GB2116888A - Semicontinuous casting apparatus - Google Patents

Abstract

A holding furnace 1 is connected through a closed metal feeding system 3 to a pneumatic metal supply means 2 on which is mounted a mould 6 with a cooling system. The mould cooling system has a device 8 for forcing out a liquid coolant from the mould 6 by compressed gas. A dummy bar 9 has a central head 10 which accommodates a heating element 11 and an adjustable valve 12 for admitting an inert gas to the interior of a casting 26 being formed. The casting withdrawal system has two casting withdrawal mechanisms 15 and 16 alternately cooperating with the dummy bar 9, of which the mechanism 15 is operated to pull out the casting 26 from the mould 6 for a distance not smaller than the length of the casting 26 minus the length of the mould; the mechanism 16 being effective to pull out the casting 26 from the mould 6 for a distance not smaller than the length of the mould 6. The apparatus can be used in the production of solid and hollow castings by a semicontinuous process in which the castings are drawn up from a mould. <IMAGE>

Description

SPECIFICATION Semicontinuous casting apparatus The present invention relates to apparatus for the semicontinuous casting of metal, e.g. for casting solid and hollow sections, by drawing-up.

Continuous and semicontinuous casting machines are now finding an ever greater application in the metallurgical industry throughout the world. The introduction of such machines makes it possible to substantially reduce the production cycle as compared to conventional techniques used in foundry practice. In addition, these types of machines allow a considerable saving in time and labour, an extra gain in yield, enhanced production efficiency, and improved working conditions. The castings produced by such machines have uniform structure and good properties.

Japanese Patent No. 45-39345 describes a machine for continuous casting by drawing-up, which comprises a sealed chamber for molten metal, a water-cooled mould immersed in the molten metal, and a dummy bar incorporated in a casting withdrawal mechanism.

The above-described machine is constructed so as to permit the production of hollow castings by uphill casting of molten metal into the mold cavity. This being the case, a solidified layer and a semisolid layer contiguous thereto are formed on the working surface of the mould (a solid-liquid phase). When the two above-mentioned layers reach a given thickness, the metal meniscus is brought down to be level with the lower end of the mould. Thereafter, upon complete solidification of the semisolid layer, the lower end of the solidified section is brought up to the top end of the mould and the metal meniscus is brought level with the lower end of the solidified section.

The mould cooling system in the above machine does not make it possible to control the casting skin formation conditions. Furthermore, the machine has no device for improving quality of the inner surface of the casting being produced.

U.S. Patent No. 3,302,252 discloses a machine for continuous casting of metal by drawing-up, which comprises a device for feeding a molten metal to an air-operated metal supply means having a metal supply duct. Mounted on the metal supply means is a mould provided with a cooling system and having a dummy bar placed on its upper part and operably connected with a casting withdrawal mechanism.

There is also provided an appliance for building up pressure in the metal supply means and a metal oscillating device.

The pipe casting produced by the machine has its wall formed on the working surface of the mould after it is filled with molten metal. The casting being.

formed is continuously withdrawn upwardly from the mould by means of a dummy bar operably connected to the casting withdrawal mechanism. In the process of casting formation the level of molten metal in the mould cavity is raised and lowered by means of the metal oscillating device.

The conditions causing the molten metal to move in the mould cavity may bring about oxidation of the inner surface of the solidified layer, as a result of which the newly forming layer will fail to adhere to the casting skin during the subsequent rise of the metal meniscus. This, in turn, will impair the quality of the cast product and, in the casting of aluminium alloys, will lead to defective products.

What is desired is a semicontinuous casting apparatus of such construction that will make it possible to produce castings of a quality good enough to render unnecessary further machining of their surfaces.

