US2380109A - Method and apparatus for casting metal bodies - Google Patents

Description

55F033 HSTBTBHCB m ly 945. R. K. HOPKINS 2,330,109

METHOD AND APPARATUS FOR CASTING METAL BODIES Filed July 29, 1943 fxqi.

INVENTOR Ruben f1. Hop/aims ATTORNEY Patented July 10, 1945 METHOD AND' APPARATUS FOR CASTING DIETAL BODIES Robert K. Hopkins, New York, N. Y., assignor to The M. W. Kellogg'Company, New York, N. Y., a corporation of Delaware Application July 29, 1943, Serial No. 496,665

14 Claims.

The present invention relates to the art. of casting metals.

One object of the present invention is to provide a new and improved method and apparatus for producing a, sound, densecasting.

Another object is to provide a new and improved method and apparatus for promoting progressive solidification of the cast metal in a mold.

A further object is to provide a new and improved method and apparatus for controlling the rate of deposition of cast metal in a mold.

Another object is to provide a new and improved method and apparatus for continuously hot-topping cast metal in a mold. The term hot-topping is applied to the procedure in which a comparatively small pool of the deposited metal is maintained in highly fluid superheated condition on the solidifying metalbeneath it so that said pool of metal will readily feed the shrinking metal below it to prevent shrinkage defects and, furthermore, since crystallization takes place from a comparatively small volume of molten metal, segregation will not take place, also, the presence of said pool of metal prevents or relieves all shrinkage stresses.

As another feature, the rate of pouring of the cast metal into the mold through the nozzle is automatically controlled to render said rate substantially uniform, and substantially equal to the rate of solidification of the metal in said mold.

As another feature, while the molten metal is teeming into the mold, the deposited metal and the current discharge nozzle, or other electrode which may be employed, are moved relatively apart substantially at uniform rate to maintain the intervening current discharge gap substantially constant in length, and the rate with which the molten metal is deposited into the mold is automatically controlled in accordance with variations in the length of said gap to maintain said gap substantially constant in length and to assure flow of molten metal in said mold at substantially constant rate.

Various other objects, features and advantages of the invention will be apparent from. the following particular description, and from an in. spection of the accompanying drawing, in which Fig. l is a vertical section somewhat diagraminatic showing an apparatus which embodies the present invention, and which may be employed to carry out the method of the present invention; and

Fig. 2 is a transverse section of the mold taken on line 2-2 of Fig. 1.

Referring to the drawing, there is provided a mold In which may be of refractory material, but which is shown of suitable metal such as copper, jacketed-to permit circulation of a cooling liquid in heat exchange relationship therewith. This mold H) has a cross-sectional Shape corresponding to the desired crossseotional shape of the article to be cast, and is shown for the purpose of illustration cylindrical to form ingot of corresponding shape. The molten metal to be cast is poured into the mold in through a basin H which has a nozzle l2 extending into the mold. Basin H and nozzle l2 are preferably refractory lined as shown. The lower portion of nozzle l2 includes an annular member l2 from whose end the electric current is discharged. Member i2 is preferably made of copper and hollowed as shown for circulation of a cooling medium therethrough to prevent its destruction in use. The electric current connection is made directly to member l2, aS shown, and an insulation ring is interposed between the upper end of member l2 and the lower end of the metal lining of basin I l to electrically separate them. The refractory lining of nozzle l2 extends substantially to the end, of member i2 to electrically separate member I2 from the teeming metal. A floating layer of flux i3 is desirably maintained in the mold l0, and. the lower discharge end of the pouring nozzle I2 is submerged in said flux layer above the surface of the deposited metal.

The flux '3 may be of suitable composition which has the proper electrical and refining characteristics. Flux comprising silicates or components of silicates, such as manganese silicate, calcium silicate, aluminum silicate, glass and the like, has been found suitable for this purpose. This flux l3 serves to refine the deposited material in the mold, protect it against atmospheric contamination and also serves to prevent rapid dissipation of the heat from the top surface of the deposited metal.

As the cast metal is teemed into the mold Hi, the upper portion of the deposited metal is maintained in highly fluid superheated condition by the heating action of an electrode. In accordance with certain aspects of the present invention, member l2 of the pouring nozzle I2 serves as the electrode to discharge heating current across a 'gap l5 intervening between the lower discharge end of member l2 and the upper surface of the deposited metal. Connections IE to member l2, as above explained, and for example to the metal mold I 0 from a power source I1, provide the necessary electrical tie-up to discharge current across the gap 15. The current discharged. is so chosen that the heat generated by it when correlated with the heat imput from the molten metal poured into the mold and the heat removed from the mold by all causes, will be proper to continuously maintain a comparatively small pool ll; of highly fluid superheated metal on the solidifying metal below it. The pouring rate will also be so adjusted that it is substantially equal to the rate of solidification. With these conditions established and maintained, the poured metal will solidify progressively upwards and because of pool l8, continuous hot-topping will take place and all defects due to shrinkage, segregation and stresses obviated.

