US2825947A - Method of continuous casting of metal - Google Patents

Description

N. P. GOSS METHOD OF CONTINUOUS CASTING 0F METAL March 11, 1958 2 sheets-sheet 1 Filed Oct. 14, 1955 INVENTOR. Noam/v f? 60;:

March 11, 1958 N. P. Goss 2,825,947

METHOD OF CONTINUOUS CASTING OF METAL 2 Sheets-Sheet 2 Filed Oct. 14, 1955 INVENTOR United States Patent 2,825,947 METHBD 0F CONTHNUUUS CASTING 0F METAL Norman ll. Goss, Cleveland, Ohio Application (lctober 14, 1955, Serial No. 540,559 Claims. (Cl. 22-4001) This invention relates to improvements in a method of continuous casting of metal and the apparatus used belongs to the general type described in my U. S. Patent No. 2,510,100 granted June 6, 1950.

This application is a continuation-in-part of my copending application Serial No. 407,211, filed February 1, 1954 entitled Method Continuous Casting of Metal, now abandoned.

According to this invention there is provided an improvement in the method of continuously casting steel by passing molten metal into the top of a cooled mold having a substantially vertical open passageway and continuously withdrawing the bar of congealed metal at the bottom of the mold, and wherein the sole heat supplied in the mold is obtained from the metal being cast. The present improvement comprises the novel step of maintaining on top of the molten metal in the mold, and in direct contact with the metal over the entire cross-section of the mold, a layer of borax or glass having a high fluidity or low viscosity rendering the refractory substantially liquid well below the melting point of steel, or other metal being cast, and pouring the molten metal on top of and through the said layer. 7

One of the problems encountered in trying to continuously cast steel was the fact that when any slag whatsoever came over with the metal poured into the top of the continuous casting mold, this slag was of such great viscosity that it got into the air gap between the freshly formed skin on the metal and the mold wall and hung up the bar of metal being cast so that the bar pulled apart and the process had to be stopped. With the new method herein disclosed, this problem has been solved. In the first place, the amount of slag carried over into the mold in the pouring process is held to the absolute minimum. Then, the blanket of borax or glass on top of the metal in the mold is relied upon to float slag and other solid particles above the molten metal so that the slag does not get into the air gap between the metal and the mold face. Much of this slag is slowly dissolved into the borax or glass thereby increasing its viscosity. The addition of fresh borax or glass from time to tirnet serves to maintain the proper viscosity of the layer on top of the metal.

Hereinafter, wherever in the specification and claims I mention plastic refractory or refractory, I include borax and glasses having a viscosity under approximately 100 poises between 1500 degrees Fahrenheit and 2800 de rees Fahrenheit.

it is essential that the surface of the metal moving through the mold should not contact the chilled surface of the mold with excessive friction and pull apart. If such fritcion occurs, it will eventually cause the mold surface to become grooved or scored and surface defects will form on the skin of the congealing metal.

However, unless reasonable contact is maintained between the metal surfaces and the mold wall, the chilling effect is greatly reduced. The gap between the skin of the metal and the mold wall is constantly changing in magnitude due to thermal contraction and expansion of 2,825,947 Patented Mar. 11, 1958 '11 the metal as it solidifies. The plastic refractory used has the quality of adhering to the hot metal surface while sliding easily over the chilled mold surface to provide a film between the metal and the mold.

The thickness of the film of refractory material will vary, depending upon the width of the gap between the molten metal and the wall of the mold; so in extreme cases some surface areas may have a very thin coating of plastic refractory material on the congealed surface. This is due to various factors including slight variation in the pull of the pinch rolls which control the movement of the casting through the mold; also to the tendency of the metal to buckle slightly after a solid shell of metal forms around the liquid metal.

The borax or glass has at elevated tern eratures a much greater heat conductivity than air, thereby facilitating the transfer of heat from the metal to the mold.

The film of plastic refractory material remains easily deformable to the bottom of the mold preventing wear on the mold walls and still adheres to the metal emerging from the bottom of the mold, thereby aiding in preventing oxidation of the cooling metal.

