EP1022078B1 - Process and apparatus for preparing metal powder by gas atomisation - Google Patents

Description

The invention relates to a method for producing metal powder from similar melts, one from a nozzle body of a metallurgical Vessel emerging melt stream in a atomization chamber Gas jets split into droplets and these into essentially spherical Powder grains are allowed to solidify.

The invention further comprises an apparatus for producing metal powder similar melts consisting essentially of a spray chamber, into which from a metallurgical vessel by means of a melt nozzle body a molten metal stream can be introduced or entered, one in this chamber Disintegration unit arranged on the entry side, with gas nozzles for Actuation of the melt stream by gas jets to break it up Droplets, a solidification space provided on the discharge side for cooling the Droplets and formation of powder grains, as well as subordinate Powder processing facilities.

Gas atomized metal powders are used in materials and surface technology Due to the increasing quality requirements for the products in increasing Dimensions used. The type of use determines an advantageous one Powder grain size and a similar grain size distribution, that is the respective one Proportion of powder grains with a certain diameter in one Diameter range. For flame spraying for surface coating of Objects is, for example, a use of a so-called Mono-grain powder is technically inexpensive and economical. At a Manufacture of hot isostatically pressed parts from metal powder, however, is intended Powder advantageously have a high bulk density and thus a corresponding Have grain size distribution.

Gas-atomized metal powder is essentially produced in such a way that a liquid metal stream with gas, preferably inert gas or inert gas, which has a high flow velocity or kinetic energy, is applied. The application of gas causes the metal flow to split into fine droplets, which subsequently solidify into grains. Next the temperature, viscosity and surface tension of the liquid Metal is in particular the acceleration of the melt by the gas jet or are the forces involved (powder production and spray forming, Advances in Powder Metallurgy & Particulate Materials- 1992, Volume 1, Metal Powder Industries Federation, Princeton, N.J., Page 137-150, Particle size prediction in an atomization system; Claes Tomberg) for the size and the Size distribution of the powder grains formed is decisive.

If there is a free falling metal stream in a atomization chamber with at least impinged on a gas jet, which can represent an operationally reliable method, so is the achievable powder grain size regarding the main part of the fraction limited below because in the area between the gas nozzle and the metal flow high proportion of the gas jet energy is broken down. By screening out the coarse parts can increase the quality of the product, the desired grain size of the metal powder can be adjusted, however, this means a low output or a low cost of manufacture associated.

To the quality of the products made of or with metal powder and In particular, improving profitability has long been a goal Process to find a spheroidal metallic powder to be created with a large proportion of fine coma and with a high yield.

If the comparatively thick melt stream is not divided immediately, but if this is flattened out for the time being, the effect of the Gas jet acting on liquid metal intensifies and it becomes finer Droplets formed before the solidification due to the surface tension take spherical shape. The diameter reduction of the powder particles is how previously stated, largely dependent on how high the melt accelerates becomes.

Gas atomization processes for metal melts are known, in which the Liquid metal immediately after it emerges from the nozzle body of the metallurgical vessel with one or more gas jets from directly on Outlet arranged nozzles is divided. Because the gas is on the one hand at the outlet has a high speed, on the other hand the high temperature effect because it expands rapidly and loses its effect towards the center of the beam an extremely wide metal powder fraction with coarse and fine fractions.

In order to avoid the above disadvantage, according to US Pat. No. 2,968,062, a Use device with a melt nozzle that widens outwards and to form the gas supply channel in a conical shape around this nozzle. The gas jet creates a negative pressure in the center, which leads to the melt Edge of the expanding outlet can flow where this thin Melt film is captured by the gas jet and effectively divided and accelerated. With Such devices can indeed be used to produce very fine-grained powders, disadvantageous, however, is their susceptibility to malfunction and the low processability Melting size.

To improve the functional reliability of the atomization device was carried out according to US 4,272,563 the proposal to remove the melt stream from the Let melt nozzle body emerge freely and after a fall to be charged with gas jets. Despite the use of nozzles, the gas jets with supersonic speed, could not be used for the formation of Powder grain with a small diameter sufficient acceleration of the Melt can be achieved.

