FR2660423A1 - METHOD AND INSTALLATION FOR DRYING AND DEGASSING POWDERS - Google Patents

Abstract

The method and the installation according to the invention make it possible to carry out the drying and degassing of the powder using a dynamic process under vacuum and at temperature in a special device, called an "hourglass" (10). This hourglass (10) is animated with various alternating slow rotational movements so as to gradually pass the powder to be treated from one compartment to another, both placed inside the hourglass (10). These rotations thus make it possible to stir the powder for a variable determined duration. The hourglass (10) is introduced into a sealed enclosure (20) placed upstream of a possible valve allowing the treated powder to be conveyed to immediate storage or use without breaking the vacuum. The degassing operation is carried out under vacuum and at temperature. Application to the manufacture of sintered parts by hot isostatic pressing.

Description

PROCESS AND INSTALLATION FOR DRYING AND DEGAVING POWDERS

DESCRIPTION

  The field of the invention is that of the drying and degassing of ceramic or metallic powders. These operations are implemented in the context of the production of massive pieces produced by hot isostatic pressing. Indeed, the consolidation of powders must use a material free of moisture and residual gas These can either react with the product to be compacted (reaction with H 20 for example), or cause gaseous inclusions disrupting the properties of the solid mass obtained (density,

weldability, ductility).

  A first existing solution is to degas the powder statically The mass of powder is in this case subjected to vacuum and temperature in its sheath With this method, it is difficult to obtain and guarantee a sufficient level of vacuum within Another drawback lies in the fact that the gaseous products extracted from the lower layers are redeposited on the upper layers, which become more reactive. Finally, there is a risk of triggering the phenomena.

natural sintering.

  A second solution is to mechanically stir the powders This mixing causes on the one hand pollution problems due to abrasion and on the other hand a technological limitation concerning the maximum temperature and the level

of empty implemented.

  The object of the invention is to overcome the disadvantages of the aforementioned methods and to propose both a method and an installation

  drying and degassing powders.

  For this purpose, a first object of the invention is a method of drying and degassing powders, comprising the following steps: loading the powder into a drying and degassing device, called "hourglass"; to make the relative emptiness in said hourglass; heat the interior of the hourglass to a temperature allowing the powder to reach a temperature equal to 6000 C and simultaneously; stir the powder very slowly according to a determined cycle of turning the hourglass; cool the interior of the hourglass; empty the hourglass of the processed powder by now

this powder stored under vacuum.

  The slow turning of the hourglass avoids the problems caused by the abrasion, the course made by the powder guarantees a

optimal degassing.

  In the case where the hourglass comprises at least two compartments communicating with each other by means of a baffle, the mixing of the powder is effected by a slow reversal of the hourglass in a first direction, to gradually pass the powder from one compartment to another, then by a slow reversal of the hourglass in a second direction opposite to the first direction to make

  return the powder to the first compartment.

  This phase makes it possible to separate the powder grains from each other when passing through the baffle. The mixing and passage of the powder from one compartment to another can be improved by at least one series of oscillations around its horizontal axis during the turning cycle. A second object of the invention is an installation for the implementation of the process which has just been described. It comprises: a drying and degassing device, called an "hourglass", mounted rotating about a horizontal axis, comprising: a conduit for loading and unloading the powder communicating with: a first compartment communicating with: a baffle communicating itself with:

* a second compartment.

  The loading and unloading duct and the baffle open into the first compartment so that, for a first series of angular positions of the hourglass, the powder introduced into the loading and unloading duct, or coming from the second compartment, falls and remains by gravity in the first compartment The baffle opens into the second compartment so that, for a second series of hourglass angular positions different from the angular positions of the first series, the powder from the first compartment falls gradually and remains in the second compartment, the angular difference of the two series of angular positions

  corresponding with the turning of the hourglass.

  heating means of the hourglass; and

  means for rotating the hourglass.

  In the preferred embodiment of this installation, the heating means are heating plates placed outside the

compartments and chicane.

  Preferably, the means for rotating the hourglass consist of a geared motor communicating a slow rotation movement to a first sleeve of a movable coupling to radial freedom, a second sleeve being secured to a

  drive shaft in rotation of the hourglass.

