EP3184201B1 - Foundry core-making device operating by gravity - Google Patents

Description

The invention relates to a foundry technique, called gravity casting, also referred to as gravity casting, which allows metal parts to be molded. Gravity casting knows several implementation variants, including, for example, the so-called shell gravity casting, in source, tilted or low pressure, the invention being interested in all these variants.

The invention relates more particularly to so-called core-making devices intended to manufacture cores for molds used in this type of technique. In foundry, the cores are, in a known manner, components of the mold, made from sand, natural or artificial, (silica, mullite, ceramic and other, ...) which make it possible to make the interior recesses of the part to be made. mold, or undercut areas thereof.

A core-making device device as a foundry technique is for example described in the document US 2003/0173049 A1 .

These core-making devices generally consist of three large parts, movable relative to each other.

First of all, there is the most upstream part, also called the “firing head”, which has an enclosure which receives the sand at the top or, more generally the sand associated with components of the organic or mineral binder type, for example. example one or more binders in pulverulent form, coming from a hopper, and which distributes this pulverulent mixture through at least one plate pierced with openings called a "firing plate" by distribution nozzles called pressure nozzles. shoot.

Then there is the “core box”, which delimits the cavities which will correspond to the shape and dimensions of the cores to be manufactured, the firing nozzles mentioned above being in fluid connection with openings arranged in the upper part of the cavities in question to allow it to be filled.

There is, finally, the part "drying (by a gas)", which allows, once the cavities of the core box filled with the pulverulent mixture, to harden it, to so that the core box can ultimately eject hardened / compacted and manipulable cores from its cavities into the molds. This hardening takes place by heating the pulverulent mixture, which causes its dehydration and the hardening of the binder, for example by crosslinking when the binder is of organic type, thus ensuring the coherence of the cores.

Generally, this hardening by heating is carried out by diffusion, at the heart, in the pulverulent mixture of hot and dry air under pressure: after having supplied the cavities with a sand / binder mixture through openings made in the cavities, we just blow hot air through these same openings in the cavities on the cores being formed.

However, we are trying to change the way we operate core hardening for different reasons. One of the reasons is that the heating process described above has a non-negligible energy cost. In addition, the heating operation is quite long, and therefore significantly lengthens the production cycle time of the cores. Finally, there is a tendency to have more and more recourse to inorganic binders, and no longer organic, in particular to follow regulatory changes in the matter, and with this type of binder, improving the efficiency of the drying is important.

The aim of the invention is therefore to improve the core-making devices, and more particularly, to improve the way of operating the hardening of the cores, in particular in order to remedy the drawbacks mentioned above.

The subject of the invention is then a core-forming device for gravity foundry, said core-forming device comprising: - means for constituting the cores comprising tools defining molding cavities, - means for supplying powdered compound (s) (S) of said cavities by supply openings, and - means for drying the cores being formed in said cavities by blowing a fluid through blowing openings, such that the blowing openings are distinct from the openings of 'food.

The invention therefore proposes to differentiate the sand supply openings and binder openings for blowing hot air (fluid), which opens up completely new possibilities for drying the cores. In fact, in the case of a binder with curing by heating / dehydration, the drying of the cores is obtained by the combination of the temperature of the metal tooling (“peripheral” hardening) and the circulation of a hot fluid under pressure which passes through the porous core (“through” hardening): the hot tooling and the hot fluid vaporize and evacuate the water contained in the binder. This dehydration of the binder contained in the core causes it to harden and makes it possible to obtain a core (sand + binder) that is hard and easy to handle. Dehydration can be obtained by two physical phenomena, namely the phase change from liquid water to water vapor, the water vapor being evacuated by the circulation of gas, and, in the case of air as a fluid drying, moisture absorption in dry air.

However, in the existing state of the art, the drying fluid is introduced through the same orifice which makes it possible to inject, firstly, sand into the metal tooling and then the hot drying fluid. It is evacuated through openings equipped with filters made in the tooling in the part opposite the tool to the part where it is injected, the filters (for example of the metallic type with lamellae) allowing a fluid to pass but not the sand. But the dehydration of a nucleus is a long manufacturing step to carry out, if we compare it with other core-making technologies (of the phenolic cold box type, etc.). Core-making processes, which implement core hardening by drying the binder, thus generally have a very long cycle time compared to other processes, the cycle time being directly related to the process's ability to remove water. contained in the nucleus. Managing the flow of hot fluid which passes through and dries up the core is therefore very important in obtaining a short cycle time.

