WO2011154561A1 - Method for producing a metal part - Google Patents

Abstract

The invention relates to methods for casting metal parts in sand moulds, characterised in that it is not necessary to use sleeves which surround the feed sprues which are disposed on the exterior of the part in order to compensate for the shrinkage that occurs during the solidification of molten metals. The method of the invention dispenses with the need for the positioning of sleeves that have to be placed around the sprues, said sleeves being created when the sand mould is obtained.

Description

 PROCEDURE FOR OBTAINING A METAL PART

DESCRIPTION TECHNICAL FIELD OF THE INVENTION

The invention is included in the processes of casting metal parts in sand molds and, in particular, it refers to a process that allows to provide insulating and / or exothermic material in areas of the sand mold that will be in contact with the metal melted and in which greater insulation or heat input is required.

BACKGROUND OF THE INVENTION The production of cast metal parts comprises the pouring of a molten metal into a mold, the solidification of the metal and demolding of the formed part by removing or destroying the mold. When molten metal is poured into a mold and allowed to solidify, the metal contracts during solidification and its volume is reduced. In order to compensate for this contraction and ensure the production of quality molded parts, it is usually necessary to use the so-called feeders located outside the part. When the molded part solidifies and contracts, the feeding of molten metal from the flask to the piece prevents the formation of rechupes.

In order to obtain a sand mold, one usually starts with two molding boxes (wood, steel, etc.), in each of which a semi-mold is obtained with a specific part of the cavity that, when joining the two half-molds of sand will determine the cavity with the shape of the piece to be obtained.

To obtain each sand semi-mold, a molding box is placed in which the corresponding part of the model is placed, filling the rest with a mixture of agglomerated sand and its catalyst.

 The union of the sand half-molds by the faces that present the cavity, gives rise to the sand mold with the cavity that must be filled with molten metal to form the metal part.

As previously mentioned, during solidification, molten metals undergo a reduction in volume. For this reason, in the casting of metals it is usually customary to use mazarotas arranged on the outside of the piece to compensate for the contraction that occurs during solidification. In order to improve the feeding effect and so that the volume of the feeding hose can be minimized, the feeding hose is usually surrounded with an exothermic sleeve and / or thermal insulator in order to keep the metal of molten state the mazarota for as long as possible.

These sleeves are placed before carrying out the casting operations on a support firmly attached to the model. After the production of the mold, the support is removed to obtain a feeding cavity, that is, the flask surrounded by the sleeve. When the molten metal is introduced through the trough or pouring channel, the metal flows through it, filling, on the one hand, the mold cavity that will make up the molded part and, on the other, the feeding tap. Because the hub is surrounded by the exothermic and / or insulating sleeve, the metal will remain longer in a liquid state while the metal solidifies and contracts in the rest of the piece, thus allowing the metal to feed cast to compensate for shrinkage and thus minimize plug formation.

Depending on the geometry of the piece to be obtained, the mold will need more or less mazarotas, and each of them will be surrounded by an exothermic and / or insulating sleeve. Therefore, before carrying out the pouring of molten metal into the mold, the sleeves must have been placed in their respective cups, which considerably increases the duty cycle.

As indicated above, the mazarotage zones are defined in the sand mold by the model itself in which, in addition to the geometry of the piece to be obtained, the mazarotage zones external to the piece are formed. These areas of mazarotage should be covered before casting with the corresponding insulating and / or exothermic sleeves.

When the piece has strangulation or difficult feeding areas that do not allow the rest of the piece to be fed before solidification occurs, the so-called "padding" is used, which consists in obtaining a widening of the area in the sand mold of throttling or difficult access of the liquid metal, to achieve an excess of metal that guarantees the complete filling of that area of the cavity. This solution that solves the problem of a good casting of the piece, has the disadvantage that afterwards, it is necessary to eliminate the "padding", which implies an expensive burr operation.

Until now the operation of placing the sleeves around the mazarotas, is an essential operation, it would therefore be desirable to be able to do without this operation by performing the sleeves when obtaining the sand mold. On the other hand, the smelter generally produces the sand molds and the sleeves come from a manufacturer specialized in sleeves, so that the smelter does not control the materials and the composition of the sleeves which implies certain risks, since currently, there are a series of materials that are frequently used in the manufacture of sleeves, whose use in the new European legislation, is restricted because during their handling or after laundry they can produce particles or emissions harmful to health.

