US2693624A - Continuous casting of metals - Google Patents

Description

Patented Nov. 9, 1954 CONTINUOUS CASTING OF METALS Ernest R. Corneil, Stamford Centre, Ontario, Canada, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application September 28, 1951, Serial No. 248,813

9 Claims. (Cl. 22-572) This invention relates to the continuous casting of metals to form elongated shapes and more particularly to the continuous casting of light metals and low melting metals, one example of which is sodium.

Sodium is one of the softest and lowest melting of the metals and yet heretofore there has not been a satisfactory method or apparatus for continuously casting sodium shapes, except for the extrusion of small quantities of sodium wire or ribbon for laboratory operations. Attempts to continuously produce smooth surfaced sodium bars on a commercial scale by methods generally used for extruding metals such as lead, aluminum or the like, have proved impracticable, because of certain peculiar properties of sodium. Sodium has a marked ability to wet and cling to the surface of structural metals, such as steel, aluminum, brass and the like and therefore tends to stick to the walls of the die or extrusion chamber. Such sticking of the sodium to the die or extrusion chamber wall cannot be overcome by an increase of the extrustion pressure, since the application of pressure increases the hardness and the melting point of the sodium, thus increasing the blocking effect of the adherence of the metal. Such blocking then can only be overcome by heating the die or extrusion chamber wall to a temperature above the melting point of sodium.

Sodium is commonly marketed in the form of molded i shapes such as 1 pound cylindrical molds or larger rectangular bricks. The molding of such sodium shapes as heretofore practiced is largely a manual process and hence relatively expensive and also somewhat hazardous.

The herein described casting process, in which a bar or cylinder is continuously produced and may be cut to de sired lengths to provide marketable shapes, markedly decreases molding costs, contamination'by oxidation and operation'hazards.

In casting other light metals, e. g., aluminum, in elongated shapes or ingots, the shrinkage of the cooling metal forms a depression or pipe in the upper end of the ingot.

This has to be cut oh and reworked. Also, the inclusion of air and consequent contamination of the metal and loss by oxidation cannot be prevented except at considerable expense. A relatively inexpensive, continuous process for casting or molding elongated shapes such as bars or rods without exposure of molten metal to air and without pipe formation is desirable in the fabrication of light and low melting metals such as aluminum, magnesium, lead, tin and the like.

An object of the invention is to provide an apparatus for the continuous casting of metals in the form of bars or the like which can be cropped to desired length without interrupting the process. Another object of the invention is to provide an apparatus for the casting of metals which eliminates the pipe caused by shrinkage of the metal on freezing, and hence eliminates the cropping of a section of each casting and its reworking due to such pipe. Still another object is to provide anapparatus for producing a smooth uniform finish and exact dimensions on cast parts. Another object is to eliminate the necessity for a large number of molds and expensive machinery normally required in the casting of metals and the maintenance involved therewith. Another object is to provide an apparatus for continuous casting easily oxidized metals out of contact with air and preliminarily cooling such castings prior to exposure to the air. Still another object is an apparatus for casting metals which will eliminate the exposure of operating personnel to the hazards contingent to the pouring of molten metal. A furtherobject is an.

apparatus to reduce drastically the labor involved in the casting processes. Another object ofthe present invention is to provide an improved apparatus for the melding of sodium. Still other objects of the invention will be apparent from the following description.

One form of the apparatus of this invention is illushated by the appended 'drawing, which is in-part a vertical cross-section. The apparatus consists essentially of a shape-defining or casting chamber 1 connected with a pump 2. The shape-defining chamber as shown is formed of two cylindrical sections 3 and a conicalend section 4. The two cylindrical sections and the conical section are c'oaxially arranged and fastened together by means of bolts, not shown. Each section is provided with a cooling chamber 5 provided with outlet and inlet pipes 6 for the circulation of cooling liquid. Each cooling jacket is provided with helical bafiles 7 in a conventional manner. The interior of the cylindrical sections 3 are lined with a layer 8 of aporous cast iron; Conduits 9 are provided to feed a lubricating oil to the porous castiron lining 8. Conical section 4 is of such shape that it is the frustrum of a right cone of such shape that the angle between a side of the cone and a line parallel to the axis thereof is about 7 degrees.

