US2191477A - Method for manufacturing cast metal bodies - Google Patents

Description

Feb. 27, 1940. R. K. HOPKINS METHOD FOR MANUFACTURING CAST METAL BODIES Filed Aug. 16, v1938 '/-CENTER OF MOLD P M E T TEMP.

FIG. 4 v

i MOLD DIAMETER FiG. I

INVENTOR ROBERT K. HOPKINS Patented Feb. 27,1940

' UNITED STATES,

2,191,477 PAT ENT- OFFICE w METHOD FOR MANUFACTURING CAST METAL BODIES Robert K. Hopkins, New York, N. Y., as'signor to M. W. Kellogg- (70., New York, N. Y., a corporation of Delaware Application. August 16, 1938, Serial 110. 225,123

This invention'relates to the manufacture of metal bodies and in particular to the manufac- 311:6 of cast metal bodies such as ingots, and the Cast metal bodies of ferrous metals and alloys, and certain non-ferrous metals and alloys are seldom produced without imperfections in the metal at and adjacent the surface. These imperfections, cold shuts, folds, cracks, gas pockets etc., materially affect the quality of the metal,

- and, .since they must be removed when it is desired to produce worked metal, they likewise seriously affect the cost of the final metal. The imperfections mentioned are always a source of trouble and expense but particularly so when the ingot, or other cast body is of metal, such as chrome-steels, chrome-nickel steel, monel metal, nickel, etc., that are sluggish and do not flow freely in the molten condition. When the 20 metals, just mentioned, are. cast the imperfections mentioned are generally more numerous than with the less sluggish and freer flowing metals and alloys. Also, due to the crystallization characteristics of the more sluggish metals r coupled with the fact that these metals do not 2 usually readily weld during working operations,

it is necessary to completely remove all of the defective metal as well as adjacent sound metal prior to working. 'This necessitates the removal of a material proportion of the total ingot metal,

and generally is a major factor in the ultimate cost of the worked metal. I v

The imperfections at and adjacent the surface of the ingots such as cold shuts, folds, cracks, gas pockets, etc., are caused in the main by the chilling effect of the mold on the molten cast metal adjacent to the mold wall and are inherent in the present accepted mode of producing metal ingots and similar cast metal bodies. I

' -I have found a simple amd comparatively cheap way of eliminating, or at least materially lessening, the bad surface conditions inherent in ac;

cepted present day practice.

It is an object of this invention to provide a in j perior surface characteristics in which the chilling effect of the mold on the molten castmetal is compensated for, so that its effects-are substantially eliminated, or at least reduced to such an extent that they do not materially affect the characterof the surface metal of the 'cast body. It is also an object of this'invention to provide a method for producing cast metal bodies of superior surface characteristics in which heat is added to the molten cast metal, adjacent the mold sides, during the casting operation to compensate for the chilling effect of the mold.

' The further objects and advantages of this invention will be better understood from a con- 60 sideration of the following description of a presmethod for producing cast metal bodies of su-.

ent preferred mode of carrying my invention out in practice, taken with the accompanying draw ing, in which, Fig. 1 is a diagrammatic front view, partly in sectionv of an. arrangement of apparatus for carrying out the novel method,

Fig. 2 is atemperature curve illustrating the temperature conditions as they exist across the mold at the molten metal surface in the present practice, and

Figs. 3 and 4 are curves similar to that of Fig. 2 illustrating the temperature conditions obtained with the novel method.-

When molten metal is cast into a mold, it is cast at such a temperature as to give the maximum yield of sound metal. The casting tem-, perature is dependent upon' the analysis of the molten metal, the character of the mold employed, the volume of metal to be cast, etc. In

the practice of the prior art, while the bulk of the metal cast may remain at the casting temperature, or substantially so, for the required time interval, the metal at and adjacent the mold sides does not and by reason of its reduced temperature produces surface imperfections.

When molten metal is cast into a mold in accordance with the practicc'of the prior art, the A metal adjacent the mold sides cools at a very.

rapid rate by reason of the heat absorbed by the mold sides, and quickly drops to temperatures much lower than the metal .further removed from the mold sides- This is true of the metal at and adjacent thesurface of the cast metal. The cur ve of Fig. 2 illustrates the temperature gradient that normally exists; in the prior art practice at'the surface of the cast metal as it is being poured. The metalbetween points A and B of the curve is all at substantially the same temperature. This temperature though somewhat lower than the casting temperature approaches the pouring temperature so that the metal between points A and B is in the condition to produce a maximum of sound metal. The bulk of the metal represented by portions AC and B-D of the curve is, however, at temperatures much below the casting temperature. The metal adjacent points C and D may actually be at or closely approach the solidification temperature of the metal. Thus, the metal between points A and C and B and- D is not .in the condi- 5 tion required for the production of sound metal as it is cooled'to such a degree that its fluidity is impaired. The required fluidity of the surface metal is responsible for the formation of .cold shuts, folds, cracks, gas pockets, impurity segrgations, etc. inand adjacent the ,surfaceof" the cast body. In some casesthefiuidity of the surface metal is so reduced that the later cast metal can only pass "to the mold sides by passing through or over the cooled surface metalxln a and columbium), pure metals such as nickel,

non-ferrous alloys such as monel metal, that do not flow readily at temperatures that tend to approach the solidification temperatures, and for that reason are generally designated as sluggish, are cast. the imperfections mentioned always occur to a troublesome extent.

