US2597269A - Apparatus for the mold casting of metals - Google Patents

Description

May 20, 1952 APPARATUS FOR THE MOLD CASTING OF METALS Filed Jan. 18, 1946 M. TAMA ETAL 5 Sheets-Sheet l INVENTOR JAMES LLOYD HOFF ATTORN-EY May 20, 1952 M, TAMA HA 2,597,269

APPARATUS FOR THE MOLD CASTING OF METALS y 20, 1952 M. TAMA ETAL 2,597,269

APPARATUS FOR' THE MOLD CASTING OF METALS Filed Jan. 18, 1946 5 Sheets-Sheet 3 INVENTOR. MANUEL TAMA MARIO TAMA y JAMES LLOYD HOFF ATTORNEY M y 20 1952 M. TAMA ETAL 2,597,269

APPARATUS FOR THE MOLD CASTING OF METALS Filed Jan. 18, 1946 5 Sheets-Sheet 4 INVENTOR. 'MANUEL TAMA MARIO TAMA By JAMES LLOYD- HOFF V/VWM ATTORNEY May 20, 1952 M. TAMA ETAL 2,597,259

' APPARATUS FOR THE'MOLD CASTING OF METALS Filed Jan. 18, 1946 5 Sheets-Sheet 5 INVENTOR MANUEI TAMA MARIO TAMA BY JAMES LLOYD HOFF ATTORNEY Patented May 20, 1952 UNITED STATES PATENT OFFICE APPARATUS FOR THE MOLD CASTING OF METALS Application January 18, 1946, Serial No. 642,092

2 Claims.

The invention is concerned with the adaptation of induction furnaces and particularly of submerged resistor type induction furnaces to the requirements of mold casting operations, and particularly to the manufacture of permanent mold and die castings which in modern foundry work have greatly gained in importance; the invention is related to subject matter which is disclosed in a co-pending application, Serial No. 576,884, filed by Mario Tama on February 8, 1945, which application has now become abandoned.

This type of work, where the molten metal is either poured continuously or at regular intervals ranging from a fraction of a minute to several minutes requires a reservoir of metals, the temperature of which must be controlled within accurately defined and comparatively small ranges. This is particularly true if metals are poured where the quality of the produced castings greatly depends on the maintenance of certain predetermined casting temperatures.

This reservoir has hitherto been provided by one of the following two ways:

(1) Separate hearth furnaces or large crucible furnaces are provided to melt down the metal in a batch type operation; when the metal reaches the described temperature, it is transported in ladles to crucible type holding furnaces located close to the casting machines or molds.

(2) Hearth furnaces, holding several thousand pounds of metal and equipped with a forehearth, serve a number of molds, in continuous operation, that is, melting and maintaining temperature at the same time; this system is used in permanent mold foundries.

The shortcomings of the first system are its requirement of space and manpower and the complications involved in transporting molten metal through a usually crowded plant; also the fact that every pound of metal has to pass through two furnaces will result in low efliciency.

The second system is objectionable because of the heat generated by the hearth furnaces, which are in the immediate vicinity of the molds; also this type of hearth furnace is usually low in efficiency.

An induction furnace, melting the metal and at the same time maintaining the temperature of the bath within the desired temperature range could offer an ideal solution of this problem. Space and manpower requirements would be reduced considerably as compared with the systems mentioned above; moreover the operating conditions around the furnace would improve over either one of the above given solutions. Besides,

the user would gain the advantages of induction melting over fuel melting in general, i. e. reduced gas pickup, no iron pickup and reduced metal losses; the efficiency of an installation of this type is very high.

The problem of the continuous melting of light metals in induction furnaces of the submerged resistor type has been successfully solved by recent developments which are represented by U. S. Patents No. 2,339,964 of Manuel Tama, No. 2,342,617 of Manuel Tama and Mario Tama, Reissue No. 22,602 of Mario Tama, and No. 2,375,049 and No. 2,381,523 of Manuel Tama and of Mario Tama.

