EA022298B1 - Device and method for cooling melt fragments - Google Patents

Abstract

The invention relates to metallurgy, in particular to a production of metal shots from a molten metal or an alloy by a casting. The claimed device for cooling metal melt fragments or alloy as obtained by passing a melt through a die comprises one or more nozzles for supplying a sprayed cooling air-droplet mixture as a spilling flow into a space under a crucible. Another aspect of this invention is a method for cooling melt fragments carried out by means of said device. The technical effect of the claimed invention is production of shot with a high degree of sphericity and fractional composition.

Description

The invention relates to metallurgy, in particular to the production of metal fractions by casting.

Fraction from various metals and alloys is widely used in metallurgical technologies, for example, in foundry, it is used for shot blasting and shot blasting of products, surface hardening of parts, etc.

In the production of shot fractions by casting, process characteristics such as productivity, acceptable material costs, stability of the fractional composition of the resulting shot, and the correct geometry of the shot are of great importance. For example, when a shot is injected into a melt with the purpose of alloying or deoxidation, the depth of its penetration into the volume of the melt, and, therefore, the efficiency of using the material deposited in this way, largely depends on the fractional composition and shape of the shot.

The specific technological problems to be solved - deoxidation, alloying, refining, etc., and the size of the shot used for this determine the injection parameters: transport gas pressure, material feed rate, fraction speed in the stream, diameter of the material pipe. These parameters determine the efficiency of use of the material and the stability of the result. If the fraction used contains fragments of different particle sizes, it is impossible to establish optimal parameters for effective injection, and the material utilization rate decreases. The material utilization coefficient is the smaller, the more heterogeneous the fraction by size classes.

Also, the shape penetrates the fraction of the fraction into the melt volume. If there are deviations from the spherical shape, the depth of penetration of the shot into the melt decreases, the probability of a rebound increases, i.e. fraction interacting with the surface of the melt does not penetrate into the volume of the melt, but bounces off its surface. The shape of the fraction is also important for gas transportation, especially in relation to large classes. A material consisting of fragments of a spherical shape wears out pipelines less and helps to reduce the effect of clogging of the material pipeline.

Various methods for producing metal fractions are known, such as spraying a stream of metal with air, steam, water; fragmentation of a stream of metal when falling onto an inclined surface moistened with water; pouring metal into the water with rain gates; casting through water sieves. Also known is the centrifugal granulation method based on crushing the melt by centrifugal force. The latter method can be implemented by rotating a perforated glass, spraying from the edge of a rotating disk or bowl, spraying a fused layer of a rotating workpiece. There is also an electrocontact method for producing a fraction or a metal powder, which consists in the action of the edge of a rotating conductive disk on a metal, for example, in the form of a strip or shavings, which is melted by the energy of an electric current.

The above methods along with the advantages have several disadvantages. So, they allow you to get a fraction of various metals in large enough quantities at relatively low cost and satisfactory geometry. However, when implementing all of the above methods, when dividing the melt of any metal or alloy into separate fragments, accurate dosing by mass is not provided, and accordingly, the obtained fraction has an unstable fractional composition by size. As a result, it is impossible to choose the optimal cooling mode that ensures the production of a fraction with a high sphericity index simultaneously for all the resulting particle size classes. Since the fraction obtained by these methods has different sizes, it is necessary to disperse it before use and, often, seek application for substandard size classes or return it to the beginning of the technological process. In addition, if a metal or alloy with an increased affinity for oxygen is processed into a fraction, the fine fractions are more susceptible to oxidation processes in contact with the atmosphere than large ones, which leads to additional losses of the final product.

The most preferred method for producing a spherical-shaped fraction is a method based on passing a metal or alloy melt through a die and then cooling the melt fragments obtained by passing.

USSR author's certificate No. 1222417 (publ. 07.04.1986; IPC V22P 9/08) describes a method for producing metal granules from a melt, in which molten metal is passed through holes in the bottom of a crucible with a diameter of 1 to 8 mm and then cooled in a liquid. In this case, an excess pressure of 0.01-1 atm is created in the chamber under the melt using an inert gas. The size of the granules is regulated by changing the diameter of the holes, the gas pressure under the crucible, the temperature of the metal and the height of its column in the crucible. The alloy level in the crucible is kept constant.

