US2837791A

US2837791A - Method and apparatus for continuous casting

Info

Publication number: US2837791A
Application number: US501693A
Authority: US
Inventors: Alfred H Tessmann
Original assignee: Ind Res And Dev Corp
Current assignee: Industrial Research and Development Corp
Priority date: 1955-02-04
Filing date: 1955-04-15
Publication date: 1958-06-10
Anticipated expiration: 1975-06-10

Description

June 10, 1958 A. H. TESSMANN 7 METHOD AND APPARATUS FOR CONTINUOUS CASTING Filed April 15, 1955 5 Sheets-Sheet 1 INVENTOR.

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METHOD AND APPARATUS FOR CONTINUOUS CASTING Filed April 15, 1955 5 Sheets-Sheet 3 l mmvron.

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June 10, 1958 Y A. H. TESSMANN 2,337,791

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METHOD AND APPARATUS FOR CONTINUOUS CAST ING Filed April 15, 1955 5 Sheets-Sheet 5 VACUUM PUMP INVENTOR.

' ATTURNEY United States Patent METHOD AND APPARATUS FOR CONTINUOUS CASTING Alfred H. Tessmann, Lookout Mountain, Ga., assignor to Industrial Research and Development Corporation, Chattanooga, Tenn., a corporation of Tennessee Application Aprli 15, 1955, Serial No. 501,693

17 Claims. (Cl. 22-57.2)

This invention relates to methods and apparatus for the continuous casting of metals.

This application is a continuing application of my co-pending application, Serial No. 486,061, filed February 4, 1955, now abandoned and entitled Methodv and Apparatus for Continuous Casting.

In processes for the continuous casting of metals, molten metal is poured or fed under continuous pressure into one end of a casting mold, wherein it solidifies sufiiciently for withdrawal from the other end of the mold, sutticient heat being removed from the metal during its passage through the mold to effect the formation of a solidified outside shell of at least sufiicient thickness to sustain the hydrostatic pressure of any molten metal within the shell. It is not necessary that the casting be solidified throughout its cross section when it emerges from the casting mold. The casting mold is usually water cooled, and additional cooling of'the casing, through water sprays or otherwise, may be utilized after it emerges from the casting mold.

The conditions which affect the metal during its passage through the mold are of critical importance in determining the quality of the cast metal, i. e. its crystal structure, its freedom from porosity, and its surface characteristics. Moreover, such conditions are of great importance in determining the rate of heat withdrawal through the mold, which, in turn, determines the casting rate or rate of production. Any improvement in these conditions, therefore, which may be reflected in improvement in the quality of the cast metal, or in improvement in casting rate, or both, is of the greatest importance in practical commercial operations.

It is an object of the present invention to provide certain novel steps and conditions which affect the metal during its passage through the casting mold, and which improve'the quality of the cast metal and make possible an increase in the casting rate.

Another general object of my invention is to provide a method and apparatus adapted to the substantially continuous casting of metal in a mold which is horizontally disposed, as well as in vertically disposed molds or those mounted for use at other intermediate angular positions.

As another relatively general object, the invention has within its purview the provision of a continuous casting method and apparatus which are suited to the casting of both non-ferrous and ferrous metals including aiuminum, copper, copper alloys, ferrous metals and ferrous metal alloys, as well titanium and other metals having characteristics such that casting can be improve/1 or made possible by being cast in avacuum.

My invention has for another object the provision of a method and apparatus for the substantially continuous casting of metal which has good grain structure and which is practically devoid of blow holes and objectionable surface blemishes, cracks or voids.

This invention further comprehends the provision of a method and structure for the substantially continuous casting of metal and wherein the mold surface is lubricated during the molding operation.

It is another object of my invention to provide a continuous casting method and apparatus wherein the molding operation and cast metal characteristics are improved by the controlled reduction of air pressure within the mold cavity during the casting operation.

The invention further has within its purview the provision of a continuous casting method and apparatus wherein molten metal is introduced into one end of a relatively short mold and solidified metal is withdrawn from the other end of the mold, and wherein the mold and the metal therein are cooled under conditions affording control of the grain characteristics of the cast metal.

Another object of the invention is to provide a casting method and apparatus in which a flow of air or other fluid is created between the mold wall and the metal in the mold during the casting process.

My method and apparatus of this invention further comprehend the enclosure of the metal supply and the provision of controlled reduced atmospheric pressure in the supply enclosure for improving the quality of the cast metal and regulating the flow of the metal to the mold.

As a further object, this invention comprehends the provision of a method and apparatus for substantially continuous casting and which afford relative ease of starting and stopping the casting operation.

For effecting the accomplishment of the foregoing objects and advantages of this invention, and for providing definite examples of method steps and a structural embodiment characterizing the features of apparatus by which my method can be carried into efiect and which is adapted to illustrate my invention, I have developed and disclosed the methods and structures herein illustrated and described. Without making detailed reference to the accompanying drawings, it may be generally observed that my method and structure for the achievement of the stated objects and others which may become apparent contemplate the use of auxiliary or ancillary equipment including a melting furnace in which raw stock is melted and brought to a desired analysis and a holding furnace for the storage of the molten raw stock pending use. From the holding furnace, the molten metal either flows to a storage reservoir in which a supply and head are maintained for effecting continuous flow under adequate pressure or may flow directly from the holding furnace to the mold during the operation of my casting mold.