A great number of kw. twin coil furnaces similar to the one disclosed in Reissue Patent No. 22,602 are in continuous operation and previously customary frequent stoppages and interruptions of the work have been successfully eliminated.

However, the requirements of temperature control in modern permanently operated mold foundries are steadily growing in severity, which is particularly truein the continuous manufacture of light metal and light metal alloy castings.

It is customary in installations of this type to charge the ingots into the molten bath at certain intervals. This is done by the operator of the mold or casting machine and the time cycle is not always rigidly observed. Moreover, it must be kept in mind that particularly in the aluminum industry there is a pronounced trend to supply the foundries with comparatively large ingots of between about 25 to 50 lbs. of guaranteed analysis either from virgin or from remelted metal; it appears that this will be the predominant rule in the future.

The aluminum producing plants have been provided with alloying equipment. They prepare casting alloys in large heats up to 20,000 lbs. and each heat is carefully sampled and analyzed. Every precaution is taken to obtain a product which will give uniformly satisfactory results in the foundry. This control is especially necessary in the case of the heat-treatable alloys, because close chemical composition and other characteristics are essential to the successful application of the heat treating process. The secondary aluminum industry takes similar precautions for supplying uniform ingots to the foundries.

Therefore, it is believed that there is and will be no necessity to prepare alloys in the foundries, and that the prevalent procedure will consist of starting with ingots of the required composition. Under these circumstances the logical method of 3 melting should consist of using furnaces which will enable the foundries to use only one furnace or furnace aggregate for melting and pouring, thus obviating the necessity of double melting and of outside transportation of the molten metal.

A furnace or furnace aggregate capable of being used in the manner just described should answer the following requirements:

(a) Large melting capacity in a comparatively small space.

(2)) Close temperature control, while cold metal is continuously charged, molten and the metal bath is poured continuosly or in regular intervals,

(c) Comfortable operating conditions with only small amounts of heat being radiated to the surroundings.

(d) Thorough mixing of the molten metal bath,

(e) Maintenance of separate melting and pouring zones,

(f) Direct constant communication between the melting and pouring zone.

(9) Continuous charging of the metal bars into the melting zone.

(71.) Maintenance of a substantially constant and equal bath level in the melting and in the pouring zone.

The standard frequency induction furnace of the submerged resistor type seems to fulfill these requirements.

Although operating conditions would be ideal if a piece of metal could be molten with higher power within a few seconds to be charged immediately into the chamber of a die casting machine or in a permanent mold, this procedure is far too expensive to be followed in practice.

In the first place, the piece of metal to be inserted would have to be of the exact weight as the article to be cast; the shape would be diiferent from the ingots delivered by the smelters and the power required to do the work would be very high bcause of the intermittent character of the operation.

In order to solve this problem in a practically satisfactory and economic manner, a new method of operation has been developed in conjunction with induction furnaces and particularly those of the submerged resistor type. comparatively small units are operated with high power capable of melting at a high production rate and of being charged and discharged continuously with standard ingots available for foundry use.

For example, a furnace of 60 kw. capacity delivers molten metal at a maximum rate of 300 lbs. per hr. The ingots are charged successively and continuously into the molten metal contained in the hearth of the furnace and the metal is ladled out from the same, keeping pace with the production of the die casting machines or permanent molds.

The separate melting and ladling zones may be provided in conformity with further embodiments of the invention.

It is obvious that the success of continuous operations of this type depends largely upon the maintenance of a uniform temperature in the molten bath during the entire production cycle, and this is particularly true when light metals or their alloys are cast as the quality of the castings, as pointed out previously, greatly depends on the maintenance of a predetermined optimum temperature. The furnace will melt all the solid metal charged into it at a certain rate corresponding to the kilowatts absorbed. If too much 4 cold metal is charged, the temperature of the bath will drop.

