US2005338A - Making composite ingots - Google Patents

Description

June 18, 1935. F, R. FRosT MAKING COMPOSITE INGOTS Filed Dec. 14, 1931 2 sheets-sheet 1 MAKING COMPOSITE INGOTS Filed Dec. .14, 1951 2 sheets-sheet 2 Patented June 19,35

UNITED sTATEs aooasss MAKING COMPOSITE mGors Frank R. Frost, Pittsburgh, Pa., assignor to Superior Steel Corporation, Pittsburgh, Fa? a corporation 'of Virginia applicati@ nember 14, i931', serial No. 580,747

ZCIaims.

Tile present inventictl relates to the making` oi' composite ingots, and more especially to the making off bimetallic ingots. One of the elements of the ingot is formed or placed in the mold and a molten metal forming the other element of the ingot is cast against the first element by centrifugal force. This is preferably .accomplished by a centrifugal casting table which forms an annular ingot or a Vseries of ingot umts arranged in an annulus, whereby relatively long ingots are secured having the dissimilar metal elements lying longitudinally of the ingot, so as to'form convenient ingots for rolling into strip or sheet.

The advantages of my procedure in casting such ingots will be later more particularly pointed out in connection with the' description of the apparatus. In the drawings, which illustrate 'the preferred apparatus for carrying out my processa- Figure 1 is a plan View of a casting table having the portion of the top mold plate broken away;

Figure 2 is a vertical section along the line II--II of Figure 1;

Figure 3 is a perspective view of an annular ingot as removed from the mold;

Figure 4 isv a detail transverse vertical section through the ingot and vingot mold illustratingdhow the facing plate is formed von the ingot;

Figures 5, 6, 7,'8and 9 are detail views similar y toiFigure 4 showing modifications yin the forma.-

, Shaft l, and provided with suitable supporting tion of the ingot.

In the illustrated embodiment of the apparatus, reference numerah 2 indicates a rotatable casting table. This table'ponsists of a Eilat base l plate I mounted to be driven by a vertical drive bearings 5. The table 2 is rapidly rotated by any suitable means, illustrated, for example, as an electric motor 6/ having suitable driving connections to the shaft l.

`lipstancling from the edge ofthe table is al rim lsuitably secured thereto, as by'bolts 8. Secured to the top vof the rim 'I-and vprojecting inwardly therefrom is the top'plate 9 removably fastened to the rim 'I by suitable means such as the bolts lo. 'instable 3, the annular rim 1, and the removable top plate 9- form an annular rmold cavity which isI open inwardly along the side face.' 'I'he table is arranged to be rotated in the direction indicated by ther arrow in Figure l. Molten metlis supplied to the casting table vby any suitable means such as the spout Il.

(ci. zii- 203) which discharges 'onto tle flat face of the table within the annular ingot mold.

In making a bimetallic ingot, as shown, for example, in Figures 2, 3 andl 4, a strip I2 of v metal which is to forni one of the elements of 5. the bimetallic ingot is laid as a liner against the inwardly facing inner face I3 of the ingot mold. 'Ihis strip is preferably of a length to extend around the circumference of the ingot mold with its two ends in butting contact. The strip I2 is 10 preferably of somewhat less width than the height of the ingot mold, so as to leave a small clearance space above and beneath the edges of the strip, and lfor this purpose the strip is spaced slightly above the bottom of theingot 15 mold by means of small metal blocks Il. After the strip I2 is thus positioned in the ingot mold the centrifugal. table 2 is rapidly rotated and molten metal run onto the table through the spout II. 'The molten metal is thrown centrifu- 2o' gally into the ingot mold and against the strip I2', solidifying to form the other element or body I5 of the ingot. 'I'he molten metal, which is forcibly urged outwardly by centrifugal force, 4 flows around the edges of the strip 1,gli forming locking tongues I6 and I1 cast tightly against the edges of the strip. After the metal is solidied the table is stopped, the top plate 9 taken oif, and the ingot I'8,'which'is shown in Figure 3, is 4removed from the table. If necessary; the 30` outer ring or rim 1 can bejtaken oi in removingthe ingot. The ingot I8 is then cut into lengths, as indicated by the division lines'IS, to form units or billets 20 which are afterward rolled downto form bimetallic strips or sheets.