The invention provides semicontinuous-casting apparatus comprising a pneumatically-operated metal supply means adapted to be connected through a closed metal feeding system to a holding furnace, a mould with a cooling system arranged on the metal supply means, and a dummy bar placed on the upper part of the mould and operably connected to a casting withdrawal system, wherein the mould cooling system is provided with a device for forcing out a liquid coolant from the mould (e.g. by means of compressed gas), the dummy bar having a central head adapted to accommodate a heating element and an adjustable valve for admitting an inert gas into the interior of the casting being formed, the casting withdrawal system preferably having two casting withdrawal mechanisms for alternate cooperation with the dummy bar, of which one mechanism is operated to pull out the casting from the mould for a distande not smaller than the length of withdrawal of the casting minus the length of the mould, and the other casting withdrawal mechanism is effective to pull out the casting from the mould for a distance not smaller than the length of the mould.

Such apparatus construction makes it possible to produce castings of uniform structure and good surface quality.

One of the casting withdrawal mechanisms is preferably provided with a movable platform having an arm through which the plafform is operably connected with the dummy bar, and a drive; the other casting withdrawal mechanism is preferably provided with a movable bar sliding in roller guides, a toothed rack, and a member for engagement with the dummy bar, and a drive. Such structural engagement of the casting withdrawal mechanism makes it possible to create favourable casting withdrawal conditions and to shorten intervals between the casting cycles.

Where hollow castings are to be produced, the semicontinuous casting apparatus is preferably provided with a device for broaching and sizing the interior of the cast product, which device is made in the form of a broaching and sizing tool located in the lower part of the central head, and a drive which may be the actuator used for driving one of the casting withdrawal mechanisms.

The use of such a device allows the production of good quality castings with adequately sized inner surfaces.

The invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a general view of a semicontinuous casting apparatus; Figure 2 diagrammatically shows a central head of a dummy bar in section; Figure 3 is a top plan view of the dummy bar; Figure 4 shows slewing sections of a secondarycooling chamber, in plan view; Figure 5 shows a closed system through which a molten metal is fed from a holding furnace to an air-operated metal supply means; Figure 6 schematically shows a system through which a coolant is fed to the mould; Figure 7 is a cross-section of line Vll-Vll of Figure 3; and Figure 8 shows a dummy bar with a piercing and sizing tool.

The semicontinuous-csting apparatus illustrated comprises a holding furnace 1 which is connected to a pneumatically operated metal supply means 2 through a closed metal feeding system 3. The metal supply means 2 is connected to a compressed gas feeding system 4. Mounted on the top cover of the supply means 2 is a metal supply duct 5 with a flange which is heated. Connected to the flange of the supply duct 5 is a cooled mould 6 having a cooling system with a coolant source 7 and a device 8 for forcing out a liquid coolant from the mould 6 by means of compressed gas.

The apparatus incorporates at least two dummy bars 9, only one of which is shown. The required dummy bar 9 is mounted on the mould 6 prior to starting the next casting cycle. The dummy bar 9 has a central opening adapted to receive a central head 10. The head 10 has a heating element 11 (Figure 2) and an adjustable valve 12. The body of the head 10 is formed with two holes through which it communicates with an inert gas supply system 13 (Figure 1).

Mounted on the dummy bar 9 are two legs 14 (Figures 3,7) formed with holes 49 through which the dummy bar 9 cooperates with a casting withdrawal mechanism 15 or 16 (Figure 1). When the dummy bar 9 cooperates with the casting withdrawal mechanism 15, pins 17 extending from an arm 18 (Figure 7) are introduced into the holes in the legs 14.

When, however, the dummy bar 9 is associated with the casting withdrawal mechanism 16, the holes in the legs 14 receive pins 19 (Figures 3,7) of a movable spring-loaded bracket 20 with a slot 21. The pins 19 of the bracket 20 and its slots 21 are aligned so that the pins 19 are permitted to enter the holes in the legs 14 of the dummy bar 9, while the bracket 20 per se, or rather its section formed with the slot 21, is accommodated in openings (grooves) formed in a member 54 of the withdrawal mechanism 16 (Figure 1) described below. The withdrawal mechanisms 15 and 16 make up a casting withdrawal system.