However, there are materials for the manufacture of sleeves of proven use that have proven their effectiveness both in terms of meeting the expectations required in terms of insulation and exothermicity, and that, in addition, can be supplied to the foundry so that it, " in situ ", produce the sleeves and the mazarotage areas required by the fabrication of the cast. Sleeves of these characteristics are described in patents EP 1543897 and EP 02651 12. Therefore, it would be desirable to be able to provide insulating and / or exothermic materials at the time of manufacture of the sand mold in those areas where it requires greater insulation or contribution of heat

 DESCRIPTION OF THE INVENTION

A subject of the invention is a method of obtaining metal parts by casting a molten metal in a sand mold, which allows an insulating or exothermic material to be applied in areas of the mold that require greater insulation or heat input by exothermic reaction, such as, areas of mazarotage or internal areas of the mold and all this during a manufacturing process of the sand mold. This allows to carry out "in situ" the sleeves that have to surround the lugs and provide insulating or exothermic material in areas of difficult feeding that do not allow feeding the rest of the piece before its solidification occurs. For this purpose, the method object of the invention comprises the following steps: a) Place, in a molding box, a model to form a cavity that will define the shape of the metal part and, at least, a tap, b) pour a molding sand in the molding box, after phase a), c) pouring a mixture, insulator or exothermic into the molding box after phase a), to retard the solidification of a molten metal, d) extract the model to form said cavity, e) cast a molten metal into said cavity, f) extract the piece obtained after solidification of the molten metal.

The mixture, exothermic or insulating, is arranged in contact with the model, in areas where the molten metal cast in phase e) is required to remain in liquid state longer than the rest of molten metal that will form the piece, in such a way that, once the model in phase d) has been eliminated, the mixture, insulating or exothermic, retards the solidification of the molten metal cast in phase e), in the areas where said mixture has been arranged. The choice of an insulating or exothermic mixture will depend on the thermal characteristics of the metal to be cast, the dimensions of the piece, its geometry and other variants, for example, if the piece is a non-ferritic metal part of Under melting point, the mixture used could be an insulating mixture.

If the model placed in the molding box has an area of difficult feeding or throttling that makes it difficult to feed another part of the piece with molten metal, the mixture, insulating or exothermic, will be deposited, in contact with the model, in that area of strangulation, before pouring the molding sand, so that when casting the molten metal, it remains in the said throttling zone in a liquid state, longer than the rest of the metal that will make up the piece and, therefore, can feed other zones ..

However, if the area in which the mixture, insulating or exothermic, is to be deposited, corresponds, for example, to a tap, an auxiliary piece can be placed around the said tap, so that, after pouring the sand from molding, the aforementioned auxiliary part is removed, forming a gap between the molding sand and the model, in which the insulating or exothermic mixture will be poured, which, once cured, becomes a sleeve.

The auxiliary part used to surround the mazarot, can be a bushing of circular section that has to be able to be extracted, that is, to separate from the mazarot with ease to form the aforementioned hole.

The insulating or exothermic mixture can be a non-fibrous mixture, such as those described in patents EP 1543897 and EP 02651 12, so that the molding sand and the said insulating or exothermic mixtures, which will form the mold, can be found in independent deposits. These input materials fall into a hopper and from this to a mixer, continuous or discontinuous, where they will be mixed with the corresponding resins and catalysts, coming from other tanks. The molding sand along with the resins and catalysts is poured into the molding box. Likewise, the insulating or exothermic materials, already mixed with the resins and catalysts, are poured into the molding box in its proper place.

DESCRIPTION OF THE DRAWINGS

To complete the description and in order to help a better understanding of the features of the invention, according to a preferred example of the realization of the same, a set of drawings is attached as an integral part of said description. Illustrative and not limiting, the following has been represented:

Figure 1 .- Shows a sectional view of the upper molding box in which the corresponding model and the mazarot have been placed, together with the casting channel.

Figure 2.- Shows a sectional view of the upper molding box in which, in an area that is difficult for the molten metal to reach, an insulating or exothermic mixture has been deposited. Furthermore, in this figure, it is also observed that an auxiliary part has been arranged around the tap.