  According to one aspect of the invention, the hourglass is rotatably mounted on the movable support by means of rollers on

  which it is laid by means of treads.

  Preferably, the rollers are mounted on articulated boogies arranged two

together.

  According to another aspect of the invention, the installation is more particularly constituted of: a vacuum chamber inside which a mobile assembly further supporting the hourglass moving horizontally relative to the enclosure; a removable door fixed on the movable support for sealing the enclosure when said movable assembly is placed inside the enclosure, the rotating drive shaft passing through said door by means of a sealed rotating passage, and on which the hourglass is supported in its loading position outside the chamber, the rotating drive shaft passing through this door by means of a sealed rotating passage; an hourglass unloading receptacle placed in the lower part of the enclosure for receiving the treated powder from the loading and unloading pipe when the hourglass is in the unloading position inside the enclosure; at least one vacuum circuit of the enclosure; and a vacuum valve placed at the outlet of the unloading receptacle to allow the isolation of upstream and downstream parts and evacuation under vacuum

  powder to a storage hopper.

  According to another aspect of the invention, the enclosure comprises inclined supports on which arise, during the horizontal translation of the movable assembly, second rollers mounted free to rotate on a base plate placed below the hourglass so that the hourglass takes support on the speaker, when it is

inside of it.

  The invention and its various technical features will be better understood

  in the light of the following description.

  This is accompanied by figures representing respectively: FIGS. 1A, 1B, 1C and 1D, four sketches showing in section the hourglass in four successive positions during a cycle of the method according to the invention; Figure 2 is a longitudinal sectional view of the installation according to the invention; Figure 3, a cross section along the line A-A in Figure 2, showing the plant according to the invention; FIG. 4 is a graph showing an exemplary turnaround cycle of the hourglass of the installation according to the invention; and FIG. 5, two installations according to the invention

  in operational use.

  The main concept of the process according to the invention is to put the powder under vacuum, to slowly stir it while raising its temperature (for example up to 600 C, maximum value on the operational installation). drying and degassing device, identified in all the figures and more commonly called hourglass It consists of a wall 19 of shape

  very special ended at its ends with a flange.

  In the process according to the invention, the hourglass 10 is placed in a chamber inside which the vacuum is evacuated to 10-6 T (1,333 10-4 Pa). The hourglass is raised to a temperature which can exceed 700 C The brewing takes place in these conditions of temperature and pressure The temperature of the powder is followed by thermocouples divers in the compartments

4 and 8.

  FIG. 1A is a sectional view of the hourglass in its position of loading the powder. The latter is not marked by a numerical reference in the figures, but is schematized by one or more spots of small dots. by the first end of a loading and unloading duct 2 is, in this position, above the body of the hourglass, that is to say in the highest position it can take, when This position is used to channel the powder, to be treated, inside the hourglass. The powder falls by gravity along the loading and unloading pipe 2 to arrive in a first compartment. 4 which communicates with the loading and unloading pipe 2 by its second end. Once the powder is in this first compartment 4, the brewing cycle can begin The hourglass 10 comprises a second compartment 8 connected to the first compartment 4 via a baffle 6 The relative positions of the two compartments 4 and 8 and their communication with the baffle 6 must be such that, in the loading position shown in FIG. 1A, the powder remains on an inner wall 16 of the first compartment 4 without being able to

  progress towards the second compartment 8.

  The outer walls of the two compartments 4 and 8 and the baffle 6 are partially covered by heating means 12, which are preferably heating plates. Once the powder is completely introduced into the first compartment 4, the hourglass 10 is rotated. in a first sense, symbolized by the arrow of Figure 1 B For the hourglass shape shown in these first figures, this rotation is of the order of a quarter turn In this case, the first compartment 4 is at above the second compartment 8 and the powder falls naturally by gravity in the baffle 6 and in the second compartment 8 A deflector 14 is located at the entrance of the baffle 6 Its function is to prevent the powder from returning directly into the conduit loading and unloading 2, when it is desired to make it fall into the second compartment 8 In these figures, this deflector 14 constitutes the extension of one of the two walls

  loading and unloading pipe 2.

