US3153822A

US3153822A - Method and apparatus for casting molten metal

Info

Publication number: US3153822A
Application number: US765809A
Authority: US
Inventors: John N Miller; Hughes Peter John
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-10-07
Filing date: 1958-10-07
Publication date: 1964-10-27
Anticipated expiration: 1981-10-27

Description

Oct. 27, 1964 J. N. MILLER ETAL.

METHOD AND APPARATUS FOR CASTING MOLTEN METAL Filed Oct. 7, 1958 INVENTORS JOHN N. MILLER TER J. HUG ES BY c aw- 2 6 5.4M

ATTO R N EY United States Patent 3,153,822 rnon AND APPARATUS non CASTHQG MOLTEN METAL John N. Miller, 272 N. Craig 84%., Pittsburgh 13, ia., and Peter John Hughes, 36 E. Chestnut Hill Ave, Chestnut Hill, Pa.

Filed 0st. 7, 1953, Ser. No. 765,899 6 Claims. (ill. 22-79) This invention relates generally to a novel method and apparatus for casting molten metal and more particularly to a method and apparatus for teeming molten metal from ladles into molds while at the same time controlling the rate of cooling of the molten metal in the molds substantially evenly on all sides so that solidification of the metal is even.

It is vitally important in the casting of high grade metals, for example tool steels, that the molten metal be teemed into molds as near to the solidification temperature as possible in order to minimize undesirable orientation and build-up of inclusions in the ingot or casting produced and also to reduce the dendritic pattern of the resultant ingot. The inclusions which are composed of various impurities and which can make weak spots in the ingots, tend to bind together during the period in which the molten metal passes from the liquid phase to the solid phase. In order to reduce the tendency of this binding together of the inclusions and also to reduce the dendritic pattern of the ingots, it is desirable to reduce the time period of the actual fusion of the molten metal as much as possible, while at the same time cool the molten metal evenly in order to prevent hot spots in the ingot which may temporarily be in a. molten phase.

It has been the practice in the industry where a number of ingots are to be teemed from a single ladle, to heat the molten metal in the ladle above the desirable teeming point in order that the average temperature of the molten metal entering the molds will be as close as possible to a desired temperature and still compensate for cooling of the molten metal in the ladle during the time of teeming. The result of this is that the first group of molds will have molten metal teemed into them which is hotter than desirable. This molten metal then takes a longer period of time to cool and solidify which results in an undesirable dendritic pattern and build up of inclusions. The middle group may be near the desirable temperature when teemed, while the final group may be too cool and not flow properly in the molds. This practice can lead to an excessive rate of rejection of the ingots since there is no control of the rate of cooling of the molten metal in the molds.

Further, in an attempt to cool the molten metal teemed into the molds progressively in order to minimize piping, it has been the practice to utilize big end up or tapered molds. Such molds have thinner side walls at the top than at the bottom so that the cooling efiect of the mold on the molten metal is uneven. Moreover, the ingots produced in big end up molds are tapered and necessitate shaping either by rolling, forging or other means to a cylindrical or otherwise uniform shape before the ingot may be utilized in further manufacturing processes. This shaping to a uniform shape of necessity adds to the ultimate cost of the ingot produced.

It has further been the practice in the industry, particularly in producing high grade tool steels, to produce a hot top section on the ingot by teeming motlen metal into an extension on top of the mold. The hot top section is to insure that the ingot is fully formed and does not contain any shrinkage cavities. This section, which may comprise as much as -15% of the total ingot, contains an undesirable orientation of inclusions because it remains in a molten phase for an extended time and therefore it must be cut away from the ingot.

We propose generally to overcome the above difi'lculties attendant with present day practice, by providing for a. novel teeming spout which is connected to a ladle and which has a cooling head on the end opposite the ladle whereby as metal is teemed from the ladle into the mold, the rate of cooling of the molten metal in the mold may be readily and evenly controlled. The novel spout and cooling head eliminate the necessity of having a tapered mold so that cast ingots produced are evenly shaped which in turn reduces their production cost. At the same time by controlling the rate of cooling of the molten metal in the mold evenly, the necessity of having a hot top portion of the ingot to compensate for shrinkage cavities is eliminated. This results in that the complete ingot produced is available for manufacturing processes rather than only -98% as heretofore.

In addition, we propose to provide means whereby pressure may be exerted on the molten .ietal in the ladle so that the molten m tal passing into the mold will be at a greater pressure than that due to the liquid head of the molten metal alone. This produces a preforging effect on the molten metal as it is teemed into the mold which increases the desirable crystalline structure of the ingot. In addition, means are provided for moving the mold axially of the ladle and cooling head connected to the spout so that the cooling head will at all times be at a predetermined distance above the bath of molten metal in the mold. By regulating this distance, the rate of cooling of the top portion of the molten metal in the mold can be eflfectively controlled.