Molten metal flows by gravity, and under some head pressure, from the storage reservoir or holding furnace into the cavity of a tubular casting mold through a nozzle into the input end of the casting mold. Near the end of the nozzle, a controlled amount of lubricant may be introduced at the periphery of the mold to prevent sticking of the metal to the mold. surface, to facilitate the movement of the metal through the mold as it solidifies and to improve the surface finish of the cast metal. The mold is cooled in a regulated amount to effect accelerated but controlled chilling and solidification of the metal as it moves therethrough. Also, and further to improve the characteristics of the cast metal by the removal of gas and air from the mold cavity and to induce the spreading and flow of lubricant around and along the mold surface as well as for reasons which will become more apparent as the description progresses, I reduce the air pressure at the output end of the mold by the provision of an effective seal and the connection of pressure reducing means, such as a vacuum pump, thereto, thereby to draw gas and air from within and around the molten metal, and to prevent the formation or existence of a static insulating air barrier between the Patented June 10, 1958 :47 metal and the mold wall to promote the cooling of the metal in the mold. The vacuum may also, in some instances, be utilized to effect the flow of an inert or non-oxidizing atmosphere, or other fluid between the mold and the metal therein.

Both the use of reduced pressure within a casting mold, and particularly those of the types herein disclosed, and the manner of accomplishing the pressure reduction to achieve the desired results are considered to be worthy of particular note. In addition to the aforementioned purposes which the reduced pressure serves to accomplish, it has been found to be effective throughout the length of the mold cavity and for the prevention of the back-feed of molten metal between the feed nozzle and the mold wall. In addition, I have found that while seals, such as mechanical seals, are particularly desirable in some instances, and for the casting of some metals, such as those having high melting points, a fluid or liquid seal, such, for example, as one utilizing water as a sealing medium, judiciously applied and effectively utilized at the output end of the mold not only serves movement of air not only atomizes, but directs the flow of a sealing liquid at the position of the emergence of the casting from the mold cavity.

Further objects, advantages and features of my invention may be apparent from the following description and reference to the accompanying drawings wherein preferred embodiments of my method and apparatus are described and illustrated.

In the five sheets of drawings:

Fig. 1 is a front elevational view of an embodiment of my apparatus for the continuous casting of metal, which apparatus is adapted to the use of the method disclosed herein;

Fig. 2 is a fragmentary front sectional view of a portion of the apparatus illustrated in Fig. 1, and wherein the section is taken substantially along a longitudinally extending vertical central plane;

Fig. 3 is a fragmentary sectional view showing parts of the apparatus depicted in Fig. 2 drawn to a larger scale than that,used in Fig. 2;

Fig. 4 is an end sectional view taken substantially at a position indicated by a line 4-4 in Fig. 2 and in the direction indicated by arrows, Fig. 4 being drawn to a larger scale than Fig. 2;

Fig. 5 is a fragmentary end elevational view of the apparatus shown in Fig. l, as the apparatus is viewed from the left-hand end of Fig. 1;

Fig. 6 is a fragmentary end elevational view similar to Fig. 5, but showing a part of the apparatus in a different position;

Fig. 7 is a fragmentary top plan view of the portion of the apparatus viewed from the end in Fig. 5;

Fig. 8 is a side elevational view of an auxiliary device adapted to use in starting the operation of the apparatus herein disclosed; and

Fig. 9 is a semi-diagrammatic sectional view adapted to disclose the principles of the invention.

In a continuous casting operation, the liquid metal which is introduced at one end of the mold forms a liquid pool which extends across the entire cross section of the mold and is in contact with the cold mold wall around its entire periphery. Contact with the cold mold wall causes the metal to cool and begin to solidify, and as the cooling metal moves along the mold wall, the thickness of the solidified metal increases until a shell 4 is formed of sufiicient strength to sustain the hydrostatic pressure of the molten metal within. At this point, continued cooling of the solidified shell begins to cause contraction of the shell. This results in shrinkage of the shell away from the mold wall, leaving a narrow space therebetween.

The foregoing is illustrated diagrammatically in Fig. 9 in which molten metal is being introduced continuously into one end of the water cooled mold 1 in any suitable manner, as through a spout 2, and solidified metal is being withdrawn continuously from the other end. As illustrated, solidification of metal in contact with the cold mold wall begins close to the surface of the pool of molten metal, and the solidified metal gradually increases in thickness until, as indicated at P, the solidified shell has acquired sufiicient strength to support the hydrostatic pressure of the liquid metal within. At this point the shell begins to contract and shrink away from the mold wall, leaving a shrinkage space S therebetween.

