APPARATUS FOR THE LOW-PRESSURE CASTING OF METAL ALLOYS, IN PARTICULAR FOR ALUMINUM ALLOYS AND/OR MAGNESIUM ALLOYS

Abstract

An apparatus for low-pressure casting of metal alloys comprising: a loading hatch, a region for holding previously loaded molten metal, pressurization elements for pressurizing the region for holding the molten metal, and a die which is in fluidic communication with the region for holding the molten metal and is at least partially superimposed on the latter; the region for holding the molten metal comprises: a first chamber, connected to the loading hatch and to the pressurization elements, a second chamber, which is fluidically connected to the die, the first chamber and the second chamber being in fluidic connection through a passage.

Claims

1. An apparatus for low-pressure casting of metal alloys comprising: a loading hatch, a region for holding previously loaded molten metal, pressurization means for pressurizing said region for holding said molten metal, and a die which is in fluidic communication with said region for holding said molten metal and is at least partially superimposed on said region, wherein said region for holding said molten metal comprises: a first chamber, connected to said loading hatch and to said pressurization means, a second chamber, which is fluidically connected to said die, said first chamber and said second chamber being in fluidic connection through a passage.

2. The apparatus according to claim 1, wherein said passage is placed proximate to/at a bottom of said first chamber and a bottom of said second chamber and so that a bottom of said passage connects said bottom of said first chamber to said bottom of said second chamber.

3. The apparatus according to claim 1, wherein said passage has a height lower than: a height of said first chamber, and a height of said second chamber.

4. The apparatus according to claim 1, wherein said passage is formed by a metal connector for connecting said first chamber to said second chamber, a ceramic bushing being present within said metal connector.

5. The apparatus according to claim 4, wherein: a seal between said ceramic bushing and said first chamber is provided by a first sealing element interposed between said ceramic bushing and said first chamber, the seal between said ceramic bushing and said second chamber is provided by a second sealing element interposed between said ceramic bushing and said second chamber.

6. The apparatus according to claim 5, wherein said ceramic bushing has a flanged portion which is flanged for shape mating with said metal connector, a seal between said bushing and said connector being provided by: a third sealing element interposed between a surface of said flanged portion directed toward said first chamber and said connector, a fourth sealing element interposed between the surface of said flanged portion directed toward said second chamber and said connector.

7. The apparatus according to claim 4, wherein said metal connector has a vent.

8. The apparatus according to claim 1, further comprising one or more casting ducts which fluidically connect said second chamber to said die, said one or more casting ducts extending from a ceiling of said second chamber toward said die.

9. The apparatus according to claim 8, wherein said first chamber has first heating means arranged proximately to/at a ceiling thereof, in an upper region with respect to said molten metal bath and outside said molten metal bath in an operating configuration.

10. The apparatus according to claim 9, wherein said second chamber has second heating means arranged within said molten metal bath in the operating configuration.

11. The apparatus according to claim 9, wherein said loading hatch is arranged at an upper portion of said first chamber, adjacent to said ceiling.

12. The apparatus according to claim 2, wherein said first chamber has an internal surface which is inclined so as to form a chute from said loading hatch toward the bottom of said first chamber.

13. The apparatus according to claim 11, wherein said pressurization means comprise one or more apparatuses for introducing pressurized gas inside said first chamber, starting from said upper portion of said first chamber, generating a pressure on a free surface of said molten metal bath.

14. The apparatus according to claim 10, further comprising third heating means for heating said one or more casting ducts, said third heating means being arranged between said second chamber and said die, substantially around said one or more casting ducts.

15. The apparatus according to claim 12, wherein an overall bottom of said region for holding said molten metal is constituted in the following order by: said bottom of said first chamber, said bottom of said passage, said bottom of said second chamber, said overall bottom of said region for holding said molten metal being inclined substantially homogeneously with: a first end at said first chamber adjacent to said inclined internal surface, a second end, at a higher level than said first end, at said second chamber and opposite said first end.

Description

[0037] Further characteristics and advantages of the invention will become more apparent from the description of a preferred but not exclusive embodiment of the apparatus for low-pressure casting according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

[0038] FIG. 1 is a partially schematic sectional general view of an apparatus for low-pressure casting according to the invention;

[0039] FIG. 2 is an enlarged-scale view of a detail of the apparatus of FIG. 1;

[0040] FIG. 3 is an enlarged-scale view of a second detail of the apparatus of FIG. 1.

[0041] With reference to the figures, an apparatus for low-pressure casting of metal alloys, according to the invention, is generally designated by the reference numeral 10.

[0042] The apparatus 10 is particularly suitable for low-pressure casting of aluminum alloys and/or magnesium alloys.

[0043] The apparatus 10 comprises: [0044] a loading hatch 11 for introducing molten metal M, [0045] a region 12 for holding previously loaded molten metal M, [0046] means 13 for pressurizing the region 12 for holding the molten metal M, [0047] and a die 14, for filling with the molten metal M, in fluidic communication with the region 12 for holding molten metal M and at least partially superimposed on the latter.