Pump 2 as shown in the drawing is the light metal pump which is described and claimed in my copending patent application Serial Number 78,051, filed February 24, 1949, now abandoned. This pump has a reciprocating piston 10 which passes through a packing gland 11 and an oil chamber 12 which is filled with lubricating oil 13. The piston is reciprocated by a conventional cam and crosshead arrangement 14 which is powered by a motor, not shown. The pump is provided with a single ball check valve assembly which consists of sleeve 17, ball 15 and spring 19 which holds the ball against the end of sleeve 17. Inlet pipe 16 is provided to lead molten sodium into the pump. Outlet pipe 18 is connected to the conical section of the extrusion chamber 1. The drawing shows the piston in its position at the end of the upward (backward) stroke. On the downward (forward) stroke the piston enters sleeve 17 in which it has a close fit and forces sodium trapped in the interior of the sleeve past the ball check valve, thus forcing an' increment of sodium through outlet pipe 18 into the conical-section of the extrusion chamber. When piston 10 moves on its upward stroke, the check valve prevents reverse How and a vacuum is created within the sleeve. As the piston moves out of the upper end of the sleeve, sodium rushes into the evacuated interior of the sleeve 17. Each stroke of the pump forces into the extrusion chamber a definite volume of liquid sodium, determined by the diameter of the sleeve 17 and the lengthv of the piston stroke therein.

To start the continuous molding of sodium with the above-described apparatus I first, place within the extrusion chamber a solid mandrelmade offiwood or other convenient material which is tapered atone end and of a size to make a close sliding fit with both the cyl' and conical sections. The pump is then operatedfto end of the conical section, while cooling oil is circulated through the cooling jackets and lubricating oil is fed to the porous lining. The first increment 'of sodium entering the chamber, caused by the downward stroke of piston 10 of the pump, pushes against the end of the mandrel thus forcing it away a short distance from the inside wall of the conical section. This creates a space between the tapered end of themandrel and the wall of the conical section and'a thin layer of molten sodium instantly fills this space where it is rapidly chilled and solidified to form a conical shell of solid sodium. The second downstroke of thepump forces in a second increment of sodium which further pushes back themandrel and also the thin shell of solid sodium formed by the solidification of the first increment. As the strokes of the pump continue, to incrementally introduce the molten metal, each added increment thus forms a relatively thin conical shell of solidified sodium; and at each stroke of the pump such shell is forced outwardly from the conical section to provide a space for the next increment which is similarly solidified. The pressure of the incoming increments of sodium thus continuously move the solid sodium through the cylindrical sections, pushing the mandrel ahead until it falls out of the chamber. Each succeeding conical shell or layer of solidified sodium adheres tightly to the preceding shell so that the mass of sodium passing through the cylindrical section of the chamber is a substantially homogeneous, solid, cylindrical bar of sodium. The emerging cylindrical bar may be cut into any desired lengths for convenient handling.

From the above description it will be seen that at the point where liquid sodium is applied to the interior surface of the mold, namely, in the conical section, there is little or no pressure of the sodium against the mold walls and hence a substantial absence of forces which would tend to make the sodium stick to the conical walls. Each increment of sodium, by forcing the solid mass in an axial direction, pulls the sodium away from the conical section wall without causing the sodium to slide against it, thereby preventing sticking of the metal to the conical section wall. In the cylindrical section, there is little or no pressure of the solidified sodium against the wall; and any tendency to stick to the wall is eliminated by the lubricated wall surface, namely, the porous cast iron lining 8 fed with a suitable lubricant such as a light or medium lubricating oil. The extruded bar may have a light film of oil, the amount depending upon the amount and viscosity of the lubricating oil fed to the porous lining. Using a lubricating oii such as S. A. E. No. 20, the amount of oil on the surface of the extruded rod is practically negligible.

