CASTING PROCESS AND CASTING MACHINE FOR METALS

Abstract

A casting method for metals, in particular lead and/or zinc, including: feeding the metal into a heated barrel, conveying the metal in the direction of a discharge opening of the barrel by rotational movement of a screw conveyor arranged in the barrel, and melting the metal and/or keeping it molten, with the result that the metal is present substantially entirely in the liquid phase at least in a subregion at the discharge opening of the barrel. The method further includes ejecting the metal which is present substantially entirely in the liquid phase through the discharge opening of the barrel by an axial piston movement of the screw conveyor, as a result of which the ejected metal at least partially fills at least one mold cavity, and cooling the metal, with the result that it is molded in the at least one mold cavity.

Claims

1. A casting method for metals, in particular lead and/or zinc, the method comprising: feeding a metal into a heated barrel, conveying the metal in the direction of a discharge opening of the barrel by a rotational movement of a screw conveyor arranged in the barrel, melting the metal and/or keeping it molten, with the result that the metal is present substantially entirely in the liquid phase at least in a subregion at the discharge opening of the barrel, ejecting the metal which is present substantially entirely in the liquid phase through the discharge opening of the barrel by means of an axial piston movement of the screw conveyor, as a result of which the ejected metal at least partially fills at least one mold cavity, and cooling the metal, with the result that it is molded in the at least one mold cavity.

2. The casting method according to claim 1, wherein the metal is fed into the barrel in a solid phase.

3. The casting method according to claim 2, wherein the metal is brought into a granular form by being comminuted before it is fed to the barrel.

4. The casting method according to claim 1, wherein the barrel is brought to, and preferably kept at, a temperature above the melting point of the metal at least between a feed site of the metal and the discharge opening.

5. The casting method according to claim 1, wherein strip heaters on the barrel and/or an induction heater and/or infrared radiation is/are used to melt the metal or to keep it molten.

6. The casting method according to claim 1, wherein only so much metal that a partial filling is present in the barrel, preferably a partial filling of less than 95%, 90%, 80% and/or 70%, is fed into the barrel.

7. The casting method according to claim 1, wherein a non-return valve is used at a leading end of the screw conveyor.

8. The casting method according to claim 7, wherein a non-return valve that can be actively actuated, preferably mechanically, is used.

9. The casting method according to claim 1, wherein a shut-off nozzle is used at the discharge opening of the barrel to selectively open the discharge opening.

10. The casting method according to claim 1, wherein, when ejected out of the barrel, the metal is poured into the at least one mold cavity under pressure, wherein a maximum pressure preferably lies below 2000 bar and/or 1500 bar and/or 1300 bar.

11. The casting method according to claim 1, wherein an inert atmosphere and/or a protective vacuum is/are used in the barrel and/or in the at least one mold cavity and/or in a connecting channel between the barrel and the mold cavity.

12. The casting method according to claim 1, wherein a pressure accumulator is used, which is in pressure-active connection with the molten metal fluidically downstream of the screw conveyor, preferably fluidically downstream of the non-return valve, preferably in the region of a connecting channel between the barrel and the mold cavity.

13. The casting method according to claim 1, wherein a casting mold containing the at least one mold cavity is temperature-controlled, in particular is heated during a filling operation and/or cooled in order to cool the metal.

14. The casting method according to claim 1, wherein a screw conveyor is used, which has a screw geometry with a compression ratio of between 1.0 and 1.4 and/or between 1.1 and 1.3 and/or between 1.15 and 1.25.

15. A casting machine for molding metals, in particular lead or zinc, suitable in particular for carrying out the casting method according to claim 1, with a barrel, a feed device for feeding the metal into the barrel, a heating device, which is set up and adjusted so as to melt the metal present in the barrel and/or to keep it molten, with the result that it is present substantially entirely in the liquid phase at least in a subregion at a discharge opening of the barrel, and a screw conveyor in the barrel and a screw conveyor drive, wherein the screw conveyor drive is formed to cause the screw conveyor to perform rotational movements and axial piston movements, and wherein the metal present substantially entirely in the liquid phase is conveyable in the direction of the discharge opening of the barrel as a result of the rotational movement of the screw conveyor and is ejectable through the discharge opening of the barrel as a result of the axial piston movement of the screw conveyor to at least partially fill at least one mold cavity with the metal.

16. A use of the casting machine according to claim 15.

Description

[0068] Further advantages and details of the invention become apparent from the figures and the associated description of the figures. There are shown in:

[0069] FIG. 1 an embodiment example according to the invention of a casting machine,

[0070] FIG. 2 a further embodiment example according to the invention of a casting machine,

[0071] FIG. 3 an embodiment example according to the invention of a casting machine in the region of a clamping unit, and

[0072] FIG. 4 an embodiment example of a pressure accumulator.

[0073] FIG. 1 schematically shows an embodiment example according to the invention of a casting machine 1.