Attempts have been made to use small nozzle spacings to achieve the Accelerating effect of the directed on the falling metal stream Increase gas jets. In the area of the nozzle, however, the suction of escaping gas jet or gas eddy currents due to the ejector effect induced with a small nozzle distance from the point of division of the metal stream Can carry or return droplets, which are ultimately on the nozzle body put on and have a destabilizing effect on the procedure. For these reasons, is a Minimum nozzle distance to be provided, which, however, the effectiveness of the Gas jets with a view to melting particles into small droplets is disproportionately reduced. For example, with a gas flow, which emerges from a Laval nozzle at supersonic speed at a distance 30 times the nozzle diameter, the force effect on about half.

A device for metal powder production is known from SE-AS-421758 become, in which the melt flow in the Atomization chamber two gas jets are used. There is a Actuation of the free-flowing melt stream by a first one Gas jet with an angle of approx. 20 °, which leads to a breakup and Deflecting the stream leads, after which this is vertical from a second gas jet is broken into metal droplets with high intensity. With this procedure is Although metal droplets adhered to the gas nozzle parts, the large distance of the second nozzle from the point of division of the melt, however, causes a broad grain size distribution with small amounts of fine powder.

A method of applying a vertical metal flow through a horizontal gas jet has been proposed in accordance with US 4,282,903, wherein a advantageously small nozzle spacing is used. To prevent the An auxiliary gas jet is thereby attached to the nozzle body by metal droplets in the nozzle area, directed obliquely to the cutting site. The The compact melt stream is almost exclusively divided by means of the horizontally directed main gas jet, so that the spreading on fine-grained powder is low.

Another process for producing metal powder by exposure of a melt stream with horizontal gas jets is in WO 89/05197 disclosed. According to this procedure, two flat, with the narrow side essentially vertically oriented gas jets at an acute angle to each other aligned and the melt flow in the area of the meeting of the Beams initiated in such a way that initially the surface area and subsequently the other partial areas of the metal stream are acted upon by the gas jets become. Due to the enlarged division area or through the The longitudinal extent in which the liquid metal is divided is the specific force on the liquid metal large, the energy of the gas jets however limited by the speed of sound limit. Such a thing Metal powder produced has a narrow range of grain diameters, the fine and coarse particles are only present in small quantities, so that this is in the direction Monocom-formed powder for some applications, the low bulk density because of, has disadvantages.

All economic processes for the production of metal powder from melts and the devices that can be used for this have the disadvantages in common that the Fine powder proportion too low and / or the grain size distribution unfavorable for one Economic further processing into high-quality products is or are.

Here, the invention seeks to remedy this and aims to Manufacturing process for metal powder from melts to specify with which high fines content and avoidance of unfavorable coarse particles desired broad particle size distribution of the powder is economically achievable. Furthermore, it is an object of the invention to provide a device with which conveniently metal powder in a fraction or with a grain size distribution Can be produced with which this, for example a high bulk density showing, possibly by hot isostatic pressing (HIPen) particularly high quality products can be processed.

This goal can be achieved in a generic method in that the emerging essentially vertically from the melt nozzle body Melt flow through at least three successive gas jets different directions are at least partially applied,

In a device of the type mentioned, the task is solved in that the disintegration unit at least three gas nozzle body has, the gas jets in an effective sequence in each case on the introduced Melt flow and on the by the upstream gas jet into one Directed and shaped melt flow with an angle between 5 ° and 170 ° can be aligned.

The advantages achieved with the invention can be seen essentially in the fact that the liquid metal when it is broken down into droplets undergoes high acceleration experiences because, on the one hand, its mass related to the area that ultimately passes through the gas jet is applied, is low and on the other hand the exposure by having a small nozzle spacing, i.e. a high one Gas jet exerting force. However, it is essential to the invention that that the melt stream before the high-energy division into small droplets by at least two upstream gas jets, each with different directions is processed, in a first step an increase in the attack surface and in a second step, the moving melt is conditioned. are synergistically the mass of the melt based on the attack surface is small and The force of the gas jet is high, so the acceleration is high and it becomes particles formed with a small diameter. Scientifically speaking, there is the following relationship: The particle size is approximately equal to the value the square root of a constant broken by the acceleration.