[0048] One of the particularities of the apparatus 10 resides in the fact that the region 12 for holding the molten metal M comprises: [0049] a first chamber 15, connected to the loading hatch 11 and to the pressurization means 13, [0050] a second chamber 16, fluidically connected to the die 14, [0051] in which the first chamber 15 and the second chamber 16 are in fluidic communication through a passage 17.

[0052] The die 14 is arranged in an upward region with respect to the second chamber 16.

[0053] Advantageously, the first chamber 15 and the second chamber 16 are internally lined with a multilayer material 18, 18, comprising: [0054] a first external layer made of insulating bricks, [0055] a second internal layer, which is coupled to the first layer, and is made using low-wettability rammed refractory.

[0056] The first chamber 15 is provided with first heating means 19 arranged proximately to/at its ceiling 40, in an upward region with respect to the molten metal bath M and outside it, in the operating configuration.

[0057] In a constructive variation, not shown in the figures, said first heating means are immersed in the molten metal bath.

[0058] The first heating means 19 are, for example, constituted by armored rod or silicon carbide rod electric heating elements.

[0059] These electric heating elements are coated with a silicon nitride sheath to protect them from the molten metal.

[0060] The second chamber 16 has second heating means 20 arranged inside the molten metal bath M in the operating configuration.

[0061] The second heating means 20 are, for example, constituted by armored rod or silicon carbide rod electric heating elements, immersed in the molten metal bath M in the operating configuration.

[0062] These electric heating elements are coated with a silicon nitride sheath to protect them from the molten metal.

[0063] The loading hatch 11 is arranged at the upper portion 23 of the first chamber 15, adjacent to the ceiling 40.

[0064] Advantageously, the first chamber 15 has an internal surface 21 which is inclined to form a chute from the loading hatch 11 towards its bottom 22.

[0065] The pressurization means 13 are per se known and comprise one or more devices for introducing pressurized gas, and in particular dry air or nitrogen in the case of aluminum castings or carbon dioxide in the case of magnesium castings, into the first chamber 15, starting from the upper portion 23 of the latter, generating a pressure on the free surface of the molten metal bath M, in the direction of the arrows P.

[0066] In particular, the passage 17 is located proximate to/at the bottom 22 of the first chamber 15 and at the bottom 24 of the second chamber 16 and so that the bottom 25 of the passage 17 connects the bottom 22 of the first chamber 15 to the bottom 24 of the second chamber 16.

[0067] Furthermore, the overall bottom of the region 12 for holding the molten metal M is constituted in the following order by: [0068] the bottom 22 of the first chamber 15, [0069] the bottom 25 of the passage 17, [0070] the bottom 24 of the second chamber 16.

[0071] Preferably, the overall bottom of the region 12 for holding the molten metal M is inclined in a substantially uniform manner with: [0072] a first end 26 at the first chamber 15 adjacent to the inclined internal surface 21, [0073] a second end 27, at a higher level with respect to the first end 26, at the second chamber 16 and opposite the first end 26.

[0074] It should be noted that such an overall bottom of the molten metal holding region 12, which is inclined, hinders the passage of any air present in the first chamber 15 toward the second chamber 16.

[0075] The passage 17 has a height H that is less than: [0076] the height H1 of the first chamber 15, [0077] and the height H2 of the second chamber 16.

[0078] With reference to FIG. 1, in the present description, the term height is understood to reference the vertical dimension measured internally between the bottom and the corresponding upper internal surface.

[0079] With particular reference to FIG. 2, the passage 17 is formed by a metal connector 28 for connecting the first chamber 15 to the second chamber 16, inside which connector 28 there is a ceramic bushing 29.

[0080] The seal between the bushing 29 and the first chamber 15 is provided by a first sealing element 30, for example a ceramic fiber gasket, interposed between the bushing 29 and the first chamber 15.

[0081] The seal between the bushing 29 and the second chamber 16 is provided by a second sealing element 31, for example a ceramic fiber gasket, interposed between the bushing 29 and the second chamber 16.

[0082] The bushing 29 has a flanged portion 32 for shape mating with the connector 28.

[0083] The seal between the bushing 29 and the connector 28 is provided by: [0084] a third sealing element 33, for example a graphite gasket, interposed between the surface of the flanged portion 32 that is directed toward the first chamber 15 and the connector 28, [0085] a fourth sealing element 34, for example a graphite gasket, interposed between the surface of the flanged portion 32 directed toward the second chamber 16 and the connector 28.

[0086] The connector 28 is constituted by two parts: [0087] a first part 36a, connected to the first chamber 15, [0088] a second part 36b, connected to the second chamber 16 and facing the first part 36a at the third sealing element 33.

[0089] The first part 36a and the second part 36b of the connector 28 are fixed by means of a plurality of screws 44.

