EP1022078A2 - Process and apparatus for preparing metal powder by gas atomisation - Google Patents

Abstract

The molten stream (S) exiting vertically from the nozzle body (D) is bombarded by at least three subsequent gas streams (1, 2, 3) in different directions. Production of metal powder from a melt comprises distributing a melt stream exiting a nozzle body of a metallurgical body (G) into drops using gas streams and leaving to solidify into powdered bodies. The molten stream (S) exiting vertically from the nozzle body (D) is bombarded by at least three subsequent gas streams (1, 2, 3) in different directions. An Independent claim is also included for a device for producing a metal powder from a melt comprising a disintegration unit with gas nozzle bodies (A, B, C) whose gas streams are directed onto the melt stream.

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 equipment.

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 Production of hot isostatically pressed parts from metal powder, however, is said to be Powder advantageously have a high bulk density and thus a corresponding Have grain size distribution.

Gas-atomized metal powder is produced essentially 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 especially 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 particles 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 be a 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 with a large amount of fine coma and high yield.

If the comparatively thick melt flow is not broken up 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 which, before solidification due to 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 molten metals 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 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 concentrically 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 Melt 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 grains with small diameter sufficient acceleration of the Melt can be achieved.

Attempts have already 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 Provide minimum nozzle spacing, 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 has become, in which for the division of 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 wide 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 flow 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 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 amounts, so that this towards Monograined 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 facilities used for this have the disadvantages in common that the Fine powder content too low and / or the grain size distribution unfavorable for one Economic further processing into high-quality products is or are.

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 leaving the melt nozzle body essentially vertically Melt flow through at least three successive gas jets different directions are applied at least partially,

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 stream 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 application 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 flow before the high-energy division into small droplets by at least two upstream gas jets, each of which is not the same direction 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 great, 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 from the 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 divided, 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 counter-directed to the prepared flat melt stream as a high-speed gas jet is formed and a fine division or atomization of the liquid jet Droplets accomplished which steel droplets subsequently solidified become. When the first gas jet deflects and widens the compact melt stream 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 detached 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 Laval 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 hits the Flat melt current is directed because this has a large force effect in the 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 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 Formation of flat current of the liquid metal, this advantageously taking place in the form of a sector, is at a deflection of the same with 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 Requirements for a breakdown into droplets with a high proportion of fine particles, especially when the high-speed gas jet causing it also deflects the flat 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 Mono-grain formation.

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. Due to the 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 essential to see that by an arrangement of at least three Gas nozzle bodies in one disintegration unit 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 °.

In an advantageous embodiment of the invention, the first gas nozzle body 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 ° to the melt flow 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 is 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 deflecting, 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 Flat current conveniently adjustable, on the other hand has a suppression of one Formation of suction vortices by 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 deflection, appearance or atomization point is less than 20 times the value of Gas nozzle diameter, is a high performance of the facility excellent powder quality achieved because of a breakdown of the metal into droplets a high force 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 further development of the invention, favorable division conditions 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 upstream.

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 another 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 Is formed nozzles, 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.

In the following, the invention will be explained using only one embodiment illustrative drawings explained in more detail.

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.

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 impact 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 acted upon.

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 γ ′ and, as a result, its division into a metal particle stream 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 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 in 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 effect a change in the flow direction of the metal stream.

According to the invention it can also be possible that by 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)

