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(11) | EP 4 205 877 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | BOTTOM GAS EXTRACTION SYSTEM FOR MANUFACTURING STEEL CAST COMPONENTS WITH REDUCED INCLUSION CONTENT |
| (57) A gas extraction system for extracting gas generated when casting metal articles
by a sand moulding process using a casting device that comprises an upper sand mold
(4) a lower sand mold (5) and a support table (6) for supporting the molds (4,5).
The extraction system comprises a gas chamber (9) located between the top surface
(7a) of the support table (6) and a bottom surface (5a) of the lower sand mold (5):
The gas chamber (9) isg connected to a vacuum pump (13). |
TECHNICAL FIELD
[0001] The present invention is encompassed within the sector of metallurgical industry, particularly in the field of casting steel articles by a sandcasting process using sand molds inside a metallic molding box comprising two halves i.e. copes and bottom halves i.e. drags.
STATE OF THE ART
[0002] Nowadays cast steel components are often manufactured by using chemically bonded sand moulds. Conventional casting devices comprise a metallic molding box, an upper sand mold and a lower sand mold. The upper and the lower sand molds are arranged within the molding box (divided in two halves to conform each one the upper and lower sand mold)) such that a bottom surface of the upper sand mold is in contact with a top surface of the lower sand mold. The sand molds are made of sand and at least one binder and comprise a molding cavity to be filled with molten metal, and a table, fix o sliding in a carrousel, having a top plate comprising a top surface for supporting the molding box.
[0003] Typically, the sand molds are made by mixing up a resin with silica sand and a catalytic product that hardness the mixture after a certain period of time. The sand molds made of sand and at least one binder such as furanic resin, phenolic resin or sodium silicate. The sand molds can also comprise different sand cores that are used to generate internal geometries of the article to be casted. A minimum of voids between sand grains but allowing at the same time the flow of air or gases in the sand molds, is desirable.
[0004] When the hot molten metal is filled into the mold cavity, it contacts the sand molds and thus the binder or binders by which the sand of the sand molds is agglomerated. The gas resulting from the degradation of the binder(s) tends to flow upwards. Gas generated in the lower sand mold thus tends to flow around and through the molten metal causing interactions with the metal and the presence of inclusions therein. During the filling process molten metal gets in touch with the bottom portion of the molding cavity as the metal fills up the empty shape or the pattern. The metal heats up the moulds and decomposes the organic or inorganic binders generating a significant quantity of gases resulting from the partial or total evaporation of the binder or by its chemical reaction with air remaining in pores between sand grains in the mould. The result of this evaporation and chemical reaction are different gases that go through the molten metal or mix up with it, getting stuck on it when it solidifies as gas bubbles when no reaction has taken place, or as non-metallic inclusions when they have reacted with chemical elements of the molten metal.
[0005] Wrought steel articles are manufactured by controlled continuous casting processes. There are standards such as ASTM E45-13 and DIN EN 10247 that are used to determine the cleanliness level in terms the presence of inclusions in the steel for the case of wrought steel articles. It is well known that the level of inclusions is very critical for a significant number of properties of the steel. For example, the elongation and fatigue are clearly influenced by the amount and type of inclusions, whereby a significant worsening of these properties is observed when inclusions are present in significant values.
[0006] It was therefore desirable to solve or at least mitigate the problem caused by gas generated in a sand mold when casting metal articles by a sand casting process.
DESCRIPTION OF THE INVENTION
[0007] A first aspect of the invention relates to a gas extraction system for extracting gas generated when casting metal articles by a sand moulding process, that is intended to solve or at least mitigate the problem caused by gas generated in a sand mold when the lower half of the mold cavity comes into contact with the hot molten metal.
[0008] A second aspect of the invention relates to a casting device for casting metal articles by a sand moulding process comprising a gas extraction system that is intended to solve or at least mitigate the problem caused by gas generated in a sand mold when the lower half of the mold cavity comes into contact with the molten metal.
[0009] Further aspects of the invention will become apparent to the skilled person on the grounds of the features disclosed in the present specification.
[0010] The gas extraction system for extracting gas generated when casting metal articles by a sand moulding process is applied in a casting device that comprises an upper sand mold and a lower sand mold defining in between a molding cavity to be filled with molten metal, and a table support for supporting the molding box.
[0011] According to the invention, the gas extraction system comprises
a gas chamber located between the top surface of the support table and a bottom surface of the lower sand mold,
the gas chamber being connected to a vacuum pump.
