EP1502676B1 - Potassium borate foundry core with dissolution cavity - Google Patents

Description

The invention relates to a core for producing hollow forms by casting, a mold and a method for producing such a core.

The invention relates more particularly to a core for producing hollow shapes by casting, obtained by molding a casting of molten mineral salts in a mold.

The document JP-A-0.1.306043 discloses and shows an arrangement for molding a core in a U-shaped cavity (2) of a mold (1). The molten material (10) by means of which the core is made is introduced into the mold (1) via a valve (5) arranged at the end of one of the branches of the mold. "U". Then the valve (5) is closed so that the material (10), while cooling, retracts with respect to the walls of the cavity (2) of the mold (1). Then, the valve (5) is opened and a valve (6) arranged at the end of the opposite branch of the "U" and a suction is provoked by these valves to extract the core from a single block of the mold (1) .

In this document, the kernel is extracted from one block. This is not always possible.

The document FR-2819205 discloses a core comprising inorganic salts such as potassium metaborate or monoborate, potassium diborate, potassium triborate, potassium tetraborate, or potassium pentaborate.

Such a core is compatible with pressure casting processes, for the realization of hollow shapes of fine geometries, and compatible with all types of light alloys used in these processes.

It allows in particular to produce parts with hollow shapes of complex geometries and having a good surface, while ensuring the cleanliness of the cavities.

It can be used in a pressure casting process, but it can also be used in a casting process with gravity casting, in order to improve the surface condition of the cavities and to make cavities of more geometries. complex, compared to a casting process using gravity casting using a core based on sand or conventional mineral salts.

Such a kernel is also described in the document EP-0613742 .

After the casting of a casting with such a core, a core, whatever it is, must be removed from the mold release part in order to use and / or machine said part .

In the particular case of the nuclei of the type described above which dissolve with water, it has been found that the dissolution of the nucleus takes place along a front of dissolution extending from one end of the core, through which the water is routed to the opposite end of the core.

This phenomenon is opposed to a rapid dissolution of the nucleus, and thus increases the duration during which the piece coming from foundry is immobilized pending the dissolution of its nucleus or nuclei.

To overcome this drawback, the invention provides a core of the type described above comprising means for promoting the penetration of water into the core and therefore accelerate its dissolution as defined in claim 1.

For this purpose, the invention proposes a core of the type described above, characterized in that it comprises an interior cavity intended to allow, after use of the core for the realization of a casting part, a solvent to have access by capillarity in the core of the core to accelerate dissolution.

• la cavité intérieure est réalisée lors de l'opération de moulage dudit noyau,
• la cavité est constituée d'une retassure interne obtenue par un refroidissement rapide de la surface extérieure du noyau.

According to other features of the invention:

• the internal cavity is made during the molding operation of said core,
• the cavity consists of an internal shrinkage obtained by rapid cooling of the outer surface of the core.

The invention also relates to a method for producing a core of the type previously described as defined in claim 4, of the type which comprises at least one molding operation of the core, characterized in that the molding operation is followed by a fast cooling operation of the outer surface of the core.

• au cours de l'opération de refroidissement rapide de la surface extérieure du noyau, on refroidit rapidement la paroi d'une empreinte du moule au contact avec le noyau,
• au cours de l'opération de moulage du noyau, on coule les sels minéraux en fusion par gravité dans le moule,
• le procédé comporte de préférence une opération préliminaire de chauffage du moule préalable à l'opération de moulage, de manière à diminuer la différence initiale de température entre les sels minéraux et le moule,

According to other characteristics of the process:

• during the rapid cooling operation of the outer surface of the core, the wall of an impression of the mold is rapidly cooled in contact with the core,
• during the molding operation of the core, the molten mineral salts are cast by gravity into the mold,
• the process preferably comprises a preliminary operation of heating the mold prior to the molding operation, so as to reduce the initial difference in temperature between the inorganic salts and the mold,

The invention also relates to a mold for producing a core comprising cooling means arranged near the wall of the mold cavity.

According to another feature of the mold, it comprises internal heating means.

• la figure 1 est une vue schématique en coupe longitudinale avec arrachement d'un moule et d'un noyau selon l'invention au cours d'une opération de moulage en grappe du noyau conforme à l'invention ;
• la figure 2 est une vue schématique en coupe longitudinale représentant la dissolution d'un noyau conventionnel dans une pièce de fonderie ;
• la figure 3 est une vue schématique en coupe longitudinale représentant la dissolution d'un noyau selon l'invention dans une pièce de fonderie ;

Other features and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

• the figure 1 is a schematic longitudinal sectional view with tearing of a mold and a core according to the invention during a core molding operation of the core according to the invention;
• the figure 2 is a schematic view in longitudinal section showing the dissolution of a conventional core in a casting;
• the figure 3 is a schematic view in longitudinal section showing the dissolution of a core according to the invention in a casting;

In the following description, like reference numerals designate like parts or having similar functions.

We have shown figure 1 a cluster molding operation of two cores 10 for producing a casting piece of the type of the piece 12 which has been shown in FIGS. Figures 2 and 3 .

As illustrated by figure 1 during the molding operation of the core 10, a casting of molten mineral salts is carried out in a feed funnel 14 of a mold 16. The feed funnel communicates at its lower end with an imprint 18 of the mold 16.

