US3800848A

US3800848A - Method for continuous vacuum casting of metals or other materials

Info

Publication number: US3800848A
Application number: US00300816A
Authority: US
Inventors: R Chaulet; C Guichard; P Menissier; J Soret
Original assignee: COMBUSTIBLE NUCLEAIRE
Current assignee: COMBUSTIBLE NUCLEAIRE; SA Ind De Combustible Nucleaire fr
Priority date: 1968-10-18
Filing date: 1972-10-25
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02
Also published as: GB1293939A; DE1952083A1; BE740337A; NL6915832A; SE360584B; CA939483A; CH514378A; JPS499937B1; AT310368B; US3724529A

Abstract

A method for continuous vacuum casting of metals or other materials, more particularly for the obtention of shapes such as tubes and bars. The method is applicable to plants comprising a spray means in the open air and a dynamic lock for emergence of a cast shape into air. The lock comprises chambers maintained under decreasing pressures by pumping devices and are separated from each other by diaphragms. The static pressure of the metal on the shape being formed is held at a constant value, for a given size of shape with respect to the liquid meniscus size, so as to render the difference between the cross-section of said shape when reaching the dynamic lock, and the cross-section of the diaphragms low enough for the rate of air admission to remain lower than the pumping rates of the pumping devices. The cast shape is cooled throughout a zone of such length, as a function of a set rate of withdrawal of the shape, that the shape will enter the spray means, when leaving the lock, at a constant temperature.

Description

United States Patent Chaulet et al. Apr. 2, 1974 [54] METHOD FOR CONTINUOUS VACUUM 2,799,065 7/1957 Whitaker 164/66 CASTING 0 METALS OR OTHER 2,818,461 12/1957 Gruber 164/283 M X MATERIALS 2,882,570 4/1959 Brennan 164/64 [75] Inventors: Roger Louis Chaulet, Grenoble;

Claude Pierre Albert Louis Primary Examiner-.1. Spencer Overholser Guichard, Voiron; Pierre Lucien Assistant Examiner-John S. Brown Menissier, Grenoble; Jean-Claud Attorney, Agent, or FirmBaldwin, Wight & Brown Georges Soret, St. Egreve, all of France [73] Assignee: Societe Anonyme: Societe [57] ABSTRACT Industrielle de Combustible Nucleaire, Annecy (Haute Savoie), A method for continuous vacuum casting of metals or France other materials, more particularly for the obtention of [22] Filed: Oct. 25, 1972 shapes such as tubes and bars. The method 15 applicable to plants comprising a spray means m the open air [21] Appl. No.: 300,816 and a dynamic lock for emergence of a cast shape into Related us Application Data :11. The lock comprises chambers maintained under ecreasmg pressures by pumping devices and are sep- [62] DlVlSlOl'l of Ser. No. 865,719, Oct. 13, 1969, Pat. No. mated from each other by diaphragms The Static pressure of the metal on the shape being formed is held at a constant value, for a given size of shape with [30] Fore'gn Apphcatmn Pnonty Data respect to the liquid meniscus size, so as to render the Oct. 18, France difference between the cross section of said hape Sept. 15, France when reaching the dynamic lock and the cross section of the diaphragms low enough for the rate of air ad- U-Se Clt mission to remain lower than the pumping rates of the [5 Cl. t u pumping devices The cast hape is cooled throughout Fleld of Search 64, 82, 83, a zone of uch length as a function of a set rate of 164/283, 122, 126, 254, 1 348, 154 withdrawal of the shape, that the shape will enter the spray means, when leaving the lock, at a constant tem- References perature UNITED STATES PATENTS 2,709,842 6/1955 Findlay 164/260 X 7 Claims, 8 Drawing Figures MENTEUAPR 2 I974 3 800 4 SHEET 2 BF 4 Fig. 3

ATENTEDMR 21974 3,800,848

sum 3 OF 4 FIGS PATENTEBAPR 219M SHEEIHUFQ F/G 7 METHOD FOR CONTINUOUS VACUUM CASTING I OF METALS OR OTHER MATERIALS This is a division of application Ser. No. 865,719 filed Oct. 13, 1969, now US. Pat. No. 3,724,529 dated Apr. 3, 1973.