The casting withdrawal mechanism 15 incorporates a drive (not shown), a feed screw 22, and a platform 23 which bears against the feed screw 22 and is movable relative to stationary guide columns (not shown). Movably mounted on the platform 23 is the arm 18 with the pins 17. The casting withdrawal mechanism 16 is placed on a trolley 24 for movement along stationary beams 25 located above the withdrawal mechanism 15.

Disposed above the mould 6 within a length corresponding to the length of withdrawal of a casting 26 from the mould 6 is a secondary-cooling zone defined by upper and lower cooling sections 27, each comprising at least two shoes 28 (Figure 4) secured to slewing arms 29. The shoes 28 are smaller in length than the mould 6 (Figure 1) and are preferably equal in length to the maximum distance for which the casting 26 is withdrawn in a single cycle.

The closed feeding system 3 intended for feeding molten metal from the holding furnace 1 to the pneumatic metal supply means 2 has a tap-hole closing appliance which is accommodated in a chamber 30. The feeding system 3 comprises a tap-hole 31 (Figure 5) which is formed in a refractory block 32 and is closed by a gate 33 placed in a holder 34 through which the gate 33 is pressed against the refractory block 32. The gate 33, together with the holder 34, is forced against the refractory block 32 by means of a connecting rod 35. The holder 34 is connected with a layer 36 resting on a pivot 38 fixed in stands 37, and driven by an actuator 39 located externally of the chamber 30.

Fitted in the wall of the metal supply duct 5 (Figure 1) below its heated flange is a hole connected to a tube 40 which communicates with the compressed gas supply system 4 and has a shutoff valve 41. The tube 40 has one of its ends flaring towards the metal duct 5. The inner wall of this flared part of the tube 40 has a protective coating preventing adhesion of the cast metal to the walls of the tube 40. The flared end of the tube 40 and the protective coating facilitate the return of metal which may penetrate into the tube in the course of operation.

The mould cooling system with the coolant supply source (coolant vessel) 7 (Figure 1) and device 8 for forced discharge of coolant from the mould includes a valve 42 (Figure 6) forfeeding compressed air to the mould 6, set in a pipeline 43 through which the coolant is delivered from the mould 6 to the coolant is delivered from the container 7 to the mould 6, and arranged in series therein are a relief valve 45 and a closed vessel 46 provided with an indicator 47 of the coolant level in the closed vessel46. A tube 48 returns coolant from relief valve 45 to the source 7.

The casting withdrawal mechanisms 15 and 16 are well adapted for rapid alternate cooperation with the dummy bar 9 in a required sequence. The first to associate with the dummy bar 9 (Figure 7) having the legs 14with holes 49, is the mechanism 15 (Figure 1) which is brought in cooperation with the dummy bar 9 through the pins 17 fixed in the guide-slid arm 18 of the movable platform 23. The platform 23 is permitted to travel for a distance at least equal to the length of the casting 26 minus the length of the mould 6.

The casting withdrawal mechanism 16, mounted on the trolley 24, is constructed so as to permit the casting 26 to be pulled out for a length not smaller than that of the mould 6. The mechanism 16 has, slidably mounted in roller guides 50, bars 51 with a pair of toothed racks 52 fixed thereon and engaged with a pair of driven pinions 53. The lower end of the bar 51 carries the member 54 with openings through which the bar 51 is connected with the bracket 20 (Figure 3) mounted on the dummy bar 9.

Where the casting 26 is to be made hollow, the semicontinuous-casting apparatus is provided with a device for broaching and sizing the interior of the casting 26. The device in question is made in the form of a broaching and sizing tool 55 (Figure 8) located in the lower part of the central head 10, and a drive, which may be constituted by an actuator 56 (Figure 1) incorporated in the casting withdrawal mechanism 16. The member 54 on the bar 51 is readily connected to and disconnected from a shank 57 (Figure 8) of the broaching and sizing tool 55, with the bar 51 (Figure 1) being made of sufficient length to permit the central head 10 to travel over the entire length of the casting 26 being produced.

