US2248628A

US2248628A - Method of casting metal bodies

Info

Publication number: US2248628A
Application number: US161373A
Authority: US
Inventors: Robert K Hopkins
Original assignee: MW Kellogg Co
Current assignee: MW Kellogg Co
Priority date: 1937-08-28
Filing date: 1937-08-28
Publication date: 1941-07-08
Anticipated expiration: 1958-07-08

Description

July 8, 1941.

FIG.

Patented July 8, 1941 arrasa llmTHGD F CASTING METAL BGDES Robert K. Hopkins, New York, N. Y., assignor to M. W. Kellogg Co., New York, N. Y., a corporation of Delaware Application August 28, 1937, Serial N0. 161,373

4 Claims. (Cl. Zit-216) This invention relates in general to the casting of metal bodies and in particular to an improved method for casting metal lbodies in which a maximum of dense sound metal is produced from the metal cast.

Metal sold in the form -of Worked shapes is generally cast into ingots preparatory to the working operations. is an important operation as the quality of the nal product, as Well as the salable yield, is largely determined by the quality of the ingots. A great deal of 4time and eiort have been expended in perfecting ingot molds and casting technique with the result thatin the present practice many of the causes of unsound metal have been eliminated. One of the main causes for the lowering of the salable yield, particularly with killedsteels and comparable materials, is the pipe Aor pipes that form in the upper end of theingot during the cooling of the cast metal. During the cooling and solidication of the cast metal furthermore, some of the impurities segre- The casting of the ingots gate out, the segregated material migrates in- Y wardly and is found in the metal around and below the pipes. l

In my copending application Serial No. 125,024 filed February 10, 1937, I disclosed a novel method for forming sound pipeless ingots in which the loss in volume of the metal of the ingot.,` that takes place during the cooling thereof and that results in the usual pipe` or pipes, is compensated for by the deposition of molten metal in the ingot, which molten metal welds to the metal of the ingot and thereby produces a sound pipeless ingot. The metal deposited is preferably deposited as fusing weld metal under the influence of the discharge of electric current through a gap between the end of the electrode and the ingot metal. The metal depositionis carried out under a blanket of iiux that protects the metal of the ingot and the deposited metal from the atmosphere and also absorbs or floats out impurities and segregations from the molten metal.

' The metal deposition may be initiated during the cooling and solidication of the cast metal or it may be initiated after the cast metal has been completely solidied.

The present inventionv relates to the novel method disclosed in my copending application,

above identified.

In accordance with one aspect of the present invention a plurality of electrodes are employed and the weldingr current is discharged through a gap or gaps between their ends so that substantially all of the heat evolved by reason of the' current flow is evolved at the gap or gaps and is effective to fuse the filler metal, the metal of the ingot and adjacent the walls of the pipe, or pipes, and to weld the filler metal to the metal of the ingot. The electrodes may all be consumable and the only supply of filler metal, or all of the electrodes may be substantially non-consumable and all of the filler metal supplied from an outside source. Also, some of the electrodes may be consumable and others substantially non-consumable. v'I'he outside source of filler metal may 'be a solid rod, bar or the like, and is.

inserted into the ingot in the region of the current discharge so that it may be fused .by the heat generated by the discharge. The outside source may also be molten metal which is passed to the region of the current discharge to be heated to the degree required to cause it to commingle with and become an integral part of the metal of the ingot.

The plurality of electrodes, furthermore, may be so charged and arranged that the current ris discharged from one or more of them through a' gap or gaps to the cast metal and from the.

cast metal through a gapy or gaps to another or others of the electrodes. In this arrangement, also, no current is dissipated by resistance in the walls of the ingot at a distance from the locus of the metal deposition so that the maximum advantage is had of the power employed.

'Ihe further objects and advantages of the invention will `be readily appreciated from a consideration of the following detailed description of the mode of carrying it out in practice, taken with the accompanying drawing in which,

Fig-1 is a View partly in side elevation and partly in section illustrating one way of carrying out my invention in practice, and

Fig. 2 is a view similar to Fig. 1 illustrating another way of carrying out vmy invention in practice.

The method of this invention may be used in connection with the forming of metal ingots in general and is not limited to any particular type of ingot or ingots of metal of any particular composition. However, since it is admirably suited to the formation of ingots of partly, or completely, deoxidized steel, it will be particularly described in connection with this type of metal.