The present invention relates to a method for continuous vacuum casting of metals, metal alloys or other materials which require good degassing and/or are liable to readily react at high temperature under normal atmospheric conditions, said method being especially suitable for the manufacture of uranium shapes and tubes.

The increasing trend to use very pure metals or alloying elements, coupled with the need to prevent oxidation of said metals during the various handling steps in a shapeor tube-making process, has led to constant improvements in the methods used in such processes and in the apparatuses for their operation.

Devices are already known whereby tubes, shapes and bars consisting of a sheath surrounding a core of a different material can be continuously cast and shaped in the open air, but such procedures lack the advantages gained by operating under vacuum or under reduced neutral gas pressure in accordance with the present invention.

Devices are also known whereby materials can be cast under vacuum, but no means providing the advantages of the present invention has been heretofore provided for continuous withdrawal of these materials from under vacuum, particularly if use is to be made of relatively high vacuum.

Finally, previously known apparatuses for the socalled continuous vacuum casting include no device having the advantages of the present invention for continuous withdrawal of the hot metal from under vacuum into air.

Moreover, no means have previously been provided to ensure the controlled cooling and, if required, the hardening of the metal in a single step according to the present invention. 7

The present invention is directed to improve the aforesaid methods and devices so as to provide a method and plant whereby the steps of vacuum degassing, continuous vacuum casting and controlled cooling of metals, metal alloys or other materials, especially those liable to readily react at high temperature under normal atmosphere, can be effected simultaneously.

The method according to the invention is especially applicable to plants comprising a ladle containing molten metal held at constant temperature, or any other isothermal source of molten metal; a cooled ingotmould, also adapted to serve sometimes as a ladle; a vacuum cooling device and, between said vacuum cooling device and a spray means in the open air, dynamic lock for emergence into air, comprised of chambers which are maintained under decreasing pressures by pumping devices of known types and are separated from each other by diaphragms.

The aforesaid method consists, on the one hand, in holding the static pressure of the metal on the shape or tube being formed at a constant value, for a given size with respect to the liquid meniscus size, so as to render the permissible difference between the cross-section of said shape or tube, when reaching the dynamic lock, and the cross-section of said diaphragms low enough for the rate of air admission to remain in all cases lower than the pumping rates of said pumping devices, and, on the other hand, in so selecting the cooling zone length, as a function of the suitably set rate of withdrawal of the moulded shape, that said shape will enter the spray means, when leaving the lock, at a constant, controlled temperature.

The plant for operating to perform said method comprises in combination: a vacuum chamber, a ladle located within said vacuum chamber; a flow-rate control system associated with the ladle, such as an electromagnetic pump or a plunger in the lower part of said ladle; a distributor provided with a nozzle and fed with the liquid metal released by the plunger; a replaceable ingot-mould with a water-cooling system; a leveldetector arranged within the mould and adapted to control a servo-mecanism acting to adjust the flow-rate controlling means, e.g. the plunger position; a cooling jacket; a dynamic lock comprising several suction chambers, each connected to a pump of a type depending on the pressure in the respective chamber, said chambers being separated from each other by diaphragms and the last of them being followed by a pneumatic seal consisting of a neutral gas blast which acts moreover as a cooling device; a cooling spray device located outside the vacuum chamber at the outlet of said dynamic lock; withdrawal and guiding rollers rotating at a rate which can be adjusted by a servomecanism under the control of a temperature detector arranged at the outlet of the vacuum cooling chamber and, finally, an ingot-cutting device of any known type.

For the manufacture of tubes with a core, the plant comprises moreover a dynamic lock for inserting the core into the vacuum chamber; a guiding unit adapted to feed said core in true axial alignment with the mould and formed of roller sets arranged on each side of the dynamic lock and, if required, a core-heating device, either in front of the dynamic lock or under vacuum between said lock and the mould.

In case where the plant includes a vacuum coreheating device, then the dynamic lock may be simplitied and include from outside to inside the vacuum chamber: a sliding, preferably double-walled seal surrounding the core and made of elastomer, a suction chamber connected to a high discharge pump and a threaded dynamic seal.