[0074] The casting machine comprises a feed device 18 and a barrel 3.

[0075] The feed device 18 contains a transport device 21, which in this embodiment example contains rollers for advancing the metal 2, in the form of a lead bar.

[0076] By means of a rotating cutting wheel 6, the lead bar is chopped and thus brought into granulate form. Because of gravity, the metal 2 falls into a feed opening at the feed site 7 of the barrel 3.

[0077] The feed device 18 in this embodiment example additionally contains a feed for inert gas 14, which likewise gets into the inside of the barrel 3 through the feed opening. The inert gas prevents the metal 2 present in the barrel 3 from reacting with gas components in air.

[0078] Alternatively, instead of the inert gas 14, suction could be provided, by means of which a protective vacuum is generated in the barrel 3.

[0079] The screw conveyor 5 is arranged inside the barrel 3 and is movable both rotationally and axially in the barrel 3.

[0080] The screw conveyor 5 contains a screw geometry 17 with a flight, with the result that as a result of the rotational movement of the screw conveyor 5 a conveying action occurs, which transports the metal 2 in the direction of a discharge opening 4 of the barrel 3.

[0081] In the present embodiment example, the flight has a constant flight volume, with the result that the compression ratio is 1.

[0082] In alternative embodiment examples, the compression ratio can be approximately 1.2, for example.

[0083] Moreover, a heating device 19 is provided, which in this embodiment example contains strip heaters 8.

[0084] By means of the strip heaters 8, the barrel 3 is kept at a temperature above the melting point of the metal 2, as a result of which the metal 2 is melted in the barrel.

[0085] Furthermore, the metal 2 could also be fed into the barrel 3 in an already molten state.

[0086] Regardless of this, in this embodiment example the strip heaters 8 ensure that the metal 2 is kept molten in the barrel.

[0087] Alternatively or additionally, inductive heating and/or heating by means of electromagnetic radiation (preferably infrared radiation) can also be used instead of strip heaters 8.

[0088] Alternatively or additionally, the barrel 3 can have at least one heating-media channel, for example in the form of a groove, through which a fluid heating medium, for example oil, is conveyed in order to melt the metal 2 or keep it molten.

[0089] In the present embodiment example, the metal 2 is fed into the barrel in granulate form by means of the feed device 18 and is conveyed therein in the direction of the discharge opening 4 of the barrel 3 by means of the screw conveyor 5, while it is melted under the action of the heating device 19, and is then present in a subregion of the barrel 3 in a substantially entirely molten phase state, wherein the subregion extends from the discharge opening 4 in the direction of the feed site 7.

[0090] An axial piston movement of the screw conveyor 5 can be used to eject the molten metal 2 out of the subregion through the discharge opening 4 and to pour it into a mold cavity 12, for which reference is made to FIG. 3.

[0091] A shut-off nozzle 11 is arranged at the discharge opening 4 of the barrel 3.

[0092] In the present embodiment example, it is provided that the shut-off nozzle 11 is selectively opened at the same time as the axial piston movement and otherwise remains closed.

[0093] It is to be mentioned that the part or the component in which the shut-off nozzle 11 is arranged is regarded as part of the barrel 3 in the context of the invention. This part of the barrel 3 can also be regarded as a filling nozzle.

[0094] In the present embodiment, only so much metal that a partial filling of 50% by volume is present in the barrel is fed into the barrel.

[0095] FIG. 2 schematically shows a further embodiment example according to the invention of a casting machine 1, which is similar to the one from FIG. 1.

[0096] A screw conveyor drive 20 has been indicated, which is formed to cause the screw conveyor 5 to perform both the rotational movement and the axial piston movement. Naturally, a screw conveyor drive 20 with these functions is likewise provided in the embodiment example according to FIG. 1.

[0097] Unlike the embodiment example from FIG. 1, in the embodiment example of FIG. 2 a non-return valve, which is represented symbolically, is provided at the leading end 9 of the screw conveyor 5.

[0098] A mechanically actively actuatable non-return valve 10 is preferred in this case.

[0099] FIG. 3 shows a casting machine 1 in the region of a clamping unit. This contains platens 22 which are movable relative to one another and on which parts of a casting mold 16 can be fitted.

[0100] The mold cavity 12 can be opened and closed by the relative movement of the platens 22.

[0101] One of the platens 22 (as a rule a fixed platen 22) has an opening through which the discharge opening 4 of the barrel 3 can be connected to the casting mold.

[0102] The part of the casting machine 1 that contains the barrel 3 can be designed, for example, as in the embodiment examples from FIG. 1 or FIG. 2.

[0103] As a result of the aforementioned axial piston movement, the molten metal 2 gets into a connecting channel 13, which is simply one channel here, and subsequently into the mold cavity 12.