The mold employed may be a big end up mold or a big end down mold and a hot top or similar devicemay or may not be used as preferred. If a hot top is used the relative volume thereof may be materially reduced below that of the best present practice. Thusa hot top that contains includes a headV Il that ls adapted to feed two electrodes I2 and I3. Head II may be arranged in any desired way to feed current at substantial- 1y constant values to the electrode ends and to maintain a more or less constant gap between them. At present, I prefer that head II include electrode feed wheels I4 and I5 arranged to drive electrodes I2 and I3 at an angle one to the other. 'I'he spacing between feed wheelsill and I5 and the angle of drive should be such that electrodes I2 and I3 may be inserted to the bottom of the usual pipe cavity and a predetermined gap maintained between their ends. In order to facilitate in any suitable way, as for instance, if one or both of the electrodes are hollow, through the hollow center or centers, or also by employing a hollow body through which they can be passed The apparatus schematically shown in Fig. 2

is generally similar to that of Fig. 1 and has been the maintenance of the predetermined gap, head II is preferably mounted on a stand I6 so that it may be raised, as by means of a wheel and rack, as required to keep the ends of electrodes I2 and I3 adjacent to but out of contact with the molten metal. In the operation of this apparatus the space between the ends of the electrodes and the bottom of the pipe cavity, or the top of the molten pool after the operation is started,

should always be greater than the gap between the electrodes. One of the feed wheels Il and I5 is arranged to feed its electrode at a predetermined rate, the arrangement being such that the rate of feed may be changed at will to'suit .the necessities of each particular operation. The

other of feed Wheels I4 and I5 is so arranged is fed electmde I2. The other side of the current is passed from head II by cable-I9 to contact device 20 through which is fed electrode I3. Contact devices I8 and 20 may be of any preferred construction. With welding electrodes whose surface is conductive I, at present, prefer to employ an elongatedwatercooled contact nozzle as shown. Contact devices IB and 20 are held together by members 2 I, which are made of insulating material, so as to facilitate the maintaining of the predetermined angle between the electrodes.

Each of electrodes I 2 and I3 may be either consumable or substantially non-consumable. At present, I prefer to make both of the electrodes consumable and of such analysis that when fused with the metal of the ingot the resulting metal is of substantially the same composition as the metal of the ingot. Electrodes I2 and I3 may be bare or covered and either solid or hollow. If covered, contact devices I8 and 20 should be such that they can pass the current continuously to the metal cores of the electrodes. All of the constituents of the electrodes may be incorporated in the metallic portions thereof, or some of them included in the metallic portions and the remainder in the coating, if one is used, or passed to the region of the gap between the electrodes to prevent direct discharge from one electrode to Y the other.

In carrying out my novel method, the metal to be cast, as for instance, carbon steel, is prepared in the usual manner. Thuis, the required additions are made and the molten metal is either partly or entirely deoxidized by the addition thereto of ferro-silicon, aluminum, or other preferred deoxidizing agents, and then allowed to come to the preferred pouring temperature. It

is then poured into mold In and allowed to cool.

When the cast metal has cooled to such a point that the sides of the ingot have solidified and substantially all 0f the molten metal that is left is to be found in the region of the usual pipe or pipes the ingot is ready for the addition of fusing metal. This condition of the ingot is readily determined by soimding it from time to time as with a metal bar. With any type and size mold and with any analysis of cast metal lthe proper condition of the ingot is readily' ascertained by any skilled operator byfollowing the above relatively simple procedin-e.

Head Il is then placed over ingot 22. Electrodes I2 and 'I3 are then passed to feed wheels II and Il and fed through contact devices I8 and 20 until they almost touch each other. An arc started such as a wad of steel wool, a sliver of graphite or the like,is placed between the electrodes after which head II is lowered until 'the ends of the electrodes approach Vthe bottom of the central cavity or pipe 23 of the ingot Pipe 23 is then filled or partly filled with flux 2l which maybe either solid or molten. A dam 25 may be provided to maintain flux 2| on ingot 22 when it is displaced by the deposited ller metal.

Flux 24 should be such that it will not liberate deleterious gas, either as to quantity or kind,

during the metal depositing operation, and will4 components, thus, for instance, in the case of calcium silicates the ux may be made up of CaO and SiOz, in the case of manganese silicates it may be made up of MnO and S102. At present,

silicates, either simple or complex of the alkaline earth metals, manganese, aluminum and iron are preferred. Flux 24 may also include constituents may be ladled while molten directly from the steel furnace.

operation there is very little molten metal and, hence no porosity, segregation or piping in the top of the ingot. 'I'he current may be tapered 0E to the value above given, or to a much lower value as required to give` the results stated.

In order to assure complete fusion of the metal deposited with the metal of the ingot, especially when the pipe is wide, the head I i (or III) may be given an oscillatory and/or rotary 'movement relative to the ingot so that all portions of the sides of the pipe will come into the direct influence of.v the current discharge.

The cost of the operation may be materially reduced in some cases by employing an additional source of filler metal. Theadditional source may take the forni of a ller rod or molten metal.

. When a ller rod is used it may be fed to the and fuse them to the ingot, Head II, as stated A above, will maintain a gap of predetermined width during the operation. As the level of the molten metal rises in pipe 23 the operator will cessity of raising head II for if the ends of the electrodes discharge directly to the molten metal the voltage reading will be less than the predetermined value.

'I'he procedure when the apparatus of Fig. 2`

is employed is generally the same. However, with the latter apparatus head II is raised from time to time merely to prevent contact devices I8 and 20 from being destroyed as the control arrangements will always maintain the predetermined gaps.