Finally, in another embodiment devised to solve the problems raised by the tendency of the solidifying metal to stick to the inner wall of the moulds and by the control of the liquid material level, the apparatus comprises means for vibrating the mould according to a definite mode and for controlling with high precision the level reached in the mould by said liquid materials, and said means will be described in details in the following.

As a matter of fact, such sticking is known to impair the quality of the cast metal and to limit to some extent the speed at which the bars can reach the mould outlet, but the sticking effects can be reduced by vibrating the ingot-moulds. On the other hand, the rate at which the liquid materials are fed to the mould can be deemed well adjusted if the level of said liquid materials in the mould remains constant.

The invention will now be described in more details, with reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatical lay-out of a plant for the continuous vacuum casting of a bar.

FIG. 2 is a detailed enlarged view of the dynamic lock.

FIG. 3 shows a dynamic seal.

FIG. 4 shows the pneumatic seal and the associated spray means.

FIG. 5 is a diagrammatic lay-out of a plant for the continuous vacuum casting of tubes including a core.

FIG. 6 is a diagrammatic view showing the setting of an external ladle for make-up metal.

FIG. 7 shows the mounting of an ingot-mould which is caused to vibrate and of a system for controlling the level of the liquid materials in said ingot-mould, according to the invention, and

FIG. 8 is a reduced scale, schematic perspective view of a cam mechanism for vibrating an ingot mould vertically.

As shown in FIG. 1, the plant comprises a vacuum chamber 1, having located therein a ladle 2 acting as a reservoir for the liquid material used, in the example illustrated, for the manufacture of bars.

The ladle 2 is surrounded by an induction heating electric coil 3.

In the lower portion of ladle 2 is located a plunger or stopper 4 which controls the exit of liquid material from said ladle and has its opening movement controlled in very precise manner from a mechanical device 5 under the control of a servo-mechanism 6.

Under ladle 2 is a funnel-shaped distributor 7 which receives the liquid material descending past the plunger 4 and pours the same into a nozzle 8 ensuring uniform flow of the liquid material from the distributor 7 into an ingot-mould 9 adapted to shape the liquid flowing therethrough and thereby form a continuous casting. The ingot-mould 9 is replaceable and of known type; its internal portion is cylindrical and has a cross-section substantially equal to that of the bars to be produced, taking into account the shrinkage of the solidifying and cooling metal. The internal portion of the ingot-mould may 3 1 3 bijli b p r 1 1 9MELQL3P angle of l-2, so asfifirtmompensate shrinkage and thus prevent too rapid impairment of the thermal contact between the ingot and the mould.

The ingot-mould 9 is provided within its wall with a hydraulic cooling circuit supplied by ducts 10 at an ajustable flow-rate. A vibrating device of known type described hereinafter, is adapted to reciprocate the ingot-mould along its axis.

Two level-

sensing cells

11 and 12 are located one above the other in recesses provided in the cylindrical portion of the mould and provide a level detector connected to the servo-mechanism 6 which operates the mechanical device 5. The level of liquid metal in the ingot-mould 9 may be observed through an inspectionhole 13. Beneath the ingot-mould is a cooling jacket 14 through which the bar passes as it emerges from the ingot-mould.

Beneath the cooling jacket 14 is a dynamic vacuum lock 15 fed with nitrogen by a source 16, under a pressure controlled by a servo-mechanism l7 operated by a temperature-detector 18 at the lower part of the lock.

At the exit of the lock 15, the bar casting is driven through a spray means 19 whereby it is cooled and hardened if required, then it is gripped by the roller sets 4 20, 20' acting to guide it and to withdraw it from the lock.

The rollers 20, 20' are driven by a motor 21 which is operated by a servo-mechanism 22 under the control of a temperature-detector 23 located at the exit of the cooling jacket 14.

A follower cutter 24 of known type can be arranged beyond rollers 20, 20' to saw the ingot at a given length, normally to its axis.

When starting the continuous production of a bar, a withdrawal means 25 is used to grip the bar and pull it from the ingot-mould 9.

Said withdrawal means 25 consists of a rod having exactly the same cross-sectional area as the uranium or other bar to be produced and is equipped with a simple, easy to disconnect lug device 26 of the dovetail lug type, such as found in the conventional known continuous casting plants.

