EP0161995B1 - Process for treating foundry sands in order to reclaim chromite, and equipment therefor - Google Patents

Abstract

The subject matter of the invention mainly relates to the technical areas of foundry, manufacture of parts by casting metal in moulds. The process consists in that after moulding the parts and stripping them from the moulds which were broken, during a first cycle the mixture resulting from the knock-out is recovered. This mixture being stored. This mixture is directed from the storage place to an intermediate container; then the mixture from the intermediate container is fed up to a sieve grading separator unit allowing to separate the grains or particles in several different grading batches; each one of these batches is directed to a separating table designed for separating chromite from silica; the chromite on the one hand and the silica on the other hand are recovered in containers. This invention mainly applies to the recovery of components of different densities, especially chromite and silica.

Description

The subject of the invention relates, in particular to the technical sectors of foundry, the manufacture of parts by casting of metal in molds, the recovery of materials or components of the molds and in particular chromite and silica, and also of the separation in general of the components of a mixture which have different densities.

After casting the pieces in the foundry, when the mold is broken in order to extract the cast part, which constitutes the unhooking operation, there is also usually a shot peening operation, i.e. a projection of shot (iron shot generally), in order to remove the sand which still adheres to the molded parts, in particular in the re-entrant forms. Efforts are currently being made to recover foundry sands which are rich in chromite, which is an expensive mineral species which is incorporated into mold sands, and which is also laced around the core, in particular in steel foundries.

By DE-A-2,252,259, there is known an installation capable of ensuring the mechanical recycling of sand followed by thermal regeneration. No means are provided to ensure the separation of the chromite from the sand mixture.

The object of the process for treating foundry sands according to the invention is to separate and recover, after casting, the silica, the chromite and the metallic shot, so as to be able to reuse the sand and the chromite which can be thus implement in repetitive cycles subject to replacing the losses due to various causes. We can see the advantage of the process from an economic, technical and rational standpoint.

To solve the problem of the separation of silica and chromite, from a mixture of sand recycled in order to recover the chromite, according to the invention, after having conveyed the mixture from a storage place into an intermediate container, the mixture is passed from the intermediate container to a size grading device with sieves making it possible to separate grains or particles in several batches of different particle sizes, each batch is conveyed to a special separating table, the mixture is subjected to combined and simultaneous effects according to which, on the one hand, the components are fluidized by the effect air or a gaseous fluid under pressure through a plate or support ensuring microsuperficial diffusion, while, on the other hand, vibrations of amplitude, frequency, intensity and adjustable directional effect combined with at least one mass adjustable in intensity and position relative to the plate or support, so as to subject said plate or support for a tilting effect tending to raise the lower part of the tray which is mounted on an assembly, so as to give the tray a spatial freedom in any direction to obtain at any point of the tray or support, an effect giving a component force projections towards the upper part and beyond, which ensures the separate evacuation from the plate or support of chromite and silica.

For the implementation of the method, the installation comprises, in known manner, a general storage silo into which the mixture is sent which is then conveyed to an intermediate silo by means of a pneumatic blower.

According to the invention, to solve the problem posed of separating the chromite and the silica, a regulating valve controls the flow rate of the mixture to be sorted which then passes by gravity, on a particle size sorter shaped to separate the grains or particles of the mixture in several batches of different particle sizes and densities, each of these batches being conveyed to a separating table shaped to separate the chromite from the silica of each batch by means of a tray inclined shaped to ensure micro-surface diffusion, one of the transverse ends of the plate on the lowest side being slaved to a vibrating device, while the other opposite end of said plate is slaved to a set of masses, the plate being mounted inclined by being subject to elastically deformable support elements; drainage channel containers or conveyor belts are shaped to collect in a common way, for the separating tables, on the one hand, the silica, and, on the other hand, the chromite.

According to another characteristic, the process for treating foundry sands can result from shot peening. For this purpose, the mixture resulting from shot peening is recovered, this mixture being stored; the mixture is conveyed from the storage location to an intermediate container; the mixture is passed from the intermediate container through a sorting device shaped to separate the particles or metal grains which are recovered and which are evacuated; the mixture free of particles and metallic grains is passed from said sorting device to a fluidized bed sorting device making it possible to separate grains or particles into several categories of different densities; concerning these categories, taken in order of increasing densities, fines and dust are collected in a general dust collector; the pure silica is collected and evacuated to an intermediate container of a facility for treating the sand for stall, the category consisting of a mixture of silica and chromite; the pure chromite is collected.