In an advantageous embodiment of the invention it is provided that the from Melt nozzle body emerging melt stream by means of at least one deflected and spread the first gas jet in its flow direction or is thinned and / or cut, followed by at least one, the same Directional component, obliquely incident second gas jet spread and / or split flat melt stream prepared in its form and a suction barrier for the nozzle (s) of at least one downstream third Gas jet builds up, which third gas jet obliquely to partially directed to the processed flat melt stream as a high-speed gas jet is formed and a Feinaufieilu or atomization of the liquid jet to Droplets accomplished which metal droplets subsequently solidified become. When the first gas jet deflects and widens the compact melt flow can have a largely flat shape on the impact side Metal flow can be created, the flow velocity and the Angle of flow of the gas jet from the thickness and from the stability or from the Length of the free-flowing melt stream and the desired thinning or Depend on spread. Opposite the inflow side, one for one is often created Ultimate division of the flat current with unfavorable surface shape loose metal particles. According to the invention, this is an unfavorable one Surface shape side of the flat current by means of a downstream second, obliquely incident gas jet and thus the stream set up for effective splitting into metal droplets. With This gas jet can also be built up with a suction barrier, which is another advantage no liquid particles can get to the last effective lavate nozzle body, so that the operational safety of the device is not impaired in this regard. It it is also important that the high speed beam is directed obliquely onto the Flat melt flow is directed because this has a large force effect in With regard to a fine division into metal droplets. The bigger the slope to the flat current, up to the partial counter-direction of the gas jet enough, is formed, the higher the acceleration of the metal and ultimately be the fine grain portion of the metal powder.

Both for a high proportion of fine grain in the powder and to avoid the The formation of large particles that have to be separated out is special Advantage if the melt flow with a diameter of 2.0 mm to 15.0 mm by at least a first gas jet in its flow direction by one Angle α between 5 ° and 85 ° m, preferably between 15 ° and 30 °, deflected and is spread substantially in a sector shape to form a melt flat stream. A deflection of the melt flow by less than 5 ° is unfavorable because of this abruptly an increase in the formation length of the flat current requires that but is limited by the temperature loss. A particularly efficient one Flat current formation of the liquid metal, this advantageously taking place in the form of a sector, is deflected at an angle between 15 ° and 30 ° reached, with deflections greater than 45 ° a disadvantageous disassembly of the Can cause electricity through the gas jet.

With regard to a high proportion of fine grain metal powder, but also a cheap one Because of grain size distribution, it is of great advantage if the sector-shaped Melt flat flow after reaching one caused by the first gas jet Width of at least 5 times, preferably at least 10 times, the free-falling Melt flow width or thickness by at least a third gas jet, the is designed as a high-speed gas jet, with an angle γ between 25 ° and 150 °, preferably between 60 ° and 90 °, deflected and into one Stream of droplets is atomized or broken up. If the melt flow is less than Spread 5 times the original melt flow thickness is its compactness large and the amount of fine powder that can be produced is comparatively low. A spread of greater than 10 times the melt flow diameter produces particularly good Prerequisites for a breakdown into droplets with a high fine fraction, especially if the high-speed gas jet causing this also deflects the melt flow at an angle between 60 ° and 90 °. larger Deflection angles up to 150 ° increase the fine grain fraction and cause a tendency to Monokombildung.

For processing the metal stream, but in particular also for the formation of a effective suction barrier, it is favorable if the melt flow from or in Area of deflection or atomization by the third High-speed beam through one, the same directional component having a second gas jet, but with an angle δ between 5 ° and 85 °, preferably between 15 ° and 30 °, to this melt flow and is processed, whereby melt droplets leading suction vortex of the High-speed gas jet can be prevented. With a smaller beam angle δ than 5 °, suction vortices of the high-speed gas jet are not perfect preventable, which creates the risk of metal deposits on the nozzle body and The process is unstable. Larger exposure angle of the second gas jet than 85 ° can the metal stream before its atomization disadvantageously deform and the relative speed between metal current and the third gas jet and thus the acceleration of the metal disadvantageous reduce.

