CA1178020A - Anchored refractory inserts for ingot mold stools - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An ingot stool of the type upon which steel is poured comprising a rectangular slab of cast iron having a top, bottom and sides, with the top having its center portion dished, a precast ceramic stool insert having a flat top and a convex bottom adapted to fit in snug relationship with center dished portion of the stool, threaded anchor means fitted within the bottom of the precast ceramic stool insert and a bolt passing through the bottom of the stool and threaded into the threaded anchor means.

Description

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INTRODUCTION
l. Field of the Invention All metal ingots are cast from molds. These molds rest on bases commonly known as "stools." The stools are large, normally rectangular, flat slabs of metal usually made of cast iron. The stools are used as support for the mold sides and also to form the bottom portion of the mold. In a "big end down" type of mold, the mold sides generally taper down in diameter from bot-tom to top. In another type of mold, known as the "big end up" mold, there is a ladle-like receiver for the molten metal, the bottom portion of which is integral with and non-removable from the entire mold.
Various problems commonly occur in use of these molds and particu-larly with respect to the surface of their base portions. The unprotected metal surface of the base portion quickly erodes and pits in the presence of molten metal which is cascaded upon its surface. Large gouges in the base portions are produced due to the force and high temperature developed by the flowing molten metal which contacts the surface of the stool.
Since many molds are generally 5-10 feet in height, the metal must be poured from a height at least equal to that distance and quite often is poured from even greater heights. A considerable pressure head is thereby developed. Thus, the hot molten metal easily gouges gaping depressions in the base members under such force and at a temperature of at least tlle liquefaction temperature of the molten metal. Moreover, the problem of creation of pits or gouges in the base portions of the molds, caused by the above factors, is agg-ravated due to the fact that the molten metal especially near the bottom of the mold, remains in its erosive hot liquid state for a considerable amount of time subsequent to pouring.
The molten metal, after solidification to an ingot has a o~o bottom form conforming to the undesirable eroded surface configuration of the stool or base member of the mold. Thus, a considerable amount of the ingot, when withdrawn from the mold and subsequently processed into slabs or blooms, is lost through a cropping of the irregularly formed end of the slab. This, of course, is highly undesirable, since it results in undue loss of usable metal and an increase in scrap which must be subsequently reprocessed.
Another extremely serious and costly problem arises after the ingot in the mold has solidified to a point where it can be removed from both the mold sides and its base platform member or stool. Considering first a big end down mold, if the surface ot the stool is unprotected or inadequately protect-ed and erosion occurs as described above, the ingot has a greater tendency to remain tightly adherent to the stool. Thus, after the mold sides are removed from around the ingot, which process can normally be efficiently achieved with a minimal film of coating selected from a variety of coating agents, the ingot must be forcibly removed from the stool.
Removal is normally achieved by raising both ingot and adherent stool, and thrusting them against some other larger object whereby the ingot is jarred loose. In many cases the stool and ingot are merely dropped on the floor from some suitable height. In such a situation, the stool is often broken into two or more smaller pieces and cannot be subsequently reused in casting other ingots. Again, replacement cost of these stools is high, making this aspect of the overall casting process somewhat disadvantageous.
The same problem exists with respect to big end up molds wherein sticking of ingots particularly occurs at their base portion. New molds of this type are especial]y vulnerable to sticking due to their smooth surface unprotected by any layers of metal oxides or scale. A tight metal-to-metal bond between mold bottoms and ingots may occur in this si~ua-tion.
¦ Crackin~ of molds and par-ticularly cracking of their base ¦ portions due to the above discussed rough handling occ~sione~
¦ by "stickers" between the base portions and ingots is enhanced ¦ by thermal sho_k d~ring ingot forma-tion. Unprotected or inadeq~ately ¦ protected bottom surfaces of molds are especially susceptible to such destructive shock.

2. Description of th_ Prior Art Many ways of alleviating the above described problems in connection with the erosion of base members of ingot molds have been proposed in the prior art. A number of refractory coatings -have been suggested but these are not entirely satisfactory.
An early solution to the erosion of ingot mold stools resided in the suggestion that refractory inserts could be placed into the bottom of the mold, which refractory would tend to mir.imize erosion.

¦ An important drawback of ceramic inserts relates ¦to the difficulty of anchoring them to the stools. ~olten metal ¦tends to work its way into the space between the insert and the ¦stool due to capillary action. In the absence o~ a sufficient ¦anchoring system, this molten metal tends to force the ceramic ¦insert from its cavi~y. When this occurs, the ceramic insert ¦positions itself above the top surface of the stool and tends to ¦become entrained -~ithin the metal ingot. This entrainment causes a ¦number of problems including the formation of metal inclusions in the ¦ingot which necessitate an expensiv~ operatior. known as butt ¦cropping.