In the ordinary continuous casting processes, the shrinkage space is filled with stagnant air which acts as a thermal insulator to retard the transfer of heat from the metal to the mold. That is, as contact between the metal and mold is lost due to shrinkageof the shell, heat transfer by conduction ceases, and although heat transfer by radiation continues, the total rate of heat transfer is substantially reduced.

According to this invention, I reduce the air pressure within the shrinkage space to a point substantially below atmospheric pressure. As explained herein, this has several beneficial effects which result in the production of castings of improved quality and makes possible an increased rate of casting. Thus, as illustrated in Fig. 9, a chamber 3 at the lower end of the mold is sealed at the bottom by a flexible gasket 4 of rubber or other suitable material which engages the emerging casting around its entire periphery. The chamber 3 is connected by conduit 5 to a suitable vacuum pumpor other source of reduced pressure. If desired, the upper end of the mold may be enclosed, as by a flexible sleeve 6 extending from the top of the mold to the reservoir R which holds the molten metal supply, the enclosure 7 having a valve controlled conduit 8 connected thereto. The valve may be closed, if desired, in which case the pressure within the enclosure will tend to equalize with the reduced pressure maintained within the chamber 3 and shrinkage space S. On the other hand, the valve may be opened to admit air, or the conduit may be connected to a suitable source of inert gas, such as propane, nitrogen, argon and the like, for example, to prevent oxidation. If the valve is opened to admit either air or gas, the reduced pressure maintained in chamber 3 and shrinkage space S will tend to draw air, or gas, as the case may be, past the liquid pool so that a current of air or gas will flow into and through the shrinkage space as the casting operation proceeds. The flexible sleeve permits reciprocation of the mold where this may be desirable.

The maintenance of reduced pressure in the shrinkage space has several desirable and beneficial results. Those listed below are not necessarily listed in the order of their relative importance.

1) It aids lubrication of the mold Wall. It has long been recognized that it is very important to successful continuous casting to lubricate the mold wall, not only to reduce friction between the casting and the mold wall, but also to prevent molten metal from adhering to the mold wall. customarily, a lubricant such as oil or grease or graphite is introduced near the molten metal surface. If the surface is exposed to trapped or relatively stationary air, a considerable amount of the lubri cant burns away, but portions reach the cold mold wall and form a film vwhich is protected by the cold wall. This film is supposed to work down between the molten metal and the mold to form a lubricant film between the molten metal and'the mold to form a lubricant film between the mold and casting. ,While this is good in theory, inpractice it has left much to be desired. Pre quently, for various reasons, the lubricant fails to form the desired film, or the film is discontinuous or too thin and sticking results. As illustrated in Fig. 9, lubricant maybe introduced through a passage 9 in the mold and tends to move into the meniscus at the edge of the liquid metal pool. By maintaining reduced pressure in the shrinkage space, the downward movement of the lubricant is induced and facilitated by the movement of air in the space and the lubrication of the mold wall is greatly improved.

(2) It removes objectionable gas. There are two sources of such gas, (1) from the decomposition of the.

lubricant, and 2) from the release of occluded gas which occurs as the metal freezes. The former frequently causes defective surfaces, while the latter is a source of porosity. Both are undesirable. By removing such gases the quality of the castings is improved.

(3) It removes carbon which might otherwise become embedded in the casting. When portions of the lubricant decompose or are burned a deposit of carbon sometimes remains which tends to collect on the mold wall. Occasionally such deposits become embedded in the casting which is undesirable. The maintenance of reduced pressure and the provision for air, gas or other fluid movement in the shrinkage space tends to remove such carbon deposits.

(4) It increases the rate of heat removal. This has two aspects, (1) the increasedv removal of heat by the flow of air or gas through the shrinkage space and (2) the increased removal of heat by increased or prolonged contact between the casting and the mold'wall. As to the former, it will be obvious that the movement of cold air, gas or other fluid which is drawn into and through the shrinkage space will absorb and carry away heat which will be dissipated with the discharge of such air, gas or other fluid. As to the latter, the reduction in pressure in the shrinkage space has the same efi'ect as an increase in the hydrostatic pressure of the liquid metal. By such reduction in pressure, therefore, a longer time is required before the shell attains the required strength. This means that the shell remains in contact with the mold wall for a longer time and that faster heat dissipation from the metal is effected.

The degree of reduction of pressure to be maintained in the shrinkage space will vary depending on the results which it is desired to produce. Likewise, the conditions maintained within the enclosure 7 may be adjusted as desired. In general, the greater the reduction in pressure in the shrinkage space the more beneficial the results. Closing the valve of conduit 8 facilitates the maintenance of lower pressures. On the other hand, opening the valve to allow air, gas or other fluid to flow to the shrinkage space facilities lubrication. The admission of inert reducing gas, such as propane, nitrogen, argon and the like protects against oxidation. The selection of conditions, therefore, will depend on the objective to be obtained during the casting operation.

