneer is required. Por large hot tops a somewhat greater thickness of veneer is desirable. Furthermore the veneer thickness will necessarily vary somewhat in different parts of the same hot top because of the human element of the workman 0r the inexactness of the.

action of the mechanical equipment employed for the. Also the safe working temperature of the particular brick used in the semipermanent lining (which is to be protected), is a factor which 1 purpose of applying the veneer.

atects the selection of Veneer thickness.

Due to the falling temperature gradient across the protective veneer, a grade of insulating brick can be selectedf. whose service temperature limit is below ther pouring;

temperature of the steel and hence make use of the added.` insulating properties and lower heat capacity without: sacricing life of the brick. Veneer of this thickness is; more than sufficient to prevent molten steel from con-- tacting the insulating lire brick, and is of such nature as: to permit easy stripping of the hot top from the sinkhead.y Furthermore, it easily absorbs any mechanical forcesy imposed by misaligned stripping.

One of the objects of the invention is the provision of a method and means for hot topping which shall reduce the amount of the metal of the sinkhead and correspondingly increase the percentage of good ingot metal in pro portion to the total metal poured.

Another object is the provision of a hot top in which'. insulating tire brick are employed but are protected in.

vsuch away against thermal shock and mechanical shock.

application, we have illustrated in the accompanying drawing, in which Patented May 6, 1958- lig. 1 is a vertical sectional view through an ingot and ingot mold. and a hot top embodying our invention, and

showing a sinkhead with a relatively thin shell, such as results from the practice of the invention.

Fig. 2is' a fragmental vertical sectional view of the hot top Aon a larger scale. l

Fig. 3 is a view similar to that of Fig. 2'showing a modified form of hot top, and Y I Fig. 4 is a fragmental external elevational view of the hot top casing. i Y

In the drawing we have illustrated at 13 a big end up mold for the casting of killedsteel ingots. The figure shows an ingot 11 therein; having a sinkhead 12 ofrelatively low mass such as results from the practice ofV the invention. The hot top comprises la casing of cast iron or the like which maybe cast in one or a plurality of sections, upper and lower sections 13 and 14 being illustrated. Any suitable means for holding the sections together may be employed. f

Casing section 14` has an inturned bottom ledge 15 extending entirely around the hot top, and section 13 has an upper inturned rim 16 also extending entirely around the hot top. A semipermanent-lining is supported on the ledge 15 and extends upwardly to a pointtjust beneath the overhanging rim 16. This lining as illustrated in Fig. 1 consists of a lower course of insulating fire brick 17 and an upper course of insulating tire brick 18. These bricks are designed and made to fit the inner surfaces of the casing walls.` The inner faces ofthe bricksV are inclined inwardly and upwardly in planes meeting the rim 16 of the casing somewhat back from the edge of the rim, the distance being preferably of the order of one-half inch in the case of hot tops of average size.'

Beneath the ledge 15 of the casing there is a refractory bottomv ring 20 intended for a single use, this ring being flat on its upper surface and preferably having an inclined lower surface as shown in Figs. l and 2. Such a ring is known as a tapered ring and has advantages in that it forms a tapered shoulder on the ingot. A somewhat different bottom ring such, for example, as that shown in Fig. 3 at 20', may be employed however without departing from the spirit of the invention. The ring 20 or 20'V extends inwardly beyond the ledge as illustrated iny the drawing. It is supported by means adapted to jfail when the hot metal is poured ork when thehot top is stripped from the ingot. Such means' may consist of a plurality of wire clips 21 having lower bent ends gripping the ring and upper hooks engaged in replaceable socket members 19 mounted in the casing section 14. When the hot top is stripped from the ingot the clips 21 break or pull out of the sockets 19 and the ring 20 or 20 remains behind on the ingot.

In preparing Vthe hot top for use the casing with its lining blocks 17 and 18 is placed in a suitable cradle and inverted. Ring 20 or 20 is put in place and fastened with the clips 21. Then a moldable refractory veneer 22 is applied to the lining. This veneer should have low heat conductivity. It may have a siliceous base' and may contain organic particles such as sawdust which add to its insulating qualities, and a binder. Exothermicmaterials may also be included. This veneer is of such physical characteristics that it has a single heat life, this phrase as hereinafter employed signifying that it cannot withstand exposure to the heat of more than a single pouring of molten metal, that degree of heat causing cracking, crumbling and breakage of the veneer with the result that when the hot top is stripped from the ingot at least a portion of the Vveneer falls away and must be renewed before the next heat. 20 and the inner'edge ofthe rim 16 may be used as guides to gauge the thickness of the'veneer upon its application.` Y 'i When the veneer has been applied it must be dried before the hot top can be used. Drying can be accomplish'ed preferably by subjecting the veneeror the entire The inner edge of the ring 20 or assembly to the action of hot air, the dried veneer, in place in the hot top, when subject to the thermal and mechanical shockimparted by the molten steel, becomes quite frangible.