• l'injection du fluide de séchage est située à l'opposé de la zone d'éjection des noyaux. La zone du noyau située côté éjection est donc séchée en dernier. Elle acquiert donc des caractéristiques mécaniques en dernier et ne permet donc pas une éjection rapide du noyau sans risque de casse. (A noter cependant, qu'une éjection du noyau même partiellement séché est possible si le noyau supporte d'être éjecté et manipulé, car le noyau continue à sécher hors de l'outillage du fait de sa propre chaleur),
• les buses d'injection de sable sont dimensionnées prioritairement de manière à obtenir un bon remplissage du mélange sable + liant, le but étant d'obtenir un noyau de bonne qualité, sans zone mal remplie ou insuffisamment compactée, ces défauts sur noyaux engendrant des défauts sur la pièce de fonderie qui sera coulée. Les buses d'injection ne sont donc pas dimensionnées de manière optimale pour l'injection du fluide de séchage du liant. Des zones du noyau peuvent donc ne pas être séchées correctement/suffisamment par la circulation du fluide chaud. Le séchage se réalise alors par conduction de chaleur, ce qui rallonge donc d'autant le temps de cycle de séchage,

The drawbacks associated with the processes according to the existing state of the art are therefore as follows:

• the injection of the drying fluid is located opposite the core ejection zone. The area of the core located on the ejection side is therefore dried last. It therefore acquires mechanical characteristics last and therefore does not allow rapid ejection of the core without risk of breakage. (Note however, that ejection of the even partially dried core is possible if the core can withstand being ejected and manipulated, as the core continues to dry out of the tooling due to its own heat),
• the sand injection nozzles are dimensioned as a priority so as to obtain a good filling of the sand + binder mixture, the aim being to obtain a good quality core, without poorly filled or insufficiently compacted areas, these defects on the cores causing defects on the foundry part that will be cast. The injection nozzles are therefore not sized optimally for the injection of the binder drying fluid. Areas of the core may therefore not be dried properly / sufficiently by the circulation of hot fluid. The drying is then carried out by heat conduction, which therefore lengthens the drying cycle time by as much,

The invention, by choosing in the cavities the openings for supplying sand and binding different openings for the blowing of drying fluid, makes it possible to separately improve the injection of sand and that of fluid, by freeing themselves from the associated constraints. at the step of filling the cavities with the sand: it is finally possible to improve the way of blowing the drying fluid through the core without risking at the same time degrading the way of injecting the sand + binder mixture. It is thus, in particular, possible to use blowing means sized appropriately for a hot fluid, it is also possible to freely choose the distribution and the dimensioning of the blowing openings of the cavities, independently of the sand supply openings.

Finally, as detailed below, we can choose routes of the hot fluid in the cores from the blowing openings that are completely different from the route of the sand + binder mixture when the cavities are filled, in particular by choosing flows in the opposite direction, which accelerates drying and facilitates the ejection of the pits.

Preferably, the blowing openings are in fluid connection with a sealed fluid supply box. The box is usually connected itself in a sealed manner to a fluid generator of the hot air or superheated water vapor type, and the arrival of fluid at the desired temperature and at the desired pressure in the box can be controlled by appropriate control means.

In this case, according to one embodiment, the casing comprises a plate provided with openings in fluid connection with the blowing openings via ducts. These conduits thus pass, in particular, through one of the indentations defining the cavities, in particular the lower indentation.

Advantageously, the device comprises a system for ejecting the hardened cores, said system being placed on the side of the blast openings and outside the sealed box. It is thus possible to dimension the volume of the sealed box as accurately as possible, and to avoid or limit as much as possible the heat losses by thus limiting the components present in the sealed box.