Referring now to Figs. 1 to 8, I have illustrated a practical embodiment of my invention which is adapted for and has been used in carrying out commercial continuous casting operations. The apparatus illustrated in Figs. 1 to 8 is of the so-called horizontal type in which the mold passage extends horizontally instead of vertically as in Fig. 9. This apparatus for the continuous casting of metal has a base structure 10 upon which a supply reservoir 12, a mold assembly 13 and a power operated withdrawing roll mechanism 14 are mounted in substantially aligned relationship. The mold assembly 13 utilizes an elongated mold 15 which is mounted in a horizontal position. A holding furnace 16 is provided, in which metal which has-been previously melted and'brought to a desired analysisis kept in a molten condition pending use.

Flow of molten metal fromthe holding furnace 16 may be either automatically or manually controlled by a suitable gate to keep a supply and a suflicient head of the molten metal in the supply reservoir 12, from which supply reservoir the metal normally flows into the mold 15. In the present instance, a trough 17 is utilized to conduct the molten metal from the holding furnace 16 to the supply reservoir 12. The .molten metal from the supply reservoir 12 flows into one end of the mold and emerges from the other end of the mold as a solidified casting 18, which casting is gripped between power driven withdrawing rolls 19 and 20 to aid in the continuous withdrawal of the casting from the mold.

The supply reservoir 12, as herein illustrated and utilized, has a relatively heavy outer metal shell 22 including side walls 23, end walls 24 and a bottom 25, with integral and aligned trunnions 26 projecting outwardly and oppositely from the end walls 24. This outer shell 22 may, for example, be made of cast iron or steel. It is supported relative to the base structure 10 through bearing

brackets

27 and 28 at its opposite ends, which bearing brackets have

bearings

29 and 30 respectively in which the aligned trunnions are journaled to support the supply reservoir for tilting movements between upright and dumping positions shown in Figs. 5 and 6 respectively.

Cap plates

32 and 33 which are removably secured to the ends of the trunnions 26 by fastening means such as cap screws 34 retain the bearing brackets '27 and 28 in their assembled relationship on the trunnions 26.

In order to provide for adjustment of the position of the supply reservoir relative to the mold 15 and for effecting entry and withdrawal of a nozzle 35 on the supply reservoir relative to the end of the mold 15, the a

bearing brackets

27 and 28 have foot portions 36' and 37 thereon, which foot portions have longitudinally extending and aligned

recesses

38 and 39 in their bottom surfaces that fit over and are slidable along aligned supporting

blocks

40 and 42 on the base structure 10. The position of the supply reservoir is determined by a screw 43 having threaded engagement with a stationary bracket 44 secured to the base structure, and which screw has a hand wheel 45 on its outer end for effecting rotation thereof and a head portion 46 on its other end which is housed in a recess 47 in the end of the trunnion 26'and engages the inner surface of the cap plate 32.

The necessity of applying heat to the supply reservoir from an external source, such as heating elements, is avoided in the disclosed apparatus by making the size and capacity of the supply reservoir commensurate with the rate of use of the metal in the continuous casting operation, so that metal from the holding furnace is not retained in the supply reservoir for a sufficient time to solidify, and by providing heat insulating walls 48 and a bottom 4-9 of a highly heat resistant material interiorly of the walls and bottom of the cast shell 22. The nozzle 35 is secured within a flange St on the cap plate 33 and projects from the end of the supply reservoir adjacent the mold 15in coaxial relationship to the trunnions 26, as well as extending through aligned

openings

52 and 53 in the shell 2.; and the insulating interior wall 48 to substantially flush relationship with the inner surface of that insulating wall. With this structural relationship of the nozzle and its associated parts, it may be removed from the supply reservoir for cleaning or replacement by the removal of the cap screw 34 holding the cap plate 33 in place and withdrawing the nozzle from the reservoir with the cap plate 33 and its adjoined flange 50. It may also be observed that by having the nozzle in co-axial relationship to the trunnions 26, the supply reservoir may be swung to its dumping position while the nozzle is engaged with the mold.

As shown in Figs. 2 and 3, the nozzle 35 constitutes a tube 54 of heat insulating and heat resistant material '7 which'extends from a position in which it is practically flush with the inner surface of the heat insulating and heat resistant wall of the supply reservoir to a position internal of the flange on the cap plate 33, which position is relatively near the projecting end of that flange. Then an end lining part of a heat insulating refractory material adjoins the end of the tube 54 within the flange 50 and has an outwardly curved end surface portion 56 which overlaps the end of the flange 5t) and extends into flush relationship with the periphery thereof. Thus, in addition to providing a surface which is smoothly curved at the end of the nozzle and over which the molten metal is discharged from the nozzle into the cavity of the mold 15, this part prevents contact of the molten metal with the end portion of the metal flange 50. It may also be observed in Fig. 3 that external ring portions 57 at the end of the flange 50 serve as bearing surfaces for engagement with the inner surface of the mold 15. It may also be observed that the inner surface of the nozzle 35 tapers outwardly toward the projecting end of the nozzle. This taper not only effects a division of the flow of molten metal when the supply reservoir is dumped at the end of a period of use of the casting apparatus, but also facilitates the removal of any relatively thin layer of metal which may possibly solidify in the nozzle when the supply resersupport the reservoir in its upright position, as shown in Fig. 5. A holding latch 62 which is manually operable by movement of a handle 63 is supported from the end of the reservoir shell 22 adjacent the counterweight 58 by a bracket 64. This latch is engageable with a bar 65 supported from the base structure it) by end brackets 66 for releasably locking the reservoir in its normal upright position and for preventing it from being inadvertently tipped to the dumping position. Both the handle 63 and the counterweight 58 may be utilized as handles for the manual movement of the reservoir between its normal and dumping positions.