AThe casting apparatus is constructed of suitable size. For example, in making ingots for rolling into strips or sheets, a table about tenl Afeet in diameter is suitable, and an ingot about six inches square is a convenient size for use in 0 rolling mill equipment. In making bimetallic strips or sheets the glement formed by the strip -or plate l2 ls'usuauy .thinnr than that formed by the cast metal I5, the thinner metal being the more expensivefacing material which it is desired. to apply to a cheaper backing material.

:For example, in making bimetallic strip orsheets where corrosion resistant properties are desired, a rolled-.strip I2 of ,stainless steel-'01'- rustless iron of, say, about onevinch thick, .is

placed in the ingot mold vand a layer I5; of about ve. inches thickv ordinary plain carbon ateelV is cast against the strip I 2., When'jthe ingot is rolled down thee-material of. thestrip I2.../forms athin corrosion-resistant facing applied to the or rustless iron containing usually about 12 tov 18 per cent chromium with the balance iron and low carbon content, or a facing materiall of alloy of about 18 per cent chromium, 8 per cent nickel,

.with the balance iron and low carbon, may be employed. The backing material is preferably of plain carbon steel which is used because of its cheapness and physical properties. A mild open hearth steel may be employed for making sheets for drawing purposes, or a higher carbon spring steel may be employed in making stock for purposes such as that of automobilebumpers. While thctwo elements of the composite ingot have been specifically described as of plain carbon steel and stainless steel or rustless iron, other metals may be usedi forming the composite or bimetallic ingot.

The centrifugal process of casting, as herein applied is peculiarly adapted for making bimetallic ingots from which billets may be cut for rolling purposes'. The welding of the facing metal to the backing metal, and particularly where a preformed strip of facing metalis laid in the ingot mold, is primarily accomplished dur.- ing' the rolling of the billets into strip or sheet form. For this purpose the billets are heated in a reheating furnace to a suitable rolling temperature and are then put through the rolling mill rolls which reduce the billets' into strip or sheet form and at the same time, by means of the rolling pressure, weld the facing layer to the backing layer so as to form an integral bimetallic body. In prder to accomplish proper rolling and welding, the sltripof facing material I2 should be firmly held to the backing material I5 andv the edges of the strip should be sealed to the backing material so as to exclude the atmosphere or furnacegases which, if they should penetrate between the adjacent faces of the strip I2 and backing I5, would oxidize the material and interfere with good welding. The tongues l5 and |1 accomplish this purpose. When the molten metal is poured onto the centrifugal table it is projected'violently outwardly against the facing strip I2 and iscaused4 to ow under the strong centrifugal force around the edges of the strip to form the locking tongues I6 and Il. Ordinarily the edges of the strip are sufficiently irregular sothat a tight'lock is formed between the tongues I6 and I1 and the edges of the Astrip so as to holdit securely for the rolling operation. The tongues also form a seal to exclude vthe atmosphere from the juncture between the inner Lfacesrof the strip I2 and the cast metal .backing Il. f

The strong pressure of the metal I5 as it is cast against the strip I2 also tends to expel any air from being entrapped between the strip I2 and the body of backing metal I5, and to force the backing metal I5, into intimate surface contact with the strip I2. Since the metal I5 is cast -under strong centrifugal force, any gases are squeezed from the molten metal inwardly, and the metal of the body portion I5, particularly the outer-'portions of such metal which are next to the strip .|2, are effectively freed from gasesA and compacted into a dense condition.

The compacted gas-free metal which is forced strongly against the strip I2 gives optimum conditions for the welding ofthe metal I5 to the strip I2. It will be readily seen that it is of material advantage to have the densest gasfree portion of the metal body I5 against the facing layer I2 which is to be united to the backing layer by` the welding operation.