The cooling effect of the mold sides may be compensated for, in accordance with my invention, by the addition of heat during the pouring of the metal so that the metal at and adjacent the mold sides will retain the necessary characteristics to produce imperfection free, or substantially imperfection free surfaces.

I supply the-heat, preferably by means of discharge of electric current from the end of one I or more electrodes, to the surface of the molten metal in such quantity and at such location that the temperature of the bulk of the metal at and adjacent the mold sides is brought to temperatures approaching or even higher than the temperatures of the remainder of the surface metal.

In the casting operation illustrated by the curveof Fig. 3 heat has. been added to portions A'-,--C' and BD' of the surface metal and the quantity of heat added so controlled that the portion of substantially uniform temperature extends from point Eto point F, the temperature at points C and D"being raised by the heat addition'until they approach the temperatures of the main part of the curve. Thus, the metal at and. adjacent the walls of the mold is at a suiliciently high temperature that it has the required flow and other characteristics to produce a substantially imperfection free surface. This heat will usually be added at a point or region between thesides of the mold and the point at which the temperature begins to drop in the old practice. The exact location of the point or region mentioned will depend on many factors such as conduction of the molten metal, conduction and design of the mold etc., and is best arrived at in each-particular case from experiment. The quantity of heat added will also vary but in any case will ,be such to render the metal at andadjacent the mold sides of sumcient fluidity that it will conform to the shape of the mold without appreciable resistance and willallow gas and solid impurities to pass through factory when casting very sluggish metal. 7

I In order to secure satisfactory results it is necessary that the heat beapplied substa ntially uni-" formly over the whole outer band of the molten surface. "This may be accomplished by use of a plurality of properly spaced electrodes or'by'the" *use of one or moreelectrodes that are moved,

: either by their movement or by the movement of the mold, at a substantially uniform rate over the portion of thesurface metal to be heated.

- a metal .01' alloy of high heat conductivity such as copper, copper alloys, etc., and provided with a jacket through which water, oil, or other heat exchange medium may be circulated. In lieu of a jacket the mold may include passageways.

within it through which the heat exchange medium may be circulated. The jacket or the passageways may be so arranged that the whole of the mold may be cooled, at one time or only selected horizontal bands may be cooled as desired. With the latter arrangement and especially when normal cooling of thecast metal is desired, that portion of the mold only can be cooled at which the heat is being applied also, the mold may be made of refractory material that will withstand the heat of the current discharge. h

The electric discharge may take place from the end of a non-consumable electrode, or electrodes, or from the end of a consumable electrode, or electrodes, of substantially the same composition as the cast metal. The electric discharge may be in the form of an open arc but more satisfactory results are obtained when the surface of the molten metal, the electric discharge and the end of the electrode, or electrodes,

are maintained beneath a thick blanket of pro- The flux may be initially solid or molten and I additions may be made as required. The slag produced in the making of the molten metal may be employed as the flux or any suitable material that will protect the electric discharge and the molten metal from the atmosphere, will not add undesirable constituents or remove desirable constituents, and will not produce deleterious gas either as to quantity or kind may be employed. At present, silicates of calcium, magnesium, manganese and iron, either alone or in mixture, or their unreacted dried or calcined components are preferred fluxes. The flux may also contain aluminates, titanates, flux thinners such as fluorspar etc.

, The illustrative form of apparatus, suitable for carrying out the novel method of the invention, diagrammatically shown in Fig. 1, includes a mold in which may be arranged for either top pouring or bottom pouring of the molten metal. Mold l0 may be of any desired construction; thus, it may be of the big end up type or the big end down type and'may be made of cast iron, as in the usual practice or of'copper, and the like, and provided with a jacket or similar means through which water or other heat exchange medium may be circulated. Mold ll] may also be of refractory materials, in which case the water circulating means are omitted. Mo1dl0, as shown, includes a plurality of passageways ll through which a heat exchange medium may be circulated. Passageways ll maybe connected into a continuous fiow path,'for the heat exchange medium or they may be 50 arranged in connectable horizontal coils that' the heat exchange medium can be circulated at will'through -one or more of them to cool desired horizontal sections of the mold.

