US1982763A - Method of casting ingots - Google Patents

Description

Dec. 4, 1934. N. F. SQRUSSELL ET AL 7 1,982,763

METHOD OF CASTING INGO'IS Filed Jan. 22, 1954 Qg N I Illl A TTORNEX Patented Dec. 4, 1934 UNITED STATES PATENT OFFICE METHOD OF CASTING INGOTS Application January'22, 1934, Serial No. 707,750

2 Claims. (Cl. 22-192) Our invention relates to the casting of metal ingots in metallic molds and particularly, though not excl 1 .vely, to the casting of steel ingots. The molds used for the casting of ingots are 5 generally of cast iron and to prevent adherence between the mold and the ingot and, in the case of steel ingots, liability to impair the portion of the mold in contact with the steel poured into the mold, it is the usual practice to coat the inside of the mold with a nonconducting coating by spraying or otherwise applying a liquid medium charged with finely divided mold coating material against the walls of the mold until a coating of suflicient thickness is deposited upon the mold wall after which and before the molten metal is poured into the mold and the liquid medium is partly driven off and partly solidified to bring about the formation of a dry incrustation over the mold surface. In applying the coating in this way, considerable time is required because the mold after being used for the casting of an ingot is very highly heated and must be'permittedto cool down to a considerable extent before the coating is applied and because, again, the coating must be permitted to dry and harden before metal is again poured into the ingot mold. Again, in coating molds in this manner, it .is impracticable to obtain a really smooth surface in the coating and this 30 leads to an undesirable roughness in the surface of the ingot and there is also an undesirable liability for portions of the crusted coating to become imbedded in and adherent to the ingot while portions of the crusted coating are also 35 liable to become quite firmly attached to the mold surface which leads to further inequalities in successive coatings applied to the mold. Again, the adherence of portions of the coating to the ingot and of portions of the coating to 40 the mold opposes resistance to the withdrawal of the ingot from the mold.

The object of our invention is to cut down the interval between successive uses of a mold for the casting of an ingot.under conditions which will provide for the ingot having a smooth metallic'surface with a minimum of adherent mold coating material and to facilitate the ready withdrawal of a cast ingot from its mold and we have discovered that all of these purposes can be effected by depositing upon the walls of the mold a coating of loosely adherent and loosely coherent dry particles of mold coating material byprogresslvely directing against successive contiguous portions of the mold surface a jet of a carrier gas charged with finely divided dry particles of mold coating material and then after the surface of the mold has been thus coated, pouring the liquid metal into the coated mold in progressive contact with the coated surface until the mold has been charged to the desired extent .60 and then, after the ingot has solidified, withdrawing it from the coated mold.

The thickness of the coating which it is desirable to apply to the mold surface by the method which we have described will vary somewhat with the size of the ingot but by building up the coating from the bottom of the mold upward by progressively directing the carrier gas jet first against the bottom portions of the walls of the mold and then progressively upward against the successively contiguous surfaces of the mold the coating so applied is, to 'a certain extent, self supporting partly in view of the fact that the walls of an ingot mold flare upward to facilitate the withdrawal of the ingot from the mold and we have found that by coating the mold in this way it is entirely practicable to build up a coating of ample thickness to serve the purposes for which a coating is applied. 86

In coating molds in the manner which we havi! described a certain amount of the coating material with which the carrier gas jet is charged will not be so impacted against the walls of the mold as to form an adherent portion of the coating but will fall to the bottom of the mold and form a coating over the bottom and the formation of this bottom coating we have found to be not detrimental but, on the contrary, advantageous as it is covered by that portion of 90 the metal, which is first poured into the mold and entrapped between the molten metal and the bottom of the mold.

