Apparatus for low-pressure casting of metal alloys

Abstract

An apparatus (10) for low-pressure casting of metal alloys, comprising: a loading port (11); a region (12) for holding previously loaded molten metal (M); means (13) for pressurizing the area (12) for holding the molten metal (M); and a mold (14) in fluid communication with the region (12) for holding the molten metal (M) and at least partially overlaid thereon; the region (12) for holding the molten metal (M) comprises: a first chamber (15) connected to the loading port (11) and to the pressurizing means (13); and a second chamber (16) fluidly connected to the mold (14), the first chamber (15) and the second chamber (16) being fluidly connected by a channel (17).

Description

Technical Field

[0001] This invention relates to an apparatus for low-pressure casting, particularly, but not exclusively, an apparatus for low-pressure casting of aluminum alloys and / or magnesium alloys. Background Technology

[0002] Currently, a technology known as "low-pressure casting" is widely used to supply metal parts, for example, for the automotive industry.

[0003] The technique uses a molten metal bath, which is contained in a holding chamber within a crucible or pot furnace made of refractory material, with casting pipes exposed from the upper region of the holding chamber.

[0004] Cast pipes have the following characteristics:

[0005] - At the top, fluidly connected to the mold,

[0006] - The lower end is located horizontally below the free surface of the molten metal and in contact with the molten metal.

[0007] In this specification, expressions such as "upper," "lower," "in the upper region," and "in the lower region" refer to the usage configuration of the equipment and the various components constituting the equipment.

[0008] In order to cast parts in a mold, pressure is applied to the free surface of molten metal by injecting gas at low pressure.

[0009] Due to this pressure, the molten metal rises through the casting pipe and into the mold.

[0010] This background technology has some drawbacks.

[0011] First, no matter how good the insulation of low-pressure casting equipment is, it is impossible to prevent air from entering the casting pipes and / or molds, and this may lead to:

[0012] - First, oxides and bubbles form on the finished parts, thus creating defects.

[0013] Secondly, oxides form inside the casting pipes, which can transfer to the mold, thus creating defects in the finished parts.

[0014] In addition, very long casting pipes are sometimes used nowadays, which results in a long time for molten metal to be transported through these pipes. This causes the solidified metal shell in contact with the pipe wall to remelt, producing oxides that are transferred to the mold and thus to the finished part, leading to defects.

[0015] In addition, cast iron pipes are typically insulated with gaskets in the following situations:

[0016] - at the inlet to the mould and / or at the outlet from the furnace by means of gaskets with the outside,

[0017] - by means of gaskets with the inside of the chamber with respect to the pressure of the inside of the furnace.

[0018] Over time and with wear, these gaskets can lose their air tightness, causing air to enter:

[0019] - the respective casting duct, which can cause defects in the castings produced (and subsequently discarded), and the need to replace the duct itself and the gaskets, thus stopping production,

[0020] - and / or the mould, which can cause defects on the parts and thus cause production to be rejected.

[0021] Furthermore, the formation of cracks on the casting ducts also causes air to penetrate, thus creating the problems described above.

[0022] These drawbacks are even more evident if large parts need to be cast, since in this case the plant usually has multiple casting ducts and multiple points of use of air seals, thus increasing the number of elements that can be subject to this phenomenon and increasing the risk of stopping production. SUMMARY

[0023] It is an object of the present application to provide a low-pressure casting plant that can improve the background art in one or more of the aspects described above.

[0024] Within this object, it is an object of the present application to provide a low-pressure casting plant that mitigates and / or eliminates the risk of air entering the casting duct and / or the mould during use, compared to similar plants of the known type.

[0025] It is another object of the present application to provide a low-pressure casting plant that shortens the path of the molten metal inside the casting duct, thus mitigating and / or eliminating the risk of formation and remelting of a metal shell during casting, compared to similar plants of the known type.

[0026] It is another object of the present application to overcome the drawbacks of the background art in a manner that is alternative to any existing solution.

[0027] It is also an important object of the present application to provide a low-pressure casting plant that is highly reliable, relatively easy to provide and cost-competitive.