As shown in FIG. 2, the dynamic lock 15 includes five

suction chambers

27, 28, 29, 30 and 31 and a pneumatic seal 32. The suction chambers are separated from each other by

dynamic seals

33, 34, 35, 36 and 37.

The

dynamic seals

33, 34, 35 consist of borings in inserted metal cylinders, adapted to receive the bar with a clearance of some tenths of a millimeter, eg of 0.8 mm, and which may be knurled or threaded to a depth of some tenths of a millimeter.

In another embodiment, a seal may also be formed, as shown in FIG. 3, ofa flat ring 38 bearing on its upper and lower faces respective funnel-shaped diaphragms 39, 40. Said diaphragms comprise annular plates 41, 42 supported respectively on the upper and lower faces of ring 38, and, frusto-

conical portions

43, 44, each of which is in fluid-tight connection with one annular plate 41, 42 and terminates in a

cylinder

45, 46.

Diaphragms 39, are slit along a generatrix, so that the diameters diameter of their cylindrical portions can vary by some tenths of a millimeter. The diaphragms are secured to ring 38 in such manner that the slits are in opposite directions with respect to the axis of the dynamic seal. The internal diameter of cylinder 45 is substantially equal to the diameter of the bars to be produced and the inner diameter of cylinder 46 is equal to the outer diameter of cylinder 45, so that the whole length of the cylinder 46 engages cylinder 45.

Referring to FIG. 2, suction chamber 27 is connected to a low pressure, mean delivery pump (not shown).

Chambers

28, 29, 30, 31 are connected through

passages

27a, 28a, 29a, 30a and 31a to pumps (not shown) of successively increasing delivery ratings. Chamber 3] I is connected to a liquid ring vacuum pump. Pumps of this type are well known, for example as shown in US. Pat. Nos. 1,849,929 to Hayton and 2, l 36,508 to Stelzer. Chamber 27 is equipped with a vacuum gauge 47. Chamber 28 is connected to a pressure-gauge 48. Pneumatic seal 32 (FIG. 4) consists of two moulded parts of

revolution

49, 50. The upper face 51 of part 49 is flat so as to be connectable with chamber 31. The lower portion of part 49 includes a frustum of revolution 52 having its axis along the axis of the bar being cast. Part 49 is provided along its axis with a bore of a diameter equal, but for the clearance of 0.8 mm, to the diameter of the bars to be produced.

The interior of part has the shape of a nozzle neck of which portion 53 forms the converging section and portion 54 the diverging section. A static seal 55 is 10- cated between the upper edge of part 50 and the lower edge of part 49. The space between

parts

49 and 50 forms the pressure chamber PC which is connected by means of a pipe 56 to the source 16 of i.e. inert neutral gas, preferably nitrogen, under pressure. The frustum 52 and

portions

53, 54 of part 50 define a crownshaped nozzle from which the neutral gas from pressure source 16 is released around and over the cooling bar. The temperature detector 18, lodged in a recess provided in the cylindrical hole of part 49, is connected to servo-mechanism 17.

The spray means 19 consists of a water chamber 58 the walls of which are made of two metal bells, 59, 60 having the same axis of revolution. Each bell is formed in its upper portion with an aperture having substantially the same cross-section as the bar to be produced. Small orifices are uniformly distributed across bell 60. A metal pipe 61 having its end welded onto bell 59 feeds water under pressure to water chamber 58.

The continuous vacuum casting plant which has just been described by mere way of example is devised for the production of uranium bars. FIG. 5 shows a modified embodiment of said plant, wherein the latter is adapted to produce uranium tubes with a graphite core.

According to this embodiment, the various units are substantially similar to those of the continuous vacuum casting plant for bars, but some of them are located differently and arranged to receive a graphite core.

As shown in FIG. 5, the graphite core 62 has the shape of a bar and is held in a vertical position by two sets of

silicon carbide rollers

63, 63.

The graphite core 62 enters vacuum chamber 1 through a dynamic lock 64 which may be identical to the afore-described dynamic lock for the exit of the moulded shape. A lock of this type must be provided whenever the core is to be heated before entering the vacuum chamber. However, when the core is heated under vacuum, dynamic lock 64 is a simplified construction since it comprises from outside to inside, a double-walled circular sliding soal 65, a suction chamber 66 with its high delivery pump and a threaded dynamic seal 67, similar to the above-described

seals

33, 34, 35.