When light metal ingots of 25 to 50 lbs. are directly dropped into the bath contained in the hearth of an induction furnace they will be completely molten in one or two minutes under average conditions.

Unless power is supplied at a rate fast enough to melt that much metal in this short time, there will be a strong temperature drop. Since, in most installations of this kind, the furnace power will range from 60 kw. to kw, the energy required to melt an ingot of the above size will only be supplied in about 3 to 10 minutes; therefore, the temperature drop may be very considerable.

It therefore is the primary object of the invention to correlate the charging speed of the ingots or pigs into a metal bath contained in the hearth of an induction furnace, the melting rate of the ingots and the ladling rate of the molten metal with the requirements of modern die-casting machines and permanent molds.

It is another object of the invention to assure the maintenance of uniform constanttemperatures of the molten bath during the entire operating cycle and to reduce during the continuous charging and melting of the ingots temperature variations to a practical minimum.

It is also an important object of the invention to provide coordinated charging, melting and pouring zones.

It is a further object of the invention to elfect a final adjustment of the casting temperature of the metal bath prior to the ladling out of the same into the molds.

It is another object of the invention to facilitate the casting of a molten metal into permanent or continuous mold installations.

It is also an object of the invention to remove contaminations of the molten metal bath prior to and during the pouring of the same into the molds.

It is another object of the invention to simplify the charging of the ingots into the melting zone and to exclude losses frequently incurred during this operating stage.

It is also an object of the invention to provide a charging device which permits a continuous gradual automatic feed of the ingots into the melting zone.

It is another object of the invention to adapt the charging of the ingots into the molten bath of an induction furnace and particularly one of the submerged resistor type to changes of the mold pouring or casting conditions.

With these and other objects in view, which will become apparent as this specification proceeds, the invention comprises in its broadest aspect the correlation of the charging speed of metal ingots into a bath contained in the hearth of one induction furnace or a combination of induction furnaces, of the melting rate of the charged ingots and of the ladling rate of the molten metal into the molds. The accurate temperature control of an induction furnace and particularly also of an induction furnace of the submerged resistor type greatly assists in the accomplishment of these correlated conditions.

The invention therefore is particularly well usable for mold casting work or for the casting of individual work pieces.

An important element of the invention resides in the maintenance of accurately predetermined temperatures in the ingot melting and in the pouring zones of the furnace and in the control of the melting and pouring temperatures.

Characteristic features of the invention comprise the automatic cooperation of the charging, melting and pouring zones.

Various modes of carrying the invention into effect ar illustrated by way of example in the accompanying drawings, of which:

Fig. 1 is a vertical sectional elevation of an induction furnace of the submerged resistor type and of a correlated ingot feeding device,

' Fig. 2 is a top view of the upper part of the furnace,

Fig. 3 is a vertical sectional elevation of a two induction furnace aggregate for coordinated charging, melting and casting, the charging equipment being shown in a partly broken view,

Fig. 4 is a vertical sectional elevation of the ingot charging equipment shown in Fig. 3 on an enlarged scale,

Fig. 5 is a vertical sectional elevation on line 411 to 4a of Fig. 4,

Fig. 6 is a vertical sectional elevation on 4b4b of Fig. 4,

Fig. 7 is a vertical sectional part elevation of a further modification of the furnace aggregate, shown in Fig. 3.

The principal parts of the furnace shown in Figs. 1 and 2 are a housing I provided with a refractory lining 3 encasing a. melting hearth 2 and a secondary loop located underneath hearth 2. The hearth is adapted to hold the bulk of the molten metal charge and is provided with a pouring spout 4.

The secondary loop comprises melting channels I4, a groove I5 provided in the bottom of the hearth and a horizontal bottom channel IS, the vertical melting channels I4 connecting groove I5 and bottom channel I6.

The melting channels I 4, I6 and groove I5 filled with the molten metal form the secondary of a transformer system, the primary of which is threaded through it.