It is advantageous to maintain the depth of the layer of plastic refractory material on top of the metal by con tinuously or intermittently adding additional material to the layer. This addition of the plastic refractory will also keep the composition and fluidity of the layer substantially constant.

It is not essential to maintain the plastic refractory at a constant depth on top of the metal in the mold. It is, however, necessary to maintain some layer of plastic refractory material on the top surface of the metal. The depth of thickness of this layer may vary from inch to 6 inches depending upon the metal being cast, although most of the advantages of my method will be realized if the plastic refractory is maintained where the metal touches the mold wall at the top metal line.

The reason for adding fresh plastic refractory material to the mold is to replenish that which coats the surface of the metal and also to maintain a plastic refractory material of constant composition, low viscosity and freefiowing character. Some slag is bound to come over with the metal although it may be hardly discernible. Such slag would tend to make the plastic refractory material more viscous and thus reduce its plasticity or free-flowing character, and it is important in carrying out this invention to prevent slag from getting into any air gap between the metal and the mold.

Other objects and advantages of the present invention will be apparent from the accompanying drawings and description and the essential features will be set forth in the appended claims.

In the drawings- Fig. l is a sectional and somewhat diagrammatic view illustrating one manner of carrying out the improved method;

Fig. 2 is a fragmentary diagram showing in an exaggerated manner the formation of a film of the plastic refractory material between the metal and the mold;

Fig. 3 is a fragmental perspective view of a preferred form of mold for carrying out my improved method;

Fig. 4 is a sectional view, enlarged, taken along the line 44 of Fig. 3;

Fig. 5 is a fragmental sectional view taken along the line 5-5 of Fig. 4; while Fig. 6 is a central sectional view through another form of mold which may be used to carry out my method.

The present improvement is intended forvuse in the continuous casting of metal as described in my United States Patent No. 2,510,100 dated June 6, 1950, and utilizing a mold of the general type therein shown adapted to carry out the continuous casting method herein dis- -in a ladle containing the molten passed into the upper end of the mold metal being poured. This blanket 3 closed. This invention is not limited specific mold.

In Figs. 1 and 2 I have illustrated the type of mold which comprises a plurality of hollow wall portions 11 each forming a complete section. A plurality of these sections 11 formed of metal and provided with hollow wall spaces 12 through which a cooling stream of water to use with any is passed, are arranged in vertical alignment.

The mold sections are held together and in alignment by a plurality of vertical aligning rods (not shown) passing through holes in lugs secured to the sections. Means may be provided for introducing acetylene or other suitable lubricant at the ports 13 as described in my above mentioned Patent No. 2,510,100 or these ports 13 may be closed up flush with the inside walls of the mold. 14 metal which is going to be cast and the ladle is pivoted as at 15 to enaole the metal to be delivered into the feed hopper or tundish 16 provided with a refractory lining 17, and the metal 18 from the hopper passes through the outlet 19 forming a stream 20 which flows into the mold. A short distance 21 (say 6 inches) separates the outlet 19 from the top of the upper mold 11 and in the gap 22 thus formed the plastic refractory is introduced as by means of trough 22a. The gap 22 itself is provided with a window (not shown) to enable the operator to see the stream of metal entering the mold and also to see the layer of plastic refractory which covers the meniscus at the top of the metal.

Fig. 2 shows in an enlarged diagrammatic manner the way in which the plastic refractory lies above the top of the metal and the way in which the film 23 of the plastic refractory is informed as a skin between the metal and the mold.

The mold here shown is for the casting of a square bar of steel but it will be understood by those skilled in this art that any cross-sectional form may be provided in the hollow mold passageway.

The solidified metal is indicated at 24 and dotted lines 25 within the body of the casting indicate how the liquid metal gradually solidifies. Pinch rolls 26, driven by means not shown, control the downward movement of the metal through the mold.

Those familiar with this type of apparatus will understand that when pouring is started, a skin of solid metal is formed near to the top of the mold and is gradually moved down, as molten metal is poured in at the top, so that the continuous slab, boom, billet, or other form is eventually brought out at the bottom of the mold and conveniently may pass through the pinch rolls 26 to control the downward movement thereof. plastic refractory layer which has a lower specific gravity than the metal will float up and down as the level of the metal pool moves up and down depending on the rate of teeming. I have shown a ladle .14 having a pouring spout, and those skilled in this art will understand that means, not shown, is provided for the careful control of the ladle so that the stream of molten metal 19 may be passageway at the rate desired. However, it is difiicult to control this rate exactly for slight variations will cause the level of the molten pool to move up and down the mold.