RF patent No. 2117553 (publ. 08/20/1998; IPC В22Р 9/06) discloses a method for producing spherical metal granules, including dispersing molten metal upon receipt through openings due to pressure drop when a constant magnetic field is applied to the metal and an alternating electric field is passed through it current, followed by cooling the granules in an atmosphere of air, and the metal leaving the holes is passed through a layer of inert gas. The acquisition of spherical droplets occurs mainly in an inert gas environment.

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From the patent application of Japan No. 4259312 (publ. 09/14/1992; IPC B22P 9/08, B23K 35/40) there is a method for producing metal granules with a low melting point, including passing liquid metal through a nozzle with many holes, the distance between which is not less than three times the diameter of the holes. The nozzle undergoes vibration to form individual drops of molten metal. The spherical shape of the droplets is attached in the process of their falling, and the solidification of the spherical granules occurs in the cooled zone.

As the closest analogue, the technical solution described in Japanese Patent Application No. 62253705 (publ. 05.11.1987; IPC B22P 9/08) can be selected. A device and a method for producing a metal fraction using a crucible with holes mounted on a vibration device are known from the application. The vibration frequency is from 40 to 100 Hz, the amplitude is 0.2-1.5 mm. The molten metal passes through the holes and, under the influence of vibration, breaks into droplets. Partial solidification of the droplets formed occurs during a fall in the atmosphere between the die and the coolant, and the final solidification of the droplets and their acquisition of a spherical shape occurs in the coolant (water).

The present invention is intended to eliminate the disadvantages of methods and devices known from the prior art for cooling fragments of a melt in the process of producing a fraction and allows to obtain a spherical fraction with stable geometric parameters and physical properties.

The claimed technical result is achieved in that the device for cooling fragments of a molten metal or alloy obtained by passing the melt through a die located in the bottom of the crucible includes at least one nozzle mounted under the bottom of the crucible for feeding the sprayed cooling air-drop mixture into the sub-crucible space, moreover, the nozzle is placed with the possibility of supplying an air-drop mixture into the space under the crucible with a flowing stream.

The melt fragment cooling device may include several nozzles mounted frontally with respect to the crucible wall at a level equal to half the distance from the crucible bottom to the level of coolant in the bath located under the crucible. Preferably, if the distance from the nozzle nozzle to the vertical plane coinciding with the crucible wall and the angle between the horizontal plane and the axis of the nozzle are chosen so that the extremum of the upper branch of the parabolic flow path of the cooling air-droplet mixture from the nozzle coincides with the point of intersection of the bottom of the crucible and its walls. It is also preferable if the distance between the nozzles frontally mounted along the length of the crucible in the horizontal plane is equal to twice the product of the distance from the nozzle to the vertical plane coinciding with the crucible wall and the tangent of half the angle of the nozzle opening.

Further, the invention is disclosed in more detail with reference to the figures and embodiments of the invention.

In FIG. 1 shows a General view of the device for producing fractions from the melt.

In FIG. 2 shows a side view of a device for cooling fragments of a molten metal or alloy.

In FIG. 3 is a top view of a device for cooling fragments of a molten metal or alloy.

A general view of a device for producing shots from molten metal or alloy is shown in FIG. 1. The device for producing shots includes a crucible (1), in the case of which a glass (2) is installed to accommodate a melt (3) of metal or alloy, a die (4), which is installed in the bottom of the crucible (1), and a bath (5 ) with coolant (6) located under the crucible (1). Between the crucible (1) and the bath (5), the inventive device (7) for cooling the fragments of the melt, forming a cooling stream (8) of an air-drop mixture, is installed.

Between the crucible body (1) and the glass (2), a heat insulating layer (9) is preferably placed. The crucible body (1) is, for example, made of stainless steel, and the heat-insulating layer (9) is a layer of refractory mass, which is both a lining and a heat insulator. In addition, for better thermal insulation and to ensure uniform temperature of the melt (3) on the crucible (1) can be installed on the cover (10) of the crucible with a filling device (11).