The primary comprises a plurality of spaced and insulated turns of an electrical conductor and is in operation connected to a supply source of low frequency alternating current, not shown. In the drawing the coil is represented by the numeral 8 and the insulation between turns by the numeral 9; an iron core I threads the primary winding and is closed in itself on either or both sides of the furnace. The transformer primary assembly is insulated from the refractory of the melting loop by an asbestos cylinder II and is contained in a housing I2 through which a cooling stream of air may pass from blower I3.

The ingot charging device consists of a feeder 65 which guides the ingot 6 head on into the molten bath H; the feeder has the same shape as the ingot to assure proper introduction into the bath in a vertical direction.

The feeder is mounted on the top of the furnace in a suitable manner; its lower end reaches down as near to the level I8 of the bath as practically possible.

A charging floor I9 for the ingot 6 is arranged underneath feeder 5; the charging floor maybe formed of the refractory lining of the furnace, as shown in the drawing, or an independent charging floor consisting of a refractory brick may be mounted in the hearth; the level of the charging floor which regulates the depth of immersion of the ingot in the bath may be varied by refractory blocks 2| of a different height, which blocks are placed on the charging floor 6 I9. A change of depth of immersion may be also attained by changing the level of the melting bath; this will in most cases sufllce to adapt the operation of the furnace to varying working conditions, as apparent from later parts of this specification.

The drawing shows the ingot shortly after its immersion into the bath, the immersed portion being shown in dotted lines, the not immersed portion in full lines.

Feeders for metal ingots shaped in conformity with the latter to guide the ingots into a molten metal bath are known in numerous varieties and means are used in conjunction with these feeders to automatically regulate the passage of the ingots into the bath and the temperature of the same in conformity with the immersion of the ingots.

The present ingot charging device is based on an ingot feeding principle which is greatly different from the art insofar as a charging floor is provided in the molten bath upon which the ingot rests during the melting period; the invention is based on the recognition that by the simple expedient of an adjustment of the depth of immersion of the ingot which is equal to the distance between the upper level of the charging floor and the level of the metal bath a constancy of the bath temperature may be maintained in induction furnaces which even satisfies the greatly raised requirements of modern continuous casting operations. If coupled with the usual temperature limiting control a constant bath temperature can be attained also when the ingots are charged at longer intervals than the intervals determined in accordance with the maximum melting rate of the furnace.

Obviously, given a comparatively small bath, only in induction furnace is practical for this type of operation, because only in this type of furnace the power supplied to the bath is constant and predetermined; only in these types of furnaces, where the heat is being generated in the metal itself, there is no time lag in transferring power to the bath as in all externally heated furnaces; only in an induction furnace, due to the strong circulation of the bath, is the -metal temperature uniform except in the immediate vicinity of the submerged ingot.

In utilizing the instant charging device the ingot will gradually melt and sink into the bath at a quite uniform speed, the temperature being regulated and rendered constant by the selection of the proper height of the charging level which determines an optimum depth of immersion.

If the metal is ladled out at the melting rate, the metal level will be maintained during the entire operation and the temperature of the bath will remain uniform.

The furnace is, of course, provided in the usual manner with automatic temperature controllers which will reduce the power, as soon as the desired temperature is reached and switch over to the full power, as soon as the desired minimum temperature is attained.

By means of the instant charging device it is possible to hold the temperature. of the bath within a narrow range, which is fully adequate to the requirements of continuous casting operations.

The invention, therefore, signifies a simple and efficient way of combining metal melting and holding units to one piece of equipment and of avoiding the hitherto customary complicated installations; it will be be advisable to charge the ingots on a certain schedule.

However, it is always possible to place the next ingot in the feeder before the previous one has been completely melted and to discharge the metal also on a certain schedule. This latter requirement is not diflicult, because the amount of molten metal required by the die-casting machines or permanent molds is uniform and on schedule.