Core 62 will then advance through means comprising a set of guiding rollers 68 located above the inlet of ingot-mould 9 and through an electrical induction heating coil 69 before entering the ingot-mould.

Rollers 68 may to advantage be replaced by three friction pads immediately above the connection of spout 8 with the ingot-mould.

As in the continuous vacuum casting plant for solid bars, the ingot-mould 9, cooling jacket 14 and vacuum lock 15 are intended to receive the bar to be vacuum cast and are to this end arranged in vertical alignment. However, the common vertical axis of the ingot-mould, cooling jacket and vacuum lock coincides with the graphite core axis and is therefore offset with respect to the ladle 2 containing a reserve of molten metal. Spout 8 is not vertical, but oblique for feeding the mo]- ten metal from plunger 4 to ingot-mould 9. From the latter, the graphite core 62 with the surrounding cast ingot metal is driven through the same units as was the bar in the continuous casting plant for bars, while being kept in precise axial alignment by the successive sets of

silicon carbide rollers

63, 63.

In FIG. 6, there is shown the setting of a ladle 70 containing make-up liquid metal, which has its bottom removably connected in fluid-tight manner with vacuum chamber 1, by means known per se. Plunger 71 can be operated from outside to pour the content of ladle 70, through the wall of vacuum chamber 1, into ladle 2, at the desired rate.

When casting a metal such as uranium, the latter is poured in the liquid state in ladle 2, eg from ladle 70 which is brought on site. Ladle 2 is held at a constant temperature by the induction heating coil 3. Once the ladle has reached the desired temperature, then liquid uranium may be released by plunger 4.

Liquid uranium is poured in ingot-mould 9 across plunger 4 and through spout 8. Both level-detectors l l and 12 act in known manner on servo-mechanism 6 which, through mechanical device 5, will so control the opening movement of plunger 4 as to keep the surface of the liquid uranium in the ingot-mould between the two levels defined by said level-detectors.

Upon contacting the cold wall of the ingot-mould, the metal solidifies to form a solid skull or skin surrounding the liquid; as heat is extracted from the ingotmould, the thickness of said skull will increase until the bar is formed; during its descent, the bar has the same cross-section as the ingot-mould until the shrinkage caused by peripheral solidification and cooling will apply to the thickening skull a pressure exceeding the static pressure of the metal, at which time the crosssection of the bar is then slightly smaller than that of the ingot-mould. The ingot-mould is replaceable to allow changeover to another ingot size or replacement in case of wear. It must be of such length that, taking into account the withdrawal rate and cooling efficiency, the solidifying wall has acquired enough strength to retain the metal remaining liquid in the central portion of the bar before leaving the ingot-mould. On the other hand, the ingot-mould should not be too long, to avoid undue friction against the ingot being withdrawn. The device for vibrating the ingot-mould serves to limit the prejudicial effects caused by said friction along the ingot surface.

At the beginning of a run, the withdrawal means 25 is introduced into vacuum chamber 1, through dynamic lock 15, its rod having the same diameter as the bar to be produced, then the lock is closed. The lug 26 at the end of the withdrawal means is arranged within the cylindrical portion of the ingot-mould so that liquid uranium will solidify around said lug. Then, a mere traction on the rod 25 will suffice to tug along the bar being formed in the ingot-mould. The withdrawing process is initiated by the

withdrawal rollers

20, 20 drawing the withdrawal device 25.

In the casting plant for tubes with cores (FIG. 5), the graphite core 62 goes through the dynamic seal 64 to enter the vacuum chamber.

Said core is then subjected by coil 69 to an induction pre-heating step which causes simultaneous degassing, whereafter it is driven through ingot-mould 9, being kept precisely centered on the axis thereof by

rollers

63, 63 and by rollers or skids 68. Uranium will solidify around the graphite bar and thus a cored tube will exit from the ingot-mould.