In the specification wherever I have used the phrase plastic refractory I indicate thereby a fusible material, refractory but fusible at the temperature of the molten of plastic refractory material floats at all times on top of the metal in the mold while molten metal continuoutly passes through the blanket and gradually moves away downwardly as the metal congeals.

The glass or borax layer has no chemical effect on the metal. The nature of the plastic refractory may vary somewhat depending on the type of metal cast and the conditions under which it is poured. The depth of this layer may vary from about inch as a minimum to 6 'or-more inches. The plastic refractory must always have Obviously the pointed out above.

a low viscosity, preferably under poises, at a temperature considerably lower than the melting point of the metal which is being cast, as will appear from the further description, and I have found that silicate glasses with a softening point between 1200 degrees Fahrenheit to 1800 degrees Fahrenheit or borax with a melting point about 1400 degrees Fahrenheit, when casting steel, can be used according to the present invention. Either of these materials is substantially liquid when floating on molten metal. Such a glass or borax layer may have sufficient viscosity to cause a diffusion or dispersion of the metal stream as it hits the glass or borax blanket floating on top of the metal. When casting a section such as a slab, where portions of the cast section are removed quite a distance from the stream (which is sometimes poured at a rate less than 500 lbs. per minute) there is a real difficulty in getting an even how of the molten metal to the far corners of the mold when no glass or borax layer is used.

If no plastic refractory is used, when pouring the metal at low rates such as 200 lbs. per minute, it is difiicult to prevent the surface of the metal in the mold which is exposed to the air from forming cold shuts. The plastic refractory material layer prevents this. Also the top surface of the metal being cast may become slightly oxidized before the metal reaches the far corners of the mold, resulting in other surface imperfections. With the use of the plastic refractory layer these difficulties are prevented. The viscosity of the plastic refractory tends to disperse the streams so that the molten metal may be seen moving away from the center and moving laterally outwardly while passing through the layer. In this way some of the molten metal is deposited directly in the metal pool some distance away from the center of the mold where the stream 39 is dropping. At the same time the flux covering the molten pool in the mold prevents oxidation of the upper surface of the metal which has previously caused trouble. This also is not the pur pose of the present invention, as this is well known by the art.

In casting molten metal directly into the mold without the use of plastic refractory, difficulties arose when the rate of teeming varied from normal. If the teeming was slightly faster than desired, the level of the metal pool might rise to the top of the top mold section passageway and overflow, and when the level of the metal subsided. as the normal rate of teeming was resumed, fins of metal hung on the top of the mold with the result that the casting operation had to be discontinued. When the plastic refractory layer is used, the operator slows down the rate of teeming immediately upon an overflow occurring. Under these conditions the overflow is plastic refractory, not metal. Even if a small amount of the plastic refractory freezes, the rest of the plastic refractory therebeneath is sufiicient fluid to ensure that it will follow the metal down into the mold and the metal itself will not hang.

Under previous conditions without the plastic refractory layer, whenever the rate of teeming stopped or became slower than normal, the metal pool would reccde down into the mold leaving a thin metal sheet along the mold walls in some instances. Then when the normal rate of pouring was resumed, the metal would rise again in the mold but without fully remelting the shell against the mold wall. This either resulted in the metal hanging up in the mold or it resulted in imperfections in the cast metal. Utilizing the plastic refractory layer, when the metal drops down in the mold a shell of plastic refractory adheres to the mold walls and when the normal rate of pouring is resumed the level of the molten pool will rise again and quickly melt the plastic refractory shell because the softening point of the plastic refractory is con siderably lower than the melting point of the metal, as Thus it will be seen that variations in the rate of teeming cause no ditficulties using the improved plastic refractory layer whereas without the layer serious difficulties resulted.