In a preferred embodiment, the bottom of the crucible (1) has a rectangular shape. It is desirable that the width of the crucible (1) does not exceed the distance B from the device (7) for cooling the melt fragments to a vertical plane coinciding with the wall of the crucible (1) (distance B is shown in Figs. 2, 3).

The crucible (1) can be connected to the swing mechanism (12) through the swing mechanism drive (13) to provide reciprocating movement of the crucible (1) in the vertical direction. Preferably, if the oscillation frequency lies in the range from 0.5 to 15 Hz. Fluctuations can have a different form, for example sawtooth.

The device (7) for cooling the fragments of the melt can be a nozzle or a series of nozzles located frontally in relation to the wall of the crucible (1). It is preferable if the nozzles are located at level C equal to half the distance B from the crucible (1) to the level of cooling fluid (2 022298) in the bath (5). It is also preferable if the distance B from the nozzle to the vertical plane coinciding with the crucible wall (1) and the angle β between the horizontal plane and the axis of the nozzle are selected so that the extremum of the upper branch of the parabolic trajectory of the cooling stream (8) of the air-drop mixture from the nozzle coincided with the point of intersection of the bottom of the crucible (1) and its wall, as shown in FIG. 2.

The distance A between the nozzles frontally mounted along the length of the crucible (1) in the horizontal plane (see Fig. 3) is preferably determined from the relation

where α is the angle of the nozzle;

B is the distance from the nozzle to the vertical plane coinciding with the crucible wall.

The bath (5) has a filling hole (14) and an overflow hole (15). A conveyor (16) can be installed in the bath (3). The distance from the bottom of the crucible (1) to the level of the coolant (6) in the bath (5) depends on the metal or alloy used to produce the shot, and can range from 65 to 250 mm.

In the die (4), channels (17) are made (Fig. 2, 3), when passing through which the melt (3) of the metal or alloy is divided into fragments.

Obtaining fractions through the inventive device (7) for cooling fragments of the melt works as follows.

From the melting furnace (18), the starting material (19) located in it, when the locking device (20) is opened, is fed by a stream (21) into the crucible glass (2) through the filling device (11).

The melt (3) in the crucible passes through the channels (17) of the die (4), by means of which it is divided into fragments. Preferably, when the melt (3) is passed through the die, a constant level of the melt in the crucible (1) is maintained.

Then the fragments fall into the area of the cooling stream of the air-drop mixture (8) formed by the device (7) for cooling the fragments of the melt.

The melt fragments are completely cooled in the cooling liquid (6) of the bath (5), from where the obtained fraction can be extracted, for example, by means of a conveyor (16). It is desirable to maintain the temperature of the upper layer of coolant (6) in the range from 45 to 80 ° C, for example, due to the constant influx of coolant (6) into the lower horizon of the bath (5) through the filler hole (14), and to ensure free flow of excess coolant (6) through the overflow hole (15) in the upper part of the bath (5). As a coolant (6), water or solutions based on it can be used.

When testing the proposed method, aluminum scrap was used as a starting material, which was loaded and melted in a melting furnace (18). After melting and heating to a predetermined temperature, the melt was poured into the crucible (1) through the filling device (11) in the lid (10). The temperature of aluminum in the crucible was 700-750 ° C, the level of the metal from the inner surface of the bottom was 70-90 mm. The level was controlled visually through a quartz window and was controlled by the feed rate of the metal from the smelter.

Simultaneously with the supply of liquid aluminum to the crucible (1) during the heating of the crucible and the die, the drive (13) of the swing mechanism was launched with a frequency of 0.5 to 2.0 Hz, which ensures a minimum melt exit (3) through the channels (17) of the die (4) in order to reduce technological waste before entering the operating mode. After heating the crucible (1) of the die (4) and the cooling liquid (6) in the bath (5) for one and a half minutes, the unit was put into operation, setting the optimum values of the amplitude and frequency of oscillations of the crucible (1), which ensured accurate dosing of the melt (3 ) into fragments that were separated from the lower cut of the channel (17) of the die (4) at the moment of changing the direction of movement of the crucible (1) from down to up. During the time spent in the channel (17) of the die (4), the fragments under the action of surface tension took a spherical shape and then cooled in two stages.