  In the example represented here, the baffle 6 consists mainly of two segments of straight tubes communicating with each other by an acute angle. The baffle 6 communicates with the two compartments 4 and 8 while being oriented so as to form with the internal walls 16 and 18 constituting the respective bottoms of the two compartments 4 and 8, an acute angle Thus, the powder in the first compartment 4 must cross three abrupt changes in direction before falling into the bottom of the second compartment 8 This embodiment is not an example, any other form of chicane that can be used from the moment

  that the desired stirring is obtained.

  In order for the powder to drop completely into the second compartment 8, and especially so that the brewing and heat treatment cycle can take place, the hourglass 10 is driven by

  several slow successive and inverted rotations.

  As a result, the hourglass is slowly shaken and the powder gradually descends to the bottom

  second compartment 8 where it is brewed.

  With reference to FIG. 1C, the cycle continues with an inverted reversal of the hourglass. Indeed, the arrow of this FIG. 1C indicates a direction reversed with respect to the direction symbolized by the arrow of FIG. 1B. In the position shown, a complete half-turn of the hourglass 10 was performed The second compartment 8 is located

  now above the first compartment 4.

  The powder therefore falls naturally by gravity into the baffle 6, and then again into the first compartment 4. In a similar manner, the cycle preferably comprises a stirring phase similar to that which takes place when the second compartment 8 is at the bottom. with the first compartment 4 placed at the bottom, however, is generally of greater amplitude It is indeed necessary to ensure the complete descent of all the powder in the baffle 6 and in the second

compartment 8.

  The number of transfers between cavities 4 and 8, as well as the oscillation cycles are

according to certain parameters.

  Finally, as shown in FIG. 1D, an ultimate rotation in the same direction of a quarter of a turn makes it possible to place the inlet of the loading and unloading duct 2 below the assembly formed by the two compartments 4 and 8 and the baffle 6 As a result, all the powder returned to the first compartment 4 falls into this loading and unloading conduit 2 and can be received below the hourglass

by a possible receptacle.

  FIG. 2 shows in longitudinal section, the entire drying and degassing installation according to the invention. The latter mainly comprises the assembly consisting of the oven itself, that is to say the vacuum chamber. 20 and the hourglass, equipped with its rotation means which are on its right This assembly is mounted integral on a carriage 16 movable in horizontal translation relative to the ground 18 The system of

  translation by mother screw is not shown here.

  The installation also comprises an enclosure fixed with respect to the ground 18 and inside which the hourglass 10 is housed so that the drying and degassing operations are carried out. This enclosure 20 is completed by a removable door 30, equipped with a seal 31, mounted on the assembly of the hourglass 10 and the movable support 16 The enclosure 20 is also completed with a first depression opening which is preferably in the form of a plug 44 attached to the walls of the chamber 20, and an outlet receptacle 52 of the powder, placed in the lower part of the chamber 20 and opening into a

vacuum valve 54.

  The loading powder hourglass 10 takes place when it is placed outside the enclosure Once this loading done, the hourglass is introduced inside the chamber which is hermetically closed using the door This is fixedly mounted relative to the mobile support 16 The vacuum is then made inside the enclosure using at least one vacuum circuit symbolized by the plug 44

  placed in the upper part of the enclosure 20.

  In fact, it is preferable to use a first primary circuit to start slowly evacuating the enclosure without sucking up the powder placed in the hourglass. A second secondary circuit is then used to obtain more quickly.

the desired depression.

  The hourglass 10 and its rotational drive means are mounted movable in translation on the carriage 16 to allow the maintenance of the hourglass 10 without mounting or dismounting thereof, and the loading of the powder therein However, the drying and degassing process according to the invention can be implemented with an installation in which a loading hole would be provided in the top of the enclosure and in which the hourglass would remain inside the enclosure. installation would remove the mobile carriage 16, the door 30 and its sealing system and the hourglass positioning system inside the enclosure On the other hand, such an installation would therefore require an additional loading opening provided in the part upper enclosure and review operations

necessary for maintenance.

  The means for rotating the hourglass 10 consist of a geared motor 22 fixed to the movable carriage 16 IL drives a drive shaft 26 of the hourglass 10, by means of a transmission assembly symbolized in dashed lines by a belt 24 The latter rotates the transmission shaft 26 via a movable coupling at liberty

  radial 25 which is preferably an OLDHAM joint.