According to a preferred embodiment, said ejection system comprises ejectors the base of which is outside the sealed casing and which pass through the plate of the sealed casing via openings made in said plate. We thus have the maximum of the components belonging to the ejection system which is well outside the box: in the proposed configuration, the sealed box is placed between the ejection system and the cores, and the box is passed through the ejectors. .

Also preferably, the openings made in the plate for the ejectors are sealed: the ejectors can therefore be moved in translation, in particular vertical, between a rest position and an ejection position, with a sliding of the body of the ejectors in the openings of the housing plate without compromising the sealing of the housing, or in a negligible way.

If we had incorporated the ejection system in the sealed casing, with the bases of the injectors and the mechanisms allowing the translation of these injectors, we would have added a mass in the casing creating thermal losses, and we would have a casing of much larger volume and the tightness of which would have been much more complex to ensure.

Advantageously, the blowing openings are equipped with filter (s). This prevents the presence of these openings from disturbing the filling of the cavities with the sand + binder mixture through the feed nozzles (the sand cannot pass through these filters). The drying fluid injection zones can thus be positioned more easily in the cavities without negative impact, without additional appearance defect on the core and therefore on the final casting. These filters also help to homogenize the circulation of drying fluid in the core.

The blowing openings and the supply openings may be arranged relatively to each other in the cavities so that the direction of introduction of the pulverulent materials into said cavities is substantially opposite to the direction of introduction of the fluid from drying in said cavities.

Preferably, all of the blow openings are grouped together on one edge of the cavity, and all of the supply openings on an opposite edge. Concretely, when the cavities are formed by two half-molds, also called cavities, the supply openings can all be on the side of one of the cavities (the upper one in particular) and the blow openings on the side of the other cavity ( the lower one in particular). This configuration allows the sand to circulate in the cavity substantially in the opposite direction to the circulation of the drying fluid, subsequently, in the core being formed.

The drying means may comprise means for discharging the fluid from the cavities through discharge openings in fluid connection with a box, optionally connected to a suction system. Providing a suction makes it possible to facilitate and better control the path of the drying fluid in the porous core.

Preferably, the discharge openings are in fluid connection with a sealed fluid discharge box, the discharge box preferably comprising a plate provided with openings in fluid connection with the discharge openings by conduits or by exhaust nozzles. Exhaust nozzles mounted on a plate can be placed above the feed openings, instead of the feed nozzles, during the blowing step.

Preferably, these discharge means are equipped with filters. Here again, the filters serve to contain the sand + binder mixture in the cavity, during the filling of the cavity and throughout the formation of the core.

More preferably, the evacuation means have recourse to the supply openings of the cavities and / or to separate openings, preferably provided with filters.

According to one variant, the device according to the invention may have at least two systems for ejecting the hardened cores, including in particular a system arranged on the side of the blowing openings and a system arranged on the side of the supply openings of the cavities. In fact, in a known manner, a core ejection system is provided, generally disposed on the side opposite the core box to the side provided with the sand + binder supply nozzles. According to the invention, provision can be made for the ejection system to be rather on the same side, therefore, according to the preferred embodiment of the invention, on the side opposite to that of the blowing openings, or to combine the two systems of ejection, by adding this additional ejection system.

Preferably, the pulverulent compounds comprise sand and at least one binder of mineral type. Advantageously, they only contain binders of a mineral nature, for example based on silicate and / or phosphate. Indeed, renouncing organic binders makes it possible to follow regulatory developments in the foundry sector.

The drying fluid is preferably air (hot and dry) or superheated water vapor.

The subject of the invention is also the method for implementing the device described above, where the cavities are fed with powdered compound (s) through feed openings, then where a fluid is blown into the cavities for drying cores being formed in said cavities by blowing a fluid through openings, the injection of the fluid taking place in the cavities in a direction opposite to the injection of the pulverulent compounds.

Conventionally, the sand and binder feed is generally provided above the core box, with the feed openings disposed on the upper edge of the cavities. According to the invention, the blowing openings are rather arranged on the lower edge of the cavities, so that the core box is fed with sand and binder in a direction generally from top to bottom, and in that hot fluid is then blown in a generally opposite direction, from the bottom to the top.