The central head 10 (FigureS) has a valve element 58 past which an inert gas is fed into the interior of the casting 26. The valve element 58 is operably connected with a piston 59. The head 10 has two radial holes 60 and 61 in its middle part. The hole 60 is connected to a chamber 62 accommodating the piston 59, and the hole 61 communicates with a chamber 63 accommodating the valve 58.

The central head 10 is received in an opening 64 in the dummy bar 9 and is held in place by means of rods 65 and 66 which are fitted into sleeves 67 and 68. The rods 65 and 66 have radial and axial holes. A radial hole 69 in the rod 65 communicates with a radial hole 70 in the rod 65, then with a hole 71 in the leg 14 of the dummy bar 9, and further with a radial hole 72 (Figure 7 and 8) as well as with an axial hole 73 in one pin 17 of the casting withdrawal mechanism 15. Connected to the hole 73 (Figure 7) at the end of the pin 17 is a nipple 74 having a flexible hose 75 coupled thereto for supplying compressed gas.

An axial hole 76 (Figure 8) in the rod 66 communicates with a radial hole 77 in the rod 66, then with a hole 78 in a support stand 79 of the dummy bar 9, further with a radial hole 80 and an axial hole 81 in the other pin 17 (referenced 82 in Figure 8) of the casing withdrawal mechanism 15. Connected to the hole 81 (FigureS) at the end of the pin 82 is a hose (not shown) forfeeding an inert gas.

When used for producing round castings, the above-described apparatus is operated in the following manner.

After prepatory operations, the metal supply duct 5 (Figure 1) is heated to a temperature close to the melting point of the metal being cast. Next, the dummy bar 9 is placed on top of the mould 6 and then is connected to the casting withdrawal mechanism 15 by means of the pins 17.

Then, the pneumatically operated metal supply means 2 and the chamber 30 of the closed metal feeding system 3 are blown through with an inert gas, such as argbn, to produce an inert atmosphere therein.

This being done, the tap-hole 31 (Figure 5) is opened by moving the holder 34 with the gate 33 upwardly through the agency of the lever 36 to permit a required amount of molten metal to be poured from the holding furnace 1 (Figure 1) into the metal supply means 2. Although the amount of molten metal fed to the pneumatic supply means 2 usually corresponds to the weight of the casting 26 being produced, it may be more or less than this weight.

After this supply means 2 has been filled with metal up to a preset level, the tap-hole 31 is closed by the gate 33 and superpressure is built up in the chamber 30 and in the supply means 2 with the aid of the compressed gas feeding system 4 (Figure 1), whereupon the molten metal is caused to pass through the duct 5 into the mould 6, thereby raising the level of metal (meniscus) until it comes in contact with the lower end of the dummy bar 9. Gas can be freely discharged from the mould cavity through the central head 10 of the dummy bar 9, the valve 12 (Figure 2) being open, i.e. the valve element 58 does not close the outlet 83 (Figure 8). However, in certain cases it may be advantageous for the molten metal to be fed into the mould 6 with superpressure acting on the rising metal meniscus.To this end, the valve element 58 is forced against its seat at a preset pressure so as to ensure a required pressure of gas on the rising metal meniscus.

Normally it takes not more than 3 to 5 seconds to fill the mould 6 with molten metal.

Once the mould 6 is filled with molten metal and the outlet 83 in the central head 10 is closed, a skin of the casting 26 to be produced is formed to a preset thickness under conditions close to those obtained in permanent-mould casting with superpressure acting from the side of molten metal. To fulfil this condition, immediately after filling the mould 6 (Figure 1) with molten metal or prior to feeding the molten metal thereinto, depending on the possibilities of the mould 6, coolant is removed from the cooling channels of the mould 6 with the aid of the compressed gas (air) supply device 8. Due to the heat liberated in the course of metal solidification, the walls of the mould 6 are heated to the required temperature, for example 150 to 250"C when aluminium alloys are cast.

Although the liquid coolant continues to be fed from the coolant supply source 7 at the time when compressed air is introduced into the channels of the mould 6, it is immediately recycled to the source 7 through the relief valve 45 (Figure 6).