  This is not shown in detail in FIG. 2 Nevertheless, the belt 24 drives a first sleeve of this OLDHAM seal, the second sleeve of this seal being integral with the drive shaft 26. such a seal allowing a slight variation in position in height (a few millimeters) of the drive shaft 26 is explained by the fact that the hourglass 10 must undergo large temperature differences between the different phases of the process and therefore a slight In addition, it must also undergo a slight height variation in its positioning inside the enclosure. Indeed, it is necessary to put the hourglass in support in the enclosure 20 during the entire

  the drying and degassing process.

  The driving shaft 26 is preferably hollow. This allows the feed-through passage of the hourglass heating plates 12 and possible control thermocouples also implanted on the hourglass 10. This drive shaft 26 passes through the door 30 L. sealing is then provided by a sealed rotating passage 27 placed

  around the drive shaft 26.

  In FIG. 2, the moving assembly of the hourglass 10 and of the mobile carriage 16 is represented in the intermediate position, that is to say that the hourglass is halfway out of the enclosure 20 In the position of loading the powder , this assembly is completely out of the enclosure 20 The hourglass 10 is then mounted cantilever on the mobile carriage 16 Precisely, it is suspended by means of a pin 34 placed in at least one notch 36 integral with the door 30 This pin 34 is integral with the hourglass 10 and is placed at the height of the upper wall of the deck 10, next to the

right flange 46 of the hourglass 10.

  The assembly of the hourglass 10 also rests on the door 30 by lower supports 38. To put the hourglass 10 in its drying and degassing position, the moving assembly is then translated to the left of the figure, until that the hourglass 10 takes the position sketched in phantom, the door 30 being applied against the right end of the tank 20 The latter is thus sealed thanks to the seal 31 placed on the door 30 and bearing on the face of the tank 20 To place the hourglass 10 in support in the tank 20, the latter comprises inclined supports 48 fixed on its bottom and positioned in correspondence with positioning rollers fixed below the hourglass 10, on a base plate 60 , but free in rotation around axes

  horizontally and thus acting as rollers.

  During translation of the hourglass 10, the relative positioning of the positioning rollers and inclined supports 48 is such that each positioning roller 50 is tangent and roll on an inclined support 48 The hourglass 10 is then slightly raised The translation of the mobile assembly ends with the arrival of the positioning rollers 50 on a horizontal portion of the inclined supports 48 corresponding to the working position of the hourglass 10 The latter is then unhooked from the hook 36 and is no longer

supported by the door 30.

  With reference to FIG. 3, the degree of freedom in horizontal rotation of the hourglass 10 is ensured by the fact that the latter is placed on rollers 40 placed on the outside of the flasks 46 of the hourglass 10. 40, the left half of Figure 3 is a vertical section of Figure 2 at the line AA The rollers 40 are grouped two by two by means of

  articulated arms 56 thus forming boogies.

  Each boogie is articulated about a horizontal hinge axis 58 integral with the base plate

Hourglass 10.

  Outside each of the flanges 46 (Figure 2), the hourglass 10 has a tread 42 Each of them is placed on at least two boogies of rollers 40 placed in correspondence below them, of such that the hourglass 10 can rotate freely about its horizontal axis because it rests only on

rollers 40.

  FIG. 3 shows the plug 44 symbolizing the means for causing the enclosure 20 to depressurize. A water inlet 62 is also shown on the top of the enclosure 20. It is intended for the circulation of water between the two. The walls of the enclosure 20 The presence of the double wall of the enclosure 20 allows a permanent flow of water around the hourglass 10 to maintain a temperature of safety on the outer surface

of the enclosure 20.

  On the left-hand part of FIG. 3, there is a wide duct 64 allowing a secondary circuit to evacuate in the enclosure. Below this latter is shown the lower receptacle 52. An unloading cone 66 is also provided below. hourglass 10, fixed to the base 60 thereof This discharge cone 66 guides the powder at the exit of the hourglass

in the receptacle 52.

  This type of assembly of the hourglass 10 on rollers 54 makes it possible to limit the contact pressures and to allow a slight vertical rise in the axis of the hourglass 10 without inducing stresses. The rise is due to a variation in the diameter of the bearing on the rollers

  caused by thermal expansion.

