EP0100272A1 - Process and apparatus for the production of castings, and castings produced by this process - Google Patents

Abstract

1. Device for the manufacture of castings and of the kind comprising a means for electrically heating a part moulded and solidified in a mould (1) into which this heating means is incorporated, characterized in that the latter consists of at least one electrical heating resistor or of at least one inductor (4) fully embedded or nested inside of the mould (1) for imposing a suitable thermal treatment on at least one portion of the solidified part within the moulding space (3).

Description

The present invention relates generally to a process for manufacturing molded parts, and more particularly relates to a new technique for heat treatment of these parts.

It also relates to a device for carrying out this process, as well as the molded parts obtained using this process and / or this device.

It has been known for a very long time to manufacture metal or other molded parts, by introducing a molten material into a suitable mold where said material will form, after cooling, the molded part which is desired. More specifically, in the case where a metal alloy is used, the production of the molded parts from this alloy has hitherto been carried out in two stages, generally.

The alloy, in the molten state, is first cast in the mold. It solidifies there, then gradually cools there to room temperature; after which we proceed to the demolding or unhooking operation.

Then, the molded part generally having to undergo a heat treatment, it is consequently advisable to reheat it at a temperature higher than room temperature to make it undergo an appropriate thermal cycle and which is a function of the alloy considered and the qualities of the part molded that we want to obtain, it being understood that the temperature range of the heat treatment adopted will always be between ambient temperature and the solidus temperature of the alloy considered.

However, such a two-step process for manufacturing a molded part from a metal alloy has many drawbacks. In fact, the step of cooling the alloy in the mold is almost never controlled or programmed. This means that the cooling takes place naturally and in a more or less random manner, because it is in fact always linked to the thermal inertia of the mold, so that, in total, the parts thus molded by such a random cooling, may already have structural or other defects.

• La pièce moulée doit être, après refroidissement, extraite du moule puis traitée par un appareillage séparé pour la soumettre au cycle thermique en question, ce qui, comme on le comprend, exige une manutention particulière et un temps de main d'oeuvre coûteux.

In addition, the heat treatment or reheating phase of the part in order to subject it to a chosen thermal cycle constitutes an additional operation which has these numerous drawbacks, some of which will be listed below:

• The molded part must be, after cooling, extracted from the mold and then treated by a separate apparatus to subject it to the thermal cycle in question, which, as it is understood, requires special handling and costly labor time.

In addition, the heat treatment consisting in reheating the molded and cooled part naturally requires considerable heat energy since it is necessary to bring the part to the temperature at the start of the thermal cycle, that is to say to a temperature very high which, without necessarily reaching it, approaches the temperature which was at the end of solidification in the mold. As a result, we are far from meeting the energy saving requirements that we are looking for today.

In addition, the rise in temperature of the alloy as well as the thermal cycle in general require a relatively long time so that not only the heat energy to be supplied must be significant, but that the finished part remains expensive.

Furthermore, processes for the production of steel blocks are already known, as described for example in German patent n ° 764 264, which consist in applying a heat flux on the steel in the liquid state in the mold. , that is to say well before solidification in said mold. These methods cause a steel bath movement to homogenize it and remove impurities, which has nothing to do with the heat treatment which must be carried out on the molded part as explained above.

The present invention aims to remedy all the above drawbacks as well as others by proposing a new method and device for manufacturing molded parts, from a liquid called to solidify, such as for example what an alloy. conch, which method and device allow in particular to achieve considerable energy and manufacturing time savings, and to give the molded part all the desired qualities.

To this end, the subject of the invention is essentially a method of manufacturing molded parts, and of the type consisting in using a molten material, such as for example a metal alloy, which is poured into the molding space of a mold where said material will form, after cooling, the molded part, characterized in that one interrupts or slows down the process of cooling at least part of the material in the mold by supplying heat energy to the solidified material, after the end of solidification of the molten material, so as to keep said material already solidified at the temperature of the start of heat treatment and thus to be able to subject it, subsequently, in the mold to heat treatment or controlled cooling, before said material is finally unmolded.

It is therefore already understood that the material being at high temperature at the end of solidification, it takes advantage of the existence of this high temperature which is maintained and which marks the start of a heat treatment or cooling cycle at any time. controlled, material. Thus, it is advantageously avoided any unnecessary loss of the heat energy of the material when it cools, and it removes any significant energy input to the material or the alloy to treat it after it has been cooled and demolded. In short, the controlled heat treatment of the material or alloy which has just solidified constitutes in a way a treatment integrated into the natural cooling process of this material.

According to another characteristic of the process of the invention, the above-mentioned temperature maintenance of at least part of the material or of the alloy already solidified as well as its controlled heat treatment are carried out by induction heating and / or by electrical heating resistance .

