SE462704B - PROCEDURES FOR ATOMIZING SCIENCES AND DEVICES FOR IMPLEMENTATION OF THE PROCEDURE - Google Patents

Abstract

The present invention relates to a method and a means for atomizing liquids, such as metal melts in which a tapping stream (6) of the liquid encounters one or more media jets (9), e.g. gas and/or liquid. The mixed stream obtained is directed towards a barrier (10) with the object of achieving effective dispersion of the liquid in the media, i.e. atomization.

Description

10 15 20 25 30 462 704 '2 why such powder due to the cost only comes for limited use.

When atomizing metal melts, where a tap jet hits of one or more gas jets, is formed in the contact surface between melt and the gas an instability on the surface of the melt as results in the melt being drawn out into thin films.

When these films have reached a certain thickness, they will due the surface tension of the melt to be broken up into wire-shaped pieces, which in turn is snatched off into a number of pieces, which assumes one shape with the least possible surface energy which is a spherical shape.

These spherical droplets solidify very rapidly due to heat radiation and convective dissipation of heat to the gas to powder particles.

How large a particle is formed in a certain volume element in the atomization process is affected by a number of parameters.

The surface tension of the melt, the density of the atomizing medium and Speed is the most influential besides the geometric the design of the atomization process.

For a given melt, atomization nozzle and atomization medium, it is difficult to influence the surface tension respectively density, which is why it is at the speed of the atomizing medium which particle size can be most easily affected. At most established atomization processes are therefore sought through high pressures on the atomizing medium and on gaseous media in addition, via Laval design of the nozzles, reach high speeds. called.

In the case of gaseous atomization media, however, the gas velocity decreases. heat very quickly after the nozzle, why usually only a small part of the atomization process takes place in the area where maximum speed is present.

A larger or smaller part of the melt will be broken up to particles in an area further from the nozzle there 10 15 20 25 30 3 462 704 the speed is significantly less, in some cases all the way down to 10% of maximum speed. This results in a coarse powder with a large spread between the smallest and largest particle.

Another problem is related to the difficulty of getting atomizing medium to "grab" the liquid, why often a much of it passes by outside the real thing the atomization area with low efficiency as a result.

The method according to the invention is based on a solution of the above and other related problems, and characterized in that close to the blow-out nozzle of the medium, that is, where its velocity is still high, a barrier in shape of a solid or a reverse media stream is achieved in and for a manifold increase in the contact area between the liquid / - the melt and the medium, at the same time as a sharp increase in turbulence achieved, favorable to the atomization process and thereby efficient dispersion of liquid in the medium, whereby the liquid decomposes into small particles, ie atomization is improved and fine-grained powder is obtained.

This is thus achieved by bringing about a manifold increase of the contact surface between the melt and the atomizing medium, at the same time as in the contact area a strong, for dispersion / atomization favorable turbulence.

Furthermore, the atomization process takes place within a short distance from the nozzle where the velocity of the atomizing medium is still high, together with a large proportion of the gas participating in the atomization process gives a high efficiency.

Through this procedure, one can thus at low cost obtain a radical reduction of the average grain size, and a reduction of the size spread of the powder can be achieved.

The barrier may consist of a solid body, possibly cooled for example with water, or of a material that is thermal 10 15 20 25 30 462 704 4 and chemically resistant to the mixed beam. The barrier can too consist of a reverse media stream, consisting of gas and / or fluid ie by barrier is meant in this case the interface / contact the surface between the mixed beam and the opposite media beam.

The procedure can be applied to both vertical and horizontal tella atomization processes. You can also with the appropriate choice of barrier atomize a steel melt or alloys with yet higher melting point.

The invention also relates to a device for carrying out the said procedures, and what characterizes this device is stated in the feeding requirements below.

The media for the media stream or the opposite media stream may consist of water, other liquid such as liquefied gas or of gas alone, such as nitrogen or argon, or mixtures thereof.

Alternatively, the barrier may consist of a stationary or rotating plate, or the gas blower can be rotated.

The invention, both the method and the device, is more detailed exemplified in the accompanying figures, of which Fig. 1 shows one device for carrying out the method according to the invention, Fig. 2a shows the actual atomization process with a gas barrier and Figs 2b with an example of a barrier-creating nozzle. Fig. 3 shows another barrier design, Fig. 4 an alternative device for the atomization process corresponding to the process and Fig. 5a with gas barrier seen from above and Fig. 5b this process seen from the side with detail of the barrier-creating nozzle. Fig. 6 shows an alternative atomization process.