  The shafts and the rollers 40 are preferably made of refractory and ceramic metals to ensure operation in an environment that does not allow lubrication

contacts.

  The use of such an installation

is done by the following method.

  The first operation is to place the powder in the hourglass 10, then to introduce the hourglass into the chamber 20 This is followed by the evacuation of the inside of the chamber 20 The powder is then slowly brewed to the interior of the hourglass 10 according to a determined cycle of hourglass turnarounds, an example of which is given later This stirring cycle varies in very large proportions The heating of the powder may be incremented stepwise or effected by a continuous rise in temperature After the brewing cycle, the powder is cooled naturally Finally, it is removed from the hourglass while being kept under vacuum for its

storage in a hopper.

  The volume of powder involved is

  preferably of the order of six liters.

  An example of a powder mixing cycle is shown schematically in FIG. 4. The mark O corresponds to the loading position of the hourglass. The first rotation to the right of the hourglass exceeds 110 The hourglass 10 then undergoes a determined number of slow oscillations of increasing amplitude to reach in some cases 90 O The hourglass 10 is then returned from 180 and is again subjected to oscillations larger amplitudes that may exceed 90 and during which the powder

  is transferred from cavities 4 to 8 and vice versa.

  The different rotations of the hourglass are

  symbolized by arrows in the shape of an arc.

  The circled numbers assigned to these arrows are

  representative of the chronology of these rotations.

  With reference to FIG. 5, the installation is used in a set of degassing and filling of envelopes for hot isostatic compaction. In this figure, two installations have been schematized. The one on the right shows a first hourglass 10 enclosed in an enclosure. This first installation schematizes a degassing operation The installation on the left shows a second hourglass 10 in a loading position Ce

  second hourglass 10 has left the enclosure 20.

  The whole is placed in a containment to allow to carry out the various operations under special atmosphere, or to avoid

contamination problems.

  Below each enclosure 20, is placed an outlet receptacle 52 for recovering the treated powder. This receptacle 52 results in a vacuum valve 54. The latter is adapted for the transfer of the powder. Downstream of each vacuum valve 54 is a hopper 56 whose capacity corresponds to that of hourglasses 10 Each hopper 56 is followed by a conveying device allowing

  the transfer of the powder to a zone of use.

  With the vacuum valve 54, the downstream assembly is maintained in a controlled atmosphere, and more precisely under vacuum, while the chamber 20 must be open and the hourglass 10 reloaded at the bottom of each hopper 56, is a calibrated and removable nozzle It ensures the accumulation closure output on the upper face of a vibrating corridor 58. The filling is fed by two channels each comprising an enclosure and an hourglass A trident device 62 comprises at least two branches that can isolated from the rest of the equipment by means of vacuum valves 54 A, 54 B In the center of the trident there is a control device 64 for checking the level of filling

sheath 67.

  The part between the valves 54,

  54 A and 54 B is under vacuum permanently.

  The filling can be carried out in the following manner, for example for the left channel: connection of the sheath 67 and evacuation by a circuit connected to the trident (not shown); opening of the valve 54; transfer of the hourglass powder into the hopper 56; closing valve 54 (hourglass reloading possible); opening of the valve 54 A; starting the vibrating corridor 58; tracking the level in the sheath by 64; stopping the vibrating corridor 58; closing the valve 54 A. The sheath 67 is then closed by a crimping and welding apparatus not shown here The use of two drying and degassing routes makes it possible to remedy a possible lack of powder on one of the two tracks during

filling.

  The entire system can be controlled by a programmable controller that manages the powder treatment cycle. The latter includes a slow primary emptying and then the vacuum

  secondary, heating and hourglass rotations.

  This programmable controller can also manage the safety associated with the functions vacuum, temperature

and opening the valves.

  The assembly described in FIG. 5 is only an example of use of the installation according to the invention. It is possible to envisage other possible arrangements using multiple channels.

  arranged for example in a carousel.