The temperature of the incoming sodium, the rate of sodium input into the extrusion chamber and the amount of cooling applied to the extrusion chamber are so regulated that the sodium enters the conical section chamber in the liquid state and each increment is rapidly chilled to the solid state so that it is substantially completely solidified before the next increment enters. This relationship between the rate of sodium input and rate of cooling is essential to obtain the effects described above, and particularly to prevent sodium from sticking to the walls of the conical section. Most commercial grades of sodium contain a small amount of calcium which is in solution in the liquid sodium but which has a tendency to crystallize out at temperatures around 100 to 110 C. In order to produce a homogeneous extruded bar of sodium from such commercial sodium it is desirable that the temperature of the incoming liquid sodium should be not lower than about 110 and preferably at 120 C. or higher.

As a specific example of the invention, a cylindrical sodium bar, approximately 2 inches in diameter was continuously cast from the apparatus illustrated by the appended drawing. The conical section was 6 inches long and its diameter was about 1 inch at the small end. The cylindrical portion was about 12 inches long (two 6 inch sections). The pump was fed from an insulated, heated tank filled with molten sodium of a commercial grade, the tank being connected with the inlet pipe 16 of the sodium pump by a short length of iron pipe. The tank was located a short distance above the pump inlet, so that the sodium would flow from the tank to the pump by gravity. The temperature of the sodium in the tank was maintained at 170 to 180 C. Considerable cooling of the sodium occurred during the passage through the pump, so that the sodium left the pump at'a temperature of about 120 C. The pump was operated at a speed of 96 strokes per minute which resulted in delivering 1.19 pounds per minute of sodium in increments of about 0.0124 lb. (5.6 grams) each. Oil was circulated through the cooling jackets at a rate of 8.75 pounds per minute. The temperature of the oil fed to the cooling jackets was 61 C. The oil left the cooling jackets at a temperature of 63 C. A motor grade of lubricating oil (S. A. E. No. 20) was fed to the porous iron lining at a rate of about 30 cc. per hour. A smooth, cylindrical, substantially homogeneous bar of sodium continuously emerged from the machine. The emerging sodium was silvery white and developed a pinkish oxide coating after a few minutes of exposure to the air. The extruded bar was readily cut into any desired lengths by forcing a knife blade across the end of the last cylindrical section.

Various modifications may be made in the method and apparatus described above without departing from the spirit and scope of my invention. The length of the cylindrical portion of the above described casting chamber may be varied greatly, and it is possible to operate with a very short cylindrical section. A cylindrical section of reasonable length, at least about the length of the conical section, is preferred, for reasons of safety. Without such cylindrical section, there exists the possibility of an occasional spurt of molten metal being forced to the outside. The cylindrical section will prevent any such spurts of molten metal from reaching the exterior before freezing. The cylindrical section may be of any desired length, but generally there is no advantage in making it more than twice the length of the conical section.

A further advantage of the cylindrical section, particularly in the case of a metal having a high heat conductivity, is that the cooling applied to the cylindrical section removes heat from the solid bar part therein and thereby utilizes the solid mass of metal in the conical section as a cooling means, increasing the amount of cooling on each successive increment of molten metal fed into the extrusion chamber.

The combination of the porous lining and the liquid lubricant fed thereto assist in the above described function of the cylindrical section in cooling the cast bar. The liquid emerging from the porous lining establishes thermal contact between the cast metal and the cooled walls of the apparatus. Also, if desired, the amount of liquid fed to the porous lining and the porosity thereof may be adjusted so that relatively large quantities of liquid are contacted with the cast bar and thereby cool it. In place of a porous lining such as porous cast iron, I may utilize other foraminous forms, such as a nonporous lining provided with slots or perforations for the inflow of liquid. By making the diameter of the cylindrical section a little larger than the dimensions of the cast bar, I provide a passage for such liquidalong the sides of the bar to thc outside; and in that manner I may provide practically any desired rate of cooling by the inflow of liquid through the porous or perforated walls. The inflowing liquid thus has the function of both lubricating the emerging bar and of cooling it. In the casting of metals substantially non-reactive with water, e. g., aluminum, tin or lead, such cooling and lubricating liquid may be water or an aqueous solution.