The initial formation of the skin of the casting 26 is carried out in the preheated mould 6 at a preset superpressure. This pressure may be in the range of 0.5 to 6 atmospheres (gauge) or more. The required pressure is achieved by means of compressed inert gas fed by the compressed gas system 4 (Figure 1).

The casting 26 is formed in the preheated mould 6 until its skin reaches a thickness of about 10 to 30 mm, whereupon compressed gas is discharged from the channels of the mould 6 and the liquid coolant, such as water, is introduced at a temperature close to ambient temperature. The rate of heat removal from the casing 26 is thus stepped up by lowering the temperature of the walls of the mould 6 and by reason of the fact that with the supply of coolant the mould 6 is substantially reduced in size and its walls come into closer contact with the casting 26. In the given case, it is possible to create conditions under which the solidified skin of the casting 26 will undergo external stresses, from the side of the mould walls 6, and internal stresses acting from the side of molten metal.

The following example is given to emphasise the importance of taking into account the expansion of the mould 6 caused by high temperatures of its walls. In the event of producing a round-shaped casting 500 mm in diameter in the mould 6, formed of aluminium alloy with a hard-anodized working surface, with the coefficient of linear expansion of this alloy being 24.10-6 in the temperature range of 20 to 300"C, the inner diameter of the mould 6 will change by 2.4 mm if the temperature of the walls of the mould 6 changes by 200"C. Obviously, such substantial change in the size of the mould 6 should be given due consideration and should be used to good advantage.

Further, with the superpressure still acting on the skin of casting being formed, its formation continues until it reaches 40 to 60 mm in thickness.

Once the skin of the casing 26 is formed to a preset thickness, the superpressure acting on the molten metal from the compressed gas feeding system 4 is released and the liquid coolant is concurrently discharged from the channels of the mould 6, whereby it becomes possible to ensure some expansion of the mould 6 due to its heating. Thus, favourable conditions are created to enable effective withdrawal of the casting 26 from the mould 6.

Next, the solidified skin of the casting 26, the upper part of which is reliably connected with the dummy bar 9, is rapidly withdrawn (in 3 to 8 s) upwardly from the mould 6 by means of the withdrawal mechanism 15 for a length not exceeding that of the mould 6. After the casting 26 has been withdrawn to this extent, the shoes 28 of the lower secondary cooling section 27 are rotated about their axes so as to be tightly pressed against the casting 26, enveloping its entire outer surface.

As the casting 26 is withdrawn from the mould 6, an inert gas is concurrently introduced into the interior of the casting 26 through the head 10 by means of the inert gas supply system 13 (Figure 1).

This is possible because in the course of initial formation of the casting 26 the temperature in the central end part of the casting 26 is maintained higher than that of the cast metal by means of the heater 11 (Figure 1) accommodated in the head 10.

If the pressure in the metal supply means 2 (Figure 1) is close to atmosphere pressure, then, with an inert gas being introduced into the interior of the casting interior and it may be completely removed from the cavity of the mould 6. However, it would be disadvantageous to bring down the metal level below the lower end of the mould 6. Thus, after introducing gas into the interior of the casting 26 being formed, the metal meniscus is first brought down, but not lower than the lower end of the casting 26. Further, by producing a required superpressure in the metal supply means 2, the metal meniscus is maintained at this level and, as the casting 26 is withdrawn from the mould 6, the metal meniscus is again raised at a speed not lower than that at which the casting 26 is withdrawn from the mould 6.

On completion of the above-described casting withdrawal operation, the metal meniscus in the interior of the casting 26 continues to be raised until it reaches a preset uppermost position, while inert gas is discharged from the casting 26 through the central head 10 of the dummy bar 9.

In certain cases, after the casting 26 has been withdrawn from the mould 6 for a given distance, it can be pulled slightly backwards to make up for the linear shrinkage of the newly forming portion of the casting 26.