Fig. 1 shows a vertical atomization chamber 1 with a _ casting box 2 for molten metal. Media (gas and / or fluid) is supplied via a gas cooler 3 and a compressor 4 to nozzles in chamber 1. Atomized powder is passed from chamber 1 via 10 15 20 25 30 35 5,462,704 pipeline to a cyclone 5 for powder treatment and separation.

Metal melt, for example steel, is drained from the casting box 2 (fig 2a) through a tombstone arranged in the bottom of this box of a preferably round pin jet 6, vertically downwards, into an inert gas-filled atomization chamber 1.

In the upper part of the chamber, around the downstream tap jet, is a gas nozzle 7 placed, consisting of an annular nozzle or several smaller nozzles.

By means of the nozzle (s), an annular gas curtain 9 is created around the pin jet, which strikes (8) the pin jet at an acute angle. one, at a distance from the nozzle (s) 7. When the gas hits the tap jet splits it and is drawn in by the gas stream.

It is placed at a suitable distance below the point of impact according to the invention called the barrier 10.

The barrier 10 consists of high-melting metals, such as steel, preferably by a gas barrier 11. This is accomplished by that, in preferably the same center line as the pin jet and the gas curtain, at a suitable distance below the nozzle (s), from a nozzle arrangement 12 directing a gas and / or fluid flow upwards, i.e. a second current is preferably directed straight towards it first stream 9-6 which in the center part contains fragments of melt 13.

When the two currents hit each other, the speed decreases the collision area whereby the pressure increases. Through the increase in pressure expands the gas radially outwards, increasing the speed again, If the kinetic energy is equal in the two rays, the result- the direction is almost completely radial, ie perpendicular to the rays direction of incidence.

The melt that is in the center of the first the beam 13 will change direction in the collision area and entrained in the radially expanding gas, whereby an effective atomization is achieved.

A further improvement of the atomization process is achieved. occurs when the kinetic energy of the opposite beam is selected smaller or larger than the first. In such a procedure 10 15 20 25 30 462 704 6 assumes the direction of the expanding gas a curved path (Fig. 2a) The better the atomization process is due to the fragments of the melt, closest to resembling a parabola form. which is dragged along by the gas, constantly forced to change direction whereby a greater exposure to the gas is achieved.

The kinetic energy in the opposite gas flow is advantageously selected less in relation to the first, the above-described the effect is achieved, at the same time as the gas-particle mixture one gets a summary direction obliquely downwards. In the reverse case, the land on the kinetic energy, the sum beam is directed obliquely upwards.

The kinetic energy of the opposite beam can be 10 more 1000% of the first preferably between 30-60%. The barrier according to this embodiment can be obtained from a nozzle according to Fig. 2b, with one or more central nozzles 14 for barrier rays. In addition to these, one can arrange nozzles 15 to prevent liquid (melt) from hitting the barrier the nozzle at unwanted places.

A similar effect as the one described above is obtained if the barrier consists of a solid body, for example a round plate which is placed race perpendicularly and with the same center line as the mixed beam.

(See Fig. 3) The compression of the gas then takes place against this plate 16 after which expansion that takes place radially outwards pulls with a thin film of the melt.

When the melt film reaches the edge of the plate there is a breakage of the film in particles similar to the process described above.

The body of which the barrier is composed may be uncooled or cooled in a suitable manner, for example by means of water channels 17. In the case of uncooled bodies, these are made of a material which is thermally and chemically resistant to the hot melt and gases.

In case the body is cooled, a protective layer is formed against it hot the metal by the metal closest to the plate solidifying. 10 15 20 25 30 7 462 704 The barrier may preferably have a geometry that is congruent with the cross section, on the part of the gas jets that is mixed with melt 13. The size of the barrier is suitably made as follows that the longitudinal scale dimensions become equal to the cross section, at the point of impact, on the part of the gas jet mixed with melt or up to 20 times larger, preferably 4 more 10 times larger.

You can also leave a fixed barrier (for example fig. 3) behind hand is melted and included in the atomized powder, (not shown).

In the method and device as above, where gas flows from nozzles or over the edge of a surface, secondary there currents (turbulence) in the boundary layer between it flowing and stagnant gas. This turbulence can at atomization of liquids with high melting point type melts cause to melt particles are drawn along and welded to nozzles and other surfaces where this is not desirable.

