US2159374A - Hot top - Google Patents

Description

Patented May 23, 1939 UNITED STATES PATENT OFFICE HOT TOP Application July 6, 1937, Serial No. 152,100

1 Claim.

This invention relates to hot tops .for ingot molds, and more particularly to improvements in a detachable hot top adapted to be made of refractory material.

The emciency :of a hot top and its ultimate accomplishment may be in the ratio of the useful portion of the ingot, to that portion which must be cropped ofi. Thus a hot top capable of drawing within itself all or substantially all of the impurities from the ingot and all or substantially all of the porosity or piping which might otherwise exist in the body of the ingot, and which concentrates the impurities and porosities into the smallest mass of steel to be cropped, approaches the maximum of efficiency for its intended Particularly where the steel of the ingot isvery costly, as, for example, in the so-called stainless steels, every pound of steel which can "be eliminated from the part necessarily cropped. from the ingot represents a corresponding saving in the costxof manufactur of finished steel.

In the art of pouring ingots with the use of hot tops, it is and understood that it is desired to maintain a .head of liquid steel, and a sufficient quantity of liquid steel in the hot top for a length of time long enough to be available to prevent the tendency toward porosity and piping in the body of the ingot as the outer and lower portions of the ingot chill and shrink, and to float up into the crop all .or substantially all of the impurities which, by gravity or other phenomena, may thus be drawn upwardly and out of the body of the ingot. Thusa hot top with relatively great heat insulating properties will maintain inliquid form the steel within its own body for a longer period of time than a hot top having poor insulating qualities. By the same token, a hot top with the better insulating O, qualities need contain a smaller cubic content of steel, 1. e. crop, since the less efilcient hot top requires a greater mass of steel for the same quantity'of fluid for the period of time when the fluid head is necessary for proper purification and solidification of the ingot.

Hot tops are subjected to the very high temperatures of molten steel when the ingot is poured, and have a very decided tendency to crack and spall under the extreme temperatures to which they are subjected. Spalllng of the hot tops or cracking oil of portions thereof, particularly during the early stages of pouring the ingot, may do' irremedlable injury to the ingot by the deposit of non-metallic substances therein. Once the body of the ingot is poured and after the crop is poured into the hot top, then the cracking of the hot top may permit an outflow of the molten steel from its body, which may jeopardize the lives or well being of workmen adjacent the ingot mold, and if the cracking permits such a leak as to lose the head of molten steel, then all or part of the ingot may be lost as a commercially acceptable product by virtue of its containing the defects which the operation of the hot top, outlined above, was intended to correct. The loss or damage due to cracking of the hot top is very much more serious if it occurs in that relatively short period of time before the surface of the crop has chilled when the molten steel may escape from the body of the hot top. Cracking in a later period, after the crop has chilled enough to form a self-sustaining skin for the fluid content thereof is particularly injurious where the cracking contributes sub stantially to a loss of the thermal-efiiciency of the hot top. Cracking may substantially destroy the insulating as well as other properties of prior art hot tops now in use.

After the ingot has solidified, there comes a point in the usual practice where the hot top must be removed or stripped from the crop end thereof, and the facility with which stripping or removal may be effected is a further measure of the efliciency and advantages of a hot top. Hot tops which crack or spall at points in contact with metal in a fluid state will tend to be bonded to the ingot or crop in a manner to impair the stripping operation, and hot tops, which by their construction or otherwise permit the fluid steel to gain a deleterious grip or a locking relation with respect to a part of the hot top, impair the stripping operation.

It is among the objects of my invention to provide a hot top of refractory material capable of bringing about the advantages sought in the casting of ingots indicated above, and capable of avoiding the hazards and failures found in the prior art hot tops, to which reference has above been-made. The objects of my invention include the provision of a hot top in which cracking is substantially reduced or eliminated, and in which the tendency toward cracking is availed of to enhance the operation of the hot top rather than impair it.

A further object is to provide a hot top having a relatively high insulating value with adequate structural strength to carry out its intended thermal and hydraulic purposes combined in a structure which may be economically manufactured and used.

A further object is to provide a hot top of stout enough construction to withstand the stresses and strains to which it is subjected in transportation and use, and in which weight and density can be controlled within desirable limits and which can be extruded accurately and easily and fired uniformly.

A further object is to provide a hot top by the use of which the segregation of impurities from the ingot is substantially complete, and in which that portion of the ingot which needs to be cropped is reduced in mass and amount whereby to increase the useful portion of the ingot with respect to the crop portion. Within the above objects I provide a hot top which may be easily stripped from the ingot or crop portion thereof.