The cross-sectional shape of the casting chamber also may be modified as desired, to cast bars of different crosssectional shapes. For example, instead of a cylindrical section one with a square or rectangular shape may be utilized, in which case, in place of a conical section, a corresponding pyramidal section is employed. Still other cross-sectional shapes can be used to produce extruded bars having curved or straight sides or combinations of curves and straight sides. In a casting chamber made in accordance with my invention, the inner walls thereof flare or taper outwardly from the port where the molten metal is introduced; and the flaring or tapered section is joined to a section, the walls of which are parallel to the axis of the flaring or tapered section. Also, the inner walls of the tapered (e. g., conical) section are flared out in such manner that the acute angle between the walls'and a line parallel to the longitudinal axis is from about 2 to 30 degrees. If this angle is less than about 2 degrees there is some tendency for the metal to stick to the walls. An angle greater than about 30 degrees requires a correspondingly shorter tapered section, which becomes difficult to properly cool so as to quickly freeze successive increments of molten metal introduced without freezing metal in the conduit leading from the pump. In general, I prefer that this angle should not exceed about 12 degrees.

The herein described method and apparatus for casting metal are not restricted to the molding of sodium but may be applied to the continuous casting of other light metals and low melting metals, for example, other alkali metals such as lithium, potassium, cesium and rubidium; aluminum, tin and lead; and alloys containing a preponderant amount, for example, or more, of such metals.

The interior surface of the tapered section should be reasonably smooth, for example at least of a smoothness equivalent to that of a machine finish on steel.

Although not essential, for the casting of sodium and some other metals, the provision of a porous lining lubricated with any liquid having lubricating properties which does not chemically react with the solidified metal is preferred, panicularlyin the cylindrical .or equivalentsection .of the. casting chamber, If :desired,.-such lubricated surface 1.01 lining also may be. provided in .the conical or equivalent section ofthe casting chamber.

The degree of cooling applied, or in other wordsthe temperature of the interior surfaces of the chamber, particularly at the tapered inlet end, may be varied over a very wide range, as may be desired. The only essential requirement is that the degree of cooling be suflicient so that each incoming increment of molten metal is substantially completely solidified before the next increment is introduced. The rate of introduction of successive increments of molten metal and the amounts of such increments likewise may be varied over a wide range limited only by the size of the tapered section and rate of cooling applied. The amount of each increment of molten metal introduced is limited by the size of the casting made and should be not more than suflicient to move the cast bar forward a short distance, so that the resulting layer of molten metal to be solidified is relatively thin and so as to avoid flowing molten metal through the tapered section into the straight-sided section in any substantial amounts. The limiting amount can be expressed in terms of the distance the cast bar is moved ahead by the addition of each increment. The preferred amount is that which moves the cast bar ahead a distance equal to about 2 to of its smallest crosssectional dimension (the bar diameter when the cast bar is cylindrical). Preferably the distance should be not more than 5% of that dimension (e. g., of the diameter of a cylindrical casting). In other words, the volume of each increment is such that it may be expressed by the formula:

where V is the volume of the increment, A is the crosssectional area of the shape defining chamber, D is the smallest cross-sectional dimension of said chamber (D is the diameter when the chamber is cylindrical) and X is a numerical value from about 0.02 to about 0.1.

While I prefer to use the pump, described above and illustrated in the appended drawing, as the means for incrementally forcing molten metal into the casting chamber, the invention is not restricted thereto; but other means for causing periodic flow of molten metal may be utilized, as will be apparent to those skilled in handling such materials. For example, molten metal may be confined in a closed feed tank under an atmosphere of an inert gas (e. g., nitrogen) and periodic flow through an outlet to the extrusion chamber obtained by periodic increases of the gas pressure or by opening and closing a valve or its equivalent in the outlet while maintaining a constant gas pressure over the molten metal. The herein described pump, however is preferred, because of its positive and reliable action in delivering a definite, fixed volume of metal at each piston stroke.

