EP1687111A1 - Device for filling a mould with a powder or a mixture of powders - Google Patents

Abstract

A device for filling at least one mold with at least one powder. The device includes a mechanism to add at least one powder, at least one mechanism to eject the powder added into the device, in the form of a layer, and at least one deflector capable of locally intercepting at least part of the powder ejected in the form of a layer and redirecting the locally intercepted powder towards a determined location in the mold.

Description

 DEVICE FOR FILLING A MOLD WITH A POWDER OR A MIXTURE OF POWDERS

DESCRIPTION

TECHNICAL FIELD The invention relates to a device for filling a mold, in particular a compression mold, with a powder or a mixture of powders in very varied fields such as building materials, pharmacy, food industry, nuclear ceramics, cement, sintered metal powders.

STATE OF THE PRIOR ART The field of the invention is that of systems for filling impressions with finely divided materials with a view to achieving their compression. In this field, solutions are sought for depositing or transporting powder in a controlled, homogeneous and rapid manner in a compression mold. In particular, we seek to achieve a controlled and modular filling of a mold for uniaxial compression, or hot isostatic compression, or sintering with a mixture of powders. In powder metallurgy, many components are produced by compression of metallic powders obtained thermochemically or by atomization. The powders are deposited in a cavity or imprint of a matrix having the shape that we want to give to the component, then the powders are compressed under very strong pressures. The tablets obtained are then sintered, that is to say heated to very high temperatures, so that the compressed powders are bonded together in a compact mass which has sufficient mechanical properties to form a solid. There are many methods of filling the compression imprint with powders. One of the most used methods is the volumetric filling by gravity of an imprint. The disadvantage presented by this technique is that it does not make it possible to control the filling of the imprint. Therefore, we observe in the footprint significant weight variations of powders, and non-homogeneous distributions of powders in the footprint. Other methods include fluidizing the powder. Many fluidized systems are today existing and marketed. For some, the fluidization of the powder can be applied in the powder storage device (see documents [1], [2], [3]) or directly in the impression (see document [4]) . However, in both cases the systems have a major common drawback. Indeed, fluidization is obtained by injecting gas into the filling system. The management of gas flows must therefore be very fine and this poses problems in terms of the robustness of the system. Furthermore, the gas in the powder is an instability initiator. The use of gas therefore leads to a powder deposition which has advantages but whose level of control remains low. Other systems exist and provide partial improvements to the problem of filling an impression with powder. For example, some systems opt for compacting the powder by pressure waves in the shoe (see document [5]), while others use a cross-moving shoe (see document [6]) or a shoe delivering the pre-compacted powder (see document [7]). However, these techniques do not allow a precise spatial filling of the imprint, nor a homogeneous filling thereof, in particular in the case of complex molds for powders which will then undergo significant compression. The control of the flow of the powder in time and in space remains weak in these systems.

PRESENTATION OF THE INVENTION The object of the invention is to provide a device which does not have these drawbacks. This object is achieved by a device for filling at least one mold with at least one powder, characterized in that it comprises:

means for introducing at least one powder,

- at least one means for ejecting, in the form of a sheet, the powder introduced into the device,

- At least one deflector capable of locally intercepting at least part of said powder ejected in the form of a sheet and redirecting it to a determined location in the mold. In other words, the device according to the invention makes it possible to spray a powder in the form of a suspended sheet which is intercepted by deflectors placed on the path of the powder and positioned in such a way that the intercepted powder falls at a precise point in the mold to be filled. Advantageously, the device can comprise several means for ejecting the powder introduced into the device in the form of a sheet, each of these means being capable of dispensing a different powder. The term “sheet of powder” is understood to mean a set of grains which occupy a volume of small thickness compared to the dimensions of its surface. This assembly can constitute a portion of plan, be of convex shape or other. Advantageously, the deflector is orientable. Advantageously, the deflector is mobile. The deflector can therefore, for example, be moved vertically and turn on itself. The deflector can, for example, be a part of a plane, be concave, convex, have a helical portion ...

