Patent Application
20240424552
The present invention relates to a casting method for metals, in particular lead and/or zinc, and to a casting machine with the features of the preamble of claim 15.
In principle, casting methods are known wherein molten metal is ejected from a barrel or a similar vessel by means of a piston and is poured into a mold cavity, for example in the form of die casting.
The processes disclosed in DE 102016006917 A1, DE 102018109322 A1 and DE 102019131011 A1 also function according to this principle.
The machines known in the state of the art for carrying out casting methods are evidently complex, which bears on the construction of the barrel or melting vessel on the one hand and the sealing of the piston on the other hand.
Moreover, melt arriving at the seal degrades the seal and sliding surfaces present in that region, with the result that relatively short maintenance intervals are to be adhered to according to experience.
Against this background, the object of the invention is to provide methods and machines for casting metal that are simpler and/or require less maintenance.
With respect to the casting method, the object is achieved by the features of claim 1, namely by carrying out at least the following:
With respect to the casting machine, the object is achieved by the features of claim 15, namely by a casting machine for molding metals, in particular lead and zinc, which is suitable in particular for carrying out a method according to the invention, with
According to the invention, elaborately constructed seals of pistons in the barrel or melting vessel are avoided and are replaced with a screw conveyor that is capable of conveying the molten metal in the direction of the barrel's discharge opening on the casting-mold side, with the result that a seal is no longer needed per se or can be designed very simply. At the same time, the screw conveyor according to the invention can implement the movement for discharging the metal out of the barrel as a result of an axial piston movement.
However, it should be noted that the screw conveyor within the meaning of the present document is not designated as a piston but rather can merely perform a piston movement and thereby assume the role of a piston.
It has surprisingly been found that screw conveyors manufactured in the modern manner can cope with the thermal stresses that occur when the screw conveyors are exposed to the metal melt.
Of course, the axial piston movement is to be understood as axial in relation to a central axis of the barrel. This applies analogously to the rotational movement of the screw conveyor about the central axis of the barrel.
In particularly preferred embodiments of the invention, metals with melting points below 450° C. and/or 440° C. and/or 430° C., such as lead or zinc in particular, are used.
In particular, alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, lanthanides and actinides are regarded as metals.
Within the meaning of the invention, by metals is also meant alloys or mixtures (single-phase or multi-phase) of metals, also mixtures of substances containing metals in significant proportions, preferably more than 25% and/or more than 50% and/or more than 75% and/or more than 90%. In this way, for example, metal components with fillers can be implemented.
In preferred embodiments of the invention, the metal can be a so-called ZAMAK alloy, i.e. an alloy of the chemical elements zinc, aluminum, magnesium and copper, as well as further substances where appropriate. Particularly preferably, zinc takes up the greatest proportion of the alloy in this case.
By screw conveyors is meant components which have a screw geometry, for example in the form of at least one flight, with the result that a material, in this case the metal, is conveyed in one direction in the barrel as a result of the rotation of the screw conveyor.
The discharge opening is preferably set up so as to be selectively opened or closed.
Preferably, a closure function can thus be present, which ensures that no metal, or only a small amount, can leak out of the barrel when this is not desired.
The discharge opening can preferably be arranged at one end of the barrel.
According to the invention, the subregion of the barrel in which the metal is present substantially entirely in the liquid phase adjoins the discharge opening such that the axial piston movement has the result that the metal which is present substantially entirely in the liquid phase is ejected through the discharge opening.
The at least one mold cavity can preferably be implemented by a casting mold which is separate from the casting machine, and which can be fitted on the machine.
For the fluid connection of the discharge opening of the barrel to the at least one mold cavity, for example a connecting channel and/or a channel and/or a channel system can be used in the casting mold containing the at least one mold cavity.
According to the invention, the at least one mold cavity can be partially filled. In preferred embodiments, however, the at least one mold cavity is entirely filled.
Protection is also sought for the use of the casting machine according to the invention in the casting method according to the invention.
Advantageous developments of the invention are defined in the dependent claims.
The metal is preferably fed into the barrel in a solid phase.
Alternatively or additionally, the metal can also be fed into the barrel already in a liquid phase.
The metal can be brought into a granular form by being comminuted before it is fed to the barrel.
By way of example, the comminution can be implemented by chopping (for example by means of a cutting wheel) at least one metal wire and/or at least one metal bar or using a different type of granulation device.
Of course, the metal can also be present already in a granulate form, with the result that comminution is no longer necessary.
In particularly preferred embodiments, 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, for example by means of the heating device. The melting of the metal, or keeping it molten, in the barrel can thus be implemented in a particularly simple manner.
Strip heaters on the barrel and/or an induction heater and/or infrared radiation, which can for example be part of the heating device, can preferably be used to melt the metal or keep it molten.
Alternatively or additionally, the barrel can have at least one heating-media channel, for example in the form of a groove (preferably shaped helically around the barrel) in which a pipe element for the heating medium is preferably arranged and through which a fluid heating medium, for example oil, is conveyed in order to melt the metal or keep it molten.
The heating device can be integrated in the barrel.
In particularly preferred embodiments, 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% (percent by volume in each case), can be fed into the barrel.