The achievable with the generic device advantages of the invention are in essentially to be seen in the fact that by an arrangement of at least three Gas nozzle body in one disintegration unit, the melt flow in three Areas can be acted upon by gas jets and can thus be shaped as well as editable, the angle of the gas jets on the melt stream conveniently between 5 ° to 170 °.

The first gas nozzle body is in an advantageous embodiment of the invention arranged such that the first gas jet formed by it is the same Having directional component, with the angle α 'between 5 ° and 85 °, preferably with an angle α between 15 ° and 30 ° on the melt stream is directed and that the length of the free-falling melt stream is equal to that Length: Distance of the gas nozzle from the point of impact of the gas jet on the Melt flow, increased or decreased by a value that at most is 10 times the diameter of the melt flow. Here is the Angle of the alignment of the gas jet with the melt stream for a thinning and sector-shaped spreading of the same important, the length of the free-falling Melt stream for its stability in the deflection and the transformation in a flat current and the shape that can be achieved are of great importance.

To particularly preferred atomization conditions for the liquid metal To be able to create, it is important if the second nozzle body is arranged in this way is that the second gas jet in the sequence of action on the by the upstream first gas jet spread and thinned flat melt stream with the same Flow direction component with an angle δ between 5 ° and 85 °, is preferably directed at an angle δ between 15 ° and 30 ° and that the Impact point of this second gas jet in the area of or before the deflection, Impact or atomization point of the downstream third gas jet lies. The Angle between the second gas jet and the flat melt stream and its The point of impact on the melt stream is of double importance. On the one hand is the condition of the one immediately subjected to the division Conveniently adjustable flat current, on the other hand has a suppression of one Formation of suction vortices due to the ejector action of the high-speed nozzle to be done effectively. The choice of the angular ranges according to the invention, particularly to the preferred extent, meets these requirements.

If, according to a particularly favorable embodiment, the third nozzle body is arranged such that a high-speed gas jet third or in the sequence of action last gas jet with an angle γ 'between 25 ° and 150 °, preferably greater than 60 ° directed to the melt flow and that the distance between the gas nozzle (s) and the deflecting, appearance or atomization point is less than 20 times the value of Gas nozzle diameter, the facility is highly efficient excellent powder quality achieved because of a breakdown of the metal into droplets a high force effect or acceleration can be used. The increases Force effect or acceleration with increasing angle, with which overall finer powder fractions can be created.

It has proven to be advantageous if at least the third or in the Sequence of action of the last nozzle body to create at least one supersonic gas jet is trained.

In the development of the invention, favorable conditions of division for the flat melt stream are created when the last one for training of a high-speed gas jet usable gas nozzle body more than two Gas nozzle body for creating those that can be set up on the melt stream Gas jets are arranged.

Advantageously good setting options for a desired metal powder fraction are given when the gas jets each in their direction and their intensity are adjustable.

If, according to a further variant, is provided as cheap, at least one Gas jet as a flat jet or multiple jet through the arrangement of several positioned next to each other and / or in particular one above the other Nozzle is formed, the available gas jet width can be applied to the Melt flow can be increased.

Ultimately, it can also be advantageous if the one determined by the gas jets Plane is different from the vertical.

Fig. 1 eine Desintegrationseinheit schematisch

Fig. 2a einen Verlauf eines Schmelzenstromes bei einer Beaufschlagung desselben durch Gasstrahlen schematisch in Ansicht

Fig. 2b einen Verlauf des Schmelzenstromes von Fig. 2a in einer um 90° gedrehten Ansicht.

The invention is explained in more detail below with the aid of drawings which illustrate only one embodiment.
Show it

Fig. 1 shows a disintegration unit schematically

Fig. 2a schematically shows a course of a melt flow when it is acted upon by gas jets

Fig. 2b shows a course of the melt flow of Fig. 2a in a view rotated by 90 °.