According to a particular embodiment, the means for ejecting the powder in the form of a sheet is a rotary device. In a first case, the rotary device advantageously has a shape chosen from a disc, a cone or a bowl. Advantageously, the device rotates around an axis of rotation located at the center of symmetry of the device. Advantageously, the rotary device comprises at least one fin. In this case, the fin will advantageously be placed along the radius of said disc, cone or bowl. Note that the fins have the same type of shape as the deflectors, i.e. they can be flat, concave, convex, helical ... The presence of fins on the disc, cone or bowl is intended to facilitate the flight of the powder and to control it. Instead of the fins, it is possible to envisage using a rough coating or one having microgrooves in order to transfer the quantity of energy necessary to form the sheet of powder. Advantageously, the at least one fin is orientable. In a second case, the rotary device comprises a lower part and an upper part spaced from each other by a determined space, the upper part having an orifice allowing the powder to enter and the space between the two parts allowing the output of the powder. In a third case, the rotary device is an element having a powder inlet and a powder outlet, said element being arranged so that the powder exiting at the outlet has sufficient inertia so that the powder is projected out of the 'element. Advantageously, this element is a curved tube. Advantageously, the axis of rotation of this rotation device is concomitant with the part of the tube where the powder inlet is located. According to another particular embodiment, the means for introducing at least one powder are at least one container comprising a powder inlet and a powder outlet, and the means for ejecting the powder in the form of a sheet is a means for quickly moving the at least one container and abruptly stopping it so that the powder it contains is projected out of the container by inertia. Note that the powder inlet can correspond to the powder outlet.

In the case where the means for ejecting the powder is a rotary device, advantageously, the at least one deflector is placed parallel to the axis of rotation ^' around which the means for ejecting the powder in the form of a sheet rotates. Advantageously, the at least one deflector can also be placed perpendicular to the mean plane of ejection of the sheet of powder, whether the means for ejecting the powder is a rotary device or not. Advantageously, the at least one deflector is a part of the internal wall of the device. Advantageously, the at least one deflector has a shape adapted to the shape of the determined location of the mold to be filled. In other words, the at least one deflector is advantageously placed above the cavity which it must fill and it has the same or a similar shape as said cavity. The device according to the invention has many advantages. First of all, the device makes it possible to quickly fill a mold. Likewise, it makes it possible to mix the powders inside the device. The filling of the powder (s) is carried out without having to introduce an additional quantity of gas into the system during the setting in motion of the powder. The device according to the invention makes it possible to supply different zones of the imprint each with a controlled flow of powder. In the end, a device is thus obtained making it possible to control, over time and in space, the flow of powder supplying each of the selected zones of the mold or of the impression. The device makes it possible to create and deposit without destabilizing it in the mold a mixture of powders whose different components have very different densities. As one can control in space the flow and the composition of the powders, one can modulate on the height of the compacted part that one wants to obtain the composition of the mixture and the apparent density of deposited powders. In particular, it is possible to control the horizontality and the flatness of the deposited powders. Furthermore, the device does not require the use of powder having good flowability. Indeed, no flow in a small diameter pipe is not used. The choice of powders is therefore widened. The invention makes it possible to crush the powders by impact during the introduction of granulated powders into the system, which is of great interest for carbides and nuclear materials. With this device, it is possible to add an additive to one or more selected areas of the imprint, the additive making it possible, for example, to improve future compaction.

BRIEF DESCRIPTION OF THE DRAWINGS Other characteristics and advantages of the invention will appear on reading a preferred embodiment of the invention made with reference to the appended figures among which:

- Figure 1 is a sectional view of a particular example of the filling device according to the invention. - Figure 2 is a sectional view of Figure 1 along the axis AA.

- Figure 3 illustrates another example of the filling device according to the invention.

- Figure 4 is a sectional view of an example of a rotary device having the shape of a cone.

- Figure 5 is a sectional view of an example of a rotary device having the shape of a bowl.