When operating with the apparatus of Fig. 1 the ingot is not in the electrical circuit at all and with the apparatus of Fig. 2 only a very small zone of the ingot is in lthe circuit.

Thus, in, both cases all of the energy dissipated is available to melt metal and fuse it to the ingot; nov energy is dissipated by electrical resistance in the body of the ingot removed from the zone ofv deposition.

While the current input is largely determined by the amount of metal Ito be deposited and the time available for'its deposition, I find it very advantageous to initiate the operation at high -current inputs and gradually reduce the current input as the operation progresses. Thus, for instance, the operation may be started at an amperage in the vicinity of 10,000 amperes per inch diameter of electrode and finished at an amperage in the vicinity of 2000 amperes per inch diameter of electrode. The values just given are illustrative only and higher or lowervalues may be used as required to obtain the desired results in each particular case. The high-initial current is highly desirable as it provides for the generation of heat at a rate high enough to assure the complete, fusion of the metal at and below the bottom of the pipe and thus, porosity and segregation in this region are eliminated. The tapering oii in current input assures the solidication of the metal deposited in the upper end of the pipe at a rate that approaches the rate of deposition so that at the end of the vicinity of the gap, or gaps at a regulated rate but-care should be exercised to so control the feed that the additional metal does not absorb #too much of the energyof the operation and prevent a proper fusion and commingling of the metal of the ingot with the deposited metal.

When molten metal is'employed for this purpose it may be poured directly onto the ux to pass bygravity to ithe molten pool, this easily takes place for the flux is either molten when placed'in the pipe, as above stated, or if solid when placed in the pipe it becomes molten as the metal depositing operation progresses. The molten metal may` also be passed. from ladle 28 through a. ceramic, or other high heat resisting material, tube or trough 26. The trough or tube is preferably positioned in the pipe before.

the pipe is filled with ux. As the operation progresses trough 26 is Withdrawn as required to keep it away from the level of the fused metal. The molten metalmay be' taken from .the .heat that went to `form the ingot or from some other molten metal source. Ladle 28 is preferably insulated and provided with heating means so that the metal in it may be maintained uid for the duration of the pipe filling operation.

The molten metal may be passed into the pipe at a more or less constant rate or it may be passed into it intermittently. Again it is necessary to guard against feeding this metal at too high a. rate so that it may be properly fused and intermingled with the metal of the ingot.

As previously stated, the electrodes may be made of material that does not supply metal for the operation. When this variation of the method is carried out all of the metal required may be supplied from the ller rods or ladle 28.

The method of this invention may also be employed .to ll the pipe cavities of ingots. orv cavities in metal bodies of whatsoever character such as castings, forgings and the like, after all of the metal thereof is solidified, or solidified and cooled to room temperature. .In the cases just mentioned, the procedure is the same as that heretofore described, however, when lling the pipes of completely solidified ingots the high initial current input becomes more important and it is necessary that it be of a high enough value to assure the meltingof a substantial portion of the ingot metal below and around the'bottom of the pipe cavity so that the imperfect metal usually,

tion is a disclosure of fact, it is to be understood that I do not wish to be bound or limited in any way by any theory advanced and that the appended claims are to be interpreted and construed in the light of the factual disclosure and ltween a plurality of metal electrodes, the electric energy supplied for said discharge being supplied to said electrodes, and passing molten metal from an` outside source to be coalesced by said energy discharge with said cast metal and the metal of the electrodes.

2. A method of'increasing the yield-of sound metal in metal bodies which comprises casting molten metal into a mold, coalescing metal with said cast nie-tal by electric energy discharge under a blanket of flux to ll the cavity formed in said cast metal, said discharge taking place between a plurality of metal electrodes, the electric energy supplied for said discharge being supplied to said electrodes, passing metal from an outside source to be coalesced by said energy discharge with said cast metal and the metal 'of the electrodes, said energy discharge being of such magnitude at the beginning of the coalesclng operation that substantial quantities of cast metal at the bottom of said cavity are fused .whereby porosity and segregations at the bottom of said cavity are eliminated.

3. A method of increasing the yield of sound plied to said electrodes, passing metal from an,

outside source to be coalesced by said energy discharge with said cast metal and the metal of the electrodes, said energy discharge being of such magnitude during the latter stages of the coalescing operation that the metal is fused at a rate that does not substantially exceed the rate of solidification of the fused metal, whereby at the end of the coalescing operation comparatively small quantities of molten metal are present.

4. A method of increasing the yield of sound metal in metal bodies which comprises casting molten metal into a mold, coalescing metal with said cast metal by electric energy discharge under a blanket of ux to iill the cavity formed in said cast metal, said discharge taking place between a plurality of metal electrodes, the electric energy supplied for said discharge being supplied .to said electrodes, passing metal from an outside source to be coalesced by said energy discharge with said cast metal and the metal of 'i the electrodes, said energy discharge being oi magnitude of said energy discharge being tapered `oif as the operation progresseswhereby at the end thereof only comparatively small 4quantities of molten metal are present.

ROBERT K. HOPMNS.