The present invention affords a relatively inexpensive, improved machine and process for molding bars, rods and other elongated shapes of sodium, aluminum, lead and other metals. A prime advantage is that it avoids exposure of molten metal to the air and thus eliminates the losses by oxidation and pipe formation which usually occur in casting operations. It has the further advantages of being a continuous process and of producing bars, etc. in any desired length without modification of the equipment.

I claim:

1. A machine for continuously casting an elongated metal shape comprising a shape-defining chamber with a first hollow section of tapered cross-section and a second hollow section of substantially constant crosssection coaxially joined with the large end of the first section, the internal cross-section of the second section being the same as the largest internal cross-section of the first section, a foraminous lining in the wall of the second section for introducing a lubricating liquid thereinto, means external to the chamber for supplying the liquid to the foraminous lining, means for forcing molten metal into the narrow end of the tapered section and means for cooling the shape-defining chamber.

2. A machine for continuously casting an elongated metal shape comprising a shape-defining chamber with a first hollow section of tapered cross-section and a I second hollow section of substantially constant crosssection coaxially joined with the large end of the first section, the internal cross-section of the second section being the same Ias .thel'largest "internal cross-section of the first .section, means in the wall of said second section forintroducing a lubricating liquid .thereinto, means for supplying the liquid to the fluid-introducing means, means for periodically forcing separate but definite fixed increments of molten metal into the narrow .end of the tapered section and meansfofcooling said tapered'section.

3. The machine of claim 2 in which the metallic fluidintroducing means is a foraminous lining in the second section.

4. The machine of claim 3 adapted for casting molten sodium and possessing an angle between the Wall of .the tapered section and a line parallel the longitudinal axis thereof of between about 2 and 30.

5. A machine for continuously casting sodium metal comprising a shape-defining chamber having a conical section coaxially joined at its large end with a cylindrical section, the angle between the wall of said conical section and a line parallel to its longitudinal axis being not less than about 2 and not greater than about 12, a foraminous lining in said cylindrical section, means for flowing oil through said lining, means for periodically forcing small but definite fixed increments of liquid sodium into the narrow end of said conical section and means for cooling said conical and cylindrical sections.

6. A machine for continuously casting sodium metal comprising a shape-defining chamber having a pyramidal section coaxially joined at its large end with an elongated rectangular section, the angle between a wall of said pyramidal section and a line parallel to its longitudinal axis being not less than about 2 and not greater than about 12, a foraminous lining in said rectangular section, means for flowing oil through said lining, means for periodically forcing separate but definite fixed increments of liquid sodium into the narrow end of said conical section and means for cooling said pyramidal and rectangular sections.

7. A machine for forming an elongated sodium casting comprising an elongated cylindrical tube tapered at one end, a foraminous lining in the untapered portion of said tube through which lubricating oil can pass into the tube, means for supplying oil externally to the foraminous lining, means for periodically forcing separate but definite fixed increments of molten sodium into the small end of the tapered portion of said tube and means for cooling at least the tapered portion of the tube.

8. The machine of claim 7 wherein the foraminous lining is made from a porous metal.

9. A machine for casting metallic sodium which comprises a shape-defining chamber having a conical section coaxially joined at its large end with a cylindrical section, the angle between the wall of said conical section and a line parallel to its longitudinal axis being between about 2 and 12, a porous metallic lining in the cylindrical section, means for supplying oil externally to said porous metallic lining, pumping means for periodically forcing separate but definite fixed increments of molten sodium into the narrow end of said conical section and a jacket external to the shape-defining chamber for cooling said chamber.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 238,515 McElroy Mar. 8, 1881 944,668 Douteur Dec. 28, 1909 1,551,838 Myers Sept. 1, 1925 1,800,938 Hedly Apr. 14, 1931 2,111,583 De Mooy Mar. 22, 1938 2,126,808 Phillips Aug. 16, 1938 2,136,394 Poland et al Nov. 15, 1938 2,225,373 Goss Dec. 17, 1940 2,245,224 Poland June 10, 1941 2,318,477 Firth May 4, 1943 2,454,961 Booth Nov. 30, 1948 2,479,364 Jocelyn Aug. 16, 1949 2,527,545 Goss Oct. 31, 1950 (Other references on following page)

Images