- Figure 6 is a sectional view of another example of a rotary device. - Figure 7 is a sectional view of a rotary device having the shape of a cone and having fins. - Figure 8 is a sectional view of another example of a rotary device. - Figure 9 illustrates another example of the filling device according to the invention. FIG. 10 is a sectional view along the axis BB of the element 37 in FIG. 9.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

By way of example, the embodiments described below will relate to the filling of molds with a powder and with a mixture of powders. The filling materials used are powders intended to be shaped, for example by sintering, by compression, by compression-sintering or by hot isostatic compression. These are for example metallic, ceramic powders or a mixture thereof. These powders must meet the manufacturing requirements of the sintered object, in particular as regards the particle size, purity and compressibility. Thus, the powders used have a diameter of less than 3 mm, preferably less than 1 mm. The filling device according to the invention is supplied by having doses defined by volumetric or weight pre-dosing of powders in said device or by introducing the powders via a hopper (reservoir in shape of truncated and inverted quadrangular pyramid) with a tubular connection. For reasons of congestion, for example, the hopper can be inclined or placed at the periphery of the disc. It can be replaced by a worm screw, by a tube ... The hopper-body connection of the device is generally controlled by a shutter, which also makes it possible to measure the quantities of powder introduced on the tray as well as the moment of 'introduction. According to a first example illustrated by Figures 1 and 2, we want to fill a mold 2 using the device 1 according to the invention. The powder 3 is contained in a hopper 4 formed in the upper part of a body 20 of the device. It falls progressively onto a plate 5, rotating around a central axis 6, located just below the hopper 4. In this example, the plate 5 has the shape of a disc. The plate 5, which is in rapid rotation, ejects the powder 3 in the form of a sheet 7 of homogeneous and almost horizontal powder whose average direction is included in an angle of plus or minus 90 ° relative to the horizontal. As shown in FIG. 1, the sheet of powder 7, ejected by the plate 5, strikes the wall 21 of the body of the device: this wall acts as a deflector. The wall 22, placed lower than the wall 21, can also play the role of deflector. Once deflected by the wall 21, the sheet of powder 7 then comes into contact with fixed, radial and vertical deflectors 9 relative to the rotary plate 5. In this example, the deflectors 9 are integral with a central element 8 which has the shape of a cylinder. The powder 3 is thus distributed in the mold 2 or cavity located below the deflectors 9. It is specified that the element 8 and the deflectors 9 are fixed; only the plate 5 turns. The sheet, after a first reflection on the body can be redirected towards other walls (like those of the body or the central element) before being reflected on the deflectors 9. All these walls form a set of deflectors making it possible to control the grain flow. The rotation speed of the turntable is 100 to 10,000 revolutions per minute depending on the powders and the energy to be supplied to the powder. Advantageously, this speed is between 100 and 5000 revolutions per minute. In FIG. 2, it can be seen that, since the deflectors are fixed and the plate rotates in this example clockwise, the powder flow is pressed against one side of the deflectors.