The specific depth of immersion which is required to obtain an optimum temperature constancy, for instance not exceeding a range of up to about 25 F. and an optimum melting rate, must be determined experimentally with the individual furnace and ingots; but as one of the characterizing elements of the invention the rule has been established that in a submerged resistor type induction furnace having a substantially equal height of the molten bath throughout its hearth the depth of immersion should not exceed about 30% of this height. Gates and risers or other solid scrap may be handled in the same manner as ingots.

The following tests which are taken from an extensive experimental program clearly evidence the efiiciency of the instant charging device.

The tests have been carried out in a 60 kw. furnace with aluminum alloy ingot 162 of the Aluminum Company of America, weighing 40 lbs. and containing approximately 1 1% silicon, 1% copper, 1% magnesium, 1% iron, 2 /270 nickel, rest aluminum.

After complete submersion of the ingots equal to their disappearance underneath the metal level 40 lbs, of the charge were ladled oil; it is true that there is a small period of time between complete submersion of the ingot equal to its disappearance in the bath and the moment when all parts of the ingot are converted into molten metal; however, this time lag cannot be measured; besides, the determination thereof would have no bearing on the significance of the tests.

A height of the bath of 12 inches was established before the introduction of the ingot and a customary TLC or temperature limiting control setting of 1340 F. was used.

The temperature range between the initial temperature of 1340 F. and the lowest temperature measured during the melting of the ingot Was determined for each test by thermocouple, which temperature range would be the indicator for the attainable temperature constancy.

The depth or immersion and the submerging time were noted, the latter being equal to the time consumed between the moment of immersing the ingot into the bath through the feeder and the moment the last part thereof disappears below the surface of the bath.

Test 1 The ingot was directly introduced into the bath the customary manner; no feeder and charging fioor was used.

D e p t h of immersion 12 inches, equal to total equal to height of bath. height of the bath.

The ingot was introduced through the feeder resting on the hearth floor; no charging floor was used.

D e p t h of immersion 12 inches, equal to total equalto height of bath. height of the bath. Temperature range 83 F. Submerging time Not recorded.

Test 3 The ingot was introduced through the feeder and supported on the charging floor during submersion.

Depth of immersion 5.2 inches, equal to 44% of the height of the bath.

Temperature range 45 F.

Submerging time Appr. 6 minutes.

Test 4 Working conditions the same as in Test 3.

Depth of immersion 4.5 inches, equal to 38% of the height of the bath.

Temperature range 45 F.

Submerging time 4 min., 50 sec.

Test 5 Working conditions the same as in Test 3.

Depth of immersion 4 inches, equal to 34% of the height of the bath.

Temperature range 35 F.

Submerging time 5 min., 10 sec.

Test 6 Working conditions the same as in Test 3.

Depth of immersion" 3% inches, equal to 27% of the height of the bath.

Temperature range 15 F.

Submerging time 6 min., 50 sec.

Test 7 Working conditions the same as in Test 3.

Depth of immersion 2.3 inches, equal to 18% of the height of the bath.

Temperature range 12 F.

Submerging time 14 min., 30 sec.

Test 8 Working conditions the same as in Test 3.

Depth of immersion 2.1 inches, equal to 18% of the height of the bath.

Temperature range 22 F.

Submerging time 11 min., 30 see.

From these experiments it is apparent that by the use of the charging device represented by the invention a satisfactory temperature constancy can be maintained for continued casting operation in a submerged resistor type induction furnace.

It is obvious that the melting rate of the ingot i proportional to the immersion and that the ingot melting time increases, if the immersion is reduced, which will result in a reduction of the melting output. Therefore, and in dependence of specific requirements best suitable working conditions will have to be established in each individual case.

This determination of optimum operating conditions and mainly of the correct immersion in relation to a satisfactory inciting time can, however, be easily attained in conformity with the invention by an adjustment of the depth of immersion equal to an adjustment of the level of the charging floor in relation to'the height of the bath.