According to one embodiment, the drying fluid is evacuated from the cavities with suction through openings made in said cavities. The fluid is then forced to be evacuated from the cavities, which makes it possible to accelerate and better guide its path in the porous core.

The subject of the invention is also the application of the device and / or the process described above for obtaining foundry cores devoid of organic binder.

The subject of the invention is also the application of the device and / or of the method described above for obtaining foundry cores corresponding to portions of heat engine parts, in particular portions of the cylinder head, and for example of chambers. water from thermal engine cylinder heads, and any other foundry part, in particular intended for the automotive industry, the geometry of which must be very precise and reproducible and the surface quality of which must be high.

The invention also relates to the cores obtained by the device described above, these cores being substantially devoid of organic components.

The subject of the invention is also a method of foundry by gravity casting of castings, which uses these cores.

• les figures 1 à 6 représentent dans son ensemble, en coupe verticale, un exemple de dispositif de noyautage selon l'état de l'art existant, la figure 1 étant une vue d'ensemble avec la boite à noyaux ouvertes, les figures 2 à 6 présentant le dispositif à différentes étapes de la production des noyaux ;
• la figure 7 est une vue en coupe verticale d'un dispositif de noyautage modifié selon une première variante de l'invention;
• la figure 8 est un agrandissement de la platine d'évacuation d'air chaud du dispositif de noyautage de la figure 7 ;
• la figure 9 est une vue en coupe verticale d'un dispositif de noyautage modifié selon une deuxième variante de l'invention.

Other particularities and advantages will become apparent on reading the following description of a particular embodiment, not limiting the invention, made with reference to the following very schematic figures:

• the figures 1 to 6 show as a whole, in vertical section, an example of a core-making device according to the existing state of the art, the figure 1 being an overview with the core box open, the figures 2 to 6 showing the device at different stages of core production;
• the figure 7 is a vertical sectional view of a core-making device modified according to a first variant of the invention;
• the figure 8 is an enlargement of the hot air discharge plate of the core-making device of the figure 7 ;
• the figure 9 is a vertical sectional view of a core-making device modified according to a second variant of the invention.

These figures are very simplified, the elements shown are therefore not necessarily to scale with respect to each other or from one figure to another. Each reference retains the same meaning from one figure to another. The tools are represented in their usual configuration of use, and it is in this sense that we must understand the spatial references of the type “upper”, “lower”, “top” or “bottom” ... ( as well as throughout this text).

The figures 1 to 6 are therefore views in vertical section of a core-making device 1 according to the existing state of the art, and of which all the compounds and the mode of operation will not therefore be detailed, at different stages in the manufacture of the cores. They make it possible to illustrate the principle of the manufacture of foundry cores, without the invention necessarily being limited to this precise device.

This device 1 therefore schematically comprises a part 2 called “firing head assembly” supplied with a pulverulent mixture of sand and binder via a duct (not shown) into which a hopper (not shown) opens. The device also comprises a part 3 called "core box", a part called "drying assembly" 4 ( figure 4 ) and a part called the “ejection system” 5.

The core box 3 is mounted to move along a vertical axis X and along a horizontal axis Z. The drying assembly 4 and the firing head assembly 2 are mounted to move along a horizontal axis Y. The core box 3 comprises a heated lower cavity 31, a heated upper cavity 32, forks (not shown), and cavities 34 jointly defined by cavities 31 and 32 to define the shapes and dimensions of the cores to be manufactured.

The firing head 2 comprises an injection plate 21 which is located in the lower part of the box containing the mixture of sand and binder S, and which is provided with openings in connection with injection nozzles 22 intended to supply the cavities 8 by channels 33 made in the upper cavity 7.

The drying system 4 ( figure 4 ) comprises an injection bell 41, with an injection point 42 connected to a source of hot fluid of the hot dry air type (not shown). The injection bell 42 is able to inject this hot fluid into the cavities 8 via the supply channels 33. Filters 35 on the openings of the cavities in the lower cavity, allow the drying fluid to be discharged by retaining the. sand in the cavity.

The ejection system 5 comprises ejectors 51 fixed on a movable ejection plate 52 placed under the lower cavity 32.