According to another example, it is desired to fill a mold having cavities of different depths with mixtures of different powders depending on the location of the mold. FIG. 3 represents a device according to the invention composed of a set of powder deflectors making it possible to distribute in a controlled and modular manner different layers of quasi-horizontal powders (mean direction between + or - 90 ° relative to the horizontal) in different places of a mold. The mold 10 in question has two cavities: a deep and narrow cavity 11, and a shallow and wide cavity 12, the bottom of which gives onto the cavity 11. In this example, two discs (13 and 14), rotating around a common central axis 15, each receive a different powder, here called powder A and powder B, which they eject in the form of a sheet of aerated powder and of determined thickness. The powders can be inserted into the discs using a hopper with two outlets or using several hoppers. It is obvious that the discs can be carried by different axes. Four deflectors of elongated shape and different widths are installed perpendicular to the plane of rotation of these two rotating discs (13 and 14) on the path of the sheets of powders A and B. In fact, there are three deflectors of identical shapes (16, 17 and 18) and a deflector 19 having a recess in the part in contact with the powder A. The deflectors are placed so that a precise place in the imprint can be filled with powder. These four deflectors being of flat shape, they are placed just above the respective cavities of the mold which they must fill. Thus, these four deflectors intercept the different layers of powders at determined locations corresponding to the cavities to be filled with a given imprint. Thus, each deflector by its geometry and its positioning (which can be modified during a filling operation) participates in the distribution of the different powders in a mold. Recall that the shapes of the deflectors are varied (concave, flat, convex, helical ...) and that the deflectors can tilt in all directions relative to the plane of the plate. The shape of each deflector has an influence on the quantity of powder that it deflects towards the impression. In FIG. 3, it can be seen that the deflector 19 is wider than the deflectors 16, 17 and 18 at the level of the interception zone of the powder B. The deflector 19 therefore captures more powder B than the other deflectors and l 'place where he deposits said powder intercepted in the impression (that is to say the cavity 11) fills faster than the other cavities. The use of deflectors of different width can be interesting if one wants to fill places in the footprint that do not have the same depths. Furthermore, it has been seen that the deflector 19 exhibited a recess at the place where it collects the powder A, and that this recess is absent at the location where it collects the powder B. The deflector 19 therefore no longer intercepts the powder A that the powder B. The cavity 11 of the imprint 10 will therefore be enriched with powder A and will contain traces of powder B. The deflectors 16, 17 and 18 intercept as much powder A as powder B. We have the possibility to vertically move the deflectors during filling or to rotate them, for example so that they deflect more than powder or to adapt them to a changing speed of rotation of the disc, which has an impact on the speed of the powder ejected. Note that the footprint used with this device according to the invention has a dimension of up to 200 mm. In FIG. 3, only one set of deflectors and only one mold is shown. It is understood that other sets of deflectors and their respective molds are present, although not shown. The molds and deflectors are placed in specific locations around the circumference of the turntable. The powder not deflected by the deflectors falls due to gravity. In FIG. 3, the non-deflected powder falls to the periphery and is recovered. In Figure 2, all of the powder is used. The layers of powders used to fill the imprints can be obtained in different ways. For example, they can be obtained by accelerating the powder on a rotary device (as is the case in Figures 1 and 3). This rotary device can be in the form of a disc, a bowl, a cone ... The rotary device can be of metallic, ceramic, polymer or other nature. Its surface condition can be adjusted from a polished state to a state very rough depending on the desired path of the powder particles. The rotary device does not necessarily have a planar geometry. The device may for example have the shape of a cone (that is to say a triangular section 30) (see FIG. 4), of a bowl (circular or approximately circular section 31) (see figure 5) or any other form making it possible to orient the sheet of powder 7. If one wishes, in addition to expelling the sheet of powder, also to control its thickness, one can add another element to the bowl or to the disc. According to Figure 6, there are two parts spaced a small distance (up to several mm), delimiting a space in which the powder can circulate: the lower part 32 has the shape of a bowl and the upper part 33 also the shape of a bowl having in its center a channel 34 allowing the powder to enter 7. The disc, the bowl or the cone may include on its surface particular shapes such as to adjust the transmission of energy from the disc to the powder. These shapes can be cylinders (made by adding pins for example), hemispheres (made by local insertion of the disc) or any other shape which will influence the entrainment of the powder on the disc or the bowl. . The disc or bowl may have fins on their surface. For example, in Figure 7, there is shown a triangular section disc having helical fins 35 extending from the top of the disc. The sheet of powder can also be obtained by scanning at a high frequency with a jet. The sheet is then the materialization of the envelope of the different trajectories of the powder particles. This sheet of powder can be defined by a jet of powder which will sweep a given area at high frequency. The whole of the swept area will be called "tablecloth". An example of a principle is illustrated in FIG. 8. In this case, the powder is for example accelerated in a bent tube 36 by the rotation of said tube. The geometry of said tube will determine the trajectory of the powder ejected. In this example, the orifice of the tube describes a circular geometry. The sheet of powder will in this case be symmetrical with respect to the axis of rotation of the tube, as when using a disc or rotating bowl. The powder layer can also be obtained by accelerating the powder contained in containers. According to FIG. 9, it can be seen that the powder is placed in a container 37 comprising one or more compartments of small height compared to its other dimensions. One of the vertical faces of the container does not contain a wall or has a removable wall allowing access to the compartments. This wall will be removed when it is desired to eject the powder from the container. In this case, the container will be accelerated towards the area where you want to create the tablecloth. A short distance from this zone 38, the container is suddenly blocked. The powder, under the effect of its inertia during said abrupt stop, is then ejected in the form of "Tablecloth" through the opening 39 provided for this purpose (see Figure 10). Optionally, this layer can then be checked and / or calibrated by adapting the shape of the outlet opening of the container. In the case where the container comprises several compartments, the sheet is composed by the different projections of powders initiated by each of the compartments. Advantageously, the superimposed compartments are filled with different powders (see Figure 10). Thus, different parallel layers are created. It is also possible to use several containers to better distribute the powder and not to have a preferred direction. This arrangement is of course advantageous for powder mixtures. For example, in the case of Figure 9, four containers are placed on the same plane and equidistant from an axis marking the center of the matrix to be filled. In this figure, the powder ejections are symbolized by arrows. It should be noted that in FIG. 9, the deflectors and the mold to be filled are not shown.