The cored bar or tube is then driven through cooling jacket 14. The bar is drawn towards vacuum chamber (dynamic vacuum lock) 15, through withdrawal rollers 20, 20' driven by motor 21, at a given linear speed. Servo-mechanism 22, controlled by temperature-detector 23, acts to adjust the speed of motor 21 to cause the bar to emerge at desired temperature from cooling jacket 14, which is of suitably selected length to cause adequate radiation cooling of the bars, e. g. down to 800C. Thus, when withdrawn at a speed of 2 cm/s from an ingot-mould having a length of 280 mm, a bar of a 60 mm-diameter will be at a temperature of 950C.

The cored bar or tube then enters vacuum lock 15. The threaded seals 33, 34, 35 (FIG. 2) are intended for the following pressure differences, in torrs: from to 10*; from 10' to 10*; from 10 to 1, respectively. Funnel-shaped seals 36, 37 are intended for pressure ratios, in torrs, of 1 to 10 and 10 to 10 Finally, pneumatic seal 32 corresponds to the pressure difference, in torrs, of from 10 to 10 Besides acting as a seal, pneumatic seal 32 (FIG. 4) has three other functions. Namely, due to its location, the pneumatic seal serves to prevent ingress of water from spray means 19. As a matter of fact, nitrogen issuing from the pressure chamber is released downwards, at high speed, along bar B, through an exhaust channel EC, acting as a nozzle-neck, located between the bottom of frustum 52 and the restricted portion of part 50.

Consequently, the nitrogen blast will drive back downwards the fine water droplets sprayed by means 19. Secondly, due to its accelerated outwards motion, the nitrogen jet prevents any ingress of oxygen from the ambient atmosphere into the pressure chamber.

Finally, the nitrogen jet acts as an adjustable cooling member on the bar issuing from the pneumatic seal. To this end, temperature-detector 18 (FIG. 1) actuates servo-mechanism 17 which, by regulating the pressure in the nitrogen source 16 and in pressure chamber 15, causes the gas to exit at a variable velocity and thus adjusts cooling so as to keep the bar issuing from the pneumatic sea] at a fixed temperature, e.g. of about 700C.

The spray means 19 ensures rapid cooling of the bar, serving several purposes, viz.: apart from thus permitting handling of the cut bars, the spray means prevents the bar from firing as a result of its rapid oxidation in the air and if the alloy is susceptible thereto, it may effect a hardening step which, in the present case, is from 700C.

The use of a vacuum chamber 1 having located therein a ladle 2 at l400C and the temperatureand pressure-adjusting processes allow, on the one hand, obtention of uranium which is very pure since subjected to thorough vacuum degassing at high temperature and, on the other hand, continuous shaping of bars and withdrawal thereof from the vacuum chamber, at high speed, and if required, hardening of the bars under precise temperature conditions.

It should be noticed that the uranium treatment was described by mere way of example, implying no limitation to the present process. In particular, the method according to the invention is of high interest for the casting of steels and other materials requiring rather intensive dehydrogenation and/or decarbonization and denitriding steps, said steps being promoted by the substantial degassing obtained under vacuum.

Moreover, the insertion of premelted metal in the vacuum chamber is not a requisite step. Within the scope of the invention, the metal may be melted directly within the ingot-mould, either under vacuum by electron bombardment or under a controlled atmosphere (e.g. argon atmosphere at torrs) by are fuslon.

Finally, the various temperature and pressure control processes and the use in the vacuum lock of a number of suction chambers separated by dynamic seals provide great operational safety.

Indeed, should some temperature-control device fail, then the other temperature control devices will suffice to control the advance of the bar through the vacuum chamber.

At last, in case of abnormal operation of one suction chamber, the pumps of the other suction chambers have sufficient delivery to maintain said chambers under the requisite low pressures.

FIG. 7 shows a modified embodiment according to which there are provided means to vibrate the ingotmould in a definite mode and means to control with great precision the level reached in the ingot-mould by the liquid materials.

In said FIG. 7, there is shown at 101 a circular plate serving as a base for the device and connected to the vacuum chamber 1. The axis of this circular plate coincides with the ingot-mould axis. A cylindrical passage having a diameter slightly greater than that of the bars to be cast is provided through the circular plate, in axial alignment with the ingot-mould.