The mold assembly 13, in addition to the mold i5, and as shown in Fig. 2, includes an outer metal jacket 67 which encompasses the exterior of the mold 115 in spaced and substantially parallel relationship thereto and extends along practically the entire length of the mold; the jacket being secured to and supported relative to the mold by an end ring 68 at the nozzle or inlet end of the mold and by an end cap 69 at the opposite end of the mold, which latter end cap includes a circular header passage 70.

Supports

72 and 73 which encompass the jacket 67 near its opposite ends carry the mold assembly relative to the base structure 19.

It being desirable to cool the mold 15, my disclosed mold assembly has a plurality of conduits or pipes 74 mounted internally of the jacket 67 in peripherally spaced relationship to one another and extending from the end ring 68 to the end cap 6%. Externally of the end ring 68, the conduits 74 are closed by end caps 75, while at their opposite ends, they communicate with the header passage 70. A supply pipe 76 is threaded into the periphery of the end cap 69 and communicates with the header passage to supply a coolant liquid, such as water, to the conduits 74. To provide effective and efiicient cooling action from a minimum amount of water, each of the conduits 74 has a plurality of spray nozzles 77 in aligned and axially spaced relationship along the conduit and directed toward the exterior surface of the mold 15. The peripheral spacing of the conduits 74 about the mold 15 and the axial spacing of the nozzles 77 along the conduits is predetermined to provide coverage of the external mold surface with sprayed coolant. Drainage of the coolant from the jacket 67 is afforded by a plurality of perforations 78 in the lower surface of the jacket, through which perforations, the used coolant flows into a pan 79 and thence to a drain pipe 80. The rate of cooling may, of course, be controlled by regulating the flow of coolant through the supply pipe 76 to the conduits 74 and nozzles 77.

In order to provide efficient and effective conduction of heat through the wall of the mold 15, I prefer to make that mold in the form of a cylindrical copper tube having a wall thickness affording adequate strength, as for example, one-half inch thick for use in the casting of aluminum having an external diameter of approximately two to three inches. Then further, to afford the proper wearing quality and finish to the internal surface of the mold, the internal surface of the copper mold cylinder is not only reamed precisely to size and polished, but it is plated with chromium and then finished and polished to provide a wear resistant surface which may, for example, have .a finished thickness of approximately .004 inches.

In addition to providing a polished finish on the interior surface of the mold for producing good surface finish on the casting produced therein and for minimizing the friction and the tendency for the cast metal to stick to the mold surface, I have found it desirable to lubricate the internal surface of the mold. For this purpose, lubricant is applied to the inner periphery of the mold from time to time, or a metered or regulated quantity of lubricant is applied to the inner periphery of the inlet end of the mold during the casting operation. In the disclosed structure, a lubricant supply pipe 82 extends radially through the jacket 67 near the inlet end of the mold and communicates with a passage 83 in the mold wall. As herein depicted, the passage 83 enters the mold cavity at a position back of the discharge end of the nozzle 35. From this position, the lubricant spreads over the periphery of the interior wall of the mold and gradually creeps outwardly and along the mold for effectively lubricating the mold surface during the movement of metal therethrough.

For accomplishing purposes such as aiding the movement of lubricant longitudinally of the mold from the inlet to the outlet end, and for other purposes set forth herein, I reduce the air pressure at the outlet end of the mold and within the shrinkage space. For this purpose I provide a chamber at the outlet end of the mold which is connected to a vacuum pump. As shown in Figs. 2 and 3, a housing 84 having a substantially cylindrical side wall 85 and end walls 86 and 87 is secured to the external end surface of the end cap 69, with a gasket 88 providing a seal between the end cap 69 and the end wall 36. Aligned

openings

89 and 90 in the end walls 86 and 87 respectively are aligned with and slightly larger than the internal diameter of the mold 15, so that the casting 18, emerging from the outlet end of the mold 15, passes freely through the openings 8? and 90 in the housing 85. At the top of the housing, a pipe fitting 92 communicates with the interior of the housing and is provided for connection to a vacuum pump.