We can thus modulate the temperature of the material already solid at the desired temperature and impose a chosen cooling law on it.

It will also be noted here that, during the abovementioned heat treatment, it is possible to carry out accelerated cooling of at least part of the material already solidified and which, in the case where an induction heating means is used, can be produced by passing temporary coolant in this medium.

Such cooling will make it possible, if the material requires it, to extract from this material already solidified in the mold, a heat flux which will be greater than the natural calorific evacuation carried out by the mold. Thus, we understand that we can easily vary at will and within significant limits the cooling law that we want to impose on the alloy or material.

According to yet another characteristic of the invention, the counterweight is subjected to induction heating at the top of the mold, before the material in the mold is solidified.

Thus, the weight will advantageously be avoided from constituting a cold spot, and a weight saving will also be achieved on said weight.

The invention also relates to a device for implementing the method meeting the above-mentioned characteristics, this device comprising a mold of any type capable of receiving a molten material, such as for example a metal alloy, and to which mold is associated with at least one means of induction heating and / or at least one electric heating resistance, characterized in that said means and / or said resistance is arranged inside said mold.

This device is further characterized by a cooling fluid circuit arranged inside the mold.

It will also be added here that this device is characterized in that the abovementioned induction heating means and / or the electrical resistance are arranged inside the mold, over the entire height of the mold or over only part of this height to affect such and such a part, for example hollow or projecting, of the molding space.

According to yet another characteristic of this device, an induction heating means is provided around the neck of the counterweight at the upper part of the mold.

This device is further characterized in that the electric heating resistance consists of conductive particles of current distributed uniformly or not in the mass of said mold according to a density capable of allowing the passage of a current supplied by a connected electric power source. said mold.

Of course, the invention also relates to the molded parts obtained using the method and / or the device corresponding to any of the above-mentioned characteristics.

However, other characteristics and advantages of the invention will appear better in the detailed description which follows and refers to the appended drawings, given only by way of example, and in which:

Figures 1 to 3 show three temperature curves (T ° C) as a function of time (t) (the temperature and time scales being the same for the three curves), and in which: Figure 1 illustrates the cooling of an example of steel being solidified in a mold; FIG. 2 illustrates the heat treatment applied to this same steel, after the cooling illustrated in FIG. 1; and FIG. 3 illustrates the controlled heat treatment carried out according to the principles of the invention, this treatment being applied to the same steel as that of FIGS. 1 and 2 which illustrate the prior art.

Laftgure 4 is a schematic view of a mold equipped with means allowing the implementation of the method according to the invention.

Figures 5 and 6 are also schematic views illustrating two embodiments of the device according to the invention.

FIG. 7 is a schematic view of a mold with a particular electric heating resistance.

For the purpose of better understanding, we will first comment on the curves of FIGS. 1 and 2 respectively illustrating the solidification by cooling of a cast steel, and the heat treatment which is made to undergo this particular steel, it being understood that 'This is a non-limiting example.

As is known, a molten alloy is poured into a mold which is then found at a temperature above about 1500 ° C. Then, by cooling in this mold, the alloy solidifies, that is to say gradually passes from the liquid state to the solid state, as shown respectively in A to B in the figure 1. Finally, the molded and solidified alloy completes its cooling down to room temperature, as shown by the portion of curve C, the latter having, for the alloy considered, a bearing D which, in the case of the alloy considered, corresponds to a short-term heat release resulting from a transformation within this alloy.

When the cast steel part is almost completely cooled, it is then subjected to the heat treatment according to the curve in FIG. 2 which again represents only one example of the thermal cycle for the alloy considered. According to this example, the material is reheated as shown by the portion of curve E, to a temperature of 1100 ° C. Then the part is kept at this temperature for a certain time, as seen in F, before allowing it to cool, as can be seen in G.

If the principles of the invention are applied to the alloy treated according to FIGS. 1 and 2, we then obtains the curve of Figure 3 which will be commented as follows. At the end of solidification, as shown in B, that is to say at a temperature in the region of 1300 ° C., a supply of heat energy is provided by means which will be described later. alloy in the mold, which keeps the alloy at the temperature of the start of heat treatment so that it can be subjected thereafter, in the mold, to controlled cooling. In other words, we will control the cooling law of the alloy in the mold, that is to say that we can for example, as before, maintain the alloy at the temperature of 1100 ° C and the allow to continue cooling thereafter. However, it can be seen here that the level H corresponds to a much shorter holding time (t ₁ ) compared to the level F (t ₂ ) with the previously known method. This is due to the fact that, according to the invention, the alloy is already at temperature when a controlled cooling law is applied to it and that, consequently, the aforementioned holding time is minimized. Thus, the process of the invention makes it possible not only to avoid the loss of heat energy from the alloy being cooled in the mold (FIG. 1) and to avoid a considerable supply of energy for the reheating treatment. (Figure 2), but it also makes it possible to treat the phases of the alloy (solid solutions, precipitates, etc.) from the start. On the other hand, according to the classic two-cycle thermal cycle (Figures 1 and 2), the phases had to be recreated or brought back into equilibrium at high temperature, which ultimately required a much longer time, significant calorific energy, and could be detrimental to the quality of the material, that is to say of the molded part.