In the operation of the apparatus so far described, the metal,.as above stated, is poured in the mold H1 at a rate substantially equal to the rate of solidification of the deposited metal in said mold. As the cast metal is poured in the mold to, and the level of the deposited metal rises in the mold, said mold is moved gradually downwardly at a substantially uniform rate to maintain the current discharge gap l5 substantially constant in length and characteristics. The current discharge across the gap 15' generates enough heat to maintain the supernatant body l8 of highly fluid superheated metal substantially constant in volume throughout substantially the entire mold pouring operation.

The cast metal is poured into the basin! 1 from a suitable receptacle, such as a conventional furnace 22 having a discharge spout 23. If desired, the furnace 22 may supply the base metal in molten condition, and alloying materials may be added to this base metal in solid or molten form in the upper larger end of the basin ll. Also, if desired, deoxidizing materials may be added to the metal in the upper receiving end of the basin H.

The molten metal is teemed from the furnace 22 at a controlled rate to deposit metal in the mold ll! through the nozzle l2 at a substantially constant rate equal substantially to the rate of solidification of the deposited metal. In accordance with certain aspects of the present invention, this control is effected automatically in accordance with the length of the current discharge gap IE, to maintain said gap substantially constant in length. For that purpose, the voltage drop across this gap I5 is employed as a control factor and the furnace 22 has a pivot support 24 or may have trunnion support, and is automatically tilted about this support according to this voltage drop.

When the rate of deposition of the cast metal in the mold i9 is reduced beyond a predetermined amount, this rate reduction is reflected in the lengthening of the gap 15, and in an increase in voltage drop across said gap. This change in voltage drop is automatically translated into pivotalmovement of the furnace 22 clockwise (Fig. 1) about its pivotal support 24. This increases the rate of discharge from the furnace 22, and the resulting increase in the static head of the molten metal in the basin H causes an increase in the rate of deposition of the metal in the mold 10. When the rate of deposition of the cast metal in the mold is increased beyond a predetermined amount, the corresponding shortening of the gap l5 causes decrease in voltage drop across said gap and tilting of the furnace 22 counterclockwise (Fig. 1) about its pivot support 24. This reduces the rate of discharge from furnace 22 and thereby reduces the rate of deposition of cast metal in the mold 10.

By the control operations described, the rate of deposition of cast metal in the mold I0 is maintained substantiallyconstant and substantially equal to the rate of solidification of the deposited metal in said mold, the current discharge gap is maintained substantially constant in length, and the volume of molten supernatant feeder metal 18 is maintained substantially constant.

The furnace 22 may be tiltably controlled automatically in any suitable manner from. a control device 30. For example, a crank 3| may be provided fixed at one end on a crank shaft 32, and pivotally connected at its other end to a link 33 pivotally secured to the furnace 22. A reversible motor 34 drives the crank shaft 32 by means of a reduction gearing 35 and a worm and worm wheel drive 36. This motor 34 is controlled from the device 30 to cause rotation of said motor in either direction according to the voltage drop across the gap 15.

The control device 30 may be of any suitable type, the arc control devices used to control the feed of electrode feed motors in the arc welding and electric furnace arts are suitable. These devices are well known and need not be described here. As shown, the power leads from a source of power 31, for motor 34, pass to device 30: power leads pass from device 30 to motor 34. Leads are also shown leading from basin II to device an and from mold ID to device 30.

Instead of controlling discharge into the basin II by tilting the furnace 22, as far as certain aspects of the invention are concerned, flow from the furnace or any other reservoir which may be employed may be controlled by means of a valve or stopper regulatingflow from said reservoir.

The casting method described may be applied to either still casting or continuous casting. By still casting is meant a process in which the deposited metal in the mold is completely solidified before it is withdrawn from the mold. By continuous casting is intended a process in which'the solidified metal is removed or with drawn from the mold while the upper portion of the deposited metal is still in molten condition, to form a casting of either finite or indefinite length.