On the one hand, this can have the advantage that no tight packing of the metal, present for example as a granulate material, prevails in an infeed zone of the screw conveyor close to the site at which the metal is fed in, which can lead to granulate material becoming stuck between the screw geometry and the barrel.
On the other hand, owing to the partial filling, gas and/or moisture evaporating out of the metal melt can escape and, for example, be extracted by suction at an end of the barrel facing away from the discharge opening of the barrel or at an infill opening. Air streaks and/or air bubbles and/or other defects in the molded part can thus be prevented, for example.
Optionally, the barrel can contain an additional degassing zone and/or a degassing opening (separate from the discharge opening).
In particularly preferred embodiments, a non-return valve can be used at a leading end of the screw conveyor. This has the advantage that, during ejection, a more precisely defined amount of the metal melt can get out of the barrel and into the at least one mold cavity and/or into the channel and/or into the channel system than would be the case without a non-return valve.
In particularly preferred embodiments, a non-return valve that can be actively actuated, preferably mechanically, can be used. For this purpose, reference is made to DE 102012015337 A1, the technical disclosure of which in relation to mechanically actively actuatable non-return valves is integrally incorporated into the present document.
In preferred embodiments, a shut-off nozzle can be used at the discharge opening of the barrel to selectively open the discharge opening.
Alternatively or additionally, at least one shut-off nozzle can be present in the channel and/or in the channel system.
When ejected out of the barrel, the metal can be 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.
An inert atmosphere and/or a protective vacuum can be 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.
The connecting channel can be implemented by the aforementioned channel and/or the aforementioned channel system.
In this case, by a protective vacuum can be meant, in the technical sense, that a negative pressure (compared with the surroundings) is generated in the aforementioned volume.
A pressure accumulator can preferably be 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.
The connecting channel can be implemented by the aforementioned channel and/or the aforementioned channel system. In terms of terminology, a distinction is drawn between the general connecting channel on the one hand and the channel and/or channel system of the casting mold on the other hand.
The pressure accumulator can compensate for pressure spikes which occur when the at least one mold cavity is being filled owing to an incompressibility of the melt.
In preferred embodiments, the pressure accumulator can have a piston-cylinder unit and/or a mechanical spring element. Preferably, a chamber of the piston-cylinder unit can be in pressure-active connection with the molten metal, and the piston of the piston-cylinder unit can be spring-loaded by means of the mechanical spring element.
A casting mold containing the at least one mold cavity can particularly preferably be temperature-controlled, in particular can be heated during a filling operation and/or cooled in order to cool the metal.
This applies analogously to the channel and/or channel system, wherein the channel and/or channel system is/are preferably substantially constantly heated so as to keep the metal molten here too (heating channel system).
A screw conveyor 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 can particularly preferably be used. For example, the compression ratio can be approximately 1.2.
By the compression ratio is meant the ratio of the flight volume and/or the flight cross-sectional area in the infeed region, thus where the metal is fed in, to the flight volume and/or the flight cross-sectional area at the end region of the screw conveyor (screw conveyor tip). The extent to which the material which is conveyed by means of the screw conveyor is compressed is substantially quantified thereby.
Within the framework of the present invention, a compression ratio greater than 1 can be used to evaporate gas and/or moisture out of the metal melt, with the result that these substances, which are undesired as a rule, do not remain in the metal melt, and subsequently in the molded part, or react with the metal melt.
Non-return valves, for example in the form of annular non-return valves or ball check valves, as well as shut-off nozzles, screw geometries, screw drives and heating channel systems are known per se from the field of injection molding and can thus be taken from a different technical field.
Further advantages and details of the invention become apparent from the figures and the associated description of the figures. There are shown in:
The casting machine comprises a feed device 18 and a barrel 3.
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.
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.
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.
Alternatively, instead of the inert gas 14, suction could be provided, by means of which a protective vacuum is generated in the barrel 3.
The screw conveyor 5 is arranged inside the barrel 3 and is movable both rotationally and axially in the barrel 3.
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.
In the present embodiment example, the flight has a constant flight volume, with the result that the compression ratio is 1.
In alternative embodiment examples, the compression ratio can be approximately 1.2, for example.
Moreover, a heating device 19 is provided, which in this embodiment example contains strip heaters 8.
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.
Furthermore, the metal 2 could also be fed into the barrel 3 in an already molten state.
Regardless of this, in this embodiment example the strip heaters 8 ensure that the metal 2 is kept molten in the barrel.
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.
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.
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.
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
A shut-off nozzle 11 is arranged at the discharge opening 4 of the barrel 3.
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.
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.
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.
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
Unlike the embodiment example from
A mechanically actively actuatable non-return valve 10 is preferred in this case.
The mold cavity 12 can be opened and closed by the relative movement of the platens 22.
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.
The part of the casting machine 1 that contains the barrel 3 can be designed, for example, as in the embodiment examples from
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.
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.
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.
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
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
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.
When the metal 2 is hardened, a crystalline or amorphous internal structure of the metal 2 can form. Naturally, mixed forms are also conceivable.
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.
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:
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
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.
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.
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.
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.
Alternatively or additionally, the spring element 25 could contain a gas spring or an air bubble (similar to a bladder accumulator).
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.
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.
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
| Number | Date | Country | Kind |
|---|---|---|---|
| A 50497/2023 | Jun 2023 | AT | national |