[0012] In some embodiments the support table comprises a top plate for supporting the molds and the extraction system comprises
a sealing joint positioned between a peripheral fringe area of the top plate of the table and a bottom edge of the lower sand mold, the sealing joint peripherally enclosing the gas chamber located between the top surface of the table and a bottom surface of the lower sand mold,
an outlet opening in the top plate of the table for connecting the gas chamber with an extraction pipeline connected to a vacuum pump.
[0013] In some embodiments the system comprises bottom vents in the lower sand mold, the bottom vents being connected to the gas chamber and extending vertically from the bottom surface of the lower sand mold towards a lower half of the molding cavity, such that the bottom vents do not penetrate into said lower half.
[0014] In some embodiments the low part of the molding box has a peripherical fringe to be coupled with the sealing joint positioned over the peripheral fringe area of the top plate of the table,
[0015] In some embodiments the gas chamber has a higher height than the sealing joint. For example, the table can comprise an additional hollow space above the top plate of the table, the how space being placed and dimensioned to increase the volume of the gas chamber.
[0016] When the hot molten metal is filled into the mold cavity, it contacts the sand molds and thus the binder or binders by which the sand of the sand molds is agglomerated, so that gas resulting from the degradation of the binder(s) tends to flow upwards. Gas generated in the lower sand mold thus tends to flow around and through the molten metal causing interactions with the metal and the presence of inclusions therein. The gas extraction system according to the present invention allows guiding at least a main proportion of the gas generated in the lower sand mold downwards so that at least a major proportion of the gas, instead of flowing upwards around and through the metal in the mold cavity, is drawn, by action of the vacuum pump, through the bottom vents into the gas chamber, and from there through the outlet opening in the table and extraction pipeline, to the outside of the casting device. Thereby, formation of inclusions in the molten metal and, thus, the presence of such inclusions in the cast metal article are substantially reduced. The fact that the bottom vents do not penetrate into the lower half of the mold cavity prevents molten metal from flowing out the mold cavity into the bottom vents.
[0017] Preferably, the bottom vents in the lower sand mold, are mainly distributed around and near areas where the mold cavity has the higher thermal modulus, and each of the bottom vents may have a diameter of about 10 mm. The bottom vents may have been drilled in the lower sand mold, or they may have been made in the lower sand mold by using a vent pattern template.
[0018] Preferably the distance between the bottom vents is greater than the diameter of a vent and lower than two times the diameter of a vent.
[0019] In some embodiments the bottom vents extend to the whole surface of the metal article to cast. The bottom vents can extend also to the feeding inlet and to the core prints.
[0021] The gas extraction system may comprise the extraction pipeline connected to the outlet opening with a flange. The gas extraction system may further comprise the vacuum pump connected to the extraction pipeline, and it may still further comprise a cooling device thermally connected to the extraction pipeline to cool gases before entering the vacuum pump. It may also comprise a filter device connected to the extraction pipeline to filter gases before entering the vacuum pump.
[0022] The extraction pipeline may comprise a connection manifold coupled to the outlet opening, and a hose coupled to the connection manifold and to the cooling device.
[0023] The casting device for casting metal articles by a sand casting process, comprises a molding box (divided in two halves to conform each one the upper and lower sand mold), and upper sand mold and a lower sand mold, the upper and the lower sand molds arranged within the molding box such that a bottom surface of the upper sand mold is in contact with a top surface of the lower sand mold, the lower sand mold comprising a bottom surface, the sand molds forming a molding cavity to be filled with molten metal, a table having a top plate comprising a top surface with a peripheral fringe area for supporting the molding box, and a gas extraction system as disclosed in this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as examples of how the invention can be carried out. The drawings comprise the following figures:
Figure 1 shows a schematic side elevational view of an embodiment of a casting device comprising the gas extraction system.
Figure 2 shows another schematic side elevational view of the casting device shown in figure 1.
Figure 3 shows a sectioned view of the casting device shown in figure 2.
Figure 4 shows a top plan view of the table plate shown in figures 2 and 3.
Figure 5 shows a bottom view of the lower part of the metallic moulding box including a peripherical fringe and the lower sand mold shown in figures 2 and 3.
Figure 6 shows a bottom view of the upper part of the molding box with the upper sand mold shown in figures 2 and 3.
Figure 7 shows a top plan view of the lower part of the molding box with the lower sand mold shown in figures 2 and 3.
Figures 8A and 8B show two different embodiments of the gas chamber.
DESCRIPTION OF WAYS OF CARRYING OUT THE INVENTION
[0025] Figures 1 to 7 show features of an embodiment of a casting device comprising a gas extraction system for extracting gas generated when casting metal articles by a sand moulding process.