It will be added here that the heat treatment according to the invention can be implemented with ease, whether it is simple or complex, that is to say if it comprises one or more thermal cycles and / or comprises one or more operations related to this cu these cycles.

Furthermore, the new way of operating according to the invention can also be applied to the material before a possible hot unhooking operation itself preceding, if necessary, other operations.

The means used, according to the present invention, for implementing the method illustrated in FIG. 3 will now be described.

According to an exemplary embodiment, and with particular reference to FIG. 4, it can be seen that a device according to the invention essentially comprises a mold 1 with, at its upper part, a counterweight 2, this mold comprising a space for molding 3 around which is arranged, according to a helical winding, an induction heating system 4 connected to a suitable supply 5. There is shown in 6 and 7 a chute and a mold supply duct, which duct communicates with the molding space 3.

Thus, thanks to the inductor 4, it will be possible to provide the sufficient amount of heat energy at the end of solidification of the material, as explained previously, so as to be able to stabilize the temperature of this material when it is desired. and to be able to modulate the subsequent cooling. Of course, the passage time and the frequencies of the current applied to the inductor 4 can be chosen at will and will depend on the metal part or the part of this part which is to be treated.

It should be noted here that the inductor 4 will preferably be constituted by a tubular element, as can be seen in FIG. 4, inside which a cooling fluid can circulate as shown by the arrows F in said figure. Thus, it is possible to accelerate the cooling of the part in the molding space 3 by imposing on this part a cooling law such that the heat flux extracted from this part is greater than the natural heat evacuation carried out by the mold. In short, the device shown in FIG. 4 remains particularly flexible in that it makes it possible to carry out all the possible thermal treatments, such as: isothermal maintenance, slow cooling, rapid cooling and stepped quenching, for example.

It is also possible, without departing from the scope of the invention, and although this is not shown, to provide a cooling circuit independent of the means 4 of induction heating.

It is also possible to use as a heating means, in place of the inductor 4 or in combination with it, an electric heating resistor (not shown) and suitably arranged in the mold so as to be able to heat the molded part or such and such a part of it.

Thus, the inductor 4 and / or the electric heating resistance can be arranged over the entire height and the entire periphery of the molding space 3, as seen in lafigurs4, or over the entire height of this space and only over part of its periphery, as seen in FIG. 5, or again over a small part of the height of the molding space, for example in a cavity 8 formed in this space, as can be seen in FIG. 6. In this figure, it can also be seen that an inductor has been provided 4a in the cavity 8, and another inductor 4b which surrounds the upper part of the molding space 3. It is of course possible to imagine an infinity of variants of shapes, numbers and locations of the inductors and / or the heating resistors , this of course being a function of the conformation of the molding space 3 and also of the heat treatments which it is desired to subject the material to such and such a place to be treated.

In the same vein, the nature and the constitution of the mold 1 can be any, without departing from the scope of the invention. Thus, the mold 1 can be a non-metallic mold, for example a sand mold as shown in FIG. 4, or even a metallic mold in which the inductor will be fixed or fitted, by any suitable means. 4 and / or the electric heating resistance.

Returning to FIG. 4, we have shown at 9 an inductor which surrounds the collar of the flyweight 2 at the upper part of the mold 1. Thus, thanks to this advantageous arrangement, the neck of the flyweight will be kept in the liquid state so that said neck does not become a "cold spot" leading to premature solidification before solidification is completed in the mold, which of course would give the molded part defects.

Also, the use of induction heating at the neck of the counterweight will make it possible to maintain this part in the liquid state according to a temperature determined according to the alloy considered, and it will thus be possible to modulate the cooling of the neck of the flyweight, including solid state cooling. In addition, the heating of the counterweight 2 by the inductor 9 will advantageously make it possible to significantly reduce the volume of said counterweight situated above the neck.

The inductor 9 may be arranged above the mold 1, as seen in Figure 4, but it could very well, without departing from the scope of the invention, be arranged in the mold around the part 2a of the neck (see figure 4). It will be added here that inductors can be provided at other parts of the device, such as for example on the trough 6 and / or the supply duct 7.