In this case, the installation for implementing the method comprises a storage silo which receives the mixture resulting from shot peening and from which said mixture is conveyed in an intermediate silo, using a blower pneumatic; the flow rate of the mixture to be sorted is controlled by a central regulating valve to pass by gravity effect, from the silo to a magnetic sorter with drum which eliminates the magnetic particles contained in the mixture, said particles being removed by means of a conveyor belt; the mixture without particles or metallic grains being directed to a fluidized bed sorting device.

The invention is explained in more detail below using the attached drawings in which:
FIG. 1 shows in a purely schematic manner and in parallel, the installation corresponding to the process for treating the mixture resulting from the release and the installation corresponding to the process for treating the mixture resulting from shot peening, it being specified that if each of the installations can be assembled and used separately, provision is made for their use in a single overall installation with useful links and transfers between the two installations.
FIG. 2 illustrates by a schematic overview, the separating table with an inclined plate which implements the method of separation of the components of different densities of a mixture.
Figures 3, 4 and 5 are corresponding views, respectively in elevation, side and plan, which show an embodiment of the separating table.

In order to make the object of the invention more concrete, there are now described non-limiting installations and embodiments for the implementation of methods according to the invention which have been described.

Regarding the installation corresponding to the process for processing the mixture resulting from the stall, we see in Figure 1, care a schematic form sufficient for understanding and implementation, a general storage silo (1) in which the mixture is sent which is then conveyed to an intermediate silo (2) by the effect of any known means and in particular by means of a pneumatic blower (not shown. The mixture to be sorted, the flow rate of which is controlled by a regulating valve (not shown) then passes, for example by gravity according to the example illustrated, on a particle size sorter (3) which separates the grains or particles of the mixture into several lots of different particle sizes, for example into five different lots ( + 800µ + 400µ + 250µ + 140µ - 140µ). Each of these batches is conveyed to a special separating table (4) (Figures 3, 4 and 5). There is therefore a separating table per batch or category, and each table allows, for each batch, to separate the chromite from the silica.

Optionally, these separating tables (4) could be produced in any way and according to any known method, for example using grids or screens having suitably calibrated openings, or else according to the characteristic arrangements which have been the subject of French Patents N ° 73.29274, 74.28510, 78.20580. Finally, we collect, in a common way for the separating tables (4), preferably, on the one hand the silica and on the other hand the chromite which are received, for each of them, in containers, evacuation channels, or, according to the example of the drawings, on conveyor belts (5 and 6).

With regard to the installation corresponding to the process for treating the mixture resulting from shot peening, FIG. 1 also illustrates this installation in a schematic manner, and we see the storage silo (7) which receives the mixture resulting from shot peening and from which said mixture is conveyed to an intermediate silo (8) by any known means and using for example a pneumatic blower. The flow rate of the mixture to be sorted, is controlled by a regulating valve to pass by gravity effect, from the silo (8) to a magnetic drum sorter (9) of the type known per se, which eliminates the magnetic particles contained in the mixture, particles which are removed for example by means of a conveyor belt (10).

The mixture without particles or metallic grains is then directed to a sorter device (11) with a fluidized bed.

• des fines et poussières collectées par un dépoussiéreur général (12) ;
• de la silice pure aspirée par un suceur (11a) que l'on évacue par exemple au moyen d'un tapis (13) ;
• un mélange composé de silice et de chromite, aspiré par un deuxième suceur (11b) du trieur (11) que l'on dirige au moyen d'un pulseur pneumatique (14) vers le circuit de sable de décochage ;
• de la chromite pure évacuée par un tapis (15) ou bande transporteuse.

The sorter (11) allows the separation of the four different products which are:

• fines and dust collected by a general dust collector (12);
• pure silica sucked up by a nozzle (11a) which is evacuated for example by means of a mat (13);
• a mixture composed of silica and chromite, sucked up by a second nozzle (11b) from the sorter (11) which is directed by means of a pneumatic blower (14) to the system of release sand;
• pure chromite discharged by a mat (15) or conveyor belt.

According to a particularly important characteristic of the invention, in the process for treating the mixture resulting from the detachment, a process is used for preparing the components (chromite and silica) which have different densities.