Another advantage of the plastic refractory layer is that normally there is always some borax or glass along the sides of the mold walls. This plastic refractory between the metal and the mold walls prevents fire checking of the walls and it prevents excessive chilling of the metal where it first enters the mold. It also prevents surface defects formed in the cast metal when the process is carried out without the plastic refractory layer. Without any plastic refractory protection the metal may splash against the relatively cold walls and quickly solidify. There solid particles will either adhere to the mold wall or fall into the congealing metal where they are not entirely remelted and form undesirable defects. With the use of the plastic refractory layer it is almost impossible for metal to splash and, if it does, the particles splash against the plastic refractory rather than against the walls It, and since the plastic refractory is very fluid when in contact with steel around 2800 degrees Fahrenheit, these small metal particles will, by both their weight and temperature, work their way quickly back through the plastic refractory into the metal pool.

The plastic refractory works down between the meniscus at the metal line and the cool mold wall. There it builds up slightly on the mold wall as indicated at 27 where the plastic refractory appears darker to the eye. The first thin skin of metal forms here at 24a against the plastic refractory instead of against the mold wall. Without the flux layer, small foreign particles from the entering metal stream tend to flow over the meniscus of the metal (which is convex upwardly) toward the side wall of the mold. If unprevented, these particles remain at the interface and tend to frictionally hold up the downward movement of the partially-solidified bar and cause surface defects. Any nondeformable material, even finely divided carbon, which enters this interface may hold up the bar. With the plastic refractory layer this difficulty is prevented because the plastic refractory covers the meniscus and floats any foreign particles, keeping them away from the interface. Some small solid particles may be surrounded by the plastic refractory so that they do no harm. The tundish 15 keeps away large particles of slag. Small particles eventually are dissolved or surrounded by the plastic refractory layer.

Furthermore, as the newly-formed metal skin shrinks away from the mold wall refractory coating by small amounts, the liquid plastic refractory flows down into such openings and supplies a shell completely surrounding the congealing metal. The metal congeals against this refractory layer and not directly against the mold wall. This leads to a more uniform congealing of the metal.

The glass or borax will adhere to the hot metal but it will not adhere to the cold surface of the mold. The refractory layer is maintained in a plastic condition by the heat of the metal clear to the bottom of the mold and therefore supplies a self-accommodating plastic refractory shell between .010 and .020 inch thick and adiusting itself to changes in the gap (which would otherwise be an air gap) between the skin of the metal and the mold wall. Glass and borax at this temperature have good thermal conductivity and therefore aid in carrying the heat from the congealing metal to the mold wall. It is much more efficient in this location than air would be. At the same time the glass or borax is plastic enough to act as a lubricant between the metal and the mold wall, thus reducing friction at this zone. The glass or borax remains sufficiently plastic to accommodate itself to the various changes in skin contour as the metal touches or shrinks away from the mold wall.

The plastic refractory fills the meniscus as shown in Fig. 2. The molten metal therefore never solidifies directly on the chill surface, but upon the plastic layer. This plastic refractory material also has a better thermal conductivity than air, and therefore permits more rapid heat removal, and at the same time it prevents excessive frictional engagement of the congealed metal with the mold surface, provided that the plastic refractory is highly fluid. This plastic refractory adheres to the just-' solidified shell or skin which forms on the metal from the instant the molten metal approaches in close proximity to the chill surface, but glass or borax will not adhere to the chill surface of the mold.

To summarize, the shell of solid metal forms continuously on a plastic refractory which completely fills the meniscus. This does two things: (a) It increases the heat extraction in that plastic refractory of the type used herein has a better conductivity than air, and (b) the film, which adheres to the congealing metal surface the instant the skin forms, reduces the frictional movement of the slab or bar as it moves through the mold due to the plastic nature of this material.

A lubricant such as acetylene or graphite may be supplied next to the mold wall itself further to reduce friction, to protect the mold wall and to protect the surface areas of the casting not sufliciently coated with a layer of plastic refractory, but this invention operates successfully without additional lubricant.