At the outer end wall 87 of the housing 84 and the side wall 85' of that housing, I have provided an inner part 93 which includes an end plate portion 94 and an inwardly projecting and substantially frusto-conical baffle 95, which baffle is concentrically disposed with respect to the

openings

89 and 90 and converges inwardly toward the end of the mold 15. The outer surface of the end plate portion 94 abuts the end wall 37 and has a channel 96 therein which encompasses the opening 90 to provide a header passage for the fiow of a coolant liquid, such as water, to a plurality of circumferentially spaced outlet passages 97 in the end plate portion 94 and dismesa-291 posed to direct jets of the coolant liquid inwardly toward the emerging casting within the confines of the baffle 95. A pipe 98 threaded into an opening in the end cap 87 in alignment with the channel 96 is adapted to be connected to a source of liquid coolant under pressure.

The inner diameter of the inner end of the bafile 95 is such that it approaches into close proximity to the casting which is emerging from the end of the mold 15. The spacing between the inner end of the bafile 95 and the emerging casting may be, for example, about oneeighth of an inch. Then, the coolant supplied through the outlet passages 97 and directed inwardly into the narrow space between the casting and the inner end of the baffle 95 is in sufiicient quantity to provide an effective seal, which seal limits the inward flow of air through the opening 90 in the outer end of the housing 84 along the emerging casting to an extent such that the reduced air pressure in the space surrounding the baffle 95 effects a reduction of pressure that is effective along the full length of the mold cavity during normal operation of the apparatus. Since the baflle 95 extends into close proximity to, but is spaced from the end wall 86 of the housing 84 and the end of the mold 15, the coolant flowing between the casting and the inner surface of the baffle 95 is directed around the end of the baffle as a result of the reduced pressure on the exterior of the baffle, and the coolant and coolant vapor are exhausted A from the housing 84 through the fitting 92 and the vacuum line. The reduced pressure in the housing 84 exterior to the baffle 95 and the movement of air and gas outwardly from the outlet end of the mold 15 prevent the seepage of coolant into the outlet end of the mold. It may also be readily appreciated that the discharge of coolant against the casting as it emerges from the mold and the vaporization of the coolant adjacent the casting as the coolant passes the end of the baffle and into the low pressure area affords effective and material cooling for the casting beyond that provided by the cooling of the mold.

From the housing 84, the casting is passed between the withdrawing rolls 19 and 20 which constitute a part of the withdrawing roll mechanism 14 mounted on the base structure in spaced relationship to the outlet end of the mold and the housing 84. As illustrated in Fig. 1, the withdrawing rolls are driven by a suitable prime mover, such as a motor 99 having a driving connection to the withdrawing rolls through a speed reducing mechanism 100 and drive means, such as a chain 102 connecting

sprockets

103 and 104 on the speed reducing mechanism and withdrawing roll mechanism respectively. Although the speed of the casting operation and the withdrawal of casting from the mold of the disclosed apparatus is quite materially affected by the material being cast and other factors including the diameter of the casting, the production of an aluminum casting of a diameter between two and three inches can be accomplished by the disclosed apparatus at a rate above eight feet per minute.

For facilitating the starting of operation of my disclosed continuous casting apparatus, I have provided a metal bar 105, made of steel or a similar high melting point metal, which bar is of substantially the size of the casting which is to be cast in the mold. This bar 105 has a tapered and threaded end portion 106 which, in the starting operation, is put into the mold from the outlet end, so that the tapered and threaded end portion is spaced somewhat from the end of the nozzle 35. The bar 105 has a length such that the outer end thereof engages the withdrawing rolls 19 and 20 when the tapered and threaded end is in closed, but spaced relationship to the end of the nozzle. With this bar in place, the withdrawing rolls are started and the supply reservoir is supplied with molten metal to an extent such that the casting operation is commenced. As the bar 105 is withdrawn, thev formation of the casting progresses and the i0 casting, cooled and in solid form, follows the bar from the mold and through the withdrawing rolls. The bar 105, after serving its purpose for starting the casting operation, can be removed from the end of the casting by merely unscrewing the threaded end thereof from the corresponding threads which are cast into the starting end of the casting as the casting operation commences.

From the foregoing description of a structural embodiment of my invention and its method of operation, it may be understood that my method for continuous casting includes the steps of supplying molten metal to the inlet end of the straight mold cavity of a metal mold under a head pressure or at a rate suflicient to keep the operative portion of the mold filled with the metal, withdrawing heat from the metal in the mold by cooling the external surface of the mold at a regulated rate to eifect solidification of the metal in the mold, and withdrawing the casting from the outlet end of the mold. The operating efiiciency and the characteristics of the product produced by my disclosed apparatus and the method outlined are improved by the lubrication of the interior surface of the mold, with that lubricant applied near or at the inlet end of the mold. Lubricants adapted to use in the mold of my disclosed apparatus include rape seed oil, castor oil, mineral oil and a mixture of oil and graphite. A further step of my method which improves the operation of the apparatus and the characteristics of the casting made therein is the reduction of the air pressure at the inlet end of the mold in a manner and in an amount such that the reduced pressure is effective throughout the length of the mold interior to accomplish results such as those herein set forth. It may be readily understood that the movement of air toward the outlet end of the mold as a result of the vacuum applied to the housing 84 is facilitated by the shrinkage of the metal of the casting during the cooling which occurs within the mold. The movement of the air in the mold improves the cooling of the metal therein.