For this purpose, the mixture is subjected to combined and simultaneous effects according to which, on the one hand, the components are fluidized by the effect of air or a gaseous fluid under pressure through an inclined plane or plate ( 16) of the separating table (4), said plate being shaped to ensure, in a known manner, a microsuperficial diffusion. One of the transverse ends of the plate (16), on the lowest side, is controlled by a vibrating device (17), while the other end is controlled by a set of adjustable masses (18). The masses (18) are mounted projecting from the active part of the plate, being supported by arms (18a) mounted in the extension and beyond the lateral sides of said plate. As a result, the plate is likely to be subjected to vibrations of adjustable amplitude, frequency, intensity and directional effect combined with an adjustable torque effect, to ensure separate evacuation from the plate, of each component, chromite and silica, of the mixture.

The diffuser plate (16) is mounted by any known and appropriate means, in an inclined and adjustable manner on the support frame (19) of the table (4) while being secured, at each of its high and low transverse ends, in particular to blocks or elements (20) with elastic deformation capacity. Under the plate (16) is formed a volume closed by a flexible membrane (22). An air generator (23) or other means opens into the bottom of the sealed volume (22), to send air under pressure inside said volume, to fluidize the components, chromite and silica, placed on the tray.

Illustrated in FIGS. 3, 4 and 5, an embodiment of the separating table corresponding to the operating principle shown in FIG. 2.

According to the method of separation of the components of different densities of a mixture, in a simultaneous manner with concomitant effects, the mixture is brought with a suitable flow rate on the inclined plate (16) of the porous type. In the example of the invention, chromite constitutes the dense products, while silica constitutes the light or less dense products.

Is sent, in a manner adjustable for flow and speed by means of the generator (20) of air or other gaseous fluid, under the support plate (16) which ensures a regular microsuperficial diffusion and the fluidization of the components including the densest (chromite) remain in contact with said plate (16), while the least dense (silica) are suspended in the air or diffused gaseous fluid.

The vibrator devices (17) subject, in its plane, the plate (16) to adjustable frequency and amplitude vibrations. These vibrations are combined with the effects of adjustable masses (18), in intensity, and in position relative to the plate (16). The masses can be adjusted in height on a vertical element (18b) of support arm (18a) and / or moved in length relative to said arms. The set of masses (18) being linked to the upper part of the plate (16), communicates to the latter, in combination with the amplitudes of the vibrator (17), a tilting effect which tends to cause the elevation of the lower part of the tray. The elastic supports (20) give the tray a spatial freedom in all directions, the flexible membrane (22) ensuring air tightness between the tray (16) and the separating table support housing (4).

It is emphasized that the mobility of the plateau is done with almost zero efforts, because the plate is ultimately carried by air cushions whose pressure substantially balances the masses.

dirigée vers la partie haute dudit plateau (16), ce qui permet aux produits ou composants les plus denses (chromite) en contact avec le plateau, de remonter.It therefore follows that the combination of the vibrator and adjustable masses, creates at all points of the plate a resultant $\genfrac{}{}{0ex}{}{\text{→}}{\text{R}}$

directed towards the upper part of said plate (16), which allows the densest products or components (chromite) in contact with the plate, to rise.

It is therefore understandable that under the effect of the ascending air streams, or other gaseous fluid, sent into the sealed enclosure (22), the plate (16) due to its conformation, fluidizes the products to be separated, so that dense products (chromite) remain in contact with the bottom of the diffuser plate (16) while lighter products (silica) remain in suspension. The vibratory movements subjected to the plate (16), in combination with the masses (18), tend to cause the rise of the dense components which overflow in the upper part of the plate, the less dense components in suspension, not subjected to the vibratory movements, descend by gravity to overflow at the other end, in the lower part of the plate (16) (Figure 2).

It is emphasized that the phenomenon of tilting of the plate superimposed on the longitudinal vibrations, accelerates the ascent of the heavy product. The masses (18) being arranged outside the range of the tray system, prevents that there is on the sole of said tray, creating vibration nodes. The nodal air is discharged beyond the active working part of the platform.

, le grain de chromite doit décoller du plateau et retomber au moment où ledit plateau a effectué son mouvement retour et ainsi de suite.It should be noted that the longitudinal tilting torque created by the adjustable masses, under the effect of the vibrations generated by the vibrator device, is also capable of advancing heavy products in contact with the table, by ballistic phenomenon. Indeed, under a very strong acceleration following very significantly the resultant $\genfrac{}{}{0ex}{}{\text{→}}{\text{R}}$

, the chromite grain must take off from the plate and fall back when the said plate has made its return movement and so on.