More particularly, it is among the objects of my invention to provide in the structure of the hot top a flexibility or elasticity of construction which permits a yielding of those portions of the structure which are first put under the stresses of the impact of heat or other forces tending to distort the body of the hot top, whereby the tendency to crack in a deleterious fashion is substantially eliminated, and relative expansion of those portions of the hot top first subjected to heat and fluid pressure is permitted with respect to the cooler portions of the hot top, especially when the temperature differences between various portions thereof is great.

Other objects and advantages will appear from the following description of one or more exemplary and preferred forms of my invention, reference being made to the accompanying drawings, in which Figure 1 is an illustrative view in cross section showing the relationship of a hot top to the upper portion of an ingot mold with the upper portion of the ingot and the crop portion thereof shown in relative position after the ingot has been cast. Figure 2 is a fragmentary transverse cross-section and partially diagrammatic representation of a prior art hot top in which are depicted by way of illustration the resolution of certain forces tending to cause the rupture thereof. Figure 3 is a similar fragmentary and diagrammatic View of a portion of a prior art hot top in which there are illustratively shown certain of the forces tending to effect rupture of that style of hot top. Figure 4 is a similar fragmentary sectional view of one form of a hot top embodying the principles of my invention. Figures 5 and 6 are similar views of modified forms of my invention.

Referring to Figure 1 I have disclosed a fragmentary portion of the upper end of the ingot mold l depicting therein in cross section the upper portion of an ingot-2 having a crop portion 3 embraced in a hot top 4. The hot top 4 is illustrative of the general position and general formof hot tops known in the art and those in which I embody my invention in that it is of cylindrical configuration, conforming particularly at its lower outer surface as at 5 to the upper opening in the end of them old I, and, as is known, the cylindrical form of the hot tops may be circular, square or rectangular depending upon the shape of the mold. Lugs 6 or notched corners 6' along with removable or combustible supporting wedges or blocks, now shown, support the hot top in about the place illustrated in Figure 1, and as the ingot solidifies the hot top rests on the shoulders l of the ingot and embraces within itself the crop 3, which may in the course of cooling develop irregular voids 8 as are found when the crop portions of the ingots are cut open for inspection. To measure the effectiveness and accomplishments of a hot top test holes A, B, C and D are commonly drilled in a cut open section of the upper portion of the ingot in and about the zone shown in Figure 1 to determine particularly whether or not the carbon, manganese and other chemical elements in the steel are evenly distributed, particularly in this critical part of the ingot. In a comparative test between a hot top embodying my invention and a prior art hot top, it was found for example that the carbon in the solidified ingot at the point A amounted to .26 as compared with the content of .22 at point D. Where an ingot, poured with a hot top embodying my invention, was similarly examined the carbon content of the point A is found to be only .24 as against a carbon content of .23 at point D. The'advantage measured by this test was that with using my hot top, it was shown that the segregation of impurities above the point A was much more complete than it was with the use of the prior art device. For the same reason the extent of the crop necessary to be cut down to the point in the ingot below which the distribution of carbon, for example, was uniform, was very much less when my hot top was employed than when the prior art hot top was used.

In Figure 2 I have shown in cross section a fragmentary portion of a curved wall of hot top of solid cross section, according to the practice of the prior art, and it will be appreciated when the hot metal bears against the inner wall |0,the same is heated very rapidly, and that high compressive forces are created in the inner portion of the wall of the hot top, as I have indicated by the arrows H. These forces in compression, measuring the tendency of the inner wall of the hot top to expand, are resolved into radial forces l2 acting through the body of the wall, and are resistant by forces in tension [3 in the outer portion of the wall. Since the tensile strength of fire clays and other refractory materials from which such hot tops have been made is relatively small, and since the heating of the inner surface of the hot top is very rapid, the inevitable result of the use of such hot tops is that fractures will occur roughly along the line I5, as indicated in Figure 2. Moreover, since the wall of the hot top is solid, the tendency to fracture is not limited to any plane of direction, and fractures may extend vertically or horizontally or in combinations of those directions with the disadvantageous results discussed above. Such hot tops are frequently bound with two or three wire hoops which add about 5 to 10 to the cost of use of each such hot tops without curing the inherent evil thereof.