[0028] This object, as well as these and other objects that will become more apparent in the following, is achieved by a plant for low-pressure casting of metal alloys, comprising:

[0029] - a loading port,

[0030] - a region for holding previously charged molten metal,

[0031] - means for pressurizing the region for holding molten metal,

[0032] - and a mold, in fluid communication with the region for holding molten metal and at least partially superimposed on the region for holding molten metal,

[0033] The region for holding molten metal of the apparatus comprises:

[0034] - a first chamber, connected to the charging mouth and to the pressurizing means,

[0035] - a second chamber, fluidically connected to the mold,

[0036] The first chamber and the second chamber are fluidically connected by a channel. BRIEF DESCRIPTION OF DRAWINGS

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

[0038] Figure 1 is a partially schematic overall view of an apparatus for low-pressure casting according to the present application;

[0039] Figure 2 is an enlarged view of a detail of the apparatus of Figure 1 ;

[0040] Figure 3 is an enlarged view of a second detail of the apparatus of Figure 1 . DETAILED DESCRIPTION

[0041] With reference to the attached drawings, an apparatus for low-pressure casting of metal alloys according to the present application is indicated overall with the reference number 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 charging mouth 11 for introducing molten metal M,

[0045] - a region 12 for holding previously charged molten metal M,

[0046] - means 13 for pressurizing the region 12 for holding molten metal M, and

[0047] - Mold 14, for filling with molten metal M, fluidly communicating with and at least partially overlapping a region 12 for holding molten metal M.

[0048] A feature of the device 10 is that the region 12 for holding the molten metal M includes:

[0049] - First chamber 15, connected to loading port 11 and pressurizing device 13.

[0050] - Second chamber 16, fluidly connected to mold 14.

[0051] The first chamber 15 and the second chamber 16 are fluidly connected through the channel 17.

[0052] The mold 14 is arranged in the upper region relative to the second chamber 16.

[0053] Advantageously, the first chamber 15 and the second chamber 16 are lined with multiple layers of material 18, 18', which include:

[0054] - The first outer layer is made of heat-insulating bricks.

[0055] - The second inner layer is connected to the first layer and is made of low-wetting rammed refractory material.

[0056] The first chamber 15 is provided with a first heating device 19, which is arranged in an operating configuration to be close to or located on the top plate 40 of the first chamber, in the upper region relative to the molten metal bath M and outside the molten metal bath.

[0057] In a structural variant not shown in the figure, the first heating device is immersed in a bath of molten metal.

[0058] The first heating device 19 is, for example, composed of an armored rod electric heating element or a silicon carbide rod electric heating element.

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

[0060] The second chamber 16 has a second heating device 20, which is arranged in the molten metal M bath in the operating configuration.

[0061] The second heating device 20 is, for example, composed of an armored rod electric heating element or a silicon carbide rod electric heating element and is immersed in a bath of molten metal M in the operating configuration.

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

[0063] The loading port 11 is located in the upper part 23 of the first chamber 15 and is adjacent to the top plate 40.

[0064] Advantageously, the first chamber 15 has an inner surface 21 that is inclined to form a ramp from the loading port 11 toward the bottom 22 of the first chamber.

[0065] The pressurizing device 13 is known in itself and includes one or more devices for introducing pressurizing gas (in particular, dry air or nitrogen in the case of aluminum castings, or carbon dioxide in the case of magnesium castings) from the upper portion 23 of the first chamber 15 into the first chamber, thereby generating pressure on the free surface of the molten metal bath in the direction of arrow P.

[0066] Specifically, the channel 17 is positioned near or at the bottom 22 of the first chamber 15 and the bottom 24 of the second chamber 16, such that the bottom 25 of the channel 17 connects the bottom 22 of the first chamber 15 to the bottom 24 of the second chamber 16.

[0067] Furthermore, the entire bottom of region 12, used to hold the molten metal M, is composed of the following parts in sequence:

[0068] - Bottom 22 of the first chamber 15

[0069] - Bottom 25 of channel 17

[0070] - Bottom 24 of the second chamber 16.

[0071] Preferably, the entire bottom of region 12 for holding molten metal M is inclined substantially uniformly, and this bottom has:

[0072] - The first end 26 is located in the first chamber 15 and is adjacent to the inclined inner surface 21, and

[0073] - The second end 27 is at a higher height than the first end 26, in the second chamber 16, and opposite to the first end 26.

[0074] It should be noted that the entire sloping bottom of the molten metal holding region 12 prevents any air present in the first chamber 15 from flowing into the second chamber 16.

[0075] The height H of channel 17:

[0076] - Lower than the height H1 of the first chamber 15, and

[0077] - Lower than the height H2 of the second chamber 16.

[0078] refer to Figure 1In this specification, the term "height" is understood to refer to the vertical dimension measured internally between the bottom and the corresponding upper inner surface.

[0079] Special Reference Figure 2 The channel 17 is formed by a metal connector 28 for connecting the first chamber 15 to the second chamber 16, and a ceramic bushing 29 is present inside the connector 28.

[0080] The seal between the bushing 29 and the first chamber 15 is provided by a first sealing element 30 (e.g., a ceramic fiber gasket) located 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 (e.g., a ceramic fiber gasket) located between the bushing 29 and the second chamber 16.

[0082] The bushing 29 has a flange portion 32 for mate with the shape of the connector 28.