Another important embodiment of the invention is illustrated in Figs. 3 to 6.

Fig. 1 is replaced by a furnace combination composed of a larger capacity submerged resistor type induction furnace A forming the melting zone of the ingots and a smaller capacity submerged resistor type induction furnace B forming the pouring or ladling zone. A changing device C is coupled with the melting and pouring zone.

Ingot charging, melting, bath refining and pouring installations have been previously devised for the melting and the purification of copper. However, the charging, melting and pouring zones of these known installations are not operatively coupled by the correlation of the charging, melting and pouring speed in relation to the melting rate of the furnace; neither is the operation of the known equipment governed by the maintenance of an equal temperature and direct constant communication of the melting and pouring zones.

On the other hand, suggestions have been made to operatively couple, two or more openring type induction furnaces of different capacity for the melting and pouring of steel the smaller furnace being used to melt the metal and the lower furnace being a holding unit. The cooperation of these two induction furnaces is however controlled by principles which have nothing in common with the continuous casting of metals according to this invention, neither is the maintenance of a constant equal metal level shown in the two furnaces which is a characterizing element of the invention.

Moreover, the steady feeding of ore into an iron producing electric furnace is known at a rate to balance the supply of electrical energy and to thus maintain a substantially constant bath temperature.

In this prior art furnace iron is produced from ore; the furnace is not built to correlate the charging speed of metal ingots, the meltin of the same and the pouring of th molten metal into permanent or continuous molds with the melting rate of the furnace; neither is the charging of the ingots shown into a metal bath contained in the hearth of the furnace. The embodiment of the invention shown in Figs. 3 to 6 will now be described in detail.

The ingot charging device C is composed of a wedge-shaped base and of an ingot pusher.

Plates 22, 23, 24 Figs. 3 and 4 form the base, plate 24 being in actual operation located in an inclined position.

The pusher superstructure is hingedly connected at 25 with the base.

This pusher superstructure consists of plates 3| and 2B, the latter having a center slot extending in the feeding direction; a hydraulic cylinder 28 provided with square shaped enlargements 28 is at its both ends supported in plate 3|; a ram 30 is in the customary manner reciprocatively displaceable in the cylinder. The projecting front end 33 of the ram is connected by means of tongue 34 with ingot pusher 5; springs 32 are interposed between plate 24 and plate 3|; the springs cushion the impacts created by the drop of the ingots on plate 26.

A magazine 35 for the superposed storage of a restricted number of ingots 6 is located above plate 26; the ingots are so located in the magazine that the lowest ingot is always in front of pusher 5.

The two submerged resistor type furnaces A and B are of a principally equal construction similar to that of the furnace shown in Fig. l;

a detailed description of the furnace construction does not seem to be required.

The larger melting furnace A is provided with a platform 31 of refractory material reaching into the molten bath; this platform is alined with plate 26 of the ingot charging device C; an intermediary platform 38 is interposed between the platform 31 and the magazine; in this manner a glideway is formed upon which the ingots 6 are successively slid into bath of melting furnace A.

Melting furnace A and the smaller pouring furnace B are maintained in direct constant communication by means of tube 40; the length of the two downward branches of the tube is so dimensioned that the ends of the branches will always be underneath level l8 of the metal baths I! and I! in the melting furnace A and in the ladlin furnace B.

Tube 40 is provided with a branch tube 4| which is connected to a vacuum pump, not shown; a valve 42 is provided in tube 4|; the purpose of this device will be explained as this specification proceeds.

Baffle wall 49 prevents the passage of impurities floating on the baths into the molds.

The operation of this furnace aggregate is, as follows:

Furnace A is filled with molten metal of the same type as that of ingots 6 until level 8 is reached; this level is substantially equal to the height of the overflow 43 of gurnace B. Ingots 6 have been charged into the magazine 35.