The fluid shell of glass covering the cooling metal will surround and usually partly dissolve any small hard particles of dirt, slag and the like which might otherwise become jammed between the skin of the metal and the mold wall, thus stopping the smooth movement of the metal downwardly in the mold. The pool of glass or borax on top of the mold will float many small particles of slag, brick and the like so as to keep them out of the air gap. Some of the slag will dissolve in the glass or borax and slowly increase its viscosity. The continuous addition of refractory plastic material maintains the plastic refractory at a constant fluidity or viscosity, and replaces the material which coats the metal bar and passes downwardly through the mold.

A preferred mold for carrying out the present process is fully disclosed and claimed in my Patent No. 2,510,100 granted June 6, 1950 and illustrated here in Figs. 3, 4 and 5. Posts 20- fixed at the four corners of a rectangle have notches 28a to receive ears 29a of parallel side walls 29. The posts also have notches 28b to receive ears 30a of parallel end walls 30 which telescope between the side walls. Resilient bolt fastening means, not shown, extend around the four sides of the mold on the outside as shown in Patent No. 2,510,100 to hold the entire structure resiliently together. Usually a plurality of sections like that shown in Fig. 3 are arranged in substantial alignment one above the other to form a continuous mold opening. Preferably the side and end walls are stepped back slightly, say from .003 inch to .015 inch as at 2% and 30b to slightly increase the cross-section of the mold interior at one or more levels as the metal passes downwardly. Figs. 4 and 5 show details of water jackets built into walls 29 and 30. This mold allows for expansion of walls 29 and 30 in every direction so that the walls will not warp, or only very slightly. This holds the amount of warpage in the walls out of a fiat plane within the thickness of the plastic refractory shell 23, so that the metal bar plus the refractory shell 23 is always within the cross-section of the mold even with slight warpage.

Fig. 6 shows another modification of a mold with a set-back shoulder in the inner faces of the mold walls.

Each section 31 has a cooling water jacket 32. Each section has a set-back or shoulder 31a at its mid-portion, and preferably another shoulder 31b is provided between sections. The shoulders 31a and 31b are of approximately the same depth as 2% and 30b. Means not shown holds the plurality of mold sections assembled as shown. The shoulders 29b, 30b, 31a and 3111 are obviously greatly exaggerated in the drawings. The refractory shell 23 is thicker than the depth of the shoulders so that the bar a of the smaller cross-section may twist slightly as it passes into the section of larger dimension immediately below it and the shell 23 will permit the cast bar to accommodate itself and pass downward easily.

Openings 33 are shown between upper and lower mold sections in Fig. 4-, and openings 34 in Fig. 6. Graphite blocks may be fed through these openings as taught in my Patent No. 2,510,100 or the openings may be closed up flush with the inside of the mold.

A typical pour of' steel, using a mold similar to that in Figs. 3, 4 and 5, and using my improved method, is as follows. The mold had an internal cross-section of approximately 4 x 4". A standard heat of low carbon steel S. A. E. 1010 was teemed from the lip of ladle 14 at about 2850 degrees Fahrenheit which is about 100 degrees Fahrenheit above the solidification point for this grade of steel. Of course, it loses some heat before the metal is inside the mold. Before starting to pour, a starting bar was placed inside the mold and with its upper end between eight and ten inches below the top of the uppermost mold section. It will be understood that this bar substantially fills the cross-section of the mold. Borax heated to about 1500 degrees Fahrenheit was then poured in on top of the starting bar to a depth of six or eight inches. The bar was held in pinch rolls like 26. As the steel started to pour, the pinch rolls were started to lower the bar. The steel was poured at the rate of about 250 lbs. per minute and the pinch rolls were con trolled to hold the molten metal line at approximately a constant level. Fresh unmelted borax was thrown in from time to time on top of the material in the mold as the original supply gradually disappeared down the shell 23. The cast steel coming out the bottom of the mold was coated with a layer of nearly solid borax about .010 inch thick.

Glasses which I may use in place of the borax mentioned above are as follows: Sodium silicate glass Na O, 33.04 percent; SiO 65.4 percent and small amounts of other oxides mostly of aluminum, iron, calcium and magnesium. Potassium silicate glass K 0 27.84 percent; Si0 70.75 percent and small amounts of other oxides mostly of aluminum, iron, calcium and magnesium.

small shown the viscosity in poises of sodium silicate with increasing silica content. This graph shows that when the silicate content is much over 65 or 70 percent, then the viscosity of the sodium silicate becomes too high for use in my method. For instance, if the sodium silicate glass mentioned above were subjected to a temperature like that of the electric are which runs to 4000 or 5000 degrees Fahrenheit, the sodium is volatilized so as to decrease the sodium content and increase the silica con tent of the sodium silicate. This would render such a glass unfit for my purpose.