Although my invention has been described in connection with specific details of the embodiments thereof, it must be understood that it is not intended to be limited thereto except insofar as set forth in the accompanying claims.

Having thus described my invention, What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for the continuous casting of metal comprising, in combination, a supporting base structure, a tubular metal m-old having a mold cavity extending longitudinally therethrough from end to end, means for supporting the mold from the base structure, a jacket surrounding the mold and having conduits therein from which coolant liquid is applied to the external surface of the mold during use, a supply reservoir for molten metal mounted on the base structure at one end of the mold, means providing a connection for the continuous flow of molten metal from the supply reservoir to the mold cavity at said one end of the mold, the last mentioned means having clearance from the mold for the flow of atmosphere to said one end of the mold cavity, means for withdrawing cast metal from the other end of the mold, and a housing enclosing said other end of the mold and providing a connection to a vacuum pump for effecting a reduction of the air pressure Within the mold cavity and continuous movement of atmosphere through the mold from said one end to the other end of the mold between the metal and the mold.

2. Apparatus for the continuous casting of metal comprising, in combination, a supporting base structure, a tubular metal mold having a mold cavity extending longitudinally therethrough from end to end, means for supporting the mold from the base structure, a jacket surrounding the mold and having conduits therein from which coolant liquid is applied to the external surface of the: mold during use, a supply reservoir for molten metal mounted on the base structure at one end of the mold, means providing a connection for the continuous flow of molten metal from the supply reservoir to the mold cavity at said one end of the mold, thelast mentioned means haying clearance from the mold to provide space for the flow of atmosphere to the mold cavity at said one end, means for withdrawing cast metal from the other end of the mold, means for effecting the flow of a metered quantity of lubricant to the internal surface of the mold near said one end thereof, and means for efiFecting a reduction of the air pressure at the other end of the mold for inducing the movement of atmosphere from said one end to the other end of the mold between the metal and the mold to effect spread of lubricant over and along the inner mold surface in the direction of movement of metal through the mold during operation of the apparatus.

3. In apparatus for the continuous casting of metal, the combination comprising a hollow metal shell of highly heat conductive metal internally plated with a layer of highly wear resistant metal and defining an elongated mold cavity extending from end to end of the shell, said wear resistant metal being finished to provide a smooth inner molding surface, a metal jacket secured to and surrounding the metal shell in spaced relationship thereto, means for effecting the flow of a coolant through the jacket and over the outer surface of the metal shell, a housing secured to one end of the jacket and having an opening therein substantially aligned with the adjacent end of the mold cavity, a frusto-conical baflie secured to the end of the housing remote from the jacket and extending inwardly of the housing while converging inwardly toward the adjacent end of the metal shell, passages in the end of the housing remote from the jacket and at positions between said opening and the baffie for directing a flow of coolant inwardly of the housing within said baffle, and means providing a connection to the housing for communication with a vacuum line for exhausting air and coolant from the portion of the housing around said balfie.

4. In apparatus for the continuous casting of metal, a metal mold having an elongated opening extending therethrough which serves as a mold cavity having an inlet end for receiving molten metal and an outlet end from which cast metal emerges in a substantially continuous strand, a nozzle having an opening therein through which molten metal is continuously supplied to the mold cavity, eans providing space for the movement of gas into the mold cavity adjacent the nozzle, and

means at the outlet end of the mold cavity through which 1 the cast metal emerges from the mold cavity and through which the air pressure is reduced at said outlet end of the mold cavity to an extent such that a flow of gas is induced between the metal and the mold.

5. Apparatus for the continuous casting of metal comprising, in combination, a casting mold having a mold passage extending therethrough, means providing a chamber enclosing the outlet end of said casting mold, said means having an opening spaced from the casting mold through which the casting is Withdrawn from the casting mold as a continuus strand, means providing a seal between said opening and said strand at a position spaced from the casting mold, and means connected to the chamber intermediate the seal and the casting mold for maintaining a pressure substantially less than atmospheric pressure within said casting mold, said seal providing means comprising a baflie extending into the chamber from a position adjacent said opening and encompassing the periphery of the strand in close proximity to said strand and near the casting mold, and means to discharge liquid into the space between said baffle and said strand on the side of the baffle remote from the casting mold.

6. In apparatus for the continuous casting of metal, the combination comprising a metal mold having an elongated opening therethrough which serves as a mold cavity having an inlet end into which molten metal is introduced for casting and an outlet end from which solidified metal emerges, means extending into the inlet end of the mold through which molten metal flows into the mold, said means and said mold having clearance therebetween for the movement of air, and structure including sealing means secured to the outlet end of the mold and through which the solidified metal emerges from the mold, said structure having means connected thereto for effecting a reduction of the air pressure at the outlet end of the mold and through the mold cavity between the metal and the mold.