[0090] Advantageously, the connector 28 has a vent 35, adapted to allow any air present proximately to/at the passage 17 to escape, in order to prevent any air present in the first chamber 15 from reaching the second chamber 16.

[0091] In particular, the vent 35 is located proximate to/at the third sealing element 33, in the region of interaction between the first part 36a and the second part 36b of the connector 28.

[0092] The apparatus 10 comprises a plurality of casting ducts 37, which fluidically connect the second chamber 16 to the impression 38 of the die 14, through corresponding ducts 42 which are internal to the die 14.

[0093] In an embodiment not shown in the figures, the apparatus 10 comprises a single casting duct 37.

[0094] Said casting ducts 37 are made of ceramic material.

[0095] The seal between the casting ducts 37 and the die 14 is provided by means of fifth sealing elements 43, for example a compressible ceramic fiber gasket, arranged between the ducts 37 and the die 14.

[0096] Another particularity of the apparatus 10 resides in the fact that the casting ducts 37 do not extend inside the second chamber 16, but extend from the ceiling 39 of the second chamber 16 towards the die 14, which is arranged above it.

[0097] In particular, the casting ducts 37 are constituted by a first ceramic bushing 45 inserted in a second bushing 46 made of stainless steel.

[0098] It should be noted that, in the event of breakage of the ceramic bushing 45, the molten metal M escapes from it but remains in any case confined within the second steel bushing 46, solidifying on contact with the latter.

[0099] In this way it is possible to continue working without interrupting the melting cycle and without the need for immediate replacement of the casting duct 37.

[0100] Advantageously, the apparatus 10 comprises third means 41 for heating the casting ducts 37, which are arranged between the second chamber 16 and the die 14, substantially around the plurality of ducts 37.

[0101] The third heating means 41 are constituted, for example, by coiled wire electric resistance heaters, and are adapted to keep the metal in the molten state inside the casting ducts 37.

[0102] With reference to FIG. 1: [0103] the reference L1 designates the maximum level of the molten metal bath M before casting, [0104] the reference L2 designates the minimum level of the molten metal bath M before casting.

[0105] The operation of the apparatus 10, according to the invention, is as follows.

[0106] The first chamber 15 is loaded with molten metal M, which is heated by the first heating means 19 to remain in this state.

[0107] The molten metal bath M never exceeds the maximum level L1, so that there is always an air sub-pocket between the molten metal bath M and the ceiling 40 of the first chamber 15.

[0108] Due to the principle of communicating vessels, the molten metal bath M also fills the second chamber 16 to the same level as the first chamber 15.

[0109] During the casting step, a gas (dry air and/or nitrogen and/or carbon dioxide) is introduced at low pressure, substantially comprised between 0 and 1.5 bar, by virtue of the pressurization means 13, into the first chamber 15, and as a result of the introduced overpressure, of the thrust of the dry air and of the principle of communicating vessels, the level of the molten metal bath M in the first chamber 15 decreases, while in the second chamber 16 it rises, and the molten metal bath M rises along the casting ducts 37 and fills the impression 38 of the die 14 through the internal ducts 42.

[0110] Once the casting in the impression 38 has cooled, the pressure in the first chamber 15 is partially released and consequently the level of the molten metal bath M of the second chamber 16 decreases until the level of the molten metal M is inside the ducts 37 but outside the die 14, awaiting a new pressurization cycle, and it is possible to open the die 14 and remove the part.

[0111] It should be noted that the apparatus 10 does not have the casting ducts of apparatuses of the known type, immersed in the molten metal bath, but has casting ducts that extend from the ceiling of the second chamber and externally to it, and this reduces the length of the passage of molten metal inside the casting ducts, preventing the remelting of solidified metal alloy shells that can generate oxides that are transferred into the casting during the rise of the metal.

[0112] Moreover, in the apparatus according to the invention the second chamber is not pressurized with gas/air but is filled with molten metal coming from the first chamber, which is in turn pressurized, and this makes it possible to have no air in the second chamber, avoiding its possible rise inside the die.

[0113] Furthermore, it should be noted that with the apparatus according to the invention, by maintaining a residual air pressure in the first chamber it is possible to ensure that the level of molten metal in the second chamber remains high, for example inside the casting ducts, further reducing the travel of the metal during the subsequent filling steps.

[0114] In practice it has been found that the invention achieves the intended aim and objects by providing a low-pressure casting apparatus that reduces and/or eliminates the risk of air entering the casting ducts and/or the die compared to similar apparatuses of the known type during use.

[0115] Moreover, with the invention a low-pressure casting apparatus has been devised that reduces the path of the molten metal inside the casting ducts with respect to similar apparatuses of the known type, reducing and/or eliminating the risk of metal shells forming and remelting during casting.

[0116] The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may furthermore be replaced with other technically equivalent elements.

[0117] In practice, the materials used, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to the requirements and the state of the art.

[0118] The disclosures in Italian Patent Application No. 102024000019984 from which this application claims priority are incorporated herein by reference.