[0026] As shown in figure 1, the casting device comprises a molding box -1- affixed to a table -6-, a connection manifold -12a- connected to an outlet opening provided in an insert -14- surrounding the outlet opening in a top plate -7- of the table -6-, a hose -12b- connected by means of a flange connection -17- to a connection manifold -12a- and to a cooling device -15-, a filter device -16-, and a vacuum pump -13-. The connection manifold -12a- and the hose -12b- are parts of an extraction pipeline -12-. During pouring of molten metal into the molding cavity formed by sand molds arranged in the molding box -1- and during cooling of the metal in the cavity, the vacuum pump -13- draws hot gas out of the molding box -1- through the manifold -12a-, the hose -12b-, a cooling coil -15a- of the cooling device -15- to cool the gas, and the filter device -16- to filter the cooled gas, and expels the cooled and filtered gas though an exhaust pipe -12c-. As shown in figure 4, the insert -14- with the outlet opening -10- is located in a center position of the top plate -7- of the table -6-.
[0027] As depicted in figures 2 and 3, the bottom edge -3a- comprises a peripherical frange metal frame -11- in the shape of peripheral flange, and the table -6- comprises a top plate -7- supported on support legs -6a- standing on the floor-G-. A sealing joint -8- is positioned between a peripheral fringe area -7b- (see figure 4) of the top plate -7- of the table -6- and the bottom edge -3a- of the molding box -1-, In figures 2 and 3 the metal frame -11- and the top plate -7- of the table -6- are connected together by means of bolt-and-nut connections -18-, so that the metal frame -11- holds the molding box -1- on the top plate -7- of the table -6- and presses the bottom edge -3a- of the molding box -1- against the sealing joint -8- on the peripheral fringe area -7b-. The bolts of the bolt-and-nut connections -18- extend through holes -18a, 18b- respectively provided in the peripheries of the top plate -7- of the table -6- (cf. figure 4) and of the metal frame -11- of the molding box -1- (cf. figure 7). In some other embodiments not represented, the bolt and nuts are not necessary, and the weight of the molding box is enough to assure a tight closing of the chamber (9) to extract the gases by the vacuum system.
[0028] An upper sand mold -4- and a lower sand mold -5- are arranged within the molding box -1- such that a bottom surface of the upper sand mold -4- is in contact with a top surface of the lower sand mold -5-, the lower sand mold -5- comprising bottom surface -5a-. The sand molds -4, 5- are made of sand and at least one binder and comprise a molding cavity -4a, 5a- to be filled with molten metal.
[0029] As illustrated in figure 8A, the sealing joint -8- peripherally encloses a gas chamber -9- between the top surface -7a- of the table -6- and the bottom surface -5a- of the lower sand mold -5-. In some embodiments, as illustrated in figure 8B, the gas chamber -9- has a height higher than the height of the sealing joint-8-. As represented the table comprises an additional hollow space above the top plate of the table.
[0030] Figures 3 shows that the upper sand mold -4- comprises top vents -4b- that extend vertically from its upper surface towards an upper half -4a- of the molding cavity -4a, 5a-. By means of the top vents -5b-, when the hot molten metal is poured through the filling channel -19- into the mold cavity -4a, 5a- and thus contacts the sand molds and thereby the binder or binders by which the sand of the sand molds is agglomerated, upstreaming gas resulting from the degradation of the binder(s) is evacuated.
[0031] Figures 3 and 5 show bottom vents -5c- in the lower sand mold -5-, the bottom vents -5c- extending vertically from the bottom surface -5b- of the lower sand mold -5- towards a lower half -5a- of the molding cavity -4a, 5a-, such that the bottom vents -5c- do not penetrate into said lower half -5a-. The bottom vents -5c- in the lower sand mold -5-, are mainly distributed around and near areas where the mold cavity -4a, 5a- has large thicknesses. The purpose of the bottom vents -5c- is that, when the hot molten metal is filled through the filling channel -19- provided in the upper and low sand mold -4- into the mold cavity -4a, 5a-, it contacts the sand molds -4, 5- and thus the binder or binders by which the sand of the sand molds -4, 5- is agglomerated. Gas resulting from the degradation of the binder(s) tending to flow upwards around and through the molten metal causing interactions with the metal and the presence of inclusions therein, is instead drawn downwards by action of the vacuum pump -13- through the bottom vents -5c- into the gas chamber -9- from where the gas is extracted. Each of the bottom vents -5c- has a diameter of about 10 mm and may be have been drilled in the lower sand mold -5- or may have been made in the lower sand mold -5- by using a vent pattern template. Figure 5 further shows that the lower sand -5- mold rests on support beams that are part of the molding box -1-. In an alternative embodiment (not represented) the support beams can be part of the supporting table -20-.