Process for the production of metal powder from the same melts, wherein a melt stream emerging from a nozzle body of a metallurgical vessel (G) is broken down into droplets in a atomization chamber by gas jets and these are solidified into essentially spherical powder grains, characterized in that the melt from the melt nozzle body ( D) essentially vertically exiting melt stream (S) is at least partially acted upon by at least three successive gas jets (1, 2, 3) each with different directions. Method according to Claim 1, characterized in that the melt stream (S) emerging from the melt nozzle body (D) is deflected and spread or thinned and / or divided in its flow direction by means of at least one first gas jet (1), whereupon at least one, the same Directional component, obliquely impinging second gas jet (2) prepares the spread and / or divided flat melt stream (FS) in its form and builds up a suction barrier for the nozzle (s) (C) of at least one downstream third gas jet (3), the third Gas jet (3) is formed obliquely to partially counter to the prepared flat melt stream (FS) as a high-speed gas jet and finely divides or atomizes the liquid steel into droplets (P), which steel droplets are subsequently solidified. Method according to Claim 1 or 2, characterized in that the melt stream (S) with a diameter (S1) of 2.0 mm to 15.0 mm by means of at least one first gas jet (1) in its flow direction by an angle (α) between 5 ° and 85 °, preferably between 15 ° and 30 °, is deflected and essentially sector-shaped to form a melt flow (FS). Method according to one of claims 1 to 3, characterized in that the sector-shaped melt flat stream (FS) after reaching a width (S2) caused by the first gas jet (1) of at least 5 times, preferably at least 10 times, the free-falling melt stream width or Thickness (S1) is deflected by at least one third gas jet (3), which is designed as a high-speed gas jet, at an angle (γ) between 25 ° and 150 °, preferably between 60 ° and 90 °, and atomized into a droplet stream (P) or is divided. Method according to one of claims 1 to 4, characterized in that the melt flat stream (FS) before or in the region (31) of the deflection or atomization by the third high-speed jet (3) by a gas jet (2) having the same directional component, however, an angle (δ) of between 5 ° and 85 °, preferably between 15 ° and 30 °, is applied to it and processed, thereby preventing droplets of the high-speed gas jet (3) leading to melt droplets. Device for producing metal powder from such melts consisting essentially of a atomization chamber, into which a metal melt stream (S) can be introduced or entered from a metallurgical vessel (G) by means of a melt nozzle body (D), with a disintegration unit arranged in this chamber on the entry side Gas nozzles for acting on the melt stream (S) by gas jets to break it down into droplets, a solidification space provided on the discharge side for cooling the droplets and forming powder grains, and downstream powder processing devices, in particular for carrying out the method according to the preceding claims, characterized in that the disintegration unit at least has three gas nozzle bodies (A, B, C), the gas jets (1, 2, 3) of which in an effective sequence each apply to the melt stream (S) introduced and to the u nd shaped melt stream (FS) are aligned with an angle between 5 ° and 170 °. Apparatus according to claim 6, characterized in that the first gas nozzle body (A) is arranged such that the first gas jet (1) has the same directional component with an angle (α ') between 5 and 85 °, preferably with an angle (α' ) between 15 and 30 ° is directed towards the melt stream (S) and that the length (L _S ) of the free-falling melt stream (S) is equal to the length dimension: distance (L _A ) of the gas nozzle (A) from the point of impact (11) of the gas jet ( 1) increased or reduced to the melt flow (S) by a value which is at most 10 times the diameter (D1) of the melt flow. L S = (L A ± 10 x S. 1 ) Apparatus according to claim 6 or 7, characterized in that the second nozzle body (B) is arranged such that the second gas jet (2) in the sequence of action acts on the flat melt stream (FS) which has been spread and thinned by the upstream first gas jet (1) same flow component with an angle (δ) between 5 ° and 85 °, preferably with an angle (δ) between 15 ° and 30 ° and that the point of impact (21) of this second gas jet (2) in the region of or before the deflection -, Impact or atomization point (31) of the downstream third gas jet (3). Device according to one of claims 6 to 8, characterized in that the third nozzle body (C) is arranged in such a way that a third gas jet (3), which is designed as a high-speed gas jet or, in effect, the last one, is at an angle (γ ') between 25 ° and 150 °, preferably greater than 60 ° is directed to the flat melt stream (FS) and that the distance (L _C ) between the gas nozzle (s) (C) and the deflection, impact or atomization point (31) is less than 20 times the value of the gas nozzle diameter. Device according to one of claims 6 to 8, characterized in that at least the third, or in the sequence of action, the last nozzle body (C) is designed to produce at least one supersonic gas jet (3). Device according to one of claims 6 to 10, characterized in that the last gas nozzle body (C) which can be used to form a high-speed gas jet (3) is preceded by more than two gas nozzle bodies for producing gas jets which can be set up on the melt stream (S, FS). Device according to one of claims 6 to 11, characterized in that the gas jets are adjustable in their direction and their intensity. Device according to one of claims 6 to 12, characterized in that at least one gas jet is designed as a flat jet or as a multiple jet, through the arrangement of a plurality of nozzles positioned next to and / or in particular one above the other. Device according to one of claims 6 to 13, characterized in that the plane determined by the gas jets deviates from the vertical.

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