Other mechanical systems can be envisaged to create the sheet. For example, the sheet can be accelerated using a gas provided that the accelerator gas does not pass or accumulate in the mold or even the area where the deflectors are located. Once the mold is filled with the sheet obtained according to one of these techniques, the powder or powders which are retained there may for example undergo compression, called uniaxial, which consists in agglomerating the powder or the mixture of powders contained in the mold by applying strong pressure (1 to 8 kbar). The tablet obtained can then be made mechanically resistant by subjecting it to a sintering treatment. This corresponds to a heat treatment of the tablet at a temperature below the melting point of the main constituent, this in order to provide it with a significant mechanical resistance.

BIBLIOGRAPHY

[1] Document WO 0126846, "Fluidized fillshoe System", published on April 19, 2002.

[2] US patent US 5,881,357, “Method and apparatus for filling powder”, filed March 28, 1997.

[3] Document WO 0156726, "Powder filling method and arrangement therefor", published on August 09, 2001.

[4] US patent US 5,897,826, "Pulsed pressurized powder feed System and method for uniform particulate material delivery", filed October 08, 1997.

[5] Document EP 1 083 125, "Method and apparatus for packing material", filed on September 06, 2000.

[6] US patent US 5,647,410, "Powder molding machine and method for filling molding materials into a die cavity thereof", filed on March 14, 1994.

[7] American patent US 5,885,625, "Pressurized feed shoe apparatus for precompacting powdered materials", filed on August 29, 1996.

Claims

1. Filling device (1) for at least one mold (2) with at least one powder (3), characterized in that it comprises: - means (4) for introducing at least one powder (3), - at least one means (5) for ejecting, in the form of a sheet (7), the powder introduced into the device, - At least one deflector (9) capable of locally intercepting at least part of said powder (3) ejected in the form of a sheet and redirecting it to a determined location in the mold (2). 2. Filling device according to claim 1, characterized in that the deflector (9) is orientable. 3. Filling device according to claim 1, characterized in that the deflector (9) is movable. 4. Filling device according to claim 1, characterized in that the means (5) for ejecting the powder in the form of a sheet (7) is a rotary device. 5. Filling device according to the preceding claim, characterized in that the rotary device has a shape chosen from a disc, a cone or a bowl. 6. Filling device according to the preceding claim, characterized in that the rotary device comprises at least one fin. 7. Filling device according to the preceding claim, characterized in that the at least one fin is orientable. 8. Filling device according to claim 4, characterized in that the rotary device comprises a lower part and an upper part spaced from each other by a determined space, the upper part having an orifice allowing the entry of the powder and the space between the two parts allowing the powder to exit. 9. Filling device according to claim 4, characterized in that the rotary device is an element having a powder inlet and a powder outlet, said element being arranged so that the powder leaving at the outlet has sufficient inertia so that the powder is sprayed out of the element. 10. Filling device according to the preceding claim, characterized in that the element is a curved tube. 11. Filling device according to claim 1, characterized in that the means for introducing at least one powder are at least one container (37) comprising a powder inlet and a powder outlet, and the means for ejecting the powder in the form of a sheet is a means enabling the at least one container (37) to be rapidly moved and stopped suddenly so that the powder which it contains is projected out of the container by inertia. 12. Filling device according to any one of claims 1 to 10, characterized in that the at least one deflector (9) is placed parallel to the axis of rotation about which the means (5) rotates to eject the powder in the form of a sheet (7). 13. A filling device according to any one of claims 1 to 11, characterized in that the at least one deflector (9) is placed perpendicular to the mean plane of ejection of the sheet of powder. 14. Filling device according to claim 1, characterized in that the at least one deflector (9) is a part of the internal wall of the device (21,22). 15. Filling device according to claim 1, characterized in that the at least one deflector (9) has a shape adapted to the shape of the determined location of the mold to be filled.