[0083] The seal between bushing 29 and connector 28 is provided by the following:

[0084] - A third sealing element 33 (e.g., a graphite gasket) is located between the surface of the flange portion 32 pointing towards the first chamber 15 and the connector 28.

[0085] - A fourth sealing element 34 (e.g., a graphite gasket) is located between the surface of the flange portion 32 pointing towards the second chamber 16 and the connector 28.

[0086] Connector 28 consists of the following two parts:

[0087] - Part 36a, connected to the first chamber 15.

[0088] - The second part 36b is connected to the second chamber 16 and faces the first part 36a at the third sealing element 33.

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

[0090] Advantageously, connector 28 has a vent 35 that is adapted to allow any air near / 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] Specifically, the vent 35 is positioned close to / at the third sealing element 33 and in the interaction area between the first portion 36a and the second portion 36b of the connector 28.

[0092] The device 10 includes a plurality of casting pipes 37 that fluidly connect the second chamber 16 to the impression 38 of the mold 14 via corresponding pipes 42 inside the mold 14.

[0093] In an embodiment not shown in the accompanying drawings, device 10 includes a single casting pipe 37.

[0094] The cast pipe 37 is made of ceramic material.

[0095] The seal between the casting pipe 37 and the mold 14 is provided by means of a fifth sealing element 43 (e.g., a compressible ceramic fiber gasket) arranged between the pipe 37 and the mold 14.

[0096] Another feature of the device 10 is that the casting pipe 37 does not extend within the second chamber 16, but extends from the top plate 39 of the second chamber 16 toward the mold 14 arranged above the second chamber.

[0097] Specifically, the cast pipe 37 is formed by a first ceramic bushing 45 inserted into a second bushing 46 made of stainless steel.

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

[0099] Therefore, it can continue to operate without interrupting the melting cycle, and there is no need to replace the casting pipe 37 immediately.

[0100] Advantageously, the device 10 includes a third device 41 for heating the casting pipes 37, which is arranged between the second chamber 16 and the mold 14 and substantially surrounds the plurality of pipes 37.

[0101] The third heating device 41 is, for example, a coil resistance heater, and is adapted to keep the metal in the casting pipe 37 in a molten state.

[0102] refer to Figure 1 :

[0103] - The reference numeral L1 in the attached diagram indicates the highest height of the molten metal bath M before casting.

[0104] - The reference numeral L2 in the attached diagram indicates the minimum height of the molten metal bath M before casting.

[0105] The device 10 according to the present invention operates as follows.

[0106] The first chamber 15 is filled with molten metal M, which is heated by the first heating device 19 to be kept in a molten state.

[0107] The molten metal bath M never exceeds the maximum height L1, therefore there is always an air cavity between the molten metal bath M and the top plate 40 of the first chamber 15.

[0108] Due to the principle of interconnected containers, 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) at a low pressure, substantially between 0 bar and 1.5 bar, is introduced into the first chamber 15 via a pressurizing device 13. Due to the introduced overpressure, the thrust of the dry air, and the principle of the connected container, the height of the molten metal M bath in the first chamber 15 decreases. In the second chamber 16, the height of the molten metal M bath increases, and the molten metal M bath rises along the casting pipe 37 and fills the mold cavity 38 of the mold 14 through the internal pipe 42.

[0110] Once the casting in cavity 38 has cooled, the pressure in the first chamber 15 is partially released, and thus the height of the molten metal M bath in the second chamber 16 decreases until the height of the molten metal M is inside the pipe 37 but outside the mold 14, to await a new pressurization cycle and the mold 14 can be opened and the part removed.

[0111] It should be noted that the apparatus 10 does not have the casting pipe of a known type of apparatus that is immersed in a bath of molten metal, but instead has a casting pipe that extends from the top plate of the second chamber and toward the outside of the second chamber. This shortens the passage length of the molten metal within the casting pipe, thereby preventing the remelting of the solidified metal alloy shell, which could potentially produce oxides that transfer to the casting during the metal rise.

[0112] Furthermore, in the device according to the invention, the second chamber is not pressurized using gas / air, but is instead filled with molten metal from the first chamber, and the second chamber is then pressurized so that there is no air in the second chamber, thereby avoiding the possible rise of air within the mold.

[0113] Furthermore, it should be noted that by maintaining the residual air pressure in the first chamber using the device according to the invention, it is possible to ensure that the height of the molten metal in the second chamber (e.g., within the casting pipe) remains high, thereby further reducing the travel of the metal during subsequent filling steps.

[0114] In practice, it has been found that the present invention achieves the intended goals and objectives by providing a low-pressure casting device that, compared with similar devices of known types, reduces and / or eliminates the risk of air entering the casting pipes and / or molds during use.