The cooling head itself is made of a high heat conducting material, such as aluminum, and has passages therein through which a cooling medium, for example water, may circulate. The outer edge of the cooling head may be curved upwards to compensate for the cooling effect of the side walls of the mold upon the molten metal to further insure even cooling.

The cooling head may be mounted eccentrically on the spout and rotation means provided to rotate the mold about the cooling head so that the complete upper surface of the molten metal, including that immediately below the spout opening, will be evenly cooled by the cooling head.

Referring to the drawing in which specific novel apparatus for carrying out our new method of teeming is illustrated, 1 denotes generally a ladle having therein a bath of molten metal 2. The ladle 1 has a removable top 3 which sealingly engages the ladle l by means of a seal 4. A conduit 5 provides means whereby gas under pressure i.e. compressed air, may be inserted into the ladle in the space above the molten metal so that when the molten metal is discharged from the ladle, it will be under pressure. A plunger valve 6 is movable up and down in the ladle so that when it is pulled up, the molten metal will be discharged from the ladle through the valve seat 7.

A teeming spout, denoted generally by 8, is connected to the bottom of the ladle l and comprises a tapered body member 9 having therein a tapered insert it) composed of a heat resistant material having high thermal shock resistance. The member 9 has on its uppr end a flange portion 11 which serves as a support by which clamp 12 may hold the spout 8 securely to the bottom of the ladle 1. By having the member 9 tapered, the insert ll) is rigidly held in place.

We mount our novel cooling head, denoted generally by 20, on the bottom end of the spout 8. The cooling head which is made of aluminum, copper or other material having high heat conducting properties, is held to the spout 8 by means of

braces

21 and 22. The bottom -39 portion 23 of the cooling head has thereon

annular flanges

24, 25, 26 and 27 which provide additional eifective cooling area. The interior of the cooling head 20 is hollow so that a cooling medium, for example water, may be circulated therein. The cooling medium may enter by means of a conduit 29 and leave by means of a similar conduit, not shown.

A mold 30 in which molten metal from ladle 1 is to be teemed, is situated beneath the spout 9. The mold may be Water-cooled and has therein passages 31 through which water may circulate, the water entering and leaving the mold through conduits 32 and 33. Itis obvious that the cooling effect on "the molten metal in the mold by the side walls of the mold alone will be greater at the edges of the mold than at the center resulting in uneven cooling of the complete upper surface of the molten metal. In order to compensate for this cooling effect of the side walls, the outer periphery of the bottom portion 23 of the cooling head is curved upwards to reduce the cooling effect on the molten metal by the cooling head near the side walls.

To further insure that the complete upper surface of the molten metal in the moldis cooled evenly, the elevator is mounted on a turn-table 41. By rotating turntable 41 during the teeming process about eccentrically mounted cooling head, that area of molten metal in the mold immediately below the spout 8 will be progressively overlapped by the portion of the cooling head trailing the spout. This results in that the complete upper surface of the molten metal in the mold will be cooled in varying amounts by the cooling head.

We propose to teem the molten metal from the ladle 1 into the mold 30 so that as the molten metal runs down the spout 8 into the mold 30 it will continuously form an exposed upper surface of molten metal in the mold. This surface is cooled by the cooling head and side walls so that it solidifies substantially as soon as it is formed, the solidification occurring progressively upwards in thin, flat, parallel, superimposed, infinitesimal layers.

It is possible to control the temperature of the molten metal at the lower end of the spout by the use of our novel cooling head so that the molten metal emitted from the spout into the mold is substantially at fusion, or freezing, temperature. The molten metal will not freeze or solidify in the spout because for molten metal to solidify, 120 B.t.u.s must be removed from each pound of molten metal at its temperature of fusion, assuming that the metal is a steel. Thus, if the temperature of fusion for a particular steel is 2700 F the molten steel is emitted from the spout into the mold at, or slightly above 2700 F. While at the same time removing evenly from the upper surface of the molten metal in the mold 120 B.t.u.s per pound of molten metal by means of the cooling head and side walls.

The rate at which the upper or exposed surface of molten metal is cooled may be eifectively regulated by Varying the distance between it and the cooling head.

As the molten metal is teemed into the mold, it is necessary that the cooling head he moved axially relative to the met-a1 being solidified in the mold so that it is at all times at a desired distance above the exposed upper surface of molten metal being continuously formed in the mold. This can be done either by moving the ladle relative to the mold or moving the mold relative to the ladle. In the drawing I have shown elevator means 40 for moving the mold relative to the ladle.