A circular sleeve 102 is secured normally to plate 101 and has a through bore parallel to the ingot-mould axis. Two further sleeves, one of which is shown at 103, are fixed onto the circular base. The spacings of the axes of sleeves to the ingot-mould axis all are equal and planes passing through the ingot-mould axis and the axes of sleeves are spaced from each other at angles of 120 around the axis of the ingot-mould. Vertical pedestals, two, 105 and 106, being shown, and a third not being shown are slidable in the bores of the afordsaid sleeves respectively. A circular plate 108 is secured to the three pedestals 105, etc. somewhat above sleeves 102 etc. A circular plate 109 is secured onto the tops of the pedestals. A cylindrical copper lining 110 forming the main body of the ingot-mould is secured to

plates

108 and 109. A hollow steel cylinder 1 11, which is coaxial to the ingot-mould and has a greater diameter than the copper lining 110, defines with liner 110 and plates 108, 109 a closed space which is filled with water. Said closed space is fed with running water from

hoses

112, 113. Said hoses are capable of withstanding, when under vacuum, an internal pressure by five to seven times higher than atmospheric pressure, without any leakage towards vacuum.

Two links, one being shown at 114, which are symmetrically arranged about the ingot-mould axis are joumalled about respective horizontal pins, one being shown at 116, mounted in bearings, one being shown at 118, which are attached to plate 108. Said links are operatively connected to the ends of crank arms, one being shown at 120, by pins, one being shown at 122. The crank arms are secured to a shaft 124 which is parallel with plate 101 and held in this position by bearings (not shown) attached to plate 101. The crank arms rotate with the shaft 124 when the shaft is operated by a cam. A previously known and suitable cam and cam drive arrangement are shown schematically in FIG. 8. The cam is shown at formed with a cam track 151. A lever 152 pivoted on a bearing 153 fixed with respect to theplate 101 and parts secured thereto has a follower roller 154 engaging the cam track 151. A link 155 is pivoted at 156 to the lever 152 and is pivoted at 157 to an arm 158 secured to the shaft 124. The cam 150 is mounted on a shaft 159 driven in the direction of the arrow a by an electric motor 160. Said cam drives the shaft 124 at a rotational speed which is low in the direction corresponding to the descending movement of crank arm pivot 157 and high in the opposite direction, corresponding to the ascending movement thereof.

There is shown at 125 the probe of a Geiger counter which extends vertically besides cylindrical tube 111. Probe 125 is connected to the electronic circuit of the Geiger counter through a flexible tube 126.

The outlet of the electronic circuit is connected to the servo-mechanism 6 controlling the rate of admission by the plunger 4. A source of radioactive radiation 127 is so arranged before the ingot-mould that the axis of the ingot-mould and the axis of probe 125 are within the radiation field. The upper horizontal boundary plane of the radio active radiation is at a level slightly above the permissible level of the liquid materials in the ingot-mould.

The jerky ingot-mould movement is generated in the following manner:

The aforementioned cam 150 driven by the electric motor 160 causes the shaft 124 to rotate slowly by a few degrees in one direction, then to rotate rapidly by the same number of degrees in the opposite direction.

When shaft 124 is rotating in the first-mentioned direction, the ends of the crank arms 120, which are connected by pins to the link 114 and the other link, not shown, cause the links move slowly downwards. When the shaft 124 is rotating in said opposite direction, the links are rapidly raised. Said links will impart a reciprocating vertical motion to plate 108 and to all parts mounted thereon, especially pedestals 105 and 106 and the third pedestal, not shown.

Sleeves

102, 103, and the third sleeve, not shown, which hold pedestals the pedestals in vertical positions allow sliding vertical motion of said pedestals to follow the verticalmovements of the links.

Parts

108, 109, 110, 111 are driven by said links in a vertical motion with a slow descending and a rapid ascending stroke.

During rapid raising of the ingot-mould, the bar being formed is prevented from being lifted, especially by means of the withdrawal rollers such as 20, however, the friction and surface tension forces might drive along a metal ring of small height, located near the meniscus. When the ingot-mould is driven downwards at a speed slightly exceeding that of the bar, said ring will be pressed onto the bar and thus again joined therewith.