Figure 3.- Shows a sectional view of the upper molding box in which the molding sand that completely fills the box has been poured. Figure 4.- Shows a sectional view of the upper molding box, once the auxiliary part that surrounds the flask has been removed and a hole formed.

Figure 5.- Shows a sectional view of the upper molding box with the hole filled with the insulating or exothermic mixture.

Figure 6.- It shows a sectional view of the upper molding box at the moment the extraction of the model and the casting channel begins.

Figure 7.- Shows a sectional view of the upper part of the sand mold, once the model and the casting channel of the upper molding box have been completely removed.

Figure 8.- It shows a sectional view of the complete sand mold, this is its upper and lower part, where the cavity that will form the piece has been filled with the molten metal supplied from the casting channel.

Figure 9.- Shows a schematic view of an installation comprising the material tanks, dispenser, mixer and other components of the installation.

PREFERRED EMBODIMENT OF THE INVENTION

In figure 1, a molding box (3) is observed, specifically, the upper box, inside which a model (4) has been arranged to form a cavity (5), which will define the shape of the metal part ( 1) and, at least one mazarota (1 1). In addition, inside this upper molding box (3), the corresponding model has also been placed to form the casting channel or drinking trough (10). Although not shown in the figures, to form the sand mold (2), it is also necessary to have a lower molding box (3), where the corresponding model will be placed to define another cavity, which when joining with The cavity defined by the model placed in the upper molding box (3), will form the cavity that corresponds to the piece to be obtained and that will be filled with molten metal. As indicated above, a model is first placed in a lower box and molding sand is poured, then flip the lower box and place the upper box on it with another model and the feed channels already arranged.

In Figure 1, some areas (41, 42) can be observed which, by their configuration, are areas in which it is required that the metal that will sneak into the cavity (5) remain in a liquid state longer than the rest of the metal that will make up the piece (1).

In this case, the zone (41) corresponds to a flask (1 1) that will be formed once the molten metal is cast, and the zone (42) is an area of difficult access for the molten metal to reach. The mazarotas are used to compensate the contraction that occurs during the solidification of the metals, so that the feeding of molten metal from the mazarota (1 1) to the cavity (5) allows the complete filling of the same and with it, Obtaining quality parts. To improve the feed from the tap (1 1) and for the molten metal to reach hard-to-reach areas, such as the area (42), the process object of the invention, allows to provide a mixture (7), insulator or exothermic, in contact with the model (4) in the zones (41, 42), so that the molten metal cast in the cavity (5), remains, in the zones (41, 42) in liquid state more time than the rest of the metal that will make up the piece (1). In figure 2, it is observed that in the zone (42), which is an area of difficult feeding that does not allow feeding the rest of the piece, the mixture (7), insulating or exothermic, has been deposited, which allows delaying, in that zone (42), the solidification of the cast metal. This mixture (7) will be placed in the area (42), before pouring the molding sand (6) into the molding box (3). In this figure 2, it can also be seen that in the area (41) that will constitute the flask (1 1), an auxiliary part (8) has been placed around it, in this case, due to the shape of the mazarota, the auxiliary part (8) is a circular section bushing.

Once the bushing is placed around the area (41) and the mixture (7) is poured, insulating or exothermic, the molding sand (6) is poured, as can be seen in Figure 3.

As seen in Figure 4, after pouring the molding sand (6) into the molding box (3), the bushing is removed, so that, between the molding sand (6) and the area (41) a hole is created (9). As can be seen in figure 5, the hole (9) is filled with the mixture (7), insulating or exothermic to allow the solidification of molten metal to be retarded in the area (41) once it has been cast in the cavity (5).

In figure 6, the model (4), together with the model that forms the casting channel or drinking fountain (10), are being removed, to define the cavity (5) that will be filled with molten metal cast through the channel of casting (10), as seen in figure 8. The total extraction of the model (4) and the model that makes up the drinking fountain (10), is seen in figure 7. At the moment when the models are removed , the molding box (3) and the molding sand is cured, the upper part of the sand mold (2) is obtained, whose cavity (5) will be filled with molten metal. The steps described above will be applied to a lower molding box (2), except that, in the lower molding box (3), it is not necessary to arrange the casting channels, simply the corresponding model must be placed to conform a cavity that together with the cavity obtained in the upper molding box (3), will form a cavity that will be filled with molten metal to form the metal part.