To prevent such effects from occurring on bodies which constitute the barrier, or on nozzles which create the gas barrier these can be provided with extra, placed in suitable places, auxiliary nozzles for the purpose of eliminating turbulence at critical areas and thus prevent molten particles from sticking. These auxiliary nozzles may look like at 15 in Fig. 2b, or like 18 in Figs 30 Fig. 4 shows a horizontal atomization plant with its atomization chamber 19 and its cyclone 20.

The atomization plant contains a closed system, which is preferably kept under a certain overpressure (see Fig. 1) and 4), which may, for example, be 500 mmVp so as to allow air access prevented. At one end of the chamber (l, l9) is as mentioned casting box 2 arranged.

Figs. 5a and 5b show the atomization according to the plant Figs 4. From the nozzles 21 (for example elongate, slit-shaped or a series of small nozzles) flows medium 22 towards the pin jet 23, and 10 15 20 25 30 462 704 8 the resulting mixed beam strikes a barrier (solid or from one or more nozzles 25) and thereby deflected, one good atomization is obtained. The auxiliary nozzles are according to Fig. 5b arranged, a slit-shaped 26 and several small separate 27.

The nozzle 26 can also provide the barrier itself.

To create the mixing beam 24 Figs. 5a-b, one is used flow engineering phenomenon that occurs when two gas or fluid jets strike each other at a certain angle. It is known to be in or just before the intersection of two media rays hitting each other at an angle are present fluid engineering phenomena as to a greater or lesser degree dominates the course depending on the size of this angle.

At small angles, for example, less than 50, the injector effect is on due to the negative pressure just before the point of intersection on dominant property, while at larger angles, for example, vis 1200 a backward flow of media occurs in relation to the main direction of the media rays.

You can take advantage of both of these phenomena by choosing one angle between two media beams 22,22 so that a backflow media emerges and that within a shorter distance again due to the injector action is retracted into the media larna. The result is that a zone is formed in front of the the point where the flow has no preferred direction but almost consists of two vortex vortices where one is constant exchange between backflow media and withdrawal of media takes place. By changing the angle, this zone can be obtained larger or smaller. The angle between the media streams can be 0-600 but is preferably between 5-200.

The nozzles 21,21 can be arranged so that two horizontally directed, in the vertical plane parallel media beams with a large height in relation to the width and with an angle in the horizontal plane in relation to each other is created, whereby the zone described above is formed. From top to bottom in the vertical, 10 15 20 25 30 a. e.- 704 .la- Ch hrs along the entire height of the nozzle formed zone, currents the tapping beam 23, the beam successively descending on its way down torn apart and mixed in the passing atomization the medium.

Media beams with a large propagation in one direction can provide through slit-shaped nozzles or through a number, in a row, close-fitting, for example, circular nozzles.

The nozzles for the media jets may depend on the current pressure and medium are designed for below respectively supercritically pressure ratio (Lavaldysa).

Then the flow of melt is properly adapted to the media nozzle capacity, the mixing takes place, ie the partial atomization along the entire height of the nozzle.

The advantage of the above-described arrangement of nozzles 21 is that a more homogeneous mixture (partial atomization) of the liquid in the median can be reached, which even after the passage of a barrier manifests itself in the form of a narrower fraction of the particles.

The nozzle arrangement 21 can also be used for complete atomization, without a barrier, leaving particles within a narrow size range can be produced however with a larger average particle size.

Fig. 6 shows an alternative embodiment of the method and the device according to the invention. Between two electrodes 28,29 an arc is arranged 30. Media currents are directed towards the arc (gas and or fluid) 31, and which serves as a barrier to media flow. from the opposite direction 32, and efficient atomization is produced by the liquid 35 formed in the arc. In this In this case, the liquid to be atomized is obtained from at least one of the electrics 29. Liquid can also be obtained from a solid body, which was melted by laser or the like (not shown) on a similar way. The feed of the electrodes in Fig. 6 or in the laser case can be arranged by means of feeders 34.

The nozzles, both for the first median and the barrier median can be 10 15 462 704 10 annular or consist of several smaller nozzles. The procedure according to Fig. 6 is suitably performed in a chamber similar to those shown in FIG previously described (not shown).

Particles formed during atomization are entrained in gas jets. one towards the other end of the chamber, whereby they before they meet the end of the chamber by radiation and convective heat conduction until the gas has solidified into powder. In the House there are step in the gable towards which the gas / powder mixture flows one outlet hall.