The skin formation process in the newly formed portion is carried out in the cavity of the mould 6 as described above with reference to the initial skin formation procedure, i.e. with superpressure acting from the side of molten metal and with the walls of the mould 6 being first heated and then cooled. The heating of the walls of the mould 6, initiated still before withdrawing the casting 26 from the mould 6, is continued until the walls are heated to a preset temperature and after the casting 26 has been withdrawn from the mould 6 when the skin of the casting 26 is still thin. Then, at a preset time a coolant is again introduced into the mould 6.

Starting from the formation of the second portion of the casting 26, in the interval between withdrawing cycles, the molten metal is continuously brought up and down in the interior of the casting 26 being formed at a preset rate, for example, at a rate of 0.5 to 2.0 m/s. During the above-mentioned up and down cycles, an inert gas is discharged and introduced through the central head 10 in the dummy bar 9. These gas discharging and feeding steps could be carried out with a required superpressure being built up on the metal meniscus, if desired.

If, for instance, continuous movement of metal relative to the solidified skin is to be carried out during initial formation of the casting 26, an inert gas is introduced before the moment of initial withdrawal of the casting 26 from the mould 6, whereupon the above-mentioned conditions will be made possible.

After the second withdrawal cycle, the cooling shoes 28 of the upper section 27 of the secondarycooling zone are swung in, and the entire production cycle is repeated until the casting 26 is pulled out to a preset height.

Further, the skin formation process is carried on until the casting 26 is completely formed in the mould 6 without being withdrawn therefrom. From this moment on, the casting 26 is being formed until it becomes solid in cross section or until a preset thickness of its wall is reached, under conditions of continuous up-and-down movement of molten metal inside the casting 26. This permits the casting 26 being produced to have sound structure and uniform chemical composition.

If stringent requirements are not imposed on the quality of the casting 26, up-and-down movement of metal inside the casting 26 is not compulsory in the course of its formation to preset sizes.

Where a sound solid casting 26 is required, the movement of molten metal inside the casting 26 is discontinued toward the end of the solidification process and, maintaining the superpressure acting from the side of the metal supply duct 5, the solidification of the casting 26 is completed.

The casting 26 is intermittently withdrawn from the mould 6 for a given distance by means of the dummy bar 9 in conjunction with the casting withdrawal mechanism 15. At the end of the intermittent withdrawal operation, the casting withdrawal mechanism 15 is disengaged from the dummy bar 9 while the casting withdrawal mechanism 16 is concurrently connected thereto. The platform 23 of the withdrawal mechanism 15 is brought down to permit its rapid connection (in 10 to 15 s) with the next dummy bar 9.

The casting withdrawal mechanisms 15 and 16 are disconnected from and connected to the dummy bar 9 simultaneously. This is carried out as follows. The pins 17 are brought out of the holes in the legs 14 of the dummy bar 9, and the pins 19 (Figure 3) of the bracket 20 are at the same time automatically received in the same holes of the legs 14. As this happens, the bracket 20 formed with the slot 21 is received in the grooves provided in the member 54 (Figure 1) secured to the bar 51 of the withdrawal mechanism 16. In this way the dummy bar 9 is disengaged from the withdrawal mechanism 15 so as to cooperate with the withdrawal mechanism 16.

With the aid of the mechanism 16, the casting 26 is completely withdrawn from the mould 6 and then is conveyed along the guides 25 by the trolley 24 to a special storage location.

To enable easy disengagement of the lower end of the solid casting 26 from the molten metal during its withdrawal from the mould 6, an inert gas is fed to the place of disengagement through the tube 40 from the systems 4 via the valve 41.

As soon as the casting 26 has been withdrawn from the mould 6, a new dummy bar 9 is mounted on the mould 6 for cooperation with the casting withdrawal mechanism 16. Simultaneously, a new portion of molten metal is fed from the holding furnace 1 to the metal supply means 2.

The metal supply means 2 may be replenished with molten metal during the casting cycle at a time when the gas pressure in the metal supply means 2 is released.

If a hollow casting 26 is to be produced, then, on withdrawing the casting 26 for a given length, the skin formation process lasts until the skin of the casting 26 reaches a required thickness over its full vertical extent. Thereafter, broaching and sizing are carried out. To this end, the rods 65 and 66 (Figure 8) are retracted from the central head 10 so as to be disengaged from the sleeves 67 and 68.