1 shows schematically a disintegration unit with three nozzles in the entry area of a spray chamber. Metal is introduced from a metallurgical vessel G by means of a melt nozzle body D to form a melt stream S, which is designed to fall essentially vertically over a distance L _S. A first gas jet 1 is formed by a first gas nozzle A, which acts at a distance L _{A on} the melt stream S in the region 11 with the same directional component but with an angle α '. As a result of this application of a first gas jet 1, a deflection or a change in the direction of flow of the compact melt stream S and its thinning and spreading take place in the region of the impingement point 11, with the formation of a flat melt stream FS.

By means of a nozzle B, a second gas jet 2 is created, which Metal melt flow FS after a spreading section of the same in one Impact point 21 with the same directional component, but with an angle δ applied.

A gas nozzle C, which is preferably designed as a Laval nozzle, creates a gas jet 3, which acts on the flat melt stream FS at a distance L _{C from} the nozzle C in a deflection, impact or atomization point 31 at an angle 'and subsequently divides it into causes a metal particle flow P. The application of the flat melt flow FS by the gas jet 3 can take place obliquely to partially in the opposite direction.

There can also be more than three differently oriented gas jets and / or several gas jets in a direction provided according to the invention be provided.

2a and 2b schematically show a melt stream S, each in a view from two directions offset by 90 ° (elevation and cross-section). A melt stream S is introduced essentially vertically from a melt nozzle body D into a disintegration unit of a spray chamber. The melt stream S with a diameter S ₁ is acted upon by a gas jet 1 after a free-fall section at a point of impact 11 and, as can be seen from FIG. 2 b, is thereby deflected and thinned with an angle α and, as shown in FIG. 2 a, spread to a flat current FS. After a width S _{2 has been reached} , the flat melt flow FS is acted upon by a high-performance gas jet 3 in a deflection point, impingement or atomization point 31, which jet causes a metal particle flow P to be formed. In the area of the atomization point 31 or upstream, the flat melt stream FS is acted upon and shaped by a gas jet 2 which strikes the flat stream FS at a point 21, it also being possible to change the flow direction of the metal stream.

According to the invention, it may also be possible for at least three Gas jets that have a component of the same direction, a melt stream is acted upon in a sequence and divided into a metal particle stream.

Claims (14)