The use of borax, or the glass described, in my above described method makes it possible to cast the metal cold or near the solidus. The borax protects the molten metal from heat loss and coldshuts. The casting of the metal near its solidification point is desirable because the physical characteristics of the cast metal are then superior. Metal cast cold shrinks away from the mold wall faster, and the cast bar gets a better and thicker coating of the plastic refractory.

in view of all of the above, it will be seen that the use of n s described, or as blanket layer is a great tr uovement in this process. it prevents surface oxidation, it prevents surface defects, it prevents cold shuts, it promotes even flow of metal to all corners of the mold and through the mold, it provides control of all) metal temperature in the mold and it minimizes defects which would otherwise occur from the continual rising and falling of the metal level in the top of the mold. Steel cast by this process has a smooth glass-like surface with practically no defects whatsoever. While it carries out all of these functions, the invention is in the maintaining of the pool of glass or borax on top of the metal in the mold for the purpose described, the coating of the steel surface with a plastic refractory material, and the congealing of the metal at the meniscus on a plastic refractory material of good thermal conductivity.

it will be appreciated that the blanket of glass or borax on top of the molten metal in the mold prevents loss of heat and allows the teeming of the metal at a temperature close to the solidification point as it enters the mold. l' have mentioned pouring the metal at about 100 degrees Fahrenheit above its solidification point, but it will be understood that the metal cools on its way to the mold and is even closer to the solidification point as it actually enters the mold. This feature of my invention allows for faster pouring and gives better characteristics in the metal as cast. it has long been known that it is desirable to cast a metal close to its solidification point, but heretofore there have been difficulties in that the metal formed folds and cold shuts as it solidified, thus spoiling the metal for its intended uses. Especially in the case of casting larger sections, the cover of glass or boraX on top of the metal in the mold permits the flow of the metal to all parts of the mold evenly before it solidifies, thus giving a uniform product.

If one desires to hold the metal temperature as near the solidification point as possible, electrical induction just before the metal passes to the mold.

ing any metal which, at its melting point, keeps the glass or borax fluid while it performs its function. These other metals are not as diificult to cast as steel.

What I claim is:

1. In the method of continuously casting steel by passing molten metal into the top of a mold having cold walls and having a substantially vertical open passageway and continuously withdrawing the bar of congealed metal at the bottom of the mold by substantially continuous relative movement between the metal and mold walls inside of the mold and wherein the sole heat sup plied in the mold is obtained from the metal being cast; the novel step of maintaining on top of the molten metal in the mold, and in direct contact with the metal at least where it engages the wall of the mold, a layer of substantially liquid refractory having a high fluidity well below the melting point of steel chosen from the class consisting of borax and alkali silicate glasses having a viscosity under approximately 100 poises between 1500 degrees Fahrenheit and 2800 degrees Fahrenheit, and exhibiting borax characteristics in that range, the refractory lying between the steel meniscus and the mold wall as the steel congeals against said refractory at the top metal line, and said refractory filling the air gap between the metal and mold walls and having a much greater heat conductivity than air.

2. The method of claim 1 wherein said molten metal is poured into a mold the walls of which can warp a limited amount and less than the thickness of said re fractory encasing the metal.

3. The method of claim 1 wherein said molten metal is poured into a mold the walls of which have a sharp shoulder suddenly increasing the mold cross-section below said shoulder by a slight amount over the mold crosssection above said shoulder, said slight amount being less than the thickness of said refractory encasing the metal.

asaaea'l 4. The method of claim 1 wherein the molten metal is poured into the mold at a temperature just slightly above the solidification point of the metal, whereupon the blanket of liquid refractory on top of the molten metal prevents folds and cold shuts.