  One can also consider the direct loading of the hourglass into the enclosure by providing an additional outlet in the upper part of the enclosure. The treatment of the powder can also be carried out in a controlled atmosphere or in a reactive atmosphere. A glove box assembly can even be envisaged for the treatment of toxic products. The assembly described in FIG. 5 is particularly suitable for vacuum encapsulation of powder intended for densification by

hot isostatic pressing.

  The choice of materials can make the installation compatible with products

  pharmaceutical or food, for example.

Claims (7)

  A method of drying and degassing powders, comprising the steps of: charging the powder in a drying and degassing device, called "hourglass" (10); to make relative emptiness in the hourglass (10);   heating the interior of the hourglass to a temperature to reach a temperature equal to 600 C in the powder and simultaneously; very slowly stir the powder inside the hourglass (10) according to a determined cycle of turnings of the hourglass (10); cool the interior of the hourglass (10); and empty the hourglass (10) of the treated powder   by keeping this powder stored under vacuum.   2 Process according to claim 1, the hourglass (10) comprising at least two compartments (4, 8) communicating with each other via a baffle (6), characterized in that the mixing of the powder is carried out by slowly reversing the hourglass (10) in a first direction to gradually pass the powder from the first compartment (4) to the second compartment (8), then by slowly turning the hourglass (10) in a second direction opposite to the first direction to make come back   powder in the first compartment (4).   3 Process according to claim 2, characterized in that the cycle of overturns of the hourglass (10) comprises at least one series of oscillations around its horizontal axis to promote the mixing and the passage of the powder from one compartment to another.   4 Installation for implementation   method according to any one of the claims   preceding, characterized in that it comprises: a device for drying and degassing, called "hourglass" (10), mounted rotating about a horizontal axis comprising: * a loading and unloading conduit (2) communicating with: a first compartment (4) communicating on the other hand with: a baffle (6) communicating itself with: a second compartment (8), the loading and unloading duct (2) and the baffle (6) opening into the first compartment (4) so that, for a first series of angular positions of the hourglass (10), the powder introduced into the loading and unloading duct (2), or coming from the second compartment (8) , falls and remains by gravity in the first compartment (4), the baffle (6) opening into the second compartment (8) so that, for a second series of angular positions of the hourglass (10), different from the positions of the first series, the powder ve the first compartment (4) falls gradually and remains in the second compartment (8), the angular difference of the two series of angular positions corresponding with the rotations of the hourglass (10), the heating means (12) of the hourglass (10). ; and   means for rotating the hourglass (10).   Installation according to claim 4, characterized in that the heating means of the interior of the hourglass (10) are heating plates (12) placed outside the compartments (4, 8) and the baffle (8). 6 Installation according to claim 4 or 5, characterized in that the rotation means of the hourglass (10) consist of a geared motor (22) communicating a slow rotation movement to a first sleeve of a movable coupling at liberty radial (25), the second sleeve being integral with a rotary drive shaft (26) Hourglass (10).   7 Installation according to any one of revendi cations 3 to 6, characterized in that the hourglass (10) is rotatably mounted on a movable support (16) by means of first rollers (40) on which it is posed   by means of two treads (42).   8 Installation according to claim 7, characterized in that it comprises: a vacuum chamber (20) within which penetrates the assembly of the movable carriage (16) and the hourglass (10) by horizontal translation; a removable door (30) fixed on the movable support (16) for sealing the enclosure (20), when the moving assembly is placed inside the enclosure (20), the drive shaft ( 26) rotating through the door (30) by means of a sealed rotating passage (27) and on which the hourglass (10) bears in its loading position outside the enclosure (20); an hourglass unloading receptacle (52) placed in the lower part of the chamber (20) for receiving the treated powder from the unloading pipe (2) of the hourglass (10) when the latter is in the unloading position and within the enclosure (20); at least one vacuum circuit (44) of the enclosure (20); and a vacuum valve (54) disposed at the outlet of the unloading receptacle (52) for isolating the upstream and downstream portions and vacuum evacuating the powder to a storage hopper (56).   9 Installation according to claim 8, characterized in that the enclosure comprises inclined supports (48) on which arise, during the horinzontal translation of the assembly of the movable carriage (16) and the hourglass (10) of the second positioning rollers (50) rotatably mounted below the hourglass (10) so that it bears on the enclosure (20) when it   is inside of it.