Moreover, the compression forces ll build up in amount very rapidly, particularly where the wall of the hot top is dense and thick and solid as shown in Figure 2, and these excessive compressive forces tend to cause spalling of fragments from the inner surface I!) of the hot top which may add non-metallics to the ingot and impair the stripping of the hot top therefrom. The more firmly the inner annular portion of the wall of the hot top is held against expansion, the more rapidly do the stresses therein build up. Thus the thicker and denser solid walls seem to crack and fracture more quickly and with more disastrous results than do the thinner and less dense ones, However when powdered coal or other carbonaceous material has been added to powdered or pulverized clay in the process of making solid wall 110? tops, the density has been reduced,

but it has been most .dimcult if not impossible to burn the carbonaceous content out of the, midportion of thick walls, whereby when such walls crack, the free carbonaceous material is exposed to enter, into the body of the ingot. Moreover, the difficulty in burning out carbonaceous material from thick and solid walls leaves the resultant density and structural characteristics uncertain and lacking in uniformity. By providing voids in the walls of my hot tops to be presently described, and by restricting the wall thicknesses, I am enabled, among other things, to burn out all the carbonaceous material that may have been added and thereby obtain and control the density and other structural characteristics of the various parts of the wall within substantially definite and desirable limits. Furthermore in carrying out the objects of my invention, I provide in the forms of my hot top, presently to be discussed, a certain freedom of the inner annular portion of the hot top with respect to the balance thereof whereby it can give or yield with the resuit that the stresses therein are not permitted to become great, and the damage resulting from excessive stress in the more critical portions of the hot top is materially reduced if not substantially eliminated.

In Figure 3 is disclosed another form of prior art hot top in which relatively large voids l6 are formed between the inner wall l1 and the outer wall i8, which walls are joined by radial webs 9. It has long been known to provide relatively large voids both-in the upper ends of ingots molds and in detachable hot tops. Where such hot tops are detachable and particularly when made of refractory material, there are various disadvantages, one of which is that the tendency for such hot tops to crack while the crop portion of the ingot is fluid is substantially the'same as that'in a l solid hot top, i. e. the expansion of the inner wall I! creating forces in compression I exert radial forces I 2 in the webs H), which in turn are resisted by forces in tension I3 in the outer wall l8 and also by shear stresses in the zones indicated by the lines |A and 5B. The result is that the tendency of such voided hot tops to fracture is great along the line I5, because the stresses and strains of both tension and shear are combined in the zone of the web l9, and experience demonstrates that these hot tops split from the outer wall through the radial webs and inner wall with disconcerting frequency. Spalling as at S can be expected to occur in this form of hot top for the same reasons discussed in respect to Figure 2,

although the same may be less in degree.

According to the precepts of my invention, I

walls or zones of my hot top a structure having a cushioning effect between the rapidly expanding inner wall or zone and the relatively cool outer wall or zone, Within the same principle, I provide a web structure between inner and outer zones orwalls of a voided hot top in which the tendency to fracture may be directed into the webs themselves, whereby to leave the inner wall and outer wall or zone intact, and to retain in the hot top all of its qualities, both thermal and hydraulic, until such timeas the intended work of the hot top has been accomplished.

Moreover, within or beyond the elastic or yieldable portions of the wall I am able to develop the insulating qualities of the hot top to a great measure because of the compensation provided for the difference in expansion between those portions. In effect, I am enabled to allocate the hydraulic function of the hot top essentially to the inner wall and develop the thermal and mechanical function in the outer portions of the hot top to an extent which has heretofore been quite impracticable if not impossible.

In Figure 5, for example, a hot top embodying the principles of my invention may have an inner surface with adjacent annular wall portion 20 and outer annular wall portion 2|, the two walls being joined by webs 22, which lie in part parallel with the inner and outer walls and define narrow voided portions 23 having short radial parts and relatively long circumferentially extending parts as shown. When the molten metal heats and expands the inner surface of the wall 20, forces in compression as at H" are created, which in turn are resolved into radially acting forces l2", but in this case these radial forces l2 can only be opposed by offset radial forces |2A resulting from the tension in the outer wall 2| indicated by the arrows at IS". The result is that a couple tends to be established by the forces l2 and I2A, and the web 22 is subjected to bending moments and shear stresses with the result that the Web will give somewhat or fail before transmitting destructive forces to the outer annular part 2| of the hot top. This will permit expansion of the inner annular portion of the hot top 20, thereby relieving the inner portion from its tendency to crack or spall under its own compressive strains and relieving the outer portion from stresses tending to rupture it in tension. Of course the flexibility of the webs 22 in refractory materials is limited, but by disposing the webs as shown in Figure 5, that is generally parallel to the inner wall of the hot top, and making the webs of less strength in their resistance to bending or shear or otherwise than have the inner wall in compression or the outer wall in tension, for instance, then I can be assured that the webs 22 yield or fail, as for example about or along the line 24, before there is any deleterious impairment in the function and operation of the hot top as a whole. Furthermore, it will be seen that even after one or more of the webs 22 fracture as along the line 24, or at any part of its length, there is no substantial change in the voided cell structure or otherwise of the whole hot top, whereby it continues its whole function and operation throughout the whole period of time when the ingot and the crop is solidifying.