[0032] Figures 6 and 7 show the respective halves -4a, 5a- of a molding cavity for casting a monkey wrench.
[0033] In this text, the term "comprises" and its derivations (such as "comprising", etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc. On the other hand, the invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.
1. A gas extraction system for extracting gas generated when casting metal articles
by a sand moulding process using a casting device that comprises an upper sand mold
(4), a lower sand mold (5) and a support table (6) for supporting the molds (4,5),
characterized in that the extraction system comprises
a gas chamber (9) located between the top surface (7a) of the support table (6) and a bottom surface (5a) of the lower sand mold (5), the gas chamber (9) being connected to a vacuum pump (13).
characterized in that the extraction system comprises
a gas chamber (9) located between the top surface (7a) of the support table (6) and a bottom surface (5a) of the lower sand mold (5), the gas chamber (9) being connected to a vacuum pump (13).
2. A gas extraction system according to claim 1 wherein the support (6) comprises a
top plate (7) for supporting the molds (4,5) and the extraction system comprises
a sealing joint (8) positioned between a peripheral fringe area (7b) of the top plate (7) of the table (6) and a bottom edge (3a) of the lower sand mold (5), the sealing joint (8) peripherally enclosing the gas chamber (9) located between the top surface (7a) of the table (6) and a bottom surface (5a) of the lower sand mold (5),
an outlet opening (10) in the top plate (7) of the table (6) for connecting the gas chamber (9) with an extraction pipeline (12, 12a, 12b) connected to a vacuum pump (13).
3. A gas extraction system according to claims 1 or 2 comprising bottom vents (5c) in
the lower sand mold (5), the bottom vents (5c) being connected to the gas chamber
and extending vertically from the bottom surface (5a) of the lower sand mold (5) towards
a lower half (5a) of the molding cavity (4a, 5a), such that the bottom vents (5c)
do not penetrate into said lower half (5a).
4. A gas extraction system according to claims 1 to 3 wherein the gas chamber (9) has
a height higher than the height of the sealing joint (8).
5. The gas extraction system according to claims 3 or 4, wherein the bottom vents (5c)
are drilled in the lower sand mold (5).
6. The gas extraction system according to any of claims 3 to 5, wherein the bottom vents
(5c) have been made in the lower sand mold (5) by using a vent pattern template.
7. The gas extraction system according to any of claims 3 to 6, wherein the distance
between the bottom vents is greater than the diameter of a vent and lower than two
times the diameter of a vent.
8. The gas extraction system according to any of claims 3 to 7, wherein the bottom vents
extend to the whole surface of the metal article to cast.
9. The gas extraction system according to any of claims 1 to 8 comprising the extraction
pipeline (12, 12a, 12b) connected to the outlet opening (10).
10. The gas extraction system according to claim 9 comprising the vacuum pump (13) connected
to the extraction pipeline (12, 12a, 12b).
11. The gas extraction system according to claim 10 comprising a cooling device (15)
thermally connected to the extraction pipeline (12, 12a, 12b) to cool gases before
entering the vacuum pump (13).
12. The gas extraction system according to claim 9, wherein the extraction pipeline (12,
12a, 12b) comprises a connection manifold (12a) connected to the outlet opening (10)
and a hose (12b) connected to a connection manifold (12a)
14. The gas extraction system according to claim 11 or 12 comprising a filter device
(16) connected to the extraction pipeline (12a, 12b) to filter gases before entering
the vacuum pump (13).
14. The gas extraction system according to any of the preceding claims, wherein the bottom
vents (5c) in the lower sand mold (5), are mainly distributed around and near areas
where the mold cavity (4a, 5a) has large thermal modulus.
15. A casting device for casting metal articles by a sand casting process, the device
comprising
a molding box (1),
an upper and the lower sand molds (4, 5) arranged within the molding box (1) such that a bottom surface of the upper sand mold (4) is in contact with a top surface of the lower sand mold (5), the lower sand mold (5) comprising bottom surface (5a), the sand molds (4, 5) made of sand and at least one binder and comprising a molding cavity (4a, 5a) to be filled with molten metal,
a table (6) having a top plate (7) comprising a top surface (7a) with a peripheral fringe area (7b) for supporting the molding box (1),
characterized in that the casting device comprises a gas extraction system as claimed in any of claims 1 to 12.