The thickness of the veneermust be such that the temperature gradient through it will give a lining face temperature not exceeding the maximum safe operating ternperature of the insulating fire brick used. A thickness of one-half inch vor more is suitable. The veneer need not be very hard and infact a relatively soft veneer has some advantages in that it permits easy stripping of the hot top from theV sinkhead, because it will absorb any force imposed by misaligned stripping. The veneer 22 of course follows the contour of the lining bricks 17 and 18 although if Adesired the thickness of the veneer at the top may be somewhat less than that at the bottom because the temperature and mechanical stresses at the top are not so severe as at the bottom.

In Fig. 3 we` have shown the invention in connection with a form of bottom ring 20 which has been conventional up to the present time. It comprises a portion 23` which extends upwardly on the inner side of the bottom ledge 15 of the casing.

In both forms of the invention illustrated the ledge 15 or 15 extends inwardly a distance less than the bottom ring 20 or 20 and somewhat le'ss than the lower inner edge of the semipermanent lining. The resulting space in the case of the form of Figs. l and 2 is filled with the veneer material, as indicated at 34. In the Fig. 3 construction such space is substantially eliminated and consequently only a very small amount of veneer material is required to till the joint.

In the casing 13, 14 there are cored weight saving pockets 35 and 36 which are joined by passages 37 to grooves 38. In the bottom ofthe casing there are grooves 39. These grooves 38 and'39 conduct away or vent any gases or vapor generated when the'molten steel strikes the vencer, the gases and vapor thenV passing through the porous insulating fire brickinto the pockets 35 and 36. Some gases andvapor escape along the inner wall of the hot top, butrthe greater amount vents through the porous lining and escapes by way of the cored Apockets 35 and 36, the vents 37 and the grooves 3S. Gases generated around the thick portions 34 of the veneer escape through the grooves 39. Y

The hot top may be supported upon the mold temporarily during pouring ofthe hot metal by wooden blocks 40 or other means.' When the metal has been poured into the hot top to the correct level, these blocks may be knocked out. After pouring and solidication of the ingot the hot top is stripped from the sinkhead. VSome of the veneer will remain "on the sinkhead and some will adhere to the hot top. In preparing the hot top for the next heat, loose veneer is removed, new blocks, wiper strips, ring and clips are put in place and a fresh veneer appliedfY Having thus described our invention, we claim:

l. A high efficiency hot top, comprising a metal casing, a low heat capacity, low heat conductivity, sernipermanent porous insulating lining for said casing and a refractory veneer of a thickness about `one-half inch and of fragile:` nature when subjected to contact by molten steel in direct contact with the inner surface of said lining, whereby said semipermancnt lining is protected from thermal shock and mechanical blows, said hot top being dimensioned to provide a sinkhead cavity of relatively low volume.

2. A hot top as defined in claim l, wherein said casing is provided with pockets behind said semipermanent lining and with vents to atmosphere from said pockets, whereby gases or vapor generated insaid veneer when contacted by hot metal may escape through said porous lining, said pockets and said vents.

3. In a high eiiiciency hot top, a metal casing, a porous refractory semiperinanent lining therefor having a capacity for withstanding temperatures of approximately 2600 F. without appreciable deterioration and having low heat capacity and conductivity, and a refractory veneer approximately one half inch in thicknessof low heat conductivity and of fragile nature when subjected to contact by molten steel covering completely the inner surface of said lining, said veneer having a temperature gradient thereacross of approximately 200 F. when the hot top contains molten steel.

4. In a high eiciency hot top, a metal casing, a refractory semipermanent lining therefor comprising low heat capacity, low heat conductivity, semipermanent porous insulating blocks carried by and backed by said casing, and a molded refractory veneer about one half inch in `thickness of low heat conductivity and limited life covering completely the inner surface of said lining.

5. In a high efficiency hot top, a metal casing, a refractory semipermanent lining therefor comprising low heat capacity, low heat conductivity, semipermanent insulating blocks carried by and backed by said casing, said blocks being covered on their inner surfaces with a protective soft refractory veneer approximately one-half inch in thickness having a temperature gradient thereacross of approximately 200 F., when the hot top contains molten steel.

6. In a high efficiency hot top, a metal casing, a refractory semipermanent lining therefor comprising blocks having a `capacity for withstanding temperatures not in excess of approximately 2600 F. without appreciable deterioration and having low heat capacity and conductivity, said blocks on their inner sides having an adherent refractory veneer about one-half inch in thickness and having a temperature gradient thereacross of approximately 200 F. when the hot top contains molten steel of a temperature of approximately 2800" F.

References Cited in the le of this patent UNITED STATES PATENTS 1,630,612 Gathmann May 31, 1927 1,665,515 Trembour Apr. 10, 1928 1,739,222 Gathmann Dec. 10, 1929 1,778,316 Forrest Oct. 14, 1930 1,969,726 Charman Aug. 14, 1934 2,088,288 Charman July 27, 1937 2,228,545 Wheaton Ian. 14, 1941 2,574,815 Charman a Nov. 13, 1951

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