As shown also in. Figure 5, I am able to make the inner wall 2!! of the hot top relatively thin, about where the whole wall may be from 2" to 3" thick, whereby the whole of this inner wall portion of the hot top can more nearly come to the same temperature at the same time, and its tendency to crack or spall for the reasons given in. connection with the description of Figure 2- is very materially reduced.

Furthermore, the tendency of the inner wall 20 to crack is confined to a vertical direction by virtue of the vertical arrangement of the adjacent Webs and voids, and even if the inner wall 29 should crack under its own stresses before the adjacent webs failed, then the forces acting through the webs would continue to hold the portions of the inner wall on opposite sides of the crack in a compressive relationship, thereby tending to hold the crack substantially leak-proof. In any event, the tendency of an inner wall to crack is greatly delayed in point time because of its relative freedom to expand, its relative freedom from excessive internal stresses and because it is not necessarily restricted to a deleterious density controlled by manufacturing limitations.

In the course of ordinary manufacture as by extruding the hot tops through auger machines, well known in the art of making hollow tile, the ordinary errors in such manufacture may cause a reasonable lack of uniformity in the thicknesses of the webs, whereby the thinner ones would naturally tend to yield or fail before the thicker ones. This condition might tend to induce cracking in the inner wall adjacent certain webs, but even in this case, as indicated above, the tendency to crack is long delayed past the critical stage when the metal is in the fluid state, and in no event is there any tendency for a crack to form traversing the whole distance from the inner surface of the hot top through the outer wall, the tendency being to initiate cracking, if any, in the webs, and to postpone deleterious cracking, particularly in the inner wall, until after the critical period has passed. By virtue of the flexible or yieldable connection between the inner and outer walls, and the insulating effect of the voids therebetween, the tendency toward cracking of the outer wall is substantially eliminated, and with it the hazard of a complete break-through or leakage of the hot top is also substantially dispensed with. The tendency to crack in the outer wall is not only very greatly reduced, but is much longer delayed by virtue of the insulating and yielding effect, particularly in the voided portions of the hot top; the delay being such that the hot top will have had time to perform substantially all of its work before any deleterious X cracking or rupture of any part of the outer wall may take place.

As depicted in Figure 5, I prefer that the voids 23 be relatively narrow, preferably varying from about 1%" or less to about 1 in those parts near the inner wall to from about to about 5%" in those parts nearer the outer wall. The connecting webs may in their thinner portions be about A; of an inch thick, and may be somewhat thicker where they join the inner and outer walls respectively to facilitate extrusion thereof. Preferably the voids are relatively long circumferentially (and extend the full height of the hot top, see Fig. 1) but are quite narrow, whereby great insulating effect is gained, particularly by the multiplicity of such voids across the direction of the flow of heat, and by virtue of their being narrow they tend to exclude the upward flow of molten steel from the top of the ingot along the shoulder I, see Figure 1, when the main body of the ingot is poured. Since the steel adjacent the shoulder 1 tends to chill and form a solid or plastic coating beginning at the point of contact with the mold wall, and since the solidification moves from the outside to the inside of the ingot, I prefer, as indicated above, to make the voided portions of the hot top nearer the center of the hot top narrower than the voided portions, whose lower ends lie closer to the walls of the mold. In either event, whatever fluid steel tends to enter the lower extremities of thesetop as do voids of much greater width, but by the use of narrow voids I am enabled to use more of them and obtain an insulating value increasing roughly in proportion to the number of voids interposed in the radial path of the flow of heat, and as indicated above also have gained other advantages including restraining the movement of fluid metal upwardly into the voids when the body of the ingot is first poured.

It will also be observed in Figure 5 that the flow of heat by conduction in the solid parts of the hot top, as from the inner wall through the web 24, has a much longer path to traverse than any straight radial path, whereby the resistance to the flow of heat through the solid material is impeded not only by the length of the path but also by its restricted cross sectional area. It will further be observed in this connection that where the webs fail by cracking, as in and about lines 24 and 25, the flow of heat through the broken webs is further restricted whereby the insulating value of the hot top as a whole is increased after the webs have been fractured. From this point of View my hot top has its insulating value enhanced by fracture of the webs, whereby I take advantage of the tendency of the hot top to fracture not only in relieving the stresses and strains therein, but also in increasing the insulating value thereof.