Fragments of the melt in the form of formed spheres fell into the primary cooling zone by a cooling stream (8) of an air-drop mixture, which was formed so that the air-drop mixture entered the space under the crucible (1) along a hinged path, as shown in FIG. 2, without creating turbulence and, accordingly, without disturbing the geometry of spherical fragments.

As a result of the cooling effect, fragments crystallized, their surface acquired initial stiffness, and they did not deform as a result of contact with the surface of the cooling liquid (6) in the bath (5) located at a distance Ό from the bottom of the crucible (1), equal to 175 mm. The location of the nozzles of the first cooling stage corresponded to that shown in FIG. 2 and 3.

After about one and a half minutes from the moment the unit was started, the cooling liquid (6) in the bath (5) was heated to a temperature of 65-85 ° C, its temperature was monitored using a temperature sensor. After reaching the set temperature, a coolant with a lower temperature was supplied to the lower level of the bath (1) through the nozzle of the filler hole (14) cut into the bottom of the bath, thereby ensuring its temperature in the surface layer was constant.

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To determine the quality indicators, we took the fraction obtained after the installation entered the operating mode.

The obtained fraction had the following characteristics: the degree of sphericity is not less than 97%, the deviation from the nominal mass for the fraction in the range of specified sizes from 4 to 8 mm is not more than 1.0% in weight ratio.

In the methods known from the prior art, inert gas is supplied to exclude the formation of a hard oxide film on the surface of the aluminum melt fragment and to facilitate the process of pulling the tail into the sub-crucible space. This approach does not allow to solve the problem completely, since the protective gas flow has a dynamic and cooling effect on the fragment surface, which prevents the formation of a sphere. In addition, this approach introduces additional technical difficulties that are not in the solution proposed in the claimed invention.

The technical result of the claimed invention is to obtain fractions with a high degree of sphericity and fractional composition.

Claims (6)

CLAIM 1. A device for cooling fragments of a molten metal or alloy obtained by passing the melt through a die located in the bottom of the crucible, including at least one nozzle installed between the bottom of the crucible and the bath under the crucible for supplying a cooling air-drop mixture into the sub-crucible space, characterized in that the nozzle is placed with the possibility of supplying an air-drop mixture into the space under the crucible with a flowing stream. 2. The melt fragment cooling device according to claim 1, characterized in that it comprises several nozzles mounted frontally with respect to the crucible wall at a level equal to half the distance from the crucible bottom to the level of coolant in the bath, and the distance B from the nozzle nozzle to the vertical plane coinciding with the crucible wall, and the angle β between the horizontal plane and the axis of the nozzle is chosen so that the extremum of the upper branch of the parabolic flow path of the cooling air-drop mixture from the nozzle coincides l with the intersection point of the bottom of the crucible and its wall. 3. The cooling device for the melt fragments according to claim 2, characterized in that the distance A between the nozzles frontally installed along the length of the crucible in the horizontal plane is determined from the relation where α is the angle of the nozzle; B is the distance from the nozzle to the vertical plane coinciding with the crucible wall. 4. The method of cooling fragments of a molten metal or alloy obtained by passing the melt through a die located in the bottom of the crucible, by means of a at least one nozzle installed between the bottom of the crucible and located under the crucible for supplying a cooling air-drop mixture into the sub-crucible space, characterized in that the supply of an airborne mixture into the space under the crucible is carried out by a flow. 5. The method of cooling fragments of the melt according to claim 4, characterized in that several nozzles are used that are installed frontally with respect to the crucible wall at a level equal to half the distance from the crucible bottom to the level of coolant in the bath, and the distance B from the nozzle nozzle to the vertical the plane coinciding with the crucible wall, and the angle β between the horizontal plane and the axis of the nozzle is chosen so that the extremum of the upper branch of the parabolic flow path of the cooling air-drop mixture from the nozzle coincides with t the point of intersection of the bottom of the crucible and its wall. 6. The method of cooling the melt fragments according to claim 5, characterized in that the distance A between the nozzles frontally mounted along the length of the crucible in the horizontal plane is determined from the ratio