The outer periphery of the cooling head 20 may be provided with a seal 50 so that the cooling head is in sealing contact with the inner sidewalls of the mold. If acompresed gas is injected into the space above the molten metal in the ladle 1 and the plunger 6 is raised so allowing molten metal to flow into the mold 359, it is obvious that the presure exerted on the upper surface of the molten metal in the mold will be greater than that due to the liquid head of the molten metal alone. Thus, if 200 lbs. 'per sq. in. of air pressure is injected into the 4. ladle, there will be a pressure exerted on the exposed upper surface of the molten metal being continuously formed in the mold of at least 200 lbs. per sq. in. plus the pressure due to the liquid head of the molten metal in spout 3 and ladle 1, plus the pressure of gases evolved from the molten metal as it fuses in the mold. The summation of these pressures tends to preforge the molten metal in the mold to produce an ingot which has preforged properties.

Because when using our novel cooling head, molten metal solidifies in a mold in layers of infinitesimal thickness, the necessity of including a hot top portion to eliminate shrinkage cavities is eliminated. Also the necessity of using a big end up mold in order to have progressive cooling is eliminated by the use of our novel cooling head since the cooling can be progressively controlled in a mold of uniform cross section. The resultant ingots produced by the use of our cooling head will be of uniform cross section, will not have the heretofore hot top section which had to be cut away, and will have a superiority of orientation of inclusions and a reduced dendritic pattern because the time of fusion is minimized. A further advantage of utilizing a cooling head according to our invention is that the effects of molten metal splashed on the side walls of the mold and resultant pitting of the mold are extinguished.

Having thus described the invention what we claim as new and desire to secure by Letters Patent is:

1. Apparatus for casting molten metal comprising a ladle for containing said molten metal, a discharge spout connected to said ladle through which said molten metal may be teemed, an open-sided mold for receiving said molten metal from said ladle, a cooling head on the end of said spout opposite said ladle, passages in said cooling head through which a cooling medium may circulate, and moving means for maintaining said head at a substantially constant distance above the bath of said molten metal as it is poured into said mold.

2. Apparatus according to claim 1 wherein the bottom portion of said cooling head adjacent said inner side wall of said mold curves upward from the bottom of said mold.

3. Apparatus according to claim 1 wherein said moving means comprises an elevator for moving said mold relative to said'head.

4. Apparatus according to claim 1 wherein said cooling head is mounted eccentrically on said spout and having in addition rotation means for rotating said mold about.

said cooling head.

5. Apparatus according to claim 1 including means to seal said cooling head to the side walls of said mold.

6. Apparatus for casting molten metal comprising a ladle for containing said molten metal, a discharge spout connected to said ladle through which said molten metal may be teemed into an open mold, a cooling head on the end of said spout opposite said ladle sealingly engaging the side walls of said openmold and passages in said cooling head through which a cooling medium circulates.

References Cited in the file of this patent UNITED STATES PATENTS 319,779 Billings June 9, 1885 770,130 Trotz Sept. 13, 1904 1,092,663 Pacher Apr. 17, 1914 1,603,662 Coates Oct. 19, 1926 1,777,657 Stay et al. Oct. 7, 1930' 2,197,660 Glunz et al Apr. 16, 1940 2,385,206 Hopkins Sept. 18, 1945 2,517,931 Rossi Aug. 8, 1950 2,793,410 Junghans et a1 May 28, 1957 2,958,913 Schaefer Nov. 8, 1960 FOREIGN PATENTS 275 Great Britain 1861 174,761 Great Britain Mar. 19, 1923 276,210 Great Britain Aug. 25, 1927 748,709 Great Britain May 9, 1956"

Claims

1. APPARATUS FOR CASTING MOLTEN METAL COMPRISING A LADLE FOR CONTAINING SAID MOLTEN METAL, A DISCHARGE SPOUT CONNECTED TO SAID LADLE THROUGH WHICH SAID MOLTEN METAL MAY BE TEEMED, AN OPEN-SIDE MOLTNE FOR RECEIVING SAID MOLTEN METAL FROM SAID LADLE, A COOLING HEAD ON THE END OF SAID SPOUT OPPOSITE SAID LADLE, PASSAGES IN SAID COOLING HEAD THROUGH WHICH A COOLING MEDIUM MAY CIRCULATE, AND MOVING MEANS FOR MAINTAINING SAID HEAD AT A SUBSTANTIALLY CONSTANT DISTANCE ABOVE THE BATH OF SAID MOLTEN METAL AS IT IS POURED INTO SAID MOLD.