In Figure 4 it will be seen that the principles of my invention discussed above are carried out in a similar way in that the inner annular wall portion is insulated from the outer annular wall portion 3| by a double row of narrow circumferentially extending voids33 and 34, and is connected therewith through web portions lying generally parallel with the inner and outer wall portions, and being preferably reduced in thickness as at points 36, whereby the yielding relationship between the inner and outer portions of the hot top is provided, and the tendency to fracture is concentrated in and about the points 36 in the webs 35. The offset disposition between the radial forces of and opposing expansion of the inner annular wall of the hot top is also maintained, and the operation and advantages, explained more fully in connection with the form shown in Figure 5, will also be found in the form shown in Figure 4. In Figure 4, I prefer that the voids 34 be arched from a state of parallelism with the inner voids 33, whereby to more sharply reduce the thickness of the webs 35 at the points 36 to concentrate the tendency to fracture at these points, and also to permit an easier flow of the clay stream during extrusion, particularly in and about the points 31 under the crowns of the voids 34 as viewed in Figure 4. The relative sizes of the webs and voids may preferably be substantially the same as those referred to in connection with the description of Figure 5, although by the arching of the webs 34 it is feasible to bring the thickness of the webs 35 down to about an A; of an inch, if that be desired, at the points 36 without any undue awkwardness in the extrusion process. The inclined relationship of the ends of the voids 34 with the voids 33 also tends to compensate for involuntary movement of the cores in the extrusion die in that undesirable mergers of the adjacent voids are avoided.

In Figure 6 I have shown a further modification of the form of the wall structure of a hot top, in which my invention may be advantageously practiced, and in which the inner wall portion 4|! is spaced from the outer wall portion 4| by three rows of voids 43, 44 and 45. The inner and preferably thinner voids 43 are closer to each other as at 46, and thereby further restrict the flow of heat in the solid portions of the hot top; the arched voids 44 with the intervening web portions 41 being preferably substantially of the shape and relationship described in connection with Figure 4, and the outer voids 45 preferably being similarly spaced with relation to each other as are the inner voids 43 thus reducing the web portions therebetween as at 4B. In this relationship it will also be seen that the web portions are disposed generally in a parallel relationship with the inner and outer wall portion, that the yielding relationship between the inner and outer portions is thereby provided, and that the other characteristics of operation and the advantages discussed particularly with respect to Figures 4 and 5 are also obtained in this modification, the insulating value of the hot top as a whole being enhanced by the additional row of voids.

With the use of hot tops embodying my invention, including those in one or another of the forms above described, I have already indicated how the segregation of impurities in the ingot is greatly improved by the use of my improved hot top. In the same comparative test the hot top in which my invention was embodied had the over-all thickness of its walls increased whereby to have one inch less internal diameter than the prior art hot top with which it was compared. Both hot tops were used on molds of the same size and both hot tops fitted into the upper end of the molds with substantially the same clearance. Both hot tops were filled to substantially the same level when the ingots were poured. The result was that not only was the segregation very much better as I have shown, but also the mass of metal in the crop portion of the ingot through which these better results were obtained was reduced by a little more than 13%, that is in proportion to the fluid content of the hot top. Had the prior art hot top been merely increased in wall thickness the tendency to deleterious cracking would have been at least proportionately increased. With my hot top with the greater over-all Wall thickness, the insulating value was increased in much higher proportion than the increase in wall thickness, its weight was increased less than the proportionate increase in wall thickness, and the tendency to deleterious cracking eliminated.

While I have spoken of certain advantages to be gained in reducing the density of my hot top as through the use of powdered coal, it should be appreciated that other of the advantages persist regardless of the exact density and that my invention in this regard is particularly advantageous in facilitating uniform manufacture and satisfactory results throughout a wide range of densities that may be chosen to meet widely varying demands and conditions.

While in the foregoing I have illustrated and described a preferred form and certain alternative forms in which my invention is embodied, various and perhaps numerous changes and modifications will occur to those skilled in the art without departing from the spirit or primary teaching of my invention, and while I have indicated a preference for certain forms and structural details of the hot tops embodying my invention, I do not care to be limited thereto or in any manner other than by the claims appended here, when construed to embrace the equivalents to which I may be entitled in view of the state of the prior art.

I claim:

A hot top having inner and outer annular wall portions embracing a voided portion therebetween, said voided portion comprising a plurality of non-radial, axially straight and continuous webs joining said wall portions and having parts extending generally circumferentially of said hot top, said webs and adjacent wall portions defining a plurality of narrow, circumferentially overlapping, axially straight voids each extending the full length of said hot top and together encircling the inner wall portion thereof.

ARTHUR C. ES'I'EP.

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