It is practicable to use in our method a wide varietyof mold coating materials. Thus, we have successfully used finely divided ferro-silicon, silica flour, calcium silicide, kaolin, ferro manganese and magnetite and we have found ferro-silicon and silica flour especially well adapted for our purpose. It will be understood that the materials used to form a coating should be such as are not materially affected by the w temperatures to which they are subjected either during application to the mold surface or by reason of their contact with the molten metal so that they retain their fine state of division and loose cohesion after the casting of the ingot and thus facilitate the withdrawal of the ingot from the mold and so also that the adhesion of the coating material to the cast ingot will not take place to any detrimental extent.

In our patent, granted March 6, 1934, Number. 1,949,433, we have described and claimed as our coating material and then pouring the molten metal to form the casting into the so coated mold, preferably and for the best results as promptly after the deposition of the coating material upon the mold surface as is practicable. We have also, in our said former patent, pointed out that in the case of cast iron pipes the best results are obtained when the depth of the deposited coating is not substantially greater than that which isfound to be sufllcient to prevent the formation of a chill on the outer surface of the cast pipe and we have also pointed out that the liability of the coating to flake off from the surface of the mold or to be fractured by the impact of the metal poured into the mold increases with the thickness of the coating deposited upon the mold and we have noted the observed fact that adsorbed films of the carrier gas by means of which the coating material is deposited upon the mold surface form in the newly deposited coating a not unimportant constituent of the coating. In our method of casting ingots and particularly steel ingots, it is practicable and desirable to coat the molds to a considerably greater depth than is either desirable or even practicable in the case of centrifugal metal molds used in the casting of cast iron pipes and the only precautions which need be had in view are that the thickness of the coating should be sufiicient to prevent such a rapid transfer of heat from the molten metal to the mold as would result in fusion taking place on the surface of the mold and that the thickness of the coating should not exceed that at which, owing to the loose cohesion of the particles, flaking off of the deposited coating and consequent contact between the molten metal and the mold surface would be liable to occur. The efflcient and cohesive stability'of the coating will vary to some extent with the character of the coating materials used but is readily ascertained and, as a generally applicable rule, we would state that good results can be obtained by progressively delivering during the coating of the mold surface an amount of coating material which, if compactly distributed over the coated surface, will form a coating of approximately fifteen thousandths of an inch in thickness.

While it is practicable and will generally be advantageous to pour the molten metal into the coated mold promptly after the mold is coated, it is by no means so important in the case of the casting of ingots as it is in the case of casting centrifugally cast cast iron pipes because the presence of occluded films of gas in the coating is not, we believe, so important in the casting of ingots as in the casting of such pipes and, while not without influence, may perhaps be disregarded owing to the fact that the coating applied to the ingot comprises a much greater quantity of solid coating material than is either desirable or applicable in the centrifugal casting of pipes.

We have in our said former patent noted the fact that the jet of charged carrier gas directed against the mold surface to be coated should be so regulated in volume and velocity that while it imparts su'flicient velocity to the solid particles with which it is charged to bring them into contact with the mold surface the gas jet itself shall not impact against the mold surface with suflicient energy to blow away the loosely adherent and coherent particles of finely divided dry coating material deposited upon the mold surface and this, of course, is true with regard to the coating of ingot molds and having in view this essential precaution a carrier gas jet of any form progressively directed against successive contiguous portions of the ingot mold to be coated may be used and the jet nozzle from which the jet of carrier gas is projected may be given the necessary relative movement with respect to the surface of the mold to be coated to bring the jet into progressive contact with successive contiguous portions of the mold in any convenient way.

As an aid to the understanding of our process and an example of simple and effective apparatus for its practice, we would refer to the drawing forming a part of this specification in which Figure 1 is a diagrammatic elevation of apparatus adapted for the practice of our process shown partly in section.

Figure-2 is a cross-section on the line 2-2 of Fig. 1.

Figure 3 is a fragmentary sectional elevation of a detail of the construction shown in Fig. 1, and

Figure 4 is a cross-section on the line 4-4 of Fig. 3.