The figure 1 is a general representation of the core-making device with the core box open, at the start of production: the two cavities 31 and 32 are not in contact with each other, the mixture feed nozzles 22 are not not in connection with the channels 33 of the upper cavity 31.

The figure 2 shows the closed core box 3, in the position of injection into the closed cavities 34 of the sand + binder mixture via the nozzles 22 then the channels 33 opening into openings arranged in the upper cavity 31 of the cavities 34.

The figure 3 represents the core box 3 still closed, with the cavities 34 being filled: this is the step of injecting the mixture S under pressure.

The figure 4 shows the step of removing the firing head and placing the drying system 4 above the upper cavity 31. The hot pressurized fluid is guided from where the supply nozzles 22 were. through the channels 33 into the cavities 34 to pass through the N cores. it is then discharged through the filters 35 arranged through openings made in the lower cavity 32. The preferential hot fluid flow flows, symbolized by arrows f ₁ at the figure 4 , are therefore linked to the location of the injection nozzles 22.

The figure 5 represents the step of stopping the blowing of the hot fluid and the opening of the core box 3, when the core is hard enough to be ejected and handled: the cores rest on the lower cavity 32.

The figure 6 represents the step of ejecting the cores N, by the ejection system 5, by a vertical thrust upwards of the cores by the ejectors 55 supported by the movable plate 52 in vertical translation.

The figure 7 represents according to the invention an alternative for drying the N cores: all other things being equal, the hot fluid circulation flow is reversed, as represented by the arrows f ₂ , by modifying the drying system 4 ', 4 ": the hot fluid is supplied via system 4 ', and its evacuation via system 4". A movable plate 41 'defining a sealed box 42' supplied by a source of hot fluid is added under the lower cavity 32. A sealed bell 42 "defined by a plate 41" having a peripheral seal is used above the upper cavity 31. The figure 8 is an enlargement of plate 41 "and will be described with the figure 7 .

Fluid injection is therefore carried out via the box 42 'in fluid connection with the channels 36 formed in the lower cavity and opening into the cavities 34 via openings provided with filters 35, therefore from below. The plate 41 'being crossed by the ejectors 51 by suitable openings, it is possible to provide these openings of peripheral sealing means 52 so as to guarantee the sealing of the box 42 'in these areas.

The hot fluid then rises by passing through the cores N, through the openings of the plate 42 "provided with discharge nozzles 43" equipped with nipples 44 ", the outlet section of which is optionally provided with a filter 45". This plate 42 "associated with the plate 41" defines a sealed casing. The nozzles 43 "are therefore not in the proper sense of the injection nozzles, but nozzles serving to capture and evacuate the hot fluid in the upper part towards the box 42", their filters 45 "guaranteeing, if necessary, the retention of the fluid. sand and binder in the cavities 34.

The figure 9 is a variant of figure 7 : all other things being equal, we add to the lower injection system 5 an upper injection system 5 'mounted mobile in vertical translation, and comprising ejectors 51' mounted on a mobile plate 52 ', and which pass through the plate 42 ". Sealing means (not shown) can be provided to maintain the leaktightness of the discharge box in the zones crossed by these additional ejectors.

It is possible that one or some of these additional injectors also come through the body of the nozzles 43 "and their filters as shown in the figure. It is also seen that it is also possible to provide, in addition to the nozzles 43" (or in their place ) simple channels 46 "in the upper cavity 31, optionally provided with filters 35 in the openings of the cavities 34 into which they open, and which are in fluid connection with the discharge box by a corresponding hole 47" in the plate .

Note that for the two variants, it is possible to provide at the level of the discharge opening of the upper box defined by the plates 41 "and 42" a suction facilitating and accelerating the discharge of the hot fluid.

The invention therefore circulates the drying fluid in the opposite direction to the injection of the sand + binder mixture. In the example of the invention, the fluid is injected through conduits in the cavity opening into the cavities through openings equipped with filters. Thus, - the filling step is not disturbed cavities by sand injection, - the drying fluid injection zones are easily positioned without negative impact on the appearance quality of the core, and therefore of the casting, - the homogeneity of circulation of the drying fluid is improved through the whole porous core.