.1 Many of the deficiencies in the prior art mentioned above have been overcome by utilizing precast ceramic inserts.
In one instance, the cast iron stool is cast onto a preformed ceramic stool insert which makes the insert integral with the stool. This is disclosed in Vnited Sta-tes 4,097,019~ ~nother method of utilizing precast ceramic inserts is disclosed in United States 4,077,600. In tnis patent a preformed insert is put into a large preformed cavity in the stool. It is anchored into the stool by means of Z-shaped brackets which are anchored into the body of the cavity and with the top portion of such anchors fitting into a preformed groove in the ceramic insert.
In the case of the ceramic insert taught in United States 4,097,019, these can be prepared only at the foundry where the stools are made. In the case of United States 4,077,600, the ceramic inserts require extensive labor to fasten the inserts and, also, the spaces between the insert and the stool must be filled or plugged with additional refractory material. Further, the teachings of United States 4,077,600 often require a number of anchor bars to hold -the insert in place.
If it were possible to utilize a prefired refractory insert which could be readily attached to a stool without extensive labor or mechanical adaptations being required and not necessitate the use of refractory filler to seal the edges of the insert, an advance would be made in the art.
According to one aspect of the invention there is provided an ingot stool of the type upon which steel is poured comprising a rectangular slab of cast iron having a top, bottom and sides, with the top haviny its center portion dished, a precast ceramic stool insert having a flat top and a convex bottom adapted to fit in snug relationship with center dishea portion of the stool, threaded anchor means fitted within the bottom of the precast ceramic stool insert and a bolt passing through the bottom of the stool and threaded into the threaded anchor means.
he Drawing Tne drawing is a vertical cross-sectional view show-ing a preferred embodiment of the invention.

5a ,l.~ O'~ID

TI-IE INVENTION

With particular reference to the drawing, there is shown a l cast iron stool 10 having a top 12 and a bottom 14. These stools ¦ a e usually 8 inches or more inches in thickness. The center ¦ portion of thP top 12, which portion is wherein n:olten metal is ¦ teemed onto the stool, is dished or concave~ This concavity 16 is fitted with a precast c~ramic stool insert 1~ which lS
¦dimensi~ned to fit exactly within the concavity 16.
¦ The bottom ~0 of the insert contains a vertically positi~ned ¦thr2aded sleeve 22. To the top of this threaded sleeve is welded la circular or ceramic plate 24 which acts to anchor the threaded ¦sleeve 2~ firmly into the ceramic stool insert. The threaded sleeve ¦22 and its top plate ~4 are positioned within the ceramic insert ¦at the time of its manufacture, while the ceramic is plastic. After ¦~iring, these assemblies become an integral part of the cexamic ¦insert. The plate 24 can be omitted and bar like member~ may be ¦fitted to the sleeve 2~.
The bottom of the stool near the center of the concavity 16 ¦contains an opening 26 whose bottom is a recessed stop 28~
¦Passing throush the opening ~6 and engaging the recessed stop 28 ¦is a long bolt 30 and washer 32. The bolt is threaded into sleev~ 22 ¦
and snugged up so that the ceramic insert 18 1S fastened securel~
to the stool 10.
Thus, by using this techni~ue, it is possible to use simple -fastening means to fasten a stool lnsert within a stool having a preformed cavity whlle, at the same time, preven-ting any movemen, of the insert within the stool.
The refractoxy insert is formed from many common refractory materials although preferably the refractory material will be composed ¦
predominancly of alumina, a binder and filler materials including vitreous silica, crystalline silica, magnesium silicate, alt~tinum silicate, graphi-te, zirconium silicate and clay. The preferred 1.

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¦refracto y material should contain 40 - 95g al mina, S - 20~ binder and the remainder filler.
Typical binders include a mixture of water and one or more of ¦ethyl silicate, sodium silicate, aluminum phosphate, colloidal ¦silica or clay, where water comprises up to 50% by weight of the binder. In a most preferred embodiment, the refractory insert will be formed fro~ a refractory mixture containing at least 70% by weight ¦alumina, 10% by weight ethyl silicate, 10% by weight wa,er and the ¦remainder crystalline silica. Another, a less desira~le insert, ¦could be formed from about 5Q% silicon carbide, a~out 20% silica, ¦about 10% alumina, and the remainder binder.
¦ According to the practice of the present invention, ~he ¦refractory insert will be formed by mixing the materials described ¦above, forming khem into the desired shape and subjecting them to heating. The temperature and length of heating will depend upon the refractories and the binders used. In a preferred mixture containing !
70% alumina, 10% binder, 10% water and the remainder silica, the mixture should be shaped and then subjected to 2000 - 3000F. ~or at least one hour and, preferably, for three hours or more before use.

Having thus described my invention, it is claimed as follows: ¦

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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An ingot stool of the type upon which steel is poured comprising a rectangular slab of cast iron having a top, bottom and sides, with the top having is center portion dished, a precast ceramic stool insert having a flat top and a convex bottom adapted to fit in snug relationship with center dished portion of the stool, threaded anchor means fitted within the bottom of the precast ceramic stool insert and a bolt passing through the bottom of the stool and threaded into the threaded anchor means.

2. The ingot stool of Claim 1 where the threaded anchor means is a threaded sleeve having its top fitted with a perpend-icular plate.