Claims (9)

1. Method for the treatment of foundry sands, resulting from a casting stripping off, according to which after the casting of the pieces and the removal thereof from the molds that have been broken, the mixture resulting from the stripping off is recovered in a first cycle, then stored, and brought from the storage location (1) up to an intermediary container (2), the method being characterized in that the mixture is passed from the intermediary container (2) up to a grain separating screen device (3) permitting the grains or particles to be separated in several batches of different grain size, whereby each batch is brought to a special separation table (4) ; the mixture is subjected to combined and simultaneous effects according to which, on the one hand, the components are fluidized by the action of the air or of a gazeous fluid under pressure through a plate or support (16) providing a surface micro-diffusion, while on the other hand there is provided the application to the plate or support of vibrations with adjustable amplitude, frequency, intensity and directional affect in combination with at least one mass (18a) the intensity and the position of which are adjustable relative to the plate or support (16), so that said plate or support will be subjected to a rocking effect tending to raise the lower portion of the plate which is mounted on an assembly, in order to give to the plate a spatial freedon in all directions permitting to obtain in any point of the plate an effect imparting a component force of throwing towards the upper portion, providing the separate discharge out of the plate or support of the chromite and of the silica (2).
2. Method for the treatment of foundry sands, resulting from a shot blasting, according to which the mixture resulting from the shot blasting is recovered, and then stored ; the mixture is forwarded from the storage location (7) up to an intermediary container (8), the method being characterised in that the mixture is passed fron the intermediary container (8) to a separating device (9) arranged for the separation of the metal particles or grains which are recovered and discharged ; the mixture, free from metal particles or grains, is passed from said separating device up to a separating device with fluidised bed (11) permitting the particles or grains to be separated in several categories of different densities ; concerning these categories, the fines and the dust are collected into a general dust extractor ; the pure silica is gathered, with discharge up to an intermediary container of an installation for the treatment of the stripping off sans, of the category formed by a mixture of silica and chromite ; the pure chromite is gathered.
3. Installation for the embodiment of the method in accordance with Claim 1, comprising a general storage bunker (1) to which the mixture is sent, and then forwarded up to an intermediary bunker (2) by means of a pneumatic pulsating device, the installation being characterized in that there is provided a monitoring valve for the control of the mixture to be sorted out, which is then passed by gravity on a grain separating device (3) arranged for separating the grains or particles of the mixture in several batches of different grain size and densities, each one of these batches being forwarded up to a separating table (4) arranged for the separation of the chromite and of the silica in each batch by means of a slanting plate (16) arranged for providing a surface micro-diffusion, one of the cross ends of the plate on the lowermost side being governed by a vibrating device, while the other opposite end of said plate is governed by an assembly of masses (18), the plate being mounted according to an inclined plane while being secured to elastically deformable supporting elements (22), with discharge channel containers or conveyor belts (5) and (6) which are arranged for the recovery in a common manner, for the separating tables (4), of the silica on the one hand, and of the chromite on the other hand.
4. Installation for the embodiment of the method in accordance with Claim 2, characterized in that said installation is comprised of a storage bunker (7) which receives the mixture resulting from the shot blasting, said mixture being forwarded therefrom into an intermediary bunker (8), while using therefor a pneumatic pulsating device, the flow of the mixture to be sorted out being monitored by a central regulating valve to be passed by gravity from the bunker (8) to a magnetic drum separating device (9) which eliminates the magnetic particles contained in the mixture, said particles being discharged by means of a conveyor belt (10), the mixture without metallic grain or particle being directed up to a separating device (11) with fluidised bed.
5. Installation as claimed in Claim 4, characterized in that the separating device (11) is arranged for permitting the separation of the fines and dust collected by a general dust extractor (12) ; of the pure silica which is sucked in by a suction device (11a) and which is discharged ; of a mixture consisting of silica and of chromite, which is sucked in by a second suction device of the separating device, said mixture being directed towards the stripping off sand circuit for the pure chromite, which is discharged.
6. Installation as claimed in Claim 3, characterized in that there is formed under the plate (16), a space which is closed by a flexible membrane (22), an air generator (23), or the like, emerging into the bottom of the space in order to send air under pressure inside said space for the purpose of fluidising the components disposed on the plate.
7. Installation as claimed in Claim 3, characterized in that the masses are mounted projecting from the active portion of the plate (16), on the uppermost side, said masses being supported by arms (18a) mounted in extension of and beyond the lateral sides of the plate (16).
8. Installation as claimed in Claim 7, characterized in that the masses (18) are vertically adjustable while being movable along a vertical element (18b) mounted endwise of each supporting arm.
9. Installation as claimed in Claim 3, characterized in that the cross ends of the diffusor plate (16) are so disposed that they will permit the discharge of the components sorted out and the recovery thereof with the aid of suitable means.

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