The advantages linked to the invention are significant. Thus, a saving of time has been observed in the drying operation which can reach up to 40% of the usual time: the core quickly acquires sufficient mechanical characteristics to withstand the following ejection step without damage, and this , all the more so as the hot fluid is injected from the lower cavity, so that the hot fluid is first put in contact with the lower part of the core in the cavity, that which is most directly subjected to the thrust of the ejectors.

With the invention, it is therefore possible to switch from organic binders to mineral binders without prejudice to the operation of drying the cores.

A gain is also obtained in the quality of drying of the core, with better dehydration of the latter, therefore more uniform hardening leading to the production of a more solid core, more resistant overall. The core also sees its storage capacity increase, through greater durability of its mechanical properties.

In addition, drying can start earlier, because it is no longer necessary to wait for the removal of the sand injection plate and the installation of the drying fluid injection bell: drying can begin as soon as the sand injection plate is removed. By injecting the hot fluid preferably with a gradual pressurization of the latter, it is therefore possible to dry earlier without risk of blowing the sand out of the cavities.

The filters positioned both in the hot fluid blowing openings and in the discharge openings of the latter ensure not only the retention of the sand in the cavity but also the absence or almost absence of traces of these openings on the core and therefore on the resulting casting (which is not always the case with sand injection nozzles). We even note that the addition of filters in the openings of the discharge ducts (which may be the same as the ducts into which the sand injection nozzles open in the injection position) makes it possible to level out the appearance defects created during sand injection.

It should also be noted that one can best adjust the blowing of the drying fluid by adjusting the blowing pressure, which can be constant or gradual, and that a suction in the evacuation zone also allows an adjustment throughout the drying.

Claims (11)

1. Core-forming device (1) for gravity foundry, said core-forming device comprising : - means for constituting the cores comprising tools defining mold cavities (34), - means for supplying powdered compound(s)) said cavities by supply openings , and - means for drying the cores being formed in said cavities (34) by blowing a fluid through blow openings which are separate from the supply openings , the blowing openings being in fluid connection with a waterproof case (42 ') to supply fluid, characterized in that said device comprises an ejection device (5) of the cores (N) cured, said system being arranged on the side blowing openings and out of the sealed casing (42 ').
2. Device (1) for coring according to the preceding claim, characterized in that the box (42 ') comprises a plate (41') provided with openings in fluid connection with the blowing openings by ducts.
3. Device (1) according to the preceding claim, characterized in that said ejection system (5) comprises ejectors (51) whose base is outside the sealed box (42 ') and which pass through the plate (41') by means of openings made in said plate (41 ').
4. Device according to the preceding claim, characterized in that the openings made in the plate (41 ') for the ejectors are sealed.
5. Device (1) for coring according to one of the preceding claims, characterized in that the blowing openings are equipped with filter(s) (35).
6. Core-forming device (1) according to one of the preceding claims, characterized in that the blowing openings and the supply openings are arranged relatively to each other in the cavities so that the direction of insertion powdery materials (S) in said cavities (34) is substantially opposite to the direction of introduction of the drying fluid into said cavities.
7. Device (1) of infiltration according to the preceding claim, characterized in that all the blowing openings are grouped e s on an edge of the cavity (34), and all the supply openings on an opposite edge.
8. Device (1) for coring according to one of the preceding claims, characterized in that the drying means comprise means for evacuating the fluid from the cavities via evacuation openings in fluid connection with a box (4 "), possibly connected to a suction system.
9. Device (1) for coring according to Claim 9, characterized in that the discharge openings are also the supply openings of the cavities (34) and / or are separate openings, preferably provided with filters (35).
10. Device (1) for coring according to one of the preceding claims, characterized in that it has at least two systems for ejecting the hardened cores (N), including in particular a system (5) arranged on the side of the blowing openings and a system (5') arranged on the side of the supply openings of the cavities (34).
11. Method of implementing the device according to one of the preceding claims, characterized in that the powdery compound(s) are fed into the cavities (34) via feed openings, then in that the a fluid in the
    cavities (34) for drying cores (N) being formed in said cavities by blowing a fluid through openings, the injection of the fluid taking place in the cavities in a direction opposite to the injection powdery compounds.

Images