A is a section of a track loop on which, as shown, are supported three cars indicated at A A and A each supporting an ingot mold, indicated at B, B and B The walls of the mold indicated at B preferably flare from the bottom upward to facilitate'the withdrawal of the ingot. At C we have indicated an adherent coating of finely divided dry coating material deposited upon the sides of the mold and at C we have indicated the coating material as deposited upon the bottom of the mold. In registry with the car A we have indicated an overhead structure consisting of a platform D supported as by beams, one indicated at D, the platform D having a passage D formed through it, through which extends an externally threaded 130 tube E having a longitudinal key-way E formed through its threads. The threadsof this tube are engaged with the internal threads F of a block F, supported, as shown, on the under-side of the platform D. G is a gear wheel fitting around the threaded tube E and having a key G fitting in the key-way E of the tube. This gear wheel is supported, as shown, in a forked bracket G secured, as shown, to the upper portion of the platform D. The gear wheel G is rotated by means of a pinion G driven by a motor indicated at G supported on the platform D. H is a conduit pipe for a carrier gas passing through the center of the tube E and secured to move longitudinally and rotatable with the threaded tube as by means of spiders indicated at H H To the lower end of the pipe H is secured a nozzle H adapted to deliver a carrier gas jet horizontally and, as shown, the nozzle is secured to the end of the pipe H by an 150 ofiset connection H the purpose of which is to bring the nozzle into closer proximity with the walls of the mold. At the upper end of the pipe H, I have diagrammatically indicated a swivel joint at J, by means of which the pipe is connected to a hose J which, in turn,"is connected to a gun J, to which a jet of gas underpressure is. delivered by a nozzle J having, as shown, a cock J and pressure gauge J J indicates the mechanism for feeding finely divided dry coating material to a hopper indicated at J", through which it is delivered to the inside of the gun. The gun and its connections are projecting lug on the top of the completed ingot, as shown at M on the ingot M formed in the mold B. At the left hand side of Fig. 1 we have shown the lug M as engaged by lifting tongs indicated at N and by means of which the ingot can be drawn up out of the mold.

In operation, the ,car A for example, supporting a mold B is brought into registry with the threaded tube E which, of course, is retracted to permit the mold to pass beneath it; then, by preference, the gear wheel G is rotated by its connected motor to rotate the threaded tube E so that it will screw down inthe internally threaded block F until the nozzle H is projected into the mold to a point near the bottom of the mold. Gas under pressure from a source not shown is then poured through the,

nozzle J as by opening the valve J and the feeding device for finely divided dry coating material is set in operation to feed the coating material to the gun J, with the result that a Jet of carrier gas charged with finely divided dry coating material is delivered through the hose J to the pipe H and issues as a Jet through the nozzle H", the jet being directed against the side of the ingot mold. The gear wheel G is then rotated in an opposite direction to that in which it feeds the threaded tube downward with the until the mold is thoroughly coated from botto'mto top and the bottom will have a layer, indicated at 0 formed upon it by the particles of coating material which do not adhere to the sides of the mold. When the mold has been coated as described, its supporting car is moved into registry with the pouring ladle, asindicated at A, a hot top L placed upon the top of the mold and molten metal permitted to flow from the ladle into the mold by opening the valve K By preference, the metal is poured until the mold is fully chargedand the lock M formed upon its tube. When the ingot has hardened, the hot top is removed and the car shifted to a position indicated at A in which the ingot is removed from the mold, which may be done in any convenient way, as indicated by means of tongs N.

Having now described our invention, what we claim as new and desire to secure by Letters Patent, is:

1. In the casting of metal ingots in metallic ',molds the method steps which consist in building up upon the walls of the mold a loosely adherent and loosely coherentcoating of finely divided dry mold coating material by progressively directing against successive contiguous areas of the upright surface of the mold a jet of a carrier gas charged with finely divided dry particles of mold coating material, then pouring molten metal into the so coated mold and after the ingot has solidified withdrawing the ingot 5 from the mold.

2. The method of claim 1, in which the charged jet of carrier gas is initially directed against the bottom portion of the upright walls of the mold and progressively moved upward in 0 the mold so as to progressively coat the mold from the bottom upward.

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