7. In apparatus for the continuous casting of metal as defined in claim 6, the combination being further characterized by means for introducing lubricant to the inner surface of the mold at the inlet end of the mold cavity between the mold and said means extending into the inlet end thereof.

8. Apparatus for the continuous casting of metal comprising, in combination, a casting mold having inlet and outlet ends and a mold passage extending therethrough between said inlet and outlet ends, means for admitting atmosphere to the inlet end of the mold passage, means providing a chamber enclosing the outlet end of said casting mold, the last-mentioned means having an opening spaced from the casting mold through which the casting is withdrawn from the casting mold as a continuous strand, means providing a seal between said opening and said strand at a position spaced from the casting mold, and means connected to the chamber intermediate the seal and the casting mold for maintaining a pressure substantially less than atmospheric pressure within the chamber.

9. Apparatus as claimed in claim 8, in which the seal providing means comprises a member having an edge surrounding and spaced from said casting, and means for filling the space between said edge and said casting with liquid.

10. Apparatus as claimed in claim 8, and including means providing a chamber surrounding and enclosing the inlet end of the mold passage, and means for supplying an inert atmosphere to the latter mentioned chamber.

11. Apparatus as claimed in claim 8, including a supply reservoir, and wherein said means for admitting atmosphere to the inlet end of the mold passage includes means providing a chamber surrounding and enclosing the inlet end of the casting mold, the last mentioned means comprising a flexible wall extending between the inlet end of the mold and said supply reservoir, thereby to provide for relative motion between the supply reservoir and the casting mold.

12. A method for the continuous casting of metal in a horizontal mold having inlet and outlet ends, which method comprises the steps of supplying molten metal to the inlet end of the mold under a head pressure sufficient to keep the mold filled, lubricating the interior of the mold near the inlet end, cooling the exterior of the mold to eflect solidification of the metal therein while providing an atmosphere in the space about the solidified metal in the mold resulting from the shrinkage of the metal due to the solidification thereof in the mold, moving the solidified metal from the mold at the outlet end thereof, eifecting a reduction of the atmospheric pressure at the outlet end of the mold and thence between the mold and the metal therein to effect movement of the lubricant and atmosphere in said space along the mold in the direction of the movement of the metal therein, and applying liquid to the cast metal as it emerges from the outlet end of the mold.

13. A method for the continuous casting of metal in an elongated mold having inlet and outlet ends, which method comprises the steps of supplying molten metal to the inlet end of the mold at a rate to keep the mold filled, moving the metal from the inlet end toward and from the outlet end of the mold, applying a continuous quantity of lubricant at a metered rate to the inner surface of the mold near the inlet end thereof, cooling the mold to effect solidification of the metal while adding an atmosphere in the space about the solidified metal in the mold resulting from shrinkage of the metal due to contraction during solidification thereof, and effecting a differential of the atmospheric pressure between the inlet and outlet ends of the mold by reducing the pressure at the outlet end thereof to provide a continuous movement of atmosphere through the mold between the metal and the mold in the direction of movement of the metal in the mold.

14. A method for the continuous casting of metal in an elongated mold having inlet and outlet ends, which method comprises the steps of supplying molten metal to the inlet end of the mold at a rate to keep the mold filled, effecting movement of the metal through the mold from the inlet to the outlet end thereof while the metal solidifies and contracts away from the mold to provide space between the metal and the mold which contains an atmosphere, applying vacuum to reduce the air pressure from the outlet end to the interior of the mold, thereby to eifect the removal of atmosphere from the outlet end of the mold, and withdrawing solidified metal from the outlet end of the mold.

15. In a method for the continuous casting of metal in a mold having inlet and outlet ends, the steps comprising supplying molten metal and atmosphere to the iniet end of the mold while applying vacuum to the outlet end of the mold to a degree sufl'lcient to eflect a reduction of atmospheric pressure throughout the length of the mold and the movement of atmosphere through the mold between the metal and the mold, cooling the metal to elfect solidification thereof as it moves through the mold, and withdrawing solidified metal from the outlet end of the mold.

16. In a method for the continuous casting of metal in a straight mold having inlet and outlet ends, the steps comprising supplying molten metal to the inlet end of the mold, moving the metal through the mold as it chills and solidifies, lubricating the mold near the inlet end, and establishing a differential of air pressure between the inlet and outlet ends of the mold by reducing the pressure at the outlet end thereof in an amount suflicient to induce the flow of lubricant toward the outlet end of the mold.

17. In a method for the continuous casting of metal in which molten metal is introduced continuously into one end of a casting mold and in which solidified metal is withdrawn continuously from the outlet end, the steps which comprise maintaining gas at atmospheric pressure at said one end of the casting mold, and maintaining a pressure substantially less than atmospheric pressure at the outlet end of said casting mold from whence the pressure is substantially reduced within the shrinkage space inside the mold between the solidified metal and the mold wall and the flow of gas is induced through the mold from said one end to the other end thereof to aid in removing heat from the metal.

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