For still casting, the mold I0 may be supported on'a stool, which in turn is supported on a platform, and the mold may be moved downwardly at substantially constant rate during pouring operations, as for example by means of a screw feed drive to said platform operated from a constant speed motor.

In the specific form shown, the apparatus is employed to carry out a continuous casting process. For that purpose, the mold to may be of split sectional construction as shown, and may comprise a series of mold sections 40 tubularly stacked and diametrically split into complemental segments 4|. These mold segments 44 may be of refractory material or of metal construction as shown, and may be solid or hollow. If liquidcooled metal mold segments 4| are employed, these may be jacketed to receive the cooling medium, or may be solid, and the cooling medium circulated in any suitable manner in heat transfer relationship with the solid segments. In the specific form shown, each of the mold segments 4| is of hollow metal construction, and has an inlet 43 and an outlet 44 for the cooling medium. This inlet 43 and outlet 44 may be connected to respective hose or tubings 45 for circulating Memes/ana am; ;.3,

the cooling medium to and from the mold segments 4|. These hose or tublngs 45 may be flexible to permit movement of the mold sections 48, and may be detachably secured to the connections 43 and 44 on the mold segments M.

The ingot A formed by the casting operation described can be continuously withdrawn away from the mold l during pouring and hot-topping operations by means of pinch rolls 48 en gaging said ingot and driven at substantially constant speed by any suitable means, as for instance from a motor and gear drive to one of said rolls.

To make the casting operations prolonged or continuous, the mold lllis moved downwardly with the solidified ingot during pouring and when the solid cast metal embraced by the lower mold section 40 is cooled to thedesired extent, this section 43 is removed from the ingot A, and this same mold section or another mold section is mounted on top of the tubular mold stack.

The frictional attachment between the ingot A and the mold I0 is suflicient to hold said mold against downward relative gravitational movement with respect to said ingot. However, if the mold ID is too heavy to prevent this relative movement, or the cooling of the cast metal proceeds to a point where said metal is shrunk loose from said mold, then suitable mold supporting means may be provided to prevent slippage of said mold along the ingot.

The electrical connection 16 may be attached to one of the upper mold segments 4| as shown and this connection moved to other segments as required. However, in practice it would be preferred to employ a contact arrangement that will maintain all of the segments that are in mold forming position constantly in the electric circuit.

If desired, the opposed mold segments M instead of being bolted together as shown, may be secured to a pair of opposed conveyors, and the opposed mold segments may be brought together into tubular relationship at the top and separated at the bottom successively and progressively by said conveyors, as shown in my copending application Serial No. 485,956, filed May 5, 1943.

As many changes can be made in the above method and apparatus, and many apparently widely different embodiments of this invention can be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A method of casting which comprises depositing molten metal into a mold through a substantially non-conductive nozzle provided with a conductive external lower portion, and discharging current across a gap between said lower'portion and the upper surface of the deposited metal while metal is being deposited in said mold, to

' heat the upper portion of the deposited metal and maintain it continuously in fluid condition to feed the solidifying metal below.

2. A method of casting which comprises depositing molten metal into a mold through a substantially non-conductive nozzle having a conductive external lower discharge end submerged in a floating layer of flux in said mold, and discharging current across a gap between said dis charge end and the upper surface of the depos ited metal while metal is 'being deposited in said mold, to heat the upper portion of the deposited molten to progressively hot-top the deposited metal continuously as its level rises with respect to the mold.

4. A method of casting which comprises depositing molten metal into a mold through a substantially non-conductive nozzle provided with a conductive external lower portion and at a rate substantially equal to the rate of solidification of the deposited metal in said mold while said conductive lower portion is submerged in a floating layer of flux in said mold, and discharging current across a gap between said conductive lower portion and the deposited metal while metal is teeming from said nozzle to heat the top portion of the deposited metal and maintain it sufiiciently molten to progressively hot-top the deposited metal continuously as its level rises with respect to the mold.

5. A method of casting which comprises depositing molten metal into a mold through a substantially non-conductive nozzle. provided with a conductive external lower portion, discharging current across a gap between said lower portion and the deposited metal while metal is teeming from said nozzle to maintain the top portion of the deposited metal in molten state. moving the nozzle and the body of deposited metal relatively apart while metal is being de posited in said mold, and simultaneously controlling the rate of discharge of the metal fromsaid nozzle to maintain said gap substantially constant in length.