Provision is made to use the radioactive radiation source 127 such as above-mentioned and a Geiger counter to control the level reached by the liquid materials in the ingot-mould and to use the level measurements from the thus devised controller for operating the servo-mechanism 6 acting to adjust the plunger 4 opening movement and, thereby, the rate of admission of liquid materials.

The radioactive source provided has the advantage of producing radiation which is bounded by two vertical planes in close parallel relationship, by a horizontal plane and by a plane which is normal to both vertical planes and at a definite angle to the horizontal plane;

therefore, by precisely adjusting the position of the radioactive radiation source along two horizontal, mutually perpendicular axes and by suitably controlling the direction of said source, both the ingot-mould axis and the Geiger probe axis can be brought within the two radiation-bounding vertical planes. By adjusting the height of the radiation source, the horizontal boundary plane of the radiation can be caused to lie above the liquid material level. Such provisions allow the operating staff to handle safely a rather strong radioactive flux, since the radiation flux area is defined by precise geometrical surfaces.

Due to the use of a strong radioactive flux, said flux undergoes substantial variations to be detected by the probe even when the variations of the liquid material are small. As a result, the servo-mechanism controlling the admission of liquid materials provides highly sensitive adjustment.

The major advantage of such a device is to allow simultaneously the obtention of a constant withdrawal rate and very precise adjustment of the liquid material level.

Of course, the present invention is not limited to the embodiments described and shown, but includes within its scope any modification or variation thereto.

We claim:

1. In forming a casting by continuously casting metallic materials or metal alloy materials requiring good degassing and which are apt to react readily at high temperatures in the presence of atmosphere: delivering such material in the molten state under vacuum into a vertically extending ingot mold; controlling the rate of delivery in response to the level of the material in said ingot mold; cooling the material in the ingot mold ini tially to form a skin surrounding a still unsolidified core which solidifies as the casting moves continuously through and out of said mold; drawing the casting from said ingot mold; further cooling the solidified casting under vacuum after it emerges from said mold; thereafter passing said casting through a succession of suction chambers; subjecting said chambers respectively to degrees of suction which increase from chamber-tochamber in the direction of passage of the casting successively through said chambers; and delivering an inert gas blast onto the casting emerging from said succession of chambers to seal the exit end of said succession of chambers and to cool the emerging casting.

2. Method according to claim 1 in which the casting is fed from the ingot mold and said succession of chambers; and in which the rate of feeding is controlled to maintain a substantially constant temperature in the casting as it emerges from said chambers and is subjected to said inert gas blast.

3. Method according to claim 1 in which the casting, after solidifying, is fed from said ingot mold; and in which the rate of feeding is controlled in response to the temperature of the casting after said further cooling thereof under vacuum after emerging from the mold.

4. Method according to claim 1 in which a preformed elongated core is introduced continuously into said mold while under vacuum so as to be surrounded by molten material delivered into said mold under vacuum.

5. Method according to claim 4 in which said core is heated upstream of said ingot mold.

6. Method according to claim 1 in which said ingot mold is reciprocated vertically during casting.

7. Method according to claim 6 in which the reciprocation of said mold is carried out with a relatively slow downward movement and a relatively rapid upward movement.

Claims

1. In forming a casting by continuously casting metallic materials or metal alloy materials requiring good degassing and which are apt to react readily at high temperatures in the presence of atmosphere: delivering such material in the molten state under vacuum into a vertically extending ingot mold; controlling the rate of delivery in response to the level of the material in said ingot mold; cooling the material in the ingot mold initially to form a skin surrounding a still unsolidified core which solidifies as the casting moves continuously through and out of said mold; drawing the casting from said ingot mold; further cooling the solidified casting under vacuum after it emerges from said mold; thereafter passing said casting through a succession of suction chambers; subjecting said chambers respectively to degrees of suction which increase from chamberto-chamber in the direction of passage of the casting successively through said chambers; and delivering an inert gas blast onto the casting emerging from said succession of chambers to seal the exit end of said succession of chambers and to cool the emerging casting.

4. Method according to claim 1 in which a pre-formed elongated core is introduced continuously into said mold while under vacuum so as to be surrounded by molten material delivered into said mold under vacuum.