5. In the method of continuously casting metal by passing molten metal into the top of a mold having cold walls and having a substantially vertical open passageway and continuously withdrawing the bar of congealed metal at the bottom of the mold by substantially continuous relative movement between the metal and mold walls inside of the mold, and wherein a starting bar is placed in position to close the cross sectional area of the mold with the top of the bar spaced below the top of the mold; the novel step of placing on top of the starting bar a small amount of a refractory chosen from the class consisting of borax and alkali silicate glasses having a viscosity under approximately 100 poises between 1500 degrees Fahrenheit and 2800 degrees Fahrenheit and exhibiting borax characteristics in that range, and then pouring molten metal into the top of the mold while moving the starting bar downwardly, and thereafter casting metal in said mold substantially continuously while maintaining a layer of said refractory on top of the metal in the mold.

6. In the method of continuously casting metal by passing molten metal into the top of a mold having cold walls and having a substantially vertical open passageway and continuously withdrawing the bar of congealed metal at the bottom of the mold by substantially continuous relative movement between the metal and mold walls inside of the mold, and wherein the sole heat supplied in the mold is obtained from the metal being cast; the novel step of maintaining on top of the molten metal in the mold, and in direct contact with the metal at least where it engages the wall of the mold, a layer of borax having a high fluidity well below the melting point of the metal being cast and having the characteristic of adhering to the metal but not to the mold wall, the borax lying between the metal meniscus and the mold wall as the metal congeals against said borax at the top metal line, and said boraX filling the air gap between the metal and mold walls.

7. In the method of continuously casting metal by passing molten metal into the top of a mold having cold walls and having a substantially vertical open passageway and continuously withdrawing the bar of congealed metal at the bottom of the mold by substantially continuous relative movement between the metal and mold walls inside of the mold, and wherein the sole heat supplied is the mold is obtained from the metal being cast; the novel step of maintaining on top of the molten metal in the mold, and in direct contact with the metal at least where it engages the wall of the mold, a layer of refractory material chosen from the group consisting of borax, sodium silicate glassesand potassium silicate glasses having a high fluidity well below the melting point of the metal being cast and having the characteristic of adhering to the metal but not to the mold wall, the refractory lying between the metal meniscus and the mold wall as the metal congeals against said refractory at the top metal line, and said refractory filling the air gap between the metal and mold walls.

8. In the method of continuously casting metal by passing molten metal into the top of a mold having cold walls and having a substantially vertical open passageway and continuously withdrawing the bar of congealed metal at the bottom of the mold by substantially continuous relative movement between the metal and mold walls inside of the mold, and wherein the sole heat supplied in the mold is obtained from the metal being cast; the novel step of maintaining on top of the molten metal in the mold, and in direct contact with the metal at least where it engages the wall of the mold, a layer of refractory material having the borax characteristics between 1500 degrees Fahrenheit and 2800 degrees Fahrenheit of having a viscosity under approximately poises, of being non-reactive chemically with molten steel, of having a much greater heat conductivity than air, of having lubricating qualities between the congealing metal and mold wall such that the frictional pull of the refractory material against the mold wall is less than the tensile strength of the first-formed skin of the congealing metal in the mold, of having a high fluidity well below the melting point of the metal being cast and having the characteristic of adhering to the metal but not to the mold wall, the refractory lying between the metal meniscus and the mold wall as the metal congeals against said refractory at the top metal line, and said refractory filling the air gap between the metal and mold walls.

9. The method of claim 8 including the steps of positioning a starting bar in position to close the cross-sectional area of the mold with the top of the bar spaced below the top of the mold, then placing on top of the starting bar a small amount of said refractory material melted to substantial liquidity, and then pouring the molten metal into the top of the mold while moving the starting bar downwardly, and thereafter continuously casting the metal while passing the same through the mold.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,258 Junghans Dec. 8, 1942 2,369,233 Hopkins Feb. 13, 1945 2,376,518 Spence May 22, 1945 2,380,109 Hopkins July 10, 1945 2,445,670 Hopkins July 20, 1948 2,510,100 Goss June 6, 1950 2,527,545 Goss Oct. 31, 1950 OTHER REFERENCES Journal of the American Ceramic Society, vol. 30, part 11, November 1947, pages 20-23, 25, 29-32, 48 and 49.

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