[0104] Alternatively or additionally, a channel system can be provided instead of a single channel, for example for connection to several mold cavities in a casting mold.

[0105] A speed at which the molten metal 2 gets into the connecting channel 13 and the mold cavity 12 can be adjusted through the choice of the movement profile of the axial piston movement of the screw conveyor 5.

[0106] The maximum pressure occurring in the process in the molten metal 2 is preferably no higher than 1300 bar. Undesired pressure spikes can optionally be compensated for by means of a pressure accumulator 15, a more specific example of which is represented in FIG. 4.

[0107] In the present case, the mold cavity 12 of the casting mold 16 can be temperature-controlled via temperature-control channels 23, which are not all provided with a reference number in FIG. 3 for reasons of clarity.

[0108] In the embodiment example presented here, it is provided that the mold cavity 12 is heated before being filled, so as to guarantee the flowability of the molten metal 2 for as long as possible. As soon as the mold cavity 12 is entirely filled, the mold cavity 12 is cooled, with the result that the metal 2 cools and hardens at the desired rate.

[0109] When the metal 2 is hardened, a crystalline or amorphous internal structure of the metal 2 can form. Naturally, mixed forms are also conceivable.

[0110] It is to be mentioned that an inert gas 14 or a protective vacuum can also be used in the region of the mold cavity 12 and/or the connecting channel 13.

[0111] Overall, the embodiment examples presented here of casting machines 1 are suitable and set up for carrying out the casting method according to the invention: [0112] feeding the metal into a heated barrel, [0113] conveying the metal in the direction of a discharge opening of the barrel by means of a rotational movement of a screw conveyor arranged in the barrel, [0114] melting the metal and/or keeping it molten, with the result that the metal is present substantially entirely in the liquid phase at least in a subregion at the discharge opening of the barrel, [0115] ejecting the metal which is present substantially entirely in the liquid phase through the discharge opening of the barrel by means of an axial piston movement of the screw conveyor, as a result of which the ejected metal at least partially fills at least one mold cavity, and [0116] cooling the metal, with the result that it is molded in the at least one mold cavity.

[0117] A pressure accumulator 15, which can optionally be used to compensate for pressure spikes while the mold cavity 12 is being filled, is represented in FIG. 4.

[0118] In this embodiment example, the pressure accumulator 15 is provided in the casting mold 16 in the region of the connecting channel 13, i.e. the pressure accumulator is in pressure-active connection with the molten metal 2 fluidically downstream of the screw conveyor 5, in particular fluidically downstream of the non-return valve 10, in the region of the connecting channel 13 between the barrel 3 and the mold cavity 12.

[0119] Alternatively or additionally, the pressure accumulator 15 could also be provided in the region of the discharge opening 4 of the barrel 3, for example.

[0120] In the present embodiment example, the pressure accumulator contains a piston-cylinder unit 24 and a mechanical spring element 25 in the form of a helical spring.

[0121] A chamber of the piston-cylinder unit 24 is in pressure-active connection with the molten metal 2, and the piston of the piston-cylinder unit 24 is spring-loaded by means of the mechanical spring element 25.

[0122] Alternatively or additionally, the spring element 25 could contain a gas spring or an air bubble (similar to a bladder accumulator).

[0123] If a pressure spike occurs in the course of the operation for filling the mold cavity 12, for example as a result of an inertial axial piston movement of the screw conveyor 5, although the mold cavity and any connecting channels are already volumetrically filled with molten metal 2, this can be compensated for by the pressure accumulator 15.

[0124] That is because in this case the spring element 25 is loaded and thereby performs a spring movement, as a result of which a volumetric relief of strain occurs in the molten metal 2. The return movement of the spring element 25 does not occur until the pressure drops again.

[0125] It is to be mentioned that the feeding of the metal 2 into the barrel 3 does not have to be effected in the solid phase, as is the case in the embodiments according to FIG. 1 and FIG. 2. It is entirely conceivable to at least partially, preferably entirely, melt the metal 2 outside the barrel 3 and feed it into the barrel 3 in this state.

LIST OF REFERENCE NUMBERS

[0126] 1 casting machine [0127] 2 metal [0128] 3 barrel [0129] 4 discharge opening (of the barrel) [0130] 5 screw conveyor [0131] 6 cutting wheel [0132] 7 feed site [0133] 8 strip heaters [0134] 9 leading end (of the screw conveyor) [0135] 10 non-return valve [0136] 11 shut-off nozzle [0137] 12 mold cavity [0138] 13 connecting channel [0139] 14 inert gas [0140] 15 pressure accumulator [0141] 16 casting mold [0142] 17 screw geometry [0143] 18 feed device [0144] 19 heating device [0145] 20 screw conveyor drive [0146] 21 transport device [0147] 22 platens [0148] 23 temperature-control channels [0149] 24 piston-cylinder unit (of the pressure accumulator) [0150] 25 spring element