From the outlet hole, the chamber is connected via pipelines a cyclone, in which powder and gas are separated. The gas can after the separation go to a compressor via a gas cooler for recirculation to the atomization nozzles.

The system also includes the necessary valves, cooling equipment and control means for regulating gas pressure, temperatures, different media flows etc.

The devices and procedures as above can be varied in many ways within the scope of the claims.

Claims (1)

A method of atomizing liquids, preferably molten metals, in which liquid, preferably molten metal, is mixed in a media jet (6,22,31), consisting of gas and / or liquid, so that it is broken up into small particles, i.e. the atomization is effected, characterized in that near the blow-out nozzle of the medium, i.e. when its velocity is still high, a barrier in the form of a solid body or an opposite media flow is produced in a manifold increase in the contact area between the liquid / melt and the medium, at the same time as a greatly increased turbulence is achieved, favorable for the atomization process, and thereby efficient dispersion of liquid in the medium, whereby the liquid decomposes into small particles, ie atomization is improved and fine grain powder is obtained. Process for atomizing metal melts according to claim 1, characterized in that a body (16) is used as the barrier, cooled, for example, with water (17), a thin solidified layer being formed on the body, which protects the body against the attack of the liquid , which body is stationary or rotating. A method according to claim 1, characterized in that a body (16) of a material which is thermally, mechanically and chemically resistant to the liquid-media mixture, which body is stationary or rotating, is used as a barrier. Method according to claims 1-3, characterized in that a gas and / or fluid stream (11) is used as the barrier (10, 25, 32), directed substantially in the opposite direction and towards the mixed jet of liquid and media. A method according to any one or more of the preceding claims, characterized in that a barrier (11) is used which has a geometry which is preferably congruent with the cross section of the part of the media jet which contains liquid. (13) (the mixed beam), where it hits the barrier, and that the barrier is given longitudinal scale dimensions, equal to or up to 20 times larger than this cross section, preferably 4 to 10 times. Method according to one or more of the preceding claims, characterized in that the gas and / or liquid flow constituting the barrier is provided with one or more nozzles, and that the kinetic energy from these is 10 to 1000% of the kinetic energy in the media jet / the rays, preferably 30 to 60%. Method according to one or more of the preceding claims, characterized in that the nozzles for gas and or fluid are provided with auxiliary nozzles (15,18,26,27) which prevent liquid / melting due to turbulence / injector action. comes into contact with the gas nozzles or the barrier body in undesirable places. Method according to one or more of the preceding claims, characterized in that liquid is produced by supplying energy to a metal or metal alloy (28), and in that media (31) are applied to the liquid (35) to obtain a mixed beam and that the mixed beam is directed towards a barrier, for example opposite media beam (32). A method according to claim 8, characterized in that the energy is provided by means of an electric arc, laser or the like. Device for carrying out the method according to one or more of the preceding claims, comprising a casting box (2) for liquid, such as molten metal, and nozzles (7,2l). ) for media jets, intended to hit a pin jet (6,23) from the casting box, or other liquid accumulation (35), characterized in that the device includes a barrier in the form of a solid body or an opposite media stream, placed in the path of the mixed liquid / media stream near the nozzles of the media jets and intended to provide a greatly increased contact surface between the liquid / melt and the media stream and to achieve an effective dispersion of liquid in the medium and thereby atomized efficiency. The device according to claim 10, characterized in that the barrier consists of a solid body (16), optionally water-cooled, optionally rotatable, and / or made of a material which is thermally and chemically resistant to the mixed beam. The device according to claim 10, characterized in that the barrier is provided by one or more nozzles (12), preferably directed in the opposite direction and towards the mixing jet, for the purpose of directing one or more gas and / or fluid jets towards the mixing jet in streamlining atomization. The device according to claim 10, characterized in that the barrier is also provided with auxiliary nozzles (l5,18,26,27) to prevent liquid due to turbulence / injector action coming into contact with the gas nozzles and / or the barrier body in undesired places. Device for carrying out the method according to one or more of claims 1 to 9, characterized in that metal or metal alloy is arranged to be supplied, for example, in wire, rod or powder form 462 704 14 (28, 29), and that energy in the form of a laser, a light arc (30) is arranged to be applied to the metal 11 for its forging and the formed liquid (35) is arranged to be exposed to media radiation (31), and the mixed beam thus formed is arranged to be subjected to a barrier, for example an opposite media straw (32), in order to efficiently atomize the liquid. ll