[0115] Furthermore, using this invention, a low-pressure casting apparatus has been designed that, compared with similar apparatus of known types, shortens the path of molten metal within the casting pipe, thereby mitigating and / or eliminating the risk of metal shell formation and remelting during casting.

[0116] The invention, conceived in this way, is readily subject to numerous modifications and variations, all of which are within the scope of the appended claims; furthermore, all details may be replaced by other technically equivalent elements.

[0117] In practice, the materials used can be any materials according to requirements and existing technology, provided that they are compatible with the specific purpose and the occasional shape and size.

Claims

1. An apparatus (10) for low pressure casting of a metal alloy, comprising: - a loading port (11), - a zone (12) for holding previously loaded molten metal (M), - pressurization means (13) for pressurizing said zone (12) for holding molten metal (M), and - a mold (14) in fluid communication with said zone (12) for holding molten metal (M) and at least partially superimposed on said zone for holding molten metal, characterized in that said zone (12) for holding molten metal (M) of the apparatus (10) comprises: - a first chamber (15) connected to said loading port (11) and to said pressurization means (13), and - a second chamber (16) fluidically connected to said mold (14), said first chamber (15) and said second chamber (16) being fluidically connected by a channel (17).

2. The apparatus (10) according to claim 1, characterized in that said channel (17) is arranged close to or at the bottom (22) of said first chamber (15) and at the bottom (24) of said second chamber (16) and in such a way that the bottom (25) of said channel (17) connects the bottom (22) of said first chamber (15) to the bottom (24) of said second chamber (16).

3. The apparatus (10) according to claim 1, characterized in that the height (H) of said channel (17) is: - lower than the height (HI) of said first chamber (15), and - lower than the height (H2) of said second chamber (16).

4. The apparatus (10) according to claim 1, characterized in that said channel (17) is formed by a metal connector (28) for connecting said first chamber (15) to said second chamber (16), inside said connector (28) there is a ceramic bushing (29).

5. The apparatus (10) according to claim 4, characterized in that: - the seal between said bushing (29) and said first chamber (15) is provided by a first sealing element (30) interposed between said bushing (29) and said first chamber (15), - the seal between said bushing (29) and said second chamber (16) is provided by a second sealing element (31) interposed between said bushing (29) and said second chamber (16).

6. The apparatus (10) according to claim 5, characterized in that said bushing (29) has a flange portion (32) for a form fit with said connector (28), the seal between said bushing (29) and said connector (28) is provided by: - a third sealing element (33) interposed between the surface of said flange portion (32) directed towards said first chamber (15) and said connector (28), and - a fourth sealing element (34) interposed between the surface of said flange portion (32) directed towards said second chamber (16) and said connector (28).

7. The apparatus (10) according to claim 4, characterized in that said connector (28) has a vent (35).

8. The apparatus (10) according to claim 1, characterized in that the apparatus comprises one or more casting ducts (37) fluidically connecting said second chamber (16) to said mold (14), said one or more casting ducts (37) extending from the top plate (39) of said second chamber (16) towards said mold (14).

9. The apparatus (10) according to claim 8, characterized in that The first chamber (15) has first heating means (19) arranged, in the operating configuration, close to or at the top wall (40) of the first chamber, in an upper region with respect to the bath of molten metal (M) and outside the bath of molten metal.

10. The apparatus (10) according to claim 9, characterized in that The second chamber (16) has second heating means (20) arranged, in the operating configuration, inside the bath of molten metal (M).

11. The apparatus (10) according to claim 9, characterized in that The loading opening (11) is arranged at an upper portion (23) of the first chamber (15) and adjacent to the top wall (40) of the first chamber.

12. The apparatus (10) according to claim 2, characterized in that The first chamber (15) has an inner surface (21) which is inclined to form a ramp from the loading opening (11) towards a bottom (22) of the first chamber.

13. The apparatus (10) according to claim 11, characterized in that The pressurization means (13) comprise one or more devices for introducing pressurized gas inside the first chamber (15), starting from the upper portion (23) of the first chamber (15), so as to generate pressure on the free surface of the bath of molten metal (M).

14. The apparatus (10) according to claim 10, characterized in that The apparatus comprises third heating means (41) for heating the one or more casting ducts (37), arranged between the second chamber (16) and the mold (14) and substantially surrounding the one or more casting ducts (37).

15. The apparatus (10) according to claim 12, characterized in that The entire bottom of the area (12) for holding molten metal (M) is constituted, in order, by: - the bottom (22) of the first chamber (15), - the bottom (25) of the passage (17), and - the bottom (24) of the second chamber (16), The entire bottom of the area (12) for holding molten metal (M) is substantially uniformly inclined, wherein: - a first end (26) is at the first chamber (15) and adjacent to the inclined inner surface (21); and - a second end (27) is at a higher level than the first end (26), at the second chamber (16) and opposite the first end (26).

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