Next, the drive 56 (Figure 1) is operated to bring down the bar 51 and, on connecting the member 54 with the shank 57 (Figure 8), the central head 10 is introduced into the interior of the casting 26. Here, the tool 55 is brought into use to cut off a part of the solidified metal from the inside walls of the casting 26 (broaching) and to effect sizing of the opening to the diameter of the tool 55.

The cut-off metal is return to the metal supply means 2 (Figure 2) to be melted down therein.

In the course of broaching, the opening in the casting 26 is not made right through but stops 20 to 30 mm short of the lower end, whereupon the central head 10 is disengaged from the bar 51, which is then lifted and held in place to permit the grooves in the member 54 to be in opposite space relationship with the slot 21 (Figure 3) in the bracket 20.

Next, the dummy bar 9 is connected with the casting withdrawal mechanism 16 while the casting withdrawal mechanism 15 is disengaged therefrom.

Further, the drive 56 is operated to effect withdrawal of the casting 26 from the mould 6, and the platform 23 with the arm 18 is brought down to the lower position so as to be connected by means of the pins 17 with a new dummy bar 9 mounted on the mould 6.

Once out of the mould 6, the casting 26 is conveyed by the trolley 24 to a specially designed place where final broaching of its opening is carried out and the central head 10 is removed therefrom.

As soon as the casting 26 is brought away from the casting line, the new dummy bar 9 is placed on the mould 6 for cooperation with the casting withdrawal mechanism 15 while the central head 10 is connected by means of the rods 65 and 66 (Figure 8) with the compressed gas supply system 13 (Figure 1).

When all the above-mentioned operations are completed, a new casting cycle is started.

The above-described semicontinuous-casting apparatus makes it possible to produce castings of good surface and structural quality and of uniform chemical composition. In addition, the apparatus is suitable for the production of hollow castings with a presized inner surface of high quality.

As a result, it becomes possible to reduce expenses required for the further mechanical treatment of castings, to diminish the number of defective castings, and to improve performance characteristics of the finished products manufactured from the castings produced by the apparatus.

The production capacity of the semicontinuouscasting apparatus can be increased 3 to 6 fold per strand as compared to conventional machines of similar type now in use (depending on the size of the casting being produced and the amount of metal poured). Consequently, a higher yield is possible with fewer machines, which affords a substantial reduction in capital investment and operational costs.

Claims (8)

1. Semicontinuous casting apparatus comprising a liquid-cooled mould mounted on metal supply means for supplying molten metal to the lower end of the mould under the effect of gas pressure; means for expelling coolant liquid from the mould; and a dummy bar mountable at the upper end of the mould,the dummy bar having a central head which accommodates a heating element and an adjustable valve for admitting an inert gas to the interior of a casting during its formation.

2. Apparatus as claimed in claim 1, including two alternately operable casting withdrawal mechanisms which cooperate successively with the dummy bar.

3. Apparatus as claimed in claim 2, in which each withdrawal mechanism is operable to withdraw the casting through a distance not smaller than the length of the mould.

4. Apparatus as claimed in claim 2 or 3, in which one of the withdrawal mechanisms comprises a vertically movable platform with an arm for cooperation with the dummy bar, and the other comprises a vertical barwhich is movable vertically in roller guides and whose lower end has a member connectable with the dummy bar.

5. Apparatus as claimed in any of claims 1 to 4, for producing a hollow casting, in which the lower part of the central head is provided with a broaching and sizing tool, and means are provided for driving the central head along the hollow of the casting.

6. Apparatus as claimed in claim 5, when dependent on claim 2, in which the driving means is constituted by a drive of one of the withdrawal mechanisms.

7. Apparatus as claimed in any preceding claim, further comprising a holding furnace connected to the metal supply means by a closed metal-feeding system.

8. Semicontinuous casting apparatus substantially as described with reference to, and as shown in, the accompanying drawings.