6. A method of casting which comprises depositing molten metal into a mold through a substantially non-conductive nozzle provided with a conductive external lower portion, discharging current across a gap between said lower portion and the deposited metal while metal is teeming from said nozzle to maintain the top portion .of the deposited metal in molten state, moving the. nozzle and the body of deposited metal relatively apart while metal is being deposited in said mold, and simultaneously con trolling the rate of discharge of the metal from said nozzle in accordance with the voltage drop across said gap to maintain said gap substantially constant in length.

'7. A method of continuous casting which comprises continuously depositing molten metal into a mold through a substantially non-conductive nozzle provided with a conductive external lower portion, withdrawing the solidified 'rhetal from said mold, and discharging current across a gap between said conductive lower portion and the deposited metal while metal is teeming from said nozzle to maintain the top portion of the deposited metal in molten state as the solidified metal is being withdrawn from said mold.

8. A method of continuous casting which comprises continuously depositing molten metal into a mold through a substantially non-conductive nozzle provided with a conductive external lower portion, withdrawing the solidified metal from said mold, discharging current across a gap be-- tween said conductive lower portion and the deposited metal while metal is teeming from said nozzle to maintain-the top portion of the deposited metal in molten state as the solidified metal is being withdrawn from said mold, and simultaneously controlling the rate of discharge of the metal from said nozzle to maintain said gap substantially constant in length.

9. A method of continuous casting which comprises continuously depositing molten metal from an outside source into a, mold through a substantially non-conductive nozzle provided with a conductive external lower portion having its lower discharge end submerged in a floating layer of flux in said mold, withdrawing the solidified metal from said mold while the top portion of the deposited metal is still fluid, discharging current across a gap submerged in said flux between said conductive lower portion and the deposited metal while metal is teeming from said nozzle to maintain the top portion of the deposited metal in molten state, and simultaneously controlling the rate of discharge of the metal from said nozzle in accordance with the voltage drop across said gap to maintain said gap substanfiially constant in length.

10. A casting apparatus comprising a mold, a nozzle made of substantially non-conductive material extending into said mold to deposit cast metal in said mold, said nozzle including a metallic member encircling the lower end thereof, and means for discharging current across a gap between said metallic member and the body of deposited metal to heat the upper portion of said metal and maintain it in molten condition for feeder purposes.

11. A casting apparatus comprising a mold, a nozzle made of substantially non-conductive material extending into said mold to deposit cast metal in said mold, said nozzle including a metallic member encircling the lower end thereof, means for discharging current across a gap be tween said metallic member and the body of deposited metal to heat the upper portion of said metal and maintain it inmolten condition for feeder purposes, means for moving said nozzle and the body of deposited metal relatively apart as metal is being deposited in said mold to maintain said gap substantially constant in length, and means for varying the rate of discharge from said nozzle automatically in accordance with changes in the length of said gap to maintain said gap substantially constant in length.

12. A casting apparatus comprising a mold, a

nozzle made of substantially non-conductive material extending into said mold to deposit cast metal in said mold, said nozzle including a metallic member encircling the lower end thereof, a receptacle for feeding cast metal into said nozzle, means for discharging current across a gap between said metallic member and the bow of deposited metal to heat the upper portion of said metal and maintain it in molten condition, means for moving the body of deposited metal away from said nozzle as metal is being deposited into said mold to maintain said gap substantially constant in length, and means for varying the rate of discharge from said receptacle automatically in accordance with changes in the length of said gap to maintain said gap length substantially constant.

13. A method of casting which comprises depositing molten metal from a tiltable molten metal containing receptacle into a mold through a substantially non-conductive nozzle provided with a conductive external lower portion, dis charging electric current across a gap between said conductive portion and the surface of the deposited metal while metal is teeming from the nozzle to maintain the top portion of the de posited metal in a highly heated condition, maintaining said gap and the deposited metal beneath the surface of a depth of protective flux, effecting relative movement between the nozzle and the deposited metal, and simultaneously controlling the tilting of said container in accordance with the voltage drop across said gap to maintain said gap substantially constant in length.

14. A casting apparatus comprising a mold, a nozzle made of substantially non-conductive material extending into said mold to deposit cast metal into said mold, said nozzle including a. metallic member encircling the lower end thereof, a tiltably supported receptacle for feeding cast metal into said noule for passage into said mold, means for discharging electric current through a gap between said metallic member and the surface of the metal deposited in the mold to supply heat to the upper portion of the deposited metal, means for efiecting relative movement between the metal in the mold and said nozzle to maintain said gap substantially constant, and automatic means for tilting said receptacle in accordance with changes in length of said gap to control the rate of discharge of metal from said receptacle as required to maintain the length of said gap substantially constant.

ROBERT K. HOPKINS.

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