In figure 8, the complete sand mold (2) is observed, with the upper and lower part, in which a cavity that corresponds to the final shape of the metal piece (1) to be obtained has been defined. The sand mold cavity (2) has been filled with molten metal through the trough (10). In the areas (41, 42) where the mixture (7), insulating or exothermic, has been deposited, the molten metal will remain in a liquid state longer than the rest of the metal, in order to achieve a complete filling of all cavity and that, as for example, in zone (42) the metal reaches hard-to-feed areas.

Although not shown in the figures, once the molten metal has solidified, the sand mold (2) is destroyed to remove the metal part (1). Once removed, it will be necessary to remove the flask (1 1) and the trough (10) by any of the procedures known in the industry.

With the process, object of the invention, it has been possible to obtain, at the time of forming the sand mold (2), areas (41, 42) in which the molten metal is required to remain in the liquid state longer. In figure 9, an industrial installation for obtaining metal parts according to the invention is schematically illustrated. Installation represented has three tanks (12) or hoppers with the materials involved in the process. Thus, for example, in one of these deposits (12) is the sand to form the sand mold (2), in another tank (12) is the insulating mixture and in another the exothermic mixture.

From each tank (12) the appropriate amount is dosed in a distribution hopper (14) that is poured into a mixer (13). Resiners and catalysts from the tanks (15) access the mixer (13), continuous or discontinuous. Once the mixtures have been obtained, either the mixed molding sand (6) or the mixed exothermic or insulating mixture (7), it is deposited by gravity, in the place that corresponds to it in the molding boxes (3) .

Claims

one . Procedure for obtaining a metal part (1) by casting a molten metal in a sand mold (2), characterized in that it comprises: a) placing, in a molding box (3), a model (4) to form a cavity (5) that will define the shape of the metal part (1) and, at least, a tap (1 1), b) pour a molding sand (6) into the molding box (3), after the phase a), to form the sand mold (2), c) pour a mixture (7), insulating or exothermic into the molding box (3), after phase a), to retard the solidification of a molten metal, d) extract the model (4) to form the said cavity (5), e) casting a molten metal into said cavity (5), f) extracting the piece (1) obtained after solidification of the molten metal, with the particularity that the mixture (7), insulating or exothermic, is arranged in contact with the model (4), in areas (41, 42) in which the molten metal cast in phase e) is required, stay in liquid state longer than the rest of the molten metal that will form the piece (1), so that once the model (4) in phase d) is removed, the mixture (7), insulating or exothermic, retards the solidification of the molten metal cast in phase e), in the zones (41, 42) where said mixture has been arranged (7). 2. Procedure for obtaining a metal part (1), according to claim 1, characterized in that after phase a) an auxiliary part (8) is placed around the area (41), so that after phase b) remove said auxiliary part (8), forming a hole (9), between the molding sand (6) and the model (4), in which the mixture (7), insulating or exothermic, is poured from phase c ). 3. Method of obtaining a metal part (1), according to claim 2, characterized in that the auxiliary part (8) is a circular section bushing. 4. Method for obtaining a metal part (1), according to any of the preceding claims, characterized in that the mixture (7), insulating or exothermic, is a non-fibrous mixture. 5. Method of obtaining a metal part (1), according to any of the preceding claims, characterized in that the mixture (7), insulating or exothermic, is in contact with the molten metal, in an area (41) that constitutes the flask (1 1), to provide heat or insulation. Method for obtaining a metal part (1), according to any of the preceding claims, characterized in that the mixture (7), insulating or exothermic, is arranged in contact with a part of the molten metal in an area of difficult access (42 ) of the piece (1) that requires heat or insulation. Method for obtaining a metal part, according to any of the preceding claims, characterized in that the molding sand (6) and the mixture (7), insulating or exothermic, that make up the sand mold (2) are in deposits (12) independent, that feed a mixer (13), where they are mixed with binder resins, so that they access by gravity to the molding box (3).