The vacuum pump is started and draws the metal from hearth 2 into furnace B: as soon as the metal communication between the two baths is established in such a manner that the end of the left branch of pipe 40 is covered with the molten metal, the vacuum pump is stopped; the metal in the branch 4| above valve 42 solidifies; the valve is closed and a constant communication between the baths in the hearths of the two furnaces A, B is now established.

The sliding of the ingots into bath and the melting rate of the same is effected in correlation with the melting rated the furnace; the metal is poured into molds 44 by a slight tilting movement of furnace B.

The power supply to the holding furnace B is only used to make up for the small temperature losses during the travel of the metal from the melting into the holding furnace and for the accurate adjustment of the final casting temperatures.

If it is desired to cast the metal from furnace B at a higher temperature, the operation of this furnace can be easily controlled to comply with this requirement; however, the melting furnace should be operated at a possibly low temperature to prevent gas inclusions.

The furnace aggregate illustrated in Fig. '7 is similar to that of Figs. 3 to 6, the identical charging device C being omitted and only the part of furnace A attached to B being shown.

The communication of furnace A with furnace B however, and the mode of casting the metal into the molds from furnace B varies and will now be described.

The communication tube 40 is replaced by a passage 50 situated beneath the lowest metal level I8 maintained in the operation of the plant.

A vertically displaceable hydraulic ram 5| which is guided in tube 52 is provided above the hearth of furnace B; this ram carries a head 53 at its lower end.

In the non-pouring stage the head is positioned directly below the level 18 of the metal bath.

If the ram is downwardly displaced and the head 53 enters the bath it will displace a quantity of metal equal to its volume; the stroke of the ram is so controlled that just the block 53 but no substantial part of the ram rod enters the bath. In this manner a predetermined quantity of metal substantially equal to the volume of head 53 is ejaculated at each stroke of the ram into the mold 44 over overflow 43.

This quantity of metal is, as in the case of the previous embodiments of the invention, controlled in correlation with the charging speed and the melting rate of furnace A.

By using exchangeable heads and corresponding variation of the ejaculated quantities of metals in correlation with the charging and melting rate of the furnace it is possible to use molds of varying capacity.

However, this purpose may be also accomplished by filling the molds with a larger or smaller series of ejaculations.

It might be convenient to interrupt the communication of the melting and the holding furnace. For this purpose a valve made of refractory material is provided. This valve consists of a stem 54 and a head 55; the valve is located in a refractory housing 56 mounted in the top structure or cover 51 of the furnace.

The downward movement of the valve 55, which will close the passage 50 and interrupt the communication of the two baths, may be effected electromagnetically by energization of solenoid 53, which in the customary manner is connected with a current supply source; the spring 59 reopens the valve as soon as the current supply is interrupted.

The invention has been shown and described in connection with a submerged resistor type induction furnace; however, it is well adapted for use in any other type of induction furnace, for instance a high frequency furnace.

What we claim is:

1. In an apparatus for mold-casting metals a submerged resistor-type induction furnace, a molten metal bath contained in the hearth of said furnace, a second tiltable submerged resistor type induction furnace provided with a pouring spout and having a smaller metal holding capacity than said first furnace, a molten metal bath contained in the hearth of said second furnace, a siphon connecting said hearths holding the metal baths in the same at an equal level, a platform to feed ingots into the molten bath in said first furnace hearth located at the substantial height of said equal metal level whereby a predetermined equal quantity of molten metal may be displaced into the mold by the tilting of said second furnace.

2. In an apparatus for mold-casting metals according to claim 1, an inclined platform located next to the first induction furnace to feed ingots from an ingot stack into the molten metal bath and a. pusher located at the level of the lowest ingot to push the latter onto the said inclined platform.

MANUEL TAMA. MARIO TAMA. JAMES LLOYD HOFF.

REFERENCES CITED The following references are of record in the file of this patent:

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