The bimetallic ingots or billets produced by this casting operation are particularly well adapted for rolling into sheets or strips. Any

variation in the density or like characteristicsA of the cast body of 'backing metal I5 will occurv along a direction normal to the facing plate I2, or inthe direction of the height of the billet as it is rolled in thel rollingmill. The sheets or strips rolled from such billets will therefore tend to be uniform throughout their length and breadth. Considering, because of the acceleration of gravity in that direction, the face I3 of the ingotmold to be the effective bottom of the mold, the ingot, in effect, has a bottom of relatively large area formed of the plate I2 against which the dense "bottom. metal of the body portion I5 of the ingot is uniformly distributed. The other face'of the body portion or what might be considered to be the top" portion of the ingotwhere `the metal may be less dense or where segregation is most likely to occur; is farthest removed from the welding contact with the facing plate I2, andin a place where such metal can be readily removed if desired. i

In the making ofbimetallic articles having a. chrome' iron facing and a plain carbon steel backing, there is a tendency during the welding operation for the carbon from the plain carbon steel to migrate into the chrome iron facing -and 'reduce its corrosion-resisting properties.

' ing and rolling operations for carbon to migrate from the steel backing into the chromium iron facing. This may be prevented by placing over the inner face of the chrome iron strip I2 a thin sheet 2| 'of an Aexceptionally low carbon iron, such, for example, as ingot iron or wrought iron, as illustrated in Figure 5, which will form a barrier to prevent absorption of carbon by the chrome iron facing from the carbon steel backing. The strip. 2|- may be about one-eighth inch thick and is preferably positioned on the facing material I2 by spot welding. Theuse of such barrier sheet of exceptionally low carbon material for the prevention of carbon migration is described and claimed in my application Serial No.- 580,748, led of even date herewith.' .1n Figure ithe liner or strip of facing material |29 is shown as having beveled edges around which the metal of the cast body I5 ows to form dovetail locking tongues I6n and |12 in order to give a more' secure lock between the ,Y

facing plate I2 and the body of backing metal I In Figure 'I the same beveled liner or facing strip I2 is s hown but with a thin sheet 2| of exceptionally low carbon iron, such as ingot iron or wrought iron, interposed between the facing material |25 which is preferably a low carbon chrome iron and the backing material I5l which is preferably plain carbon steel.

While the liner I2 which lies against the face I3 of the ingot mold, as shown in Figures 4, 5, 6 and 7,.is formed of a strip of metal laid into the ingot mold, the hner may be otherwise formed. In Figure 8 I have illustrated the liner |2b as formed by casting the facing metal first inthe ingot mold by the centrifugal casting operation. For example, a small ladle of chrome iron can be first poured through the spout Il on the rotating centrifugal table and the liner I2b cast in place. This. can be followed by pouring in a larger ladle of plain carbon steel to form the body Ib which is cast against' the liner I2". In this case the plain carbon steel may be poured while the chrome steel is still hot and plastic so that at least incipient welding lmay take place between the two metals, or the chrome steel liner may be allowed to chill before plain carbon steel is cast against it.

In Figure 9 is shown another modification of the process in which the plain carbon steel body I 5 of the ingot is first centrifugally cast to form'a thick liner in the mold and then the facing metal, such as the chrome steel, is cast to form the thin facing layer 12 against' such liner. the second-poured metal may be introduced while the first-poured metal is still somewhat plastic in order to get some weldingeffectbe'- tween them, or the first-poured metal may be allowed to completely solidify or to cool somewhat before the `second-poured metal is intro-V duced.

While I have specifically described my process with reference to making composite ingots having a rustless iron facing and a plain carbon steel backing, it may be employed in making composite ingots of other metals. It also may be employed in making composite ingots having three or more metal layers if desired.

As Ain the modification last described,

The composite ingot produced according to the present invention is the subject matter of a divisional application, Serial No. 732,655, led June 27, 1934.

While the preferred embodiment of the invention' has been specifically illustrated and de-g scribed, it should be understood that the invention is not so linited but may be otherwise embodied and practiced within the scope of the following claims. f

I claim:

1. The process of making composite metal lngots, which comprises placing a liner of onev metal in an ingot mold, leaving spaces between the edges of the liner and the mold walls, re-

. gots which'comprises forming a liner against the inwardly facing inner face of Athe mold and leaving spaces between the edges'of the liner and -the mold walls,`revolving the'mold, and introducing molten metal into the revolving mold so as to cast it by centrifugal force against the liner and form a composite' ingot having the liner held to the 'body of the cast metal by tongues of the cast metal formed in. 4the spaces vbetween the edges of the liner and the walls of the -mold.

FRANK R. FROST.

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