In FIG. 7, a mold 1 has been shown containing around the molding cavity 3, current-conducting particles 10 embedded in the mass of said mold and allowing the transfer of heat energy to the molding cavity 3 to heat it appropriately and function of the particle distribution. In other words, a thermal gradient control can be obtained by the distribution, the particle size and the density of the particles embedded in the mold 1.

These particles 10 are distributed uniformly or not in the mass of the mold which may consist of sand or any other suitable material. As seen in Figure 7, the particles 10 can be more or less dispersed or agglomerated together in a more or less compact form, and this so as to allow the passage of a current which is supplied for example by means of electrodes 11 secured to an insulating wall 12 surrounding the mold 1, said electrodes being connected to a power source not shown.

Thus, the more or less dispersed or agglomerated conductive particles 10 constitute as many points or zones of transfer of electric energy making it possible to control the heating of the molding cavity 3, this heating obviously being a function of the particle size and of the density. distribution.

The particles 10 may be particles based on suitable metals or alloys, or alternatively particles of oxides, such as for example metal oxides, or particles of metallic silicates. It is also possible to use particles either sintered or composite.

A binder can be added to the mass of the mold 1 to maintain the structure of particles in said mass, this binder can be mineral or organic.

Finally, it will be added here that the method and the device of the invention can be applied to all moldable materials and in particular to all heat treatments of cast metal alloys, resulting in a structural evolution of these alloys, therefore in general an appearance new features. And, by structural evolution, one must understand any evolution of the metallographic structure having called upon either a so-called "diffusional" mechanism, either to a mechanism called "shear", or to the association of these two mechanisms.

We have therefore achieved according to the invention, a method and a device for manufacturing molded parts which allow substantial energy savings, which make it possible to produce molded parts quickly, and which are very flexible to use. , which gives them possibilities of application to the treatment of very diverse materials and alloys.

Claims (14)

1. A method of manufacturing molded parts and of the type consisting in using a molten material, such as for example a metal alloy, which is poured into the molding space (3) of a mold (1) where said material will form, after cooling, the molded part, characterized in that one interrupts or slows down the process of cooling at least part of the material in the mold by adding heat energy to the solidified material, after the end of solidification of the material melted, so as to maintain said already solidified material at the temperature of the start of heat treatment and thus to be able to subject it, thereafter, in the mold to heat treatment or controlled cooling, before said material is finally demolded. 2. Method according to claim 1, characterized in that the temperature maintenance of at least part of the aforementioned already solidified material and its controlled heat treatment are carried out by induction heating (4) and / or by electric heating resistance. 3. Method according to claim 1 or 2, characterized in that during the aforementioned heat treatment, one proceeds to an accelerated cooling of at least a part of the aforementioned already solidified material, and which in the case where a means is used Induction heating (4) can be achieved by temporarily passing a cooling fluid through this means. 4. Method according to one of claims 1 to 3, characterized in that subjected to an induction heating the weight (2) at the top of the mold, before the material in the mold is solidified. 5. Device for implementing the method according to one of claims 1 to 4, and comprising a mold (1) of any type capable of receiving a molten material, such as for example a metal alloy, and to which mold is associated with at least one means of induction heating (4) and / or at least one electric heating resistance, characterized in that said means and / or said resistance is arranged inside said mold (1). 6. Device according to claim 5, and wherein is provided at least one cooling fluid circuit, characterized in that said cooling circuit is arranged inside the mold (1). 7. Device according to claim 5 or 6, characterized in that the induction heating means and / or the aforesaid electrical resistance are arranged inside the mold (1), over the entire height of the mold or on only a part of this height to affect this or that part, for example recessed (8) or projecting, of the molding space. 8. Device according to one of claims 5 to 7, characterized in that at least one inductor is provided at the supply system (6,7) of the mold. 9. Device according to one of claims 5 to 8, characterized in that around the flyweight neck (2) at the upper part of the mold (1) is provided an induction heating means (9). 10. Device according to claim 5 or 7, characterized in that the electric heating resistance consists of particles (10) conducting current distributed uniformly or not in the mass of said mold according to a density capable of allowing the passage of a current supplied by an electric power source connected to said mold. 11. Device according to claim 10, characterized in that the aforementioned particles (10) consist of metallic particles based on metals or alloys., Particles of oxides such as for example metallic oxides, particles of metallic silicates., or a mixture of the aforementioned particles. 12. Device according to claim 10 or 11, characterized in that the particles (10) mentioned above and distributed in the mass of the mold (1) can be more or less dispersed or else agglomerated together in a more or less compact form. 13. Device according to one of claims 10 to 12, characterized in that optionally added to the mass of the mold (1) an inorganic or organic binder for maintaining the structure of the particles in said mass. 14. Molded parts obtained using the method or device according to any one of the preceding claims.

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