Mold I may be supported on a fixed stand or it may be supported on rotatable means for rotation about a vertical axis. When top pouring is employed the molten metal passes from ladle l2 through a suitable conduit l3 to discharge into the mold beneath flux blanket I4. When bottom pouring is resorted to the molten metal is supplied from a ladle Hi to a suitable conduit I6 that opens in the bottom of the mold and discharges the molten metal beneath fiux blanket l4.

Shortly after the casting operation is initiated electric current is discharged from the end of electrode I! tothesurface of the molten metal l8. The end of the electrode as well as the electric discharge is maintained beneath the blanket of flux l4. Electrode I1 is fed by feed wheels l9 through a .contact nozzle-.20 to the surface of the molten metal H3 at the required rate to maintain a discharge of predetermined characteristics. This result is obtained by reason of the control arrangements located in welding head 2|. Head 2! may be of any of the types well known in the arc welding art. Current is supplied to contact device 20 through cable 22; cable 23 conducts the current to the mold Ill.

Welding head electrode l1 around the mold or itmay be fixed in positionl While only one electrode I! has been shown, it is to be understood that as large a number may be used as is found necessary in order to obtain the desired heat input to the whole body of surface metal at and adjacent the mold sides.

vAs stated, the electrode, or electrodes, may be moved around the mold or they may be maintained in fixed position and the mold rotated. Also, both molds and electrodes may be fixed. In

such case a plurality of closely spaced electrodes are employed.

y While the welding head 2| will raise the end of electrode I I as required to maintainthe de-. sired discharge, it is advisable to provide means, I

either manual or automatic for raising head 2| with the risinglevel of molten metal II! to prevent injury by the heat to contact device 20 and head 2|. ,When mold I0 is not of constant cross section provision must also be made to -move head 2| and electrode" laterally so that the discharge end of electrode ll may be'maintained at the predetermined'distance from the sides of mold "I. As heretofore stated, the location of the discharge'and its intensity depends on. the characteristics of the metal cast, the size and design of the mold, etc. To obtain the desired results it will often be necessary to locate the discharge near the mold walls. In such cases the "mold will be of refractory material or it may be made of copper or similar high heat conductivity metal and a cooling medium circulated through passageways H. The whole of the mold may be cooled simultaneously or only the horizontal zone thereof adjacent the level of the molten .metal l8.

The molten metal may be supplied entirely from ladies I! and IE or only some of it may be so supplied and the remainder supplied from one or more electrodes of the required composition. .Also, ladles l2 and I5 may be dispensed with and all of the molten metal supplied from one or more electrodes. their discharge will also be maintained beneath flux blanket ll. The feed motors, control arrangements of these electrodes may be incorporated in head 2| or a separate head may be provided.

In the usual case the desired results are ob- :a tained, as explained above, by the addition of 2| may be arranged to carry.

When electrodes are employed 9 the required heat to the surface metal at and adjacent the mold sides. In some cases, however, the desired results may be obtained by the addition'of heat to substantially the whole of the surface metal, the heat being added in such quantity and in such manner to compensate for the chilling of the surface metal during the casting. 4 V

In these cases the heat may be added by, the use of electrodes l1, as heretofore, but heat is also added to the center surface metal, 1. e., the metal between points A and B "of the curve of Fig. 2, so that the whole of the surface metal is raised above the temperatures of the prior practice, as represented by the curve of Fig. 2. Thus, in

addition to electrodes 11, electrodes may be posleliminated and all of the heat supplied by additional electrodes.

When the whole or a part of the cast metal is obtained, as pointed out above, by the fusion of consumable electrodes, the consumable electrodes may be so operated to supply a part or all of the compensating heat required. As with electrodes H, the additional may be non-consumable or consumable. In the latter event they are made of such composition to provide fused metal of the same composition as the cast metal. The discharge, or discharges, from the'additional electrodes is also submerged beneath flux blanket l8.

I claim: i

1. The method of casting .metal bodies which comprises, placing a depth of protective flux in the bottom of a mold, casting molten metal into said mold beneath said flux to progressively fill said mold, discharging electric current from one or more electrodes against the rising molten metal surface adjacent the sides of said mold, said electric discharge being maintained beneath said blanket of flux and being of an intensity to maintain the surface metal at and adjacent the mold sides in substantially the same degree of mobility as the remainder of said surface metal.

2. The method of casting metal bodies made of metal of a melting point within the melting point range of ferrous alloys, which comprises, placing a depth of protective flux in the bottom of a metalmold, casting molten metal into said electrodes mold beneath said flux to progressively fill said mold, and discharging electric current from one or more electrodes against the rising molten metal surface adjacent the sides of the mold to maintain the molten surface metal adjacent the mold sides at temperatures approaching the pouring temperature.

of metal of a melting point within the melting point range of ferrous alloys, which comprises, placing a depth of protective flux in the bottom of a metal mold, casting molten metal into said 1 mold beneath said flux to progressively fill said ROBERT K. HOPKINS.

3. The method of casting metal bodies made

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