1. A method of producing metallic powder from such melts, wherein a flow of melt issuing from a nozzle member of a metallurgical tank (G) is separated into droplets in an atomization chamber by gas jets and the said droplets are allowed to solidify to form substantially spherical grains of powder, characterized in that the flow (S) of melt issuing substantially vertically out of the nozzle member (D) for the melt is acted upon at least in part by at least three gas jets (1, 2, 3) following in succession and in different directions in each case.
2. A method according to Claim 1, characterized in that the flow (S) of melt issuing out of the nozzle member (D) for the melt is deflected in its flow direction and is widened or thinned and/or separated by means of at least one first gas jet (1), after which at least one second gas jet (2) having an equal direction component and striking in an oblique manner treats the widened and/or separated flat flow (FS) of melt in its shape and builds up a suction barrier for the nozzle or nozzles (C) of at least one third gas jet (3) which is situated downstream and which, directed in a manner oblique to partially contrary to the flat flow (FS) of melt treated, is produced as a high-speed gas jet and results in a fine distribution or atomization of the liquid jet to form droplets (P), which metallic droplets are subsequently allowed to solidify.
3. A method according to Claim 1 or 2, characterized in that the flow of melt (S) with a diameter (S1) of 2·0 mm to 15·0 mm is deflected at an angle (α) of between 5° and 85°, preferably between 15° and 30°, in its flow direction by means of at least one first gas jet (1) and is widened substantially in sector shapes to form a flat flow (FS) of melt.
4. A method according to one of Claims 2 or 3, characterized in that after the sector-shaped flat flow (FS) of melt reaches a width (S2) - caused by the first gas jet (1) - of at least 5 times, preferably at least 10 times, the free-falling width or thickness (S1) of the flow of melt, it is deflected at an angle (γ) of between 25° and 150°, preferably between 60° and 90°, by at least one third gas jet (3) which is formed as a high-speed gas jet, and it is atomized or is separated into a flow of droplets (P).
5. A method according to one of Claims 2 to 4, characterized in that upstream of or in the region (31) of the deflexion or atomization by the third high-speed gas jet (3) the flat flow (FS) of melt is acted upon and treated by a gas jet (2), having an equal direction component, but at an angle (δ) of between 5° and 85°, preferably between 15° and 30°, to the latter, as a result of which eddying swirls of the high-speed gas jet (3) conveying melt droplets are prevented.
6. A device for producing metallic powder from metallic melts, essentially comprising an atomization chamber, into which a flow (S) of metallic melt can be introduced or charged from a metallurgical tank (G) by means of a nozzle member (D) for the melt, a disintegration unit arranged on the charging side of the said chamber and with gas nozzles for acting upon the flow (S) of melt by gas jets in order to separate the said flow to form droplets, a solidification chamber provided on the discharge side for cooling the droplets and forming grains of powder, as well as powder-treatment devices arranged downstream, characterized in that the disintegration unit comprises at least three gas nozzle members (A, B, C), the gas jets (1, 2, 3) of which are in each case orientated in an operational sequence at an angle of between 5° and 170° towards the flow of melt (S) introduced and towards the flow (FS) of melt set in one direction and shaped by the gas jet situated upstream in each case.
7. A device according to Claim 6, characterized in that the first gas nozzle member (A) is arranged in such a way that the first gas jet (1), having an equal direction component, is directed onto the flow of melt (S) at an angle (α') of between 5° and 85°, preferably at an angle (α') of between 15° and 30°, and the length (L_S ) of the free-falling flow (S) of melt is increased or reduced by a value which amounts at most to 10 times the diameter (D1) of the flow of melt, in accordance with the longitudinal dimension: the distance (L_A) of the gas member (A) from the point of impact (11) of the gas jet (1) on the flow of melt (S). LS = (LA ± 10 × D1)
8. A device according to Claim 6 or 7, characterized in that the second nozzle member (B) is arranged in such a way that the second gas jet (2) in the operational sequence is directed at an angle (δ) of between 5° and 85°, preferably at an angle (δ) of between 15° and 30°, onto the flat flow (FS) of melt widened and thinned by the first gas jet (1) situated upstream, and the point of impact (21) of the said second gas jet (2) is situated in the region of or upstream of the point of deflexion, impact or atomization (31) of the third gas jet (3) situated downstream.
9. A device according to one of Claims 6 to 8, characterized in that the third nozzle member (C) is arranged in such a way that a third gas jet (3) or a last gas jet (3) in the operational sequence formed as a high-speed gas jet is directed at an angle (γ') of between 25° and 150°, preferably of more than 60°, onto the flat flow (FS) of melt, and the distance (L_C) between the gas nozzle or nozzles (C) and the point of deflexion, impact or atomization (31) is less than 20 times the value of the diameter of the gas nozzle or nozzles.
10. A device according to one of Claims 6 to 8, characterized in that at least the third nozzle member (C) or the last nozzle member (C) in the operational sequence is designed in order to produce at least one supersonic gas jet (3).
11. A device according to one of Claims 6 to 10, characterized in that, in order to produce gas jets which can be directed onto the flow (S, FS) of melt, more than two gas nozzle members are arranged in front of the last gas nozzle member (C) which can be used in order to form a high-speed gas jet (3).
12. A device according to one of Claims 6 to 11, characterized in that the gas jets can be adjusted in their direction and their intensity in each case.
13. A device according to one of Claims 6 to 12, characterized in that at least one gas jet is formed as a flat jet or as a multiple jet by the arrangement of a plurality of nozzles positioned adjacent and/or, in particular, in an interposed manner one above the other.
14. A device according to one of Claims 6 to 13, characterized in that the plane defined by the gas jets diverges from the vertical.

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