At least a part of the inorganic salts is chosen for example from potassium borates to obtain a core 10 having high mechanical characteristics.

Under these conditions, the mineral salts are distributed by gravity in the footprint 18 of the mold 16 according to the arrows "F" to constitute, after cooling, the core 12.

The result obtained is a nucleus 12 similar to that which has been shown in Figures 2 and 3 .

As illustrated by Figures 2 and 3 , a casting piece 12 having a hollow shape 20 is obtained by an operation of molding with the previously obtained core. The hollow form 20 is complementary to the core 10, and it is necessary to be able to exploit this hollow form 20 to dissolve the core 10 with the aid of a solvent, for example water in the case of a core 10 according to the invention comprising salts based on potassium borate.

As illustrated by figure 2 which represents an operation of dissolution of a conventional core, the solvent is introduced through an end opening 22 of the mold 12. With the solid conventional core which has been shown in FIG. figure 2 the solvent propagates in the core 10 along successive front lines 24, progressively dissolving the core 10 from the line to the left of the figure 2 .

Therefore, the operation of dissolving the core 10 is a long operation which, in the case of mass production, generates high immobilization costs in the workshop where the dissolution of the cores 10 is carried out.

As illustrated by figure 3 , to overcome this drawback, the invention proposes a core 10 having an internal cavity 26 intended, after use of the core 10 for producing a casting part 12, to allow a solvent to have access by capillarity to the core the core 10 to accelerate the dissolution in the room 12.

Thus, during the dissolution operation of the core 10, the solvent enters the cavity 26 as shown in FIG. figure 3 and propagates from the inside to the outside of the core along various directions represented by the arrows of the figure 3 .

According to the invention, the internal cavity 26 is made during the molding operation of the core 10.

The cavity 26 could, in a non-limiting manner of the invention, be made by drilling or by introducing, before molding the core, a temperature element of higher melting than the potassium borate salts, which element would be removed from the core prior to the dissolution operation of the core 10 to form the cavity 26.

However, in the embodiment of the invention, the cavity 26 consists of an inner core shrinkage obtained by rapid cooling of the outer surface 28 of the core 10 during its molding.

For this purpose, a method of manufacturing the core 10 comprises at least one molding operation as previously mentioned with reference to FIG. figure 1 followed by a rapid cooling operation of the outer surface 28 of the core 10.

During this rapid cooling operation of the outer surface 28 of the core 10, the wall of the cavity 18 of the mold 16, which is in contact with the core 10, is rapidly cooled.

For this purpose, as illustrated by figure 1 the mold 16 comprises cooling means 30 arranged near the wall of the cavity 18 of the mold 16,

All the cooling means known from the state of the art can be used for the good realization of the invention.

On the wrenching of the figure 1 , by way of example and in a nonlimiting manner, there is shown cooling means constituted by an exchanger 32 housed in the mold 16. As illustrated by the arrows, the exchanger is supplied with heat transfer fluid by a arrival conduit 34 and this fluid is discharged through a conduit 36. This configuration allows to evacuate a large number of calories in a very short time.

Such exchangers 34 are distributed along the entire periphery of the cavity 18, to ensure rapid and uniform cooling of the cavity 18.

Finally, prior to the molding operation of the core 10, the method may comprise a preliminary heating operation of the mold 16 so as to reduce the initial difference in temperature between the inorganic salts and the mold 16.

For this purpose, the mold 16 comprises internal heating means 38, for example one or more electrical resistors 40 housed in the mold 16 and intended to allow its temperature rise uniformly.

The invention thus makes it possible to produce potassium borate mineral salts which have the particularity of being rapidly dissolvable, which makes it possible to reduce the costs and the production times of parts 12 molded with such cores.

Claims (7)

1. Core (10) for creating hollow shapes by casting, obtained by pouring molten mineral salts into a mould (16),
   characterized in that it comprises an interior cavity (26) intended to allow a solvent to gain access through capillarity to the heart of the core in order to accelerate the dissolving of this core within the component (12) after the core has been used.
2. Core (10) according to the preceding claim, characterized in that the interior cavity (26) is formed at the time of the casting of the core.
3. Core (10) according to the preceding claim, characterized in that the cavity (26) consists of an internal contraction cavity of the core which is obtained as a result of more rapid cooling of the exterior surface (28) than of the heart of the core.
4. Method of manufacturing a core (10) according to Claim 3, characterized in that the casting operation is followed by an operation of rapid cooling of the exterior surface (28) of the core (10).
5. Method of manufacturing a core (10) according to the preceding claim, characterized in that, during the operation of rapid cooling of the exterior surface (28) of the core (10), the wall of a moulding cavity (18) of the mould (10) in contact with the core (10) is rapidly cooled by using cooling means (30) positioned in close proximity to the wall of the moulding cavity (18) of the mould (16).
6. Method of manufacturing a core (10) according to one of the preceding Claims 4 or 5, characterized in that the molten mineral salts are poured under gravity into the mould (16) during the operation of casting the core.
7. Method of manufacturing a core (10) according to any one of Claims 4 to 6, characterized in that it comprises a preliminary operation of heating the mould (16) using heating means (38) internal to the mould (16) prior to the casting operation, so as to reduce the initial temperature difference between the mineral salts and the mould (16).

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